                       Kea Administrator Reference Manual

   This is the reference guide for Kea version 1.5.0.

   Copyright (c) 2010-2018 Internet Systems Consortium, Inc. ("ISC")

   Abstract

   Kea is an open source implementation of the Dynamic Host Configuration
   Protocol (DHCP) servers, developed and maintained by Internet Systems
   Consortium (ISC).

   This is the reference guide for Kea version 1.5.0. The most up-to-date
   version of this document (in PDF, HTML, and plain text formats), along
   with other documents for Kea, can be found at kb.isc.org/docs.

   --------------------------------------------------------------------------

   Table of Contents

   1. Introduction

                1.1. Supported Platforms

                1.2. Required Software at Run-time

                1.3. Kea Software

   2. Quick Start

                2.1. Quick Start Guide for DHCPv4 and DHCPv6 Services

                2.2. Running the Kea Servers Directly

   3. Installation

                3.1. Packages

                3.2. Installation Hierarchy

                3.3. Building Requirements

                3.4. Installation from Source

                             3.4.1. Download Tar File

                             3.4.2. Retrieve from Git

                             3.4.3. Configure Before the Build

                             3.4.4. Build

                             3.4.5. Install

                3.5. DHCP Database Installation and Configuration

                             3.5.1. Building with MySQL Support

                             3.5.2. Building with PostgreSQL support

                             3.5.3. Building with CQL (Cassandra) support

   4. Kea Database Administration

                4.1. Databases and Database Version Numbers

                4.2. The kea-admin Tool

                4.3. Supported Databases

                             4.3.1. memfile

                             4.3.2. MySQL

                             4.3.3. PostgreSQL

                             4.3.4. CQL (Cassandra)

                             4.3.5. Using Read-Only Databases with Host
                             Reservations

                             4.3.6. Limitations Related to the use of SQL
                             Databases

   5. Kea Configuration

                5.1. JSON Configuration

                             5.1.1. JSON Syntax

                             5.1.2. Simplified Notation

   6. Managing Kea with keactrl

                6.1. Overview

                6.2. Command Line Options

                6.3. The keactrl Configuration File

                6.4. Commands

                6.5. Overriding the Server Selection

   7. Kea Control Agent

                7.1. Overview

                7.2. Configuration

                7.3. Secure Connections

                7.4. Starting Control Agent

                7.5. Connecting to the Control Agent

   8. The DHCPv4 Server

                8.1. Starting and Stopping the DHCPv4 Server

                8.2. DHCPv4 Server Configuration

                             8.2.1. Introduction

                             8.2.2. Lease Storage

                             8.2.3. Hosts Storage

                             8.2.4. Interface Configuration

                             8.2.5. Issues with Unicast Responses to
                             DHCPINFORM

                             8.2.6. IPv4 Subnet Identifier

                             8.2.7. Configuration of IPv4 Address Pools

                             8.2.8. Standard DHCPv4 Options

                             8.2.9. Custom DHCPv4 options

                             8.2.10. DHCPv4 Private Options

                             8.2.11. DHCPv4 Vendor Specific Options

                             8.2.12. Nested DHCPv4 Options (Custom Option
                             Spaces)

                             8.2.13. Unspecified Parameters for DHCPv4 Option
                             Configuration

                             8.2.14. Stateless Configuration of DHCPv4
                             Clients

                             8.2.15. Client Classification in DHCPv4

                             8.2.16. DDNS for DHCPv4

                             8.2.17. Next Server (siaddr)

                             8.2.18. Echoing Client-ID (RFC 6842)

                             8.2.19. Using Client Identifier and Hardware
                             Address

                             8.2.20. Authoritative DHCPv4 Server Behavior

                             8.2.21. DHCPv4-over-DHCPv6: DHCPv4 Side

                             8.2.22. Sanity checks in DHCPv4

                8.3. Host Reservation in DHCPv4

                             8.3.1. Address Reservation Types

                             8.3.2. Conflicts in DHCPv4 Reservations

                             8.3.3. Reserving a Hostname

                             8.3.4. Including Specific DHCPv4 Options in
                             Reservations

                             8.3.5. Reserving Next Server, Server Hostname
                             and Boot File Name

                             8.3.6. Reserving Client Classes in DHCPv4

                             8.3.7. Storing Host Reservations in MySQL,
                             PostgreSQL or Cassandra

                             8.3.8. Fine Tuning DHCPv4 Host Reservation

                             8.3.9. Global reservations in DHCPv4

                8.4. Shared networks in DHCPv4

                             8.4.1. Local and relayed traffic in shared
                             networks

                             8.4.2. Client classification in shared networks

                             8.4.3. Host reservations in shared networks

                8.5. Server Identifier in DHCPv4

                8.6. How the DHCPv4 Server Selects a Subnet for the Client

                             8.6.1. Using a Specific Relay Agent for a Subnet

                             8.6.2. Segregating IPv4 Clients in a Cable
                             Network

                8.7. Duplicate Addresses (DHCPDECLINE Support)

                8.8. Statistics in the DHCPv4 Server

                8.9. Management API for the DHCPv4 Server

                8.10. Supported DHCP Standards

                8.11. User contexts in IPv4

                8.12. DHCPv4 Server Limitations

                8.13. Kea DHCPv4 server examples

   9. The DHCPv6 Server

                9.1. Starting and Stopping the DHCPv6 Server

                9.2. DHCPv6 Server Configuration

                             9.2.1. Introduction

                             9.2.2. Lease Storage

                             9.2.3. Hosts Storage

                             9.2.4. Interface Selection

                             9.2.5. IPv6 Subnet Identifier

                             9.2.6. Unicast Traffic Support

                             9.2.7. Subnet and Address Pool

                             9.2.8. Subnet and Prefix Delegation Pools

                             9.2.9. Prefix Exclude Option

                             9.2.10. Standard DHCPv6 Options

                             9.2.11. Common Softwire46 Options

                             9.2.12. Custom DHCPv6 Options

                             9.2.13. DHCPv6 Vendor-Specific Options

                             9.2.14. Nested DHCPv6 Options (Custom Option
                             Spaces)

                             9.2.15. Unspecified Parameters for DHCPv6 Option
                             Configuration

                             9.2.16. IPv6 Subnet Selection

                             9.2.17. Rapid Commit

                             9.2.18. DHCPv6 Relays

                             9.2.19. Relay-Supplied Options

                             9.2.20. Client Classification in DHCPv6

                             9.2.21. DDNS for DHCPv6

                             9.2.22. DHCPv4-over-DHCPv6: DHCPv6 Side

                             9.2.23. Sanity checks in DHCPv6

                9.3. Host Reservation in DHCPv6

                             9.3.1. Address/Prefix Reservation Types

                             9.3.2. Conflicts in DHCPv6 Reservations

                             9.3.3. Reserving a Hostname

                             9.3.4. Including Specific DHCPv6 Options in
                             Reservations

                             9.3.5. Reserving Client Classes in DHCPv6

                             9.3.6. Storing Host Reservations in MySQL,
                             PostgreSQL or Cassandra

                             9.3.7. Fine Tuning DHCPv6 Host Reservation

                             9.3.8. Global reservations in DHCPv6

                9.4. Shared networks in DHCPv6

                             9.4.1. Local and relayed traffic in shared
                             networks

                             9.4.2. Client classification in shared networks

                             9.4.3. Host reservations in shared networks

                9.5. Server Identifier in DHCPv6

                9.6. Stateless DHCPv6 (Information-Request Message)

                9.7. Support for RFC 7550 (being now part of RFC 8415)

                9.8. Using Specific Relay Agent for a Subnet

                9.9. Segregating IPv6 Clients in a Cable Network

                9.10. MAC/Hardware Addresses in DHCPv6

                9.11. Duplicate Addresses (DECLINE Support)

                9.12. Statistics in the DHCPv6 Server

                9.13. Management API for the DHCPv6 Server

                9.14. User contexts in IPv6

                9.15. Supported DHCPv6 Standards

                9.16. DHCPv6 Server Limitations

                9.17. Kea DHCPv6 server examples

   10. Lease Expiration in DHCPv4 and DHCPv6

                10.1. Lease Reclamation

                10.2. Configuring Lease Reclamation

                10.3. Configuring Lease Affinity

                10.4. Default Configuration Values for Leases Reclamation

                10.5. Reclaiming Expired Leases with Command

   11. Congestion Handling in DHCPv4 and DHCPv6

                11.1. What is Congestion?

                11.2. Configuring Congestion Handling

   12. The DHCP-DDNS Server

                12.1. Overview

                             12.1.1. DNS Server selection

                             12.1.2. Conflict Resolution

                             12.1.3. Dual Stack Environments

                12.2. Starting and Stopping the DHCP-DDNS Server

                12.3. Configuring the DHCP-DDNS Server

                             12.3.1. Global Server Parameters

                             12.3.2. TSIG Key List

                             12.3.3. Forward DDNS

                             12.3.4. Reverse DDNS

                             12.3.5. User context in DDNS

                             12.3.6. Example DHCP-DDNS Server Configuration

                12.4. DHCP-DDNS Server Limitations

   13. The LFC process

                13.1. Overview

                13.2. Command Line Options

   14. Client Classification

                14.1. Client Classification Overview

                14.2. Builtin Client Classes

                14.3. Using Expressions In Classification

                             14.3.1. Logical operators

                             14.3.2. Substring

                             14.3.3. Concat

                             14.3.4. Ifelse

                             14.3.5. Hexstring

                14.4. Configuring Classes

                14.5. Using Static Host Reservations In Classification

                14.6. Configuring Subnets With Class Information

                14.7. Configuring Pools With Class Information

                14.8. Using Classes

                14.9. Classes and Hooks

                14.10. Debugging Expressions

   15. Hooks Libraries

                15.1. Introduction

                15.2. Installing Hook packages

                15.3. Configuring Hooks Libraries

                15.4. Available Hooks Libraries

                             15.4.1. user_chk: Checking User Access

                             15.4.2. legal_log: Forensic Logging Hooks

                             15.4.3. flex_id: Flexible Identifiers for Host
                             Reservations

                             15.4.4. host_cmds: Host Commands

                             15.4.5. lease_cmds: Lease Commands

                             15.4.6. subnet_cmds: Subnet Commands

                             15.4.7. class_cmds: Class Commands

                             15.4.8. ha: High Availability

                             15.4.9. stat_cmds: Supplemental Statistics
                             Commands

                             15.4.10. radius: RADIUS server support

                             15.4.11. host_cache: Caching Host Reservations

                15.5. User contexts

   16. Statistics

                16.1. Statistics Overview

                16.2. Statistics Lifecycle

                16.3. Commands for Manipulating Statistics

                             16.3.1. statistic-get command

                             16.3.2. statistic-reset command

                             16.3.3. statistic-remove command

                             16.3.4. statistic-get-all command

                             16.3.5. statistic-reset-all command

                             16.3.6. statistic-remove-all command

   17. Management API

                17.1. Data Syntax

                17.2. Using the Control Channel

                17.3. Commands Supported by Both the DHCPv4 and DHCPv6
                Servers

                             17.3.1. build-report

                             17.3.2. config-get

                             17.3.3. config-reload

                             17.3.4. config-test

                             17.3.5. config-write

                             17.3.6. leases-reclaim

                             17.3.7. libreload

                             17.3.8. list-commands

                             17.3.9. config-set

                             17.3.10. shutdown

                             17.3.11. dhcp-disable

                             17.3.12. dhcp-enable

                             17.3.13. version-get

                17.4. Commands Supported by Control Agent

   18. The libdhcp++ Library

                18.1. Interface detection and Socket handling

   19. Logging

                19.1. Logging Configuration

                             19.1.1. Loggers

                             19.1.2. Logging Message Format

                             19.1.3. Logging During Kea Startup

   20. The Kea Shell

                20.1. Overview

                20.2. Shell Usage

   21. YANG/NETCONF Support

                21.1. Overview

                21.2. Installing NETCONF

                             21.2.1. Installing NETCONF on Ubuntu 18.04

                             21.2.2. Installing NETCONF on CentOS 7.5

                21.3. Quick sysrepo overview

                21.4. Supported YANG models

                21.5. Using the Netconf agent

                21.6. Configuration

                21.7. Kea-netconf Configuration Example

                21.8. Starting and Stopping the Netconf Agent

                21.9. Step by Step Netconf Operation Example

                             21.9.1. Setup of Netconf Operation Example

                             21.9.2. Error handling in Netconf Operation
                             Example

                             21.9.3. Netconf Operation Example with Two Pools

                             21.9.4. Netconf Operation Example with Two
                             Subnets

                             21.9.5. Netconf Operation Example with Logging

   A. API Reference

                A.1. build-report reference

                A.2. cache-clear reference

                A.3. cache-get reference

                A.4. cache-insert reference

                A.5. cache-load reference

                A.6. cache-remove reference

                A.7. cache-write reference

                A.8. class-add reference

                A.9. class-del reference

                A.10. class-get reference

                A.11. class-list reference

                A.12. class-update reference

                A.13. config-get reference

                A.14. config-reload reference

                A.15. config-set reference

                A.16. config-test reference

                A.17. config-write reference

                A.18. dhcp-disable reference

                A.19. dhcp-enable reference

                A.20. ha-continue reference

                A.21. ha-heartbeat reference

                A.22. ha-scopes reference

                A.23. ha-sync reference

                A.24. lease4-add reference

                A.25. lease4-del reference

                A.26. lease4-get reference

                A.27. lease4-get-all reference

                A.28. lease4-update reference

                A.29. lease4-wipe reference

                A.30. lease6-add reference

                A.31. lease6-del reference

                A.32. lease6-get reference

                A.33. lease6-get-all reference

                A.34. lease6-update reference

                A.35. lease6-wipe reference

                A.36. leases-reclaim reference

                A.37. libreload reference

                A.38. list-commands reference

                A.39. network4-add reference

                A.40. network4-del reference

                A.41. network4-get reference

                A.42. network4-list reference

                A.43. network4-subnet-add reference

                A.44. network4-subnet-del reference

                A.45. network6-add reference

                A.46. network6-del reference

                A.47. network6-get reference

                A.48. network6-list reference

                A.49. network6-subnet-add reference

                A.50. network6-subnet-del reference

                A.51. reservation-add reference

                A.52. reservation-del reference

                A.53. reservation-get reference

                A.54. shutdown reference

                A.55. stat-lease4-get reference

                A.56. stat-lease6-get reference

                A.57. statistic-get reference

                A.58. statistic-get-all reference

                A.59. statistic-remove reference

                A.60. statistic-remove-all reference

                A.61. statistic-reset reference

                A.62. statistic-reset-all reference

                A.63. subnet4-add reference

                A.64. subnet4-del reference

                A.65. subnet4-get reference

                A.66. subnet4-list reference

                A.67. subnet6-add reference

                A.68. subnet6-del reference

                A.69. subnet6-get reference

                A.70. subnet6-list reference

                A.71. version-get reference

   B. Acknowledgments

   List of Tables

   4.1. List of available backends

   8.1. List of standard DHCPv4 options

   8.2. List of standard DHCP option types

   8.3. Default FQDN Flag Behavior

   8.4. DHCPv4 Statistics

   9.1. List of Standard DHCPv6 Options

   9.2. List of Experimental DHCPv6 Options

   9.3. Default FQDN Flag Behavior

   9.4. DHCPv6 Statistics

   12.1. Our example network

   12.2. Forward DDNS Domains Needed

   12.3. Reverse DDNS Domains Needed

   14.1. List of Classification Values

   14.2. List of Classification Expressions

   15.1. List of available hooks libraries

   15.2. Default behavior of the server in various HA states

   19.1. List of loggers supported by Kea servers and hooks libraries shipped
   with Kea and premium packages

                            Chapter 1. Introduction

   Table of Contents

   1.1. Supported Platforms

   1.2. Required Software at Run-time

   1.3. Kea Software

   Kea is the next generation of DHCP software developed by ISC. It supports
   both DHCPv4 and DHCPv6 protocols along with their extensions, e.g. prefix
   delegation and dynamic updates to DNS.

   Kea was initially developed as a part of the BIND 10 framework. In early
   2014, ISC made the decision to discontinue active development of BIND 10
   and continue development of Kea as standalone DHCP software.

   This guide covers Kea version 1.5.0.

1.1. Supported Platforms

   Kea is officially supported on CentOS, Fedora, Ubuntu, Debian and FreeBSD
   systems. It is also likely to work on many other platforms. Kea-1.5.0
   builds have been tested on:

     * CentOS Linux -- 7.1804 (aka 7.5)
     * Fedora -- 28, 29
     * Ubuntu -- 16.04, 18.04
     * Debian GNU/Linux -- 7, 8, 9
     * FreeBSD -- 11.0
     * macOS -- 10.13, 10.14

   There are currently no plans to port Kea to Windows platforms.

1.2. Required Software at Run-time

   Running Kea uses various extra software which may not be provided in the
   default installation of some operating systems, nor in the standard
   package collections. You may need to install this required software
   separately. (For the build requirements, also see Section 3.3, "Building
   Requirements".)

     * Kea supports two crypto libraries: Botan and OpenSSL. Only one of them
       is required to be installed during compilation. Kea uses the Botan
       crypto library for C++ (http://botan.randombit.net/), version 1.9 or
       later. Note that support for Botan versions earlier than 2.0 will be
       dropped in Kea 1.6.0 release. As an alternative to Botan, Kea can use
       the OpenSSL crypto library (http://www.openssl.org/), version 1.0.2 or
       later.
     * Kea uses the log4cplus C++ logging library
       (http://log4cplus.sourceforge.net/). It requires log4cplus version
       1.0.3 or later.
     * Kea requires Boost system library (http://www.boost.org/) at run-time,
       as building with header only version of Boost is no longer
       recommended.
     * In order to store lease information in a MySQL database, Kea requires
       MySQL headers and libraries. This is an optional dependency in that
       Kea can be built without MySQL support.
     * In order to store lease information in a PostgreSQL database, Kea
       requires PostgreSQL headers and libraries. This is an optional
       dependency in that Kea can be built without PostgreSQL support.
     * In order to store lease information in a Cassandra database (CQL), Kea
       requires Cassandra headers and libraries. This is an optional
       dependency in that Kea can be built without Cassandra support.
     * As of Kea 1.4.0 release, the integration with RADIUS is provided in
       Kea via the hooks library available to our Support Customers. Use of
       this library requires FreeRadius-client library to be present on the
       system where Kea is running. This is an optional dependency in that
       Kea can be built without RADIUS support.
     * As of 1.5.0 release, Kea provides NETCONF interface with the
       kea-netconf agent. This Kea module is built optionally and requires
       Sysrepo software when used. Building Kea with NETCONF support requires
       many dependencies to be installed which are described in more details
       in Section 21.2, "Installing NETCONF".

1.3. Kea Software

   Kea is modular. Part of this modularity is accomplished using multiple
   cooperating processes which, together, provide the server functionality.
   The following software is included with Kea:

     * keactrl -- Tool to start, stop, reconfigure, and report status for the
       Kea servers.
     * kea-dhcp4 -- The DHCPv4 server process. This process responds to
       DHCPv4 queries from clients.
     * kea-dhcp6 -- The DHCPv6 server process. This process responds to
       DHCPv6 queries from clients.
     * kea-dhcp-ddns -- The DHCP Dynamic DNS process. This process acts as an
       intermediary between the DHCP servers and DNS servers. It receives
       name update requests from the DHCP servers and sends DNS Update
       messages to the DNS servers.
     * kea-admin -- A useful tool for database backend maintenance (creating
       a new database, checking versions, upgrading etc.)
     * kea-lfc -- This process removes redundant information from the files
       used to provide persistent storage for the memfile data base backend.
       While it can be run standalone, it is normally run as and when
       required by the Kea DHCP servers.
     * kea-ctrl-agent -- Kea Control Agent (CA) is a daemon that exposes a
       RESTful control interface for managing Kea servers.
     * kea-netconf - Kea netconf is an agent that provides a YANG/NETCONF
       interface for the Kea environment.
     * kea-shell -- Simple text client that uses REST interface to connect to
       Kea Control Agent.
     * perfdhcp -- A DHCP benchmarking tool which simulates multiple clients
       to test both DHCPv4 and DHCPv6 server performance.

   The tools and modules are covered in full detail in this guide. In
   addition, manual pages are also provided in the default installation.

   Kea also provides C++ libraries and programmer interfaces for DHCP. These
   include detailed developer documentation and code examples.

                             Chapter 2. Quick Start

   Table of Contents

   2.1. Quick Start Guide for DHCPv4 and DHCPv6 Services

   2.2. Running the Kea Servers Directly

   This section describes the basic steps needed to get Kea up and running.
   For further details, full customizations, and troubleshooting, see the
   respective chapters in the Kea guide.

2.1. Quick Start Guide for DHCPv4 and DHCPv6 Services

    1. Install required run-time and build dependencies. See Section 3.3,
       "Building Requirements" for details.
    2. Download Kea source tarball from ISC.org downloads page or ISC ftp
       server.

    3. Extract the tarball. For example:

 $ tar xvzf kea-1.5.0.tar.gz

    4. Go into the source directory and run the configure script:

 $ cd kea-1.5.0
 $ ./configure [your extra parameters]

    5. Build it:

 $ make

    6. Install it (by default it will be placed in /usr/local/, so it is
       likely that you will need root privileges for this step):

 # make install

    7. Edit the Kea configuration files which by default are installed in the
       [kea-install-dir]/etc/kea/ directory. These are: kea-dhcp4.conf,
       kea-dhcp6.conf, kea-dhcp-ddns.conf and kea-ctrl-agent.conf, for DHCPv4
       server, DHCPv6 server, D2 and Control Agent respectively.

    8. In order to start the DHCPv4 server in background, run the following
       command (as root):

 # keactrl start -s dhcp4

       Or run the following command to start DHCPv6 server instead:

 # keactrl start -s dhcp6

       Note that it is also possible to start all servers simultaneously:

 $ keactrl start

    9. Verify that Kea server(s) are running:

 # keactrl status

       A server status of "inactive" may indicate a configuration error.
       Please check the log file (by default named
       [kea-install-dir]/var/kea/kea-dhcp4.log,
       [kea-install-dir]/var/kea/kea-dhcp6.log,
       [kea-install-dir]/var/kea/kea-ddns.log or
       [kea-install-dir]/var/kea/kea-ctrl-agent.log) for the details of the
       error.

   10. If the server has been started successfully, test that it is
       responding to DHCP queries and that the client receives a
       configuration from the server; for example, use the ISC DHCP client.

   11. Stop running the server(s):

 # keactrl stop

   For instructions specific to your system, please read the system specific
   notes, available in the Kea section of ISC's Knowledgebase.

   The details of keactrl script usage can be found in Chapter 6, Managing
   Kea with keactrl.

2.2. Running the Kea Servers Directly

   The Kea servers can be started directly, without the need to use the
   keactrl. To start the DHCPv4 server run the following command:

 # kea-dhcp4 -c /path/to/your/kea4/config/file.json

   Similarly, to start the DHCPv6 server run the following command:

 # kea-dhcp6 -c /path/to/your/kea6/config/file.json

                            Chapter 3. Installation

   Table of Contents

   3.1. Packages

   3.2. Installation Hierarchy

   3.3. Building Requirements

   3.4. Installation from Source

                3.4.1. Download Tar File

                3.4.2. Retrieve from Git

                3.4.3. Configure Before the Build

                3.4.4. Build

                3.4.5. Install

   3.5. DHCP Database Installation and Configuration

                3.5.1. Building with MySQL Support

                3.5.2. Building with PostgreSQL support

                3.5.3. Building with CQL (Cassandra) support

3.1. Packages

   Some operating systems or software package vendors may provide
   ready-to-use, pre-built software packages for Kea. Installing a pre-built
   package means you do not need to install the software required only to
   build Kea and do not need to make the software.

3.2. Installation Hierarchy

   The following is the directory layout of the complete Kea installation.
   (All directory paths are relative to the installation directory):

     * bin/ -- utility programs.
     * etc/kea/ -- configuration files.
     * include/ -- C++ development header files.
     * lib/ -- libraries.
     * lib/hooks -- additional hooks libraries.
     * sbin/ -- server software and commands used by the system
       administrator.
     * share/kea/ -- configuration specifications and examples.
     * share/doc/kea/ -- this guide, other supplementary documentation, and
       examples.
     * share/man/ -- manual pages (online documentation).
     * var/kea/ -- server identification, lease databases, and log files.

3.3. Building Requirements

   In addition to the run-time requirements (listed in Section 1.2, "Required
   Software at Run-time"), building Kea from source code requires various
   development include headers and program development tools.

  Note

   Some operating systems have split their distribution packages into a
   run-time and a development package. You will need to install the
   development package versions, which include header files and libraries, to
   build Kea from the source code.

   Building from source code requires the following software installed on the
   system:

     * Boost C++ Libraries (http://www.boost.org/). The oldest Boost version
       used for testing is 1.57 (it may work with older versions). Boost
       system library is required. Building boost header only is no longer
       recommended.

     * Botan (at least version 1.9) or OpenSSL (at least version 1.0.1). Note
       that Botan version 2 or later and OpenSSL version 1.0.2 or 1.1.0 or
       later are strongly recommended.

     * log4cplus (at least version 1.0.3) development include headers.

     * A C++ compiler (with C++11 support) and standard development headers.
       Kea builds have been tested with GCC g++ 4.7.2 4.7.3 4.8.2 4.8.4 4.8.5
       4.9.3 4.9.4 5.3.1 5.4.0 6.3.0 6.3.1 clang-800.0.38 clang-802.0.42
       clang-900.0.37

     * The development tools automake, libtool, pkg-config.

     * The MySQL client and the client development libraries, when using the
       --with-mysql configuration flag to build the Kea MySQL database
       backend. In this case an instance of the MySQL server running locally
       or on a machine reachable over a network is required. Note that
       running the unit tests requires a local MySQL server.

     * The PostgreSQL client and the client development libraries, when using
       the --with-pgsql configuration flag to build the Kea PostgreSQL
       database backend. In this case an instance of the PostgreSQL server
       running locally or on some other machine, reachable over the network
       from the machine running Kea, is required. Note that running the unit
       tests requires a local PostgreSQL server.

     * Cpp-driver from DataStax is needed when using the --with-cql
       configuration flag to build Kea with Cassandra database backend. In
       this case an instance of the Cassandra server running locally or on
       some other machine, reachable over the network from the machine
       running Kea, is required. Note that running the unit tests requires a
       local Cassandra server.

     * FreeRADIUS client library when --with-freeradius configuration flag
       used.

     * Sysrepo (version 0.7.6 or later) and libyang (version 0.16-r2 or
       later) when --with-sysrepo configuration flag used.

     * googletest (version 1.8 or later), when using the --with-gtest
       configuration option to build the unit tests.

     * The documentation generation tools elinks, docbook-xsl, libxslt and
       Doxygen, if using the --enable-generate-docs configuration option to
       create the documentation.

   Visit ISC's Knowledgebase at https://kb.isc.org/docs/installing-kea for
   system-specific installation tips.

3.4. Installation from Source

   Kea is open source software written in C++. It is freely available in
   source code form from ISC as a downloadable tar file. A copy of the Kea
   source code repository is accessible from Gitlab
   (https://gitlab.isc.org/isc-projects/kea). Kea may also be available in
   pre-compiled ready-to-use packages from operating system vendors.

  3.4.1. Download Tar File

   The Kea release tarballs may be downloaded from:
   http://ftp.isc.org/isc/kea/ (using FTP or HTTP).

  3.4.2. Retrieve from Git

   Downloading this "bleeding edge" code is recommended only for developers
   or advanced users. Using development code in a production environment is
   not recommended.

  Note

   When building from source code retrieved via Git, additional software will
   be required: automake (v1.11 or later), libtoolize, and autoconf (v2.69 or
   later). These may need to be installed.

   The latest development code is available on Gitlab (see
   https://gitlab.isc.org/isc-projects/kea). The Kea source is public and
   development is done in the "master" branch.

   The code can be checked out from
   https://gitlab.isc.org/isc-projects/kea.git:

 $ git clone https://gitlab.isc.org/isc-projects/kea.git

   The code checked out from the git repository does not include the
   generated configure script, Makefile.in files, nor their related build
   files. They can be created by running autoreconf with the --install
   switch. This will run autoconf, aclocal, libtoolize, autoheader, automake,
   and related commands.

   Write access to the Kea repository is only granted to ISC staff. If you
   are a developer planning to contribute to Kea, please check our
   Contributor's Guide. The Kea Developer's Guide contains more information
   about the process, as well as describes the requirements for contributed
   code to be accepted by ISC.

  3.4.3. Configure Before the Build

   Kea uses the GNU Build System to discover build environment details. To
   generate the makefiles using the defaults, simply run:

 $ ./configure

   Run ./configure with the --help switch to view the different options. Some
   commonly-used options are:

   --prefix
           Define the installation location (the default is /usr/local).

   --with-boost-include
           Define the path to find the Boost headers.

   --with-botan-config
           Specify the path to the botan-config script to build with Botan
           for cryptographic functions.

   --with-mysql
           Build Kea with code to allow it to store leases and host
           reservations in a MySQL database.

   --with-pgsql
           Build Kea with code to allow it to store leases and host
           reservations in a PostgreSQL database.

   --with-cql
           Build Kea with code to allow it to store leases and host
           reservations in a Cassandra (CQL) database.

   --with-gtest, --with-gtest-source
           Enable the building of the C++ Unit Tests using the Google Test
           framework. This option specifies the path to the gtest source. (If
           the framework is not installed on your system, it can be
           downloaded from https://github.com/google/googletest.) from
           https://github.com/google/googletest.)

   --with-benchmark, --with-benchmark-source
           Enable the building of the database backend benchmarks using the
           Google Benchmark framework. This option specifies the path to the
           gtest source. (If the framework is not installed on your system,
           it can be downloaded from https://github.com/google/benchmark.)

   --with-log4cplus
           Define the path to find the Log4cplus headers and libraries.

   --with-openssl
           Replace Botan by the OpenSSL the cryptographic library. By default
           configure searches for a valid Botan installation: if one is not
           found, it searches for OpenSSL.

  Note

   For instructions concerning the installation and configuration of database
   backends for Kea, see Section 3.5, "DHCP Database Installation and
   Configuration".

   For example, the following command configures Kea to find the Boost
   headers in /usr/pkg/include, specifies that PostgreSQL support should be
   enabled, and sets the installation location to /opt/kea:

 $ ./configure \
       --with-boost-include=/usr/pkg/include \
       --with-pgsql=/usr/local/bin/pg_config \
       --prefix=/opt/kea

   If you have some problems with building Kea using the header-only Boost
   code or you'd like to use the Boost system library (assumed for the sake
   of this example to be located in /usr/pkg/lib):

 $ ./configure \
       --with-boost-libs=-lboost_system \
       --with-boost-lib-dir=/usr/pkg/lib

   If configure fails, it may be due to missing or old dependencies.

   If configure succeeds, it displays a report with the parameters used to
   build the code. This report is saved into the file config.report and is
   also embedded into the executable binaries, e.g., kea-dhcp4.

  3.4.4. Build

   After the configure step is complete, build the executables from the C++
   code and prepare the Python scripts by running the command:

 $ make

  3.4.5. Install

   To install the Kea executables, support files, and documentation, issue
   the command:

 $ make install

   Do not use any form of parallel or job server options (such as GNU make's
   -j option) when performing this step: doing so may cause errors.

  Note

   The install step may require superuser privileges.

   If required, run ldconfig as root with /usr/local/lib (or with prefix/lib
   if configured with --prefix) in /etc/ld.so.conf (or the relevant linker
   cache configuration file for your OS):

 $ ldconfig

  Note

   If you do not run ldconfig where it is required, you may see errors like
   the following:

               program: error while loading shared libraries: libkea-something.so.1:
               cannot open shared object file: No such file or directory


3.5. DHCP Database Installation and Configuration

   Kea stores its leases in a lease database. The software has been written
   in a way that makes it possible to choose which database product should be
   used to store the lease information. At present, Kea supports four
   database backends: MySQL, PostgreSQL, Cassandra and Memfile. To limit
   external dependencies, MySQL, PostgreSQL and Cassandra support are
   disabled by default and only Memfile is available. Support for the
   optional external database backend must be explicitly included when Kea is
   built. This section covers the building of Kea with one of the optional
   backends and the creation of the lease database.

  Note

   When unit tests are built with Kea (the --with-gtest configuration option
   is specified), the databases must be manually pre-configured for the unit
   tests to run. The details of this configuration can be found in the Kea
   Developer's Guide.

  3.5.1. Building with MySQL Support

   Install MySQL according to the instructions for your system. The client
   development libraries must be installed.

   Build and install Kea as described in Chapter 3, Installation, with the
   following modification. To enable the MySQL database code, at the
   "configure" step (see Section 3.4.3, "Configure Before the Build"), the
   --with-mysql switch should be specified:

 ./configure [other-options] --with-mysql

   If MySQL was not installed in the default location, the location of the
   MySQL configuration program "mysql_config" should be included with the
   switch, i.e.

 ./configure [other-options] --with-mysql=path-to-mysql_config

   See Section 4.3.2.1, "First Time Creation of the MySQL Database" for
   details regarding MySQL database configuration.

  3.5.2. Building with PostgreSQL support

   Install PostgreSQL according to the instructions for your system. The
   client development libraries must be installed. Client development
   libraries are often packaged as "libpq".

   Build and install Kea as described in Chapter 3, Installation, with the
   following modification. To enable the PostgreSQL database code, at the
   "configure" step (see Section 3.4.3, "Configure Before the Build"), the
   --with-pgsql switch should be specified:

 ./configure [other-options] --with-pgsql

   If PostgreSQL was not installed in the default location, the location of
   the PostgreSQL configuration program "pg_config" should be included with
   the switch, i.e.

 ./configure [other-options] --with-pgsql=path-to-pg_config

   See Section 4.3.3.1, "First Time Creation of the PostgreSQL Database" for
   details regarding PostgreSQL database configuration.

  3.5.3. Building with CQL (Cassandra) support

   Install Cassandra according to the instructions for your system. The
   Cassandra project website contains useful pointers:
   http://cassandra.apache.org.

   If you have a cpp-driver package available as binary or as source simply
   install or build and install the package. Then build and install Kea as
   described in Chapter 3, Installation: To enable the Cassandra (CQL)
   database code, at the "configure" step (see Section 3.4.3, "Configure
   Before the Build"), do:

 ./configure [other-options] --with-cql=path-to-pkg-config

   Note if pkg-config is at its standard location (and thus in the shell
   path) you do not need to supply its path. If it does not work (e.g. no
   pkg-config, package not available in pkg-config with the cassandra name),
   you can still use the cql_config script in tools/ as described below.

   Download and compile cpp-driver from DataStax. For details regarding
   dependencies for building cpp-driver, see the project homepage
   https://github.com/datastax/cpp-driver. In June 2016, the following
   commands were used:

 $ git clone https://github.com/datastax/cpp-driver
 $ cd cpp-driver
 $ mkdir build
 $ cd build
 $ cmake ..
 $ make

   As of June 2016, cpp-driver does not include cql_config script yet. Work
   is in progress to contribute such a script to the cpp-driver project but,
   until that is complete, intermediate steps need to be conducted. A
   cql_config script is present in the tools/ directory of the Kea sources.
   Before using it, please create a cql_config_defines.sh in the same
   directory (there is an example in cql_config_define.sh.sample available,
   you may copy it over to cql_config_defines.sh and edit path specified in
   it) and change the environment variable CPP_DRIVER_PATH to point to the
   directory, where cpp-driver sources are located. Make sure that
   appropriate access rights are set on this file. It should be executable by
   the system user building Kea.

   Build and install Kea as described in Chapter 3, Installation, with the
   following modification. To enable the Cassandra (CQL) database code, at
   the "configure" step (see Section 3.4.3, "Configure Before the Build"),
   do:

 ./configure [other-options] --with-cql=path-to-cql_config

                     Chapter 4. Kea Database Administration

   Table of Contents

   4.1. Databases and Database Version Numbers

   4.2. The kea-admin Tool

   4.3. Supported Databases

                4.3.1. memfile

                4.3.2. MySQL

                4.3.3. PostgreSQL

                4.3.4. CQL (Cassandra)

                4.3.5. Using Read-Only Databases with Host Reservations

                4.3.6. Limitations Related to the use of SQL Databases

4.1. Databases and Database Version Numbers

   Kea supports storing leases and host reservations (i.e. static assignments
   of addresses, prefixes and options) in one of the several supported
   databases. As future versions of Kea are released, the structure of those
   databases will change. For example, Kea currently only stores lease
   information and host reservations. Future versions of Kea will store
   additional data such as subnet definitions: the database structure will
   need to be updated to accommodate the extra information.

   A given version of Kea expects a particular structure in the database and
   checks for this by examining the version of database it is using. Separate
   version numbers are maintained for backend databases, independent of the
   version of Kea itself. It is possible that the backend database version
   will stay the same through several Kea revisions: similarly, it is
   possible that the version of backend database may go up several revisions
   during a Kea upgrade. Versions for each database are independent, so an
   increment in the MySQL database version does not imply an increment in
   that of PostgreSQL.

   Backend versions are specified in a major.minor format. The minor number
   is increased when there are backward compatible changes introduced. For
   example, the addition of a new index. It is desirable, but not mandatory
   to apply such a change; you can run on older database version if you want
   to. (Although, in the example given, running without the new index may be
   at the expense of a performance penalty.) On the other hand, the major
   number is increased when an incompatible change is introduced, for example
   an extra column is added to a table. If you try to run Kea software on a
   database that is too old (as signified by mismatched backend major version
   number), Kea will refuse to run: administrative action will be required to
   upgrade the database.

4.2. The kea-admin Tool

   To manage the databases, Kea provides the kea-admin tool. It is able to
   initialize a new database, check its version number, perform a database
   upgrade, and dump lease data to a text file.

   kea-admin takes two mandatory parameters: command and backend. Additional,
   non-mandatory options may be specified. Currently supported commands are:

     * lease-init -- Initializes a new lease database. This is useful during
       a new Kea installation. The database is initialized to the latest
       version supported by the version of the software being installed.
     * lease-version -- Reports the lease database version number. This is
       not necessarily equal to the Kea version number as each backend has
       its own versioning scheme.
     * lease-upgrade -- Conducts a lease database upgrade. This is useful
       when upgrading Kea.
     * lease-dump -- Dumps the contents of the lease database (for MySQL,
       PostgreSQL or CQL backends) to a CSV (comma separated values) text
       file. The first line of the file contains the column names. This is
       meant to be used as a diagnostic tool, so it provides a portable,
       human-readable form of the lease data.

   backend specifies the backend type. Currently supported types are:

     * memfile -- Lease information is stored on disk in a text file.
     * mysql -- Lease information is stored in a MySQL relational database.
     * pgsql -- Lease information is stored in a PostgreSQL relational
       database.
     * cql -- Lease information is stored in a CQL database.

   Additional parameters may be needed, depending on your setup and specific
   operation: username, password and database name or the directory where
   specific files are located. See the appropriate manual page for details
   (man 8 kea-admin).

4.3. Supported Databases

   The following table presents the capabilities of available backends.
   Please refer to the specific sections dedicated to each backend to better
   understand their capabilities and limitations. Choosing the right backend
   may be essential for success or failure of your deployment.

   Table 4.1. List of available backends

   +------------------------------------------------------------------------+
   |      Feature      | Memfile  |  MySQL   | PostgreSQL | CQL (Cassandra) |
   |-------------------+----------+----------+------------+-----------------|
   | Status            | Stable   | Stable   | Stable     | Experimental    |
   |-------------------+----------+----------+------------+-----------------|
   | Data format       | CSV file | SQL RMDB | SQL RMDB   | NoSQL database  |
   |                   |          |          |            | (CQL)           |
   |-------------------+----------+----------+------------+-----------------|
   | Leases            | yes      | yes      | yes        | yes             |
   |-------------------+----------+----------+------------+-----------------|
   | Host Reservations | no       | yes      | yes        | yes             |
   |-------------------+----------+----------+------------+-----------------|
   | Options defined   | no       | yes      | yes        | yes             |
   | on per host basis |          |          |            |                 |
   +------------------------------------------------------------------------+

  4.3.1. memfile

   The memfile backend is able to store lease information, but is not able to
   store host reservation details: these must be stored in the configuration
   file. (There are no plans to add a host reservations storage capability to
   this backend.)

   No special initialization steps are necessary for the memfile backend.
   During the first run, both kea-dhcp4 and kea-dhcp6 will create an empty
   lease file if one is not present. Necessary disk write permission is
   required.

    4.3.1.1. Upgrading Memfile Lease Files from an Earlier Version of Kea

   There are no special steps required to upgrade memfile lease files from an
   earlier version of Kea to a new version of Kea. During startup the servers
   will check the schema version of the lease files against their own. If
   there is a mismatch, the servers will automatically launch the LFC process
   to convert the files to the server's schema version. While this mechanism
   is primarily meant to ease the process of upgrading to newer versions of
   Kea, it can also be used for downgrading should the need arise. When
   upgrading, any values not present in the original lease files will be
   assigned appropriate default values. When downgrading, any data present in
   the files but not in the server's schema will be dropped. If you wish to
   convert the files manually, prior to starting the servers you may do so by
   running the LFC process yourself. See Chapter 13, The LFC process for more
   information.

  4.3.2. MySQL

   MySQL is able to store leases, host reservations and options defined on a
   per host basis. This section can be safely ignored if you chose to store
   the data in other backends.

    4.3.2.1. First Time Creation of the MySQL Database

   If you are setting the MySQL database for the first time, you need to
   create the database area within MySQL and set up the MySQL user ID under
   which Kea will access the database. This needs to be done manually:
   kea-admin is not able to do this for you.

   To create the database:

    1. Log into MySQL as "root":

 $ mysql -u root -p
 Enter password:
 mysql>

    2. Create the MySQL database:

 mysql> CREATE DATABASE database-name;

       (database-name is the name you have chosen for the database.)

    3. Create the user under which Kea will access the database (and give it
       a password), then grant it access to the database tables:

 mysql> CREATE USER 'user-name'@'localhost' IDENTIFIED BY 'password';
 mysql> GRANT ALL ON database-name.* TO 'user-name'@'localhost';

       (user-name and password are the user ID and password you are using to
       allow Keas access to the MySQL instance. All apostrophes in the
       command lines above are required.)

    4. At this point, you may elect to create the database tables.
       (Alternatively, you can exit MySQL and create the tables using the
       kea-admin tool, as explained below.) To do this:

 mysql> CONNECT database-name;
 mysql> SOURCE path-to-kea/share/kea/scripts/mysql/dhcpdb_create.mysql

       (path-to-kea is the location where you installed Kea.)

    5. Exit MySQL:

 mysql> quit
 Bye
 $

   If you elected not to create the tables in step 4, you can do so now by
   running the kea-admin tool:

 $ kea-admin lease-init mysql -u database-user -p database-password -n database-name

   (Do not do this if you did create the tables in step 4.) kea-admin
   implements rudimentary checks: it will refuse to initialize a database
   that contains any existing tables. If you want to start from scratch, you
   must remove all data manually. (This process is a manual operation on
   purpose to avoid possibly irretrievable mistakes by kea-admin.)

    4.3.2.2. Upgrading a MySQL Database from an Earlier Version of Kea

   Sometimes a new Kea version may use newer database schema, so there will
   be a need to upgrade the existing database. This can be done using the
   kea-admin lease-upgrade command.

   To check the current version of the database, use the following command:

 $ kea-admin lease-version mysql -u database-user -p database-password -n database-name

   (See Section 4.1, "Databases and Database Version Numbers" for a
   discussion about versioning.) If the version does not match the minimum
   required for the new version of Kea (as described in the release notes),
   the database needs to be upgraded.

   Before upgrading, please make sure that the database is backed up. The
   upgrade process does not discard any data but, depending on the nature of
   the changes, it may be impossible to subsequently downgrade to an earlier
   version. To perform an upgrade, issue the following command:

 $ kea-admin lease-upgrade mysql -u database-user -p database-password -n database-name

  4.3.3. PostgreSQL

   PostgreSQL is able to store leases, host reservations and options defined
   on a per host basis. A PostgreSQL database must be set up if you want Kea
   to store lease and other information in PostgreSQL. This step can be
   safely ignored if you are using other database backends.

    4.3.3.1. First Time Creation of the PostgreSQL Database

   The first task is to create both the lease database and the user under
   which the servers will access it. A number of steps are required:

    1. Log into PostgreSQL as "root":

 $ sudo -u postgres psql postgres
 Enter password:
 postgres=#

    2. Create the database:

 postgres=# CREATE DATABASE database-name;
 CREATE DATABASE
 postgres=#

       (database-name is the name you have chosen for the database.)

    3. Create the user under which Kea will access the database (and give it
       a password), then grant it access to the database:

 postgres=# CREATE USER user-name WITH PASSWORD 'password';
 CREATE ROLE
 postgres=# GRANT ALL PRIVILEGES ON DATABASE database-name TO user-name;
 GRANT
 postgres=#

    4. Exit PostgreSQL:

 postgres=# \q
 Bye
 $

    5. At this point you are ready to create the database tables. This can be
       done using the kea-admin tool as explained in the next section
       (recommended), or manually. To create the tables manually enter the
       following command. Note that PostgreSQL will prompt you to enter the
       new user's password you specified in Step 3. When the command
       completes you will be returned to the shell prompt. You should see
       output similar to following:

 $ psql -d database-name -U user-name -f path-to-kea/share/kea/scripts/pgsql/dhcpdb_create.pgsql
 Password for user user-name:
 CREATE TABLE
 CREATE INDEX
 CREATE INDEX
 CREATE TABLE
 CREATE INDEX
 CREATE TABLE
 START TRANSACTION
 INSERT 0 1
 INSERT 0 1
 INSERT 0 1
 COMMIT
 CREATE TABLE
 START TRANSACTION
 INSERT 0 1
 COMMIT
 $

       (path-to-kea is the location where you installed Kea.)

       If instead you encounter an error like:

 psql: FATAL:  no pg_hba.conf entry for host "[local]", user "user-name", database "database-name", SSL off

       ... you will need to alter the PostgreSQL configuration. Kea uses
       password authentication when connecting to the database and must have
       the appropriate entries added to PostgreSQL's pg_hba.conf file. This
       file is normally located in the primary data directory for your
       PostgreSQL server. The precise path may vary but the default location
       for PostgreSQL 9.3 on Centos 6.5 is:
       /var/lib/pgsql/9.3/data/pg_hba.conf.

       Assuming Kea is running on the same host as PostgreSQL, adding lines
       similar to following should be sufficient to provide
       password-authenticated access to Kea's database:

 local   database-name    user-name                                 password
 host    database-name    user-name          127.0.0.1/32           password
 host    database-name    user-name          ::1/128                password

       These edits are primarily intended as a starting point not a
       definitive reference on PostgreSQL administration or database
       security. Please consult your PostgreSQL user manual before making
       these changes as they may expose other databases that you run. It may
       be necessary to restart PostgreSQL in order for these changes to take
       effect.

    4.3.3.2. Initialize the PostgreSQL Database Using kea-admin

   If you elected not to create the tables manually, you can do so now by
   running the kea-admin tool:

 $ kea-admin lease-init pgsql -u database-user -p database-password -n database-name

   Do not do this if you already created the tables in manually. kea-admin
   implements rudimentary checks: it will refuse to initialize a database
   that contains any existing tables. If you want to start from scratch, you
   must remove all data manually. (This process is a manual operation on
   purpose to avoid possibly irretrievable mistakes by kea-admin.)

    4.3.3.3. Upgrading a PostgreSQL Database from an Earlier Version of Kea

   The PostgreSQL database schema can be upgraded using the same tool and
   commands as described in Section 4.3.2.2, "Upgrading a MySQL Database from
   an Earlier Version of Kea", with the exception that the "pgsql" database
   backend type must be used in the commands.

   Use the following command to check the current schema version:

 $ kea-admin lease-version pgsql -u database-user -p database-password -n database-name

   Use the following command to perform an upgrade:

 $ kea-admin lease-upgrade pgsql -u database-user -p database-password -n database-name

  4.3.4. CQL (Cassandra)

   Cassandra, or Cassandra Query Language (CQL), is the newest backend added
   to Kea. Since it was added recently and has not undergone as much testing
   as other backends, it is considered experimental. Please use with caution.
   The Cassandra backend is able to store leases, host reservations and
   options defined on a per host basis.

   The CQL database must be properly set up if you want Kea to store
   information in CQL. This section can be safely ignored if you chose to
   store the data in other backends.

    4.3.4.1. First Time Creation of the Cassandra Database

   If you are setting up the CQL database for the first time, you need to
   create the keyspace area within CQL. This needs to be done manually:
   kea-admin is not able to do this for you.

   To create the database:

    1. Export CQLSH_HOST environment variable:

 $ export CQLSH_HOST=localhost

    2. Log into CQL:

 $ cqlsh
 cql>

    3. Create the CQL keyspace:

 cql> CREATE KEYSPACE keyspace-name WITH replication = {'class' : 'SimpleStrategy','replication_factor' : 1};

       (keyspace-name is the name you have chosen for the keyspace)

    4. At this point, you may elect to create the database tables.
       (Alternatively, you can exit CQL and create the tables using the
       kea-admin tool, as explained below) To do this:

 cqslh -k keyspace-name -f path-to-kea/share/kea/scripts/cql/dhcpdb_create.cql

       (path-to-kea is the location where you installed Kea)

   If you elected not to create the tables in step 4, you can do so now by
   running the kea-admin tool:

 $ kea-admin lease-init cql -n database-name

   (Do not do this if you did create the tables in step 4.) kea-admin
   implements rudimentary checks: it will refuse to initialize a database
   that contains any existing tables. If you want to start from scratch, you
   must remove all data manually. (This process is a manual operation on
   purpose to avoid possibly irretrievable mistakes by kea-admin)

    4.3.4.2. Upgrading a CQL Database from an Earlier Version of Kea

   Sometimes a new Kea version may use newer database schema, so there will
   be a need to upgrade the existing database. This can be done using the
   kea-admin lease-upgrade command.

   To check the current version of the database, use the following command:

 $ kea-admin lease-version cql -n database-name

   (See Section 4.1, "Databases and Database Version Numbers" for a
   discussion about versioning) If the version does not match the minimum
   required for the new version of Kea (as described in the release notes),
   the database needs to be upgraded.

   Before upgrading, please make sure that the database is backed up. The
   upgrade process does not discard any data but, depending on the nature of
   the changes, it may be impossible to subsequently downgrade to an earlier
   version. To perform an upgrade, issue the following command:

 $ kea-admin lease-upgrade cql -n database-name

  4.3.5. Using Read-Only Databases with Host Reservations

   If a read-only database is used for storing host reservations, Kea must be
   explicitly configured to operate on the database in read-only mode.
   Sections Section 8.2.3.2, "Using Read-Only Databases for Host
   Reservations" and Section 9.2.3.2, "Using Read-Only Databases for Host
   Reservations" describe when such configuration may be required and how to
   configure Kea to operate using a read-only host database.

  4.3.6. Limitations Related to the use of SQL Databases

    4.3.6.1. Year 2038 issue

   The lease expiration time is stored in the SQL database for each lease as
   a timestamp value. Kea developers observed that MySQL database doesn't
   accept timestamps beyond 2147483647 seconds (maximum signed 32-bit number)
   from the beginning of the epoch. At the same time, some versions of
   PostgreSQL do accept greater values but the value is altered when it is
   read back. For this reason the lease database backends put the restriction
   for the maximum timestamp to be stored in the database, which is equal to
   the maximum signed 32-bit number. This effectively means that the current
   Kea version can't store the leases which expiration time is later than
   2147483647 seconds since the beginning of the epoch (around year 2038).
   This will be fixed when the database support for longer timestamps is
   available.

                          Chapter 5. Kea Configuration

   Table of Contents

   5.1. JSON Configuration

                5.1.1. JSON Syntax

                5.1.2. Simplified Notation

   Kea is using JSON structures to represent servers' configurations. The
   following sections describe how the configuration structures are
   organized.

5.1. JSON Configuration

   JSON is notation used throughout the Kea project. The most obvious usage
   is for the configuration file, but it is also used for sending commands
   over Management API (see Chapter 17, Management API) and for communicating
   between DHCP servers and DDNS update daemon.

   Typical usage assumes that the servers are started from the command line
   (either directly or using a script, e.g. keactrl). The configuration file
   is specified upon startup using the -c parameter.

  5.1.1. JSON Syntax

   Configuration files for DHCPv4, DHCPv6, DDNS, Control Agent and Netconf
   modules are defined in an extended JSON format. Basic JSON is defined in
   RFC 7159 and ECMA 404. Note that Kea 1.2.0 introduced a new parser which
   better adheres to the JSON specification. In particular, the only values
   allowed for boolean are true or false (all lowercase). The capitalized
   versions (True or False) are not accepted.

   Kea components use an extended JSON with additional features allowed:

     * shell comments: any text after the hash (#) character is ignored.
     * C comments: any text after the double slashes (//) character is
       ignored.
     * Multiline comments: any text between /* and */ is ignored. This
       commenting can span multiple lines.
     * File inclusion: JSON files can include other JSON files. This can be
       done by using <?include "file.json"?>.

   The configuration file consists of a single object (often colloquially
   called a map) started with a curly bracket. It comprises one or more of
   the "Dhcp4", "Dhcp6", "DhcpDdns", "Control-agent", "Netconf", and
   "Logging" objects. It is possible to define additional elements but they
   will be ignored.

   A very simple configuration for DHCPv4 could look like this:

 # The whole configuration starts here.
 {
     # DHCPv4 specific configuration starts here.
     "Dhcp4": {
         "interfaces-config": {
             "interfaces": [ "eth0" ],
             "dhcp-socket-type": "raw"
         },
         "valid-lifetime": 4000,
         "renew-timer": 1000,
         "rebind-timer": 2000,
         "subnet4": [{
            "pools": [ { "pool": "192.0.2.1-192.0.2.200" } ],
            "subnet": "192.0.2.0/24"
         }]
     },

     # Logger configuration starts here.
     "Logging": {
        "loggers": [{
             "name": "*",
             "severity": "DEBUG"
         }]
     }

 # The whole configuration structure ends here.
 }

   More examples are available in the installed share/doc/kea/examples
   directory.

  Note

   The "Logging" element will be removed in Kea 1.6.0 and its contents (the
   "loggers" object) moved inside the configuration objects (maps) for
   respective Kea modules. For example: the "Dhcp4" map will contain the
   "loggers" object specifying logging configuration for the DHCPv4 server.
   Backward compatibility will be maintained until at least Kea 1.7.0
   release: it will be possible to specify "Logging" object at the top
   configuration level and "loggers" objects at module configuration level.
   Ultimately though, support for the top-level "Logging" object will be
   removed.

   The specification of several supported elements (e.g. "Dhcp4", "Dhcp6") in
   a single configuration file can be confusing and works badly with the
   commands that fetch and write new configurations. Support for it will be
   removed in a future release of Kea, after which each component will
   require its own configuration file.

   To avoid repetition of mostly similar structures, examples in the rest of
   this guide will showcase only the subset of parameters appropriate for a
   given context. For example, when discussing the IPv6 subnets configuration
   in DHCPv6, only subnet6 parameters will be mentioned. It is implied that
   the remaining elements (the global map that holds Dhcp6 and Logging) are
   present, but they are omitted for clarity. Usually, locations where extra
   parameters may appear are denoted by an ellipsis.

  5.1.2. Simplified Notation

   It is sometimes convenient to refer to a specific element in the
   configuration hierarchy. Each hierarchy level is separated by a slash. If
   there is an array, a specific instance within that array is referenced by
   a number in square brackets (with numbering starting at zero). For
   example, in the above configuration the valid-lifetime in the Dhcp4
   component can be referred to as Dhcp4/valid-lifetime and the pool in the
   first subnet defined in the DHCPv4 configuration as Dhcp4/subnet4[0]/pool.

                      Chapter 6. Managing Kea with keactrl

   Table of Contents

   6.1. Overview

   6.2. Command Line Options

   6.3. The keactrl Configuration File

   6.4. Commands

   6.5. Overriding the Server Selection

6.1. Overview

   keactrl is a shell script which controls the startup, shutdown and
   reconfiguration of the Kea servers (kea-dhcp4, kea-dhcp6, kea-dhcp-ddns,
   kea-ctrl-agent and kea-netconf). It also provides the means for checking
   the current status of the servers and determining the configuration files
   in use.

6.2. Command Line Options

   keactrl is run as follows:

 keactrl <command> [-c keactrl-config-file] [-s server[,server,..]]

   <command> is the one of the commands described in Section 6.4, "Commands".

   The optional -c keactrl-config-file switch allows specification of an
   alternate keactrl configuration file. (--ctrl-config is a synonym for -c.)
   In the absence of -c, keactrl will use the default configuration file
   [kea-install-dir]/etc/kea/keactrl.conf.

   The optional -s server[,server ...] switch selects the servers to which
   the command is issued. (--server is a synonym for -s.) If absent, the
   command is sent to all servers enabled in the keactrl configuration file.
   If multiple servers are specified, they should be separated by commas with
   no intervening spaces.

6.3. The keactrl Configuration File

   Depending on requirements, not all of the available servers need be run.
   The keactrl configuration file sets which servers are enabled and which
   are disabled. The default configuration file is
   [kea-install-dir]/etc/kea/keactrl.conf, but this can be overridden on a
   per-command basis using the -c switch.

   The contents of keactrl.conf are:

 # This is a configuration file for keactrl script which controls
 # the startup, shutdown, reconfiguration and gathering the status
 # of the Kea's processes.

 # prefix holds the location where the Kea is installed.
 prefix=@prefix@

 # Location of Kea configuration file.
 kea_dhcp4_config_file=@sysconfdir@/@PACKAGE@/kea-dhcp4.conf
 kea_dhcp6_config_file=@sysconfdir@/@PACKAGE@/kea-dhcp6.conf
 kea_dhcp_ddns_config_file=@sysconfdir@/@PACKAGE@/kea-dhcp-ddns.conf
 kea_ctrl_agent_config_file=@sysconfdir@/@PACKAGE@/kea-ctrl-agent.conf
 kea_netconf_config_file=@sysconfdir@/@PACKAGE@/kea-netconf.conf


 # Location of Kea binaries.
 exec_prefix=@exec_prefix@
 dhcp4_srv=@sbindir@/kea-dhcp4
 dhcp6_srv=@sbindir@/kea-dhcp6
 dhcp_ddns_srv=@sbindir@/kea-dhcp-ddns
 ctrl_agent_srv=@sbindir@/kea-ctrl-agent
 netconf_srv=@sbindir@/kea-netconf

 # Start DHCPv4 server?
 dhcp4=yes

 # Start DHCPv6 server?
 dhcp6=yes

 # Start DHCP DDNS server?
 dhcp_ddns=no

 # Start Control Agent?
 ctrl_agent=yes

 # Start Netconf?
 netconf=no

 # Be verbose?
 kea_verbose=no

   The dhcp4, dhcp6, dhcp_ddns, ctrl_agent and netconf parameters set to
   "yes" will configure keactrl to manage (start, reconfigure) all servers,
   i.e. kea-dhcp4, kea-dhcp6, kea-dhcp-ddns, kea-ctrl-agent and kea-netconf.
   When any of these parameters is set to "no" the keactrl will ignore the
   corresponding server when starting or reconfiguring Kea. Some daemons
   (ddns and netconf) are disabled by default.

   By default, Kea servers managed by keactrl are located in
   [kea-install-dir]/sbin. This should work for most installations. If the
   default location needs to be altered for any reason, the paths specified
   with the dhcp4_srv, dhcp6_srv, dhcp_ddns_srv ctrl_agent_srv and
   netconf_srv parameters should be modified.

   The kea_verbose parameter specifies the verbosity of the servers being
   started. When kea_verbose is set to "yes" the logging level of the server
   is set to DEBUG. Modification of the logging severity in a configuration
   file, as described in Chapter 19, Logging, will have no effect as long as
   the kea_verbose is set to "yes". Setting it to "no" will cause the server
   to use the logging levels specified in the Kea configuration file for
   respective loggers. If no logging configuration is specified, the default
   settings will be used.

  Note

   The verbosity for the server is set when it is started. Once started, the
   verbosity can be only changed by stopping the server and starting it again
   with the new value of the kea_verbose parameter.

6.4. Commands

   The following commands are supported by keactrl:

     * start - starts selected servers.
     * stop - stops all running servers.
     * reload - triggers reconfiguration of the selected servers by sending
       the SIGHUP signal to them.
     * status - returns the status of the servers (active or inactive) and
       the names of the configuration files in use.
     * version - prints out a version of the keactrl tool itself, but also
       the Kea daemons.

   Typical output from keactrl when starting the servers looks similar to the
   following:

 $ keactrl start
 INFO/keactrl: Starting kea-dhcp4 -c /usr/local/etc/kea/kea-dhcp4.conf -d
 INFO/keactrl: Starting kea-dhcp6 -c /usr/local/etc/kea/kea-dhcp6.conf -d
 INFO/keactrl: Starting kea-dhcp-ddns -c /usr/local/etc/kea/kea-dhcp-ddns.conf -d
 INFO/keactrl: Starting kea-ctrl-agent -c /usr/local/etc/kea/kea-ctrl-agent.conf -d
 INFO/keactrl: Starting kea-netconf -c /usr/local/etc/kea/kea-netconf.conf -d

   Kea's servers create PID files upon startup. These files are used by
   keactrl to determine whether or not a given server is running. If one or
   more servers are running when the start command is issued, the output will
   look similar to the following:

 $ keactrl start
 INFO/keactrl: kea-dhcp4 appears to be running, see: PID 10918, PID file: /usr/local/var/kea/kea.kea-dhcp4.pid.
 INFO/keactrl: kea-dhcp6 appears to be running, see: PID 10924, PID file: /usr/local/var/kea/kea.kea-dhcp6.pid.
 INFO/keactrl: kea-dhcp-ddns appears to be running, see: PID 10930, PID file: /usr/local/var/kea/kea.kea-dhcp-ddns.pid.
 INFO/keactrl: kea-ctrl-agent appears to be running, see: PID 10931, PID file: /usr/local/var/kea/kea.kea-ctrl-agent.pid.
 INFO/keactrl: kea-netconf appears to be running, see: PID 10123, PID file: /usr/local/var/kea/kea.kea-netconf.pid.

   During normal shutdowns these PID files are deleted. They may, however, be
   left over as remnants following a system crash. It is possible, though
   highly unlikely, that upon system restart the PIDs they contain actually
   refer to processes unrelated to Kea. This condition will cause keactrl to
   decide that the servers are running, when in fact they are not. In such a
   case the PID files as listed in the keactrl output must be manually
   deleted.

   The following command stops all servers:

 $ keactrl stop
 INFO/keactrl: Stopping kea-dhcp4...
 INFO/keactrl: Stopping kea-dhcp6...
 INFO/keactrl: Stopping kea-dhcp-ddns...
 INFO/keactrl: Stopping kea-ctrl-agent...
 INFO/keactrl: Stopping kea-netconf...

   Note that the stop will attempt to stop all servers regardless of whether
   they are "enabled" in the keactrl.conf. If any of the servers are not
   running, an informational message is displayed as in the stop command
   output below.

 $ keactrl stop
 INFO/keactrl: kea-dhcp4 isn't running.
 INFO/keactrl: kea-dhcp6 isn't running.
 INFO/keactrl: kea-dhcp-ddns isn't running.
 INFO/keactrl: kea-ctrl-agent isn't running.
 INFO/keactrl: kea-netconf isn't running.

   As already mentioned, the reconfiguration of each Kea server is triggered
   by the SIGHUP signal. The reload command sends the SIGHUP signal to the
   servers that are enabled in the keactrl configuration file and are
   currently running. When a server receives the SIGHUP signal it re-reads
   its configuration file and, if the new configuration is valid, uses the
   new configuration. A reload is executed as follows:

 $ keactrl reload
 INFO/keactrl: Reloading kea-dhcp4...
 INFO/keactrl: Reloading kea-dhcp6...
 INFO/keactrl: Reloading kea-dhcp-ddns...
 INFO/keactrl: Reloading kea-ctrl-agent...

   If any of the servers are not running, an informational message is
   displayed as in the reload command output below. Note that as of 1.5.0
   kea-netconf does not support SIGHUP signal yet. If its configuration has
   changed, please stop and start it. This limitation will be removed in
   upcoming Kea releases.

 $ keactrl stop
 INFO/keactrl: kea-dhcp4 isn't running.
 INFO/keactrl: kea-dhcp6 isn't running.
 INFO/keactrl: kea-dhcp-ddns isn't running.
 INFO/keactrl: kea-ctrl-agent isn't running.
 INFO/keactrl: kea-netconf isn't running.

  Note

   NETCONF is an optional feature that is disabled by default and can be
   enabled during compilation. If Kea was compiled without NETCONF support,
   keactrl will do it's best to not bother the user with information about
   it. The netconf entries will still be present in the keactrl.conf file,
   but netconf status will not be shown and other commands will ignore it.

  Note

   Currently keactrl does not report configuration failures when the server
   is started or reconfigured. To check if the server's configuration
   succeeded the Kea log must be examined for errors. By default, this is
   written to the syslog file.

   Sometimes it is useful to check which servers are running. The status
   reports this, typical output looking like:

 $ keactrl status
 DHCPv4 server: active
 DHCPv6 server: inactive
 DHCP DDNS: active
 Control Agent: active
 Netconf agent: inactive
 Kea configuration file: /usr/local/etc/kea/kea.conf
 Kea DHCPv4 configuration file: /usr/local/etc/kea/kea-dhcp4.conf
 Kea DHCPv6 configuration file: /usr/local/etc/kea/kea-dhcp6.conf
 Kea DHCP DDNS configuration file: /usr/local/etc/kea/kea-dhcp-ddns.conf
 Kea Control Agent configuration file: /usr/local/etc/kea/kea-ctrl-agent.conf
 Kea Netconf configuration file: /usr/local/etc/kea/kea-netconf.conf
 keactrl configuration file: /usr/local/etc/kea/keactrl.conf

6.5. Overriding the Server Selection

   The optional -s switch allows the selection of the servers to which
   keactrl command is issued. For example, the following instructs keactrl to
   stop the kea-dhcp4 and kea-dhcp6 servers and leave the kea-dhcp-ddns and
   kea-ctrl-agent running:

 $ keactrl stop -s dhcp4,dhcp6

   Similarly, the following will only start the kea-dhcp4 and kea-dhcp-ddns
   servers and not: kea-dhcp6, kea-ctrl-agent.

 $ keactrl start -s dhcp4,dhcp_ddns

   Note that the behavior of the -s switch with the start and reload commands
   is different to its behavior with the stop command. On start and reload,
   keactrl will check if the servers given as parameters to the -s switch are
   enabled in the keactrl configuration file: if not, the server will be
   ignored. For stop however, this check is not made: the command is applied
   to all listed servers, regardless of whether they have been enabled in the
   file.

   The following keywords can be used with the -s command line option:

     * dhcp4 for kea-dhcp4.
     * dhcp6 for kea-dhcp6.
     * dhcp_ddns for kea-dhcp-ddns.
     * ctrl_agent for kea-ctrl-agent.
     * netconf for kea-netconf.
     * all for all servers (default).

                          Chapter 7. Kea Control Agent

   Table of Contents

   7.1. Overview

   7.2. Configuration

   7.3. Secure Connections

   7.4. Starting Control Agent

   7.5. Connecting to the Control Agent

7.1. Overview

   Kea Control Agent (CA) is a daemon, first included in Kea 1.2, which
   exposes a RESTful control interface for managing Kea servers. The daemon
   can receive control commands over HTTP and either forward these commands
   to the respective Kea servers or handle these commands on its own. The
   determination whether the command should be handled by the CA or forwarded
   is made by checking the value of the 'service' parameter which may be
   included in the command from the controlling client. The details of the
   supported commands as well as their structures are provided in Chapter 17,
   Management API.

   Hook libraries can be loaded by the CA to provide support for additional
   commands or custom behavior of existing commands. Such hook libraries must
   implement callouts for 'control_command_receive' hook point. Details about
   creating new hook libraries and supported hook points can be found in Kea
   Developer's Guide.

   The CA processes received commands according to the following algorithm:

     * Pass command into any installed hooks (regardless of service
       value(s)). If the command is handled by a hook, return the response.
     * If the service specifies one more or services, the CA will forward the
       command to specified services and return the accumulated responses.
     * If service is not specified or is an empty list, the CA will handle
       the command if it supports it.

7.2. Configuration

   The following example demonstrates the basic CA configuration.

 {
     "Control-agent": {
         "http-host": "10.20.30.40",
         "http-port": 8080,

         "control-sockets": {
             "dhcp4": {
                 "comment": "main server",
                 "socket-type": "unix",
                 "socket-name": "/path/to/the/unix/socket-v4"
             },
             "dhcp6": {
                 "socket-type": "unix",
                 "socket-name": "/path/to/the/unix/socket-v6",
                 "user-context": { "version": 3 }
             }
         },

         "hooks-libraries": [
         {
             "library": "/opt/local/control-agent-commands.so",
             "parameters": {
                 "param1": "foo"
             }
         } ]
     },

     "Logging": {
         "loggers": [ {
             "name": "kea-ctrl-agent",
             "severity": "INFO"
         } ]
     }
 }

   The http-host and http-port specify an IP address and port to which HTTP
   service will be bound. In case of the example configuration provided
   above, the RESTful service will be available under the URL of
   http://10.20.30.40:8080/. If these parameters are not specified, the
   default URL is http://127.0.0.1:8000/

   It has been mentioned in the Section 7.1, "Overview" that CA can forward
   received commands to the specific Kea servers for processing. For example,
   config-get is sent to retrieve configuration of one of the Kea services.
   When CA receives this command, including a service parameter indicating
   that the client desires to retrieve configuration of the DHCPv4 server,
   the CA will forward this command to this server and then pass the received
   response back to the client. More about the service parameter and general
   structure of the commands can be found in Chapter 17, Management API.

   The CA uses unix domain sockets to forward control commands and receive
   responses from other Kea services. The dhcp4, dhcp6 and d2 maps specify
   the files to which unix domain sockets are bound. In case of the
   configuration above, the CA will connect to the DHCPv4 server via
   /path/to/the/unix/socket-v4 to forward the commands to it. Obviously, the
   DHCPv4 server must be configured to listen to connections via this same
   socket. In other words, the command socket configuration for the DHCPv4
   server and CA (for this server) must match. Consult the Section 8.9,
   "Management API for the DHCPv4 Server" and the Section 9.13, "Management
   API for the DHCPv6 Server" to learn how the socket configuration is
   specified for the DHCPv4 and DHCPv6 services.

  Warning

   We have renamed "dhcp4-server", "dhcp6-server" and "d2-server" to "dhcp4",
   "dhcp6" and "d2" respectively after release of Kea 1.2. If you are
   migrating from Kea 1.2 you need to tweak your CA config to use this new
   naming convention. We have made this incompatible change to facilitate
   future use cases where it will be possible to specify additional values of
   the "service" parameter to point to the particular instances of the Kea
   servers, e.g. "dhcp4/3" pointing to the 3rd instance of the DHCPv4 server
   in the multi-processed configuration. This is not yet supported but the
   current renaming lays the ground for it.

   User contexts can store arbitrary data as long as it is valid JSON syntax
   and its top level element is a map (i.e. the data must be enclosed in
   curly brackets). Some hook libraries may expect specific formatting,
   though. Please consult specific hook library documentation for details.

   User contexts can be specified on either global scope, control socket and
   loggers. One other useful usage is the ability to store comments or
   descriptions: the parser translates a "comment" entry into a user-context
   with the entry, this allows to attach a comment inside the configuration
   itself.

   Hooks libraries can be loaded by the Control Agent just like to DHCPv4 and
   DHCPv6 servers. It currently supports one hook point
   'control_command_receive' which makes it possible to delegate processing
   of some commands to the hooks library. The hooks-libraries list contains
   the list of hooks libraries that should be loaded by the CA, along with
   their configuration information specified with parameters.

   Please consult Chapter 19, Logging for the details how to configure
   logging. The CA's root logger's name is kea-ctrl-agent as given in the
   example above.

7.3. Secure Connections

   Control Agent doesn't natively support secure HTTP connections like SSL or
   TLS. In order to setup secure connection please use one of the available
   third party HTTP servers and configure it to run as a reverse proxy to the
   Control Agent. Kea has been tested with two major HTTP server
   implentations working as a reverse proxy: Apache2 and nginx. Example
   configurations including extensive comments are provided in the
   doc/examples/https/ directory.

   The reverse proxy forwards HTTP requests received over secure connection
   to the Control Agent using (not secured) HTTP. Typically, the reverse
   proxy and the Control Agent are running on the same machine, but it is
   possible to configure them to run on separate machines as well. In this
   case, security depends on the protection of the communications between the
   reverse proxy and the Control Agent.

   Apart from providing the encryption layer for the control channel, a
   reverse proxy server is also often used for authentication of the
   controlling clients. In this case, the client must present a valid
   certificate when it connects via reverse proxy. The proxy server
   authenticates the client by checking if the presented certificate is
   signed by the certificate authority used by the server.

   To illustrate this, we provide a sample configuration for the nginx server
   running as a reverse proxy to the Kea Control Agent. The server enables
   authentication of the clients using certificates.

 #   The server certificate and key can be generated as follows:
 #
 #   openssl genrsa -des3 -out kea-proxy.key 4096
 #   openssl req -new -x509 -days 365 -key kea-proxy.key -out kea-proxy.crt
 #
 #   The CA certificate and key can be generated as follows:
 #
 #   openssl genrsa -des3 -out ca.key 4096
 #   openssl req -new -x509 -days 365 -key ca.key -out ca.crt
 #
 #
 #   The client certificate needs to be generated and signed:
 #
 #   openssl genrsa -des3 -out kea-client.key 4096
 #   openssl req -new -key kea-client.key -out kea-client.csr
 #   openssl x509 -req -days 365 -in kea-client.csr -CA ca.crt \
 #           -CAkey ca.key -set_serial 01 -out kea-client.crt
 #
 #   Note that the 'common name' value used when generating the client
 #   and the server certificates must differ from the value used
 #   for the CA certificate.
 #
 #   The client certificate must be deployed on the client system.
 #   In order to test the proxy configuration with 'curl' run
 #   command similar to the following:
 #
 #   curl -k --key kea-client.key --cert kea-client.crt -X POST \
 #        -H Content-Type:application/json -d '{ "command": "list-commands" }' \
 #         https://kea.example.org/kea
 #
 #
 #
 #   nginx configuration starts here.

 events {
 }

 http {
         #   HTTPS server
     server {
         #     Use default HTTPS port.
         listen 443 ssl;
         #     Set server name.
         server_name kea.example.org;

         #   Server certificate and key.
         ssl_certificate /path/to/kea-proxy.crt;
         ssl_certificate_key /path/to/kea-proxy.key;

         #   Certificate Authority. Client certificate must be signed by the CA.
         ssl_client_certificate /path/to/ca.crt;

         # Enable verification of the client certificate.
         ssl_verify_client on;

         # For URLs such as https://kea.example.org/kea, forward the
         # requests to http://127.0.0.1:8080.
         location /kea {
             proxy_pass http://127.0.0.1:8080;
         }
     }
 }

  Note

   Note that the configuration snippet provided above is for testing purposes
   only. Consult security policies and best practices of your organization
   which apply to this setup.

   When you use an HTTP client without TLS support as kea-shell you can use
   an HTTP/HTTPS translator such as stunnel in client mode. A sample
   configuration is provided in the doc/examples/https/shell/ directory

7.4. Starting Control Agent

   The CA is started by running its binary and specifying the configuration
   file it should use. For example:

 $ ./kea-ctrl-agent -c /usr/local/etc/kea/kea-ctrl-agent.conf

   It can be started by keactrl as well (see Chapter 6, Managing Kea with
   keactrl).

7.5. Connecting to the Control Agent

   For an example of tool that can take advantage of the RESTful API, see
   Chapter 20, The Kea Shell.

                          Chapter 8. The DHCPv4 Server

   Table of Contents

   8.1. Starting and Stopping the DHCPv4 Server

   8.2. DHCPv4 Server Configuration

                8.2.1. Introduction

                8.2.2. Lease Storage

                8.2.3. Hosts Storage

                8.2.4. Interface Configuration

                8.2.5. Issues with Unicast Responses to DHCPINFORM

                8.2.6. IPv4 Subnet Identifier

                8.2.7. Configuration of IPv4 Address Pools

                8.2.8. Standard DHCPv4 Options

                8.2.9. Custom DHCPv4 options

                8.2.10. DHCPv4 Private Options

                8.2.11. DHCPv4 Vendor Specific Options

                8.2.12. Nested DHCPv4 Options (Custom Option Spaces)

                8.2.13. Unspecified Parameters for DHCPv4 Option
                Configuration

                8.2.14. Stateless Configuration of DHCPv4 Clients

                8.2.15. Client Classification in DHCPv4

                8.2.16. DDNS for DHCPv4

                8.2.17. Next Server (siaddr)

                8.2.18. Echoing Client-ID (RFC 6842)

                8.2.19. Using Client Identifier and Hardware Address

                8.2.20. Authoritative DHCPv4 Server Behavior

                8.2.21. DHCPv4-over-DHCPv6: DHCPv4 Side

                8.2.22. Sanity checks in DHCPv4

   8.3. Host Reservation in DHCPv4

                8.3.1. Address Reservation Types

                8.3.2. Conflicts in DHCPv4 Reservations

                8.3.3. Reserving a Hostname

                8.3.4. Including Specific DHCPv4 Options in Reservations

                8.3.5. Reserving Next Server, Server Hostname and Boot File
                Name

                8.3.6. Reserving Client Classes in DHCPv4

                8.3.7. Storing Host Reservations in MySQL, PostgreSQL or
                Cassandra

                8.3.8. Fine Tuning DHCPv4 Host Reservation

                8.3.9. Global reservations in DHCPv4

   8.4. Shared networks in DHCPv4

                8.4.1. Local and relayed traffic in shared networks

                8.4.2. Client classification in shared networks

                8.4.3. Host reservations in shared networks

   8.5. Server Identifier in DHCPv4

   8.6. How the DHCPv4 Server Selects a Subnet for the Client

                8.6.1. Using a Specific Relay Agent for a Subnet

                8.6.2. Segregating IPv4 Clients in a Cable Network

   8.7. Duplicate Addresses (DHCPDECLINE Support)

   8.8. Statistics in the DHCPv4 Server

   8.9. Management API for the DHCPv4 Server

   8.10. Supported DHCP Standards

   8.11. User contexts in IPv4

   8.12. DHCPv4 Server Limitations

   8.13. Kea DHCPv4 server examples

8.1. Starting and Stopping the DHCPv4 Server

   It is recommended that the Kea DHCPv4 server be started and stopped using
   keactrl (described in Chapter 6, Managing Kea with keactrl). However, it
   is also possible to run the server directly: it accepts the following
   command-line switches:

     * -c file - specifies the configuration file. This is the only mandatory
       switch.
     * -d - specifies whether the server logging should be switched to
       debug/verbose mode. In verbose mode, the logging severity and
       debuglevel specified in the configuration file are ignored and "debug"
       severity and the maximum debuglevel (99) are assumed. The flag is
       convenient, for temporarily switching the server into maximum
       verbosity, e.g. when debugging.
     * -p port - specifies UDP port on which the server will listen. This is
       only useful during testing, as a DHCPv4 server listening on ports
       other than the standard ones will not be able to handle regular DHCPv4
       queries.
     * -t file - specifies the configuration file to be tested. Kea-dhcp4
       will attempt to load it, and will conduct sanity checks. Note that
       certain checks are possible only while running the actual server. The
       actual status is reported with exit code (0 = configuration looks ok,
       1 = error encountered). Kea will print out log messages to standard
       output and error to standard error when testing configuration.
     * -v - prints out the Kea version and exits.
     * -V - prints out the Kea extended version with additional parameters
       and exits. The listing includes the versions of the libraries
       dynamically linked to Kea.
     * -W - prints out the Kea configuration report and exits. The report is
       a copy of the config.report file produced by ./configure: it is
       embedded in the executable binary.

   The config.report may also be accessed more directly. The following
   command may be used to extract this information. The binary path may be
   found in the install directory or in the .libs subdirectory in the source
   tree. For example kea/src/bin/dhcp4/.libs/kea-dhcp4.

 strings path/kea-dhcp4 | sed -n 's/;;;; //p'

   On start-up, the server will detect available network interfaces and will
   attempt to open UDP sockets on all interfaces mentioned in the
   configuration file. Since the DHCPv4 server opens privileged ports, it
   requires root access. Make sure you run this daemon as root.

   During startup the server will attempt to create a PID file of the form:
   localstatedir]/[conf name].kea-dhcp6.pid where:

     * localstatedir: The value as passed into the build configure script. It
       defaults to "/usr/local/var". (Note that this value may be overridden
       at run time by setting the environment variable KEA_PIDFILE_DIR. This
       is intended primarily for testing purposes.)
     * conf name: The configuration file name used to start the server, minus
       all preceding path and file extension. For example, given a pathname
       of "/usr/local/etc/kea/myconf.txt", the portion used would be
       "myconf".

   If the file already exists and contains the PID of a live process, the
   server will issue a DHCP4_ALREADY_RUNNING log message and exit. It is
   possible, though unlikely, that the file is a remnant of a system crash
   and the process to which the PID belongs is unrelated to Kea. In such a
   case it would be necessary to manually delete the PID file.

   The server can be stopped using the kill command. When running in a
   console, the server can also be shut down by pressing ctrl-c. It detects
   the key combination and shuts down gracefully.

8.2. DHCPv4 Server Configuration

  8.2.1. Introduction

   This section explains how to configure the DHCPv4 server using a
   configuration file. Before DHCPv4 is started, its configuration file has
   to be created. The basic configuration is as follows:

 {
 # DHCPv4 configuration starts in this line
 "Dhcp4": {

 # First we set up global values
     "valid-lifetime": 4000,
     "renew-timer": 1000,
     "rebind-timer": 2000,

 # Next we setup the interfaces to be used by the server.
     "interfaces-config": {
         "interfaces": [ "eth0" ]
     },

 # And we specify the type of lease database
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/var/kea/dhcp4.leases"
     },

 # Finally, we list the subnets from which we will be leasing addresses.
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 {
                      "pool": "192.0.2.1 - 192.0.2.200"
                 }
             ]
         }
     ]
 # DHCPv4 configuration ends with the next line
 }

 }

   The following paragraphs provide a brief overview of the parameters in the
   above example together with their format. Subsequent sections of this
   chapter go into much greater detail for these and other parameters.

   The lines starting with a hash (#) are comments and are ignored by the
   server; they do not impact its operation in any way.

   The configuration starts in the first line with the initial opening curly
   bracket (or brace). Each configuration must contain an object specifying
   the configuration of the Kea module using it. In the example above this
   object is called Dhcp4.

  Note

   In the current Kea release it is possible to specify configurations of
   multiple modules within a single configuration file, but this is not
   recommended and support for it will be removed in the future releases. The
   only object, besides the one specifying module configuration, which can
   (and usually is) included in the same file is Logging. However, we don't
   include this object in the example above for clarity.

   The Dhcp4 configuration starts with the "Dhcp4": { line and ends with the
   corresponding closing brace (in the above example, the brace after the
   last comment). Everything defined between those lines is considered to be
   the Dhcp4 configuration.

   In the general case, the order in which those parameters appear does not
   matter. There are two caveats here though. The first one is to remember
   that the configuration file must be well formed JSON. That means that the
   parameters for any given scope must be separated by a comma and there must
   not be a comma after the last parameter. When reordering a configuration
   file, keep in mind that moving a parameter to or from the last position in
   a given scope may also require moving the comma. The second caveat is that
   it is uncommon -- although legal JSON -- to repeat the same parameter
   multiple times. If that happens, the last occurrence of a given parameter
   in a given scope is used while all previous instances are ignored. This is
   unlikely to cause any confusion as there are no real life reasons to keep
   multiple copies of the same parameter in your configuration file.

   Moving onto the DHCPv4 configuration elements, the first few elements
   define some global parameters. valid-lifetime defines how long the
   addresses (leases) given out by the server are valid. If nothing changes,
   a client that got an address is allowed to use it for 4000 seconds. (Note
   that integer numbers are specified as is, without any quotes around them.)
   renew-timer and rebind-timer are values (also in seconds) that define T1
   and T2 timers that govern when the client will begin the renewal and
   rebind procedures.

  Note

   Both renew-timer and rebind-timer are optional. The server will only send
   rebind-timer to the client, via DHPv4 option code 59, if it is less than
   valid-lifetime; and it will only send renew-timer, via DHCPv4 option code
   58, if it is less than rebind-timer (or valid-lifetime if rebind-timer was
   not specified). In their absence, the client should select values for T1
   and T2 timers according to the RFC 2131.

   The interfaces-config map specifies the server configuration concerning
   the network interfaces, on which the server should listen to the DHCP
   messages. The interfaces parameter specifies a list of network interfaces
   on which the server should listen. Lists are opened and closed with square
   brackets, with elements separated by commas. Had we wanted to listen on
   two interfaces, the interfaces-config would look like this:

 "interfaces-config": {
     "interfaces": [ "eth0", "eth1" ]
 },

   The next couple of lines define the lease database, the place where the
   server stores its lease information. This particular example tells the
   server to use memfile, which is the simplest (and fastest) database
   backend. It uses an in-memory database and stores leases on disk in a CSV
   file. This is a very simple configuration. Usually the lease database
   configuration is more extensive and contains additional parameters. Note
   that lease-database is an object and opens up a new scope, using an
   opening brace. Its parameters (just one in this example - type) follow.
   Had there been more than one, they would be separated by commas. This
   scope is closed with a closing brace. As more parameters for the Dhcp4
   definition follow, a trailing comma is present.

   Finally, we need to define a list of IPv4 subnets. This is the most
   important DHCPv4 configuration structure as the server uses that
   information to process clients' requests. It defines all subnets from
   which the server is expected to receive DHCP requests. The subnets are
   specified with the subnet4 parameter. It is a list, so it starts and ends
   with square brackets. Each subnet definition in the list has several
   attributes associated with it, so it is a structure and is opened and
   closed with braces. At a minimum, a subnet definition has to have at least
   two parameters: subnet (that defines the whole subnet) and pools (which is
   a list of dynamically allocated pools that are governed by the DHCP
   server).

   The example contains a single subnet. Had more than one been defined,
   additional elements in the subnet4 parameter would be specified and
   separated by commas. For example, to define three subnets, the following
   syntax would be used:

 "subnet4": [
     {
         "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
         "subnet": "192.0.2.0/24"
     },
     {
         "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
         "subnet": "192.0.3.0/24"
     },
     {
         "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
         "subnet": "192.0.4.0/24"
     }
 ]

   Note that indentation is optional and is used for aesthetic purposes only.
   In some cases in may be preferable to use more compact notation.

   After all the parameters have been specified, we have two contexts open:
   global and Dhcp4, hence we need two closing curly brackets to close them.
   In a real life configuration file there most likely would be an additional
   component defined such as Logging, so the closing brace would be followed
   by a comma and another object definition.

  8.2.2. Lease Storage

   All leases issued by the server are stored in the lease database.
   Currently there are four database backends available: memfile (which is
   the default backend), MySQL, PostgreSQL and Cassandra.

    8.2.2.1. Memfile - Basic Storage for Leases

   The server is able to store lease data in different repositories. Larger
   deployments may elect to store leases in a database. Section 8.2.2.2,
   "Lease Database Configuration" describes this option. In typical smaller
   deployments though, the server will store lease information in a CSV file
   rather than a database. As well as requiring less administration, an
   advantage of using a file for storage is that it eliminates a dependency
   on third-party database software.

   The configuration of the file backend (Memfile) is controlled through the
   Dhcp4/lease-database parameters. The type parameter is mandatory and it
   specifies which storage for leases the server should use. The value of
   "memfile" indicates that the file should be used as the storage. The
   following list gives additional, optional, parameters that can be used to
   configure the Memfile backend.

     * persist: controls whether the new leases and updates to existing
       leases are written to the file. It is strongly recommended that the
       value of this parameter is set to true at all times, during the
       server's normal operation. Not writing leases to disk will mean that
       if a server is restarted (e.g. after a power failure), it will not
       know what addresses have been assigned. As a result, it may hand out
       addresses to new clients that are already in use. The value of false
       is mostly useful for performance testing purposes. The default value
       of the persist parameter is true, which enables writing lease updates
       to the lease file.
     * name: specifies an absolute location of the lease file in which new
       leases and lease updates will be recorded. The default value for this
       parameter is "[kea-install-dir]/var/kea/kea-leases4.csv" .
     * lfc-interval: specifies the interval in seconds, at which the server
       will perform a lease file cleanup (LFC). This removes redundant
       (historical) information from the lease file and effectively reduces
       the lease file size. The cleanup process is described in more detailed
       fashion further in this section. The default value of the lfc-interval
       is 3600. A value of 0 disables the LFC.

   An example configuration of the Memfile backend is presented below:

 "Dhcp4": {
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/tmp/kea-leases4.csv",
         "lfc-interval": 1800
     }
 }

   This configuration selects the /tmp/kea-leases4.csv as the storage for
   lease information and enables persistence (writing lease updates to this
   file). It also configures the backend perform the periodic cleanup of the
   lease files, executed every 30 minutes.

   It is important to know how the lease file contents are organized to
   understand why the periodic lease file cleanup is needed. Every time the
   server updates a lease or creates a new lease for the client, the new
   lease information must be recorded in the lease file. For performance
   reasons, the server does not update the existing client's lease in the
   file, as it would potentially require rewriting the entire file. Instead,
   it simply appends the new lease information to the end of the file: the
   previous lease entries for the client are not removed. When the server
   loads leases from the lease file, e.g. at the server startup, it assumes
   that the latest lease entry for the client is the valid one. The previous
   entries are discarded. This means that the server can re-construct the
   accurate information about the leases even though there may be many lease
   entries for each client. However, storing many entries for each client
   results in bloated lease file and impairs the performance of the server's
   startup and reconfiguration as it needs to process a larger number of
   lease entries.

   Lease file cleanup (LFC) removes all previous entries for each client and
   leaves only the latest ones. The interval at which the cleanup is
   performed is configurable, and it should be selected according to the
   frequency of lease renewals initiated by the clients. The more frequent
   the renewals, the smaller the value of lfc-interval should be. Note
   however, that the LFC takes time and thus it is possible (although
   unlikely) that new cleanup is started while the previous cleanup instance
   is still running, if the lfc-interval is too short. The server would
   recover from this by skipping the new cleanup when it detects that the
   previous cleanup is still in progress. But it implies that the actual
   cleanups will be triggered more rarely than configured. Moreover,
   triggering a new cleanup adds an overhead to the server which will not be
   able to respond to new requests for a short period of time when the new
   cleanup process is spawned. Therefore, it is recommended that the
   lfc-interval value is selected in a way that would allow for the LFC to
   complete the cleanup before a new cleanup is triggered.

   Lease file cleanup is performed by a separate process (in background) to
   avoid a performance impact on the server process. In order to avoid the
   conflicts between two processes both using the same lease files, the LFC
   process operates on the copy of the original lease file, rather than on
   the lease file used by the server to record lease updates. There are also
   other files being created as a side effect of the lease file cleanup. The
   detailed description of the LFC is located in the Kea Administrator's
   Reference Manual:
   https://jenkins.isc.org/job/Kea_doc/guide/kea-guide.html#kea-lfc.

    8.2.2.2. Lease Database Configuration

  Note

   Lease database access information must be configured for the DHCPv4
   server, even if it has already been configured for the DHCPv6 server. The
   servers store their information independently, so each server can use a
   separate database or both servers can use the same database.

   Lease database configuration is controlled through the
   Dhcp4/lease-database parameters. The type of the database must be set to
   "memfile", "mysql", "postgresql" or "cql", e.g.

 "Dhcp4": { "lease-database": { "type": "mysql", ... }, ... }

   Next, the name of the database to hold the leases must be set: this is the
   name used when the database was created (see Section 4.3.2.1, "First Time
   Creation of the MySQL Database", Section 4.3.3.1, "First Time Creation of
   the PostgreSQL Database" or Section 4.3.4.1, "First Time Creation of the
   Cassandra Database").

 "Dhcp4": { "lease-database": { "name": "database-name" , ... }, ... }

   For Cassandra:

 "Dhcp4": { "lease-database": { "keyspace": "database-name" , ... }, ... }

   If the database is located on a different system to the DHCPv4 server, the
   database host name must also be specified. (It should be noted that this
   configuration may have a severe impact on server performance.):

 "Dhcp4": { "lease-database": { "host": "remote-host-name", ... }, ... }

   The usual state of affairs will be to have the database on the same
   machine as the DHCPv4 server. In this case, set the value to the empty
   string:

 "Dhcp4": { "lease-database": { "host" : "", ... }, ... }

   Should the database use a port different than default, it may be specified
   as well:

 "Dhcp4": { "lease-database": { "port" : 12345, ... }, ... }

   Should the database be located on a different system, you may need to
   specify a longer interval for the connection timeout:

 "Dhcp4": { "lease-database": { "connect-timeout" : timeout-in-seconds, ... }, ... }

   The default value of five seconds should be more than adequate for local
   connections. If a timeout is given though, it should be an integer greater
   than zero.

   The maxiumum number of times the server will automatically attempt to
   reconnect to the lease database after connectivity has been lost may be
   specified:

 "Dhcp4": { "lease-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }

   If the server is unable to reconnect to the database after making the
   maximum number of attempts the server will exit. A value of zero (the
   default) disables automatic recovery and the server will exit immediately
   upon detecting a loss of connectivity (MySQL and Postgres only).

   The number of milliseconds the server will wait in between attempts to
   reconnect to the lease database after connectivity has been lost may also
   be specified:

 "Dhcp4": { "lease-database": { "reconnect-wait-time" : number-of-milliseconds, ... }, ... }

   The default value for MySQL and Postgres is 0, which disables automatic
   recovery and causes the server to exit immediately upon detecting the loss
   of connectivity. The default value for Cassandra is 2000 ms.

  Note

   Automatic reconnect to database backends is configured individually per
   backend. This allows you to tailor the recovery parameters to the each
   backend you use. We do suggest that you either enable it for all backends
   or no backends so you have consistent behavior. Losing connectivity to a
   backend for which reconnect is disabled will result in the server shutting
   itself down. This includes the cases when lease database backend and hosts
   database backend is connected to the same database instance.

   Finally, the credentials of the account under which the server will access
   the database should be set:

 "Dhcp4": { "lease-database": { "user": "user-name",
                                "password": "password",
                               ... },
            ... }

   If there is no password to the account, set the password to the empty
   string "". (This is also the default.)

    8.2.2.3. Cassandra specific parameters

   Cassandra backend is configured slightly differently. Cassandra has a
   concept of contact points that could be used to contact the cluster,
   instead of a single IP or hostname. It takes a list of comma separated IP
   addresses. This may be specified as:

 "Dhcp4": {
     "lease-database": {
         "type": "cql",
         "contact-points": "ip-address1, ip-address2 [,...]",
         ...
     },
     ...
 }

   Cassandra also supports a number of optional parameters:

     * reconnect-wait-time - governs how long Kea waits before attempting to
       reconnect. Expressed in milliseconds. The default is 2000 [ms].
     * connect-timeout - sets the timeout for connecting to a node. Expressed
       in milliseconds. The default is 5000 [ms].
     * request-timeout - this parameter sets the timeout for waiting for a
       response from a node. Expressed in milliseconds. The default is 12000
       [ms].
     * tcp-keepalive - This parameter governs the TCP keep-alive mechanism.
       Expressed in seconds of delay. If the parameter is not present, the
       mechanism is disabled.
     * tcp-nodelay - This parameter enables/disabled Nagle's algorithm on
       connections. The default is true.

   For example, a complex Cassandra configuration with most parameters
   specified could look as follows:

 "Dhcp4": {
   "lease-database": {
       "type": "cql",
       "keyspace": "keatest",
       "contact-points": "192.0.2.1, 192.0.2.2, 192.0.2.3",
       "port": 9042,
       "reconnect-wait-time": 2000,
       "connect-timeout": 5000,
       "request-timeout": 12000,
       "tcp-keepalive": 1,
       "tcp-nodelay": true
     },
     ...
 }

   Similar parameters can be specified for hosts database.

  8.2.3. Hosts Storage

   Kea is also able to store information about host reservations in the
   database. The hosts database configuration uses the same syntax as the
   lease database. In fact, a Kea server opens independent connections for
   each purpose, be it lease or hosts information. This arrangement gives the
   most flexibility. Kea can be used to keep leases and host reservations
   separately, but can also point to the same database. Currently the
   supported hosts database types are MySQL, PostgreSQL and Cassandra.

   Please note that usage of hosts storage is optional. A user can define all
   host reservations in the configuration file. That is the recommended way
   if the number of reservations is small. However, when the number of
   reservations grows it's more convenient to use host storage. Please note
   that both storage methods (configuration file and one of the supported
   databases) can be used together. If hosts are defined in both places, the
   definitions from the configuration file are checked first and external
   storage is checked later, if necessary.

   Version 1.4 extends the host storage to multiple storages. Operations are
   performed on host storages in the configuration order with a special case
   for addition: read-only storages must be configured after a required
   read-write storage, or host reservation addition will always fail.

    8.2.3.1. DHCPv4 Hosts Database Configuration

   Hosts database configuration is controlled through the
   Dhcp4/hosts-database parameters. If enabled, the type of the database must
   be set to "mysql" or "postgresql". Other hosts backends may be added in
   later versions of Kea.

 "Dhcp4": { "hosts-database": { "type": "mysql", ... }, ... }

   Next, the name of the database to hold the reservations must be set: this
   is the name used when the lease database was created (see Section 4.3,
   "Supported Databases" for instructions how to setup the desired database
   type).

 "Dhcp4": { "hosts-database": { "name": "database-name" , ... }, ... }

   If the database is located on a different system than the DHCPv4 server,
   the database host name must also be specified. (Again it should be noted
   that this configuration may have a severe impact on server performance.):

 "Dhcp4": { "hosts-database": { "host": remote-host-name, ... }, ... }

   The usual state of affairs will be to have the database on the same
   machine as the DHCPv4 server. In this case, set the value to the empty
   string:

 "Dhcp4": { "hosts-database": { "host" : "", ... }, ... }

   Should the database use a port different than default, it may be specified
   as well:

 "Dhcp4": { "hosts-database": { "port" : 12345, ... }, ... }

   The maxiumum number of times the server will automatically attempt to
   reconnect to the host database after connectivity has been lost may be
   specified:

 "Dhcp4": { "hosts-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }

   If the server is unable to reconnect to the database after making the
   maximum number of attempts the server will exit. A value of zero (the
   default) disables automatic recovery and the server will exit immediately
   upon detecting a loss of connectivity (MySQL and Postgres only).

   The number of milliseconds the server will wait in between attempts to
   reconnect to the host database after connectivity has been lost may also
   be specified:

 "Dhcp4": { "hosts-database": { "reconnect-wait-time" : number-of-milliseconds, ... }, ... }

   The default value for MySQL and Postgres is 0, which disables automatic
   recovery and causes the server to exit immediately upon detecting the loss
   of connectivity. The default value for Cassandra is 2000 ms.

  Note

   Automatic reconnect to database backends is configured individually per
   backend. This allows you to tailor the recovery parameters to the each
   backend you use. We do suggest that you either enable it for all backends
   or no backends so you have consistent behavior. Losing connectivity to a
   backend for which reconnect is disabled will result in the server shutting
   itself down. This includes the cases when lease database backend and hosts
   database backend is connected to the same database instance.

   Finally, the credentials of the account under which the server will access
   the database should be set:

 "Dhcp4": { "hosts-database": { "user": "user-name",
                                "password": "password",
                               ... },
            ... }

   If there is no password to the account, set the password to the empty
   string "". (This is also the default.)

   The multiple storage extension uses a similar syntax: a configuration is
   placed into a "hosts-databases" list instead of into a "hosts-database"
   entry as in:

 "Dhcp4": { "hosts-databases": [ { "type": "mysql", ... }, ... ], ... }

   For additional Cassandra specific parameters, see Section 8.2.2.3,
   "Cassandra specific parameters".

    8.2.3.2. Using Read-Only Databases for Host Reservations

   In some deployments the database user whose name is specified in the
   database backend configuration may not have write privileges to the
   database. This is often required by the policy within a given network to
   secure the data from being unintentionally modified. In many cases
   administrators have inventory databases deployed, which contain
   substantially more information about the hosts than static reservations
   assigned to them. The inventory database can be used to create a view of a
   Kea hosts database and such view is often read only.

   Kea host database backends operate with an implicit configuration to both
   read from and write to the database. If the database user does not have
   write access to the host database, the backend will fail to start and the
   server will refuse to start (or reconfigure). However, if access to a read
   only host database is required for retrieving reservations for clients
   and/or assign specific addresses and options, it is possible to explicitly
   configure Kea to start in "read-only" mode. This is controlled by the
   readonly boolean parameter as follows:

 "Dhcp4": { "hosts-database": { "readonly": true, ... }, ... }

   Setting this parameter to false would configure the database backend to
   operate in "read-write" mode, which is also a default configuration if the
   parameter is not specified.

  Note

   The readonly parameter is currently only supported for MySQL and
   PostgreSQL databases.

  8.2.4. Interface Configuration

   The DHCPv4 server has to be configured to listen on specific network
   interfaces. The simplest network interface configuration tells the server
   to listen on all available interfaces:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "*" ]
     }
     ...
 },


   The asterisk plays the role of a wildcard and means "listen on all
   interfaces". However, it is usually a good idea to explicitly specify
   interface names:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ]
     },
     ...
 }


   It is possible to use wildcard interface name (asterisk) concurrently with
   explicit interface names:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3", "*" ]
     },
     ...
 }


   It is anticipated that this form of usage will only be used when it is
   desired to temporarily override a list of interface names and listen on
   all interfaces.

   Some deployments of DHCP servers require that the servers listen on the
   interfaces with multiple IPv4 addresses configured. In these situations,
   the address to use can be selected by appending an IPv4 address to the
   interface name in the following manner:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1/10.0.0.1", "eth3/192.0.2.3" ]
     },
     ...
 }


   Should the server be required to listen on multiple IPv4 addresses
   assigned to the same interface, multiple addresses can be specified for an
   interface as in the example below:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1/10.0.0.1", "eth1/10.0.0.2" ]
     },
     ...
 }


   Alternatively, if the server should listen on all addresses for the
   particular interface, an interface name without any address should be
   specified.

   Kea supports responding to directly connected clients which don't have an
   address configured. This requires that the server injects the hardware
   address of the destination into the data link layer of the packet being
   sent to the client. The DHCPv4 server utilizes the raw sockets to achieve
   this, and builds the entire IP/UDP stack for the outgoing packets. The
   down side of raw socket use, however, is that incoming and outgoing
   packets bypass the firewalls (e.g. iptables). It is also troublesome to
   handle traffic on multiple IPv4 addresses assigned to the same interface,
   as raw sockets are bound to the interface and advanced packet filtering
   techniques (e.g. using the BPF) have to be used to receive unicast traffic
   on the desired addresses assigned to the interface, rather than capturing
   whole traffic reaching the interface to which the raw socket is bound.
   Therefore, in the deployments where the server doesn't have to provision
   the directly connected clients and only receives the unicast packets from
   the relay agents, the DHCP server should be configured to utilize IP/UDP
   datagram sockets instead of raw sockets. The following configuration
   demonstrates how this can be achieved:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ],
         "dhcp-socket-type": "udp"
     },
     ...
 }


   The dhcp-socket-type specifies that the IP/UDP sockets will be opened on
   all interfaces on which the server listens, i.e. "eth1" and "eth3" in our
   case. If the dhcp-socket-type is set to raw, it configures the server to
   use raw sockets instead. If the dhcp-socket-type value is not specified,
   the default value raw is used.

   Using UDP sockets automatically disables the reception of broadcast
   packets from directly connected clients. This effectively means that the
   UDP sockets can be used for relayed traffic only. When using the raw
   sockets, both the traffic from the directly connected clients and the
   relayed traffic will be handled. Caution should be taken when configuring
   the server to open multiple raw sockets on the interface with several IPv4
   addresses assigned. If the directly connected client sends the message to
   the broadcast address all sockets on this link will receive this message
   and multiple responses will be sent to the client. Hence, the
   configuration with multiple IPv4 addresses assigned to the interface
   should not be used when the directly connected clients are operating on
   that link. To use a single address on such interface, the
   "interface-name/address" notation should be used.

  Note

   Specifying the value raw as the socket type, doesn't guarantee that the
   raw sockets will be used! The use of raw sockets to handle the traffic
   from the directly connected clients is currently supported on Linux and
   BSD systems only. If the raw sockets are not supported on the particular
   OS, the server will issue a warning and fall back to use IP/UDP sockets.

   In typical environment the DHCP server is expected to send back a response
   on the same network interface on which the query is received. This is the
   default behavior. However, in some deployments it is desired that the
   outbound (response) packets will be sent as regular traffic and the
   outbound interface will be determined by the routing tables. This kind of
   asymetric traffic is uncommon, but valid. Kea now supports a parameter
   called outbound-interface that controls this behavior. It supports two
   values. The first one, same-as-inbound, tells Kea to send back the
   response on the same inteface the query packet is received. This is the
   default behavior. The second one, use-routing tells Kea to send regular
   UDP packets and let the kernel's routing table to determine most
   appropriate interface. This only works when dhcp-socket-type is set to
   udp. An example configuration looks as follows:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ],
         "dhcp-socket-type": "udp",
         "outbound-interface": "use-routing"
     },
     ...
 }

   Interfaces are re-detected at each reconfiguration. This behavior can be
   disabled by setting re-detect value to false, for instance:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ],
         "re-detect": false
     },
     ...
 }


   Note interfaces are not re-detected during config-test.

   Usually loopback interfaces (e.g. the "lo" or "lo0" interface) may not be
   configured but if a loopback interface is explicitely configured and
   IP/UDP sockets are specified the loopback interface is accepted.

   It can be used for instance to run Kea in a FreeBSD jail having only a
   loopback interface, servicing relayed DHCP request:

 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "lo0" ],
         "dhcp-socket-type": "udp"
     },
     ...
 }

  8.2.5. Issues with Unicast Responses to DHCPINFORM

   The use of UDP sockets has certain benefits in deployments where the
   server receives only relayed traffic; these benefits are mentioned in
   Section 8.2.4, "Interface Configuration". From the administrator's
   perspective it is often desirable to configure the system's firewall to
   filter out the unwanted traffic, and the use of UDP sockets facilitates
   this. However, the administrator must also be aware of the implications
   related to filtering certain types of traffic as it may impair the DHCP
   server's operation.

   In this section we are focusing on the case when the server receives the
   DHCPINFORM message from the client via a relay. According to RFC 2131, the
   server should unicast the DHCPACK response to the address carried in the
   "ciaddr" field. When the UDP socket is in use, the DHCP server relies on
   the low level functions of an operating system to build the data link, IP
   and UDP layers of the outgoing message. Typically, the OS will first use
   ARP to obtain the client's link layer address to be inserted into the
   frame's header, if the address is not cached from a previous transaction
   that the client had with the server. When the ARP exchange is successful,
   the DHCP message can be unicast to the client, using the obtained address.

   Some system administrators block ARP messages in their network, which
   causes issues for the server when it responds to the DHCPINFORM messages,
   because the server is unable to send the DHCPACK if the preceding ARP
   communication fails. Since the OS is entirely responsible for the ARP
   communication and then sending the DHCP packet over the wire, the DHCP
   server has no means to determine that the ARP exchange failed and the DHCP
   response message was dropped. Thus, the server does not log any error
   messages when the outgoing DHCP response is dropped. At the same time, all
   hooks pertaining to the packet sending operation will be called, even
   though the message never reaches its destination.

   Note that the issue described in this section is not observed when the raw
   sockets are in use, because, in this case, the DHCP server builds all the
   layers of the outgoing message on its own and does not use ARP. Instead,
   it inserts the value carried in the 'chaddr' field of the DHCPINFORM
   message into the link layer.

   Server administrators willing to support DHCPINFORM messages via relays
   should not block ARP traffic in their networks or should use raw sockets
   instead of UDP sockets.

  8.2.6. IPv4 Subnet Identifier

   The subnet identifier is a unique number associated with a particular
   subnet. In principle, it is used to associate clients' leases with their
   respective subnets. When a subnet identifier is not specified for a subnet
   being configured, it will be automatically assigned by the configuration
   mechanism. The identifiers are assigned from 1 and are monotonically
   increased for each subsequent subnet: 1, 2, 3 ....

   If there are multiple subnets configured with auto-generated identifiers
   and one of them is removed, the subnet identifiers may be renumbered. For
   example: if there are four subnets and the third is removed the last
   subnet will be assigned the identifier that the third subnet had before
   removal. As a result, the leases stored in the lease database for subnet 3
   are now associated with subnet 4, something that may have unexpected
   consequences. It is planned to implement a mechanism to preserve
   auto-generated subnet ids in a future version of Kea. However, the only
   remedy for this issue at present is to manually specify a unique
   identifier for each subnet.

  Note

   Subnet IDs must be greater than zero and less than 4294967295.

   The following configuration will assign the specified subnet identifier to
   the newly configured subnet:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "id": 1024,
             ...
         }
     ]
 }

   This identifier will not change for this subnet unless the "id" parameter
   is removed or set to 0. The value of 0 forces auto-generation of the
   subnet identifier.

  8.2.7. Configuration of IPv4 Address Pools

   The main role of a DHCPv4 server is address assignment. For this, the
   server has to be configured with at least one subnet and one pool of
   dynamic addresses for it to manage. For example, assume that the server is
   connected to a network segment that uses the 192.0.2.0/24 prefix. The
   Administrator of that network has decided that addresses from range
   192.0.2.10 to 192.0.2.20 are going to be managed by the Dhcp4 server. Such
   a configuration can be achieved in the following way:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 { "pool": "192.0.2.10 - 192.0.2.20" }
             ],
             ...
         }
     ]
 }

   Note that subnet is defined as a simple string, but the pools parameter is
   actually a list of pools: for this reason, the pool definition is enclosed
   in square brackets, even though only one range of addresses is specified.

   Each pool is a structure that contains the parameters that describe a
   single pool. Currently there is only one parameter, pool, which gives the
   range of addresses in the pool. Additional parameters will be added in
   future releases of Kea.

   It is possible to define more than one pool in a subnet: continuing the
   previous example, further assume that 192.0.2.64/26 should be also be
   managed by the server. It could be written as 192.0.2.64 to 192.0.2.127.
   Alternatively, it can be expressed more simply as 192.0.2.64/26. Both
   formats are supported by Dhcp4 and can be mixed in the pool list. For
   example, one could define the following pools:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 { "pool": "192.0.2.10-192.0.2.20" },
                 { "pool": "192.0.2.64/26" }
             ],
             ...
         }
     ],
     ...
 }

   White space in pool definitions is ignored, so spaces before and after the
   hyphen are optional. They can be used to improve readability.

   The number of pools is not limited, but for performance reasons it is
   recommended to use as few as possible.

   The server may be configured to serve more than one subnet:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.1 - 192.0.2.200" } ],
             ...
         },
         {
             "subnet": "192.0.3.0/24",
             "pools": [ { "pool": "192.0.3.100 - 192.0.3.200" } ],
             ...
         },
         {
             "subnet": "192.0.4.0/24",
             "pools": [ { "pool": "192.0.4.1 - 192.0.4.254" } ],
             ...
         }
     ]
 }

   When configuring a DHCPv4 server using prefix/length notation, please pay
   attention to the boundary values. When specifying that the server can use
   a given pool, it will also be able to allocate the first (typically
   network address) and the last (typically broadcast address) address from
   that pool. In the aforementioned example of pool 192.0.3.0/24, both
   192.0.3.0 and 192.0.3.255 addresses may be assigned as well. This may be
   invalid in some network configurations. If you want to avoid this, please
   use the "min-max" notation.

  8.2.8. Standard DHCPv4 Options

   One of the major features of the DHCPv4 server is to provide configuration
   options to clients. Most of the options are sent by the server only if the
   client explicitly requests them using the Parameter Request List option.
   Those that do not require inclusion in the Parameter Request List option
   are commonly used options, e.g. "Domain Server", and options which require
   special behavior, e.g. "Client FQDN" is returned to the client if the
   client has included this option in its message to the server.

   Table 8.1, "List of standard DHCPv4 options" comprises the list of the
   standard DHCPv4 options whose values can be configured using the
   configuration structures described in this section. This table excludes
   the options which require special processing and thus cannot be configured
   with some fixed values. The last column of the table indicates which
   options can be sent by the server even when they are not requested in the
   Parameter Request list option, and those which are sent only when
   explicitly requested.

   The following example shows how to configure the addresses of DNS servers,
   which is one of the most frequently used options. Options specified in
   this way are considered global and apply to all configured subnets.

 "Dhcp4": {
     "option-data": [
         {
            "name": "domain-name-servers",
            "code": 6,
            "space": "dhcp4",
            "csv-format": true,
            "data": "192.0.2.1, 192.0.2.2"
         },
         ...
     ]
 }


   Note that only one of name or code is required, you don't need to specify
   both. Space has a default value of "dhcp4", so you can skip this as well
   if you define a regular (not encapsulated) DHCPv4 option. Finally,
   csv-format defaults to true, so it too can be skipped, unless you want to
   specify the option value as hexstring. Therefore the above example can be
   simplified to:

 "Dhcp4": {
     "option-data": [
         {
            "name": "domain-name-servers",
            "data": "192.0.2.1, 192.0.2.2"
         },
         ...
     ]
 }


   Defined options are added to response when the client requests them at a
   few exceptions which are always added. To enforce the addition of a
   particular option set the always-send flag to true as in:

 "Dhcp4": {
     "option-data": [
         {
            "name": "domain-name-servers",
            "data": "192.0.2.1, 192.0.2.2",
            "always-send": true
         },
         ...
     ]
 }


   The effect is the same as if the client added the option code in the
   Parameter Request List option (or its equivalent for vendor options) so
   in:

 "Dhcp4": {
     "option-data": [
         {
            "name": "domain-name-servers",
            "data": "192.0.2.1, 192.0.2.2",
            "always-send": true
         },
         ...
     ],
     "subnet4": [
         {
            "subnet": "192.0.3.0/24",
            "option-data": [
                {
                    "name": "domain-name-servers",
                    "data": "192.0.3.1, 192.0.3.2"
                },
                ...
            ],
            ...
         },
         ...
     ],
     ...
 }


   The Domain Name Servers option is always added to responses (the
   always-send is "sticky") but the value is the subnet one when the client
   is localized in the subnet.

   The name parameter specifies the option name. For a list of currently
   supported names, see Table 8.1, "List of standard DHCPv4 options" below.
   The code parameter specifies the option code, which must match one of the
   values from that list. The next line specifies the option space, which
   must always be set to "dhcp4" as these are standard DHCPv4 options. For
   other option spaces, including custom option spaces, see Section 8.2.12,
   "Nested DHCPv4 Options (Custom Option Spaces)". The next line specifies
   the format in which the data will be entered: use of CSV (comma separated
   values) is recommended. The sixth line gives the actual value to be sent
   to clients. Data is specified as normal text, with values separated by
   commas if more than one value is allowed.

   Options can also be configured as hexadecimal values. If csv-format is set
   to false, option data must be specified as a hexadecimal string. The
   following commands configure the domain-name-servers option for all
   subnets with the following addresses: 192.0.3.1 and 192.0.3.2. Note that
   csv-format is set to false.

 "Dhcp4": {
     "option-data": [
         {
             "name": "domain-name-servers",
             "code": 6,
             "space": "dhcp4",
             "csv-format": false,
             "data": "C0 00 03 01 C0 00 03 02"
         },
         ...
     ],
     ...
 }

   Care should be taken to use proper encoding when using hexadecimal format
   as Kea's ability to validate data correctness in hexadecimal is limited.

   Most of the parameters in the "option-data" structure are optional and can
   be omitted in some circumstances as discussed in the Section 8.2.13,
   "Unspecified Parameters for DHCPv4 Option Configuration".

   It is possible to specify or override options on a per-subnet basis. If
   clients connected to most of your subnets are expected to get the same
   values of a given option, you should use global options: you can then
   override specific values for a small number of subnets. On the other hand,
   if you use different values in each subnet, it does not make sense to
   specify global option values (Dhcp4/option-data), rather you should set
   only subnet-specific values (Dhcp4/subnet[X]/option-data[Y]).

   The following commands override the global DNS servers option for a
   particular subnet, setting a single DNS server with address 192.0.2.3.

 "Dhcp4": {
     "subnet4": [
         {
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.3"
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   In some cases it is useful to associate some options with an address pool
   from which a client is assigned a lease. Pool specific option values
   override subnet specific and global option values. The server's
   administrator must not try to prioritize assignment of pool specific
   options by trying to order pools declarations in the server configuration.
   Future Kea releases may change the order in which options are assigned
   from the pools without any notice.

   The following configuration snippet demonstrates how to specify the DNS
   servers option, which will be assigned to a client only if the client
   obtains an address from the given pool:

 "Dhcp4": {
     "subnet4": [
         {
             "pools": [
                 {
                     "pool": "192.0.2.1 - 192.0.2.200",
                     "option-data": [
                         {
                             "name": "domain-name-servers",
                             "data": "192.0.2.3"
                          },
                          ...
                     ],
                     ...
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   Options can be specified also in class of host reservation scope. In Kea
   1.4 options precedence order is (from most important): host reservation,
   pool, subnet, shared network, class, global. In Kea 1.5 order will be
   changed to: host reservation, class, pool, subnet, shared network, global
   OR it will be fully configurable.

   The currently supported standard DHCPv4 options are listed in Table 8.1,
   "List of standard DHCPv4 options". The "Name" and "Code" are the values
   that should be used as a name in the option-data structures. "Type"
   designates the format of the data: the meanings of the various types is
   given in Table 8.2, "List of standard DHCP option types".

   When a data field is a string, and that string contains the comma (,;
   U+002C) character, the comma must be escaped with a double reverse solidus
   character (\; U+005C). This double escape is required, because both the
   routine splitting CSV data into fields and JSON use the same escape
   character: a single escape (\,) would make the JSON invalid. For example,
   the string "foo,bar" would be represented as:

 "Dhcp4": {
     "subnet4": [
         {
             "pools": [
                 {
                     "option-data": [
                         {
                             "name": "boot-file-name",
                             "data": "foo\\,bar"
                         }
                     ]
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   Some options are designated as arrays, which means that more than one
   value is allowed in such an option. For example the option time-servers
   allows the specification of more than one IPv4 address, so allowing
   clients to obtain the addresses of multiple NTP servers.

   The Section 8.2.9, "Custom DHCPv4 options" describes the configuration
   syntax to create custom option definitions (formats). It is generally not
   allowed to create custom definitions for standard options, even if the
   definition being created matches the actual option format defined in the
   RFCs. There is an exception from this rule for standard options for which
   Kea currently does not provide a definition. In order to use such options,
   a server administrator must create a definition as described in
   Section 8.2.9, "Custom DHCPv4 options" in the 'dhcp4' option space. This
   definition should match the option format described in the relevant RFC
   but the configuration mechanism will allow any option format as it
   presently has no means to validate it.

   Table 8.1. List of standard DHCPv4 options

+-------------------------------------------------------------------------------------+
|                                      |    |                      |      |Returned if|
|                 Name                 |Code|         Type         |Array?|    not    |
|                                      |    |                      |      |requested? |
|--------------------------------------+----+----------------------+------+-----------|
|time-offset                           | 2  |        int32         |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|routers                               | 3  |     ipv4-address     | true |   true    |
|--------------------------------------+----+----------------------+------+-----------|
|time-servers                          | 4  |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|name-servers                          | 5  |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|domain-name-servers                   | 6  |     ipv4-address     | true |   true    |
|--------------------------------------+----+----------------------+------+-----------|
|log-servers                           | 7  |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|cookie-servers                        | 8  |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|lpr-servers                           | 9  |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|impress-servers                       | 10 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|resource-location-servers             | 11 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|boot-size                             | 13 |        uint16        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|merit-dump                            | 14 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|domain-name                           | 15 |         fqdn         |false |   true    |
|--------------------------------------+----+----------------------+------+-----------|
|swap-server                           | 16 |     ipv4-address     |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|root-path                             | 17 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|extensions-path                       | 18 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|ip-forwarding                         | 19 |       boolean        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|non-local-source-routing              | 20 |       boolean        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|policy-filter                         | 21 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|max-dgram-reassembly                  | 22 |        uint16        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|default-ip-ttl                        | 23 |        uint8         |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|path-mtu-aging-timeout                | 24 |        uint32        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|path-mtu-plateau-table                | 25 |        uint16        | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|interface-mtu                         | 26 |        uint16        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|all-subnets-local                     | 27 |       boolean        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|broadcast-address                     | 28 |     ipv4-address     |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|perform-mask-discovery                | 29 |       boolean        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|mask-supplier                         | 30 |       boolean        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|router-discovery                      | 31 |       boolean        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|router-solicitation-address           | 32 |     ipv4-address     |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|static-routes                         | 33 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|trailer-encapsulation                 | 34 |       boolean        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|arp-cache-timeout                     | 35 |        uint32        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|ieee802-3-encapsulation               | 36 |       boolean        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|default-tcp-ttl                       | 37 |        uint8         |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|tcp-keepalive-interval                | 38 |        uint32        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|tcp-keepalive-garbage                 | 39 |       boolean        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|nis-domain                            | 40 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|nis-servers                           | 41 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|ntp-servers                           | 42 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|vendor-encapsulated-options           | 43 |        empty         |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|netbios-name-servers                  | 44 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|netbios-dd-server                     | 45 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|netbios-node-type                     | 46 |        uint8         |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|netbios-scope                         | 47 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|font-servers                          | 48 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|x-display-manager                     | 49 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|dhcp-option-overload                  | 52 |        uint8         |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|dhcp-server-identifier                | 54 |     ipv4-address     |false |   true    |
|--------------------------------------+----+----------------------+------+-----------|
|dhcp-message                          | 56 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|dhcp-max-message-size                 | 57 |        uint16        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|vendor-class-identifier               | 60 |         hex          |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|nwip-domain-name                      | 62 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|nwip-suboptions                       | 63 |         hex          |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|nisplus-domain-name                   | 64 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|nisplus-servers                       | 65 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|tftp-server-name                      | 66 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|boot-file-name                        | 67 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|mobile-ip-home-agent                  | 68 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|smtp-server                           | 69 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|pop-server                            | 70 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|nntp-server                           | 71 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|www-server                            | 72 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|finger-server                         | 73 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|irc-server                            | 74 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|streettalk-server                     | 75 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|streettalk-directory-assistance-server| 76 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|user-class                            | 77 |         hex          |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|slp-directory-agent                   | 78 |   record (boolean,   | true |   false   |
|                                      |    |    ipv4-address)     |      |           |
|--------------------------------------+----+----------------------+------+-----------|
|slp-service-scope                     | 79 |   record (boolean,   |false |   false   |
|                                      |    |       string)        |      |           |
|--------------------------------------+----+----------------------+------+-----------|
|nds-server                            | 85 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|nds-tree-name                         | 86 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|nds-context                           | 87 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|bcms-controller-names                 | 88 |         fqdn         | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|bcms-controller-address               | 89 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|client-system                         | 93 |        uint16        | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|client-ndi                            | 94 |record (uint8, uint8, |false |   false   |
|                                      |    |        uint8)        |      |           |
|--------------------------------------+----+----------------------+------+-----------|
|uuid-guid                             | 97 | record (uint8, hex)  |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|uap-servers                           | 98 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|geoconf-civic                         | 99 |         hex          |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|pcode                                 |100 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|tcode                                 |101 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|netinfo-server-address                |112 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|netinfo-server-tag                    |113 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|default-url                           |114 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|auto-config                           |116 |        uint8         |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|name-service-search                   |117 |        uint16        | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|subnet-selection                      |118 |     ipv4-address     |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|domain-search                         |119 |         fqdn         | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|vivco-suboptions                      |124 |         hex          |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|vivso-suboptions                      |125 |         hex          |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|pana-agent                            |136 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|v4-lost                               |137 |         fqdn         |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|capwap-ac-v4                          |138 |     ipv4-address     | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|sip-ua-cs-domains                     |142 |         fqdn         | true |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|                                      |    |    record (uint8,    |      |           |
|rdnss-selection                       |146 |    ipv4-address,     | true |   false   |
|                                      |    | ipv4-address, fqdn)  |      |           |
|--------------------------------------+----+----------------------+------+-----------|
|v4-portparams                         |159 | record (uint8, psid) |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|v4-captive-portal                     |160 |        string        |false |   false   |
|--------------------------------------+----+----------------------+------+-----------|
|                                      |    |record (uint8, uint8, |      |           |
|option-6rd                            |212 |    ipv6-address,     | true |   false   |
|                                      |    |    ipv4-address)     |      |           |
|--------------------------------------+----+----------------------+------+-----------|
|v4-access-domain                      |213 |         fqdn         |false |   false   |
+-------------------------------------------------------------------------------------+

   Table 8.2. List of standard DHCP option types

   +------------------------------------------------------------------------+
   |     Name     |                         Meaning                         |
   |--------------+---------------------------------------------------------|
   | binary       | An arbitrary string of bytes, specified as a set of     |
   |              | hexadecimal digits.                                     |
   |--------------+---------------------------------------------------------|
   | boolean      | Boolean value with allowed values true or false         |
   |--------------+---------------------------------------------------------|
   | empty        | No value, data is carried in suboptions                 |
   |--------------+---------------------------------------------------------|
   | fqdn         | Fully qualified domain name (e.g. www.example.com)      |
   |--------------+---------------------------------------------------------|
   | ipv4-address | IPv4 address in the usual dotted-decimal notation (e.g. |
   |              | 192.0.2.1)                                              |
   |--------------+---------------------------------------------------------|
   | ipv6-address | IPv6 address in the usual colon notation (e.g.          |
   |              | 2001:db8::1)                                            |
   |--------------+---------------------------------------------------------|
   |              | IPv6 prefix and prefix length specified using CIDR      |
   | ipv6-prefix  | notation, e.g. 2001:db8:1::/64. This data type is used  |
   |              | to represent an 8-bit field conveying a prefix length   |
   |              | and the variable length prefix value                    |
   |--------------+---------------------------------------------------------|
   |              | PSID and PSID length separated by a slash, e.g. 3/4     |
   |              | specifies PSID=3 and PSID length=4. In the wire format  |
   |              | it is represented by an 8-bit field carrying PSID       |
   | psid         | length (in this case equal to 4) and the 16-bits long   |
   |              | PSID value field (in this case equal to                 |
   |              | "0011000000000000b" using binary notation). Allowed     |
   |              | values for a PSID length are 0 to 16. See RFC 7597 for  |
   |              | the details about the PSID wire representation          |
   |--------------+---------------------------------------------------------|
   |              | Structured data that may be comprised of any types      |
   | record       | (except "record" and "empty"). The array flag applies   |
   |              | to the last field only.                                 |
   |--------------+---------------------------------------------------------|
   | string       | Any text                                                |
   |--------------+---------------------------------------------------------|
   | tuple        | A length encoded as a 8 (16 for DHCPv6) bit unsigned    |
   |              | integer followed by a string of this length             |
   |--------------+---------------------------------------------------------|
   | uint8        | 8 bit unsigned integer with allowed values 0 to 255     |
   |--------------+---------------------------------------------------------|
   | uint16       | 16 bit unsigned integer with allowed values 0 to 65535  |
   |--------------+---------------------------------------------------------|
   | uint32       | 32 bit unsigned integer with allowed values 0 to        |
   |              | 4294967295                                              |
   |--------------+---------------------------------------------------------|
   | int8         | 8 bit signed integer with allowed values -128 to 127    |
   |--------------+---------------------------------------------------------|
   | int16        | 16 bit signed integer with allowed values -32768 to     |
   |              | 32767                                                   |
   |--------------+---------------------------------------------------------|
   | int32        | 32 bit signed integer with allowed values -2147483648   |
   |              | to 2147483647                                           |
   +------------------------------------------------------------------------+

  8.2.9. Custom DHCPv4 options

   Kea supports custom (non-standard) DHCPv4 options. Assume that we want to
   define a new DHCPv4 option called "foo" which will have a code 222 and
   will convey a single unsigned 32 bit integer value. We can define such an
   option by using the following entry in the configuration file:

 "Dhcp4": {
     "option-def": [
         {
             "name": "foo",
             "code": 222,
             "type": "uint32",
             "array": false,
             "record-types": "",
             "space": "dhcp4",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The false value of the array parameter determines that the option does NOT
   comprise an array of "uint32" values but is, instead, a single value. Two
   other parameters have been left blank: record-types and encapsulate. The
   former specifies the comma separated list of option data fields if the
   option comprises a record of data fields. This should be non-empty if the
   type is set to "record". Otherwise it must be left blank. The latter
   parameter specifies the name of the option space being encapsulated by the
   particular option. If the particular option does not encapsulate any
   option space it should be left blank. Note that the above set of comments
   define the format of the new option and do not set its values.

   The name, code and type parameters are required, all others are optional.
   The array default value is false. The record-types and encapsulate default
   values are blank (i.e. ""). The default space is "dhcp4".

   Once the new option format is defined, its value is set in the same way as
   for a standard option. For example the following commands set a global
   value that applies to all subnets.

 "Dhcp4": {
     "option-data": [
         {
             "name": "foo",
             "code": 222,
             "space": "dhcp4",
             "csv-format": true,
             "data": "12345"
         }, ...
     ],
     ...
 }

   New options can take more complex forms than simple use of primitives
   (uint8, string, ipv4-address etc): it is possible to define an option
   comprising a number of existing primitives. Assume we want to define a new
   option that will consist of an IPv4 address, followed by an unsigned 16
   bit integer, followed by a boolean value, followed by a text string. Such
   an option could be defined in the following way:

 "Dhcp4": {
     "option-def": [
         {
             "name": "bar",
             "code": 223,
             "space": "dhcp4",
             "type": "record",
             "array": false,
             "record-types": "ipv4-address, uint16, boolean, string",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The type is set to "record" to indicate that the option contains multiple
   values of different types. These types are given as a comma-separated list
   in the record-types field and should be ones from those listed in
   Table 8.2, "List of standard DHCP option types".

   The values of the option are set as follows:

 "Dhcp4": {
     "option-data": [
         {
             "name": "bar",
             "space": "dhcp4",
             "code": 223,
             "csv-format": true,
             "data": "192.0.2.100, 123, true, Hello World"
         }
     ],
     ...
 }

   csv-format is set to true to indicate that the data field comprises a
   command-separated list of values. The values in the data must correspond
   to the types set in the record-types field of the option definition.

   When array is set to true and type is set to "record", the last field is
   an array, i.e., it can contain more than one value as in:

 "Dhcp4": {
     "option-def": [
         {
             "name": "bar",
             "code": 223,
             "space": "dhcp4",
             "type": "record",
             "array": true,
             "record-types": "ipv4-address, uint16",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The new option content is one IPv4 address followed by one or more 16 bit
   unsigned integers.

  Note

   In the general case, boolean values are specified as true or false,
   without quotes. Some specific boolean parameters may accept also "true",
   "false", 0, 1, "0" and "1". Future versions of Kea will accept all those
   values for all boolean parameters.

  Note

   Numbers can be specified in decimal or hexadecimal format. The hexadecimal
   format can be either plain (e.g. abcd) or prefixed with 0x (e.g. 0xabcd).

  8.2.10. DHCPv4 Private Options

   Options with code between 224 and 254 are reserved for private use. They
   can be defined at the global scope or at client class local scope: this
   allows to use option definitions depending on context and to set option
   data accordingly. For instance to configure an old PXEClient vendor:

 "Dhcp4": {
     "client-classes": [
         {
             "name": "pxeclient",
             "test": "option[vendor-class-identifier].text == 'PXEClient'",
             "option-def": [
                 {
                     "name": "configfile",
                     "code": 209,
                     "type": "string"
                 }
             ],
             ...
         }, ...
     ],
     ...
 }

   As the Vendor Specific Information option (code 43) has vendor specific
   format, i.e. can carry either raw binary value or sub-options, this
   mechanism is available for this option too.

   In the following example taken from a real configuration two vendor
   classes use the option 43 for different and incompatible purposes:

 "Dhcp4": {
     "option-def": [
         {
             "name": "cookie",
             "code": 1,
             "type": "string",
             "space": "APC"
         },
         {
             "name": "mtftp-ip",
             "code": 1,
             "type": "ipv4-address",
             "space": "PXE"
         },
         ...
     ],
     "client-classes": [
         {
             "name": "APC",
             "test": "(option[vendor-class-identifier].text == 'APC'",
             "option-def": [
                 {
                     "name": "vendor-encapsulated-options",
                     "type": "empty",
                     "encapsulate": "APC"
                 }
             ],
             "option-data": [
                 {
                     "name": "cookie",
                     "space": "APC",
                     "data": "1APC"
                 },
                 {
                     "name": "vendor-encapsulated-options"
                 },
                 ...
             ],
             ...
         },
         {
             "name": "PXE",
             "test": "(option[vendor-class-identifier].text == 'PXE'",
             "option-def": [
                 {
                     "name": "vendor-encapsulated-options",
                     "type": "empty",
                     "encapsulate": "PXE"
                 }
             ],
             "option-data": [
                 {
                     "name": "mtftp-ip",
                     "space": "PXE",
                     "data": "0.0.0.0"
                 },
                 {
                     "name": "vendor-encapsulated-options"
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   The definition used to decode a VSI option is:

    1. The local definition of a client class the incoming packet belongs to

    2. If none, the global definition

    3. If none, the last resort definition described in the next section
       Section 8.2.11, "DHCPv4 Vendor Specific Options" (backward compatible
       with previous Kea versions).

  Note

   This last resort definition for the Vendor Specific Information option
   (code 43) is not compatible with a raw binary value. So when there are
   some known cases where a raw binary value will be used, a client class
   must be defined with a classification expression matching these cases and
   an option definition for the VSI option with a binary type and no
   encapsulation.

  Note

   Option definitions in client classes is allowed only for these limited
   option set (codes 43 and from 224 to 254), and only for DHCPv4.

  8.2.11. DHCPv4 Vendor Specific Options

   Currently there are two option spaces defined for the DHCPv4 daemon:
   "dhcp4" (for the top level DHCPv4 options) and
   "vendor-encapsulated-options-space", which is empty by default but in
   which options can be defined. Such options will be carried in the Vendor
   Specific Information option (code 43). The following examples show how to
   define an option "foo" in that space that has a code 1, and comprises an
   IPv4 address, an unsigned 16 bit integer and a string. The "foo" option is
   conveyed in a Vendor Specific Information option.

   The first step is to define the format of the option:

 "Dhcp4": {
     "option-def": [
         {
             "name": "foo",
             "code": 1,
             "space": "vendor-encapsulated-options-space",
             "type": "record",
             "array": false,
             "record-types": "ipv4-address, uint16, string",
             "encapsulate": ""
         }
     ],
     ...
 }

   (Note that the option space is set to
   "vendor-encapsulated-options-space".) Once the option format is defined,
   the next step is to define actual values for that option:

 "Dhcp4": {
     "option-data": [
         {
             "name": "foo",
             "space": "vendor-encapsulated-options-space",
             "code": 1,
             "csv-format": true,
             "data": "192.0.2.3, 123, Hello World"
         }
     ],
     ...
 }

   We also include the Vendor Specific Information option, the option that
   conveys our sub-option "foo". This is required, else the option will not
   be included in messages sent to the client.

 "Dhcp4": {
     "option-data": [
         {
             "name": "vendor-encapsulated-options"
         }
     ],
     ...
 }

   Alternatively, the option can be specified using its code.

 "Dhcp4": {
     "option-data": [
         {
             "code": 43
         }
     ],
     ...
 }

   Another possibility, since Kea 1.3, is to redefine the option, see
   Section 8.2.10, "DHCPv4 Private Options".

  8.2.12. Nested DHCPv4 Options (Custom Option Spaces)

   It is sometimes useful to define a completely new option space. This is
   the case when user creates new option in the standard option space
   ("dhcp4") and wants this option to convey sub-options. Since they are in a
   separate space, sub-option codes will have a separate numbering scheme and
   may overlap with the codes of standard options.

   Note that creation of a new option space when defining sub-options for a
   standard option is not required, because it is created by default if the
   standard option is meant to convey any sub-options (see Section 8.2.11,
   "DHCPv4 Vendor Specific Options").

   Assume that we want to have a DHCPv4 option called "container" with code
   222 that conveys two sub-options with codes 1 and 2. First we need to
   define the new sub-options:

 "Dhcp4": {
     "option-def": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "type": "ipv4-address",
             "record-types": "",
             "array": false,
             "encapsulate": ""
         },
         {
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "type": "string",
             "record-types": "",
             "array": false,
             "encapsulate": ""
         }
     ],
     ...
 }

   Note that we have defined the options to belong to a new option space (in
   this case, "isc").

   The next step is to define a regular DHCPv4 option with our desired code
   and specify that it should include options from the new option space:

 "Dhcp4": {
     "option-def": [
         ...,
         {
             "name": "container",
             "code": 222,
             "space": "dhcp4",
             "type": "empty",
             "array": false,
             "record-types": "",
             "encapsulate": "isc"
         }
     ],
     ...
 }

   The name of the option space in which the sub-options are defined is set
   in the encapsulate field. The type field is set to "empty" to indicate
   that this option does not carry any data other than sub-options.

   Finally, we can set values for the new options:

 "Dhcp4": {
     "option-data": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "data": "192.0.2.3"
         },
         }
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "data": "Hello world"
         },
         {
             "name": "container",
             "code": 222,
             "space": "dhcp4"
         }
     ],
     ...
 }

   Note that it is possible to create an option which carries some data in
   addition to the sub-options defined in the encapsulated option space. For
   example, if the "container" option from the previous example was required
   to carry an uint16 value as well as the sub-options, the type value would
   have to be set to "uint16" in the option definition. (Such an option would
   then have the following data structure: DHCP header, uint16 value,
   sub-options.) The value specified with the data parameter -- which should
   be a valid integer enclosed in quotes, e.g. "123" -- would then be
   assigned to the uint16 field in the "container" option.

  8.2.13. Unspecified Parameters for DHCPv4 Option Configuration

   In many cases it is not required to specify all parameters for an option
   configuration and the default values may be used. However, it is important
   to understand the implications of not specifying some of them as it may
   result in configuration errors. The list below explains the behavior of
   the server when a particular parameter is not explicitly specified:

     * name - the server requires an option name or option code to identify
       an option. If this parameter is unspecified, the option code must be
       specified.
     * code - the server requires an option name or option code to identify
       an option. This parameter may be left unspecified if the name
       parameter is specified. However, this also requires that the
       particular option has its definition (it is either a standard option
       or an administrator created a definition for the option using an
       'option-def' structure), as the option definition associates an option
       with a particular name. It is possible to configure an option for
       which there is no definition (unspecified option format).
       Configuration of such options requires the use of option code.
     * space - if the option space is unspecified it will default to 'dhcp4'
       which is an option space holding DHCPv4 standard options.
     * data - if the option data is unspecified it defaults to an empty
       value. The empty value is mostly used for the options which have no
       payload (boolean options), but it is legal to specify empty values for
       some options which carry variable length data and which the
       specification allows for the length of 0. For such options, the data
       parameter may be omitted in the configuration.
     * csv-format - if this value is not specified the server will assume
       that the option data is specified as a list of comma separated values
       to be assigned to individual fields of the DHCP option. This behavior
       has changed in Kea 1.2. Older versions used additional logic to
       determine whether the csv-format should be true or false. That is no
       longer the case.

  8.2.14. Stateless Configuration of DHCPv4 Clients

   The DHCPv4 server supports the stateless client configuration whereby the
   client has an IP address configured (e.g. using manual configuration) and
   only contacts the server to obtain other configuration parameters, e.g.
   addresses of DNS servers. In order to obtain the stateless configuration
   parameters the client sends the DHCPINFORM message to the server with the
   "ciaddr" set to the address that the client is currently using. The server
   unicasts the DHCPACK message to the client that includes the stateless
   configuration ("yiaddr" not set).

   The server will respond to the DHCPINFORM when the client is associated
   with a subnet defined in the server's configuration. An example subnet
   configuration will look like this:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24"
             "option-data": [ {
                 "name": "domain-name-servers",
                 "code": 6,
                 "data": "192.0.2.200,192.0.2.201",
                 "csv-format": true,
                 "space": "dhcp4"
             } ]
         }
     ]
 }

   This subnet specifies the single option which will be included in the
   DHCPACK message to the client in response to DHCPINFORM. Note that the
   subnet definition does not require the address pool configuration if it
   will be used solely for the stateless configuration.

   This server will associate the subnet with the client if one of the
   following conditions is met:

     * The DHCPINFORM is relayed and the giaddr matches the configured
       subnet.
     * The DHCPINFORM is unicast from the client and the ciaddr matches the
       configured subnet.
     * The DHCPINFORM is unicast from the client, the ciaddr is not set but
       the source address of the IP packet matches the configured subnet.
     * The DHCPINFORM is not relayed and the IP address on the interface on
       which the message is received matches the configured subnet.

  8.2.15. Client Classification in DHCPv4

   The DHCPv4 server includes support for client classification. For a deeper
   discussion of the classification process see Chapter 14, Client
   Classification.

   In certain cases it is useful to differentiate between different types of
   clients and treat them accordingly. It is envisaged that client
   classification will be used for changing the behavior of almost any part
   of the DHCP message processing. In the current release of the software
   however, there are only some mechanisms that take advantage of client
   classification: private options and option 43 deferred unpacking, subnet
   selection, pool selection, assignment of different options, and, for cable
   modems, there are specific options for use with the TFTP server address
   and the boot file field.

   Kea can be instructed to limit access to given subnets based on class
   information. This is particularly useful for cases where two types of
   devices share the same link and are expected to be served from two
   different subnets. The primary use case for such a scenario is cable
   networks. Here, there are two classes of devices: the cable modem itself,
   which should be handed a lease from subnet A and all other devices behind
   the modem that should get a lease from subnet B. That segregation is
   essential to prevent overly curious users from playing with their cable
   modems. For details on how to set up class restrictions on subnets, see
   Section 14.6, "Configuring Subnets With Class Information".

   When subnets belong to a shared network the classification applies to
   subnet selection but not to pools, e.g., a pool in a subnet limited to a
   particular class can still be used by clients which do not belong to the
   class if the pool they are expected to use is exhausted. So the limit
   access based on class information is also available at the pool level, see
   Section 14.7, "Configuring Pools With Class Information", within a subnet.
   This is useful when to segregate clients belonging to the same subnet into
   different address ranges.

   In a similar way a pool can be constrained to serve only known clients,
   i.e. clients which have a reservation, using the built-in "KNOWN" or
   "UNKNOWN" classes. One can assign addresses to registered clients without
   giving a different address per reservations, for instance when there is
   not enough available addresses. The determination whether there is a
   reservation for a given client is made after a subnet is selected. As
   such, it is not possible to use KNOWN/UNKNOWN classes to select a shared
   network or a subnet.

   The process of doing classification is conducted in five steps. The first
   step is to assess an incoming packet and assign it to zero or more
   classes. The second step is to choose a subnet, possibly based on the
   class information. The next step is to evaluate class expressions
   depending on the built-in "KNOWN"/"UNKNOWN" classes after host reservation
   lookup, using them for pool selection and to assign classes from host
   reservations. After the list of required classes is built and each class
   of the list has its expression evaluated: when it returns true the packet
   is added as a member of the class. The last step is to assign options,
   again possibly based on the class information. More complete and detailed
   description is available in Chapter 14, Client Classification.

   There are two main methods of doing classification. The first is automatic
   and relies on examining the values in the vendor class options or
   existence of a host reservation. Information from these options is
   extracted and a class name is constructed from it and added to the class
   list for the packet. The second allows for specifying an expression that
   is evaluated for each packet. If the result is true the packet is a member
   of the class.

  Note

   Care should be taken with client classification as it is easy for clients
   that do not meet class criteria to be denied any service altogether.

    8.2.15.1. Setting Fixed Fields in Classification

   It is possible to specify that clients belonging to a particular class
   should receive packets with specific values in certain fixed fields. In
   particular, three fixed fields are supported: next-server (that conveys an
   IPv4 address, which is set in the siaddr field), server-hostname (that
   conveys a server hostname, can be up to 64 bytes long and will be sent in
   the sname field) and boot-file-name (that conveys the configuration file,
   can be up to 128 bytes long and will be sent using file field).

   Obviously, there are many ways to assign clients to specific classes, but
   for the PXE clients the client architecture type option (code 93) seems to
   be particularly suited to make the distinction. The following example
   checks if the client identifies itself as PXE device with architecture EFI
   x86-64, and sets several fields if it does. See Section 2.1 of RFC 4578)
   or the documentation of your client for specific values.

 "Dhcp4": {
     "client-classes": [
         {
             "name": "ipxe_efi_x64",
             "test": "option[93].hex == 0x0009",
             "next-server": "192.0.2.254",
             "server-hostname": "hal9000",
             "boot-file-name": "/dev/null"
         },
         ...
     ],
     ...
           }

   If there are multiple classes defined and an incoming packet is matched to
   multiple classes, the class which is evaluated first is used.

  Note

   In Kea versions prior to 1.4.0 the alphabetical order of class names was
   used. Starting from Kea 1.4.0 the classes are ordered as specified in the
   configuration.

    8.2.15.2. Using Vendor Class Information in Classification

   The server checks whether an incoming packet includes the vendor class
   identifier option (60). If it does, the content of that option is
   prepended with "VENDOR_CLASS_", it is interpreted as a class. For example,
   modern cable modems will send this option with value "docsis3.0" and as a
   result the packet will belong to class "VENDOR_CLASS_docsis3.0".

  Note

   Kea 1.0 and earlier versions performed special actions for clients that
   were in VENDOR_CLASS_docsis3.0. This is no longer the case in Kea 1.1 and
   later. In these versions the old behavior can be achieved by defining
   VENDOR_CLASS_docsis3.0 and setting its next-server and boot-file-name
   values appropriately.

   This example shows a configuration using an automatically generated
   "VENDOR_CLASS_" class. The administrator of the network has decided that
   addresses from range 192.0.2.10 to 192.0.2.20 are going to be managed by
   the Dhcp4 server and only clients belonging to the docsis3.0 client class
   are allowed to use that pool.

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "client-class": "VENDOR_CLASS_docsis3.0"
         }
     ],
     ...
 }

    8.2.15.3. Defining and Using Custom Classes

   The following example shows how to configure a class using an expression
   and a subnet that makes use of the class. This configuration defines the
   class named "Client_foo". It is comprised of all clients who's client ids
   (option 61) start with the string "foo". Members of this class will be
   given addresses from 192.0.2.10 to 192.0.2.20 and the addresses of their
   DNS servers set to 192.0.2.1 and 192.0.2.2.

 "Dhcp4": {
     "client-classes": [
         {
             "name": "Client_foo",
             "test": "substring(option[61].hex,0,3) == 'foo'",
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.1, 192.0.2.2"
                 }
             ]
         },
         ...
     ],
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "client-class": "Client_foo"
         },
         ...
     ],
     ...
 }

    8.2.15.4. Required Classification

   In some cases it is useful to limit the scope of a class to a
   shared-network, subnet or pool. There are two parameters which are used to
   limit the scope of the class by instructing the server to perform
   evaluation of test expressions when required.

   The first one is the per-class only-if-required flag which is false by
   default. When it is set to true the test expression of the class is not
   evaluated at the reception of the incoming packet but later and only if
   the class evaluation is required.

   The second is the require-client-classes which takes a list of class names
   and is valid in shared-network, subnet and pool scope. Classes in these
   lists are marked as required and evaluated after selection of this
   specific shared-network/subnet/pool and before output option processing.

   In this example, a class is assigned to the incoming packet when the
   specified subnet is used.

 "Dhcp4": {
     "client-classes": [
        {
            "name": "Client_foo",
            "test": "member('ALL')",
            "only-if-required": true
        },
        ...
     ],
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "require-client-classes": [ "Client_foo" ],
             ...
         },
         ...
     ],
     ...
 }

   Required evaluation can be used to express complex dependencies, for
   example, subnet membership. It can also be used to reverse the precedence:
   if you set an option-data in a subnet it takes precedence over an
   option-data in a class. When you move the option-data to a required class
   and require it in the subnet, a class evaluated earlier may take
   precedence.

   Required evaluation is also available at shared-network and pool levels.
   The order in which required classes are considered is: shared-network,
   subnet and pool, i.e. the opposite order option-data are processed.

  8.2.16. DDNS for DHCPv4

   As mentioned earlier, kea-dhcp4 can be configured to generate requests to
   the DHCP-DDNS server (referred to here as "D2" ) to update DNS entries.
   These requests are known as NameChangeRequests or NCRs. Each NCR contains
   the following information:

    1. Whether it is a request to add (update) or remove DNS entries

    2. Whether the change requests forward DNS updates (A records), reverse
       DNS updates (PTR records), or both.

    3. The FQDN, lease address, and DHCID

   The parameters for controlling the generation of NCRs for submission to D2
   are contained in the dhcp-ddns section of the kea-dhcp4 server
   configuration. The mandatory parameters for the DHCP DDNS configuration
   are enable-updates which is unconditionally required, and
   qualifying-suffix which has no default value and is required when
   enable-updates is set to true. The two (disabled and enabled) minimal DHCP
   DDNS configurations are:

 "Dhcp4": {
     "dhcp-ddns": {
         "enable-updates": false
     },
     ...
 }

   and for example:

 "Dhcp4": {
     "dhcp-ddns": {
         "enable-updates": true,
         "qualifying-suffix": "example."
     },
     ...
 }

   The default values for the "dhcp-ddns" section are as follows:

     * "server-ip": "127.0.0.1"
     * "server-port": 53001
     * "sender-ip": ""
     * "sender-port": 0
     * "max-queue-size": 1024
     * "ncr-protocol": "UDP"
     * "ncr-format": "JSON"
     * "override-no-update": false
     * "override-client-update": false
     * "replace-client-name": "never"
     * "generated-prefix": "myhost"
     * "hostname-char-set": ""
     * "hostname-char-replacement": ""

    8.2.16.1. DHCP-DDNS Server Connectivity

   In order for NCRs to reach the D2 server, kea-dhcp4 must be able to
   communicate with it. kea-dhcp4 uses the following configuration parameters
   to control this communication:

     * enable-updates - determines whether or not kea-dhcp4 will generate
       NCRs. By default, this value is false hence DDNS updates are disabled.
       To enable DDNS updates set this value to true:
     * server-ip - IP address on which D2 listens for requests. The default
       is the local loopback interface at address 127.0.0.1. You may specify
       either an IPv4 or IPv6 address.
     * server-port - port on which D2 listens for requests. The default value
       is 53001.
     * sender-ip - IP address which kea-dhcp4 should use to send requests to
       D2. The default value is blank which instructs kea-dhcp4 to select a
       suitable address.
     * sender-port - port which kea-dhcp4 should use to send requests to D2.
       The default value of 0 instructs kea-dhcp4 to select a suitable port.
     * max-queue-size - maximum number of requests allowed to queue waiting
       to be sent to D2. This value guards against requests accumulating
       uncontrollably if they are being generated faster than they can be
       delivered. If the number of requests queued for transmission reaches
       this value, DDNS updating will be turned off until the queue backlog
       has been sufficiently reduced. The intention is to allow the kea-dhcp4
       server to continue lease operations without running the risk that its
       memory usage grows without limit. The default value is 1024.
     * ncr-protocol - socket protocol use when sending requests to D2.
       Currently only UDP is supported. TCP may be available in an upcoming
       release.
     * ncr-format - packet format to use when sending requests to D2.
       Currently only JSON format is supported. Other formats may be
       available in future releases.

   By default, kea-dhcp-ddns is assumed to be running on the same machine as
   kea-dhcp4, and all of the default values mentioned above should be
   sufficient. If, however, D2 has been configured to listen on a different
   address or port, these values must be altered accordingly. For example, if
   D2 has been configured to listen on 192.168.1.10 port 900, the following
   configuration would be required:

 "Dhcp4": {
     "dhcp-ddns": {
         "server-ip": "192.168.1.10",
         "server-port": 900,
         ...
     },
     ...
 }

    8.2.16.2. When Does the kea-dhcp4 Server Generate DDNS Requests?

   kea-dhcp4 follows the behavior prescribed for DHCP servers in RFC 4702. It
   is important to keep in mind that kea-dhcp4 provides the initial decision
   making of when and what to update and forwards that information to D2 in
   the form of NCRs. Carrying out the actual DNS updates and dealing with
   such things as conflict resolution are within the purview of D2 itself
   (Chapter 12, The DHCP-DDNS Server). This section describes when kea-dhcp4
   will generate NCRs and the configuration parameters that can be used to
   influence this decision. It assumes that the enable-updates parameter is
   true.

   In general, kea-dhcp4 will generate DDNS update requests when:

    1. A new lease is granted in response to a DHCP REQUEST

    2. An existing lease is renewed but the FQDN associated with it has
       changed.

    3. An existing lease is released in response to a DHCP RELEASE

   In the second case, lease renewal, two DDNS requests will be issued: one
   request to remove entries for the previous FQDN and a second request to
   add entries for the new FQDN. In the last case, a lease release, a single
   DDNS request to remove its entries will be made.

   The decision making involved when granting a new lease (the first case) is
   more involved. When a new lease is granted, kea-dhcp4 will generate a DDNS
   update request if the DHCP REQUEST contains either the FQDN option (code
   81) or the Host Name option (code 12). If both are present, the server
   will use the FQDN option. By default kea-dhcp4 will respect the FQDN N and
   S flags specified by the client as shown in the following table:

   Table 8.3. Default FQDN Flag Behavior

   +------------------------------------------------------------------------+
   | Client    | Client Intent           | Server Response    | Server      |
   | Flags:N-S |                         |                    | Flags:N-S-O |
   |-----------+-------------------------+--------------------+-------------|
   |           | Client wants to do      | Server generates   |             |
   | 0-0       | forward updates, server | reverse-only       | 1-0-0       |
   |           | should do reverse       | request            |             |
   |           | updates                 |                    |             |
   |-----------+-------------------------+--------------------+-------------|
   |           | Server should do both   | Server generates   |             |
   | 0-1       | forward and reverse     | request to update  | 0-1-0       |
   |           | updates                 | both directions    |             |
   |-----------+-------------------------+--------------------+-------------|
   | 1-0       | Client wants no updates | Server does not    | 1-0-0       |
   |           | done                    | generate a request |             |
   +------------------------------------------------------------------------+

   The first row in the table above represents "client delegation". Here the
   DHCP client states that it intends to do the forward DNS updates and the
   server should do the reverse updates. By default, kea-dhcp4 will honor the
   client's wishes and generate a DDNS request to the D2 server to update
   only reverse DNS data. The parameter override-client-update can be used to
   instruct the server to override client delegation requests. When this
   parameter is true, kea-dhcp4 will disregard requests for client delegation
   and generate a DDNS request to update both forward and reverse DNS data.
   In this case, the N-S-O flags in the server's response to the client will
   be 0-1-1 respectively.

   (Note that the flag combination N=1, S=1 is prohibited according to RFC
   4702. If such a combination is received from the client, the packet will
   be dropped by kea-dhcp4.)

   To override client delegation, set the following values in the
   configuration file:

 "Dhcp4": {
     "dhcp-ddns": {
         "override-client-update": true,
         ...
     },
     ...
 }

   The third row in the table above describes the case in which the client
   requests that no DNS updates be done. The parameter, override-no-update,
   can be used to instruct the server to disregard the client's wishes. When
   this parameter is true, kea-dhcp4 will generate DDNS update requests to
   kea-dhcp-ddns even if the client requests that no updates be done. The
   N-S-O flags in the server's response to the client will be 0-1-1.

   To override client delegation, the following values should be set in your
   configuration:

 "Dhcp4": {
     "dhcp-ddns": {
         "override-no-update": true,
         ...
     },
     ...
 }

   kea-dhcp4 will always generate DDNS update requests if the client request
   only contains the Host Name option. In addition it will include an FQDN
   option in the response to the client with the FQDN N-S-O flags set to
   0-1-0 respectively. The domain name portion of the FQDN option will be the
   name submitted to D2 in the DDNS update request.

    8.2.16.3. kea-dhcp4 name generation for DDNS update requests

   Each NameChangeRequest must of course include the fully qualified domain
   name whose DNS entries are to be affected. kea-dhcp4 can be configured to
   supply a portion or all of that name based upon what it receives from the
   client in the DHCP REQUEST.

   The default rules for constructing the FQDN that will be used for DNS
   entries are:

    1. If the DHCPREQUEST contains the client FQDN option, the candidate name
       is taken from there, otherwise it is taken from the Host Name option.

    2. If the candidate name is a partial (i.e. unqualified) name then add a
       configurable suffix to the name and use the result as the FQDN.

    3. If the candidate name provided is empty, generate a FQDN using a
       configurable prefix and suffix.

    4. If the client provided neither option, then no DNS action will be
       taken.

   These rules can amended by setting the replace-client-name parameter which
   provides the following modes of behavior:

     * never - Use the name the client sent. If the client sent no name, do
       not generate one. This is the default mode.

     * always - Replace the name the client sent. If the client sent no name,
       generate one for the client.

     * when-present - Replace the name the client sent. If the client sent no
       name, do not generate one.

     * when-not-present - Use the name the client sent. If the client sent no
       name, generate one for the client.

  Note

   Note that formerly, this parameter was a boolean and permitted only values
   of true and false. Boolean values have been deprecated and are no longer
   accepted. If you are currently using booleans, you must replace them with
   the desired mode name. A value of true maps to "when-present", while false
   maps to "never".

   For example, To instruct kea-dhcp4 to always generate the FQDN for a
   client, set the parameter replace-client-name to always as follows:

 "Dhcp4": {
     "dhcp-ddns": {
         "replace-client-name": "always",
         ...
     },
     ...
 }

   The prefix used in the generation of a FQDN is specified by the
   generated-prefix parameter. The default value is "myhost". To alter its
   value, simply set it to the desired string:

 "Dhcp4": {
     "dhcp-ddns": {
         "generated-prefix": "another.host",
         ...
     },
     ...
 }

   The suffix used when generating a FQDN or when qualifying a partial name
   is specified by the qualifying-suffix parameter. This parameter has no
   default value, thus it is mandatory when DDNS updates are enabled. To set
   its value simply set it to the desired string:

 "Dhcp4": {
     "dhcp-ddns": {
         "qualifying-suffix": "foo.example.org",
         ...
     },
     ...
 }

   When generating a name, kea-dhcp4 will construct name of the format:

   [generated-prefix]-[address-text].[qualifying-suffix].

   where address-text is simply the lease IP address converted to a
   hyphenated string. For example, if the lease address is 172.16.1.10, the
   qualifying suffix "example.com", and the default value is used for
   generated-prefix, the generated FQDN would be:

   myhost-172-16-1-10.example.com.

    8.2.16.4. Sanitizing Client Host Name and FQDN Names

   It may be that some of your DHCP clients provide values in the Host Name
   option (Option code 12) or FQDN option (Option code 81), that contain
   undesirable characters. It is possible to configure kea-dhcp4 to sanitize
   these values. The most typical use case would be ensuring that only
   characters that are permitted by RFC 1035 be included: A-Z,a-z,0-9, and
   '-'. This may be accomplished with following two parameters:

     * hostname-char-set - a regular expression describing the invalid
       character set. This can be any valid, regular expression using POSIX
       extended expression syntax. For example, "[^A-Za-z0-9-]" would replace
       any character other then the letters A through z, digits 0 through 9,
       and '-'. An empty string, the default value, disables sanitization.
     * hostname-char-replacement - a string of zero or more characters with
       which to replace each invalid character in the host name. The default
       value is an empty string and will cause invalid characters to be
       OMITTED rather than replaced.

   The following configuration, will replace anything other than a letter,
   digit, hyphen, or dot with the letter 'x':

 "Dhcp4": {
     "dhcp-ddns": {
         "hostname-char-set": "[^A-Za-z0-9.-]",
         "hostname-char-replacement": "x",
         ...
     },
     ...
 }

   Thus, a client supplied value of "myhost-$[123.org" would become
   "myhost-xx123.org". Sanitizing is performed only on the portion of the
   name supplied by the client and it is performed before applying a
   qualifying suffix (if one is defined and needed).

  Note

   The following are some considerations to keep in mind:

   Name sanitizing is meant to catch the more common cases of invalid
   characters through a relatively simple character replacement scheme. It is
   difficult to devise a scheme that works well in all cases, for both Host
   Name and FQDN options. If you find you have clients that are using odd,
   corner cases of character combinations that cannot be readily handled with
   this mechanism, you should consider writing a hook that can carry out
   sufficiently complex logic to address your needs.

   If your clients include domain names in the Host Name option and you want
   these preserved, you will need to make sure that the dot, '.', is
   considered a valid character by the hostname-char-set expression, such as
   this: "[^A-Za-z0-9.-]". This will not affect dots in FQDN Option values.
   When scrubbing FQDNs, dots are treated as delimiters and used to separate
   the option value into individual domain labels that are scrubbed and then
   re-assembled.

   If your clients are sending values that differ only by characters
   considered as invalid by your hostname-char-set, be aware that scrubbing
   them will yield identical values. In such cases, DDNS conflict rules will
   permit only one of them from registering the name.

   Finally, given the latitude clients have in the values they send, it is
   virtually impossible to guarantee that a combination of these two
   parameters will always yield a name that is valid for use in DNS. For
   example, using an empty value for hostname-char-replacment could yield an
   empty domain label within a name, if that label consists only of invalid
   characters.

  8.2.17. Next Server (siaddr)

   In some cases, clients want to obtain configuration from a TFTP server.
   Although there is a dedicated option for it, some devices may use the
   siaddr field in the DHCPv4 packet for that purpose. That specific field
   can be configured using next-server directive. It is possible to define it
   in the global scope or for a given subnet only. If both are defined, the
   subnet value takes precedence. The value in subnet can be set to 0.0.0.0,
   which means that next-server should not be sent. It may also be set to an
   empty string, which means the same as if it was not defined at all, i.e.
   use the global value.

   The server-hostname (that conveys a server hostname, can be up to 64 bytes
   long and will be sent in the sname field) and boot-file-name (that conveys
   the configuration file, can be up to 128 bytes long and will be sent using
   file field) directives are handled the same way as next-server.

 "Dhcp4": {
     "next-server": "192.0.2.123",
     "boot-file-name": "/dev/null",
     ...,
     "subnet4": [
         {
             "next-server": "192.0.2.234",
             "server-hostname": "some-name.example.org",
             "boot-file-name": "bootfile.efi",
             ...
         }
     ]
 }

  8.2.18. Echoing Client-ID (RFC 6842)

   The original DHCPv4 specification (RFC 2131) states that the DHCPv4 server
   must not send back client-id options when responding to clients. However,
   in some cases that confused clients that did not have MAC address or
   client-id; see RFC 6842. for details. That behavior has changed with the
   publication of RFC 6842 which updated RFC 2131. That update states that
   the server must send client-id if the client sent it. That is Kea's
   default behavior. However, in some cases older devices that do not support
   RFC 6842. may refuse to accept responses that include the client-id
   option. To enable backward compatibility, an optional configuration
   parameter has been introduced. To configure it, use the following
   configuration statement:

 "Dhcp4": {
     "echo-client-id": false,
     ...
 }

  8.2.19. Using Client Identifier and Hardware Address

   The DHCP server must be able to identify the client (and distinguish it
   from other clients) from which it receives the message. There are many
   reasons why this identification is required and the most important ones
   are:

     * When the client contacts the server to allocate a new lease, the
       server must store the client identification information in the lease
       database as a search key.
     * When the client is trying to renew or release the existing lease, the
       server must be able to find the existing lease entry in the database
       for this client, using the client identification information as a
       search key.
     * Some configurations use static reservations for the IP addresses and
       other configuration information. The server's administrator uses
       client identification information to create these static assignments.
     * In the dual stack networks there is often a need to correlate the
       lease information stored in DHCPv4 and DHCPv6 server for a particular
       host. Using common identification information by the DHCPv4 and DHCPv6
       client allows the network administrator to achieve this correlation
       and better administer the network.

   DHCPv4 makes use of two distinct identifiers which are placed by the
   client in the queries sent to the server and copied by the server to its
   responses to the client: "chaddr" and "client identifier". The former was
   introduced as a part of the BOOTP specification and it is also used by
   DHCP to carry the hardware address of the interface used to send the query
   to the server (MAC address for the Ethernet). The latter is carried in the
   Client-identifier option, introduced in RFC 2132.

   RFC 2131 indicates that the server may use both of these identifiers to
   identify the client but the "client identifier", if present, takes
   precedence over "chaddr". One of the reasons for this is that "client
   identifier" is independent from the hardware used by the client to
   communicate with the server. For example, if the client obtained the lease
   using one network card and then the network card is moved to another host,
   the server will wrongly identify this host is the one which has obtained
   the lease. Moreover, RFC 4361 gives the recommendation to use a DUID (see
   RFC 8415, the DHCPv6 specification) carried as "client identifier" when
   dual stack networks are in use to provide consistent identification
   information of the client, regardless of the protocol type it is using.
   Kea adheres to these specifications and the "client identifier" by default
   takes precedence over the value carried in "chaddr" field when the server
   searches, creates, updates or removes the client's lease.

   When the server receives a DHCPDISCOVER or DHCPREQUEST message from the
   client, it will try to find out if the client already has a lease in the
   database and will hand out that lease rather than allocate a new one. Each
   lease in the lease database is associated with the "client identifier"
   and/or "chaddr". The server will first use the "client identifier" (if
   present) to search the lease. If the lease is found, the server will treat
   this lease as belonging to the client even if the current "chaddr" and the
   "chaddr" associated with the lease do not match. This facilitates the
   scenario when the network card on the client system has been replaced and
   thus the new MAC address appears in the messages sent by the DHCP client.
   If the server fails to find the lease using the "client identifier" it
   will perform another lookup using the "chaddr". If this lookup returns no
   result, the client is considered as not having a lease and the new lease
   will be created.

   A common problem reported by network operators is that poor client
   implementations do not use stable client identifiers, instead generating a
   new "client identifier" each time the client connects to the network.
   Another well known case is when the client changes its "client identifier"
   during the multi-stage boot process (PXE). In such cases, the MAC address
   of the client's interface remains stable and using "chaddr" field to
   identify the client guarantees that the particular system is considered to
   be the same client, even though its "client identifier" changes.

   To address this problem, Kea includes a configuration option which enables
   client identification using "chaddr" only by instructing the server to
   disregard server to "ignore" the "client identifier" during lease lookups
   and allocations for a particular subnet. Consider the following simplified
   server configuration:

 "Dhcp4": {
     ...
     "match-client-id": true,
     ...
     "subnet4": [
     {
         "subnet": "192.0.10.0/24",
         "pools": [ { "pool": "192.0.2.23-192.0.2.87" } ],
         "match-client-id": false
     },
     {
         "subnet": "10.0.0.0/8",
         "pools": [ { "pool": "10.0.0.23-10.0.2.99" } ],
     }
     ]
 }

   The match-client-id is a boolean value which controls this behavior. The
   default value of true indicates that the server will use the "client
   identifier" for lease lookups and "chaddr" if the first lookup returns no
   results. The false means that the server will only use the "chaddr" to
   search for client's lease. Whether the DHCID for DNS updates is generated
   from the "client identifier" or "chaddr" is controlled through the same
   parameter accordingly.

   The match-client-id parameter may appear both in the global configuration
   scope and/or under any subnet declaration. In the example shown above, the
   effective value of the match-client-id will be false for the subnet
   192.0.10.0/24, because the subnet specific setting of the parameter
   overrides the global value of the parameter. The effective value of the
   match-client-id for the subnet 10.0.0.0/8 will be set to true because the
   subnet declaration lacks this parameter and the global setting is by
   default used for this subnet. In fact, the global entry for this parameter
   could be omitted in this case, because true is the default value.

   It is important to explain what happens when the client obtains its lease
   for one setting of the match-client-id and then renews when the setting
   has been changed. First consider the case when the client obtains the
   lease when the match-client-id is set to true. The server will store the
   lease information including "client identifier" (if supplied) and "chaddr"
   in the lease database. When the setting is changed and the client renews
   the lease the server will determine that it should use the "chaddr" to
   search for the existing lease. If the client hasn't changed its MAC
   address the server should successfully find the existing lease. The
   "client identifier" associated with the returned lease is ignored and the
   client is allowed to use this lease. When the lease is renewed only the
   "chaddr" is recorded for this lease according to the new server setting.

   In the second case the client has the lease with only a "chaddr" value
   recorded. When the setting is changed to match-client-id set to true the
   server will first try to use the "client identifier" to find the existing
   client's lease. This will return no results because the "client
   identifier" was not recorded for this lease. The server will then use the
   "chaddr" and the lease will be found. If the lease appears to have no
   "client identifier" recorded, the server will assume that this lease
   belongs to the client and that it was created with the previous setting of
   the match-client-id. However, if the lease contains "client identifier"
   which is different from the "client identifier" used by the client the
   lease will be assumed to belong to another client and the new lease will
   be allocated.

  8.2.20. Authoritative DHCPv4 Server Behavior

   The original DHCPv4 specification (RFC 2131) states that if a clients
   requests an address in the INIT-REBOOT state of which, the server has no
   knowledge of, the server must remain silent, except if the server knows
   that the client requests an IP address from the wrong network. By default
   Kea follows the behavior of the ISC dhcpd instead of the specification and
   also remains silent, if the client requests an IP address from the wrong
   network, because configuration information about a given network segment
   is not known to be correct. Kea only rejects a client's DHCPREQUEST with a
   DHCPNAK message, if it already has a lease for the client, but with a
   different IP address. Administrators can override this behavior through
   the boolean authoritative (false by default) setting.

   In authoritative mode, authoritative set to true, Kea always rejects
   INIT-REBOOT requests from unknown clients with DHCPNAK messages. The
   authoritative setting can be specified in global, shared-network, and
   subnet configuration scope and is automatically inherited from the parent
   scope, if not specified. All subnets in a shared-network must have the
   same authoritative setting.

  8.2.21. DHCPv4-over-DHCPv6: DHCPv4 Side

   The support of DHCPv4-over-DHCPv6 transport is described in RFC 7341 and
   is implemented using cooperating DHCPv4 and DHCPv6 servers. This section
   is about the configuration of the DHCPv4 side (the DHCPv6 side is
   described in Section 9.2.22, "DHCPv4-over-DHCPv6: DHCPv6 Side").

  Note

   DHCPv4-over-DHCPv6 support is experimental and the details of the
   inter-process communication can change: both the DHCPv4 and DHCPv6 sides
   should be running the same version of Kea. For instance the support of
   port relay (RFC 8357) introduced such incompatible change.

   The dhcp4o6-port global parameter specifies the first of the two
   consecutive ports of the UDP sockets used for the communication between
   the DHCPv6 and DHCPv4 servers (the DHCPv4 server is bound to ::1 on port +
   1 and connected to ::1 on port).

   With DHCPv4-over-DHCPv6 the DHCPv4 server does not have access to several
   of the identifiers it would normally use to select a subnet. In order to
   address this issue three new configuration entries have been added. The
   presence of any of these allows the subnet to be used with
   DHCPv4-over-DHCPv6. These entries are:

     * 4o6-subnet: Takes a prefix (i.e., an IPv6 address followed by a slash
       and a prefix length) which is matched against the source address.
     * 4o6-interface-id: Takes a relay interface ID option value.
     * 4o6-interface: Takes an interface name which is matched against the
       incoming interface name.

   The following configuration was used during some tests:

 {

 # DHCPv4 conf
 "Dhcp4": {
     "interfaces-config": {
         "interfaces": [ "eno33554984" ]
     },

     "lease-database": {
         "type": "memfile",
         "name": "leases4"
     },

     "valid-lifetime": 4000,

     "subnet4": [ {
         "subnet": "10.10.10.0/24",
         "4o6-interface": "eno33554984",
         "4o6-subnet": "2001:db8:1:1::/64",
         "pools": [ { "pool": "10.10.10.100 - 10.10.10.199" } ]
     } ],

     "dhcp4o6-port": 6767

 },

 "Logging": {
     "loggers": [ {
         "name": "kea-dhcp4",
         "output_options": [ {
             "output": "/tmp/kea-dhcp4.log"
         } ],
         "severity": "DEBUG",
         "debuglevel": 0
     } ]
 }

 }

  8.2.22. Sanity checks in DHCPv4

   An important aspect of a well running DHCP system is an assurance that the
   data remains consisent. However, in some cases it may be convenient to
   tolerate certain inconsistent data. For example, a network administrator
   that temporarily removed a subnet from a configuration wouldn't want all
   the leases associated with it disappear from the lease database. Kea 1.5
   introduced a mechanism to better control sanity checks such as this. While
   currently the scope of configurable sanity checks is limited and their
   default value is set low, it is expected that over time the default
   settings will be set to more aggressive values and more parameters of
   similar nature will be added in the future.

   Kea now supports a new configuration scope called sanity-checks. It
   currently allows only a single parameter called lease-checks. It governs
   what sort of verification is done when a new lease is being loaded from a
   lease file. With the introduction of sanity checks mechanism, it is now
   possible to tell Kea to try to correct inconsistent data.

   Every subnet has a subnet-id value. This is how Kea internally identifies
   subnets. Each lease has a subnet-id parameter as well, which identifies
   which subnet it belongs to. However, if configuration has changed, it is
   possible that a lease could exist with a subnet-id without any subnet that
   matches it. Also, it may be possible that subnets configuration has
   changed and the subnet-id now belongs to a subnet that does not match the
   lease. Kea corrective algorithm first checks if there is a subnet with
   subnet-id specified by the lease. If there is, it checks whether the lease
   belongs to that subnet. If not, depending on the lease-checks setting, the
   lease is discarded, a warning is printed or a new subnet is selected for
   the lease that matches it topologically.

   There are five levels which are supported:

     * none - do no special checks, accept the lease as is
     * warn - if problems are detected, a warning will be printed, but the
       lease data will be accepted anyway. This is the default value. If not
       explicitly configured to some other value, this level will be used.
     * fix - If data inconsistency is discovered, Kea will try to correct it.
       If the correction is not successful, the data will be inserted anyway.
     * fix-del - If data inconsistency is discovered, Kea will try to correct
       it. If the correction is not succesful, the lease will be rejected.
       This setting ensures the data correctness, but some incorrect data may
       be lost. Use with care.
     * del - This is the strictest mode. If any inconsistency is detected,
       the lease is rejected. Use with care.

   This feature is currently implemented for memfile backend.

   An example configuration that sets this parameter looks as follows:

 "Dhcp4": {
     "sanity-checks": {
         // This parameter determines what to do when a new lease appears in the
         // system (i.e. either is read from disk during memfile startup or is
         // added via lease commands). There are five modes supported:
         // none - do nothing, accept them as is
         // warn - if subnet-id problems are detected, print a warning, but
         //        otherwise load the lease as is. This is the default value.
         // fix - attempt to fix the lease by finding appropriate subnet-id value.
         //       if there is no suitable subnet, the lease is loaded as is.
         // fix-del - attempt to fix the lease by findind appropriate subnet-id
         //           value. If there is no suitable subnet, the lease is deleted.
         // del - delete leases that have incorrect subnet-id values.
         "lease-checks": "fix-del"
     },
     ...
 }

8.3. Host Reservation in DHCPv4

   There are many cases where it is useful to provide a configuration on a
   per host basis. The most obvious one is to reserve a specific, static
   address for exclusive use by a given client (host) - the returning client
   will receive the same address from the server every time, and other
   clients will generally not receive that address. Another example when the
   host reservations are applicable is when a host has specific requirements,
   e.g. a printer that needs additional DHCP options. Yet another possible
   use case is to define unique names for hosts.

   Note that there may be cases when the new reservation has been made for
   the client for the address being currently in use by another client. We
   call this situation a "conflict". The conflicts get resolved automatically
   over time as described in subsequent sections. Once the conflict is
   resolved, the client will keep receiving the reserved configuration when
   it renews.

   Host reservations are defined as parameters for each subnet. Each host has
   to be identified by an identifier, for example the hardware/MAC address.
   There is an optional reservations array in the Subnet4 element. Each
   element in that array is a structure that holds information about
   reservations for a single host. In particular, the structure has to have
   an identifier that uniquely identifies a host. In the DHCPv4 context, the
   identifier is usually a hardware or MAC address. In most cases an IP
   address will be specified. It is also possible to specify a hostname, host
   specific options or fields carried within DHCPv4 message such as siaddr,
   sname or file.

   In Kea 1.0.0 it was only possible to create host reservations using
   client's hardware address. Host reservations by client identifier, DUID
   and circuit-id have been added in Kea 1.1.0.

   The following example shows how to reserve addresses for specific hosts in
   a subnet:

 "subnet4": [
     {
         "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
         "subnet": "192.0.2.0/24",
         "interface": "eth0",
         "reservations": [
             {
                 "hw-address": "1a:1b:1c:1d:1e:1f",
                 "ip-address": "192.0.2.202"
             },
             {
                 "duid": "0a:0b:0c:0d:0e:0f",
                 "ip-address": "192.0.2.100",
                 "hostname": "alice-laptop"
             },
             {
                 "circuit-id": "'charter950'",
                 "ip-address": "192.0.2.203"
             },
             {
                 "client-id": "01:11:22:33:44:55:66",
                 "ip-address": "192.0.2.204"
             }
         ]
     }
 ]

   The first entry reserves the 192.0.2.202 address for the client that uses
   a MAC address of 1a:1b:1c:1d:1e:1f. The second entry reserves the address
   192.0.2.100 and the hostname of alice-laptop for the client using a DUID
   0a:0b:0c:0d:0e:0f. (Note that if you plan to do DNS updates, it is
   strongly recommended for the hostnames to be unique.) The third example
   reserves address 192.0.3.203 to a client whose request would be relayed by
   a relay agent that inserts a circuit-it option with the value
   'charter950'. The fourth entry reserves address 192.0.2.204 for a client
   that uses a client identifier with value 01:11:22:33:44:55:66.

   The above example is used for illustrational purposes only and in actual
   deployments it is recommended to use as few types as possible (preferably
   just one). See Section 8.3.8, "Fine Tuning DHCPv4 Host Reservation" for a
   detailed discussion of this point.

   Making a reservation for a mobile host that may visit multiple subnets
   requires a separate host definition in each subnet it is expected to
   visit. It is not allowed to define multiple host definitions with the same
   hardware address in a single subnet. Multiple host definitions with the
   same hardware address are valid if each is in a different subnet.

   Adding host reservation incurs a performance penalty. In principle, when a
   server that does not support host reservation responds to a query, it
   needs to check whether there is a lease for a given address being
   considered for allocation or renewal. The server that also supports host
   reservation has to perform additional checks: not only if the address is
   currently used (i.e. if there is a lease for it), but also whether the
   address could be used by someone else (i.e. there is a reservation for
   it). That additional check incurs additional overhead.

  8.3.1. Address Reservation Types

   In a typical scenario there is an IPv4 subnet defined, e.g. 192.0.2.0/24,
   with certain part of it dedicated for dynamic allocation by the DHCPv4
   server. That dynamic part is referred to as a dynamic pool or simply a
   pool. In principle, a host reservation can reserve any address that
   belongs to the subnet. The reservations that specify addresses that belong
   to configured pools are called "in-pool reservations". In contrast, those
   that do not belong to dynamic pools are called "out-of-pool reservations".
   There is no formal difference in the reservation syntax and both
   reservation types are handled uniformly. However, upcoming releases may
   offer improved performance if there are only out-of-pool reservations as
   the server will be able to skip reservation checks when dealing with
   existing leases. Therefore, system administrators are encouraged to use
   out-of-pool reservations if possible.

   Beginning with Kea 1.5.0, there is now support for global host
   reservations. These are reservations that are specified at the global
   level within the configuration and that do not belong to any specific
   subnet. Kea will still match inbound client packets to a subnet as before,
   but when the subnet's reservation mode is set to "global", Kea will look
   for host reservations only among the global reservations defined.
   Typcially, such resrvations would be used to reserve hostnames for clients
   which may move from one subnet to another.

  Note

   You can reserve any ip-address in a global reservation. Just keep in mind
   that Kea will not do any sanity checking on the address and for Kea 1.5.0,
   support for global reservations should be considered experimental.

  8.3.2. Conflicts in DHCPv4 Reservations

   As the reservations and lease information are stored separately, conflicts
   may arise. Consider the following series of events. The server has
   configured the dynamic pool of addresses from the range of 192.0.2.10 to
   192.0.2.20. Host A requests an address and gets 192.0.2.10. Now the system
   administrator decides to reserve address 192.0.2.10 for Host B. In
   general, reserving an address that is currently assigned to someone else
   is not recommended, but there are valid use cases where such an operation
   is warranted.

   The server now has a conflict to resolve. Let's analyze the situation
   here. If Host B boots up and requests an address, the server is not able
   to assign the reserved address 192.0.2.10. A naive approach would to be
   immediately remove the existing lease for the Host A and create a new one
   for the Host B. That would not solve the problem, though, because as soon
   as the Host B gets the address, it will detect that the address is already
   in use by the Host A and would send the DHCPDECLINE message. Therefore, in
   this situation, the server has to temporarily assign a different address
   (not matching what has been reserved) to the Host B.

   When Host A renews its address, the server will discover that the address
   being renewed is now reserved for another host - Host B. Therefore the
   server will inform the Host A that it is no longer allowed to use it by
   sending a DHCPNAK message. The server will not remove the lease, though,
   as there's small chance that the DHCPNAK may be lost if the network is
   lossy. If that happens, the client will not receive any responses, so it
   will retransmit its DHCPREQUEST packet. Once the DHCPNAK is received by
   Host A, it will revert to the server discovery and will eventually get a
   different address. Besides allocating a new lease, the server will also
   remove the old one. As a result, address 192.0.2.10 will become free .
   When Host B tries to renew its temporarily assigned address, the server
   will detect that it has a valid lease, but there is a reservation for a
   different address. The server will send DHCPNAK to inform Host B that its
   address is no longer usable, but will keep its lease (again, the DHCPNAK
   may be lost, so the server will keep it, until the client returns for a
   new address). Host B will revert to the server discovery phase and will
   eventually send a DHCPREQUEST message. This time the server will find out
   that there is a reservation for that host and the reserved address
   192.0.2.10 is not used, so it will be granted. It will also remove the
   lease for the temporarily assigned address that Host B previously
   obtained.

   This recovery will succeed, even if other hosts will attempt to get the
   reserved address. Had the Host C requested address 192.0.2.10 after the
   reservation was made, the server will either offer a different address
   (when responding to DHCPDISCOVER) or would send DHCPNAK (when responding
   to DHCPREQUEST).

   This recovery mechanism allows the server to fully recover from a case
   where reservations conflict with the existing leases. This procedure takes
   time and will roughly take as long as the value set for of renew-timer.
   The best way to avoid such recovery is to not define new reservations that
   conflict with existing leases. Another recommendation is to use
   out-of-pool reservations. If the reserved address does not belong to a
   pool, there is no way that other clients could get this address.

  Note

   The conflict resolution mechanism does not work for global reservations.
   As of Kea 1.5.0, it is generally recommended to not use global
   reservations for addresses. If you want to use it anyway, you have to
   manually ensure that the reserved addressed are not in the dynamic pools.

  8.3.3. Reserving a Hostname

   When the reservation for a client includes the hostname, the server will
   return this hostname to the client in the Client FQDN or Hostname options.
   The server responds with the Client FQDN option only if the client has
   included Client FQDN option in its message to the server. The server will
   respond with the Hostname option if the client included Hostname option in
   its message to the server or when the client requested Hostname option
   using Parameter Request List option. The server will return the Hostname
   option even if it is not configured to perform DNS updates. The reserved
   hostname always takes precedence over the hostname supplied by the client
   or the autogenerated (from the IPv4 address) hostname.

   The server qualifies the reserved hostname with the value of the
   qualifying-suffix parameter. For example, the following subnet
   configuration:

     {
         "subnet4": [ {
             "subnet": "10.0.0.0/24",
             "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
             "reservations": [
                {
                  "hw-address": "aa:bb:cc:dd:ee:ff",
                  "hostname": "alice-laptop"
                }
             ]
          }],
         "dhcp-ddns": {
             "enable-updates": true,
             "qualifying-suffix": "example.isc.org."
         }
     }

   will result in assigning the "alice-laptop.example.isc.org." hostname to
   the client using the MAC address "aa:bb:cc:dd:ee:ff". If the
   qualifying-suffix is not specified, the default (empty) value will be
   used, and in this case the value specified as a hostname will be treated
   as fully qualified name. Thus, by leaving the qualifying-suffix empty it
   is possible to qualify hostnames for the different clients with different
   domain names:

     {
         "subnet4": [ {
             "subnet": "10.0.0.0/24",
             "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
             "reservations": [
                {
                  "hw-address": "aa:bb:cc:dd:ee:ff",
                  "hostname": "alice-laptop.isc.org."
                },
                {
                  "hw-address": "12:34:56:78:99:AA",
                  "hostname": "mark-desktop.example.org."
                }

             ]
          }],
         "dhcp-ddns": {
             "enable-updates": true,
         }
     }

  8.3.4. Including Specific DHCPv4 Options in Reservations

   Kea 1.1.0 introduced the ability to specify options on a per host basis.
   The options follow the same rules as any other options. These can be
   standard options (see Section 8.2.8, "Standard DHCPv4 Options"), custom
   options (see Section 8.2.9, "Custom DHCPv4 options") or vendor specific
   options (see Section 8.2.11, "DHCPv4 Vendor Specific Options"). The
   following example demonstrates how standard options can be defined.

 {
     "subnet4": [ {
         "reservations": [
         {
             "hw-address": "aa:bb:cc:dd:ee:ff",
             "ip-address": "192.0.2.1",
             "option-data": [
             {
                 "name": "cookie-servers",
                 "data": "10.1.1.202,10.1.1.203"
             },
             {
                 "name": "log-servers",
                 "data": "10.1.1.200,10.1.1.201"
             } ]
         } ]
     } ]
 }

   Vendor specific options can be reserved in a similar manner:

 {
     "subnet4": [ {
         "reservations": [
         {
             "hw-address": "aa:bb:cc:dd:ee:ff",
             "ip-address": "10.0.0.7",
             "option-data": [
             {
                 "name": "vivso-suboptions",
                 "data": "4491"
             },
             {
                 "name": "tftp-servers",
                 "space": "vendor-4491",
                 "data": "10.1.1.202,10.1.1.203"
             } ]
         } ]
     } ]
 }

   Options defined at host level have the highest priority. In other words,
   if there are options defined with the same type on global, subnet, class
   and host level, the host specific values will be used.

  8.3.5. Reserving Next Server, Server Hostname and Boot File Name

   BOOTP/DHCPv4 messages include "siaddr", "sname" and "file" fields. Even
   though, DHCPv4 includes corresponding options, such as option 66 and
   option 67, some clients may not support these options. For this reason,
   server administrators often use the "siaddr", "sname" and "file" fields
   instead.

   With Kea, it is possible to make static reservations for these DHCPv4
   message fields:

 {
     "subnet4": [ {
         "reservations": [
         {
             "hw-address": "aa:bb:cc:dd:ee:ff",
             "next-server": "10.1.1.2",
             "server-hostname": "server-hostname.example.org",
             "boot-file-name": "/tmp/bootfile.efi"
         } ]
     } ]
 }

   Note that those parameters can be specified in combination with other
   parameters for a reservation, e.g. reserved IPv4 address. These parameters
   are optional, i.e. a subset of them can specified, or all of them can be
   omitted.

  8.3.6. Reserving Client Classes in DHCPv4

   Section 14.3, "Using Expressions In Classification" explains how to
   configure the server to assign classes to a client based on the content of
   the options that this client sends to the server. Host reservations
   mechanisms also allow for statically assigning classes to the clients. The
   definitions of these classes should exist in the Kea configuration. The
   following configuration snippet shows how to specify that a client belongs
   to classes reserved-class1 and reserved-class2. Those classes are
   associated with specific options being sent to the clients which belong to
   them.

 {
     "client-classes": [
     {
        "name": "reserved-class1",
        "option-data": [
        {
            "name": "routers",
            "data": "10.0.0.200"
        }
        ]
     },
     {
        "name": "reserved-class2",
        "option-data": [
        {
            "name": "domain-name-servers",
            "data": "10.0.0.201"
        }
        ]
     }
     ],
     "subnet4": [ {
         "subnet": "10.0.0.0/24",
         "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ],
         "reservations": [
         {
             "hw-address": "aa:bb:cc:dd:ee:ff",

             "client-classes": [ "reserved-class1", "reserved-class2" ]

         }
         ]
     } ]
 }


   Static class assignments, as shown above, can be used in conjunction with
   classification using expressions. The "KNOWN" or "UNKNOWN" builtin class
   is added to the packet and any class depending on it directly or
   indirectly and not only-if-required is evaluated.

  Note

   If you want to force the evaluation of a class expression after the host
   reservation lookup, for instance because of a dependency on
   "reserved-class1" from the previous example, you should add a
   "member('KNOWN')" in the expression.

  8.3.7. Storing Host Reservations in MySQL, PostgreSQL or Cassandra

   It is possible to store host reservations in MySQL, PostgreSQL or
   Cassandra. See Section 9.2.3, "Hosts Storage" for information on how to
   configure Kea to use reservations stored in MySQL, PostgreSQL or
   Cassandra. Kea provides dedicated hook for managing reservations in a
   database, section Section 15.4.4, "host_cmds: Host Commands" provide
   detailed information.
   https://gitlab.isc.org/isc-projects/kea/wikis/designs/commands#23-host-reservations-hr-management
   provides some examples how to conduct common host reservation operations.

  Note

   In Kea maximum length of an option specified per host is arbitrarily set
   to 4096 bytes.

  8.3.8. Fine Tuning DHCPv4 Host Reservation

   The host reservation capability introduces additional restrictions for the
   allocation engine (the component of Kea that selects an address for a
   client) during lease selection and renewal. In particular, three major
   checks are necessary. First, when selecting a new lease, it is not
   sufficient for a candidate lease to not be used by another DHCP client. It
   also must not be reserved for another client. Second, when renewing a
   lease, additional check must be performed whether the address being
   renewed is not reserved for another client. Finally, when a host renews an
   address, the server has to check whether there is a reservation for this
   host, so the existing (dynamically allocated) address should be revoked
   and the reserved one be used instead.

   Some of those checks may be unnecessary in certain deployments and not
   performing them may improve performance. The Kea server provides the
   reservation-mode configuration parameter to select the types of
   reservations allowed for the particular subnet. Each reservation type has
   different constraints for the checks to be performed by the server when
   allocating or renewing a lease for the client. Allowed values are:

     * all - enables both in-pool and out-of-pool host reservation types.
       This is the default value. This setting is the safest and the most
       flexible. As all checks are conducted, it is also the slowest. This
       does not check against global reservations.
     * out-of-pool - allows only out of pool host reservations. With this
       setting in place, the server may assume that all host reservations are
       for addresses that do not belong to the dynamic pool. Therefore it can
       skip the reservation checks when dealing with in-pool addresses, thus
       improving performance. Do not use this mode if any of your
       reservations use in-pool address. Caution is advised when using this
       setting: Kea does not sanity check the reservations against
       reservation-mode and misconfiguration may cause problems.
     * global - allows only global host reservations. With this setting in
       place, the server searches for reservations for a client only among
       the defined global reservations. If an address is specified, the
       server will skip the reservation checks done when dealing in other
       modes, thus improving performance. Caution is advised when using this
       setting: Kea does not sanity check the reservations when global and
       misconfiguration may cause problems.
     * disabled - host reservation support is disabled. As there are no
       reservations, the server will skip all checks. Any reservations
       defined will be completely ignored. As the checks are skipped, the
       server may operate faster in this mode.

   The parameter can be specified at global, subnet and shared network
   levels.

   An example configuration that disables reservation appears as follows:

 "Dhcp4": {
     "subnet4": [
     {
         "subnet": "192.0.2.0/24",
         "reservation-mode": "disabled",
         ...
     }
     ]
 }

   An example configuration using global reservations is shown below:

 "Dhcp4": {


     "reservation-mode": "global",
     "reservations": [
        {
         "hw-address": "01:bb:cc:dd:ee:ff",
         "hostname": "host-one"
        },
        {
         "hw-address": "02:bb:cc:dd:ee:ff",
         "hostname": "host-two"
        }
     ],

     "subnet4": [
     {
         "subnet": "192.0.2.0/24",
         ...
     }
     ]
 }

   For more details regarding global reservations, see Section 8.3.9, "Global
   reservations in DHCPv4".

   Another aspect of the host reservations are the different types of
   identifiers. Kea 1.1.0 supports four types of identifiers (hw-address,
   duid, client-id and circuit-id), but more identifier types are likely to
   be added in the future. This is beneficial from a usability perspective.
   However, there is a drawback. For each incoming packet Kea has to to
   extract each identifier type and then query the database to see if there
   is a reservation done by this particular identifier. If nothing is found,
   the next identifier is extracted and the next query is issued. This
   process continues until either a reservation is found or all identifier
   types have been checked. Over time with an increasing number of supported
   identifier types, Kea would become slower and slower.

   To address this problem, a parameter called host-reservation-identifiers
   has been introduced. It takes a list of identifier types as a parameter.
   Kea will check only those identifier types enumerated in
   host-reservation-identifiers. From a performance perspective the number of
   identifier types should be kept to a minimum, ideally limited to one. If
   your deployment uses several reservation types, please enumerate them from
   most to least frequently used as this increases the chances of Kea finding
   the reservation using the fewest number of queries. An example of host
   reservation identifiers looks as follows:

 "host-reservation-identifiers": [ "circuit-id", "hw-address", "duid", "client-id" ],
 "subnet4": [
     {
         "subnet": "192.0.2.0/24",
         ...
     }
 ]

   If not specified, the default value is:

 "host-reservation-identifiers": [ "hw-address", "duid", "circuit-id", "client-id" ]

  8.3.9. Global reservations in DHCPv4

   In some deployments, such as mobile, clients can roam within the network
   and there is a desire to specify certain parameters regardless of the
   client's current location. To facilitate such a need, a global reservation
   mechanism has been implemented. The idea behind it is that regular host
   reservations are tied to specific subnets, by using specific subnet-id.
   Kea 1.5.0 introduced a new capability to specify global reservation that
   can be used in every subnet that has global reservations enabled.

   This feature can be used to assign certain parameters, such as hostname or
   other dedicated, host-specific options. It can also be used to assign
   addresses. However, global reservations that assign addresses bypass the
   whole topology determination provided by DHCP logic implemented in Kea. It
   is very easy to misuse this feature and get configuration that is
   inconsistent. To give a specific example, imagine a global reservation for
   address 192.0.2.100 and two subnets 192.0.2.0/24 and 192.0.5.0/24. If
   global reservations are used in both subnets and a device matching global
   host reservations visits part of the network that is serviced by
   192.0.5.0/24, it will get an IP address 192.0.2.100, a subnet 192.0.5.0
   and a default router 192.0.5.1. Obviously such a configuration is
   unusable, as the client won't be able to reach its default gateway.

   To use global host reservations a configuration similar to the following
   can be used:

 "Dhcp4:" {
     // This specify global reservations. They will apply to all subnets that
     // have global reservations enabled.

     "reservations": [
     {
        "hw-address": "aa:bb:cc:dd:ee:ff",
        "hostname": "hw-host-dynamic"
     },
     {
        "hw-address": "01:02:03:04:05:06",
        "hostname": "hw-host-fixed",

        // Use of IP address is global reservation is risky. If used outside of
        // matching subnet, such as 192.0.1.0/24, it will result in a broken
        // configuration being handled to the client.
        "ip-address": "192.0.1.77"
     },
     {
        "duid": "01:02:03:04:05",
        "hostname": "duid-host"
     },
     {
        "circuit-id": "'charter950'",
        "hostname": "circuit-id-host"
     },
     {
        "client-id": "01:11:22:33:44:55:66",
        "hostname": "client-id-host"
     }
     ],
     "valid-lifetime": 600,
     "subnet4": [ {
         "subnet": "10.0.0.0/24",
         "reservation-mode": "global",
         "pools": [ { "pool": "10.0.0.10-10.0.0.100" } ]
     } ]
 }

   When using database backends, the global host reservations are
   distinguished from regular reservations by using subnet-id value of zero.

8.4. Shared networks in DHCPv4

   DHCP servers use subnet information in two ways. First, it is used to
   determine the point of attachment, or simply put, where the client is
   connected to the network. Second, the subnet information is used to group
   information pertaining to specific location in the network. This approach
   works well in general case, but the are scenarios where the boundaries are
   blurred. Sometimes it is useful to have more than one logical IP subnet
   being deployed on the same physical link. The need to understand that two
   or more subnets are used on the same link requires additional logic in the
   DHCP server. This capability has been added in Kea 1.3.0. It is called
   "shared networks" in Kea and ISC DHCP projects. It is sometimes also
   called "shared subnets". In Microsoft's nomenclature it is called
   "multinet".

   There are many use cases where the feature is useful. This paragraph
   explains just a handful of the most common ones. The first and by far the
   most common use case is an existing network that has grown and is running
   out of available address space. Rather than migrating all devices to a
   new, larger subnet, it is easier to simply configure additional subnet on
   top of the existing one. Sometimes, due to address space fragmentation
   (e.g. only many disjoint /24s are available) this is the only choice.
   Also, configuring additional subnet has the advantage of not disrupting
   the operation of existing devices.

   Another very frequent use case comes from cable networks. There are two
   types of devices in cable networks: cable modems and the end user devices
   behind them. It is a common practice to use different subnet for cable
   modems to prevent users from tinkering with their cable modems. In this
   case, the distinction is based on the type of device, rather than address
   space exhaustion.

   A client connected to a shared network may be assigned an address from any
   of the address pools defined within the subnets belonging to the shared
   network. Internally, the server selects one of the subnets belonging to a
   shared network and tries to allocate an address from this subnet. If the
   server is unable to allocate an address from the selected subnet (e.g. due
   to address pools exhaustion) it will use another subnet from the same
   shared network and try to allocate an address from this subnet etc.
   Therefore, in the typical case, the server will allocate all addresses
   available for a given subnet before it starts allocating addresses from
   other subnets belonging to the same shared network. However, in certain
   situations the client can be allocated an address from the other subnets
   before the address pools in the first subnet get exhausted, e.g. when the
   client provides a hint that belongs to another subnet or the client has
   reservations in a different than default subnet.

  Note

   It is strongly discouraged for the Kea deployments to assume that the
   server doesn't allocate addresses from other subnets until it uses all the
   addresses from the first subnet in the shared network. Apart from the fact
   that hints, host reservations and client classification affect subnet
   selection, it is also foreseen that we will enhance allocation strategies
   for shared networks in the future versions of Kea, so as the selection of
   subnets within a shared network is equally probable (unpredictable).

   In order to define a shared network an additional configuration scope is
   introduced:

 {
 "Dhcp4": {
     "shared-networks": [
         {
             // Name of the shared network. It may be an arbitrary string
             // and it must be unique among all shared networks.
             "name": "my-secret-lair-level-1",

             // Subnet selector can be specifed at the shared network level.
             // Subnets from this shared network will be selected for directly
             // connected clients sending requests to server's "eth0" interface.
             "interface": "eth0",

             // This starts a list of subnets in this shared network.
             // There are two subnets in this example.
             "subnet4": [
                 {
                     "subnet": "10.0.0.0/8",
                     "pools": [ { "pool":  "10.0.0.1 - 10.0.0.99" } ],
                 },
                 {
                     "subnet": "192.0.2.0/24",
                     "pools": [ { "pool":  "192.0.2.100 - 192.0.2.199" } ]
                 }
             ],
         } ], // end of shared-networks

     // It is likely that in your network you'll have a mix of regular,
     // "plain" subnets and shared networks. It is perfectly valid to mix
     // them in the same config file.
     //
     // This is regular subnet. It's not part of any shared-network.
     "subnet4": [
         {
             "subnet": "192.0.3.0/24",
             "pools": [ { "pool":  "192.0.3.1 - 192.0.3.200" } ],
             "interface": "eth1"
         }
     ]

 } // end of Dhcp4
 }

   As you see in the example, it is possible to mix shared and regular
   ("plain") subnets. Each shared network must have a unique name. This is
   similar to ID for subnets, but gives you more flexibility. This is used
   for logging, but also internally for identifying shared networks.

   In principle it makes sense to define only shared networks that consist of
   two or more subnets. However, for testing purposes it is allowed to define
   a shared network with just one subnet or even an empty one. This is not a
   recommended practice in production networks, as the shared network logic
   requires additional processing and thus lowers server's performance. To
   avoid unnecessary performance degradation the shared subnets should only
   be defined when required by the deployment.

   Shared networks provide an ability to specify many parameters in the
   shared network scope that will apply to all subnets within it. If
   necessary, you can specify a parameter on the shared network scope and
   then override its value in the subnet scope. For example:

 "shared-networks": [
     {
         "name": "lab-network3",

         "interface": "eth0",

         // This applies to all subnets in this shared network, unless
         // values are overridden on subnet scope.
         "valid-lifetime": 600,

         // This option is made available to all subnets in this shared
         // network.
         "option-data": [ {
             "name": "log-servers",
             "data": "1.2.3.4"
         } ],

         "subnet4": [
             {
                 "subnet": "10.0.0.0/8",
                 "pools": [ { "pool":  "10.0.0.1 - 10.0.0.99" } ],

                 // This particular subnet uses different values.
                 "valid-lifetime": 1200,
                 "option-data": [
                 {
                     "name": "log-servers",
                     "data": "10.0.0.254"
                 },
                 {
                     "name": "routers",
                     "data": "10.0.0.254"
                 } ]
             },
             {
                  "subnet": "192.0.2.0/24",
                  "pools": [ { "pool":  "192.0.2.100 - 192.0.2.199" } ],

                  // This subnet does not specify its own valid-lifetime value,
                  // so it is inherited from shared network scope.
                  "option-data": [
                  {
                      "name": "routers",
                      "data": "192.0.2.1"
                  } ]
             }
         ]
     } ]

   In this example, there is a log-servers option defined that is available
   to clients in both subnets in this shared network. Also, a valid lifetime
   is set to 10 minutes (600s). However, the first subnet overrides some of
   the values (valid lifetime is 20 minutes, different IP address for
   log-servers), but also adds its own option (router address). Assuming a
   client asking for router and log servers options is assigned a lease from
   this subnet, he will get a lease for 20 minutes and log-servers and
   routers value of 10.0.0.254. If the same client is assigned to the second
   subnet, he will get a 10 minutes long lease, log-servers value of 1.2.3.4
   and routers set to 192.0.2.1.

  8.4.1. Local and relayed traffic in shared networks

   It is possible to specify interface name in the shared network scope to
   tell the server that this specific shared network is reachable directly
   (not via relays) using local network interface. It is sufficient to
   specify it once at the shared network level. As all subnets in a shared
   network are expected to be used on the same physical link, it is a
   configuration error to attempt to define a shared network using subnets
   that are reachable over different interfaces. It is allowed to specify
   interface parameter on each subnet, although its value must be the same
   for each subnet. Thus it's usually more convenient to specify it once at
   the shared network level.

 "shared-networks": [
     {
         "name": "office-floor-2",

         // This tells Kea that the whole shared networks is reachable over
         // local interface. This applies to all subnets in this network.
         "interface": "eth0",

         "subnet4": [
             {
                 "subnet": "10.0.0.0/8",
                 "pools": [ { "pool":  "10.0.0.1 - 10.0.0.99" } ],
                 "interface": "eth0"
             },
             {
                  "subnet": "192.0.2.0/24",
                  "pools": [ { "pool":  "192.0.2.100 - 192.0.2.199" } ]

                  // Specifying a different interface name is configuration
                  // error:
                  // "interface": "eth1"
             }
         ]
     } ]

   Somewhat similar to interface names, also relay IP addresses can be
   specified for the whole shared network. However, depending on your relay
   configuration, it may use different IP addresses depending on which subnet
   is being used. Thus there is no requirement to use the same IP relay
   address for each subnet. Here's an example:

 "shared-networks": [
     {
         "name": "kakapo",
         "relay": {
             "ip-addresses": [ "192.3.5.6" ]
         },
         "subnet4": [
             {
                 "subnet": "192.0.2.0/26",
                 "relay": {
                     "ip-addresses": [ "192.1.1.1" ]
                 },
                 "pools": [ { "pool": "192.0.2.63 - 192.0.2.63" } ]
             },
             {
                 "subnet": "10.0.0.0/24",
                 "relay": {
                     "ip-addresses": [ "192.2.2.2" ]
                 },
                 "pools": [ { "pool": "10.0.0.16 - 10.0.0.16" } ]
             }
         ]
     }
 ]

   In this particular case the relay IP address specified at network level
   doesn't have much sense, as it is overridden in both subnets, but it was
   left there as an example of how one could be defined at network level.
   Note that the relay agent IP address typically belongs to the subnet it
   relays packets from, but this is not a strict requirement. Therefore Kea
   accepts any value here as long as it is valid IPv4 address.

  8.4.2. Client classification in shared networks

   Sometimes it is desired to segregate clients into specific subnets based
   on some properties. This mechanism is called client classification and is
   described in Chapter 14, Client Classification. Client classification can
   be applied to subnets belonging to shared networks in the same way as it
   is used for subnets specified outside of shared networks. It is important
   to understand how the server selects subnets for the clients when client
   classification is in use, to assure that the desired subnet is selected
   for a given client type.

   If a subnet is associated with a class, only the clients belonging to this
   class can use this subnet. If there are no classes specified for a subnet,
   any client connected to a given shared network can use this subnet. A
   common mistake is to assume that the subnet including a client class is
   preferred over subnets without client classes. Consider the following
   example:

 {
     "client-classes": [
         {
             "name": "b-devices",
             "test": "option[93].hex == 0x0002"
         }
     ],
     "shared-networks": [
         {
             "name": "galah",
             "interface": "eth0",
             "subnet4": [
                 {
                     "subnet": "192.0.2.0/26",
                     "pools": [ { "pool": "192.0.2.1 - 192.0.2.63" } ],
                 },
                 {
                     "subnet": "10.0.0.0/24",
                     "pools": [ { "pool": "10.0.0.2 - 10.0.0.250" } ],
                     "client-class": "b-devices"
                 }
             ]
         }
     ]
 }

   If the client belongs to "b-devices" class (because it includes option 93
   with a value of 0x0002) it doesn't guarantee that the subnet 10.0.0.0/24
   will be used (or preferred) for this client. The server can use any of the
   two subnets because the subnet 192.0.2.0/26 is also allowed for this
   client. The client classification used in this case should be pereceived
   as a way to restrict access to certain subnets, rather than a way to
   express subnet preference. For example, if the client doesn't belong to
   the "b-devices" class it may only use the subnet 192.0.2.0/26 and will
   never use the subnet 10.0.0.0/24.

   A typical use case for client classification is in the cable network,
   where cable modems should use one subnet and other devices should use
   another subnet within the same shared network. In this case it is required
   to apply classification on all subnets. The following example defines two
   classes of devices. The subnet selection is made based on option 93
   values.

 {
     "client-classes": [
         {

             "name": "a-devices",
             "test": "option[93].hex == 0x0001"
         },
         {
             "name": "b-devices",
             "test": "option[93].hex == 0x0002"
         }
     ],
     "shared-networks": [
         {
             "name": "galah",
             "interface": "eth0",
             "subnet4": [
                 {
                     "subnet": "192.0.2.0/26",
                     "pools": [ { "pool": "192.0.2.1 - 192.0.2.63" } ],
                     "client-class": "a-devices"
                 },
                 {
                     "subnet": "10.0.0.0/24",
                     "pools": [ { "pool": "10.0.0.2 - 10.0.0.250" } ],
                     "client-class": "b-devices"
                 }
             ]
         }
     ]
 }

   In this example each class has its own restriction. Only clients that
   belong to class "a-devices" will be able to use subnet 192.0.2.0/26 and
   only clients belonging to b-devices will be able to use subnet
   10.0.0.0/24. Care should be taken to not define too restrictive
   classification rules, as clients that are unable to use any subnets will
   be refused service. Although, this may be a desired outcome if one desires
   to service only clients of known properties (e.g. only VoIP phones allowed
   on a given link).

   Note that it is possible to achieve similar effect as presented in this
   section without the use of shared networks. If the subnets are placed in
   the global subnets scope, rather than in the shared network, the server
   will still use classification rules to pick the right subnet for a given
   class of devices. The major benefit of placing subnets within the shared
   network is that common parameters for the logically grouped subnets can be
   specified once, in the shared network scope, e.g. "interface" or "relay"
   parameter. All subnets belonging to this shared network will inherit those
   parameters.

  8.4.3. Host reservations in shared networks

   Subnets being part of a shared network allow host reservations, similar to
   regular subnets:

 {
     "shared-networks": [
     {
         "name": "frog",
         "interface": "eth0",
         "subnet4": [
             {
                 "subnet": "192.0.2.0/26",
                 "id": 100,
                 "pools": [ { "pool": "192.0.2.1 - 192.0.2.63" } ],
                 "reservations": [
                     {
                         "hw-address": "aa:bb:cc:dd:ee:ff",
                         "ip-address": "192.0.2.28"
                     }
                 ]
             },
             {
                 "subnet": "10.0.0.0/24",
                 "id": 101,
                 "pools": [ { "pool": "10.0.0.1 - 10.0.0.254" } ],
                 "reservations": [
                     {
                         "hw-address": "11:22:33:44:55:66",
                         "ip-address": "10.0.0.29"
                     }
                 ]
             }
         ]
     }
     ]
 }


   It is worth noting that Kea conducts additional checks when processing a
   packet if shared networks are defined. First, instead of simply checking
   if there's a reservation for a given client in his initially selected
   subnet, it goes through all subnets in a shared network looking for a
   reservation. This is one of the reasons why defining a shared network may
   impact performance. If there is a reservation for a client in any subnet,
   that particular subnet will be picked for the client. Although it's
   technically not an error, it is considered a bad practice to define
   reservations for the same host in multiple subnets belonging to the same
   shared network.

   While not strictly mandatory, it is strongly recommended to use explicit
   "id" values for subnets if you plan to use database storage for host
   reservations. If ID is not specified, the values for it be autogenerated,
   i.e. it will assign increasing integer values starting from 1. Thus, the
   autogenerated IDs are not stable across configuration changes.

8.5. Server Identifier in DHCPv4

   The DHCPv4 protocol uses a "server identifier" to allow clients to
   discriminate between several servers present on the same link: this value
   is an IPv4 address of the server. The server chooses the IPv4 address of
   the interface on which the message from the client (or relay) has been
   received. A single server instance will use multiple server identifiers if
   it is receiving queries on multiple interfaces.

   It is possible to override default server identifier values by specifying
   "dhcp-server-identifier" option. This option is only supported at the
   global, shared network and subnet level. It must not be specified on
   client class and host reservation level.

   The following example demonstrates how to override server identifier for a
   subnet:

 "subnet4": [
     {
         "subnet": "192.0.2.0/24",
         "option-data": [
             {
                 "name": "dhcp-server-identifier",
                 "data": "10.2.5.76"
             }
         ],
         ...
     }
 ]

8.6. How the DHCPv4 Server Selects a Subnet for the Client

   The DHCPv4 server differentiates between the directly connected clients,
   clients trying to renew leases and clients sending their messages through
   relays. For directly connected clients, the server will check the
   configuration for the interface on which the message has been received
   and, if the server configuration doesn't match any configured subnet, the
   message is discarded.

   Assuming that the server's interface is configured with the IPv4 address
   192.0.2.3, the server will only process messages received through this
   interface from a directly connected client if there is a subnet configured
   to which this IPv4 address belongs, e.g. 192.0.2.0/24. The server will use
   this subnet to assign IPv4 address for the client.

   The rule above does not apply when the client unicasts its message, i.e.
   is trying to renew its lease. Such a message is accepted through any
   interface. The renewing client sets ciaddr to the currently used IPv4
   address. The server uses this address to select the subnet for the client
   (in particular, to extend the lease using this address).

   If the message is relayed it is accepted through any interface. The giaddr
   set by the relay agent is used to select the subnet for the client.

   It is also possible to specify a relay IPv4 address for a given subnet. It
   can be used to match incoming packets into a subnet in uncommon
   configurations, e.g. shared networks. See Section 8.6.1, "Using a Specific
   Relay Agent for a Subnet" for details.

  Note

   The subnet selection mechanism described in this section is based on the
   assumption that client classification is not used. The classification
   mechanism alters the way in which a subnet is selected for the client,
   depending on the classes to which the client belongs.

  8.6.1. Using a Specific Relay Agent for a Subnet

   A relay has to have an interface connected to the link on which the
   clients are being configured. Typically the relay has an IPv4 address
   configured on that interface that belongs to the subnet from which the
   server will assign addresses. In the typical case, the server is able to
   use the IPv4 address inserted by the relay (in the giaddr field of the
   DHCPv4 packet) to select the appropriate subnet.

   However, that is not always the case. In certain uncommon -- but valid --
   deployments, the relay address may not match the subnet. This usually
   means that there is more than one subnet allocated for a given link. The
   two most common examples where this is the case are long lasting network
   renumbering (where both old and new address space is still being used) and
   a cable network. In a cable network both cable modems and the devices
   behind them are physically connected to the same link, yet they use
   distinct addressing. In such a case, the DHCPv4 server needs additional
   information (the IPv4 address of the relay) to properly select an
   appropriate subnet.

   The following example assumes that there is a subnet 192.0.2.0/24 that is
   accessible via a relay that uses 10.0.0.1 as its IPv4 address. The server
   will be able to select this subnet for any incoming packets that came from
   a relay that has an address in 192.0.2.0/24 subnet. It will also select
   that subnet for a relay with address 10.0.0.1.

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "relay": {
                 "ip-addresses": [ "10.0.0.1" ]
             },
             ...
         }
     ],
     ...
 }

   If "relay" is specified, the "ip-addresses" parameter within it is
   mandatory.

  Note

   As of Kea 1.4, the "ip-address" parameter has been deprecated in favor of
   "ip-addresses" which supports specifying a list of addresses.
   Configuration parsing, will honor the singular form for now but users are
   encouraged to migrate.

  8.6.2. Segregating IPv4 Clients in a Cable Network

   In certain cases, it is useful to mix relay address information,
   introduced in Section 8.6.1, "Using a Specific Relay Agent for a Subnet"
   with client classification, explained in Chapter 14, Client
   Classification. One specific example is cable network, where typically
   modems get addresses from a different subnet than all devices connected
   behind them.

   Let us assume that there is one CMTS (Cable Modem Termination System) with
   one CM MAC (a physical link that modems are connected to). We want the
   modems to get addresses from the 10.1.1.0/24 subnet, while everything
   connected behind modems should get addresses from another subnet
   (192.0.2.0/24). The CMTS that acts as a relay uses address 10.1.1.1. The
   following configuration can serve that configuration:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "10.1.1.0/24",
             "pools":  [ { "pool": "10.1.1.2 - 10.1.1.20" } ],
             "client-class" "docsis3.0",
             "relay": {
                 "ip-addresses": [ "10.1.1.1 ]"
             }
         },
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "relay": {
                 "ip-addresses": [ "10.1.1.1" ]
             }
         }
     ],
     ...
 }

8.7. Duplicate Addresses (DHCPDECLINE Support)

   The DHCPv4 server is configured with a certain pool of addresses that it
   is expected to hand out to the DHCPv4 clients. It is assumed that the
   server is authoritative and has complete jurisdiction over those
   addresses. However, due to various reasons, such as misconfiguration or a
   faulty client implementation that retains its address beyond the valid
   lifetime, there may be devices connected that use those addresses without
   the server's approval or knowledge.

   Such an unwelcome event can be detected by legitimate clients (using ARP
   or ICMP Echo Request mechanisms) and reported to the DHCPv4 server using a
   DHCPDECLINE message. The server will do a sanity check (if the client
   declining an address really was supposed to use it), and then will conduct
   a clean up operation. Any DNS entries related to that address will be
   removed, the fact will be logged and hooks will be triggered. After that
   is done, the address will be marked as declined (which indicates that it
   is used by an unknown entity and thus not available for assignment to
   anyone) and a probation time will be set on it. Unless otherwise
   configured, the probation period lasts 24 hours. After that period, the
   server will recover the lease (i.e. put it back into the available state)
   and the address will be available for assignment again. It should be noted
   that if the underlying issue of a misconfigured device is not resolved,
   the duplicate address scenario will repeat. On the other hand, it provides
   an opportunity to recover from such an event automatically, without any
   sysadmin intervention.

   To configure the decline probation period to a value other than the
   default, the following syntax can be used:

   "Dhcp4": {
     "decline-probation-period": 3600,
     "subnet4": [ ... ],
     ...
 }

   The parameter is expressed in seconds, so the example above will instruct
   the server to recycle declined leases after an hour.

   There are several statistics and hook points associated with the Decline
   handling procedure. The lease4_decline hook is triggered after the
   incoming DHCPDECLINE message has been sanitized and the server is about to
   decline the lease. The declined-addresses statistic is increased after the
   hook returns (both global and subnet specific variants). (See Section 8.8,
   "Statistics in the DHCPv4 Server" and Chapter 15, Hooks Libraries for more
   details on DHCPv4 statistics and Kea hook points.)

   Once the probation time elapses, the declined lease is recovered using the
   standard expired lease reclamation procedure, with several additional
   steps. In particular, both declined-addresses statistics (global and
   subnet specific) are decreased. At the same time,
   reclaimed-declined-addresses statistics (again in two variants, global and
   subnet specific) are increased.

   Note about statistics: The server does not decrease the assigned-addresses
   statistics when a DHCPDECLINE is received and processed successfully.
   While technically a declined address is no longer assigned, the primary
   usage of the assigned-addresses statistic is to monitor pool utilization.
   Most people would forget to include declined-addresses in the calculation,
   and simply do assigned-addresses/total-addresses. This would have a bias
   towards under-representing pool utilization. As this has a potential for
   major issues, we decided not to decrease assigned addresses immediately
   after receiving DHCPDECLINE, but to do it later when we recover the
   address back to the available pool.

8.8. Statistics in the DHCPv4 Server

  Note

   This section describes DHCPv4-specific statistics. For a general overview
   and usage of statistics, see Chapter 16, Statistics.

   The DHCPv4 server supports the following statistics:

   Table 8.4. DHCPv4 Statistics

 +-----------------------------------------------------------------------------+
 |               Statistic               |Data Type|Description                |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPv4 packets   |
 |                                       |         |received. This includes all|
 |             pkt4-received             | integer |packets: valid, bogus,     |
 |                                       |         |corrupted, rejected etc.   |
 |                                       |         |This statistic is expected |
 |                                       |         |to grow rapidly.           |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPDISCOVER     |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |                                       |         |grow. Its increase means   |
 |        pkt4-discover-received         | integer |that clients that just     |
 |                                       |         |booted started their       |
 |                                       |         |configuration process and  |
 |                                       |         |their initial packets      |
 |                                       |         |reached your server.       |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPOFFER packets|
 |                                       |         |received. This statistic is|
 |                                       |         |expected to remain zero at |
 |                                       |         |all times, as DHCPOFFER    |
 |                                       |         |packets are sent by the    |
 |                                       |         |server and the server is   |
 |                                       |         |never expected to receive  |
 |          pkt4-offer-received          | integer |them. Non-zero value       |
 |                                       |         |indicates an error. One    |
 |                                       |         |likely cause would be a    |
 |                                       |         |misbehaving relay agent    |
 |                                       |         |that incorrectly forwards  |
 |                                       |         |DHCPOFFER messages towards |
 |                                       |         |the server, rather back to |
 |                                       |         |the clients.               |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPREQUEST      |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |                                       |         |grow. Its increase means   |
 |         pkt4-request-received         | integer |that clients that just     |
 |                                       |         |booted received server's   |
 |                                       |         |response (DHCPOFFER),      |
 |                                       |         |accepted it and now        |
 |                                       |         |requesting an address      |
 |                                       |         |(DHCPREQUEST).             |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPACK packets  |
 |                                       |         |received. This statistic is|
 |                                       |         |expected to remain zero at |
 |                                       |         |all times, as DHCPACK      |
 |                                       |         |packets are sent by the    |
 |                                       |         |server and the server is   |
 |                                       |         |never expected to receive  |
 |           pkt4-ack-received           | integer |them. Non-zero value       |
 |                                       |         |indicates an error. One    |
 |                                       |         |likely cause would be a    |
 |                                       |         |misbehaving relay agent    |
 |                                       |         |that incorrectly forwards  |
 |                                       |         |DHCPACK messages towards   |
 |                                       |         |the server, rather back to |
 |                                       |         |the clients.               |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPNAK packets  |
 |                                       |         |received. This statistic is|
 |                                       |         |expected to remain zero at |
 |                                       |         |all times, as DHCPNAK      |
 |                                       |         |packets are sent by the    |
 |                                       |         |server and the server is   |
 |                                       |         |never expected to receive  |
 |           pkt4-nak-received           | integer |them. Non-zero value       |
 |                                       |         |indicates an error. One    |
 |                                       |         |likely cause would be a    |
 |                                       |         |misbehaving relay agent    |
 |                                       |         |that incorrectly forwards  |
 |                                       |         |DHCPNAK messages towards   |
 |                                       |         |the server, rather back to |
 |                                       |         |the clients.               |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPRELEASE      |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |         pkt4-release-received         | integer |grow. Its increase means   |
 |                                       |         |that clients that had an   |
 |                                       |         |address are shutting down  |
 |                                       |         |or stop using their        |
 |                                       |         |addresses.                 |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPDECLINE      |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |                                       |         |remain close to zero. Its  |
 |                                       |         |increase means that a      |
 |         pkt4-decline-received         | integer |client that leased an      |
 |                                       |         |address, but discovered    |
 |                                       |         |that the address is        |
 |                                       |         |currently used by an       |
 |                                       |         |unknown device in your     |
 |                                       |         |network.                   |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPINFORM       |
 |                                       |         |packets received. This     |
 |                                       |         |statistic is expected to   |
 |                                       |         |grow. Its increase means   |
 |         pkt4-inform-received          | integer |that there are clients that|
 |                                       |         |either do not need an      |
 |                                       |         |address or already have an |
 |                                       |         |address and are interested |
 |                                       |         |only in getting additional |
 |                                       |         |configuration parameters.  |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of packets received |
 |                                       |         |of an unknown type.        |
 |                                       |         |Non-zero value of this     |
 |                                       |         |statistic indicates that   |
 |         pkt4-unknown-received         | integer |the server received a      |
 |                                       |         |packet that it wasn't able |
 |                                       |         |to recognize: either with  |
 |                                       |         |unsupported type or        |
 |                                       |         |possibly malformed (without|
 |                                       |         |message type option).      |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPv4 packets   |
 |                                       |         |sent. This statistic is    |
 |                                       |         |expected to grow every time|
 |                                       |         |the server transmits a     |
 |                                       |         |packet. In general, it     |
 |                                       |         |should roughly match       |
 |               pkt4-sent               | integer |pkt4-received, as most     |
 |                                       |         |incoming packets cause     |
 |                                       |         |server to respond. There   |
 |                                       |         |are exceptions (e.g.       |
 |                                       |         |DHCPRELEASE), so do not    |
 |                                       |         |worry, if it is lesser than|
 |                                       |         |pkt4-received.             |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPOFFER packets|
 |                                       |         |sent. This statistic is    |
 |                                       |         |expected to grow in most   |
 |                                       |         |cases after a DHCPDISCOVER |
 |                                       |         |is processed. There are    |
 |            pkt4-offer-sent            | integer |certain uncommon, but valid|
 |                                       |         |cases where incoming       |
 |                                       |         |DHCPDISCOVER is dropped,   |
 |                                       |         |but in general this        |
 |                                       |         |statistic is expected to be|
 |                                       |         |close to                   |
 |                                       |         |pkt4-discover-received.    |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPACK packets  |
 |                                       |         |sent. This statistic is    |
 |                                       |         |expected to grow in most   |
 |                                       |         |cases after a DHCPREQUEST  |
 |                                       |         |is processed. There are    |
 |             pkt4-ack-sent             | integer |certain cases where DHCPNAK|
 |                                       |         |is sent instead. In        |
 |                                       |         |general, the sum of        |
 |                                       |         |pkt4-ack-sent and          |
 |                                       |         |pkt4-nak-sent should be    |
 |                                       |         |close to                   |
 |                                       |         |pkt4-request-received.     |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of DHCPNAK packets  |
 |                                       |         |sent. This statistic is    |
 |                                       |         |expected to grow when the  |
 |                                       |         |server chooses to not honor|
 |             pkt4-nak-sent             | integer |the address requested by a |
 |                                       |         |client. In general, the sum|
 |                                       |         |of pkt4-ack-sent and       |
 |                                       |         |pkt4-nak-sent should be    |
 |                                       |         |close to                   |
 |                                       |         |pkt4-request-received.     |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of incoming packets |
 |                                       |         |that could not be parsed. A|
 |                                       |         |non-zero value of this     |
 |                                       |         |statistic indicates that   |
 |           pkt4-parse-failed           | integer |the server received        |
 |                                       |         |malformed or truncated     |
 |                                       |         |packet. This may indicate  |
 |                                       |         |problems in your network,  |
 |                                       |         |faulty clients or a bug in |
 |                                       |         |the server.                |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |Number of incoming packets |
 |                                       |         |that were dropped. The     |
 |                                       |         |exact reason for dropping  |
 |                                       |         |packets is logged, but the |
 |                                       |         |most common reasons may be:|
 |           pkt4-receive-drop           | integer |an unacceptable packet     |
 |                                       |         |type, direct responses are |
 |                                       |         |forbidden, or the server-id|
 |                                       |         |sent by the client does not|
 |                                       |         |match the server's         |
 |                                       |         |server-id.                 |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |The total number of        |
 |                                       |         |addresses available for    |
 |                                       |         |DHCPv4 management. In other|
 |                                       |         |words, this is the sum of  |
 |                                       |         |all addresses in all       |
 |                                       |         |configured pools. This     |
 |                                       |         |statistic changes only     |
 |                                       |         |during configuration       |
 |                                       |         |changes. Note it does not  |
 |      subnet[id].total-addresses       | integer |take into account any      |
 |                                       |         |addresses that may be      |
 |                                       |         |reserved due to host       |
 |                                       |         |reservation. The id is the |
 |                                       |         |subnet-id of a given       |
 |                                       |         |subnet. This statistic is  |
 |                                       |         |exposed for each subnet    |
 |                                       |         |separately. This statistic |
 |                                       |         |is reset during            |
 |                                       |         |reconfiguration event.     |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of assigned         |
 |                                       |         |addresses in a given       |
 |                                       |         |subnet. It increases every |
 |                                       |         |time a new lease is        |
 |                                       |         |allocated (as a result of  |
 |                                       |         |receiving a DHCPREQUEST    |
 |                                       |         |message) and is decreased  |
 |     subnet[id].assigned-addresses     | integer |every time a lease is      |
 |                                       |         |released (a DHCPRELEASE    |
 |                                       |         |message is received) or    |
 |                                       |         |expires. The id is the     |
 |                                       |         |subnet-id of the subnet.   |
 |                                       |         |This statistic is exposed  |
 |                                       |         |for each subnet separately.|
 |                                       |         |This statistic is reset    |
 |                                       |         |during reconfiguration     |
 |                                       |         |event.                     |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic is the      |
 |                                       |         |number of expired leases   |
 |                                       |         |that have been reclaimed   |
 |           reclaimed-leases            | integer |since server startup. It is|
 |                                       |         |incremented each time an   |
 |                                       |         |expired lease is reclaimed |
 |                                       |         |and is reset when the      |
 |                                       |         |server is reconfigured.    |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic is the      |
 |                                       |         |number of expired leases   |
 |                                       |         |associated with a given    |
 |                                       |         |subnet (id is the          |
 |                                       |         |subnet-id) that have been  |
 |      subnet[id].reclaimed-leases      | integer |reclaimed since server     |
 |                                       |         |startup. It is incremented |
 |                                       |         |each time an expired lease |
 |                                       |         |is reclaimed and is reset  |
 |                                       |         |when the server is         |
 |                                       |         |reconfigured.              |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of IPv4 addresses   |
 |                                       |         |that are currently         |
 |                                       |         |declined, so counting the  |
 |                                       |         |number of leases currently |
 |                                       |         |unavailable. Once a lease  |
 |                                       |         |is recovered, this         |
 |                                       |         |statistic will be          |
 |                                       |         |decreased. Ideally, this   |
 |          declined-addresses           | integer |statistic should be zero.  |
 |                                       |         |If this statistic is       |
 |                                       |         |non-zero (or worse         |
 |                                       |         |increasing), a network     |
 |                                       |         |administrator should       |
 |                                       |         |investigate if there is a  |
 |                                       |         |misbehaving device in his  |
 |                                       |         |network. This is a global  |
 |                                       |         |statistic that covers all  |
 |                                       |         |subnets.                   |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of IPv4 addresses   |
 |                                       |         |that are currently declined|
 |                                       |         |in a given subnet, so is a |
 |                                       |         |count of the number of     |
 |                                       |         |leases currently           |
 |                                       |         |unavailable. Once a lease  |
 |                                       |         |is recovered, this         |
 |                                       |         |statistic will be          |
 |                                       |         |decreased. Ideally, this   |
 |     subnet[id].declined-addresses     | integer |statistic should be zero.  |
 |                                       |         |If this statistic is       |
 |                                       |         |non-zero (or worse         |
 |                                       |         |increasing), a network     |
 |                                       |         |administrator should       |
 |                                       |         |investigate if there is a  |
 |                                       |         |misbehaving device in his  |
 |                                       |         |network. The id is the     |
 |                                       |         |subnet-id of a given       |
 |                                       |         |subnet. This statistic is  |
 |                                       |         |exposed for each subnet    |
 |                                       |         |separately.                |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of IPv4 addresses   |
 |                                       |         |that were declined, but    |
 |                                       |         |have now been recovered.   |
 |                                       |         |Unlike declined-addresses, |
 |                                       |         |this statistic never       |
 |     reclaimed-declined-addresses      | integer |decreases. It can be used  |
 |                                       |         |as a long term indicator of|
 |                                       |         |how many actual valid      |
 |                                       |         |Declines were processed and|
 |                                       |         |recovered from. This is a  |
 |                                       |         |global statistic that      |
 |                                       |         |covers all subnets.        |
 |---------------------------------------+---------+---------------------------|
 |                                       |         |This statistic shows the   |
 |                                       |         |number of IPv4 addresses   |
 |                                       |         |that were declined, but    |
 |                                       |         |have now been recovered.   |
 |                                       |         |Unlike declined-addresses, |
 |                                       |         |this statistic never       |
 |                                       |         |decreases. It can be used  |
 |subnet[id].reclaimed-declined-addresses| integer |as a long term indicator of|
 |                                       |         |how many actual valid      |
 |                                       |         |Declines were processed and|
 |                                       |         |recovered from. The id is  |
 |                                       |         |the subnet-id of a given   |
 |                                       |         |subnet. This statistic is  |
 |                                       |         |exposed for each subnet    |
 |                                       |         |separately.                |
 +-----------------------------------------------------------------------------+

8.9. Management API for the DHCPv4 Server

   The management API allows the issuing of specific management commands,
   such as statistics retrieval, reconfiguration or shutdown. For more
   details, see Chapter 17, Management API. Currently the only supported
   communication channel type is UNIX stream socket. By default there are no
   sockets open. To instruct Kea to open a socket, the following entry in the
   configuration file can be used:

 "Dhcp4": {
     "control-socket": {
         "socket-type": "unix",
         "socket-name": "/path/to/the/unix/socket"
     },

     "subnet4": [
         ...
     ],
     ...
 }

   The length of the path specified by the socket-name parameter is
   restricted by the maximum length for the unix socket name on your
   operating system, i.e. the size of the sun_path field in the sockaddr_un
   structure, decreased by 1. This value varies on different operating
   systems between 91 and 107 characters. Typical values are 107 on Linux and
   103 on FreeBSD.

   Communication over control channel is conducted using JSON structures. See
   the Control Channel section in the Kea Developer's Guide for more details.

   The DHCPv4 server supports the following operational commands:

     * build-report
     * config-get
     * config-reload
     * config-set
     * config-test
     * config-write
     * dhcp-disable
     * dhcp-enable
     * leases-reclaim
     * list-commands
     * shutdown
     * version-get

   as described in Section 17.3, "Commands Supported by Both the DHCPv4 and
   DHCPv6 Servers". In addition, it supports the following statistics related
   commands:

     * statistic-get
     * statistic-reset
     * statistic-remove
     * statistic-get-all
     * statistic-reset-all
     * statistic-remove-all

   as described here Section 16.3, "Commands for Manipulating Statistics".

8.10. Supported DHCP Standards

   The following standards are currently supported:

     * Dynamic Host Configuration Protocol, RFC 2131: Supported messages are
       DHCPDISCOVER (1), DHCPOFFER (2), DHCPREQUEST (3), DHCPRELEASE (7),
       DHCPINFORM (8), DHCPACK (5), and DHCPNAK(6).
     * DHCP Options and BOOTP Vendor Extensions, RFC 2132: Supported options
       are: PAD (0), END(255), Message Type(53), DHCP Server Identifier (54),
       Domain Name (15), DNS Servers (6), IP Address Lease Time (51), Subnet
       mask (1), and Routers (3).
     * DHCP Relay Agent Information Option, RFC 3046: Relay Agent Information
       option is supported.
     * Vendor-Identifying Vendor Options for Dynamic Host Configuration
       Protocol version 4, RFC 3925: Vendor-Identifying Vendor Class and
       Vendor-Identifying Vendor-Specific Information options are supported.
     * Client Identifier Option in DHCP Server Replies, RFC 6842: Server by
       default sends back client-id option. That capability may be disabled.
       See Section 8.2.18, "Echoing Client-ID (RFC 6842)" for details.

8.11. User contexts in IPv4

   Kea allows loading hook libraries that sometimes could benefit from
   additional parameters. If such a parameter is specific to the whole
   library, it is typically defined as a parameter for the hook library.
   However, sometimes there is a need to specify parameters that are
   different for each pool.

   User contexts can store arbitrary data as long as it is valid JSON syntax
   and its top level element is a map (i.e. the data must be enclosed in
   curly brackets). Some hook libraries may expect specific formatting,
   though. Please consult specific hook library documentation for details.

   User contexts can be specified at either global scope, shared network,
   subnet, pool, client class, option data or definition level, and host
   reservation. One other useful usage is the ability to store comments or
   descriptions.

   Let's consider an imaginary case of devices that have color LED lights.
   Depending on their location, they should glow red, blue or green. It would
   be easy to write a hook library that would send specific values as maybe a
   vendor option. However, the server has to have some way to specify that
   value for each pool. This need is addressed by user contexts. In essence,
   any user data can specified in the user context as long as it is a valid
   JSON map. For example, the forementioned case of LED devices could be
   configured in the following way:

 "Dhcp4": {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ {
                 "pool": "192.0.2.10 - 192.0.2.20",
                 // This is pool specific user context
                 "user-context": { "colour": "red" }
             } ],

             // This is a subnet specific user context. You can put whatever type
             // of information you want as long as it is a valid JSON.
             "user-context": {
                 "comment": "network on the second floor",
                 "last-modified": "2017-09-04 13:32",
                 "description": "you can put here anything you like",
                 "phones": [ "x1234", "x2345" ],
                 "devices-registered": 42,
                 "billing": false
             }
         },
         ...
     ],
     ...
 }

   It should be noted that Kea will not use that information, but will simply
   store and make it available to hook libraries. It is up to the hook
   library to extract that information and make use of it. The parser
   translates a "comment" entry into a user-context with the entry, this
   allows to attach a comment inside the configuration itself.

   For more background information, see Section 15.5, "User contexts".

8.12. DHCPv4 Server Limitations

   These are the current limitations of the DHCPv4 server software. Most of
   them are reflections of the current stage of development and should be
   treated as "not implemented yet", rather than actual limitations. However,
   some of them are implications of the design choices made. Those are
   clearly marked as such.

     * BOOTP (RFC 951) is not supported. This is a design choice: BOOTP
       support is not planned.
     * On Linux and BSD system families the DHCP messages are sent and
       received over the raw sockets (using LPF and BPF) and all packet
       headers (including data link layer, IP and UDP headers) are created
       and parsed by Kea, rather than the system kernel. Currently, Kea can
       only parse the data link layer headers with a format adhering to IEEE
       802.3 standard and assumes this data link layer header format for all
       interfaces. Hence, Kea will fail to work on interfaces which use
       different data link layer header formats (e.g. Infiniband).
     * The DHCPv4 server does not verify that assigned address is unused.
       According to RFC 2131, the allocating server should verify that
       address is not used by sending ICMP echo request.

8.13. Kea DHCPv4 server examples

   A collection of simple to use examples for DHCPv4 component of Kea is
   available with the sources. It is located in doc/examples/kea4 directory.
   At the time of writing this text there were 15 examples, but the number is
   growing slowly with each release.

                          Chapter 9. The DHCPv6 Server

   Table of Contents

   9.1. Starting and Stopping the DHCPv6 Server

   9.2. DHCPv6 Server Configuration

                9.2.1. Introduction

                9.2.2. Lease Storage

                9.2.3. Hosts Storage

                9.2.4. Interface Selection

                9.2.5. IPv6 Subnet Identifier

                9.2.6. Unicast Traffic Support

                9.2.7. Subnet and Address Pool

                9.2.8. Subnet and Prefix Delegation Pools

                9.2.9. Prefix Exclude Option

                9.2.10. Standard DHCPv6 Options

                9.2.11. Common Softwire46 Options

                9.2.12. Custom DHCPv6 Options

                9.2.13. DHCPv6 Vendor-Specific Options

                9.2.14. Nested DHCPv6 Options (Custom Option Spaces)

                9.2.15. Unspecified Parameters for DHCPv6 Option
                Configuration

                9.2.16. IPv6 Subnet Selection

                9.2.17. Rapid Commit

                9.2.18. DHCPv6 Relays

                9.2.19. Relay-Supplied Options

                9.2.20. Client Classification in DHCPv6

                9.2.21. DDNS for DHCPv6

                9.2.22. DHCPv4-over-DHCPv6: DHCPv6 Side

                9.2.23. Sanity checks in DHCPv6

   9.3. Host Reservation in DHCPv6

                9.3.1. Address/Prefix Reservation Types

                9.3.2. Conflicts in DHCPv6 Reservations

                9.3.3. Reserving a Hostname

                9.3.4. Including Specific DHCPv6 Options in Reservations

                9.3.5. Reserving Client Classes in DHCPv6

                9.3.6. Storing Host Reservations in MySQL, PostgreSQL or
                Cassandra

                9.3.7. Fine Tuning DHCPv6 Host Reservation

                9.3.8. Global reservations in DHCPv6

   9.4. Shared networks in DHCPv6

                9.4.1. Local and relayed traffic in shared networks

                9.4.2. Client classification in shared networks

                9.4.3. Host reservations in shared networks

   9.5. Server Identifier in DHCPv6

   9.6. Stateless DHCPv6 (Information-Request Message)

   9.7. Support for RFC 7550 (being now part of RFC 8415)

   9.8. Using Specific Relay Agent for a Subnet

   9.9. Segregating IPv6 Clients in a Cable Network

   9.10. MAC/Hardware Addresses in DHCPv6

   9.11. Duplicate Addresses (DECLINE Support)

   9.12. Statistics in the DHCPv6 Server

   9.13. Management API for the DHCPv6 Server

   9.14. User contexts in IPv6

   9.15. Supported DHCPv6 Standards

   9.16. DHCPv6 Server Limitations

   9.17. Kea DHCPv6 server examples

9.1. Starting and Stopping the DHCPv6 Server

   It is recommended that the Kea DHCPv6 server be started and stopped using
   keactrl (described in Chapter 6, Managing Kea with keactrl). However, it
   is also possible to run the server directly: it accepts the following
   command-line switches:

     * -c file - specifies the configuration file. This is the only mandatory
       switch.
     * -d - specifies whether the server logging should be switched to
       verbose mode. In verbose mode, the logging severity and debuglevel
       specified in the configuration file are ignored and "debug" severity
       and the maximum debuglevel (99) are assumed. The flag is convenient,
       for temporarily switching the server into maximum verbosity, e.g. when
       debugging.
     * -p port - specifies UDP port on which the server will listen. This is
       only useful during testing, as a DHCPv6 server listening on ports
       other than the standard ones will not be able to handle regular DHCPv6
       queries.
     * -t file - specifies the configuration file to be tested. Kea-dhcp6
       will attempt to load it, and will conduct sanity checks. Note that
       certain checks are possible only while running the actual server. The
       actual status is reported with exit code (0 = configuration looks ok,
       1 = error encountered). Kea will print out log messages to standard
       output and error to standard error when testing configuration.
     * -v - prints out the Kea version and exits.
     * -V - prints out the Kea extended version with additional parameters
       and exits. The listing includes the versions of the libraries
       dynamically linked to Kea.
     * -W - prints out the Kea configuration report and exits. The report is
       a copy of the config.report file produced by ./configure: it is
       embedded in the executable binary.

   The config.report may also be accessed more directly. The following
   command may be used to extract this information. The binary path may be
   found in the install directory or in the .libs subdirectory in the source
   tree. For example kea/src/bin/dhcp6/.libs/kea-dhcp6.

 strings path/kea-dhcp6 | sed -n 's/;;;; //p'

   On start-up, the server will detect available network interfaces and will
   attempt to open UDP sockets on all interfaces mentioned in the
   configuration file. Since the DHCPv6 server opens privileged ports, it
   requires root access. Make sure you run this daemon as root.

   During startup the server will attempt to create a PID file of the form:
   localstatedir]/[conf name].kea-dhcp6.pid where:

     * localstatedir: The value as passed into the build configure script. It
       defaults to "/usr/local/var". Note that this value may be overridden
       at run time by setting the environment variable KEA_PIDFILE_DIR. This
       is intended primarily for testing purposes.
     * conf name: The configuration file name used to start the server, minus
       all preceding path and file extension. For example, given a pathname
       of "/usr/local/etc/kea/myconf.txt", the portion used would be
       "myconf".

   If the file already exists and contains the PID of a live process, the
   server will issue a DHCP6_ALREADY_RUNNING log message and exit. It is
   possible, though unlikely, that the file is a remnant of a system crash
   and the process to which the PID belongs is unrelated to Kea. In such a
   case it would be necessary to manually delete the PID file.

   The server can be stopped using the kill command. When running in a
   console, the server can be shut down by pressing ctrl-c. It detects the
   key combination and shuts down gracefully.

9.2. DHCPv6 Server Configuration

  9.2.1. Introduction

   This section explains how to configure the DHCPv6 server using a
   configuration file. Before DHCPv6 is started, its configuration file has
   to be created. The basic configuration is as follows:

 {
 # DHCPv6 configuration starts on the next line
 "Dhcp6": {

 # First we set up global values
     "valid-lifetime": 4000,
     "renew-timer": 1000,
     "rebind-timer": 2000,
     "preferred-lifetime": 3000,

 # Next we setup the interfaces to be used by the server.
     "interfaces-config": {
         "interfaces": [ "eth0" ]
     },

 # And we specify the type of lease database
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/var/kea/dhcp6.leases"
     },

 # Finally, we list the subnets from which we will be leasing addresses.
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
              ]
         }
     ]
 # DHCPv6 configuration ends with the next line
 }

 }

   The following paragraphs provide a brief overview of the parameters in the
   above example together with their format. Subsequent sections of this
   chapter go into much greater detail for these and other parameters.

   The lines starting with a hash (#) are comments and are ignored by the
   server; they do not impact its operation in any way.

   The configuration starts in the first line with the initial opening curly
   bracket (or brace). Each configuration must contain an object specifying
   the configuration of the Kea module using it. In the example above this
   object is called Dhcp6.

  Note

   In the current Kea release it is possible to specify configurations of
   multiple modules within a single configuration file, but this is not
   recommended and support for it will be removed in the future releases. The
   only object, besides the one specifying module configuration, which can
   (and usually is) included in the same file is Logging. However, we don't
   include this object in the example above for clarity.

   The Dhcp6 configuration starts with the "Dhcp6": { line and ends with the
   corresponding closing brace (in the above example, the brace after the
   last comment). Everything defined between those lines is considered to be
   the Dhcp6 configuration.

   In the general case, the order in which those parameters appear does not
   matter. There are two caveats here though. The first one is to remember
   that the configuration file must be well formed JSON. That means that
   parameters for any given scope must be separated by a comma and there must
   not be a comma after the last parameter. When reordering a configuration
   file, keep in mind that moving a parameter to or from the last position in
   a given scope may also require moving the comma. The second caveat is that
   it is uncommon -- although legal JSON -- to repeat the same parameter
   multiple times. If that happens, the last occurrence of a given parameter
   in a given scope is used while all previous instances are ignored. This is
   unlikely to cause any confusion as there are no real life reasons to keep
   multiple copies of the same parameter in your configuration file.

   Moving onto the DHCPv6 configuration elements, the very first few elements
   define some global parameters. valid-lifetime defines for how long the
   addresses (leases) given out by the server are valid. If nothing changes,
   a client that got an address is allowed to use it for 4000 seconds. (Note
   that integer numbers are specified as is, without any quotes around them.)
   The address will become deprecated in 3000 seconds (clients are allowed to
   keep old connections, but can't use this address for creating new
   connections). renew-timer and rebind-timer are values that define T1 and
   T2 timers that govern when the client will begin the renewal and rebind
   procedures.

   The interfaces-config map specifies the server configuration concerning
   the network interfaces, on which the server should listen to the DHCP
   messages. The interfaces parameter specifies a list of network interfaces
   on which the server should listen. Lists are opened and closed with square
   brackets, with elements separated by commas. Had we wanted to listen on
   two interfaces, the interfaces-config would look like this:

 "interfaces-config": {
     "interfaces": [ "eth0", "eth1" ]
 },

   The next couple of lines define the lease database, the place where the
   server stores its lease information. This particular example tells the
   server to use memfile, which is the simplest (and fastest) database
   backend. It uses an in-memory database and stores leases on disk in a CSV
   file. This is a very simple configuration. Usually the lease database
   configuration is more extensive and contains additional parameters. Note
   that lease-database is an object and opens up a new scope, using an
   opening brace. Its parameters (just one in this example - type) follow.
   Had there been more than one, they would be separated by commas. This
   scope is closed with a closing brace. As more parameters for the Dhcp6
   definition follow, a trailing comma is present.

   Finally, we need to define a list of IPv6 subnets. This is the most
   important DHCPv6 configuration structure as the server uses that
   information to process clients' requests. It defines all subnets from
   which the server is expected to receive DHCP requests. The subnets are
   specified with the subnet6 parameter. It is a list, so it starts and ends
   with square brackets. Each subnet definition in the list has several
   attributes associated with it, so it is a structure and is opened and
   closed with braces. At minimum, a subnet definition has to have at least
   two parameters: subnet (that defines the whole subnet) and pools (which is
   a list of dynamically allocated pools that are governed by the DHCP
   server).

   The example contains a single subnet. Had more than one been defined,
   additional elements in the subnet6 parameter would be specified and
   separated by commas. For example, to define two subnets, the following
   syntax would be used:

 "subnet6": [
     {
         "pools": [ { "pool": "2001:db8:1::/112" } ],
         "subnet": "2001:db8:1::/64"
     },
     {
         "pools": [ { "pool": "2001:db8:2::1-2001:db8:2::ffff" } ],
         "subnet": "2001:db8:2::/64"
     }
 ]

   Note that indentation is optional and is used for aesthetic purposes only.
   In some cases in may be preferable to use more compact notation.

   After all parameters are specified, we have two contexts open: global and
   Dhcp6, hence we need two closing curly brackets to close them. In a real
   life configuration file there most likely would be additional components
   defined such as Logging, so the closing brace would be followed by a comma
   and another object definition.

  9.2.2. Lease Storage

   All leases issued by the server are stored in the lease database.
   Currently there are four database backends available: memfile (which is
   the default backend), MySQL, PostgreSQL and Cassandra.

    9.2.2.1. Memfile - Basic Storage for Leases

   The server is able to store lease data in different repositories. Larger
   deployments may elect to store leases in a database. Section 9.2.2.2,
   "Lease Database Configuration" describes this option. In typical smaller
   deployments though, the server will store lease information in a CSV file
   rather than a database. As well as requiring less administration, an
   advantage of using a file for storage is that it eliminates a dependency
   on third-party database software.

   The configuration of the file backend (Memfile) is controlled through the
   Dhcp6/lease-database parameters. The type parameter is mandatory and it
   specifies which storage for leases the server should use. The value of
   "memfile" indicates that the file should be used as the storage. The
   following list gives additional, optional, parameters that can be used to
   configure the Memfile backend.

     * persist: controls whether the new leases and updates to existing
       leases are written to the file. It is strongly recommended that the
       value of this parameter is set to true at all times, during the
       server's normal operation. Not writing leases to disk will mean that
       if a server is restarted (e.g. after a power failure), it will not
       know what addresses have been assigned. As a result, it may hand out
       addresses to new clients that are already in use. The value of false
       is mostly useful for performance testing purposes. The default value
       of the persist parameter is true, which enables writing lease updates
       to the lease file.
     * name: specifies an absolute location of the lease file in which new
       leases and lease updates will be recorded. The default value for this
       parameter is "[kea-install-dir]/var/kea/kea-leases6.csv" .
     * lfc-interval: specifies the interval in seconds, at which the server
       will perform a lease file cleanup (LFC). This removes redundant
       (historical) information from the lease file and effectively reduces
       the lease file size. The cleanup process is described in more detailed
       fashion further in this section. The default value of the lfc-interval
       is 3600. A value of 0 disables the LFC.

   An example configuration of the Memfile backend is presented below:

 "Dhcp6": {
     "lease-database": {
         "type": "memfile",
         "persist": true,
         "name": "/tmp/kea-leases6.csv",
         "lfc-interval": 1800
     }
 }

   This configuration selects the /tmp/kea-leases6.csv as the storage for
   lease information and enables persistence (writing lease updates to this
   file). It also configures the backend perform the periodic cleanup of the
   lease files, executed every 30 minutes.

   It is important to know how the lease file contents are organized to
   understand why the periodic lease file cleanup is needed. Every time the
   server updates a lease or creates a new lease for the client, the new
   lease information must be recorded in the lease file. For performance
   reasons, the server does not update the existing client's lease in the
   file, as it would potentially require rewriting the entire file. Instead,
   it simply appends the new lease information to the end of the file: the
   previous lease entries for the client are not removed. When the server
   loads leases from the lease file, e.g. at the server startup, it assumes
   that the latest lease entry for the client is the valid one. The previous
   entries are discarded. This means that the server can re-construct the
   accurate information about the leases even though there may be many lease
   entries for each client. However, storing many entries for each client
   results in bloated lease file and impairs the performance of the server's
   startup and reconfiguration as it needs to process a larger number of
   lease entries.

   Lease file cleanup (LFC) removes all previous entries for each client and
   leaves only the latest ones. The interval at which the cleanup is
   performed is configurable, and it should be selected according to the
   frequency of lease renewals initiated by the clients. The more frequent
   the renewals, the smaller the value of lfc-interval should be. Note
   however, that the LFC takes time and thus it is possible (although
   unlikely) that new cleanup is started while the previous cleanup instance
   is still running, if the lfc-interval is too short. The server would
   recover from this by skipping the new cleanup when it detects that the
   previous cleanup is still in progress. But it implies that the actual
   cleanups will be triggered more rarely than configured. Moreover,
   triggering a new cleanup adds an overhead to the server which will not be
   able to respond to new requests for a short period of time when the new
   cleanup process is spawned. Therefore, it is recommended that the
   lfc-interval value is selected in a way that would allow for the LFC to
   complete the cleanup before a new cleanup is triggered.

   Lease file cleanup is performed by a separate process (in background) to
   avoid a performance impact on the server process. In order to avoid the
   conflicts between two processes both using the same lease files, the LFC
   process operates on the copy of the original lease file, rather than on
   the lease file used by the server to record lease updates. There are also
   other files being created as a side effect of the lease file cleanup. The
   detailed description of the LFC is located in the Kea Administrator's
   Reference Manual:
   https://jenkins.isc.org/job/Kea_doc/guide/kea-guide.html#kea-lfc.

    9.2.2.2. Lease Database Configuration

  Note

   Lease database access information must be configured for the DHCPv6
   server, even if it has already been configured for the DHCPv4 server. The
   servers store their information independently, so each server can use a
   separate database or both servers can use the same database.

   Lease database configuration is controlled through the
   Dhcp6/lease-database parameters. The type of the database must be set to
   "memfile", "mysql", "postgresql" or "cql", e.g.

 "Dhcp6": { "lease-database": { "type": "mysql", ... }, ... }

   Next, the name of the database is to hold the leases must be set: this is
   the name used when the database was created (see Section 4.3.2.1, "First
   Time Creation of the MySQL Database", Section 4.3.3.1, "First Time
   Creation of the PostgreSQL Database" or Section 4.3.4.1, "First Time
   Creation of the Cassandra Database").

 "Dhcp6": { "lease-database": { "name": "database-name" , ... }, ... }

   For Cassandra:

 "Dhcp6": { "lease-database": { "keyspace": "database-name" , ... }, ... }

   If the database is located on a different system to the DHCPv6 server, the
   database host name must also be specified. (It should be noted that this
   configuration may have a severe impact on server performance.):

 "Dhcp6": { "lease-database": { "host": "remote-host-name", ... }, ... }

   For Cassandra, multiple contact points can be provided:

 "Dhcp6": { "lease-database": { "contact-points": "remote-host-name[, ...]" , ... }, ... }

   The usual state of affairs will be to have the database on the same
   machine as the DHCPv6 server. In this case, set the value to the empty
   string:

 "Dhcp6": { "lease-database": { "host" : "", ... }, ... }

   For Cassandra:

 "Dhcp6": { "lease-database": { "contact-points": "", ... }, ... }

   Should the database use a port different than default, it may be specified
   as well:

 "Dhcp6": { "lease-database": { "port" : 12345, ... }, ... }

   Should the database be located on a different system, you may need to
   specify a longer interval for the connection timeout:

 "Dhcp6": { "lease-database": { "connect-timeout" : timeout-in-seconds, ... }, ... }

   The default value of five seconds should be more than adequate for local
   connections. If a timeout is given though, it should be an integer greater
   than zero.

   The maxiumum number of times the server will automatically attempt to
   reconnect to the lease database after connectivity has been lost may be
   specified:

 "Dhcp6": { "lease-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }

   If the server is unable to reconnect to the database after making the
   maximum number of attempts the server will exit. A value of zero (the
   default) disables automatic recovery and the server will exit immediately
   upon detecting a loss of connectivity (MySQL and Postgres only).

   The number of milliseconds the server will wait in between attempts to
   reconnect to the lease database after connectivity has been lost may also
   be specified:

 "Dhcp6": { "lease-database": { "reconnect-wait-time" : number-of-milliseconds, ... }, ... }

   The default value for MySQL and Postgres is 0, which disables automatic
   recovery and causes the server to exit immediately upon detecting the loss
   of connectivity. The default value for Cassandra is 2000 ms.

  Note

   Automatic reconnect to database backends is configured individually per
   backend. This allows you to tailor the recovery parameters to the each
   backend you use. We do suggest that you either enable it for all backends
   or no backends so you have consistent behavior. Losing connectivity to a
   backend for which reconnect is disabled will result in the server shutting
   itself down. This includes the cases when lease database backend and hosts
   database backend is connected to the same database instance.

   Note that host parameter is used by MySQL and PostgreSQL backends.
   Cassandra has a concept of contact points that could be used to contact
   the cluster, instead of a single IP or hostname. It takes a list of comma
   separated IP addresses. This may be specified as:

 "Dhcp6": { "lease-database": { "contact-points" : "192.0.2.1,192.0.2.2", ... }, ... }

   Finally, the credentials of the account under which the server will access
   the database should be set:

 "Dhcp6": { "lease-database": { "user": "user-name",
                                "password": "password",
                               ... },
            ... }

   If there is no password to the account, set the password to the empty
   string "". (This is also the default.)

    9.2.2.3. Cassandra specific parameters

   The parameters are the same for DHCPv4 and DHCPv6. See Section 8.2.2.3,
   "Cassandra specific parameters" for details.

  9.2.3. Hosts Storage

   Kea is also able to store information about host reservations in the
   database. The hosts database configuration uses the same syntax as the
   lease database. In fact, a Kea server opens independent connections for
   each purpose, be it lease or hosts information. This arrangement gives the
   most flexibility. Kea can be used to keep leases and host reservations
   separately, but can also point to the same database. Currently the
   supported hosts database types are MySQL and PostgreSQL. The Cassandra
   backend does not support host reservations yet.

   Please note that usage of hosts storage is optional. A user can define all
   host reservations in the configuration file. That is the recommended way
   if the number of reservations is small. However, when the number of
   reservations grows it's more convenient to use host storage. Please note
   that both storage methods (configuration file and one of the supported
   databases) can be used together. If hosts are defined in both places, the
   definitions from the configuration file are checked first and external
   storage is checked later, if necessary.

   Version 1.4 extends the host storage to multiple storages. Operations are
   performed on host storages in the configuration order with a special case
   for addition: read-only storages must be configured after a required
   read-write storage, or host reservation addition will always fail.

    9.2.3.1. DHCPv6 Hosts Database Configuration

   Hosts database configuration is controlled through the
   Dhcp6/hosts-database parameters. If enabled, the type of the database must
   be set to "mysql" or "postgresql". Other hosts backends may be added in
   later version of Kea.

 "Dhcp6": { "hosts-database": { "type": "mysql", ... }, ... }

   Next, the name of the database to hold the reservations must be set: this
   is the name used when the database was created (see Section 4.3,
   "Supported Databases" for instructions how to setup desired database
   type).

 "Dhcp6": { "hosts-database": { "name": "database-name" , ... }, ... }

   If the database is located on a different system than the DHCPv6 server,
   the database host name must also be specified. (Again it should be noted
   that this configuration may have a severe impact on server performance):

 "Dhcp6": { "hosts-database": { "host": remote-host-name, ... }, ... }

   The usual state of affairs will be to have the database on the same
   machine as the DHCPv6 server. In this case, set the value to the empty
   string:

 "Dhcp6": { "hosts-database": { "host" : "", ... }, ... }

 "Dhcp6": { "hosts-database": { "port" : 12345, ... }, ... }

   The maxiumum number of times the server will automatically attempt to
   reconnect to the host database after connectivity has been lost may be
   specified:

 "Dhcp6": { "host-database": { "max-reconnect-tries" : number-of-tries, ... }, ... }

   If the server is unable to reconnect to the database after making the
   maximum number of attempts the server will exit. A value of zero (the
   default) disables automatic recovery and the server will exit immediately
   upon detecting a loss of connectivity (MySQL and Postgres only).

   The number of milliseconds the server will wait in between attempts to
   reconnect to the host database after connectivity has been lost may also
   be specified:

 "Dhcp6": { "hosts-database": { "reconnect-wait-time" : number-of-milliseconds, ... }, ... }

   The default value for MySQL and Postgres is 0, which disables automatic
   recovery and causes the server to exit immediately upon detecting the loss
   of connectivity. The default value for Cassandra is 2000 ms.

  Note

   Automatic reconnect to database backends is configured individually per
   backend. This allows you to tailor the recovery parameters to the each
   backend you use. We do suggest that you either enable it for all backends
   or no backends so you have consistent behavior. Losing connectivity to a
   backend for which reconnect is disabled will result in the server shutting
   itself down. This includes the cases when lease database backend and hosts
   database backend is connected to the same database instance.

   Finally, the credentials of the account under which the server will access
   the database should be set:

 "Dhcp6": { "hosts-database": { "user": "user-name",
                                "password": "password",
                               ... },
            ... }

   If there is no password to the account, set the password to the empty
   string "". (This is also the default.)

   The multiple storage extension uses a similar syntax: a configuration is
   placed into a "hosts-databases" list instead of into a "hosts-database"
   entry as in:

 "Dhcp6": { "hosts-databases": [ { "type": "mysql", ... }, ... ], ... }

   For additional Cassandra specific parameters, see Section 8.2.2.3,
   "Cassandra specific parameters".

    9.2.3.2. Using Read-Only Databases for Host Reservations

   In some deployments the database user whose name is specified in the
   database backend configuration may not have write privileges to the
   database. This is often required by the policy within a given network to
   secure the data from being unintentionally modified. In many cases
   administrators have inventory databases deployed, which contain
   substantially more information about the hosts than static reservations
   assigned to them. The inventory database can be used to create a view of a
   Kea hosts database and such view is often read only.

   Kea host database backends operate with an implicit configuration to both
   read from and write to the database. If the database user does not have
   write access to the host database, the backend will fail to start and the
   server will refuse to start (or reconfigure). However, if access to a read
   only host database is required for retrieving reservations for clients
   and/or assign specific addresses and options, it is possible to explicitly
   configure Kea to start in "read-only" mode. This is controlled by the
   readonly boolean parameter as follows:

 "Dhcp6": { "hosts-database": { "readonly": true, ... }, ... }

   Setting this parameter to false would configure the database backend to
   operate in "read-write" mode, which is also a default configuration if the
   parameter is not specified.

  Note

   The readonly parameter is currently only supported for MySQL and
   PostgreSQL databases.

  9.2.4. Interface Selection

   The DHCPv6 server has to be configured to listen on specific network
   interfaces. The simplest network interface configuration instructs the
   server to listen on all available interfaces:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "*" ]
     }
     ...
 }

   The asterisk plays the role of a wildcard and means "listen on all
   interfaces". However, it is usually a good idea to explicitly specify
   interface names:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ]
     },
     ...
 }


   It is possible to use wildcard interface name (asterisk) concurrently with
   the actual interface names:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3", "*" ]
     },
     ...
 }


   It is anticipated that this will form of usage only be used where it is
   desired to temporarily override a list of interface names and listen on
   all interfaces.

   As for the DHCPv4 server binding to specific addresses and disabling
   re-detection of interfaces are supported. But dhcp-socket-type is not
   because DHCPv6 uses UDP/IPv6 sockets only. The following example shows how
   to disable the interface detection:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1", "eth3" ],
         "re-detect": false
     },
     ...
 }


   The loopback interfaces (i.e. the "lo" or "lo0" interface) are not
   configured by default, unles explicitely mentioned in the configration.
   Note Kea requires a link-local address which does not exist on all
   systems, or a specified unicast address as in:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "lo/::1" ]
     },
     ...
 }


  9.2.5. IPv6 Subnet Identifier

   The subnet identifier is a unique number associated with a particular
   subnet. In principle, it is used to associate clients' leases with their
   respective subnets. When a subnet identifier is not specified for a subnet
   being configured, it will be automatically assigned by the configuration
   mechanism. The identifiers are assigned from 1 and are monotonically
   increased for each subsequent subnet: 1, 2, 3 ....

   If there are multiple subnets configured with auto-generated identifiers
   and one of them is removed, the subnet identifiers may be renumbered. For
   example: if there are four subnets and the third is removed the last
   subnet will be assigned the identifier that the third subnet had before
   removal. As a result, the leases stored in the lease database for subnet 3
   are now associated with subnet 4, something that may have unexpected
   consequences. It is planned to implement a mechanism to preserve
   auto-generated subnet ids in a future version of Kea. However, the only
   remedy for this issue at present is to manually specify a unique
   identifier for each subnet.

  Note

   Subnet IDs must be greater than zero and less than 4294967295.

   The following configuration will assign the specified subnet identifier to
   the newly configured subnet:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "id": 1024,
             ...
         }
     ]
 }

   This identifier will not change for this subnet unless the "id" parameter
   is removed or set to 0. The value of 0 forces auto-generation of the
   subnet identifier.

  9.2.6. Unicast Traffic Support

   When the DHCPv6 server starts, by default it listens to the DHCP traffic
   sent to multicast address ff02::1:2 on each interface that it is
   configured to listen on (see Section 9.2.4, "Interface Selection"). In
   some cases it is useful to configure a server to handle incoming traffic
   sent to the global unicast addresses as well. The most common reason for
   this is to have relays send their traffic to the server directly. To
   configure the server to listen on a specific unicast address, nn interface
   name can be optionally followed by a slash, followed by the global unicast
   address on which the server should listen. The server listens to this
   address in addition to normal link-local binding and listening on
   ff02::1:2 address. The sample configuration below shows how to listen on
   2001:db8::1 (a global address) configured on the eth1 interface.

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "eth1/2001:db8::1" ]
     },
     ...
     "option-data": [
         {
             "name": "unicast",
             "data": "2001:db8::1"
         } ],
     ...
 }


   This configuration will cause the server to listen on eth1 on the
   link-local address, the multicast group (ff02::1:2) and 2001:db8::1.

   Usually unicast support is associated with a server unicast option which
   allows clients to send unicast messages to the server. The example above
   includes a server unicast option specification which will cause the client
   to send messages to the specified unicast address.

   It is possible to mix interface names, wildcards and interface
   name/addresses in the list of interfaces. It is not possible however to
   specify more than one unicast address on a given interface.

   Care should be taken to specify proper unicast addresses. The server will
   attempt to bind to the addresses specified without any additional checks.
   This approach has selected on purpose to allow the software to communicate
   over uncommon addresses if so desired.

  9.2.7. Subnet and Address Pool

   The main role of a DHCPv6 server is address assignment. For this, the
   server has to be configured with at least one subnet and one pool of
   dynamic addresses to be managed. For example, assume that the server is
   connected to a network segment that uses the 2001:db8:1::/64 prefix. The
   Administrator of that network has decided that addresses from range
   2001:db8:1::1 to 2001:db8:1::ffff are going to be managed by the Dhcp6
   server. Such a configuration can be achieved in the following way:

 "Dhcp6": {
     "subnet6": [
        {
            "subnet": "2001:db8:1::/64",
            "pools": [
                {
                    "pool": "2001:db8:1::1-2001:db8:1::ffff"
                }
            ],
            ...
        }
     ]
 }

   Note that subnet is defined as a simple string, but the pools parameter is
   actually a list of pools: for this reason, the pool definition is enclosed
   in square brackets, even though only one range of addresses is specified.

   Each pool is a structure that contains the parameters that describe a
   single pool. Currently there is only one parameter, pool, which gives the
   range of addresses in the pool. Additional parameters will be added in
   future releases of Kea.

   It is possible to define more than one pool in a subnet: continuing the
   previous example, further assume that 2001:db8:1:0:5::/80 should also be
   managed by the server. It could be written as 2001:db8:1:0:5:: to
   2001:db8:1::5:ffff:ffff:ffff, but typing so many 'f's is cumbersome. It
   can be expressed more simply as 2001:db8:1:0:5::/80. Both formats are
   supported by Dhcp6 and can be mixed in the pool list. For example, one
   could define the following pools:

 "Dhcp6": {
     "subnet6": [
     {
         "subnet": "2001:db8:1::/64",
         "pools": [
             { "pool": "2001:db8:1::1-2001:db8:1::ffff" },
             { "pool": "2001:db8:1:05::/80" }
         ],
         ...
     }
     ]
 }

   White space in pool definitions is ignored, so spaces before and after the
   hyphen are optional. They can be used to improve readability.

   The number of pools is not limited, but for performance reasons it is
   recommended to use as few as possible.

   The server may be configured to serve more than one subnet. To add a
   second subnet, use a command similar to the following:

 "Dhcp6": {
     "subnet6": [
     {
         "subnet": "2001:db8:1::/64",
         "pools": [
             { "pool": "2001:db8:1::1-2001:db8:1::ffff" }
         ]
     },
     {
         "subnet": "2001:db8:2::/64",
         "pools": [
             { "pool": "2001:db8:2::/64" }
         ]
     },

         ...
     ]
 }

   In this example, we allow the server to dynamically assign all addresses
   available in the whole subnet. Although rather wasteful, it is certainly a
   valid configuration to dedicate the whole /64 subnet for that purpose.
   Note that the Kea server does not preallocate the leases, so there is no
   danger in using gigantic address pools.

   When configuring a DHCPv6 server using prefix/length notation, please pay
   attention to the boundary values. When specifying that the server can use
   a given pool, it will also be able to allocate the first (typically
   network address) address from that pool. For example, for pool
   2001:db8:2::/64 the 2001:db8:2:: address may be assigned as well. If you
   want to avoid this, use the "min-max" notation.

  9.2.8. Subnet and Prefix Delegation Pools

   Subnets may also be configured to delegate prefixes, as defined in RFC
   8415, section 6.3. A subnet may have one or more prefix delegation pools.
   Each pool has a prefixed address, which is specified as a prefix (prefix)
   and a prefix length (prefix-len), as well as a delegated prefix length
   (delegated-len). The delegated length must not be shorter (that is it must
   be numerically greater or equal) than the prefix length. If both the
   delegated and prefix lengths are equal, the server will be able to
   delegate only one prefix. The delegated prefix does not have to match the
   subnet prefix.

   Below is a sample subnet configuration which enables prefix delegation for
   the subnet:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:d8b:1::/64",
             "pd-pools": [
                 {
                     "prefix": "3000:1::",
                     "prefix-len": 64,
                     "delegated-len": 96
                 }
             ]
         }
     ],
     ...
 }

  9.2.9. Prefix Exclude Option

   For each delegated prefix the delegating router may choose to exclude a
   single prefix out of the delegated prefix as specified in the RFC 6603.
   The requesting router must not assign the excluded prefix to any of its
   downstream interfaces and it is intended to be used on a link through
   which the delegating router exchanges DHCPv6 messages with the requesting
   router. The configuration example below demonstrates how to specify an
   excluded prefix within a prefix pool definition. The excluded prefix
   "2001:db8:1:babe:cafe:80::/72" will be sent to a requesting router which
   includes Prefix Exclude option in the ORO, and which is delegated a prefix
   from this pool.

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/48",
             "pd-pools": [
                 {
                     "prefix": "2001:db8:1:8000::",
                     "prefix-len": 48,
                     "delegated-len": 64,
                     "excluded-prefix": "2001:db8:1:babe:cafe:80::",
                     "excluded-prefix-len": 72
                 }
             ]
         }
     ]
 }

  9.2.10. Standard DHCPv6 Options

   One of the major features of a DHCPv6 server is to provide configuration
   options to clients. Although there are several options that require
   special behavior, most options are sent by the server only if the client
   explicitly requests them. The following example shows how to configure DNS
   servers, one of the most frequently used options. Options specified in
   this way are considered global and apply to all configured subnets.

 "Dhcp6": {
     "option-data": [
         {
            "name": "dns-servers",
            "code": 23,
            "space": "dhcp6",
            "csv-format": true,
            "data": "2001:db8::cafe, 2001:db8::babe"
         },
         ...
     ]
 }

   The option-data line creates a new entry in the option-data table. This
   table contains information on all global options that the server is
   supposed to configure in all subnets. The name line specifies the option
   name. (For a complete list of currently supported names, see Table 9.1,
   "List of Standard DHCPv6 Options".) The next line specifies the option
   code, which must match one of the values from that list. The line
   beginning with space specifies the option space, which must always be set
   to "dhcp6" as these are standard DHCPv6 options. For other name spaces,
   including custom option spaces, see Section 9.2.14, "Nested DHCPv6 Options
   (Custom Option Spaces)". The following line specifies the format in which
   the data will be entered: use of CSV (comma separated values) is
   recommended. Finally, the data line gives the actual value to be sent to
   clients. Data is specified as normal text, with values separated by commas
   if more than one value is allowed.

   Options can also be configured as hexadecimal values. If "csv-format" is
   set to false, the option data must be specified as a string of hexadecimal
   numbers. The following commands configure the DNS-SERVERS option for all
   subnets with the following addresses: 2001:db8:1::cafe and
   2001:db8:1::babe.

 "Dhcp6": {
     "option-data": [
         {
            "name": "dns-servers",
            "code": 23,
            "space": "dhcp6",
            "csv-format": false,
            "data": "2001 0DB8 0001 0000 0000 0000 0000 CAFE
                     2001 0DB8 0001 0000 0000 0000 0000 BABE"
         },
         ...
     ]
 }


  Note

   The value for the setting of the "data" element is split across two lines
   in this example for clarity: when entering the command, the whole string
   should be entered on the same line.

   Care should be taken to use proper encoding when using hexadecimal format
   as Kea's ability to validate data correctness in hexadecimal is limited.

   Most of the parameters in the "option-data" structure are optional and can
   be omitted in some circumstances as discussed in the Section 9.2.15,
   "Unspecified Parameters for DHCPv6 Option Configuration". Only one of name
   or code is required, so you don't need to specify both. Space has a
   default value of "dhcp6", so you can skip this as well if you define a
   regular (not encapsulated) DHCPv6 option. Finally, csv-format defaults to
   true, so it too can be skipped, unless you want to specify the option
   value as hexstring. Therefore the above example can be simplified to:

 "Dhcp6": {
     "option-data": [
         {
            "name": "dns-servers",
            "data": "2001:db8::cafe, 2001:db8::babe"
         },
         ...
     ]
 }


   Defined options are added to response when the client requests them at a
   few exceptions which are always added. To enforce the addition of a
   particular option set the always-send flag to true as in:

 "Dhcp6": {
     "option-data": [
         {
            "name": "dns-servers",
            "data": "2001:db8::cafe, 2001:db8::babe",
            "always-send": true
         },
         ...
     ]
 }


   The effect is the same as if the client added the option code in the
   Option Request Option (or its equivalent for vendor options) so in:

 "Dhcp6": {
     "option-data": [
         {
            "name": "dns-servers",
            "data": "2001:db8::cafe, 2001:db8::babe",
            "always-send": true
         },
         ...
     ],
     "subnet6": [
         {
            "subnet": "2001:db8:1::/64",
            "option-data": [
                {
                    "name": "dns-servers",
                    "data": "2001:db8:1::cafe, 2001:db8:1::babe"
                },
                ...
            ],
            ...
         },
         ...
     ],
     ...
 }


   The DNS Servers option is always added to responses (the always-send is
   "sticky") but the value is the subnet one when the client is localized in
   the subnet.

   It is possible to override options on a per-subnet basis. If clients
   connected to most of your subnets are expected to get the same values of a
   given option, you should use global options: you can then override
   specific values for a small number of subnets. On the other hand, if you
   use different values in each subnet, it does not make sense to specify
   global option values (Dhcp6/option-data), rather you should set only
   subnet-specific values (Dhcp6/subnet[X]/option-data[Y]).

   The following commands override the global DNS servers option for a
   particular subnet, setting a single DNS server with address 2001:db8:1::3.

 "Dhcp6": {
     "subnet6": [
         {
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:1::3"
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   In some cases it is useful to associate some options with an address or
   prefix pool from which a client is assigned a lease. Pool specific option
   values override subnet specific and global option values. If the client is
   assigned multiple leases from different pools, the server will assign
   options from all pools from which the leases have been obtained. However,
   if the particular option is specified in multiple pools from which the
   client obtains the leases, only one instance of this option will be handed
   out to the client. The server's administrator must not try to prioritize
   assignment of pool specific options by trying to order pools declarations
   in the server configuration. Future Kea releases may change the order in
   which options are assigned from the pools without any notice.

   The following configuration snippet demonstrates how to specify the DNS
   servers option, which will be assigned to a client only if the client
   obtains an address from the given pool:

 "Dhcp6": {
     "subnet6": [
         {
             "pools": [
                 {
                     "pool": "2001:db8:1::100-2001:db8:1::300",
                     "option-data": [
                         {
                             "name": "dns-servers",
                             "data": "2001:db8:1::10"
                         }
                     ]
                 }
             ]
         },
         ...
     ],
     ...
 }

   Options can be specified also in class of host reservation scope. In Kea
   1.4 options precedence order is (from most important): host reservation,
   pool, subnet, shared network, class, global. In Kea 1.5 order will be
   changed to: host reservation, class, pool, subnet, shared network, global
   OR it will be fully configurable.

   The currently supported standard DHCPv6 options are listed in Table 9.1,
   "List of Standard DHCPv6 Options". The "Name" and "Code" are the values
   that should be used as a name in the option-data structures. "Type"
   designates the format of the data: the meanings of the various types is
   given in Table 8.2, "List of standard DHCP option types".

   Experimental options (like standard options but with a code which was not
   assigned by IANA) are listed in Table 9.2, "List of Experimental DHCPv6
   Options".

   When a data field is a string, and that string contains the comma (,;
   U+002C) character, the comma must be escaped with a reverse solidus
   character (\; U+005C). This double escape is required, because both the
   routine splitting CSV data into fields and JSON use the same escape
   character: a single escape (\,) would make the JSON invalid. For example,
   the string "EST5EDT4,M3.2.0/02:00,M11.1.0/02:00" would be represented as:

 "Dhcp6": {
     "subnet6": [
         {
             "pools": [
                 {
                     "option-data": [
                         {
                             "name": "new-posix-timezone",
                             "data": "EST5EDT4\,M3.2.0/02:00\,M11.1.0/02:00"
                         }
                     ]
                 },
                 ...
             ],
             ...
         },
         ...
     ],
     ...
 }

   Some options are designated as arrays, which means that more than one
   value is allowed in such an option. For example the option dns-servers
   allows the specification of more than one IPv6 address, allowing clients
   to obtain the addresses of multiple DNS servers.

   The Section 9.2.12, "Custom DHCPv6 Options" describes the configuration
   syntax to create custom option definitions (formats). It is generally not
   allowed to create custom definitions for standard options, even if the
   definition being created matches the actual option format defined in the
   RFCs. There is an exception from this rule for standard options for which
   Kea does not yes provide a definition. In order to use such options, a
   server administrator must create a definition as described in
   Section 9.2.12, "Custom DHCPv6 Options" in the 'dhcp6' option space. This
   definition should match the option format described in the relevant RFC
   but the configuration mechanism would allow any option format as it has no
   means to validate the format at the moment.

   Table 9.1. List of Standard DHCPv6 Options

   +------------------------------------------------------------------------+
   |           Name           | Code |            Type             | Array? |
   |--------------------------+------+-----------------------------+--------|
   | preference               |  7   |            uint8            | false  |
   |--------------------------+------+-----------------------------+--------|
   | unicast                  |  12  |        ipv6-address         | false  |
   |--------------------------+------+-----------------------------+--------|
   | vendor-opts              |  17  |           uint32            | false  |
   |--------------------------+------+-----------------------------+--------|
   | sip-server-dns           |  21  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | sip-server-addr          |  22  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | dns-servers              |  23  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | domain-search            |  24  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nis-servers              |  27  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nisp-servers             |  28  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nis-domain-name          |  29  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nisp-domain-name         |  30  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | sntp-servers             |  31  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | information-refresh-time |  32  |           uint32            | false  |
   |--------------------------+------+-----------------------------+--------|
   | bcmcs-server-dns         |  33  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | bcmcs-server-addr        |  34  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | geoconf-civic            |  36  | record (uint8, uint16, hex) | false  |
   |--------------------------+------+-----------------------------+--------|
   | remote-id                |  37  |    record (uint32, hex)     | false  |
   |--------------------------+------+-----------------------------+--------|
   | subscriber-id            |  38  |             hex             | false  |
   |--------------------------+------+-----------------------------+--------|
   | client-fqdn              |  39  |    record (uint8, fqdn)     | false  |
   |--------------------------+------+-----------------------------+--------|
   | pana-agent               |  40  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | new-posix-timezone       |  41  |           string            | false  |
   |--------------------------+------+-----------------------------+--------|
   | new-tzdb-timezone        |  42  |           string            | false  |
   |--------------------------+------+-----------------------------+--------|
   | ero                      |  43  |           uint16            |  true  |
   |--------------------------+------+-----------------------------+--------|
   | lq-query (1)             |  44  |       record (uint8,        | false  |
   |                          |      |        ipv6-address)        |        |
   |--------------------------+------+-----------------------------+--------|
   | client-data (1)          |  45  |            empty            | false  |
   |--------------------------+------+-----------------------------+--------|
   | clt-time (1)             |  46  |           uint32            | false  |
   |--------------------------+------+-----------------------------+--------|
   | lq-relay-data (1)        |  47  | record (ipv6-address, hex)  | false  |
   |--------------------------+------+-----------------------------+--------|
   | lq-client-link (1)       |  48  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | v6-lost                  |  51  |            fqdn             | false  |
   |--------------------------+------+-----------------------------+--------|
   | capwap-ac-v6             |  52  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   | relay-id                 |  53  |             hex             | false  |
   |--------------------------+------+-----------------------------+--------|
   | v6-access-domain         |  57  |            fqdn             | false  |
   |--------------------------+------+-----------------------------+--------|
   | sip-ua-cs-list           |  58  |            fqdn             |  true  |
   |--------------------------+------+-----------------------------+--------|
   | bootfile-url             |  59  |           string            | false  |
   |--------------------------+------+-----------------------------+--------|
   | bootfile-param           |  60  |            tuple            |  true  |
   |--------------------------+------+-----------------------------+--------|
   | client-arch-type         |  61  |           uint16            |  true  |
   |--------------------------+------+-----------------------------+--------|
   | nii                      |  62  |    record (uint8, uint8,    | false  |
   |                          |      |           uint8)            |        |
   |--------------------------+------+-----------------------------+--------|
   | aftr-name                |  64  |            fqdn             | false  |
   |--------------------------+------+-----------------------------+--------|
   | erp-local-domain-name    |  65  |            fqdn             | false  |
   |--------------------------+------+-----------------------------+--------|
   | rsoo                     |  66  |            empty            | false  |
   |--------------------------+------+-----------------------------+--------|
   | pd-exclude               |  67  |             hex             | false  |
   |--------------------------+------+-----------------------------+--------|
   | rdnss-selection          |  74  |    record (ipv6-address,    |  true  |
   |                          |      |        uint8, fqdn)         |        |
   |--------------------------+------+-----------------------------+--------|
   | client-linklayer-addr    |  79  |             hex             | false  |
   |--------------------------+------+-----------------------------+--------|
   | link-address             |  80  |        ipv6-address         | false  |
   |--------------------------+------+-----------------------------+--------|
   | solmax-rt                |  82  |           uint32            | false  |
   |--------------------------+------+-----------------------------+--------|
   | inf-max-rt               |  83  |           uint32            | false  |
   |--------------------------+------+-----------------------------+--------|
   | dhcp4o6-server-addr      |  88  |        ipv6-address         |  true  |
   |--------------------------+------+-----------------------------+--------|
   |                          |      |    record (uint8, uint8,    |        |
   | s46-rule                 |  89  |    uint8, ipv4-address,     | false  |
   |                          |      |        ipv6-prefix)         |        |
   |--------------------------+------+-----------------------------+--------|
   | s46-br                   |  90  |        ipv6-address         | false  |
   |--------------------------+------+-----------------------------+--------|
   | s46-dmr                  |  91  |         ipv6-prefix         | false  |
   |--------------------------+------+-----------------------------+--------|
   | s46-v4v6bind             |  92  |    record (ipv4-address,    | false  |
   |                          |      |        ipv6-prefix)         |        |
   |--------------------------+------+-----------------------------+--------|
   | s46-portparams           |  93  |     record(uint8, psid)     | false  |
   |--------------------------+------+-----------------------------+--------|
   | s46-cont-mape            |  94  |            empty            | false  |
   |--------------------------+------+-----------------------------+--------|
   | s46-cont-mapt            |  95  |            empty            | false  |
   |--------------------------+------+-----------------------------+--------|
   | s46-cont-lw              |  96  |            empty            | false  |
   |--------------------------+------+-----------------------------+--------|
   | v6-captive-portal        | 103  |           string            | false  |
   |--------------------------+------+-----------------------------+--------|
   | ipv6-address-andsf       | 143  |        ipv6-address         |  true  |
   +------------------------------------------------------------------------+

   Options marked with (1) have option definitions, but the logic behind them
   is not implemented. That means that technically Kea knows how to parse
   them in incoming message or how to send them if configured to do so, but
   not what to do with them. Since the related RFCs require certain
   processing, the support for those options is non-functional. However, it
   may be useful in some limited lab testing, hence the definition formats
   are listed here.

   Table 9.2. List of Experimental DHCPv6 Options

   +----------------------------------------------------------+
   |    Name     | Code |            Type            | Array? |
   |-------------+------+----------------------------+--------|
   | public-key  | 701  |            hex             | false  |
   |-------------+------+----------------------------+--------|
   | certificate | 702  |            hex             | false  |
   |-------------+------+----------------------------+--------|
   | signature   | 703  | record (uint8, uint8, hex) | false  |
   |-------------+------+----------------------------+--------|
   | timestamp   | 704  |            hex             | false  |
   +----------------------------------------------------------+

  9.2.11. Common Softwire46 Options

   Softwire46 options are involved in IPv4 over IPv6 provisioning by means of
   tunneling or translation as specified in the RFC 7598. The following
   sections provide configuration examples of these options.

    9.2.11.1. Softwire46 Container Options

   S46 container options group rules and optional port parameters for a
   specified domain. There are three container options specified in the
   "dhcp6" (top level) option space: MAP-E Container option, MAP-T Container
   option and S46 Lightweight 4over6 Container option. These options only
   contain encapsulated options specified below. They do not include any data
   fields.

   In order to configure the server to send specific container option along
   with all encapsulated options, the container option must be included in
   the server configuration as shown below:

 "Dhcp6": {
     ...
     "option-data": [
         {
             "name": "s46-cont-mape"
         } ],
     ...
 }

   This configuration will cause the server to include MAP-E Container option
   to the client. Use "s46-cont-mapt" or "s46-cont-lw" for the MAP-T
   Container and S46 Lightweight 4over6 Container options respectively.

   All remaining softwire options described below are included in one of the
   container options. Thus, they have to be included in appropriate option
   spaces by selecting a "space" name, which specifies in which option they
   are supposed to be included.

    9.2.11.2. S46 Rule Option

   The S46 Rule option is used for conveying the Basic Mapping Rule (BMR) and
   Forwarding Mapping Rule (FMR).

 {
     "space": "s46-cont-mape-options",
     "name": "s46-rule",
     "data": "128, 0, 24, 192.0.2.0, 2001:db8:1::/64"
 }

   Other possible "space" value is "s46-cont-mapt-options".

   The S46 Rule option conveys a number of parameters:

     * flags, an unsigned 8 bits integer, with currently only the most
       significant bit specified. It denotes whether the rule can be used for
       forwarding (128) or not (0).
     * ea-len, an 8 bits long Embedded Address length. Allowed values range
       from 0 to 48.
     * IPv4 prefix length, 8 bits long; expresses the prefix length of the
       Rule IPv4 prefix specified in the ipv4-prefix field. Allowed values
       range from 0 to 32.
     * IPv4 prefix, a fixed-length 32-bit field that specifies the IPv4
       prefix for the S46 rule. The bits in the prefix after prefix4-len
       number of bits are reserved and MUST be initialized to zero by the
       sender and ignored by the receiver.
     * IPv6 prefix in prefix/length notation that specifies the IPv6 domain
       prefix for the S46 rule. The field is padded on the right with zero
       bits up to the nearest octet boundary when prefix6-len is not evenly
       divisible by 8.

    9.2.11.3. S46 BR Option

   The S46 BR option is used to convey the IPv6 address of the Border Relay.
   This option is mandatory in the MAP-E Container option and not permitted
   in the MAP-T and S46 Lightweight 4over6 Container options.

 {
     "space": "s46-cont-mape-options",
     "name": "s46-br",
     "data": "2001:db8:cafe::1",
 }

   Other possible "space" value is "s46-cont-lw-options".

    9.2.11.4. S46 DMR Option

   The S46 DMR option is used to convey values for the Default Mapping Rule
   (DMR). This option is mandatory in the MAP-T container option and not
   permitted in the MAP-E and S46 Lightweight 4over6 Container options.

 {
     "space": "s46-cont-mapt-options",
     "name": "s46-dmr",
     "data": "2001:db8:cafe::/64",
 }

   This option must not be included in other containers.

    9.2.11.5. S46 IPv4/IPv6 Address Binding option.

   The S46 IPv4/IPv6 Address Binding option may be used to specify the full
   or shared IPv4 address of the Customer Edge (CE). The IPv6 prefix field is
   used by the CE to identify the correct prefix to use for the tunnel
   source.

 {
     "space": "s46-cont-lw",
     "name": "s46-v4v6bind",
     "data": "192.0.2.3, 2001:db8:1:cafe::/64"
 }

   This option must not be included in other containers.

    9.2.11.6. S46 Port Parameters

   The S46 Port Parameters option specifies optional port set information
   that MAY be provided to CEs

 {
     "space": "s46-rule-options",
     "name": "s46-portparams",
     "data": "2, 3/4",
 }

   Other possible "space" value is "s46-v4v6bind" to include this option in
   the S46 IPv4/IPv6 Address Binding option.

   Note that the second value in the example above specifies the PSID and
   PSID length fields in the format of PSID/PSID length. This is equivalent
   to the values of PSID-len=4 and PSID=12288 conveyed in the S46 Port
   Parameters option.

  9.2.12. Custom DHCPv6 Options

   It is possible to define options in addition to the standard ones. Assume
   that we want to define a new DHCPv6 option called "foo" which will have
   code 100 and which will convey a single unsigned 32 bit integer value. We
   can define such an option by using the following commands:

 "Dhcp6": {
     "option-def": [
         {
             "name": "foo",
             "code": 100,
             "type": "uint32",
             "array": false,
             "record-types": "",
             "space": "dhcp6",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The "false" value of the array parameter determines that the option does
   NOT comprise an array of "uint32" values but rather a single value. Two
   other parameters have been left blank: record-types and encapsulate. The
   former specifies the comma separated list of option data fields if the
   option comprises a record of data fields. The record-types value should be
   non-empty if the type is set to "record". Otherwise it must be left blank.
   The latter parameter specifies the name of the option space being
   encapsulated by the particular option. If the particular option does not
   encapsulate any option space it should be left blank. Note that the above
   example only defines the format of the new option, it does not set its
   value(s).

   The name, code and type parameters are required, all others are optional.
   The array default value is false. The record-types and encapsulate default
   values are blank (i.e. ""). The default space is "dhcp6".

   Once the new option format is defined, its value is set in the same way as
   for a standard option. For example the following commands set a global
   value that applies to all subnets.

 "Dhcp6": {
     "option-data": [
         {
             "name": "foo",
             "code": 100,
             "space": "dhcp6",
             "csv-format": true,
             "data": "12345"
         }, ...
     ],
     ...
 }

   New options can take more complex forms than simple use of primitives
   (uint8, string, ipv6-address etc): it is possible to define an option
   comprising a number of existing primitives.

   For example, assume we want to define a new option that will consist of an
   IPv6 address, followed by an unsigned 16 bit integer, followed by a
   boolean value, followed by a text string. Such an option could be defined
   in the following way:

 "Dhcp6": {
     "option-def": [
         {
             "name": "bar",
             "code": 101,
             "space": "dhcp6",
             "type": "record",
             "array": false,
             "record-types": "ipv6-address, uint16, boolean, string",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The "type" is set to "record" to indicate that the option contains
   multiple values of different types. These types are given as a
   comma-separated list in the "record-types" field and should be those
   listed in Table 8.2, "List of standard DHCP option types".

   The values of the option are set as follows:

 "Dhcp6": {
     "option-data": [
         {
             "name": "bar",
             "space": "dhcp6",
             "code": 101,
             "csv-format": true,
             "data": "2001:db8:1::10, 123, false, Hello World"
         }
     ],
     ...
 }

   csv-format is set true to indicate that the data field comprises a
   command-separated list of values. The values in the "data" must correspond
   to the types set in the "record-types" field of the option definition.

   When array is set to true and type is set to "record", the last field is
   an array, i.e., it can contain more than one value as in:

 "Dhcp6": {
     "option-def": [
         {
             "name": "bar",
             "code": 101,
             "space": "dhcp6",
             "type": "record",
             "array": true,
             "record-types": "ipv6-address, uint16",
             "encapsulate": ""
         }, ...
     ],
     ...
 }

   The new option content is one IPv6 address followed by one or more 16 bit
   unsigned integers.

  Note

   In the general case, boolean values are specified as true or false,
   without quotes. Some specific boolean parameters may accept also "true",
   "false", 0, 1, "0" and "1". Future versions of Kea will accept all those
   values for all boolean parameters.

  9.2.13. DHCPv6 Vendor-Specific Options

   Currently there are two option spaces defined for the DHCPv6 daemon:
   "dhcp6" (for top level DHCPv6 options) and "vendor-opts-space", which is
   empty by default, but in which options can be defined. Those options will
   be carried in the Vendor-Specific Information option (code 17). The
   following examples show how to define an option "foo" with code 1 that
   consists of an IPv6 address, an unsigned 16 bit integer and a string. The
   "foo" option is conveyed in a Vendor-Specific Information option. This
   option comprises a single uint32 value that is set to "12345". The
   sub-option "foo" follows the data field holding this value.

 "Dhcp6": {
     "option-def": [
         {
             "name": "foo",
             "code": 1,
             "space": "vendor-opts-space",
             "type": "record",
             "array": false,
             "record-types": "ipv6-address, uint16, string",
             "encapsulate": ""
         }
     ],
     ...
 }

   (Note that the option space is set to vendor-opts-space.) Once the option
   format is defined, the next step is to define actual values for that
   option:

 "Dhcp6": {
     "option-data": [
         {
             "name": "foo",
             "space": "vendor-opts-space",
             "data": "2001:db8:1::10, 123, Hello World"
         },
         ...
     ],
     ...
 }

   We should also define a value (enterprise-number) for the Vendor-specific
   Information option, that conveys our option "foo".

 "Dhcp6": {
     "option-data": [
         ...,
         {
             "name": "vendor-opts",
             "data": "12345"
         }
     ],
     ...
 }

   Alternatively, the option can be specified using its code.

 "Dhcp6": {
     "option-data": [
         ...,
         {
             "code": 17,
             "data": "12345"
         }
     ],
     ...
 }

  9.2.14. Nested DHCPv6 Options (Custom Option Spaces)

   It is sometimes useful to define completely new option spaces. This is
   useful if the user wants their new option to convey sub-options that use a
   separate numbering scheme, for example sub-options with codes 1 and 2.
   Those option codes conflict with standard DHCPv6 options, so a separate
   option space must be defined.

   Note that it is not required to create a new option space when defining
   sub-options for a standard option because it is created by default if the
   standard option is meant to convey any sub-options (see Section 9.2.13,
   "DHCPv6 Vendor-Specific Options").

   Assume that we want to have a DHCPv6 option called "container" with code
   102 that conveys two sub-options with codes 1 and 2. First we need to
   define the new sub-options:

 "Dhcp6": {
     "option-def": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "type": "ipv6-address",
             "record-types": "",
             "array": false,
             "encapsulate": ""
         },
         {
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "type": "string",
             "record-types": "",
             "array": false
             "encapsulate": ""
         }
     ],
     ...
 }

   Note that we have defined the options to belong to a new option space (in
   this case, "isc").

   The next step is to define a regular DHCPv6 option and specify that it
   should include options from the isc option space:

 "Dhcp6": {
     "option-def": [
         ...,
         {
             "name": "container",
             "code": 102,
             "space": "dhcp6",
             "type": "empty",
             "array": false,
             "record-types": "",
             "encapsulate": "isc"
         }
     ],
     ...
 }

   The name of the option space in which the sub-options are defined is set
   in the encapsulate field. The type field is set to empty which limits this
   option to only carrying data in sub-options.

   Finally, we can set values for the new options:

 "Dhcp6": {
     "option-data": [
         {
             "name": "subopt1",
             "code": 1,
             "space": "isc",
             "data": "2001:db8::abcd"
         },
         }
             "name": "subopt2",
             "code": 2,
             "space": "isc",
             "data": "Hello world"
         },
         {
             "name": "container",
             "code": 102,
             "space": "dhcp6"
         }
     ],
     ...
 }

   Note that it is possible to create an option which carries some data in
   addition to the sub-options defined in the encapsulated option space. For
   example, if the "container" option from the previous example was required
   to carry an uint16 value as well as the sub-options, the "type" value
   would have to be set to "uint16" in the option definition. (Such an option
   would then have the following data structure: DHCP header, uint16 value,
   sub-options.) The value specified with the "data" parameter -- which
   should be a valid integer enclosed in quotes, e.g. "123" -- would then be
   assigned to the uint16 field in the "container" option.

  9.2.15. Unspecified Parameters for DHCPv6 Option Configuration

   In many cases it is not required to specify all parameters for an option
   configuration and the default values can be used. However, it is important
   to understand the implications of not specifying some of them as it may
   result in configuration errors. The list below explains the behavior of
   the server when a particular parameter is not explicitly specified:

     * name - the server requires an option name or option code to identify
       an option. If this parameter is unspecified, the option code must be
       specified.
     * code - the server requires an option name or option code to identify
       an option. This parameter may be left unspecified if the name
       parameter is specified. However, this also requires that the
       particular option has its definition (it is either a standard option
       or an administrator created a definition for the option using an
       'option-def' structure), as the option definition associates an option
       with a particular name. It is possible to configure an option for
       which there is no definition (unspecified option format).
       Configuration of such options requires the use of option code.
     * space - if the option space is unspecified it will default to 'dhcp6'
       which is an option space holding DHCPv6 standard options.
     * data - if the option data is unspecified it defaults to an empty
       value. The empty value is mostly used for the options which have no
       payload (boolean options), but it is legal to specify empty values for
       some options which carry variable length data and which spec allows
       for the length of 0. For such options, the data parameter may be
       omitted in the configuration.
     * csv-format - if this value is not specified the server will assume
       that the option data is specified as a list of comma separated values
       to be assigned to individual fields of the DHCP option. This behavior
       has changed in Kea 1.2. Older versions used additional logic to
       determine whether the csv-format should be true or false. That is no
       longer the case.

  9.2.16. IPv6 Subnet Selection

   The DHCPv6 server may receive requests from local (connected to the same
   subnet as the server) and remote (connecting via relays) clients. As the
   server may have many subnet configurations defined, it must select an
   appropriate subnet for a given request.

   The server can not assume which of the configured subnets are local. In
   IPv4 it is possible as there is a reasonable expectation that the server
   will have a (global) IPv4 address configured on the interface, and can use
   that information to detect whether a subnet is local or not. That
   assumption is not true in IPv6: the DHCPv6 server must be able to operate
   while only using link-local addresses. Therefore an optional interface
   parameter is available within a subnet definition to designate that a
   given subnet is local, i.e. reachable directly over the specified
   interface. For example the server that is intended to serve a local subnet
   over eth0 may be configured as follows:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:beef::/48",
             "pools": [
                  {
                      "pool": "2001:db8:beef::/48"
                  }
              ],
             "interface": "eth0"
         }
     ],
     ...
 }

  9.2.17. Rapid Commit

   The Rapid Commit option, described in RFC 8415, is supported by the Kea
   DHCPv6 server. However, support is disabled by default for all subnets. It
   can be enabled for a particular subnet using the rapid-commit parameter as
   shown below:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:beef::/48",
             "rapid-commit": true,
             "pools": [
                  {
                      "pool": "2001:db8:beef::1-2001:db8:beef::10"
                  }
              ],
         }
     ],
     ...
 }

   This setting only affects the subnet for which the rapid-commit is set to
   true. For clients connected to other subnets, the server will ignore the
   Rapid Commit option sent by the client and will follow the 4-way exchange
   procedure, i.e. respond with an Advertise for a Solicit containing a Rapid
   Commit option.

  9.2.18. DHCPv6 Relays

   A DHCPv6 server with multiple subnets defined must select the appropriate
   subnet when it receives a request from a client. For clients connected via
   relays, two mechanisms are used:

   The first uses the linkaddr field in the RELAY_FORW message. The name of
   this field is somewhat misleading in that it does not contain a link-layer
   address: instead, it holds an address (typically a global address) that is
   used to identify a link. The DHCPv6 server checks if the address belongs
   to a defined subnet and, if it does, that subnet is selected for the
   client's request.

   The second mechanism is based on interface-id options. While forwarding a
   client's message, relays may insert an interface-id option into the
   message that identifies the interface on the relay that received the
   message. (Some relays allow configuration of that parameter, but it is
   sometimes hardcoded and may range from the very simple (e.g. "vlan100") to
   the very cryptic: one example seen on real hardware was
   "ISAM144|299|ipv6|nt:vp:1:110"). The server can use this information to
   select the appropriate subnet. The information is also returned to the
   relay which then knows the interface to use to transmit the response to
   the client. In order for this to work successfully, the relay interface
   IDs must be unique within the network and the server configuration must
   match those values.

   When configuring the DHCPv6 server, it should be noted that two
   similarly-named parameters can be configured for a subnet:

     * interface defines which local network interface can be used to access
       a given subnet.
     * interface-id specifies the content of the interface-id option used by
       relays to identify the interface on the relay to which the response
       packet is sent.

   The two are mutually exclusive: a subnet cannot be both reachable locally
   (direct traffic) and via relays (remote traffic). Specifying both is a
   configuration error and the DHCPv6 server will refuse such a
   configuration.

   The following example configuration shows how to specify an interface-id
   with a value of "vlan123".

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:beef::/48",
             "pools": [
                  {
                      "pool": "2001:db8:beef::/48"
                  }
              ],
             "interface-id": "vlan123"
         }
     ],
     ...
 }

  9.2.19. Relay-Supplied Options

   RFC 6422 defines a mechanism called Relay-Supplied DHCP Options. In
   certain cases relay agents are the only entities that may have specific
   information. They can insert options when relaying messages from the
   client to the server. The server will then do certain checks and copy
   those options to the response that will be sent to the client.

   There are certain conditions that must be met for the option to be
   included. First, the server must not provide the option itself. In other
   words, if both relay and server provide an option, the server always takes
   precedence. Second, the option must be RSOO-enabled. IANA maintains a list
   of RSOO-enabled options here. However, there may be cases when system
   administrators want to echo other options. Kea can be instructed to treat
   other options as RSOO-enabled. For example, to mark options 110, 120 and
   130 as RSOO-enabled, the following syntax should be used:

 "Dhcp6": {
     "relay-supplied-options": [ "110", "120", "130" ],
     ...
 }

   As of March 2015, only option 65 is RSOO-enabled by IANA. This option will
   always be treated as such and there's no need to explicitly mark it. Also,
   when enabling standard options, it is possible to use their names, rather
   than option code, e.g. (e.g. use dns-servers instead of 23). See
   Table 9.1, "List of Standard DHCPv6 Options" for the names. In certain
   cases it could also work for custom options, but due to the nature of the
   parser code this may be unreliable and should be avoided.

  9.2.20. Client Classification in DHCPv6

   The DHCPv6 server includes support for client classification. For a deeper
   discussion of the classification process see Chapter 14, Client
   Classification.

   In certain cases it is useful to configure the server to differentiate
   between DHCP clients types and treat them accordingly. It is envisaged
   that client classification will be used for modifying the behavior of
   almost any part of the DHCP message processing. In the current release of
   Kea, there are three mechanisms that take advantage of the client
   classification in DHCPv6: subnet selection, address pool selection and
   DHCP options assignment.

   In certain cases it is useful to differentiate between different types of
   clients and treat them accordingly. It is envisaged that client
   classification will be used for changing the behavior of almost any part
   of the DHCP message processing. In the current release of the software
   however, there are only some mechanisms that take advantage of client
   classification: subnet selection, pool selection, and assignment of
   different options.

   Kea can be instructed to limit access to given subnets based on class
   information. This is particularly useful for cases where two types of
   devices share the same link and are expected to be served from two
   different subnets. The primary use case for such a scenario is cable
   networks. Here, there are two classes of devices: the cable modem itself,
   which should be handed a lease from subnet A and all other devices behind
   the modem that should get a lease from subnet B. That segregation is
   essential to prevent overly curious users from playing with their cable
   modems. For details on how to set up class restrictions on subnets, see
   Section 14.6, "Configuring Subnets With Class Information".

   When subnets belong to a shared network the classification applies to
   subnet selection but not to pools, e.g., a pool in a subnet limited to a
   particular class can still be used by clients which do not belong to the
   class if the pool they are expected to use is exhausted. So the limit
   access based on class information is also available at the address/prefix
   pool level, see Section 14.7, "Configuring Pools With Class Information"
   within a subnet. This is useful when to segregate clients belonging to the
   same subnet into different address ranges.

   In a similar way a pool can be constrained to serve only known clients,
   i.e. clients which have a reservation, using the built-in "KNOWN" or
   "UNKNOWN" classes. One can assign addresses to registered clients without
   giving a different address per reservations, for instance when there is
   not enough available addresses. The determination whether there is a
   reservation for a given client is made after a subnet is selected. As
   such, it is not possible to use KNOWN/UNKNOWN classes to select a shared
   network or a subnet.

   The process of doing classification is conducted in five steps. The first
   step is to assess an incoming packet and assign it to zero or more
   classes. The second step is to choose a subnet, possibly based on the
   class information. The next step is to evaluate class expressions
   depending on the built-in "KNOWN"/"UNKNOWN" classes after host reservation
   lookup, using them for pool/pd-pool selection and to assign classes from
   host reservations. After the list of required classes is built and each
   class of the list has its expression evaluated: when it returns true the
   packet is added as a member of the class. The last step is to assign
   options again possibly based on the class information. More complete and
   detailed description is available in Chapter 14, Client Classification.

   There are two main methods of doing classification. The first is automatic
   and relies on examining the values in the vendor class options or
   existence of a host reservation. Information from these options is
   extracted and a class name is constructed from it and added to the class
   list for the packet. The second allows for specifying an expression that
   is evaluated for each packet. If the result is true the packet is a member
   of the class.

  Note

   Care should be taken with client classification as it is easy for clients
   that do not meet class criteria to be denied any service altogether.

    9.2.20.1. Defining and Using Custom Classes

   The following example shows how to configure a class using an expression
   and a subnet making use of that class. This configuration defines the
   class named "Client_enterprise". It is comprised of all clients whose
   client identifiers start with the given hex string (which would indicate a
   DUID based on an enterprise id of 0xAABBCCDD). They will be given an
   address from 2001:db8:1::0 to 2001:db8:1::FFFF and the addresses of their
   DNS servers set to 2001:db8:0::1 and 2001:db8:2::1.

 "Dhcp6": {
     "client-classes": [
         {
             "name": "Client_enterprise",
             "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:0::1, 2001:db8:2::1"
                 }
             ]
         },
         ...
     ],
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
             "client-class": "Client_enterprise"
         }
     ],
     ...
 }

   This example shows a configuration using an automatically generated
   "VENDOR_CLASS_" class. The Administrator of the network has decided that
   addresses from range 2001:db8:1::1 to 2001:db8:1::ffff are going to be
   managed by the Dhcp6 server and only clients belonging to the eRouter1.0
   client class are allowed to use that pool.

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::-2001:db8:1::ffff"
                  }
              ],
             "client-class": "VENDOR_CLASS_eRouter1.0"
         }
     ],
     ...
 }

    9.2.20.2. Required classification

   In some cases it is useful to limit the scope of a class to a
   shared-network, subnet or pool. There are two parameters which are used to
   limit the scope of the class by instructing the server to perform
   evaluation of test expressions when required.

   The first one is the per-class only-if-required flag which is false by
   default. When it is set to true the test expression of the class is not
   evaluated at the reception of the incoming packet but later and only if
   the class evaluation is required.

   The second is the require-client-classes which takes a list of class names
   and is valid in shared-network, subnet and pool scope. Classes in these
   lists are marked as required and evaluated after selection of this
   specific shared-network/subnet/pool and before output option processing.

   In this example, a class is assigned to the incoming packet when the
   specified subnet is used.

 "Dhcp6": {
     "client-classes": [
        {
            "name": "Client_foo",
            "test": "member('ALL')",
            "only-if-required": true
        },
        ...
     ],
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64"
             "pools": [
                  {
                      "pool": "2001:db8:1::-2001:db8:1::ffff"
                  }
              ],
             "require-client-classes": [ "Client_foo" ],
             ...
         },
         ...
     ],
     ...
 }

   Required evaluation can be used to express complex dependencies, for
   example, subnet membership. It can also be used to reverse the precedence:
   if you set an option-data in a subnet it takes precedence over an
   option-data in a class. When you move the option-data to a required class
   and require it in the subnet, a class evaluated earlier may take
   precedence.

   Required evaluation is also available at shared-network and pool/pd-pool
   levels. The order in which required classes are considered is:
   shared-network, subnet and (pd-)pool, i.e. the opposite order option-data
   are processed.

  9.2.21. DDNS for DHCPv6

   As mentioned earlier, kea-dhcp6 can be configured to generate requests to
   the DHCP-DDNS server (referred to here as "D2") to update DNS entries.
   These requests are known as NameChangeRequests or NCRs. Each NCR contains
   the following information:

    1. Whether it is a request to add (update) or remove DNS entries

    2. Whether the change requests forward DNS updates (AAAA records),
       reverse DNS updates (PTR records), or both.

    3. The FQDN, lease address, and DHCID

   The parameters controlling the generation of NCRs for submission to D2 are
   contained in the dhcp-ddns section of the kea-dhcp6 configuration. The
   mandatory parameters for the DHCP DDNS configuration are enable-updates
   which is unconditionally required, and qualifying-suffix which has no
   default value and is required when enable-updates is set to true. The two
   (disabled and enabled) minimal DHCP DDNS configurations are:

 "Dhcp6": {
     "dhcp-ddns": {
         "enable-updates": false
     },
     ...
 }

   and for example:

 "Dhcp6": {
     "dhcp-ddns": {
         "enable-updates": true,
         "qualifying-suffix": "example."
     },
     ...
 }

   The default values for the "dhcp-ddns" section are as follows:

     * "server-ip": "127.0.0.1"
     * "server-port": 53001
     * "sender-ip": ""
     * "sender-port": 0
     * "max-queue-size": 1024
     * "ncr-protocol": "UDP"
     * "ncr-format": "JSON"
     * "override-no-update": false
     * "override-client-update": false
     * "replace-client-name": "never"
     * "generated-prefix": "myhost"
     * "hostname-char-set": ""
     * "hostname-char-replacement": ""

    9.2.21.1. DHCP-DDNS Server Connectivity

   In order for NCRs to reach the D2 server, kea-dhcp6 must be able to
   communicate with it. kea-dhcp6 uses the following configuration parameters
   to control this communication:

     * enable-updates - determines whether or not kea-dhcp6 will generate
       NCRs. If missing, this value is assumed to be false hence DDNS updates
       are disabled. To enable DDNS updates set this value to true:
     * server-ip - IP address on which D2 listens for requests. The default
       is the local loopback interface at address 127.0.0.1. You may specify
       either an IPv4 or IPv6 address.
     * server-port - port on which D2 listens for requests. The default value
       is 53001.
     * sender-ip - IP address which kea-dhcp6 should use to send requests to
       D2. The default value is blank which instructs kea-dhcp6 to select a
       suitable address.
     * sender-port - port which kea-dhcp6 should use to send requests to D2.
       The default value of 0 instructs kea-dhcp6 to select a suitable port.
     * max-queue-size - maximum number of requests allowed to queue waiting
       to be sent to D2. This value guards against requests accumulating
       uncontrollably if they are being generated faster than they can be
       delivered. If the number of requests queued for transmission reaches
       this value, DDNS updating will be turned off until the queue backlog
       has been sufficiently reduced. The intent is to allow kea-dhcp6 to
       continue lease operations. The default value is 1024.
     * ncr-protocol - socket protocol use when sending requests to D2.
       Currently only UDP is supported. TCP may be available in an upcoming
       release.
     * ncr-format - packet format to use when sending requests to D2.
       Currently only JSON format is supported. Other formats may be
       available in future releases.

   By default, kea-dhcp-ddns is assumed to running on the same machine as
   kea-dhcp6, and all of the default values mentioned above should be
   sufficient. If, however, D2 has been configured to listen on a different
   address or port, these values must altered accordingly. For example, if D2
   has been configured to listen on 2001:db8::5 port 900, the following
   configuration would be required:

 "Dhcp6": {
     "dhcp-ddns": {
         "server-ip": "2001:db8::5",
         "server-port": 900,
         ...
     },
     ...
 }

    9.2.21.2. When Does kea-dhcp6 Generate a DDNS Request?

   kea-dhcp6 follows the behavior prescribed for DHCP servers in RFC 4704. It
   is important to keep in mind that kea-dhcp6 provides the initial decision
   making of when and what to update and forwards that information to D2 in
   the form of NCRs. Carrying out the actual DNS updates and dealing with
   such things as conflict resolution are within the purview of D2 itself
   (Chapter 12, The DHCP-DDNS Server). This section describes when kea-dhcp6
   will generate NCRs and the configuration parameters that can be used to
   influence this decision. It assumes that the enable-updates parameter is
   true.

  Note

   Currently the interface between kea-dhcp6 and D2 only supports requests
   which update DNS entries for a single IP address. If a lease grants more
   than one address, kea-dhcp6 will create the DDNS update request for only
   the first of these addresses. Support for multiple address mappings may be
   provided in a future release.

   In general, kea-dhcp6 will generate DDNS update requests when:

    1. A new lease is granted in response to a REQUEST

    2. An existing lease is renewed but the FQDN associated with it has
       changed.

    3. An existing lease is released in response to a RELEASE

   In the second case, lease renewal, two DDNS requests will be issued: one
   request to remove entries for the previous FQDN and a second request to
   add entries for the new FQDN. In the last case, a lease release, a single
   DDNS request to remove its entries will be made.

   The decision making involved when granting a new lease the first case) is
   more involved. When a new lease is granted, kea-dhcp6 will generate a DDNS
   update request only if the REQUEST contains the FQDN option (code 39). By
   default kea-dhcp6 will respect the FQDN N and S flags specified by the
   client as shown in the following table:

   Table 9.3. Default FQDN Flag Behavior

   +------------------------------------------------------------------------+
   | Client    | Client Intent           | Server Response    | Server      |
   | Flags:N-S |                         |                    | Flags:N-S-O |
   |-----------+-------------------------+--------------------+-------------|
   |           | Client wants to do      | Server generates   |             |
   | 0-0       | forward updates, server | reverse-only       | 1-0-0       |
   |           | should do reverse       | request            |             |
   |           | updates                 |                    |             |
   |-----------+-------------------------+--------------------+-------------|
   |           | Server should do both   | Server generates   |             |
   | 0-1       | forward and reverse     | request to update  | 0-1-0       |
   |           | updates                 | both directions    |             |
   |-----------+-------------------------+--------------------+-------------|
   | 1-0       | Client wants no updates | Server does not    | 1-0-0       |
   |           | done                    | generate a request |             |
   +------------------------------------------------------------------------+

   The first row in the table above represents "client delegation". Here the
   DHCP client states that it intends to do the forward DNS updates and the
   server should do the reverse updates. By default, kea-dhcp6 will honor the
   client's wishes and generate a DDNS request to D2 to update only reverse
   DNS data. The parameter, override-client-update, can be used to instruct
   the server to override client delegation requests. When this parameter is
   true, kea-dhcp6 will disregard requests for client delegation and generate
   a DDNS request to update both forward and reverse DNS data. In this case,
   the N-S-O flags in the server's response to the client will be 0-1-1
   respectively.

   (Note that the flag combination N=1, S=1 is prohibited according to RFC
   4702. If such a combination is received from the client, the packet will
   be dropped by kea-dhcp6.)

   To override client delegation, set the following values in the
   configuration:

 "Dhcp6": {
     "dhcp-ddns": {
         "override-client-update": true,
         ...
     },
     ...
 }

   The third row in the table above describes the case in which the client
   requests that no DNS updates be done. The parameter, override-no-update,
   can be used to instruct the server to disregard the client's wishes. When
   this parameter is true, kea-dhcp6 will generate DDNS update requests to
   kea-dhcp-ddns even if the client requests no updates be done. The N-S-O
   flags in the server's response to the client will be 0-1-1.

   To override client delegation, issue the following commands:

 "Dhcp6": {
     "dhcp-ddns": {
         "override-no-update": true,
         ...
     },
     ...
 }

    9.2.21.3. kea-dhcp6 Name Generation for DDNS Update Requests

   Each NameChangeRequest must of course include the fully qualified domain
   name whose DNS entries are to be affected. kea-dhcp6 can be configured to
   supply a portion or all of that name based upon what it receives from the
   client.

   The default rules for constructing the FQDN that will be used for DNS
   entries are:

    1. If the DHCPREQUEST contains the client FQDN option, the candidate name
       is taken from there.

    2. If the candidate name is a partial (i.e. unqualified) name then add a
       configurable suffix to the name and use the result as the FQDN.

    3. If the candidate name provided is empty, generate an FQDN using a
       configurable prefix and suffix.

    4. If the client provided neither option, then no DNS action will be
       taken.

   These rules can amended by setting the replace-client-name parameter which
   provides the following modes of behavior:

     * never - Use the name the client sent. If the client sent no name, do
       not generate one. This is the default mode.

     * always - Replace the name the client sent. If the client sent no name,
       generate one for the client.

     * when-present - Replace the name the client sent. If the client sent no
       name, do not generate one.

     * when-not-present - Use the name the client sent. If the client sent no
       name, generate one for the client.

  Note

   Note that formerly, this parameter was a boolean and permitted only values
   of true and false. Boolean values have been deprecated and are no longer
   accepted. If you are currently using booleans, you must replace them with
   the desired mode name. A value of true maps to "when-present", while false
   maps to "never".

   For example, To instruct kea-dhcp6 to always generate the FQDN for a
   client, set the parameter replace-client-name to always as follows:

 "Dhcp6": {
     "dhcp-ddns": {
         "replace-client-name": "always",
         ...
     },
     ...
 }

   The prefix used in the generation of an FQDN is specified by the
   generated-prefix parameter. The default value is "myhost". To alter its
   value, simply set it to the desired string:

 "Dhcp6": {
     "dhcp-ddns": {
         "generated-prefix": "another.host",
         ...
     },
     ...
 }

   The suffix used when generating an FQDN or when qualifying a partial name
   is specified by the qualifying-suffix parameter. This parameter has no
   default value, thus it is mandatory when DDNS updates are enabled. To set
   its value simply set it to the desired string:

 "Dhcp6": {
     "dhcp-ddns": {
         "qualifying-suffix": "foo.example.org",
         ...
     },
     ...
 }

   When qualifying a partial name, kea-dhcp6 will construct a name with the
   format:

   [candidate-name].[qualifying-suffix].

   where candidate-name is the partial name supplied in the REQUEST. For
   example, if FQDN domain name value was "some-computer" and
   qualifying-suffix "example.com", the generated FQDN would be:

   some-computer.example.com.

   When generating the entire name, kea-dhcp6 will construct name of the
   format:

   [generated-prefix]-[address-text].[qualifying-suffix].

   where address-text is simply the lease IP address converted to a
   hyphenated string. For example, if lease address is 3001:1::70E, the
   qualifying suffix "example.com", and the default value is used for
   generated-prefix, the generated FQDN would be:

   myhost-3001-1--70E.example.com.

    9.2.21.4. Sanitizing Client FQDN Names

   It may be that some of your DHCP clients provide values in the name
   component of the FQDN option (Option code 39), that contain undesirable
   characters. It is possible to configure kea-dhcp5 to sanitize these
   values. The most typical use case would be ensuring that only characters
   that are permitted by RFC 1035 be included: A-Z,a-z,0-9, and '-'. This may
   be accomplished with following two parameters:

     * hostname-char-set - a regular expression describing the invalid
       character set. This can be any valid, regular expression using POSIX
       extended expression syntax. For example, "[^A-Za-z0-9-]" would replace
       any character other then the letters A through z, digits 0 through 9,
       and '-'. An empty string, the default value, disables sanitization.
     * hostname-char-replacement - a string of zero or more characters with
       which to replace each invalid character in the client value. The
       default value is an empty string and will cause invalid characters to
       be OMITTED rather than replaced.

   The following configuration, will replace anything other than a letter,
   digit, hyphen, or dot with the letter 'x':

 "Dhcp4": {
     "dhcp-ddns": {
         "hostname-char-set": "[^A-Za-z0-9.-]",
         "hostname-char-replacement": "x",
         ...
     },
     ...
 }

   Thus, a client supplied value of "myhost-$[123.org" would become
   "myhost-xx123.org". Sanitizing is performed only on the portion of the
   name supplied by the client and it is performed before applying a
   qualifying suffix (if one is defined and needed).

  Note

   The following are some considerations to keep in mind:

   Name sanitizing is meant to catch the more common cases of invalid
   characters through a relatively simple character replacement scheme. It is
   difficult to devise a scheme that works well in all cases and should you
   find you have clients that are using odd, corner cases of character
   combinations that cannot be readily handled with this mechanism, you
   should consider writing a hook that can carry out sufficiently complex
   logic to address your needs.

   You do not account for dots ins your hostname-char-set expression. When
   scrubbing FQDNs, dots are treated as delimiters and used to separate the
   option value into individual domain labels that are scrubbed and then
   re-assembled.

   If your clients are sending values that differ only by characters
   considered as invalid by your hostname-char-set, be aware that scrubbing
   them will yield identical values. In such cases, DDNS conflict rules will
   permit only one of them from registering the name.

   Finally, given the latitude clients have in the values they send, it is
   virtually impossible to guarantee that a combination of these two
   parameters will always yield a name that is valid for use in DNS. For
   example, using an empty value for hostname-char-replacment could yield an
   empty domain label within a name, if that label consists only of invalid
   characters.

  9.2.22. DHCPv4-over-DHCPv6: DHCPv6 Side

   The support of DHCPv4-over-DHCPv6 transport is described in RFC 7341 and
   is implemented using cooperating DHCPv4 and DHCPv6 servers. This section
   is about the configuration of the DHCPv6 side (the DHCPv4 side is
   described in Section 8.2.21, "DHCPv4-over-DHCPv6: DHCPv4 Side").

  Note

   DHCPv4-over-DHCPv6 support is experimental and the details of the
   inter-process communication can change: both the DHCPv4 and DHCPv6 sides
   should be running the same version of Kea. For instance the support of
   port relay (RFC 8357) introduced such such incompatible change.

   There is only one specific parameter for the DHCPv6 side: dhcp4o6-port
   which specifies the first of the two consecutive ports of the UDP sockets
   used for the communication between the DHCPv6 and DHCPv4 servers (the
   DHCPv6 server is bound to ::1 on port and connected to ::1 on port + 1).

   Two other configuration entries are in general required: unicast traffic
   support (see Section 9.2.6, "Unicast Traffic Support") and DHCP 4o6 server
   address option (name "dhcp4o6-server-addr", code 88).

   The following configuration was used during some tests:

 {

 # DHCPv6 conf
 "Dhcp6": {

     "interfaces-config": {
         "interfaces": [ "eno33554984/2001:db8:1:1::1" ]
     },

     "lease-database": {
         "type": "memfile",
         "name": "leases6"
     },

     "preferred-lifetime": 3000,
     "valid-lifetime": 4000,
     "renew-timer": 1000,
     "rebind-timer": 2000,

     "subnet6": [ {
         "subnet": "2001:db8:1:1::/64",
         "interface": "eno33554984",
         "pools": [ { "pool": "2001:db8:1:1::1:0/112" } ]
     } ],

     "dhcp4o6-port": 6767,

     "option-data": [ {
         "name": "dhcp4o6-server-addr",
         "code": 88,
         "space": "dhcp6",
         "csv-format": true,
         "data": "2001:db8:1:1::1"
     } ]

 },

 "Logging": {
     "loggers": [ {
         "name": "kea-dhcp6",
         "output_options": [ {
             "output": "/tmp/kea-dhcp6.log"
         } ],
         "severity": "DEBUG",
         "debuglevel": 0
     } ]
 }

 }

  Note

   Relayed DHCPv4-QUERY DHCPv6 messages are not yet supported.

  9.2.23. Sanity checks in DHCPv6

   An important aspect of a well running DHCP system is an assurance that the
   data remains consisent. However, in some cases it may be convenient to
   tolerate certain inconsistent data. For example, a network administrator
   that temporarily removed a subnet from a configuration wouldn't want all
   the leases associated with it disappear from the lease database. Kea 1.5
   introduced a mechanism to better control sanity checks such as this. While
   currently the scope of configurable sanity checks is limited and their
   default value is set low, it is expected that over time the default
   settings will be set to more aggressive values and more parameters of
   similar nature will be added in the future.

   Kea now supports a new configuration scope called sanity-checks. It
   currently allows only a single parameter called lease-checks. It governs
   what sort of verification is done when a new lease is being loaded from a
   lease file. With the introduction of sanity checks mechanism, it is now
   possible to tell Kea to try to correct inconsistent data.

   Every subnet has a subnet-id value. This is how Kea internally identifies
   subnets. Each lease has a subnet-id parameter as well, which identifies
   which subnet it belongs to. However, if configuration has changed, it is
   possible that a lease could exist with a subnet-id without any subnet that
   matches it. Also, it may be possible that subnets configuration has
   changed and the subnet-id now belongs to a subnet that does not match the
   lease. Kea corrective algorithm first checks if there is a subnet with
   subnet-id specified by the lease. If there is, it checks whether the lease
   belongs to that subnet. If not, depending on the lease-checks setting, the
   lease is discarded, a warning is printed or a new subnet is selected for
   the lease that matches it topologically.

   Since delegated prefixes do not have to belong to a subnet in which
   they're offered, there is no way to implement such a mechanism for IPv6
   prefixes. As such, the mechanism works for IPv6 addresses only.

   There are five levels which are supported:

     * none - do no special checks, accept the lease as is
     * warn - if problems are detected, a warning will be printed, but the
       lease data will be accepted anyway. This is the default value. If not
       explicitly configured to some other value, this level will be used.
     * fix - If data inconsistency is discovered, Kea will try to correct it.
       If the correction is not successful, the data will be inserted anyway.
     * fix-del - If data inconsistency is discovered, Kea will try to correct
       it. If the correction is not succesful, the lease will be rejected.
       This setting ensures the data correctness, but some incorrect data may
       be lost. Use with care.
     * del - This is the strictest mode. If any inconsistency is detected,
       the lease is rejected. Use with care.

   This feature is currently implemented for memfile backend.

   An example configuration that sets this parameter looks as follows:

 "Dhcp6": {
     "sanity-checks": {
         // This parameter determines what to do when a new lease appears in the
         // system (i.e. either is read from disk during memfile startup or is
         // added via lease commands). There are five modes supported:
         // none - do nothing, accept them as is
         // warn - if subnet-id problems are detected, print a warning, but
         //        otherwise load the lease as is. This is the default value.
         // fix - attempt to fix the lease by finding appropriate subnet-id value.
         //       if there is no suitable subnet, the lease is loaded as is.
         // fix-del - attempt to fix the lease by findind appropriate subnet-id
         //           value. If there is no suitable subnet, the lease is deleted.
         // del - delete leases that have incorrect subnet-id values.
         "lease-checks": "fix-del"
     },
     ...
 }

9.3. Host Reservation in DHCPv6

   There are many cases where it is useful to provide a configuration on a
   per host basis. The most obvious one is to reserve specific, static IPv6
   address or/and prefix for exclusive use by a given client (host) -
   returning client will get the same address or/and prefix every time and
   other clients will never get that address. Note that there may be cases
   when the new reservation has been made for the client for the address or
   prefix being currently in use by another client. We call this situation a
   "conflict". The conflicts get resolved automatically over time as
   described in the subsequent sections. Once conflict is resolved, the
   client will keep receiving the reserved configuration when it renews.

   Another example when the host reservations are applicable is when a host
   has specific requirements, e.g. a printer that needs additional DHCP
   options or a cable modem needs specific parameters. Yet another possible
   use case for host reservation is to define unique names for hosts.

   Hosts reservations are defined as parameters for each subnet. Each host
   can be identified by either DUID or its hardware/MAC address. See
   Section 9.10, "MAC/Hardware Addresses in DHCPv6" for details. There is an
   optional reservations array in the subnet6 structure. Each element in that
   array is a structure, that holds information about a single host. In
   particular, the structure has an identifier that uniquely identifies a
   host. In the DHCPv6 context, such an identifier is usually a DUID, but can
   also be a hardware or MAC address. Also, either one or more addresses or
   prefixes may be specified. It is possible to specify a hostname and DHCPv6
   options for a given host.

   The following example shows how to reserve addresses and prefixes for
   specific hosts:

 "subnet6": [
     {
         "subnet": "2001:db8:1::/48",
         "pools": [ { "pool": "2001:db8:1::/80" } ],
         "pd-pools": [
             {
                 "prefix": "2001:db8:1:8000::",
                 "prefix-len": 48,
                 "delegated-len": 64
             }
         ],
         "reservations": [
             {
                 "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
                 "ip-addresses": [ "2001:db8:1::100" ]
             },
             {
                 "hw-address": "00:01:02:03:04:05",
                 "ip-addresses": [ "2001:db8:1::101", "2001:db8:1::102" ]
             },
             {
                 "duid": "01:02:03:04:05:06:07:08:09:0A",
                 "ip-addresses": [ "2001:db8:1::103" ],
                 "prefixes": [ "2001:db8:2:abcd::/64" ],
                 "hostname": "foo.example.com"
             }
         ]
     }
 ]

   This example includes reservations for three different clients. The first
   reservation is made for the address 2001:db8:1::100 for a client using
   DUID 01:02:03:04:05:0A:0B:0C:0D:0E. The second reservation is made for two
   addresses 2001:db8:1::101 and 2001:db8:1::102 for a client using MAC
   address 00:01:02:03:04:05. Lastly, address 2001:db8:1::103 and prefix
   2001:db8:2:abcd::/64 are reserved for a client using DUID
   01:02:03:04:05:06:07:08:09:0A. The last reservation also assigns a
   hostname to this client.

   Note that DHCPv6 allows for a single client to lease multiple addresses
   and multiple prefixes at the same time. Therefore ip-addresses and
   prefixes are plural and are actually arrays. When the client sends
   multiple IA options (IA_NA or IA_PD), each reserved address or prefix is
   assigned to an individual IA of the appropriate type. If the number of IAs
   of specific type is lower than the number of reservations of that type,
   the number of reserved addresses or prefixes assigned to the client is
   equal to the number of IA_NAs or IA_PDs sent by the client, i.e. some
   reserved addresses or prefixes are not assigned. However, they still
   remain reserved for this client and the server will not assign them to any
   other client. If the number of IAs of specific type sent by the client is
   greater than the number of reserved addresses or prefixes, the server will
   try to assign all reserved addresses or prefixes to the individual IAs and
   dynamically allocate addresses or prefixes to remaining IAs. If the server
   cannot assign a reserved address or prefix because it is in use, the
   server will select the next reserved address or prefix and try to assign
   it to the client. If the server subsequently finds that there are no more
   reservations that can be assigned to the client at the moment, the server
   will try to assign leases dynamically.

   Making a reservation for a mobile host that may visit multiple subnets
   requires a separate host definition in each subnet it is expected to
   visit. It is not allowed to define multiple host definitions with the same
   hardware address in a single subnet. Multiple host definitions with the
   same hardware address are valid if each is in a different subnet. The
   reservation for a given host should include only one identifier, either
   DUID or hardware address. Defining both for the same host is considered a
   configuration error, but as of 1.1.0, it is not rejected.

   Adding host reservation incurs a performance penalty. In principle, when a
   server that does not support host reservation responds to a query, it
   needs to check whether there is a lease for a given address being
   considered for allocation or renewal. The server that also supports host
   reservation, has to perform additional checks: not only if the address is
   currently used (i.e. if there is a lease for it), but also whether the
   address could be used by someone else (i.e. if there is a reservation for
   it). That additional check incurs additional overhead.

  9.3.1. Address/Prefix Reservation Types

   In a typical scenario there is an IPv6 subnet defined with a certain part
   of it dedicated for dynamic address allocation by the DHCPv6 server. There
   may be an additional address space defined for prefix delegation. Those
   dynamic parts are referred to as dynamic pools, address and prefix pools
   or simply pools. In principle, the host reservation can reserve any
   address or prefix that belongs to the subnet. The reservations that
   specify an address that belongs to configured pools are called "in-pool
   reservations". In contrast, those that do not belong to dynamic pools are
   called "out-of-pool reservations". There is no formal difference in the
   reservation syntax and both reservation types are handled uniformly.
   However, upcoming releases may offer improved performance if there are
   only out-of-pool reservations as the server will be able to skip
   reservation checks when dealing with existing leases. Therefore, system
   administrators are encouraged to use out-of-pool reservations if possible.

   Beginning with Kea 1.5.0, there is now support for global host
   reservations. These are reservations that are specified at the global
   level within the configuration and that do not belong to any specific
   subnet. Kea will still match inbound client packets to a subnet as before,
   but when the subnet's reservation mode is set to "global", Kea will look
   for host reservations only among the global reservations defined.
   Typcially, such reservations would be used to reserve hostnames for
   clients which may move from one subnet to another.

  Note

   You can reserve any ip-address or prefix in a global reservation. Just
   keep in mind that Kea will not do any sanity checking on the address or
   prefix and that for Kea 1.5.0, support for global reservations should be
   considered experimental.

  9.3.2. Conflicts in DHCPv6 Reservations

   As reservations and lease information are stored separately, conflicts may
   arise. Consider the following series of events. The server has configured
   the dynamic pool of addresses from the range of 2001:db8::10 to
   2001:db8::20. Host A requests an address and gets 2001:db8::10. Now the
   system administrator decides to reserve address 2001:db8::10 for Host B.
   In general, reserving an address that is currently assigned to someone
   else is not recommended, but there are valid use cases where such an
   operation is warranted.

   The server now has a conflict to resolve. Let's analyze the situation
   here. If Host B boots up and request an address, the server is not able to
   assign the reserved address 2001:db8::10. A naive approach would to be
   immediately remove the lease for Host A and create a new one for Host B.
   That would not solve the problem, though, because as soon as Host B get
   the address, it will detect that the address is already in use by someone
   else (Host A) and would send a Decline message. Therefore in this
   situation, the server has to temporarily assign a different address from
   the dynamic pool (not matching what has been reserved) to Host B.

   When Host A renews its address, the server will discover that the address
   being renewed is now reserved for someone else (Host B). Therefore the
   server will remove the lease for 2001:db8::10, select a new address and
   create a new lease for it. It will send two addresses in its response: the
   old address with lifetime set to 0 to explicitly indicate that it is no
   longer valid and the new address with a non-zero lifetime. When Host B
   renews its temporarily assigned address, the server will detect that the
   existing lease does not match reservation, so it will release the current
   address Host B has and will create a new lease matching the reservation.
   Similar as before, the server will send two addresses: the temporarily
   assigned one with zeroed lifetimes, and the new one that matches
   reservation with proper lifetimes set.

   This recovery will succeed, even if other hosts will attempt to get the
   reserved address. Had Host C requested address 2001:db8::10 after the
   reservation was made, the server will propose a different address.

   This recovery mechanism allows the server to fully recover from a case
   where reservations conflict with existing leases. This procedure takes
   time and will roughly take as long as renew-timer value specified. The
   best way to avoid such recovery is to not define new reservations that
   conflict with existing leases. Another recommendation is to use
   out-of-pool reservations. If the reserved address does not belong to a
   pool, there is no way that other clients could get this address.

  Note

   The conflict resolution mechanism does not work for global reservations.
   As of Kea 1.5.0, it is generally recommended to not use global
   reservations for addresses or prefixes. If you want to use it anyway, you
   have to manually ensure that the reserved values are not in the dynamic
   pools.

  9.3.3. Reserving a Hostname

   When the reservation for the client includes the hostname, the server will
   assign this hostname to the client and send it back in the Client FQDN, if
   the client sent the FQDN option to the server. The reserved hostname
   always takes precedence over the hostname supplied by the client (via the
   FQDN option) or the autogenerated (from the IPv6 address) hostname.

   The server qualifies the reserved hostname with the value of the
   qualifying-suffix parameter. For example, the following subnet
   configuration:

 "subnet6": [
     {
         "subnet": "2001:db8:1::/48",
         "pools": [ { "pool": "2001:db8:1::/80" } ],
         "reservations": [
             {
                 "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
                 "ip-addresses": [ "2001:db8:1::100" ]
                 "hostname": "alice-laptop"
             }
         ]
     }
 ],
 "dhcp-ddns": {
     "enable-updates": true,
     "qualifying-suffix": "example.isc.org."
 }

   will result in assigning the "alice-laptop.example.isc.org." hostname to
   the client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E". If the
   qualifying-suffix is not specified, the default (empty) value will be
   used, and in this case the value specified as a hostname will be treated
   as fully qualified name. Thus, by leaving the qualifying-suffix empty it
   is possible to qualify hostnames for the different clients with different
   domain names:

 "subnet6": [
     {
         "subnet": "2001:db8:1::/48",
         "pools": [ { "pool": "2001:db8:1::/80" } ],
         "reservations": [
             {
                 "duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
                 "ip-addresses": [ "2001:db8:1::100" ]
                 "hostname": "mark-desktop.example.org."
             }
         ]
     }
 ],
 "dhcp-ddns": {
     "enable-updates": true,
 }

   The above example results in the assignment of the
   "mark-desktop.example.org." hostname to the client using the DUID
   "01:02:03:04:05:0A:0B:0C:0D:0E".

  9.3.4. Including Specific DHCPv6 Options in Reservations

   Kea 1.1.0 introduced the ability to specify options on a per host basis.
   The options follow the same rules as any other options. These can be
   standard options (see Section 9.2.10, "Standard DHCPv6 Options"), custom
   options (see Section 9.2.12, "Custom DHCPv6 Options") or vendor specific
   options (see Section 9.2.13, "DHCPv6 Vendor-Specific Options"). The
   following example demonstrates how standard options can be defined.

 "reservations": [
 {
    "duid": "01:02:03:05:06:07:08",
    "ip-addresses": [ "2001:db8:1::2" ],
     "option-data": [
     {
         "option-data": [ {
             "name": "dns-servers",
             "data": "3000:1::234"
         },
         {
             "name": "nis-servers",
             "data": "3000:1::234"
         }
     } ]
 } ]

   Vendor specific options can be reserved in a similar manner:

 "reservations": [
 {
     "duid": "aa:bb:cc:dd:ee:ff",
     "ip-addresses": [ "2001:db8::1" ],
     "option-data": [
     {
         "name": "vendor-opts",
         "data": 4491
     },
     {
         "name": "tftp-servers",
         "space": "vendor-4491",
         "data": "3000:1::234"
     } ]
 } ]

   Options defined at host level have the highest priority. In other words,
   if there are options defined with the same type on global, subnet, class
   and host level, the host specific values will be used.

  9.3.5. Reserving Client Classes in DHCPv6

   The Section 14.3, "Using Expressions In Classification" explains how to
   configure the server to assign classes to a client based on the content of
   the options that this client sends to the server. Host reservations
   mechanisms also allow for the static assignment of classes to clients. The
   definitions of these classes are placed in the Kea configuration. The
   following configuration snippet shows how to specify that the client
   belongs to classes reserved-class1 and reserved-class2. Those classes are
   associated with specific options being sent to the clients which belong to
   them.

 {
     "client-classes": [
     {
        "name": "reserved-class1",
        "option-data": [
        {
            "name": "dns-servers",
            "data": "2001:db8:1::50"
        }
        ]
    },
    {
        "name": "reserved-class2",
        "option-data": [
        {
            "name": "nis-servers",
            "data": "2001:db8:1::100"
        }
        ]
     }
     ],
     "subnet6": [
     {   "pools": [ { "pool": "2001:db8:1::/64" } ],
         "subnet": "2001:db8:1::/48",
         "reservations": [
         {
             "duid": "01:02:03:04:05:06:07:08",

             "client-classes": [ "reserved-class1", "reserved-class2" ]

          } ]
      } ]
  }


   Static class assignments, as shown above, can be used in conjunction with
   classification using expressions. The "KNOWN" or "UNKNOWN" builtin class
   is added to the packet and any class depending on it directly or
   indirectly and not only-if-required is evaluated.

  Note

   If you want to force the evaluation of a class expression after the host
   reservation lookup, for instance because of a dependency on
   "reserved-class1" from the previous example, you should add a
   "member('KNOWN')" in the expression.

  9.3.6. Storing Host Reservations in MySQL, PostgreSQL or Cassandra

   It is possible to store host reservations in MySQL, PostgreSQL or
   Cassandra. See Section 9.2.3, "Hosts Storage" for information on how to
   configure Kea to use reservations stored in MySQL, PostgreSQL or
   Cassandra. Kea provides dedicated hook for managing reservations in a
   database, section Section 15.4.4, "host_cmds: Host Commands" provide
   detailed information. The Kea wiki
   https://gitlab.isc.org/isc-projects/kea/wikis/designs/commands#23-host-reservations-hr-management
   provides some examples how to conduct some common operations on host
   reservations.

  Note

   In Kea maximum length of an option specified per host is arbitrarily set
   to 4096 bytes.

  9.3.7. Fine Tuning DHCPv6 Host Reservation

   The host reservation capability introduces additional restrictions for the
   allocation engine (the component of Kea that selects an address for a
   client) during lease selection and renewal. In particular, three major
   checks are necessary. First, when selecting a new lease, it is not
   sufficient for a candidate lease to not be used by another DHCP client. It
   also must not be reserved for another client. Second, when renewing a
   lease, additional check must be performed whether the address being
   renewed is not reserved for another client. Finally, when a host renews an
   address or a prefix, the server has to check whether there is a
   reservation for this host, so the existing (dynamically allocated) address
   should be revoked and the reserved one be used instead.

   Some of those checks may be unnecessary in certain deployments and not
   performing them may improve performance. The Kea server provides the
   reservation-mode configuration parameter to select the types of
   reservations allowed for the particular subnet. Each reservation type has
   different constraints for the checks to be performed by the server when
   allocating or renewing a lease for the client. Allowed values are:

     * all - enables both in-pool and out-of-pool host reservation types.
       This is the default value. This setting is the safest and the most
       flexible. As all checks are conducted, it is also the slowest. This
       does not check against global reservations.
     * out-of-pool - allows only out of pool host reservations. With this
       setting in place, the server may assume that all host reservations are
       for addresses that do not belong to the dynamic pool. Therefore it can
       skip the reservation checks when dealing with in-pool addresses, thus
       improving performance. Do not use this mode if any of your
       reservations use in-pool address. Caution is advised when using this
       setting. Kea does not sanity check the reservations against
       reservation-mode and misconfiguration may cause problems.
     * global - allows only global host reservations. With this setting in
       place, the server searches for reservations for a client only among
       the defined global reservations. If an address is specified, the
       server will skip the reservation checks done when dealing in other
       modes, thus improving performance. Caution is advised when using this
       setting: Kea does not sanity check the reservations when global and
       misconfiguration may cause problems.
     * disabled - host reservation support is disabled. As there are no
       reservations, the server will skip all checks. Any reservations
       defined will be completely ignored. As the checks are skipped, the
       server may operate faster in this mode.

   The parameter can be specified at global, subnet and shared network
   levels.

   An example configuration that disables reservation looks like follows:

 "Dhcp6": {
     "subnet6": [
         {
         "subnet": "2001:db8:1::/64",
         "reservation-mode": "disabled",
         ...
         }
     ]
 }


   An example configuration using global reservations is shown below:

 "Dhcp6": {


     "reservation-mode": "global",
     "reservations": [
        {
         "duid": "00:03:00:01:11:22:33:44:55:66",
         "hostname": "host-one"
        },
        {
         "duid": "00:03:00:01:99:88:77:66:55:44",
         "hostname": "host-two"
        }
     ],

     "subnet6": [
     {
         "subnet": "2001:db8:1::/64",
         ...
     }
     ]
 }

   For more details regarding global reservations, see Section 9.3.8, "Global
   reservations in DHCPv6".

   Another aspect of the host reservations are different types of
   identifiers. Kea 1.1.0 supports two types of identifiers in DHCPv6:
   hw-address and duid, but more identifier types are likely to be added in
   the future. This is beneficial from a usability perspective. However,
   there is a drawback. For each incoming packet Kea has to to extract each
   identifier type and then query the database to see if there is a
   reservation done by this particular identifier. If nothing is found, the
   next identifier is extracted and next query is issued. This process
   continues until either a reservation is found or all identifier types have
   been checked. Over time with an increasing number of supported identifier
   types, Kea would become slower and slower.

   To address this problem, a parameter called host-reservation-identifiers
   has been introduced. It takes a list of identifier types as a parameter.
   Kea will check only those identifier types enumerated in
   host-reservation-identifiers. From a performance perspective the number of
   identifier types should be kept to minimum, ideally limited to one. If
   your deployment uses several reservation types, please enumerate them from
   most to least frequently used as this increases the chances of Kea finding
   the reservation using the fewest number of queries. An example of host
   reservation identifiers looks as follows:

 "host-reservation-identifiers": [ "duid", "hw-address" ],
 "subnet6": [
     {
         "subnet": "2001:db8:1::/64",
         ...
     }
 ]

   If not specified, the default value is:

 "host-reservation-identifiers": [ "hw-address", "duid" ]

  9.3.8. Global reservations in DHCPv6

   In some deployments, such as mobile, clients can roam within the network
   and there is a desire to specify certain parameters regardless of the
   client's current location. To facilitate such a need, a global reservation
   mechanism has been implemented. The idea behind it is that regular host
   reservations are tied to specific subnets, by using specific subnet-id.
   Kea 1.5.0 introduced a new capability to specify global reservation that
   can be used in every subnet that has global reservations enabled.

   This feature can be used to assign certain parameters, such as hostname or
   other dedicated, host-specific options. It can also be used to assign
   addresses or prefixes. However, global reservations that assign either of
   these bypass the whole topology determination provided by DHCP logic
   implemented in Kea. It is very easy to misuse this feature and get
   configuration that is inconsistent. To give a specific example, imagine a
   global reservation for an address 2001:db8:1111::1 and two subnets
   2001:db8:1111::/48 and 2001:db8:ffff::/48. If global reservations are used
   in both subnets and a device matching global host reservations visits part
   of the network that is covered by 2001:db8:ffff::/48, it will get an IP
   address 2001:db8:ffff::1, which will be outside of the prefix announced by
   its local router using Router Advertisements. Such a configuration would
   be unsuable or at the very least ridden with issues, such as the downlink
   traffic not reaching the device.

   To use global host reservations a configuration similar to the following
   can be used:

 "Dhcp6:" {
     // This specifies global reservations. They will apply to all subnets that
     // have global reservations enabled.

     "reservations": [
     {
        "hw-address": "aa:bb:cc:dd:ee:ff",
        "hostname": "hw-host-dynamic"
     },
     {
        "hw-address": "01:02:03:04:05:06",
        "hostname": "hw-host-fixed",

        // Use of IP address is global reservation is risky. If used outside of
        // matching subnet, such as 3001::/64, it will result in a broken
        // configuration being handled to the client.
        "ip-address": "2001:db8:ff::77"
     },
     {
        "duid": "01:02:03:04:05",
        "hostname": "duid-host"
     }
     ],
     "valid-lifetime": 600,
     "subnet4": [ {
         "subnet": "2001:db8:1::/64",
         "reservation-mode": "global",
         "pools": [ { "pool": "2001:db8:1::-2001:db8:1::100" } ]
     } ]
 }

   When using database backends, the global host reservations are
   distinguished from regular reservations by using subnet-id value of zero.

9.4. Shared networks in DHCPv6

   DHCP servers use subnet information in two ways. First, it is used to
   determine the point of attachment, or simply put, where the client is
   connected to the network. Second, the subnet information is used to group
   information pertaining to specific location in the network. This approach
   works well in general case, but the are scenarios where the boundaries are
   blurred. Sometimes it is useful to have more than one logical IP subnet
   being deployed on the same physical link. The need to understand that two
   or more subnets are used on the same link requires additional logic in the
   DHCP server. This capability has been added in Kea 1.3.0. It is called
   "shared networks" in Kea and ISC DHCP projects. It is sometimes also
   called "shared subnets". In Microsoft's nomenclature it is called
   "multinet".

   There are many use cases where the feature is useful. The most common
   example in the IPv4 case is when the server is running out of available
   addresses in a subnet. This is less common in IPv6, but the shared
   networks are still useful in IPv6. One of the use cases is an exhaustion
   of IPv6 delegated prefixes within a subnet. Another IPv6 specific example
   is an experiment with addressing scheme. With the advent of IPv6
   deployment and vast address space, many organizations split the address
   space into subnets, then deploy it and after a while discover that they
   want to split it differently. In the transition period they want both old
   and new addressing to be available. Thus the need for more than one subnet
   on the same physical link.

   Finally, the case of cable networks is directly applicable in IPv6. There
   are two types of devices in cable networks: cable modems and the end user
   devices behind them. It is a common practice to use different subnet for
   cable modems to prevent users from tinkering with their cable modems. In
   this case, the distinction is based on the type of device, rather than
   coming out of running out address space.

   A client connected to a shared network may be assigned a lease (address or
   prefix) from any of the pools defined within the subnets belonging to the
   shared network. Internally, the server selects one of the subnets
   belonging to the shared network and tries to allocate a lease from this
   subnet. If the server is unable to allocate a lease from the selected
   subnet (e.g. due to pools exhaustion) it will use another subnet from the
   same shared network and try to allocate a lease from this subnet etc.
   Therefore, in the typical case, the server will allocate all leases
   available in a given subnet before it starts allocating leases from other
   subnets belonging to the same shared network. However, in certain
   situations the client can be allocated a lease from the other subnets
   before the pools in the first subnet get exhausted, e.g. when the client
   provides a hint that belongs to another subnet or the client has
   reservations in a different than default subnet.

  Note

   It is strongly discouraged for the Kea deployments to assume that the
   server doesn't allocate leases from other subnets until it uses all the
   leases from the first subnet in the shared network. Apart from the fact
   that hints, host reservations and client classification affect subnet
   selection, it is also foreseen that we will enhance allocation strategies
   for shared networks in the future versions of Kea, so as the selection of
   subnets within a shared network is equally probable (unpredictable).

   In order to define a shared network an additional configuration scope is
   introduced:

 {
 "Dhcp6": {
     "shared-networks": [
         {
             // Name of the shared network. It may be an arbitrary string
             // and it must be unique among all shared networks.
             "name": "ipv6-lab-1",

             // Subnet selector can be specifed on the shared network level.
             // Subnets from this shared network will be selected for clients
             // communicating via relay agent having the specified IP address.
             "relay": {
                 "ip-addresses": [ "2001:db8:2:34::1" ]
             },

             // This starts a list of subnets in this shared network.
             // There are two subnets in this example.
             "subnet6": [
                 {
                     "subnet": "2001:db8::/48",
                     "pools": [ { "pool":  "2001:db8::1 - 2001:db8::ffff" } ]
                 },
                 {
                     "subnet": "3ffe:ffe::/64",
                     "pools": [ { "pool":  "3ffe:ffe::/64" } ]
                 }
             ]
         } ], // end of shared-networks

     // It is likely that in your network you'll have a mix of regular,
     // "plain" subnets and shared networks. It is perfectly valid to mix
     // them in the same config file.
     //
     // This is regular subnet. It's not part of any shared-network.
     "subnet6": [
         {
             "subnet": "2001:db9::/48",
             "pools": [ { "pool":  "2001:db9::/64" } ],
             "relay": {
                 "ip-addresses": [ "2001:db8:1:2::1" ]
             }
         }
     ]

 } // end of Dhcp6
 }

   As you see in the example, it is possible to mix shared and regular
   ("plain") subnets. Each shared network must have a unique name. This is a
   similar concept to ID for subnets, but it offers more flexibility. This is
   used for logging, but also internally for identifying shared networks.

   In principle it makes sense to define only shared networks that consist of
   two or more subnets. However, for testing purposes it is allowed to define
   a shared network with just one subnet or even an empty one. This is not a
   recommended practice in production networks, as the shared network logic
   requires additional processing and thus lowers server's performance. To
   avoid unnecessary performance degradation the shared subnets should only
   be defined when required by the deployment.

   Shared networks provide an ability to specify many parameters in the
   shared network scope that will apply to all subnets within it. If
   necessary, you can specify a parameter in the shared network scope and
   then override its value on the subnet scope. For example:

 "shared-networks": [
     {
         "name": "lab-network3",
         "relay": {
              "ip-addresses": [ "2001:db8:2:34::1" ]
         },

         // This applies to all subnets in this shared network, unless
         // values are overridden on subnet scope.
         "valid-lifetime": 600,

         // This option is made available to all subnets in this shared
         // network.
         "option-data": [ {
             "name": "dns-servers",
             "data": "2001:db8::8888"
         } ],

         "subnet6": [
             {
                 "subnet": "2001:db8:1::/48",
                 "pools": [ { "pool":  "2001:db8:1::1 - 2001:db8:1::ffff" } ],

                 // This particular subnet uses different values.
                 "valid-lifetime": 1200,
                 "option-data": [
                 {
                     "name": "dns-servers",
                     "data": "2001:db8::1:2"
                 },
                 {
                     "name": "unicast",
                     "data": "2001:abcd::1"
                 } ]
             },
             {
                  "subnet": "2001:db8:2::/48",
                  "pools": [ { "pool":  "2001:db8:2::1 - 2001:db8:2::ffff" } ],

                  // This subnet does not specify its own valid-lifetime value,
                  // so it is inherited from shared network scope.
                  "option-data": [
                  {
                      "name": "dns-servers",
                      "data": "2001:db8:cafe::1"
                  } ]
             }
         ],
     } ]

   In this example, there is a dns-servers option defined that is available
   to clients in both subnets in this shared network. Also, a valid lifetime
   is set to 10 minutes (600s). However, the first subnet overrides some of
   the values (valid lifetime is 20 minutes, different IP address for
   dns-servers), but also adds its own option (unicast address). Assuming a
   client asking for a server unicast and dns servers options is assigned a
   lease from this subnet, he will get a lease for 20 minutes and dns-servers
   and be allowed to use server unicast at address 2001:abcd::1. If the same
   client is assigned to the second subnet, he will get a 10 minutes long
   lease, dns-servers value of 2001:db8:cafe::1 and no server unicast.

   Some parameters must be the same in all subnets in the same shared
   network. This restriction applies to interface and rapid-commit settings.
   The most convenient way is to define them on shared network scope, but you
   may specify them for each subnet. However, care should be taken for each
   subnet to have the same value.

  9.4.1. Local and relayed traffic in shared networks

   It is possible to specify interface name in the shared network scope to
   tell the server that this specific shared network is reachable directly
   (not via relays) using local network interface. It is sufficient to
   specify it once at the shared network level. As all subnets in a shared
   network are expected to be used on the same physical link, it is a
   configuration error to attempt to make a shared network out of subnets
   that are reachable over different interfaces. It is allowed to specify
   interface parameter on each subnet, although its value must be the same
   for each subnet. Thus it's usually more convenient to specify it once at
   the shared network level.

 "shared-networks": [
     {
         "name": "office-floor-2",

         // This tells Kea that the whole shared networks is reachable over
         // local interface. This applies to all subnets in this network.
         "interface": "eth0",

         "subnet6": [
             {
                 "subnet": "2001:db8::/64",
                 "pools": [ { "pool":  "2001:db8::1 - 2001:db8::ffff" } ],
                 "interface": "eth0"
             },
             {
                  "subnet": "3ffe:abcd::/64",
                  "pools": [ { "pool":  "3ffe:abcd::1 - 3ffe:abcd::ffff" } ]

                  // Specifying a different interface name is configuration
                  // error:
                  // "interface": "eth1"
             }
         ],
     } ]

   Somewhat similar to interface names, also relay IP addresses can be
   specified for the whole shared network. However, depending on your relay
   configuration, it may use different IP addresses depending on which subnet
   is being used. Thus there is no requirement to use the same IP relay
   address for each subnet. Here's an example:

 "shared-networks": [
     {
         "name": "kakapo",
         "relay": {
             "ip-addresses":  [ "2001:db8::abcd" ]
         },
         "subnet6": [
             {
                 "subnet": "2001:db8::/64",
                 "relay": {
                     "ip-addresses": [ "2001:db8::1234" ]
                 },
                 "pools": [ { "pool":  "2001:db8::1 - 2001:db8::ffff" } ]
             },
             {
                  "subnet": "3ffe:abcd::/64",
                  "pools": [ { "pool":  "3ffe:abcd::1 - 3ffe:abcd::ffff" } ],
                  "relay": {
                     "ip-addresses": [ "3ffe:abcd::cafe" ]
                  }
             }
         ]
     }
 ]

   In this particular case the relay IP address specified at network level
   doesn't have much sense, as it is overridden in both subnets, but it was
   left there as an example of how one could be defined at network level.
   Note that the relay agent IP address typically belongs to the subnet it
   relays packets from, but this is not a strict requirement. Therefore Kea
   accepts any value here as long as it is valid IPv6 address.

  9.4.2. Client classification in shared networks

   Sometimes it is desired to segregate clients into specific subnets based
   on some properties. This mechanism is called client classification and is
   described in Chapter 14, Client Classification. Client classification can
   be applied to subnets belonging to shared networks in the same way as it
   is used for subnets specified outside of shared networks. It is important
   to understand how the server selects subnets for the clients when client
   classification is in use, to assure that the desired subnet is selected
   for a given client type.

   If a subnet is associated with a class, only the clients belonging to this
   class can use this subnet. If there are no classes specified for a subnet,
   any client connected to a given shared network can use this subnet. A
   common mistake is to assume that the subnet including a client class is
   preferred over subnets without client classes. Consider the following
   example:

 {
     "client-classes": [
         {
             "name": "b-devices",
             "test": "option[1234].hex == 0x0002"
         }
     ],
     "shared-networks": [
         {
             "name": "galah",
             "relay": {
                 "ip-address": [ "2001:db8:2:34::1" ]
             },
             "subnet6": [
                 {
                     "subnet": "2001:db8:1::/64",
                     "pools": [ { "pool": "2001:db8:1::20 - 2001:db8:1::ff" } ],
                 },
                 {
                     "subnet": "2001:db8:3::/64",
                     "pools": [ { "pool": "2001:db8:3::20 - 2001:db8:3::ff" } ],
                     "client-class": "b-devices"
                 }
             ]
         }
     ]
 }

   If the client belongs to "b-devices" class (because it includes option
   1234 with a value of 0x0002) it doesn't guarantee that the subnet
   2001:db8:3::/64 will be used (or preferred) for this client. The server
   can use any of the two subnets because the subnet 2001:db8:1::/64 is also
   allowed for this client. The client classification used in this case
   should be pereceived as a way to restrict access to certain subnets,
   rather than a way to express subnet preference. For example, if the client
   doesn't belong to the "b-devices" class it may only use the subnet
   2001:db8:1::/64 and will never use the subnet 2001:db8:3::/64.

   A typical use case for client classification is in the cable network,
   where cable modems should use one subnet and other devices should use
   another subnet within the same shared network. In this case it is required
   to apply classification on all subnets. The following example defines two
   classes of devices. The subnet selection is made based on option 1234
   values.

 {
     "client-classes": [
         {

             "name": "a-devices",
             "test": "option[1234].hex == 0x0001"
         },
         {
             "name": "b-devices",
             "test": "option[1234].hex == 0x0002"
         }
     ],
     "shared-networks": [
         {
             "name": "galah",
             "relay": {
                 "ip-addresses":  [ "2001:db8:2:34::1" ]
             },
             "subnet6": [
                 {
                     "subnet": "2001:db8:1::/64",
                     "pools": [ { "pool": "2001:db8:1::20 - 2001:db8:1::ff" } ],
                     "client-class": "a-devices"
                 },
                 {
                     "subnet": "2001:db8:3::/64",
                     "pools": [ { "pool": "2001:db8:3::20 - 2001:db8:3::ff" } ],
                     "client-class": "b-devices"
                 }
             ]
         }
     ]
 }

   In this example each class has its own restriction. Only clients that
   belong to class a-devices will be able to use subnet 2001:db8:1::/64 and
   only clients belonging to b-devices will be able to use subnet
   2001:db8:3::/64. Care should be taken to not define too restrictive
   classification rules, as clients that are unable to use any subnets will
   be refused service. Although, this may be desired outcome if one desires
   to service only clients of known properties (e.g. only VoIP phones allowed
   on a given link).

   Note that it is possible to achieve similar effect as presented in this
   section without the use of shared networks. If the subnets are placed in
   the global subnets scope, rather than in the shared network, the server
   will still use classification rules to pick the right subnet for a given
   class of devices. The major benefit of placing subnets within the shared
   network is that common parameters for the logically grouped subnets can be
   specified once, in the shared network scope, e.g. "interface" or "relay"
   parameter. All subnets belonging to this shared network will inherit those
   parameters.

  9.4.3. Host reservations in shared networks

   Subnets being part of a shared network allow host reservations, similar to
   regular subnets:

 {
     "shared-networks": [
     {
         "name": "frog",
         "relay": {
             "ip-addresses": [ "2001:db8:2:34::1" ]
         },
         "subnet6": [
             {
                 "subnet": "2001:db8:1::/64",
                 "id": 100,
                 "pools": [ { "2001:db8:1::1 - 2001:db8:1::64" } ],
                 "reservations": [
                 {
                     "duid": "00:03:00:01:11:22:33:44:55:66",
                     "ip-addresses": [ "2001:db8:1::28" ]
                 }
                 ]
             },
             {
                 "subnet": "2001:db8:3::/64",
                 "id": 101,
                 "pools": [ { "pool": "2001:db8:3::1 - 2001:db8:3::64" } ],
                 "reservations": [
                     {
                         "duid": "00:03:00:01:aa:bb:cc:dd:ee:ff",
                         "ip-addresses": [ "2001:db8:2::28" ]
                     }
                 ]
             }
         ]
     }
     ]
 }


   It is worth noting that Kea conducts additional checks when processing a
   packet if shared networks are defined. First, instead of simply checking
   if there's a reservation for a given client in his initially selected
   subnet, it goes through all subnets in a shared network looking for a
   reservation. This is one of the reasons why defining a shared network may
   impact performance. If there is a reservation for a client in any subnet,
   that particular subnet will be picked for the client. Although it's
   technically not an error, it is considered a bad practice to define
   reservations for the same host in multiple subnets belonging to the same
   shared network.

   While not strictly mandatory, it is strongly recommended to use explicit
   "id" values for subnets if you plan to use database storage for host
   reservations. If ID is not specified, the values for it be autogenerated,
   i.e. it will assign increasing integer values starting from 1. Thus, the
   autogenerated IDs are not stable across configuration changes.

9.5. Server Identifier in DHCPv6

   The DHCPv6 protocol uses a "server identifier" (also known as a DUID) for
   clients to be able to discriminate between several servers present on the
   same link. RFC 8415 defines four DUID types: DUID-LLT, DUID-EN, DUID-LL
   and DUID-UUID. Future specifications may introduce new DUID types.

   The Kea DHCPv6 server generates a server identifier once, upon the first
   startup, and stores it in a file. This identifier isn't modified across
   restarts of the server and so is a stable identifier.

   Kea follows recommendation from RFC 8415 to use DUID-LLT as the default
   server identifier. However, we have received reports that some deployments
   require different DUID types, and there is a need to administratively
   select both DUID type and/or its contents.

   The server identifier can be configured using parameters within the
   server-id map element in the global scope of the Kea configuration file.
   The following example demonstrates how to select DUID-EN as a server
   identifier:

 "Dhcp6": {
     "server-id": {
         "type": "EN"
     },
     ...
 }

   Currently supported values for type parameter are: "LLT", "EN" and "LL",
   for DUID-LLT, DUID-EN and DUID-LL respectively.

   When a new DUID type is selected the server will generate its value and
   replace any existing DUID in the file. The server will then use the new
   server identifier in all future interactions with the clients.

  Note

   If the new server identifier is created after some clients have obtained
   their leases, the clients using the old identifier will not be able to
   renew the leases: the server will ignore messages containing the old
   server identifier. Clients will continue sending Renew until they
   transition to the rebinding state. In this state they will start sending
   Rebind messages to multicast address without a server identifier. The
   server will respond to the Rebind messages with a new server identifier
   and the clients will associate the new server identifier with their
   leases. Although the clients will be able to keep their leases and will
   eventually learn the new server identifier, this will be at the cost of
   increased number of renewals and multicast traffic due to a need to
   rebind. Therefore it is recommended that modification of the server
   identifier type and value is avoided if the server has already assigned
   leases and these leases are still valid.

   There are cases when an administrator needs to explicitly specify a DUID
   value rather than allow the server to generate it. The following example
   demonstrates how to explicitly set all components of a DUID-LLT.

 "Dhcp6": {
     "server-id": {
         "type": "LLT",
         "htype": 8,
         "identifier": "A65DC7410F05",
         "time": 2518920166
     },
     ...
 }

   where:

     * htype is a 16-bit unsigned value specifying hardware type,
     * identifier is a link layer address, specified as a string of
       hexadecimal digits,
     * time is a 32-bit unsigned time value.

   The hexadecimal representation of the DUID generated as a result of the
   configuration specified above will be:

  00:01:00:08:96:23:AB:E6:A6:5D:C7:41:0F:05
 |type |htype|   time    |   identifier    |

   It is allowed to use special value of 0 for "htype" and "time", which
   indicates that the server should use ANY value for these components. If
   the server already uses a DUID-LLT it will use the values from this DUID.
   If the server uses a DUID of a different type or doesn't use any DUID yet,
   it will generate these values. Similarly, if the "identifier" is assigned
   an empty string, the value of the identifier will be generated. Omitting
   any of these parameters is equivalent to setting them to those special
   values.

   For example, the following configuration:

 "Dhcp6": {
     "server-id": {
         "type": "LLT",
         "htype": 0,
         "identifier": "",
         "time": 2518920166
     },
     ...
 }

   indicates that the server should use ANY link layer address and hardware
   type. If the server is already using DUID-LLT it will use the link layer
   address and hardware type from the existing DUID. If the server is not
   using any DUID yet, it will use link layer address and hardware type from
   one of the available network interfaces. The server will use an explicit
   value of time. If it is different than a time value present in the
   currently used DUID, that value will be replaced, effectively causing
   modification of the current server identifier.

   The following example demonstrates an explicit configuration of a DUID-EN:

 "Dhcp6": {
     "server-id": {
         "type": "EN",
         "enterprise-id": 2495,
         "identifier": "87ABEF7A5BB545"
     },
     ...
 }

   where:

     * enterprise-id is a 32-bit unsigned value holding enterprise number,
     * identifier is a variable length identifier within DUID-EN.

   The hexadecimal representation of the DUID-EN created according to the
   configuration above is:

  00:02:00:00:09:BF:87:AB:EF:7A:5B:B5:45
 |type |  ent-id   |     identifier     |

   As in the case of the DUID-LLT, special values can be used for the
   configuration of the DUID-EN. If enterprise-id is 0, the server will use a
   value from the existing DUID-EN. If the server is not using any DUID or
   the existing DUID has a different type, the ISC enterprise id will be
   used. When an empty string is used for identifier, the identifier from the
   existing DUID-EN will be used. If the server is not using any DUID-EN the
   new 6-bytes long identifier will be generated.

   DUID-LL is configured in the same way as DUID-LLT with an exception that
   the time parameter has no effect for DUID-LL, because this DUID type only
   comprises a hardware type and link layer address. The following example
   demonstrates how to configure DUID-LL:

 "Dhcp6": {
     "server-id": {
         "type": "LL",
         "htype": 8,
         "identifier": "A65DC7410F05"
     },
     ...
 }

   which will result in the following server identifier:

  00:03:00:08:A6:5D:C7:41:0F:05
 |type |htype|   identifier    |

   The server stores the generated server identifier in the following
   location: [kea-install-dir]/var/kea/kea-dhcp6-serverid.

   In some uncommon deployments where no stable storage is available, the
   server should be configured not to try to store the server identifier.
   This choice is controlled by the value of persist boolean parameter:

 "Dhcp6": {
     "server-id": {
         "type": "EN",
         "enterprise-id": 2495,
         "identifier": "87ABEF7A5BB545",
         "persist": false
     },
     ...
 }

   The default value of the "persist" parameter is true which configures the
   server to store the server identifier on a disk.

   In the example above, the server is configured to not store the generated
   server identifier on a disk. But, if the server identifier is not modified
   in the configuration the same value will be used after server restart,
   because entire server identifier is explicitly specified in the
   configuration.

9.6. Stateless DHCPv6 (Information-Request Message)

   Typically DHCPv6 is used to assign both addresses and options. These
   assignments (leases) have state that changes over time, hence their name,
   stateful. DHCPv6 also supports a stateless mode, where clients request
   configuration options only. This mode is considered lightweight from the
   server perspective as it does not require any state tracking; hence its
   name.

   The Kea server supports stateless mode. Clients can send
   Information-Request messages and the server will send back answers with
   the requested options (providing the options are available in the server
   configuration). The server will attempt to use per-subnet options first.
   If that fails - for whatever reason - it will then try to provide options
   defined in the global scope.

   Stateless and stateful mode can be used together. No special configuration
   directives are required to handle this. Simply use the configuration for
   stateful clients and the stateless clients will get just options they
   requested.

   This usage of global options allows for an interesting case. It is
   possible to run a server that provides just options and no addresses or
   prefixes. If the options have the same value in each subnet, the
   configuration can define required options in the global scope and skip
   subnet definitions altogether. Here's a simple example of such a
   configuration:

 "Dhcp6": {
     "interfaces-config": {
         "interfaces": [ "ethX" ]
     },
     "option-data": [ {
         "name": "dns-servers",
         "data": "2001:db8::1, 2001:db8::2"
     } ],
     "lease-database": { "type": "memfile" }
  }

   This very simple configuration will provide DNS server information to all
   clients in the network, regardless of their location. Note the
   specification of the memfile lease database: this is needed as Kea
   requires a lease database to be specified even if it is not used.

9.7. Support for RFC 7550 (being now part of RFC 8415)

   The RFC 7550 introduced some changes to the previous DHCPv6
   specifications, RFC 3315 and RFC 3633, to resolve a few issues with the
   coexistence of multiple stateful options in the messages sent between the
   clients and servers. Those changes were later included in the most recent
   DHCPv6 protocol specification, RFC 8415, which obsoleted RFC 7550. Kea
   supports RFC 8415 along with these protocol changes, which are briefly
   described below.

   When a client, such as a requesting router, requests an allocation of both
   addresses and prefixes during the 4-way (SARR) exchange with the server,
   and the server is not configured to allocate any prefixes but it can
   allocate some addresses, it will respond with the IA_NA(s) containing
   allocated addresses and the IA_PD(s) containing the NoPrefixAvail status
   code. According to the updated specifications, if the client can operate
   without prefixes it should accept allocated addresses and transition to
   the 'bound' state. When the client subsequently sends Renew/Rebind
   messages to the server, according to the T1 and T2 times, to extend the
   lifetimes of the allocated addresses, if the client is still interested in
   obtaining prefixes from the server, it may also include an IA_PD in the
   Renew/Rebind to request allocation of the prefixes. If the server still
   cannot allocate the prefixes it will respond with the IA_PD(s) containing
   NoPrefixAvail status code. However, if the server can allocate the
   prefixes it will allocate and send them in the IA_PD(s) to the client.
   Similar situation occurs when the server is unable to allocate addresses
   for the client but can delegate prefixes. The client may request
   allocation of the addresses while renewing the delegated prefixes.
   Allocating leases for other IA types while renewing existing leases is by
   default supported by the Kea DHCPv6 server, and the server provides no
   configuration mechanisms to disable this behavior.

   The following are the other behaviors first introduced in the RFC 7550
   (now being part of the RFC 8415) and supported by the Kea DHCPv6 server:

     * Set T1/T2 timers to the same value for all stateful (IA_NA and IA_PD)
       options to facilitate renewal of all client's leases at the same time
       (in a single message exchange),
     * NoAddrsAvail and NoPrefixAvail status codes are placed in the IA_NA
       and IA_PD options in the Advertise message, rather than as the top
       level options.

9.8. Using Specific Relay Agent for a Subnet

   The relay has to have an interface connected to the link on which the
   clients are being configured. Typically the relay has a global IPv6
   address configured on the interface that belongs to the subnet from which
   the server will assign addresses. In the typical case, the server is able
   to use the IPv6 address inserted by the relay (in the link-addr field in
   RELAY-FORW message) to select the appropriate subnet.

   However, that is not always the case. The relay address may not match the
   subnet in certain deployments. This usually means that there is more than
   one subnet allocated for a given link. The two most common examples where
   this is the case are long lasting network renumbering (where both old and
   new address space is still being used) and a cable network. In a cable
   network both cable modems and the devices behind them are physically
   connected to the same link, yet they use distinct addressing. In such
   case, the DHCPv6 server needs additional information (like the value of
   interface-id option or IPv6 address inserted in the link-addr field in
   RELAY-FORW message) to properly select an appropriate subnet.

   The following example assumes that there is a subnet 2001:db8:1::/64 that
   is accessible via a relay that uses 3000::1 as its IPv6 address. The
   server will be able to select this subnet for any incoming packets that
   came from a relay with an address in 2001:db8:1::/64 subnet. It will also
   select that subnet for a relay with address 3000::1.

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
              ],
              "relay": {
                  "ip-addresses": [ "3000::1" ]
              }
         }
     ]
 }

   If "relay" is specified, the "ip-addresses" parameter within it is
   mandatory.

  Note

   As of Kea 1.4, the "ip-address" parameter in "relay" has been deprecated
   in favor of "ip-addresses" which supports specifying a list of addresses.
   Configuration parsing, will honor the singular form for now but users are
   encouraged to migrate.

9.9. Segregating IPv6 Clients in a Cable Network

   In certain cases, it is useful to mix relay address information,
   introduced in Section 9.8, "Using Specific Relay Agent for a Subnet" with
   client classification, explained in Chapter 14, Client Classification. One
   specific example is a cable network, where typically modems get addresses
   from a different subnet than all devices connected behind them.

   Let's assume that there is one CMTS (Cable Modem Termination System) with
   one CM MAC (a physical link that modems are connected to). We want the
   modems to get addresses from the 3000::/64 subnet, while everything
   connected behind modems should get addresses from another subnet
   (2001:db8:1::/64). The CMTS that acts as a relay an uses address 3000::1.
   The following configuration can serve that configuration:

 "Dhcp6": {
     "subnet6": [
         {
             "subnet": "3000::/64",
             "pools": [
                 { "pool": "3000::2 - 3000::ffff" }
             ],
             "client-class": "VENDOR_CLASS_docsis3.0",
             "relay": {
                 "ip-addresses": [ "3000::1" ]
             }
         },

         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
              ],
              "relay": {
                  "ip-addresses": [ "3000::1" ]
              }
         }
     ]
 }

9.10. MAC/Hardware Addresses in DHCPv6

   MAC/hardware addresses are available in DHCPv4 messages from the clients
   and administrators frequently use that information to perform certain
   tasks, like per host configuration, address reservation for specific MAC
   addresses and other. Unfortunately, the DHCPv6 protocol does not provide
   any completely reliable way to retrieve that information. To mitigate that
   issue a number of mechanisms have been implemented in Kea that attempt to
   gather it. Each of those mechanisms works in certain cases, but may fail
   in other cases. Whether the mechanism works or not in the particular
   deployment is somewhat dependent on the network topology and the
   technologies used.

   Kea allows configuration of which of the supported methods should be used
   and in what order. This configuration may be considered a fine tuning of
   the DHCP deployment. In a typical deployment the default value of "any" is
   sufficient and there is no need to select specific methods. Changing the
   value of this parameter is the most useful in cases when an administrator
   wants to disable certain method, e.g. if the administrator trusts the
   network infrastructure more than the information provided by the clients
   themselves, the administrator may prefer information provided by the
   relays over that provided by the clients.

   The configuration is controlled by the mac-sources parameter as follows:

 "Dhcp6": {
     "mac-sources": [ "method1", "method2", "method3", ... ],

     "subnet6": [ ... ],

     ...
 }

   When not specified, a special value of "any" is used, which instructs the
   server to attempt to use all the methods in sequence and use value
   returned by the first one that succeeds. If specified, it has to have at
   least one value.

   Supported methods are:

     * any - Not an actual method, just a keyword that instructs Kea to try
       all other methods and use the first one that succeeds. This is the
       default operation if no mac-sources are defined.
     * raw - In principle, a DHCPv6 server could use raw sockets to receive
       incoming traffic and extract MAC/hardware address information. This is
       currently not implemented for DHCPv6 and this value has no effect.
     * duid - DHCPv6 uses DUID identifiers instead of MAC addresses. There
       are currently four DUID types defined, with two of them (DUID-LLT,
       which is the default one and DUID-LL) convey MAC address information.
       Although RFC 8415 forbids it, it is possible to parse those DUIDs and
       extract necessary information from them. This method is not completely
       reliable, as clients may use other DUID types, namely DUID-EN or
       DUID-UUID.
     * ipv6-link-local - Another possible acquisition method comes from the
       source IPv6 address. In typical usage, clients are sending their
       packets from IPv6 link-local addresses. There is a good chance that
       those addresses are based on EUI-64, which contains MAC address. This
       method is not completely reliable, as clients may use other link-local
       address types. In particular, privacy extensions, defined in RFC 4941,
       do not use MAC addresses. Also note that successful extraction
       requires that the address's u-bit must be set to 1 and its g-bit set
       to 0, indicating that it is an interface identifier as per RFC 2373,
       section 2.5.1.
     * client-link-addr-option - One extension defined to alleviate missing
       MAC issues is client link-layer address option, defined in RFC 6939.
       This is an option that is inserted by a relay and contains information
       about client's MAC address. This method requires a relay agent that
       supports the option and is configured to insert it. This method is
       useless for directly connected clients. This parameter can also be
       specified as rfc6939, which is an alias for client-link-addr-option.
     * remote-id - RFC 4649 defines a remote-id option that is inserted by a
       relay agent. Depending on the relay agent configuration, the inserted
       option may convey the client's MAC address information. This parameter
       can also be specified as rfc4649, which is an alias for remote-id.
     * subscriber-id - Another option that is somewhat similar to the
       previous one is subscriber-id, defined in RFC 4580. It is, too,
       inserted by a relay agent that is configured to insert it. This
       parameter can also be specified as rfc4580, which is an alias for
       subscriber-id. This method is currently not implemented.
     * docsis-cmts - Yet another possible source of MAC address information
       are the DOCSIS options inserted by a CMTS that acts as a DHCPv6 relay
       agent in cable networks. This method attempts to extract MAC address
       information from suboption 1026 (cm mac) of the vendor specific option
       with vendor-id=4491. This vendor option is extracted from the
       relay-forward message, not the original client's message.
     * docsis-modem - Yet another possible source of MAC address information
       are the DOCSIS options inserted by the cable modem itself. This method
       attempts to extract MAC address information from suboption 36 (device
       id) of the vendor specific option with vendor-id=4491. This vendor
       option is extracted from the original client's message, not from any
       relay options.

   Empty mac-sources is not allowed. If you do not want to specify it, either
   simply omit mac-sources definition or specify it with the "any" value
   which is the default.

9.11. Duplicate Addresses (DECLINE Support)

   The DHCPv6 server is configured with a certain pool of addresses that it
   is expected to hand out to the DHCPv6 clients. It is assumed that the
   server is authoritative and has complete jurisdiction over those
   addresses. However, due to various reasons, such as misconfiguration or a
   faulty client implementation that retains its address beyond the valid
   lifetime, there may be devices connected that use those addresses without
   the server's approval or knowledge.

   Such an unwelcome event can be detected by legitimate clients (using
   Duplicate Address Detection) and reported to the DHCPv6 server using a
   DECLINE message. The server will do a sanity check (if the client
   declining an address really was supposed to use it), then will conduct a
   clean up operation and confirm it by sending back a REPLY message. Any DNS
   entries related to that address will be removed, the fact will be logged
   and hooks will be triggered. After that is done, the address will be
   marked as declined (which indicates that it is used by an unknown entity
   and thus not available for assignment to anyone) and a probation time will
   be set on it. Unless otherwise configured, the probation period lasts 24
   hours. After that period, the server will recover the lease (i.e. put it
   back into the available state) and the address will be available for
   assignment again. It should be noted that if the underlying issue of a
   misconfigured device is not resolved, the duplicate address scenario will
   repeat. On the other hand, it provides an opportunity to recover from such
   an event automatically, without any sysadmin intervention.

   To configure the decline probation period to a value other than the
   default, the following syntax can be used:

   "Dhcp6": {
     "decline-probation-period": 3600,
     "subnet6": [ ... ],
     ...
 }

   The parameter is expressed in seconds, so the example above will instruct
   the server to recycle declined leases after an hour.

   There are several statistics and hook points associated with the Decline
   handling procedure. The lease6_decline hook is triggered after the
   incoming Decline message has been sanitized and the server is about to
   decline the lease. The declined-addresses statistic is increased after the
   hook returns (both global and subnet specific variants). (See Section 8.8,
   "Statistics in the DHCPv4 Server" and Chapter 15, Hooks Libraries for more
   details on DHCPv4 statistics and Kea hook points.)

   Once the probation time elapses, the declined lease is recovered using the
   standard expired lease reclamation procedure, with several additional
   steps. In particular, both declined-addresses statistics (global and
   subnet specific) are decreased. At the same time,
   reclaimed-declined-addresses statistics (again in two variants, global and
   subnet specific) are increased.

   Note about statistics: The server does not decrease the assigned-addresses
   statistics when a DECLINE message is received and processed successfully.
   While technically a declined address is no longer assigned, the primary
   usage of the assigned-addresses statistic is to monitor pool utilization.
   Most people would forget to include declined-addresses in the calculation,
   and simply do assigned-addresses/total-addresses. This would have a bias
   towards under-representing pool utilization. As this has a potential for
   major issues, we decided not to decrease assigned addresses immediately
   after receiving Decline, but to do it later when we recover the address
   back to the available pool.

9.12. Statistics in the DHCPv6 Server

  Note

   This section describes DHCPv6-specific statistics. For a general overview
   and usage of statistics, see Chapter 16, Statistics.

   The DHCPv6 server supports the following statistics:

   Table 9.4. DHCPv6 Statistics

  +----------------------------------------------------------------------------+
  |               Statistic               |Data Type|Description               |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of DHCPv6 packets  |
  |                                       |         |received. This includes   |
  |             pkt6-received             | integer |all packets: valid, bogus,|
  |                                       |         |corrupted, rejected etc.  |
  |                                       |         |This statistic is expected|
  |                                       |         |to grow rapidly.          |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of incoming packets|
  |                                       |         |that were dropped. The    |
  |                                       |         |exact reason for dropping |
  |                                       |         |packets is logged, but the|
  |                                       |         |most common reasons may   |
  |                                       |         |be: an unacceptable or not|
  |           pkt6-receive-drop           | integer |supported packet type,    |
  |                                       |         |direct responses are      |
  |                                       |         |forbidden, the server-id  |
  |                                       |         |sent by the client does   |
  |                                       |         |not match the server's    |
  |                                       |         |server-id or the packet is|
  |                                       |         |malformed.                |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of incoming packets|
  |                                       |         |that could not be parsed. |
  |                                       |         |A non-zero value of this  |
  |                                       |         |statistic indicates that  |
  |                                       |         |the server received a     |
  |           pkt6-parse-failed           | integer |malformed or truncated    |
  |                                       |         |packet. This may indicate |
  |                                       |         |problems in your network, |
  |                                       |         |faulty clients, faulty    |
  |                                       |         |relay agents or a bug in  |
  |                                       |         |the server.               |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of SOLICIT packets |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to grow. Its  |
  |                                       |         |increase means that       |
  |         pkt6-solicit-received         | integer |clients that just booted  |
  |                                       |         |started their             |
  |                                       |         |configuration process and |
  |                                       |         |their initial packets     |
  |                                       |         |reached your server.      |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of ADVERTISE       |
  |                                       |         |packets received.         |
  |                                       |         |Advertise packets are sent|
  |                                       |         |by the server and the     |
  |                                       |         |server is never expected  |
  |                                       |         |to receive them. A        |
  |                                       |         |non-zero value of this    |
  |        pkt6-advertise-received        | integer |statistic indicates an    |
  |                                       |         |error occurring in the    |
  |                                       |         |network. One likely cause |
  |                                       |         |would be a misbehaving    |
  |                                       |         |relay agent that          |
  |                                       |         |incorrectly forwards      |
  |                                       |         |ADVERTISE messages towards|
  |                                       |         |the server rather back to |
  |                                       |         |the clients.              |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of REQUEST packets |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to grow. Its  |
  |                                       |         |increase means that       |
  |         pkt6-request-received         | integer |clients that just booted  |
  |                                       |         |received the server's     |
  |                                       |         |response (ADVERTISE),     |
  |                                       |         |accepted it and are now   |
  |                                       |         |requesting an address     |
  |                                       |         |(REQUEST).                |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of REPLY packets   |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to remain zero|
  |                                       |         |at all times, as REPLY    |
  |                                       |         |packets are sent by the   |
  |                                       |         |server and the server is  |
  |                                       |         |never expected to receive |
  |          pkt6-reply-received          | integer |them. A non-zero value    |
  |                                       |         |indicates an error. One   |
  |                                       |         |likely cause would be a   |
  |                                       |         |misbehaving relay agent   |
  |                                       |         |that incorrectly forwards |
  |                                       |         |REPLY messages towards the|
  |                                       |         |server, rather back to the|
  |                                       |         |clients.                  |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of RENEW packets   |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to grow. Its  |
  |          pkt6-renew-received          | integer |increase means that       |
  |                                       |         |clients received their    |
  |                                       |         |addresses and prefixes and|
  |                                       |         |are trying to renew them. |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of REBIND packets  |
  |                                       |         |received. A non-zero value|
  |                                       |         |indicates that clients    |
  |                                       |         |didn't receive responses  |
  |                                       |         |to their RENEW messages   |
  |                                       |         |(regular lease renewal    |
  |         pkt6-rebind-received          | integer |mechanism) and are        |
  |                                       |         |attempting to find any    |
  |                                       |         |server that is able to    |
  |                                       |         |take over their leases. It|
  |                                       |         |may mean that some        |
  |                                       |         |server's REPLY messages   |
  |                                       |         |never reached the clients.|
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of RELEASE packets |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to grow when a|
  |                                       |         |device is being shut down |
  |                                       |         |in the network. It        |
  |                                       |         |indicates that the address|
  |                                       |         |or prefix assigned is     |
  |         pkt6-release-received         | integer |reported as no longer     |
  |                                       |         |needed. Note that many    |
  |                                       |         |devices, especially       |
  |                                       |         |wireless, do not send     |
  |                                       |         |RELEASE packets either    |
  |                                       |         |because of design choice  |
  |                                       |         |or due to the client      |
  |                                       |         |moving out of range.      |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of DECLINE packets |
  |                                       |         |received. This statistic  |
  |                                       |         |is expected to remain     |
  |                                       |         |close to zero. Its        |
  |                                       |         |increase means that a     |
  |                                       |         |client leased an address, |
  |                                       |         |but discovered that the   |
  |         pkt6-decline-received         | integer |address is currently used |
  |                                       |         |by an unknown device in   |
  |                                       |         |your network. If this     |
  |                                       |         |statistic is growing, it  |
  |                                       |         |may indicate a            |
  |                                       |         |misconfigured server or   |
  |                                       |         |devices that have         |
  |                                       |         |statically assigned       |
  |                                       |         |conflicting addresses.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of                 |
  |                                       |         |INFORMATION-REQUEST       |
  |                                       |         |packets received. This    |
  |                                       |         |statistic is expected to  |
  |                                       |         |grow if there are devices |
  |                                       |         |that are using stateless  |
  |       pkt6-infrequest-received        | integer |DHCPv6.                   |
  |                                       |         |INFORMATION-REQUEST       |
  |                                       |         |messages are used by      |
  |                                       |         |clients that request      |
  |                                       |         |stateless configuration,  |
  |                                       |         |i.e. options and          |
  |                                       |         |parameters other than     |
  |                                       |         |addresses or prefixes.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of DHCPv4-QUERY    |
  |                                       |         |packets received. This    |
  |                                       |         |statistic is expected to  |
  |                                       |         |grow if there are devices |
  |                                       |         |that are using            |
  |      pkt6-dhcpv4-query-received       | integer |DHCPv4-over-DHCPv6.       |
  |                                       |         |DHCPv4-QUERY messages are |
  |                                       |         |used by DHCPv4 clients on |
  |                                       |         |an IPv6 only line which   |
  |                                       |         |encapsulates the requests |
  |                                       |         |over DHCPv6.              |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of DHCPv4-RESPONSE |
  |                                       |         |packets received. This    |
  |                                       |         |statistic is expected to  |
  |                                       |         |remain zero at all times, |
  |                                       |         |as DHCPv4-RESPONSE packets|
  |                                       |         |are sent by the server and|
  |                                       |         |the server is never       |
  |     pkt6-dhcpv4-response-received     | integer |expected to receive them. |
  |                                       |         |A non-zero value indicates|
  |                                       |         |an error. One likely cause|
  |                                       |         |would be a misbehaving    |
  |                                       |         |relay agent that          |
  |                                       |         |incorrectly forwards      |
  |                                       |         |DHCPv4-RESPONSE message   |
  |                                       |         |towards the server rather |
  |                                       |         |back to the clients.      |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of packets received|
  |                                       |         |of an unknown type. A     |
  |                                       |         |non-zero value of this    |
  |                                       |         |statistic indicates that  |
  |         pkt6-unknown-received         | integer |the server received a     |
  |                                       |         |packet that it wasn't able|
  |                                       |         |to recognize: either it   |
  |                                       |         |had an unsupported type or|
  |                                       |         |was possibly malformed.   |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of DHCPv6 packets  |
  |                                       |         |sent. This statistic is   |
  |                                       |         |expected to grow every    |
  |                                       |         |time the server transmits |
  |                                       |         |a packet. In general, it  |
  |                                       |         |should roughly match      |
  |                                       |         |pkt6-received, as most    |
  |               pkt6-sent               | integer |incoming packets cause the|
  |                                       |         |server to respond. There  |
  |                                       |         |are exceptions (e.g.      |
  |                                       |         |server receiving a REQUEST|
  |                                       |         |with server-id matching   |
  |                                       |         |other server), so do not  |
  |                                       |         |worry, if it is lesser    |
  |                                       |         |than pkt6-received.       |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of ADVERTISE       |
  |                                       |         |packets sent. This        |
  |                                       |         |statistic is expected to  |
  |                                       |         |grow in most cases after a|
  |                                       |         |SOLICIT is processed.     |
  |          pkt6-advertise-sent          | integer |There are certain         |
  |                                       |         |uncommon, but valid cases |
  |                                       |         |where incoming SOLICIT is |
  |                                       |         |dropped, but in general   |
  |                                       |         |this statistic is expected|
  |                                       |         |to be close to            |
  |                                       |         |pkt6-solicit-received.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of REPLY packets   |
  |                                       |         |sent. This statistic is   |
  |                                       |         |expected to grow in most  |
  |                                       |         |cases after a SOLICIT     |
  |                                       |         |(with rapid-commit),      |
  |            pkt6-reply-sent            | integer |REQUEST, RENEW, REBIND,   |
  |                                       |         |RELEASE, DECLINE or       |
  |                                       |         |INFORMATION-REQUEST is    |
  |                                       |         |processed. There are      |
  |                                       |         |certain cases where there |
  |                                       |         |is no response.           |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |Number of DHCPv4-RESPONSE |
  |                                       |         |packets sent. This        |
  |                                       |         |statistic is expected to  |
  |       pkt6-dhcpv4-response-sent       | integer |grow in most cases after a|
  |                                       |         |DHCPv4-QUERY is processed.|
  |                                       |         |There are certain cases   |
  |                                       |         |where there is no         |
  |                                       |         |response.                 |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |total number of NA        |
  |                                       |         |addresses available for   |
  |                                       |         |DHCPv6 management for a   |
  |                                       |         |given subnet. In other    |
  |                                       |         |words, this is the sum of |
  |                                       |         |all addresses in all      |
  |                                       |         |configured pools. This    |
  |                                       |         |statistic changes only    |
  |                                       |         |during configuration      |
  |         subnet[id].total-nas          | integer |changes. Note that it does|
  |                                       |         |not take into account any |
  |                                       |         |addresses that may be     |
  |                                       |         |reserved due to host      |
  |                                       |         |reservation. The id is the|
  |                                       |         |subnet-id of a given      |
  |                                       |         |subnet. This statistic is |
  |                                       |         |exposed for each subnet   |
  |                                       |         |separately and is reset   |
  |                                       |         |during a reconfiguration  |
  |                                       |         |event.                    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of NA addresses in |
  |                                       |         |a given subnet that are   |
  |                                       |         |assigned. This statistic  |
  |                                       |         |increases every time a new|
  |                                       |         |lease is allocated (as a  |
  |                                       |         |result of receiving a     |
  |                                       |         |REQUEST message) and is   |
  |        subnet[id].assigned-nas        | integer |decreased every time a    |
  |                                       |         |lease is released (a      |
  |                                       |         |RELEASE message is        |
  |                                       |         |received) or expires. The |
  |                                       |         |id is the subnet-id of a  |
  |                                       |         |given subnet. This        |
  |                                       |         |statistic is exposed for  |
  |                                       |         |each subnet separately and|
  |                                       |         |is reset during a         |
  |                                       |         |reconfiguration event.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |total number of PD        |
  |                                       |         |prefixes available for    |
  |                                       |         |DHCPv6 management for a   |
  |                                       |         |given subnet. In other    |
  |                                       |         |words, this is the sum of |
  |                                       |         |all prefixes in all       |
  |                                       |         |configured pools. This    |
  |                                       |         |statistic changes only    |
  |                                       |         |during configuration      |
  |         subnet[id].total-pds          | integer |changes. Note it does not |
  |                                       |         |take into account any     |
  |                                       |         |prefixes that may be      |
  |                                       |         |reserved due to host      |
  |                                       |         |reservation. The id is the|
  |                                       |         |subnet-id of a given      |
  |                                       |         |subnet. This statistic is |
  |                                       |         |exposed for each subnet   |
  |                                       |         |separately and is reset   |
  |                                       |         |during a reconfiguration  |
  |                                       |         |event.                    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of PD prefixes in a|
  |                                       |         |given subnet that are     |
  |                                       |         |assigned. This statistic  |
  |                                       |         |increases every time a new|
  |                                       |         |lease is allocated (as a  |
  |                                       |         |result of receiving a     |
  |                                       |         |REQUEST message) and is   |
  |        subnet[id].assigned-pds        | integer |decreased every time a    |
  |                                       |         |lease is released (a      |
  |                                       |         |RELEASE message is        |
  |                                       |         |received) or expires. The |
  |                                       |         |id is the subnet-id of a  |
  |                                       |         |given subnet. This        |
  |                                       |         |statistic is exposed for  |
  |                                       |         |each subnet separately and|
  |                                       |         |is reset during a         |
  |                                       |         |reconfiguration event.    |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic is the     |
  |                                       |         |number of expired leases  |
  |                                       |         |that have been reclaimed  |
  |                                       |         |since server startup. It  |
  |           reclaimed-leases            | integer |is incremented each time  |
  |                                       |         |an expired lease is       |
  |                                       |         |reclaimed (it counts both |
  |                                       |         |NA and PD reclamations)   |
  |                                       |         |and is reset when the     |
  |                                       |         |server is reconfigured.   |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic is the     |
  |                                       |         |number of expired leases  |
  |                                       |         |associated with a given   |
  |                                       |         |subnet ("id" is the       |
  |                                       |         |subnet-id) that have been |
  |                                       |         |reclaimed since server    |
  |      subnet[id].reclaimed-leases      | integer |startup. It is incremented|
  |                                       |         |each time an expired lease|
  |                                       |         |is reclaimed (it counts   |
  |                                       |         |both NA and PD            |
  |                                       |         |reclamations) and is reset|
  |                                       |         |when the server is        |
  |                                       |         |reconfigured.             |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of IPv6 addresses  |
  |                                       |         |that are currently        |
  |                                       |         |declined and so counts the|
  |                                       |         |number of leases currently|
  |                                       |         |unavailable. Once a lease |
  |                                       |         |is recovered, this        |
  |                                       |         |statistic will be         |
  |                                       |         |decreased. Ideally, this  |
  |          declined-addresses           | integer |statistic should be zero. |
  |                                       |         |If this statistic is      |
  |                                       |         |non-zero (or worse,       |
  |                                       |         |increasing), the network  |
  |                                       |         |administrator should      |
  |                                       |         |investigate if there is a |
  |                                       |         |misbehaving device in the |
  |                                       |         |network. This is a global |
  |                                       |         |statistic that covers all |
  |                                       |         |subnets.                  |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of IPv6 addresses  |
  |                                       |         |that are currently        |
  |                                       |         |declined in a given       |
  |                                       |         |subnet. This statistic    |
  |                                       |         |counts the number of      |
  |                                       |         |leases currently          |
  |                                       |         |unavailable. Once a lease |
  |                                       |         |is recovered, this        |
  |                                       |         |statistic will be         |
  |                                       |         |decreased. Ideally, this  |
  |     subnet[id].declined-addresses     | integer |statistic should be zero. |
  |                                       |         |If this statistic is      |
  |                                       |         |non-zero (or worse,       |
  |                                       |         |increasing), a network    |
  |                                       |         |administrator should      |
  |                                       |         |investigate if there is a |
  |                                       |         |misbehaving device in the |
  |                                       |         |network. The id is the    |
  |                                       |         |subnet-id of a given      |
  |                                       |         |subnet. This statistic is |
  |                                       |         |exposed for each subnet   |
  |                                       |         |separately.               |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of IPv6 addresses  |
  |                                       |         |that were declined, but   |
  |                                       |         |have now been recovered.  |
  |                                       |         |Unlike declined-addresses,|
  |                                       |         |this statistic never      |
  |     reclaimed-declined-addresses      | integer |decreases. It can be used |
  |                                       |         |as a long term indicator  |
  |                                       |         |of how many actual valid  |
  |                                       |         |Declines were processed   |
  |                                       |         |and recovered from. This  |
  |                                       |         |is a global statistic that|
  |                                       |         |covers all subnets.       |
  |---------------------------------------+---------+--------------------------|
  |                                       |         |This statistic shows the  |
  |                                       |         |number of IPv6 addresses  |
  |                                       |         |that were declined, but   |
  |                                       |         |have now been recovered.  |
  |                                       |         |Unlike declined-addresses,|
  |                                       |         |this statistic never      |
  |                                       |         |decreases. It can be used |
  |subnet[id].reclaimed-declined-addresses| integer |as a long term indicator  |
  |                                       |         |of how many actual valid  |
  |                                       |         |Declines were processed   |
  |                                       |         |and recovered from. The id|
  |                                       |         |is the subnet-id of a     |
  |                                       |         |given subnet. This        |
  |                                       |         |statistic is exposed for  |
  |                                       |         |each subnet separately.   |
  +----------------------------------------------------------------------------+

9.13. Management API for the DHCPv6 Server

   The management API allows the issuing of specific management commands,
   such as statistics retrieval, reconfiguration or shutdown. For more
   details, see Chapter 17, Management API. Currently the only supported
   communication channel type is UNIX stream socket. By default there are no
   sockets open. To instruct Kea to open a socket, the following entry in the
   configuration file can be used:

 "Dhcp6": {
     "control-socket": {
         "socket-type": "unix",
         "socket-name": "/path/to/the/unix/socket"
     },

     "subnet6": [
         ...
     ],
     ...
 }

   The length of the path specified by the socket-name parameter is
   restricted by the maximum length for the unix socket name on your
   operating system, i.e. the size of the sun_path field in the sockaddr_un
   structure, decreased by 1. This value varies on different operating
   systems between 91 and 107 characters. Typical values are 107 on Linux and
   103 on FreeBSD.

   Communication over control channel is conducted using JSON structures. See
   the Control Channel section in the Kea Developer's Guide for more details.

   The DHCPv6 server supports the following operational commands:

     * build-report
     * config-get
     * config-reload
     * config-set
     * config-test
     * config-write
     * dhcp-disable
     * dhcp-enable
     * leases-reclaim
     * list-commands
     * shutdown
     * version-get

   as described in Section 17.3, "Commands Supported by Both the DHCPv4 and
   DHCPv6 Servers". In addition, it supports the following statistics related
   commands:

     * statistic-get
     * statistic-reset
     * statistic-remove
     * statistic-get-all
     * statistic-reset-all
     * statistic-remove-all

   as described here Section 16.3, "Commands for Manipulating Statistics".

9.14. User contexts in IPv6

   Kea allows loading hook libraries that sometimes could benefit from
   additional parameters. If such a parameter is specific to the whole
   library, it is typically defined as a parameter for the hook library.
   However, sometimes there is a need to specify parameters that are
   different for each pool.

   User contexts can store arbitrary data as long as it is valid JSON syntax
   and its top level element is a map (i.e. the data must be enclosed in
   curly brackets). Some hook libraries may expect specific formatting,
   though. Please consult specific hook library documentation for details.

   User contexts can be specified at either global scope, shared network,
   subnet, pool, client class, option data or definition level, and host
   reservation. One other useful usage is the ability to store comments or
   descriptions.

   Let's consider a lightweight 4over6 deployment as an example. It is an
   IPv6 transition technology that allows mapping IPv6 prefix into full or
   parts of IPv4 addresses. In DHCP context, these are certain parameters
   that are supposed to be delivered to clients in form of additional
   options. Values of those options are correlated to delegated prefixes, so
   it is reasonable to keep those parameters together with the PD pool. On
   the other hand, lightweight 4over6 is not a commonly used feature, so it
   is not a part of the base Kea code. The solution to this problem is to use
   user context. For each PD pool that is expected to be used for lightweight
   4over6, user context with extra parameters is defined. Those extra
   parameters will be used by hook library that would be loaded only when
   dynamic calculation of the lightweight 4over6 option is actually needed.
   An example configuration looks as follows:

 "Dhcp6": {
     "subnet6": [ {
         "pd-pools": [
         {
             "prefix":  "2001:db8::",
             "prefix-len": 56,
             "delegated-len": 64,

             // This is a pool specific context.
             "user-context": {
                 "threshold-percent": 85,
                 "v4-network": "192.168.0.0/16",
                 "v4-overflow": "10.0.0.0/16",
                 "lw4over6-sharing-ratio": 64,
                 "lw4over6-v4-pool": "192.0.2.0/24",
                 "lw4over6-sysports-exclude": true,
                 "lw4over6-bind-prefix-len": 56
             }
         } ],
         "subnet": "2001:db8::/32",

         // This is a subnet specific context. You can put any type of
         // information here as long as it is a valid JSON.
         "user-context": {
             "comment": "Those v4-v6 migration technologies are tricky.",
             "experimental": true,
             "billing-department": 42,
             "contact-points": [ "Alice", "Bob" ]
         }
     } ],
     ...
 }

   Kea does not interpret or use the content of the user context: it just
   stores it, making it available to the hook libraries. It is up to each
   hook library to extract the information and make use of it. The parser
   translates a "comment" entry into a user-context with the entry, this
   allows to attach a comment inside the configuration itself.

   For more background information, see Section 15.5, "User contexts".

9.15. Supported DHCPv6 Standards

   The following standards are currently supported:

     * Dynamic Host Configuration Protocol for IPv6, RFC 3315: Supported
       messages are SOLICIT, ADVERTISE, REQUEST, RELEASE, RENEW, REBIND,
       INFORMATION-REQUEST, CONFIRM and REPLY.
     * IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP)
       version 6, RFC 3633: Supported options are IA_PD and IA_PREFIX. Also
       supported is the status code NoPrefixAvail.
     * DNS Configuration options for Dynamic Host Configuration Protocol for
       IPv6 (DHCPv6), RFC 3646: Supported option is DNS_SERVERS.
     * The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent
       Remote-ID Option, RFC 4649: REMOTE-ID option is supported.
     * The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client Fully
       Qualified Domain Name (FQDN) Option, RFC 4704: Supported option is
       CLIENT_FQDN.
     * Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Option for
       Dual-Stack Lite, RFC 6334: the AFTR-Name DHCPv6 Option is supported.
     * Relay-Supplied DHCP Options, RFC 6422: Full functionality is
       supported: OPTION_RSOO, ability of the server to echo back the
       options, checks whether an option is RSOO-enabled, ability to mark
       additional options as RSOO-enabled.
     * Prefix Exclude Option for DHCPv6-based Prefix Delegation, RFC 6603:
       Prefix Exclude option is supported.
     * Client Link-Layer Address Option in DHCPv6, RFC 6939: Supported option
       is client link-layer address option.
     * Issues and Recommendations with Multiple Stateful DHCPv6 Options, RFC
       7550: All recommendations related to the DHCPv6 server operation are
       supported.
     * DHCPv6 Options for Configuration of Softwire Address and Port-Mapped
       Clients, RFC 7598: All options specified in this specification are
       supported by the DHCPv6 server.
     * Dynamic Host Configuration Protocol for IPv6 (DHCPv6), RFC 8415: New
       DHCPv6 protocol specification which obsoletes RFC 3315, RFC 3633, RFC
       3736, RFC 4242, RFC 7083, RFC 7283 and RFC 7550

9.16. DHCPv6 Server Limitations

   These are the current limitations of the DHCPv6 server software. Most of
   them are reflections of the early stage of development and should be
   treated as "not implemented yet", rather than actual limitations.

     * The server will allocate, renew or rebind a maximum of one lease for a
       particular IA option (IA_NA or IA_PD) sent by a client. RFC 8415
       allows for multiple addresses or prefixes to be allocated for a single
       IA.
     * Temporary addresses are not supported.
     * Client reconfiguration (RECONFIGURE) is not yet supported.

9.17. Kea DHCPv6 server examples

   A collection of simple to use examples for DHCPv6 component of Kea is
   available with the sources. It is located in doc/examples/kea6 directory.
   At the time of writing this text there were 18 examples, but the number is
   growing slowly with each release.

               Chapter 10. Lease Expiration in DHCPv4 and DHCPv6

   Table of Contents

   10.1. Lease Reclamation

   10.2. Configuring Lease Reclamation

   10.3. Configuring Lease Affinity

   10.4. Default Configuration Values for Leases Reclamation

   10.5. Reclaiming Expired Leases with Command

   The primary role of the DHCP server is to assign addresses and/or delegate
   prefixes to DHCP clients. These addresses and prefixes are often referred
   to as "leases". Leases are typically assigned to clients for a finite
   amount of time, known as the "valid lifetime". DHCP clients who wish to
   continue using their assigned leases, will periodically renew them by
   sending the appropriate message to the DHCP server. The DHCP server
   records the time when these leases are renewed and calculates new
   expiration times for them.

   If the client does not renew a lease before its valid lifetime elapses,
   the lease is considered expired. There are many situations when the client
   may cease lease renewals. A common scenario is when the machine running
   the client shuts down for an extended period of time.

   The process through which the DHCP server makes expired leases available
   for reassignment is referred to as "lease reclamation" and expired leases
   returned to availability through this process are referred to as
   "reclaimed". The DHCP server attempts to reclaim an expired lease as soon
   as it detects that it has expired. One way in which the server detects
   expiration occurs when it is trying to allocate a lease to a client and
   finds this lease already present in the database but expired. Another way
   is by periodically querying the lease database for them. Regardless of how
   an expired lease is detected, before it may assigned to a client, it must
   be reclaimed.

   This chapter explains how to configure the server to periodically query
   for the expired leases and how to minimize the impact of the periodic
   lease reclamation process on the server's responsiveness. Finally, it
   explains "lease affinity", which provides the means to assign the same
   lease to a returning client after its lease has expired.

   Although, all configuration examples in this section are provided for the
   DHCPv4 server, the same parameters may be used for the DHCPv6 server
   configuration.

10.1. Lease Reclamation

   Lease reclamation is the process through which an expired lease becomes
   available for assignment to the same or different client. This process
   involves the following steps for each reclaimed lease:

     * Invoke callouts for the lease4_expire or lease6_expire hook points if
       hook libraries supporting those callouts are currently loaded.
     * Update DNS, i.e. remove any DNS entries associated with the expired
       lease.
     * Update lease information in the lease database to indicate that the
       lease is now available for re-assignment.
     * Update counters on the server, which includes increasing the number of
       reclaimed leases and decreasing the number of assigned addresses or
       delegated prefixes.

   Please refer to Chapter 12, The DHCP-DDNS Server to see how to configure
   DNS updates in Kea, and to Chapter 15, Hooks Libraries for information
   about using hooks libraries.

10.2. Configuring Lease Reclamation

   Kea can be configured to periodically detect and reclaim expired leases.
   During this process the lease entries in the database are modified or
   removed. While this is happening the server will not process incoming DHCP
   messages to avoid issues with concurrent access to database information.
   As a result, the server will be unresponsive while lease reclamation is
   performed and DHCP queries will accumulate; responses will be sent once
   the leases reclamation cycle is complete.

   In deployments where response time is critical, administrators may wish to
   minimize the interruptions in service caused by lease reclamation. Toward
   this end, Kea provides configuration parameters to control: the frequency
   of lease reclamation cycles, the maximum number of leases processed in a
   single reclamation cycle, and the maximum amount of time a single
   reclamation cycle is allowed to run before being interrupted. The
   following examples demonstrate how these parameters can be used:

 "Dhcp4": {
     ...

     "expired-leases-processing": {
         "reclaim-timer-wait-time": 5,
         "max-reclaim-leases": 0,
         "max-reclaim-time": 0,
         "flush-reclaimed-timer-wait-time": 0,
     },

     ...
 }

   The first parameter is expressed in seconds and specifies an interval
   between the two consecutive lease reclamation cycles. This is explained by
   the following diagram.


 |  c1  |            | c2 |            |c3|            | c4 |
 |<---->|<---------->|<-->|<---------->|<>|<---------->|<-->|
 ---------------------------------------------------------------->
 |      |     5s     |    |     5s     |  |     5s     |    | time


   This diagram shows four lease reclamation cycles (c1 through c4) of
   variable duration. Note that the duration of the reclamation cycle depends
   on the number of expired leases detected and processed in the particular
   cycle. This duration is also usually significantly shorter than the
   interval between the cycles.

   According to the reclaim-timer-wait-time the server keeps fixed intervals
   of five seconds between the end of one cycle and the start of the next
   cycle. This guarantees the presence of 5s long periods during which the
   server remains responsive to DHCP queries and does not perform lease
   reclamation. The max-reclaim-leases and max-reclaim-time are set to 0,
   which sets no restriction on the maximum number of leases reclaimed in the
   particular cycle, or on the maximum duration of each cycle.

   In deployments with high lease pool utilization, relatively short valid
   lifetimes, and frequently disconnecting clients which allow leases to
   expire, the number of expired leases requiring reclamation at any given
   time may rise significantly. In this case it is often desirable to apply
   restrictions on the maximum duration of a reclamation cycle or the maximum
   number of leases reclaimed in a cycle. The following configuration
   demonstrates how this can be done:

 "Dhcp4": {
     ...

     "expired-leases-processing": {
         "reclaim-timer-wait-time": 3,
         "max-reclaim-leases": 100,
         "max-reclaim-time": 50,
         "unwarned-reclaim-cycles": 10,
     },

     ...
 }


   The max-reclaim-leases parameter limits the number of leases reclaimed in
   a single cycle to 100. The max-reclaim-time limits the maximum duration of
   each cycle to 50ms. The lease reclamation cycle will be interrupted if
   either of these limitations is reached. The reclamation of all unreclaimed
   leases will be attempted in subsequent cycles.

   The following diagram illustrates the behavior of the system in the
   presence of many expired leases, when the limits are applied for the
   reclamation cycles.


 | c1 |                | c2 |                | c3 |                | c4 |
 |<-->|<-------------->|<-->|<-------------->|<-->|<-------------->|<-->|<--
 ------------------------------------------------------------------------------>
 |50ms|       3s       |50ms|       3s       |50ms|       3s       |50ms|  time


   The diagram demonstrates the case when each reclamation cycle would take
   more than 50ms, and thus is interrupted according to the value of the
   max-reclaim-time. This results in equal durations of all reclamation
   cycles over time. Note that in this example the limitation of maximum 100
   leases is not reached. This may be the case when database transactions are
   slow or callouts in the hook libraries attached to the server are slow.
   Regardless, the choosing values for either the maximum number of leases or
   a maximum cycle time strongly depends on the particular deployment, lease
   database backend being used, and any hooks libraries etc. Administrators
   may need to experiment to tune the system to suit the dynamics of their
   deployment.

   It is important to realize that with the use of these limits, there is a
   risk that expired leases will accumulate faster than the server can
   reclaim them. This should not be the problem if the server is dealing with
   a temporary burst of expirations, because it should be able to eventually
   deal with them over time. However, if leases expire at a high rate for a
   longer period of time, the unreclaimed leases will pile up in the
   database. In order to notify the administrator that the current
   configuration does not satisfy the needs for reclamation of expired
   leases, the server issues a warning message in the log if it was unable to
   reclaim all leases within the last couple of reclamation cycles. The
   number of cycles after which such warning is issued is specified with the
   unwarned-reclaim-cycles configuration parameter.

   Setting the reclaim-timer-wait-time to 0 disables periodic reclamation of
   the expired leases.

10.3. Configuring Lease Affinity

   Suppose that a laptop goes to a sleep mode after a period of user
   inactivity. While the laptop is in sleep mode, its DHCP client will not
   renew leases obtained from the server and these leases will eventually
   expire. When the laptop wakes up, it is often desirable for it to continue
   using its previous assigned IP addresses. In order to facilitate this, the
   server needs to correlate returning clients with their expired leases When
   the client returns, the server will first check for those leases and
   re-assign them if they have not been assigned to another client. The
   ability of the server to re-assign the same lease to a returning client is
   referred to as "lease affinity".

   When lease affinity is enabled, the server will still reclaim leases
   according to the parameters described in Section 10.2, "Configuring Lease
   Reclamation", but the reclaimed leases will be held in the database
   (rather than removed) for the specified amount of time. When the client
   returns, the server will first check if there are any reclaimed leases
   associated with this client and re-assign them if possible. However, it is
   important to note that any reclaimed lease may be assigned to another
   client if that client specifically asks for it. Therefore, the lease
   affinity does not guarantee that the reclaimed lease will be available for
   the client who used it before; it merely increases the chances for the
   client to be assigned the same lease. If the lease pool is small (this
   mostly applies to DHCPv4 for which address space is small), there is an
   increased likelihood that the expired lease will be assigned to another
   client.

   Consider the following configuration:

 "Dhcp4": {
     ...

     "expired-leases-processing": {
         "reclaim-timer-wait-time": 3,
         "hold-reclaimed-time": 1800,
         "flush-reclaimed-timer-wait-time": 5
     },

     ...
 }

   The hold-reclaim-time specifies how many seconds after an expiration a
   reclaimed lease should be held in the database for re-assignment to the
   same client. In the example given above, reclaimed leases will be held for
   30 minutes (1800s) after their expiration. During this time, the server
   will likely be able to re-assign the same lease to the returning client,
   unless another client requests this lease and the server assigns it.

   The server must periodically remove reclaimed leases for which the time
   indicated by hold-reclaim-time has elapsed. The
   flush-reclaimed-timer-wait-time controls how often the server removes such
   leases. In the example provided above, the server will initiate removal of
   such leases 5 seconds after the previous removal attempt was completed.
   Setting this value to 0 disables lease affinity, in which case leases will
   be removed from the lease database when they are reclaimed. If lease
   affinity is enabled, it is recommended that hold-reclaim-time be set to a
   value significantly higher than the reclaim-timer-wait-time, as timely
   removal of expired-reclaimed leases is less critical while the removal
   process may impact server responsiveness.

10.4. Default Configuration Values for Leases Reclamation

   The following list presents all configuration parameters pertaining to
   processing expired leases with their default values:

     * reclaim-timer-wait-time = 10 [seconds]
     * flush-reclaimed-timer-wait-time = 25 [seconds]
     * hold-reclaimed-time = 3600 [seconds]
     * max-reclaim-leases = 100
     * max-reclaim-time = 250 [milliseconds]
     * unwarned-reclaim-cycles = 5

   The default value for any parameter is used when this parameter not
   explicitly specified in the configuration. Also, the
   expired-leases-processing map may be omitted entirely in the
   configuration, in which case the default values are used for all
   parameters listed above.

10.5. Reclaiming Expired Leases with Command

   The leases-reclaim command can be used to trigger leases reclamation at
   any time. Please consult the Section 17.3.6, "leases-reclaim" for the
   details about using this command.

              Chapter 11. Congestion Handling in DHCPv4 and DHCPv6

   Table of Contents

   11.1. What is Congestion?

   11.2. Configuring Congestion Handling

11.1. What is Congestion?

   Congestion occurs when servers are subjected to client queries faster than
   they can be fulfilled. Subsequently, the servers begin accumulating a
   backlog of pending queries. The longer the high rate of traffic continues
   the farther behind the servers fall. Depending on the client
   implementations, those that fail to get leases either give up or simply
   continue to retry forever. In the former case, the server may eventually
   recover. The latter case is vicious cycle from which the server is unable
   escape.

   In a well-planned deployment, the number and capacity of servers is
   matched to the maximum client loads expected. As long as capacity is
   matched to load, congestion does not occur. If the load is routinely too
   heavy, then the deployment needs to be re-evaluated. Congestion typically
   occurs when there is a network event that causes overly large numbers of
   clients to simultaneously need leases such as recovery after a network
   outage.

   The goal of Congestion handling is to help the servers mitigate the peak
   in traffic by fulfilling as many of the most relevant requests as possible
   until it subsides.

   Prior to Kea 1.5, kea-dhcp4 and kea-dhcp4 read inbound packets directly
   from the interface sockets in the main application thread. This meant that
   packets waiting to be processed were held in socket buffers themselves.
   Once these buffers fill any new packets are discarded. Under swamped
   conditions the servers can end up processing client packets that may no
   longer be relevant, or worse are redundant. In other words, the packets
   waiting in the FIFO socket buffers become increasingly stale.

11.2. Configuring Congestion Handling

   Kea 1.5 introduces a new feature referred to as Congestion Handling.
   Congestion handling offers the ability to configure the server to use a
   separate thread to read packets from the interface socket buffers. As the
   thread reads packets from the buffers they are added to an internal packet
   queue. The server's main application thread process packets from this
   queue rather than the socket buffers. By structuring it this way, we've
   introduced a configurable layer which can make decisions on which packets
   to process, how to store them, and the order in which they are processed
   by the server.

   The default packet queue implemenation for both kea-dhcp4 and kea-dhcp6 is
   a simple ring buffer. Once it reaches capacity, new packets get added to
   the back of queue by discarding packets from the front of queue. Rather
   than always discarding the newest packets, we now always discard the
   oldest packets. The capacity of the buffer, (i.e the maximum number of
   packets the buffer can contain) is configurable. A reasonable starting
   point would be to match the capacity to the number of leases per second
   your installation of Kea can handle. Please note this figure varies widely
   depending on the specifics of your deployment. We anticipate adding more
   knobs as we learn from experience, testing, and user feedback.

   As there is no one algorithm that will best handle the dynamics of all
   sites, and because over time new approaches will evolve, the packet queue
   is implemented as plug-in, which can replaced by a custom queue
   implementation via hook library. This should make it straight forward for
   interested parties to experiment with their own solutions. (Developers may
   refer to isc::dhcp::PacketQueue and isc::dhcp::PacketQueueMgr, in our
   Developer's guide).

   Packet queue behavior is configured in both kea-dhcp4 and kea-dhcp6
   servers through an optional, top level configuration element,
   'dhcp-queue-control' (Omitting this element disables packet queueing):

    "dhcp-queue-control": {
        "enable-queue": true|false,
        "queue-type": "queue type",
        "capacity" : n
    }

   where:

     * enable-queue true|false. Enables or disables packet queueing. When
       true, the server will process packets from the packet queue, which is
       filled by a separate thread. When false, the server will process
       packets directly from the socket buffers in the main thread (as done
       in all releases prior Kea 1.5). It is disabled by default.
     * queue-type name of the queue implementation to use. This value exists
       such that custom implementations can be registered (via hook lib) and
       then selected. There is a default packet queue implementation that is
       pre-registered during server start up: "kea-ring4" for kea-dhcp4 and
       "kea-ring6" for kea-dhcp6.
     * capacity = n [packets]. This is the maximum number of packets the
       packet queue can hold before packets are discarded. The optimal value
       for this is extremely site dependent. The default value for is 500 for
       both kea-ring4 and kea-ring6.

   The following example enables the default packet queue for kea-dhcp4, with
   a queue capacity of 250 packets:

 "Dhcp4":
 {
     ...
    "dhcp-queue-control": {
        "enable-queue": true,
        "queue-type": "kea-ring4",
        "capacity" : 250
     },
     ...
 }

   The following example enables the default packet queue for kea-dhcp6, with
   a queue capacity of 300 packets:

 "Dhcp6":
 {
     ...
    "dhcp-queue-control": {
        "enable-queue": true,
        "queue-type": "kea-ring6",
        "capacity" : 300
     },
     ...
 }

   The number of parameters and plug-ins is expected to grow over time.

                        Chapter 12. The DHCP-DDNS Server

   Table of Contents

   12.1. Overview

                12.1.1. DNS Server selection

                12.1.2. Conflict Resolution

                12.1.3. Dual Stack Environments

   12.2. Starting and Stopping the DHCP-DDNS Server

   12.3. Configuring the DHCP-DDNS Server

                12.3.1. Global Server Parameters

                12.3.2. TSIG Key List

                12.3.3. Forward DDNS

                12.3.4. Reverse DDNS

                12.3.5. User context in DDNS

                12.3.6. Example DHCP-DDNS Server Configuration

   12.4. DHCP-DDNS Server Limitations

12.1. Overview

   The DHCP-DDNS Server (kea-dhcp-ddns, known informally as D2) conducts the
   client side of the DDNS protocol (defined in RFC 2136) on behalf of the
   DHCPv4 and DHCPv6 servers (kea-dhcp4 and kea-dhcp6 respectively). The DHCP
   servers construct DDNS update requests, known as NameChangeRequests
   (NCRs), based upon DHCP lease change events and then post these to D2. D2
   attempts to match each such request to the appropriate DNS server(s) and
   carry out the necessary conversation with those servers to update the DNS
   data.

  12.1.1. DNS Server selection

   In order to match a request to the appropriate DNS servers, D2 must have a
   catalog of servers from which to select. In fact, D2 has two such
   catalogs, one for forward DNS and one for reverse DNS; these catalogs are
   referred to as DDNS Domain Lists. Each list consists of one or more named
   DDNS Domains. Further, each DDNS Domain has a list of one or more DNS
   servers that publish the DNS data for that domain.

   When conducting forward domain matching, D2 will compare the FQDN in the
   request against the name of each forward DDNS Domain. The domain whose
   name matches the longest portion of the FQDN is considered the best match.
   For example, if the FQDN is "myhost.sample.example.com.", and there are
   two forward domains in the catalog: "sample.example.com." and
   "example.com.", the former is regarded as the best match. In some cases,
   it may not be possible to find a suitable match. Given the same two
   forward domains there would be no match for the FQDN, "bogus.net", so the
   request would be rejected. Finally, if there are no forward DDNS Domains
   defined, D2 will simply disregard the forward update portion of requests.

   When conducting reverse domain matching, D2 constructs a reverse FQDN from
   the lease address in the request and compare that against the name of each
   reverse DDNS Domain. Again, the domain whose name matches the longest
   portion of the FQDN is considered the best match. For instance, if the
   lease address is "172.16.1.40" and there are two reverse domains in the
   catalog: "1.16.172.in-addr.arpa." and "16.172.in-addr.arpa", the former is
   the best match. As with forward matching, it is possible to not find a
   suitable match. Given the same two domains, there would be no match for
   the lease address, "192.168.1.50", and the request would be rejected.
   Finally, if there are no reverse DDNS Domains defined, D2 will simply
   disregard the reverse update portion of requests.

  12.1.2. Conflict Resolution

   D2 implements the conflict resolution strategy prescribed by RFC 4703.
   Conflict resolution is intended to prevent different clients from mapping
   to the same FQDN at the same time. To make this possible, the RFC requires
   that forward DNS entries for a given FQDN must be accompanied by a DHCID
   resource record (RR). This record contains a client identifier that
   uniquely identifies the client to whom the name belongs. Furthermore, any
   DNS updater who wishes to update or remove existing forward entries for an
   FQDN may only do so if their client matches that of the DHCID RR.

   In other words, the DHCID RR maps an FQDN to the client to whom it belongs
   and thereafter only changes to that mapping should only be done by or at
   the behest of that client.

   Currently, conflict detection is always performed. Future releases may
   offer alternative behavior.

  12.1.3. Dual Stack Environments

   RFC 4703, sec. 5.2, describes issues that may arise with dual stack
   clients. These are clients that wish to have have both IPv4 and IPv6
   mappings for the same FQDN. In order for this work properly, such clients
   are required to embed ther IPv6 DUID within their IPv4 client identifier
   option as described in RFC 4703. In this way, DNS updates for both IPv4
   and IPv6 can be managed under the same DHCID RR. Support for this does not
   yet exist in Kea but is called for in the ticket,
   http://oldkea.isc.org/ticket/4519, which we hope to include in a future
   release.

12.2. Starting and Stopping the DHCP-DDNS Server

   kea-dhcp-ddns is the Kea DHCP-DDNS server and, due to the nature of DDNS,
   it is run alongside either the DHCPv4 or DHCPv6 components (or both). Like
   other parts of Kea, it is a separate binary that can be run on its own or
   through keactrl (see Chapter 6, Managing Kea with keactrl). In normal
   operation, controlling kea-dhcp-ddns with keactrl is recommended. However,
   it is also possible to run the DHCP-DDNS server directly. It accepts the
   following command-line switches:

     * -c file - specifies the configuration file. This is the only mandatory
       switch.
     * -d - specifies whether the server logging should be switched to
       debug/verbose mode. In verbose mode, the logging severity and
       debuglevel specified in the configuration file are ignored and "debug"
       severity and the maximum debuglevel (99) are assumed. The flag is
       convenient, for temporarily switching the server into maximum
       verbosity, e.g. when debugging.
     * -v - prints out Kea version and exits.
     * -W - prints out the Kea configuration report and exits. The report is
       a copy of the config.report file produced by ./configure: it is
       embedded in the executable binary.
     * -t file specifies the configuration file to be tested. Kea-dhcp-ddns
       will attempt to load it, and will conduct sanity checks. Note that
       certain checks are possible only while running the actual server. The
       actual status is reported with exit code (0 = configuration looks ok,
       1 = error encountered). Kea will print out log messages to standard
       output and error to standard error when testing configuration.

   The config.report may also be accessed more directly. The following
   command may be used to extract this information. The binary path may be
   found in the install directory or in the .libs subdirectory in the source
   tree. For example kea/src/bin/d2/.libs/kea-dhcp-ddns.

 strings path/kea-dhcp-ddns | sed -n 's/;;;; //p'

   Upon start up the module will load its configuration and begin listening
   for NCRs based on that configuration.

   During startup the server will attempt to create a PID file of the form:
   [localstatedir]/[conf name].kea-dhcp-ddns.pid where:

     * localstatedir: The value as passed into the build configure script. It
       defaults to "/usr/local/var". Note that this value may be overridden
       at run time by setting the environment variable KEA_PIDFILE_DIR. This
       is intended primarily for testing purposes.
     * conf name: The configuration file name used to start the server, minus
       all preceding path and file extension. For example, given a pathname
       of "/usr/local/etc/kea/myconf.txt", the portion used would be
       "myconf".

   If the file already exists and contains the PID of a live process, the
   server will issue a DHCP_DDNS_ALREADY_RUNNING log message and exit. It is
   possible, though unlikely, that the file is a remnant of a system crash
   and the process to which the PID belongs is unrelated to Kea. In such a
   case it would be necessary to manually delete the PID file.

12.3. Configuring the DHCP-DDNS Server

   Before starting kea-dhcp-ddns module for the first time, a configuration
   file needs to be created. The following default configuration is a
   template that can be customized to your requirements.

 "DhcpDdns": {
     "ip-address": "127.0.0.1",
     "port": 53001,
     "dns-server-timeout": 100,
     "ncr-protocol": "UDP",
     "ncr-format": "JSON",
     "tsig-keys": [ ],
     "forward-ddns": {
         "ddns-domains": [ ]
     },
     "reverse-ddns": {
         "ddns-domains": [ ]
     }
 }

   The configuration can be divided as follows, each of which is described in
   its own section:

     * Global Server Parameters - values which control connectivity and
       global server behavior
     * TSIG Key Info - defines the TSIG keys used for secure traffic with DNS
       servers
     * Forward DDNS - defines the catalog of Forward DDNS Domains
     * Reverse DDNS - defines the catalog of Forward DDNS Domains

  12.3.1. Global Server Parameters

     * ip-address - IP address on which D2 listens for requests. The default
       is the local loopback interface at address 127.0.0.1. You may specify
       either an IPv4 or IPv6 address.
     * port - Port on which D2 listens for requests. The default value is
       53001.
     * dns-server-timeout - The maximum amount of time in milliseconds, that
       D2 will wait for a response from a DNS server to a single DNS update
       message.
     * ncr-protocol - Socket protocol to use when sending requests to D2.
       Currently only UDP is supported. TCP may be available in a future
       release.
     * ncr-format - Packet format to use when sending requests to D2.
       Currently only JSON format is supported. Other formats may be
       available in future releases.

   D2 must listen for change requests on a known address and port. By default
   it listens at 127.0.0.1 on port 53001. The following example illustrates
   how to change D2's global parameters so it will listen at 192.168.1.10
   port 900:

 "DhcpDdns": {
     "ip-address": "192.168.1.10",
     "port": 900,
     ...
     }
 }

  Warning

   It is possible for a malicious attacker to send bogus NameChangeRequests
   to the DHCP-DDNS server. Addresses other than the IPv4 or IPv6 loopback
   addresses (127.0.0.1 or ::1) should only be used for testing purposes, but
   note that local users may still communicate with the DHCP-DDNS server. A
   future version of Kea will implement authentication to guard against such
   attacks.

  Note

   If the ip-address and port are changed, it will be necessary to change the
   corresponding values in the DHCP servers' "dhcp-ddns" configuration
   section.

  12.3.2. TSIG Key List

   A DDNS protocol exchange can be conducted with or without TSIG (defined in
   RFC 2845). This configuration section allows the administrator to define
   the set of TSIG keys that may be used in such exchanges.

   To use TSIG when updating entries in a DNS Domain, a key must be defined
   in the TSIG Key List and referenced by name in that domain's configuration
   entry. When D2 matches a change request to a domain, it checks whether the
   domain has a TSIG key associated with it. If so, D2 will use that key to
   sign DNS update messages sent to and verify responses received from the
   domain's DNS server(s). For each TSIG key required by the DNS servers that
   D2 will be working with there must be a corresponding TSIG key in the TSIG
   Key list.

   As one might gather from the name, the tsig-key section of the D2
   configuration lists the TSIG keys. Each entry describes a TSIG key used by
   one or more DNS servers to authenticate requests and sign responses. Every
   entry in the list has three parameters:

     * name - a unique text label used to identify this key within the list.
       This value is used to specify which key (if any) should be used when
       updating a specific domain. So long as it is unique its content is
       arbitrary, although for clarity and ease of maintenance it is
       recommended that it match the name used on the DNS server(s). It
       cannot be blank.
     * algorithm - specifies which hashing algorithm should be used with this
       key. This value must specify the same algorithm used for the key on
       the DNS server(s). The supported algorithms are listed below:

          * HMAC-MD5
          * HMAC-SHA1
          * HMAC-SHA224
          * HMAC-SHA256
          * HMAC-SHA384
          * HMAC-SHA512

       This value is not case sensitive.
     * digest-bits - is used to specify the minimum truncated length in bits.
       The default value 0 means truncation is forbidden, non-zero values
       must be an integral number of octets, be greater than 80 and the half
       of the full length. Note in BIND9 this parameter is appended after a
       dash to the algorithm name.
     * secret - is used to specify the shared secret key code for this key.
       This value is case sensitive and must exactly match the value
       specified on the DNS server(s). It is a base64-encoded text value.

   As an example, suppose that a domain D2 will be updating is maintained by
   a BIND9 DNS server which requires dynamic updates to be secured with TSIG.
   Suppose further that the entry for the TSIG key in BIND9's named.conf file
   looks like this:

    :
    key "key.four.example.com." {
        algorithm hmac-sha224;
        secret "bZEG7Ow8OgAUPfLWV3aAUQ==";
    };
    :

   By default, the TSIG Key list is empty:

 "DhcpDdns": {
    "tsig-keys": [ ],
    ...
 }

   We must extend the list with a new key:

 "DhcpDdns": {
     "tsig-keys": [
         {
             "name": "key.four.example.com.",
             "algorithm": "HMAC-SHA224",
             "secret": "bZEG7Ow8OgAUPfLWV3aAUQ=="
         }
     ],
     ...
 }

   These steps would be repeated for each TSIG key needed. Note that the same
   TSIG key can be used with more than one domain.

  12.3.3. Forward DDNS

   The Forward DDNS section is used to configure D2's forward update
   behavior. Currently it contains a single parameter, the catalog of forward
   DDNS Domains, which is a list of structures.

 "DhcpDdns": {
     "forward-ddns": {
         "ddns-domains": [ ]
     },
     ...
 }

   By default, this list is empty, which will cause the server to ignore the
   forward update portions of requests.

    12.3.3.1. Adding Forward DDNS Domains

   A forward DDNS Domain maps a forward DNS zone to a set of DNS servers
   which maintain the forward DNS data (i.e. name to address mapping) for
   that zone. You will need one forward DDNS Domain for each zone you wish to
   service. It may very well be that some or all of your zones are maintained
   by the same servers. You will still need one DDNS Domain per zone.
   Remember that matching a request to the appropriate server(s) is done by
   zone and a DDNS Domain only defines a single zone.

   This section describes how to add Forward DDNS Domains. Repeat these steps
   for each Forward DDNS Domain desired. Each Forward DDNS Domain has the
   following parameters:

     * name - The fully qualified domain name (or zone) that this DDNS Domain
       can update. This is value used to compare against the request FQDN
       during forward matching. It must be unique within the catalog.
     * key-name - If TSIG is used with this domain's servers, this value
       should be the name of the key from within the TSIG Key List to use. If
       the value is blank (the default), TSIG will not be used in DDNS
       conversations with this domain's servers.
     * dns-servers - A list of one or more DNS servers which can conduct the
       server side of the DDNS protocol for this domain. The servers are used
       in a first to last preference. In other words, when D2 begins to
       process a request for this domain it will pick the first server in
       this list and attempt to communicate with it. If that attempt fails,
       it will move to next one in the list and so on until the it achieves
       success or the list is exhausted.

   To create a new forward DDNS Domain, one must add a new domain element and
   set its parameters:

 "DhcpDdns": {
     "forward-ddns": {
         "ddns-domains": [
             {
                 "name": "other.example.com.",
                 "key-name": "",
                 "dns-servers": [
                 ]
             }
         ]
     }
 }

   It is permissible to add a domain without any servers. If that domain
   should be matched to a request, however, the request will fail. In order
   to make the domain useful though, we must add at least one DNS server to
   it.

      12.3.3.1.1. Adding Forward DNS Servers

   This section describes how to add DNS servers to a Forward DDNS Domain.
   Repeat them for as many servers as desired for a each domain.

   Forward DNS Server entries represent actual DNS servers which support the
   server side of the DDNS protocol. Each Forward DNS Server has the
   following parameters:

     * hostname - The resolvable host name of the DNS server. This value is
       not yet implemented.
     * ip-address - The IP address at which the server listens for DDNS
       requests. This may be either an IPv4 or an IPv6 address.
     * port - The port on which the server listens for DDNS requests. It
       defaults to the standard DNS service port of 53.

   To create a new forward DNS Server, one must add a new server element to
   the domain and fill in its parameters. If for example the service is
   running at "172.88.99.10", then set it as follows:

 "DhcpDdns": {
     "forward-ddns": {
         "ddns-domains": [
             {
                 "name": "other.example.com.",
                 "key-name": "",
                 "dns-servers": [
                     {
                         "hostname": "",
                         "ip-address": "172.88.99.10",
                         "port": 53
                     }
                 ]
             }
         ]
     }
 }

  Note

   As stated earlier, "hostname" is not yet supported so, the parameter
   "ip-address" must be set to the address of the DNS server.

  12.3.4. Reverse DDNS

   The Reverse DDNS section is used to configure D2's reverse update
   behavior, and the concepts are the same as for the forward DDNS section.
   Currently it contains a single parameter, the catalog of reverse DDNS
   Domains, which is a list of structures.

 "DhcpDdns": {
     "reverse-ddns": {
         "ddns-domains": [ ]
     }
     ...
 }

   By default, this list is empty, which will cause the server to ignore the
   reverse update portions of requests.

    12.3.4.1. Adding Reverse DDNS Domains

   A reverse DDNS Domain maps a reverse DNS zone to a set of DNS servers
   which maintain the reverse DNS data (address to name mapping) for that
   zone. You will need one reverse DDNS Domain for each zone you wish to
   service. It may very well be that some or all of your zones are maintained
   by the same servers; even then, you will still need one DDNS Domain entry
   for each zone. Remember that matching a request to the appropriate
   server(s) is done by zone and a DDNS Domain only defines a single zone.

   This section describes how to add Reverse DDNS Domains. Repeat these steps
   for each Reverse DDNS Domain desired. Each Reverse DDNS Domain has the
   following parameters:

     * name - The fully qualified reverse zone that this DDNS Domain can
       update. This is the value used during reverse matching which will
       compare it with a reversed version of the request's lease address. The
       zone name should follow the appropriate standards: for example, to to
       support the IPv4 subnet 172.16.1, the name should be.
       "1.16.172.in-addr.arpa.". Similarly, to support an IPv6 subnet of
       2001:db8:1, the name should be "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa."
       Whatever the name, it must be unique within the catalog.
     * key-name - If TSIG should be used with this domain's servers, then
       this value should be the name of that key from the TSIG Key List. If
       the value is blank (the default), TSIG will not be used in DDNS
       conversations with this domain's servers. Currently this value is not
       used as TSIG has not been implemented.
     * dns-servers - a list of one or more DNS servers which can conduct the
       server side of the DDNS protocol for this domain. Currently the
       servers are used in a first to last preference. In other words, when
       D2 begins to process a request for this domain it will pick the first
       server in this list and attempt to communicate with it. If that
       attempt fails, it will move to next one in the list and so on until
       the it achieves success or the list is exhausted.

   To create a new reverse DDNS Domain, one must add a new domain element and
   set its parameters. For example, to support subnet 2001:db8:1::, the
   following configuration could be used:

 "DhcpDdns": {
     "reverse-ddns": {
         "ddns-domains": [
             {
                 "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
                 "key-name": "",
                 "dns-servers": [
                 ]
             }
         ]
     }
 }

   It is permissible to add a domain without any servers. If that domain
   should be matched to a request, however, the request will fail. In order
   to make the domain useful though, we must add at least one DNS server to
   it.

      12.3.4.1.1. Adding Reverse DNS Servers

   This section describes how to add DNS servers to a Reverse DDNS Domain.
   Repeat them for as many servers as desired for each domain.

   Reverse DNS Server entries represents a actual DNS servers which support
   the server side of the DDNS protocol. Each Reverse DNS Server has the
   following parameters:

     * hostname - The resolvable host name of the DNS server. This value is
       currently ignored.
     * ip-address - The IP address at which the server listens for DDNS
       requests.
     * port - The port on which the server listens for DDNS requests. It
       defaults to the standard DNS service port of 53.

   To create a new reverse DNS Server, one must first add a new server
   element to the domain and fill in its parameters. If for example the
   service is running at "172.88.99.10", then set it as follows:

 "DhcpDdns": {
     "reverse-ddns": {
         "ddns-domains": [
             {
                 "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
                 "key-name": "",
                 "dns-servers": [
                     {
                         "hostname": "",
                         "ip-address": "172.88.99.10",
                         "port": 53
                     }
                 ]
             }
         ]
     }
 }

  Note

   As stated earlier, "hostname" is not yet supported so, the parameter
   "ip-address" must be set to the address of the DNS server.

  12.3.5. User context in DDNS

  Note

   User contexts were designed for hook libraries which are not yet supported
   for DHCP-DDNS server configuration.

   User contexts can store arbitrary data as long as it is valid JSON syntax
   and its top level element is a map (i.e. the data must be enclosed in
   curly brackets).

   User contexts can be specified on either global scope, ddns domain, dns
   server, tsig key and loggers. One other useful usage is the ability to
   store comments or descriptions: the parser translates a "comment" entry
   into a user-context with the entry, this allows to attach a comment inside
   the configuration itself.

  12.3.6. Example DHCP-DDNS Server Configuration

   This section provides an example DHCP-DDNS server configuration based on a
   small example network. Let's suppose our example network has three
   domains, each with their own subnet.

   Table 12.1. Our example network

   +------------------------------------------------------------------------+
   | Domain           | Subnet          | Forward DNS Servers | Reverse DNS |
   |                  |                 |                     | Servers     |
   |------------------+-----------------+---------------------+-------------|
   | four.example.com | 192.0.2.0/24    | 172.16.1.5,         | 172.16.1.5, |
   |                  |                 | 172.16.2.5          | 172.16.2.5  |
   |------------------+-----------------+---------------------+-------------|
   | six.example.com  | 2001:db8:1::/64 | 3001:1::50          | 3001:1::51  |
   |------------------+-----------------+---------------------+-------------|
   | example.com      | 192.0.0.0/16    | 172.16.2.5          | 172.16.2.5  |
   +------------------------------------------------------------------------+

   We need to construct three forward DDNS Domains:

   Table 12.2. Forward DDNS Domains Needed

   +-------------------------------------------------+
   | #  | DDNS Domain Name  | DNS Servers            |
   |----+-------------------+------------------------|
   | 1. | four.example.com. | 172.16.1.5, 172.16.2.5 |
   |----+-------------------+------------------------|
   | 2. | six.example.com.  | 3001:1::50             |
   |----+-------------------+------------------------|
   | 3. | example.com.      | 172.16.2.5             |
   +-------------------------------------------------+

   As discussed earlier, FQDN to domain matching is based on the longest
   match. The FQDN, "myhost.four.example.com.", will match the first domain
   ("four.example.com") while "admin.example.com." will match the third
   domain ("example.com"). The FQDN, "other.example.net." will fail to match
   any domain and would be rejected.

   The following example configuration specified the Forward DDNS Domains.

 "DhcpDdns": {
     "comment": "example configuration: forward part",
     "forward-ddns": {
         "ddns-domains": [
             {
                 "name": "four.example.com.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "172.16.1.5" },
                     { "ip-address": "172.16.2.5" }
                 ]
             },
             {
                 "name": "six.example.com.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "2001:db8::1" }
                 ]
             },
             {
                 "name": "example.com.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "172.16.2.5" }
                 ],
                 "user-context": { "backup": false }
             },

         ]
     }
 }

   Similarly, we need to construct the three reverse DDNS Domains:

   Table 12.3. Reverse DDNS Domains Needed

   +-----------------------------------------------------------------+
   | #  | DDNS Domain Name                  | DNS Servers            |
   |----+-----------------------------------+------------------------|
   | 1. | 2.0.192.in-addr.arpa.             | 172.16.1.5, 172.16.2.5 |
   |----+-----------------------------------+------------------------|
   | 2. | 1.0.0.0.8.d.b.0.1.0.0.2.ip6.arpa. | 3001:1::50             |
   |----+-----------------------------------+------------------------|
   | 3. | 0.182.in-addr.arpa.               | 172.16.2.5             |
   +-----------------------------------------------------------------+

   An address of "192.0.2.150" will match the first domain, "2001:db8:1::10"
   will match the second domain, and "192.0.50.77" the third domain.

   These Reverse DDNS Domains are specified as follows:

 "DhcpDdns": {
     "comment": "example configuration: reverse part",
     "reverse-ddns": {
         "ddns-domains": [
             {
                 "name": "2.0.192.in-addr.arpa.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "172.16.1.5" },
                     { "ip-address": "172.16.2.5" }
                 ]
             }
             {
                 "name": "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "2001:db8::1" }
                 ]
             }
             {
                 "name": "0.192.in-addr.arpa.",
                 "key-name": "",
                 "dns-servers": [
                     { "ip-address": "172.16.2.5" }
                 ]
             }
         ]
     }
 }

12.4. DHCP-DDNS Server Limitations

   The following are the current limitations of the DHCP-DDNS Server.

     * Requests received from the DHCP servers are placed in a queue until
       they are processed. Currently all queued requests are lost when the
       server shuts down.

                          Chapter 13. The LFC process

   Table of Contents

   13.1. Overview

   13.2. Command Line Options

13.1. Overview

   kea-lfc is a service process that removes redundant information from the
   files used to provide persistent storage for the memfile data base
   backend. This service is written to run as a stand alone process.

   While kea-lfc can be started externally, there is usually no need to do
   this. kea-lfc is run on a periodic basis by the Kea DHCP servers.

   The process operates on a set of files, using them for input and output of
   the lease entries and to indicate where it is in the process in case of an
   interruption. Currently the caller must supply names for all of the files,
   in the future this requirement may be relaxed with the process getting the
   names from either the configuration file or from defaults.

13.2. Command Line Options

   kea-lfc is run as follows:

 kea-lfc [-4 | -6] -c config-file -p pid-file -x previous-file -i copy-file -o output-file -f finish-file

   The argument -4 or -6 selects the protocol version of the lease files.

   The -c argument specifies the configuration file. This is required, but
   not currently used by the process.

   The -p argument specifies the PID file. When the kea-lfc process starts it
   attempts to determine if another instance of the process is already
   running by examining the pid file. If one is already running the new
   process is terminated. If one isn't running it writes its pid into the pid
   file.

   The other filenames specify where the kea-lfc process should look for
   input, write its output and use for bookkeeping.

     * previous -- When kea-lfc starts this is the result of any previous run
       of kea-lfc. When kea-lfc finishes it is the result of this run. If
       kea-lfc is interrupted before completing, this file may not exist.
     * input -- Before the DHCP server invokes kea-lfc it will move the
       current lease file here and then call kea-lfc with this file.
     * output -- The temporary file kea-lfc should use to write the leases.
       Upon completion of writing this file, it will be moved to the finish
       file (see below).
     * finish -- Another temporary file kea-lfc uses for bookkeeping. When
       kea-lfc completes writing the outputfile it moves it to this file
       name. After kea-lfc finishes deleting the other files (previous and
       input) it moves this file to previous lease file. By moving the files
       in this fashion the kea-lfc and the DHCP server processes can
       determine the correct file to use even if one of the processes was
       interrupted before completing its task.

   There are several additional arguments mostly for debugging purposes. -d
   Sets the logging level to debug. -v and -V print out version stamps with
   -V providing a longer form. -h prints out the usage string.

                       Chapter 14. Client Classification

   Table of Contents

   14.1. Client Classification Overview

   14.2. Builtin Client Classes

   14.3. Using Expressions In Classification

                14.3.1. Logical operators

                14.3.2. Substring

                14.3.3. Concat

                14.3.4. Ifelse

                14.3.5. Hexstring

   14.4. Configuring Classes

   14.5. Using Static Host Reservations In Classification

   14.6. Configuring Subnets With Class Information

   14.7. Configuring Pools With Class Information

   14.8. Using Classes

   14.9. Classes and Hooks

   14.10. Debugging Expressions

14.1. Client Classification Overview

   In certain cases it is useful to differentiate between different types of
   clients and treat them accordingly. Common reasons include:

     * The clients represent different pieces of topology, e.g. a cable modem
       is different to the clients behind that modem.

     * The clients have different behavior, e.g. a smart phone behaves
       differently to a laptop.

     * The clients require different values for some options, e.g. a
       docsis3.0 cable modem requires different settings to docsis2.0 cable
       modem.

   Conversely, different clients can be grouped into a client class to get a
   common option.

   An incoming packet can be associated with a client class in serveral ways:

     * Implicitly, using a vendor class option or another builtin condition.

     * Using an expression which evaluates to true.

     * Using static host reservations, a shared network, a subnet, etc.

     * Using a hook.

   It is envisaged that client classification will be used for changing the
   behavior of almost any part of the DHCP message processing. In the current
   release of the software however, there are only five mechanisms that take
   advantage of client classification: subnet selection, pool selection,
   definition of DHCPv4 private (codes 224-254) and code 43 options,
   assignment of different options and, for DHCPv4 cable modems, the setting
   of specific options for use with the TFTP server address and the boot file
   field.

   The process of doing classification is conducted in several steps:

    1. The ALL class is associated with the incoming packet.

    2. Vendor class options are processed.

    3. Classes with matching expressions and not marked for later ("on
       request" or depending on the KNOWN/UNKNOWN builtin classes) evaluation
       are processed in the order they are defined in the configuration: the
       boolean expression is evaluated and when it returns true ("match") the
       incoming packet is associated to the class.

    4. If a private or code 43 DHCPv4 option is received, decoding it
       following its client class or global (or for option 43 last resort)
       definition.

    5. Choose a subnet, possibly based on the class information when some
       subnets are guarded. More precisely: when choosing a subnet, the
       server will iterate over all of the subnets that are feasible given
       the information found in the packet (client address, relay address
       etc). It will use the first subnet it finds that either doesn't have a
       class associated with it or that has a class which matches one of the
       packet's classes.

    6. Host reservations are looked for. If an identifier from the incoming
       packet matches a host reservation in the subnet or shared network, the
       packet is associated with the KNOWN class and all classes of the host
       reservation. If a reservation is not found, the packet is assigned to
       UNKNOWN class.

    7. Classes with matching expressions using directly or indirectly the
       KNOWN/UNKNOWN builtin classes and not marked for later ("on request")
       evaluation are processed in the order they are defined in the
       configuration: the boolean expression is evaluated and when it returns
       true ("match") the incoming packet is associated to the class. The
       determination whether there is a reservation for a given client is
       made after a subnet is selected. As such, it is not possible to use
       KNOWN/UNKNOWN classes to select a shared network or a subnet.

    8. If needed, addresses and prefixes from pools are assigned, possibly
       based on the class information when some pools are reserved to class
       members.

    9. Evaluate classes marked as "required" in the order in which they are
       listed as required: first shared network, then the subnet and to
       finally pools assigned resources belong too.

   10. Assign options, again possibly based on the class information in order
       classes were associated with the incoming packet. For DHCPv4 private
       and code 43 options this includes class local option definitions.

  Note

   Beginning with Kea 1.4.0 release, client classes follow the order in which
   they are specified in the configuration (vs. alphabetical order in
   previous releases). Required classes follow the order in which they are
   required.

   When determining which options to include in the response, the server will
   examine the union of options from all of the assigned classes. In case
   when two or more classes include the same option, the value from the first
   class examined will be used, and classes are examined in the order they
   were associated so ALL is always the first class and matching required
   classes are last.

   As an example, imagine that an incoming packet matches two classes. Class
   "foo" defines values for an NTP server (option 42 in DHCPv4) and an SMTP
   server (option 69 in DHCPv4) while class "bar" defines values for an NTP
   server and a POP3 server (option 70 in DHCPv4). The server will examine
   the three options NTP, SMTP and POP3 and return any of them that the
   client requested. As the NTP server was defined twice the server will
   choose only one of the values for the reply: the class from which the
   value is obtained is unspecified.

  Note

   Care should be taken with client classification as it is easy for clients
   that do not meet class criteria to be denied any service altogether.

14.2. Builtin Client Classes

   Some classes are builtin so do not need to be defined. The main example
   uses Vendor Class information: The server checks whether an incoming
   DHCPv4 packet includes the vendor class identifier option (60) or an
   incoming DHCPv6 packet includes the vendor class option (16). If it does,
   the content of that option is prepended with "VENDOR_CLASS_" and the
   result is interpreted as a class. For example, modern cable modems will
   send this option with value "docsis3.0" and so the packet will belong to
   class "VENDOR_CLASS_docsis3.0".

   The "HA_" prefix is used by the High Availability hooks library to
   designate certain servers to process DHCP packets as a result of load
   balancing. The class name is constructed by prepending the "HA_" prefix to
   the name of the server which should process the DHCP packet. This server
   will use appropriate pool or subnet to allocate IP addresses (and/or
   prefixes) from, based on the assigned client classes. The details can be
   found in Section 15.4.8, "ha: High Availability".

   Other examples are: the ALL class which all incoming packets belong to,
   and the KNOWN class assigned when host reservations exist for the
   particular client. By convention, builtin classes' names begin with all
   capital letters.

   Currently recognized builtin class names are ALL, KNOWN and UNKNOWN, and
   prefixes VENDOR_CLASS_, HA_, AFTER_ and EXTERNAL_. The AFTER_ prefix is a
   provision for a not yet written hook, the EXTERNAL_ prefix can be freely
   used: builtin classes are implicitly defined so never raise warnings if
   they do not appear in the configuration.

14.3. Using Expressions In Classification

   The expression portion of classification contains operators and values.
   All values are currently strings and operators take a string or strings
   and return another string. When all the operations have completed the
   result should be a value of "true" or "false". The packet belongs to the
   class (and the class name is added to the list of classes) if the result
   is "true". Expressions are written in standard format and can be nested.

   Expressions are pre-processed during the parsing of the configuration file
   and converted to an internal representation. This allows certain types of
   errors to be caught and logged during parsing. Examples of these errors
   include an incorrect number or types of arguments to an operator. The
   evaluation code will also check for this class of error and generally
   throw an exception, though this should not occur in a normally functioning
   system.

   Other issues, for example the starting position of a substring being
   outside of the substring or an option not existing in the packet, result
   in the operator returning an empty string.

   Expressions are a work in progress and the supported operators and values
   are limited. The expectation is that additional operators and values will
   be added over time, however the basic mechanisms will remain the same.

   Dependencies between classes are checked too: for instance forward
   dependencies are rejected when the configuration is parsed: an expression
   can only depend on already defined classes (including builtin classes) and
   which are evaluated in a previous or the same evaluation phase. This does
   not apply to the KNOWN or UNKNOWN classes.

   Table 14.1. List of Classification Values

+----------------------------------------------------------------------------------+
|     Name      |     Example expression      | Example value  |    Description    |
|---------------+-----------------------------+----------------+-------------------|
|String literal |'example'                    |'example'       |A string           |
|---------------+-----------------------------+----------------+-------------------|
|Hexadecimal    |0x5a7d                       |'Z}'            |A hexadecimal      |
|string literal |                             |                |string             |
|---------------+-----------------------------+----------------+-------------------|
|IP address     |10.0.0.1                     |0x0a000001      |An IP address      |
|literal        |                             |                |                   |
|---------------+-----------------------------+----------------+-------------------|
|Integer literal|123                          |'123'           |A 32 bit unsigned  |
|               |                             |                |integer value      |
|----------------------------------------------------------------------------------|
|----------------------------------------------------------------------------------|
|               |                             |                |The value of the   |
|Binary content |option[123].hex              |'(content of the|option with given  |
|of the option  |                             |option)'        |code from the      |
|               |                             |                |packet as hex      |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |If the option with |
|Option         |                             |                |given code is      |
|existence      |option[123].exists           |'true'          |present in the     |
|               |                             |                |packet "true" else |
|               |                             |                |"false"            |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |If the packet      |
|Client class   |member('foobar')             |'true'          |belongs to the     |
|membership     |                             |                |given client class |
|               |                             |                |"true" else "false"|
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |If there is a host |
|Known client   |known                        |member('KNOWN') |reservation for the|
|               |                             |                |client "true" else |
|               |                             |                |"false"            |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |If there is a host |
|Unknown client |unknown                      |not             |reservation for the|
|               |                             |member('KNOWN') |client "false" else|
|               |                             |                |"true"             |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of       |
|DHCPv4 relay   |                             |                |sub-option with    |
|agent          |relay4[123].hex              |'(content of the|given code from the|
|sub-option     |                             |RAI sub-option)'|DHCPv4 Relay Agent |
|               |                             |                |Information option |
|               |                             |                |(option 82)        |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|DHCPv6 Relay   |                             |(value of the   |option with code   |
|Options        |relay6[nest].option[code].hex|option)         |"code" from the    |
|               |                             |                |relay encapsulation|
|               |                             |                |"nest"             |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|DHCPv6 Relay   |                             |                |peer address field |
|Peer Address   |relay6[nest].peeraddr        |2001:DB8::1     |from the relay     |
|               |                             |                |encapsulation      |
|               |                             |                |"nest"             |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|DHCPv6 Relay   |                             |                |link address field |
|Link Address   |relay6[nest].linkaddr        |2001:DB8::1     |from the relay     |
|               |                             |                |encapsulation      |
|               |                             |                |"nest"             |
|---------------+-----------------------------+----------------+-------------------|
|Interface name |                             |                |The name of the    |
|of packet      |pkt.iface                    |eth0            |incoming interface |
|               |                             |                |of a DHCP packet.  |
|---------------+-----------------------------+----------------+-------------------|
|Source address |                             |                |The IP source      |
|of packet      |pkt.src                      |10.1.2.3        |address of a DHCP  |
|               |                             |                |packet.            |
|---------------+-----------------------------+----------------+-------------------|
|Destination    |                             |                |The IP destination |
|address of     |pkt.dst                      |10.1.2.3        |address of a DHCP  |
|packet         |                             |                |packet.            |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The length of a    |
|               |                             |                |DHCP packet (UDP   |
|Length of      |pkt.len                      |513             |header field),     |
|packet         |                             |                |expressed as a 32  |
|               |                             |                |bit unsigned       |
|               |                             |                |integer.           |
|---------------+-----------------------------+----------------+-------------------|
|Hardware       |                             |                |The value of the   |
|address in     |pkt4.mac                     |0x010203040506  |chaddr field of the|
|DHCPv4 packet  |                             |                |DHCPv4 packet, hlen|
|               |                             |                |(0 to 16) bytes    |
|---------------+-----------------------------+----------------+-------------------|
|Hardware length|                             |                |The value of the   |
|in DHCPv4      |pkt4.hlen                    |6               |hlen field of the  |
|packet         |                             |                |DHCPv4 packet      |
|               |                             |                |padded to 4 bytes  |
|---------------+-----------------------------+----------------+-------------------|
|Hardware type  |                             |                |The value of the   |
|in DHCPv4      |pkt4.htype                   |6               |htype field of the |
|packet         |                             |                |DHCPv4 packet      |
|               |                             |                |padded to 4 bytes  |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|ciaddr field in|pkt4.ciaddr                  |192.0.2.1       |ciaddr field of the|
|DHCPv4 packet  |                             |                |DHCPv4 packet (IPv4|
|               |                             |                |address, 4 bytes)  |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|giaddr field in|pkt4.giaddr                  |192.0.2.1       |giaddr field of the|
|DHCPv4 packet  |                             |                |DHCPv4 packet (IPv4|
|               |                             |                |address, 4 bytes)  |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|yiaddr field in|pkt4.yiaddr                  |192.0.2.1       |yiaddr field of the|
|DHCPv4 packet  |                             |                |DHCPv4 packet (IPv4|
|               |                             |                |address, 4 bytes)  |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|siaddr field in|pkt4.siaddr                  |192.0.2.1       |siaddr field of the|
|DHCPv4 packet  |                             |                |DHCPv4 packet (IPv4|
|               |                             |                |address, 4 bytes)  |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|               |                             |                |message type field |
|Message Type in|pkt4.msgtype                 |1               |in the DHCPv4      |
|DHCPv4 packet  |                             |                |packet (expressed  |
|               |                             |                |as a 32 bit        |
|               |                             |                |unsigned integer). |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|Transaction ID |                             |                |transaction id in  |
|(xid) in DHCPv4|pkt4.transid                 |12345           |the DHCPv4 packet  |
|packet         |                             |                |(expressed as a 32 |
|               |                             |                |bit unsigned       |
|               |                             |                |integer).          |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|               |                             |                |message type field |
|Message Type in|pkt6.msgtype                 |1               |in the DHCPv6      |
|DHCPv6 packet  |                             |                |packet (expressed  |
|               |                             |                |as a 32 bit        |
|               |                             |                |unsigned integer). |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |The value of the   |
|Transaction ID |                             |                |transaction id in  |
|in DHCPv6      |pkt6.transid                 |12345           |the DHCPv6 packet  |
|packet         |                             |                |(expressed as a 32 |
|               |                             |                |bit unsigned       |
|               |                             |                |integer).          |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |Returns whether a  |
|Vendor option  |                             |                |vendor option from |
|existence (any |vendor[*].exists             |true            |any vendor is      |
|vendor)        |                             |                |present ('true') or|
|               |                             |                |absent ('false').  |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |Returns whether a  |
|Vendor option  |                             |                |vendor option from |
|existence      |                             |                |specified vendor   |
|(specific      |vendor[4491].exists          |true            |(determined by its |
|vendor)        |                             |                |enterprise-id) is  |
|               |                             |                |present ('true') or|
|               |                             |                |absent ('false').  |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |If the vendor      |
|               |                             |                |option is present, |
|Enterprise-id  |                             |                |it returns the     |
|from vendor    |vendor.enterprise            |4491            |value of the       |
|option         |                             |                |enterprise-id field|
|               |                             |                |padded to 4 bytes. |
|               |                             |                |Returns ""         |
|               |                             |                |otherwise.         |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |Returns 'true' if  |
|               |                             |                |there is vendor    |
|Vendor         |                             |                |option with        |
|sub-option     |vendor[4491].option[1].exists|true            |specified          |
|existence      |                             |                |enterprise-id and  |
|               |                             |                |given sub-option is|
|               |                             |                |present. Returns   |
|               |                             |                |'false' otherwise. |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |Returns content of |
|               |                             |                |the specified      |
|               |                             |                |sub-option of a    |
|Vendor         |                             |                |vendor option with |
|sub-option     |vendor[4491].option[1].hex   |docsis3.0       |specified          |
|content        |                             |                |enterprise id.     |
|               |                             |                |Returns '' if no   |
|               |                             |                |such option or     |
|               |                             |                |sub-option is      |
|               |                             |                |present.           |
|---------------+-----------------------------+----------------+-------------------|
|Vendor class   |                             |                |Returns whether a  |
|option         |                             |                |vendor class option|
|existence (any |vendor-class[*].exists       |true            |from any vendor is |
|vendor)        |                             |                |present ('true') or|
|               |                             |                |absent ('false').  |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |Returns whether a  |
|Vendor class   |                             |                |vendor class option|
|option         |                             |                |from specified     |
|existence      |vendor-class[4491].exists    |true            |vendor (determined |
|(specific      |                             |                |by its             |
|vendor)        |                             |                |enterprise-id) is  |
|               |                             |                |present ('true') or|
|               |                             |                |absent ('false').  |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |If the vendor      |
|               |                             |                |option is present, |
|Enterprise-id  |                             |                |it returns the     |
|from vendor    |vendor-class.enterprise      |4491            |value of the       |
|class option   |                             |                |enterprise-id field|
|               |                             |                |padded to 4 bytes. |
|               |                             |                |Returns ""         |
|               |                             |                |otherwise.         |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |Returns content of |
|               |                             |                |the first data     |
|First data     |                             |                |chunk from the     |
|chunk from     |vendor-class[4491].data      |docsis3.0       |vendor class option|
|vendor class   |                             |                |with specified     |
|option         |                             |                |enterprise-id.     |
|               |                             |                |Returns "" if      |
|               |                             |                |missing.           |
|---------------+-----------------------------+----------------+-------------------|
|               |                             |                |Returns content of |
|               |                             |                |the specified data |
|Specific data  |                             |                |chunk of a vendor  |
|chunk from     |                             |                |class option with  |
|vendor class   |vendor-class[4491].data[3]   |docsis3.0       |specified          |
|option         |                             |                |enterprise id.     |
|               |                             |                |Returns '' if no   |
|               |                             |                |such option or data|
|               |                             |                |chunk is present.  |
+----------------------------------------------------------------------------------+

   Notes:

     * Hexadecimal strings are converted into a string as expected. The
       starting "0X" or "0x" is removed and if the string is an odd number of
       characters a "0" is prepended to it.

     * IP addresses are converted into strings of length 4 or 16. IPv4, IPv6,
       and IPv4 embedded IPv6 (e.g., IPv4 mapped IPv6) addresses are
       supported.

     * Integers in an expression are converted to 32 bit unsigned integers
       and are represented as four-byte strings. For example 123 is
       represented as 0x0000007b. All expressions that return numeric values
       use 32-bit unsigned integers, even if the field in the packet is
       smaller. In general it is easier to use decimal notation to represent
       integers, but it is also possible to use hex notation. When using hex
       notation to represent an integer care should be taken to make sure the
       value is represented as 32 bits, e.g. use 0x00000001 instead of 0x1 or
       0x01. Also, make sure the value is specified in network order, e.g. 1
       is represented as 0x00000001.

     * "option[code].hex" extracts the value of the option with the code
       "code" from the incoming packet. If the packet doesn't contain the
       option, it returns the empty string. The string is presented as a byte
       string of the option payload without the type code or length fields.

     * "option[code].exists" checks if an option with the code "code" is
       present in the incoming packet. It can be used with empty options.

     * "member('foobar')" checks if the packet belongs to the client class
       "foobar". To avoid dependency loops the configuration file parser
       checks if client classes were already defined or are built-in, i.e.,
       beginning by "VENDOR_CLASS_", "AFTER__" (for the to come "after" hook)
       and "EXTERNAL_" or equal to "ALL", "KNOWN", "UNKNOWN"etc.

       "known" and "unknown" are short hands for "member('KNOWN')" and "not
       member('KNOWN')". Note the evaluation of any expression using directly
       or indirectly the "KNOWN" class is deferred after the host reservation
       lookup (i.e. when the "KNOWN" or "UNKNOWN" partition is determined).

     * "relay4[code].hex" attempts to extract the value of the sub-option
       "code" from the option inserted as the DHCPv4 Relay Agent Information
       (82) option. If the packet doesn't contain a RAI option, or the RAI
       option doesn't contain the requested sub-option, the expression
       returns an empty string. The string is presented as a byte string of
       the option payload without the type code or length fields. This
       expression is allowed in DHCPv4 only.

     * "relay4" shares the same representation types as "option", for
       instance "relay4[code].exists" is supported.

     * "relay6[nest]" allows access to the encapsulations used by any DHCPv6
       relays that forwarded the packet. The "nest" level specifies the relay
       from which to extract the information, with a value of 0 indicating
       the relay closest to the DHCPv6 server. Negative values allow to
       specify relays counted from the DHCPv6 client, -1 indicating the relay
       closest to the client. In general negative "nest" level is the same as
       the number of relays + "nest" level. If the requested encapsulation
       doesn't exist an empty string "" is returned. This expression is
       allowed in DHCPv6 only.

     * "relay6[nest].option[code]" shares the same representation types as
       "option", for instance "relay6[nest].option[code].exists" is
       supported.

     * Expressions starting with "pkt4" can be used only in DHCPv4. They
       allows access to DHCPv4 message fields.

     * "pkt6" refers to information from the client request. To access any
       information from an intermediate relay use "relay6". "pkt6.msgtype"
       and "pkt6.transid" output a 4 byte binary string for the message type
       or transaction id. For example the message type SOLICIT will be
       "0x00000001" or simply 1 as in "pkt6.msgtype == 1".

     * Vendor option means Vendor-Identifying Vendor-specific Information
       option in DHCPv4 (code 125, see Section 4 of RFC 3925) and
       Vendor-specific Information Option in DHCPv6 (code 17, defined in
       Section 21.17 of RFC 8415). Vendor class option means
       Vendor-Identifying Vendor Class Option in DHCPv4 (code 124, see
       Section 3 of RFC 3925) in DHCPv4 and Class Option in DHCPv6 (code 16,
       see Section 21.16 of RFC 8415). Vendor options may have sub-options
       that are referenced by their codes. Vendor class options do not have
       sub-options, but rather data chunks, which are referenced by index
       value. Index 0 means the first data chunk, Index 1 is for the second
       data chunk (if present), etc.

     * In the vendor and vendor-class constructs Asterisk (*) or 0 can be
       used to specify a wildcard enterprise-id value, i.e. it will match any
       enterprise-id value.

     * Vendor Class Identifier (option 60 in DHCPv4) can be accessed using
       option[60] expression.

     * RFC 3925 and RFC 8415 allow for multiple instances of vendor options
       to appear in a single message. The client classification code
       currently examines the first instance if more than one appear. For
       vendor.enterprise and vendor-class.enterprise expressions, the value
       from the first instance is returned. Please submit a feature request
       on Kea website if you need support for multiple instances.

   Table 14.2. List of Classification Expressions

   +------------------------------------------------------------------------+
   |   Name    |            Example             |        Description        |
   |-----------+--------------------------------+---------------------------|
   |           |                                | Compare the two values    |
   | Equal     | 'foo' == 'bar'                 | and return "true" or      |
   |           |                                | "false"                   |
   |-----------+--------------------------------+---------------------------|
   | Not       | not ('foo' == 'bar')           | Logical negation          |
   |-----------+--------------------------------+---------------------------|
   | And       | ('foo' == 'bar') and ('bar' == | Logical and               |
   |           | 'foo')                         |                           |
   |-----------+--------------------------------+---------------------------|
   | Or        | ('foo' == 'bar') or ('bar' ==  | Logical or                |
   |           | 'foo')                         |                           |
   |-----------+--------------------------------+---------------------------|
   | Substring | substring('foobar',0,3)        | Return the requested      |
   |           |                                | substring                 |
   |-----------+--------------------------------+---------------------------|
   | Concat    | concat('foo','bar')            | Return the concatenation  |
   |           |                                | of the strings            |
   |-----------+--------------------------------+---------------------------|
   |           | ifelse('foo' ==                | Return the branch value   |
   | Ifelse    | 'bar','us','them')             | according to the          |
   |           |                                | condition                 |
   |-----------+--------------------------------+---------------------------|
   |           |                                | Converts the value to a   |
   | Hexstring | hexstring('foo', '-')          | hexadecimal string, e.g.  |
   |           |                                | 0a:1b:2c:3e               |
   +------------------------------------------------------------------------+

  14.3.1. Logical operators

   The Not, And and Or logical operators are the common operators. Not has
   the highest precedence and Or the lowest. And and Or are (left)
   associative, parentheses around a logical expression can be used to
   enforce a specific grouping, for instance in "A and (B or C)" (without
   parentheses "A and B or C" means "(A and B) or C").

  14.3.2. Substring

   The substring operator "substring(value, start, length)" accepts both
   positive and negative values for the starting position and the length. For
   "start", a value of 0 is the first byte in the string while -1 is the last
   byte. If the starting point is outside of the original string an empty
   string is returned. "length" is the number of bytes to extract. A negative
   number means to count towards the beginning of the string but doesn't
   include the byte pointed to by "start". The special value "all" means to
   return all bytes from start to the end of the string. If length is longer
   than the remaining portion of the string then the entire remaining portion
   is returned. Some examples may be helpful:

         substring('foobar', 0, 6) == 'foobar'
         substring('foobar', 3, 3) == 'bar'
         substring('foobar', 3, all) == 'bar'
         substring('foobar', 1, 4) == 'ooba'
         substring('foobar', -5, 4) == 'ooba'
         substring('foobar', -1, -3) == 'oba'
         substring('foobar', 4, -2) == 'ob'
         substring('foobar', 10, 2) == ''


  14.3.3. Concat

   The concat function "concat(string1, string2)" returns the concatenation
   of its two arguments. For instance:

         concat('foo', 'bar') == 'foobar'


  14.3.4. Ifelse

   The ifelse function "ifelse(cond, iftrue, ifelse)" returns the "iftrue" or
   "ifelse" branch value following the boolean condition "cond". For
   instance:

          ifelse(option[230].exists, option[230].hex, 'none')


  14.3.5. Hexstring

   The hexstring function "hexstring(binary, separator)" returns the binary
   value as its hexadecimal string representation: pairs of hexadecimal
   digits separated by the separator, e.g ':', '-', '' (empty separator).

           hexstring(pkt4.mac, ':')


  Note

   The expression for each class is executed on each packet received. If the
   expressions are overly complex, the time taken to execute them may impact
   the performance of the server. If you need complex or time consuming
   expressions you should write a hook to perform the necessary work.

14.4. Configuring Classes

   A class contains five items: a name, a test expression, option data,
   option definition and only-if-required flag. The name must exist and must
   be unique amongst all classes. The test expression, option data and
   definition, and only-if-required flag are optional.

   The test expression is a string containing the logical expression used to
   determine membership in the class. The entire expression is in double
   quotes.

   The option data is a list which defines any options that should be
   assigned to members of this class.

   The option definition is for DHCPv4 option 43 (Section 8.2.11, "DHCPv4
   Vendor Specific Options" and DHCPv4 private options (Section 8.2.10,
   "DHCPv4 Private Options").

   Usually the test expression is evaluated before subnet selection but in
   some cases it is useful to evaluate it later when the subnet,
   shared-network or pools are known but output option processing not yet
   done. The only-if-required flag, false by default, allows to perform the
   evaluation of the test expression only when it was required, i.e. in a
   require-client-classes list of the selected subnet, shared-network or
   pool.

   The require-client-classes list which is valid for shared-network, subnet
   and pool scope specifies the classes which are evaluated in the second
   pass before output option processing. The list is built in the reversed
   precedence order of option data, i.e. an option data in a subnet takes
   precedence on one in a shared-network but required class in a subnet is
   added after one in a shared-network. The mechanism is related to the
   only-if-required flag but it is not mandatory that the flag was set to
   true.

   In the following example the class named "Client_foo" is defined. It is
   comprised of all clients whose client ids (option 61) start with the
   string "foo". Members of this class will be given 192.0.2.1 and 192.0.2.2
   as their domain name servers.

 "Dhcp4": {
     "client-classes": [
         {
             "name": "Client_foo",
             "test": "substring(option[61].hex,0,3) == 'foo'",
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.1, 192.0.2.2"
                 }
             ]
         },
         ...
     ],
     ...
 }

   This example shows a client class being defined for use by the DHCPv6
   server. In it the class named "Client_enterprise" is defined. It is
   comprised of all clients who's client identifiers start with the given hex
   string (which would indicate a DUID based on an enterprise id of
   0xAABBCCDD). Members of this class will be given an 2001:db8:0::1 and
   2001:db8:2::1 as their domain name servers.

 "Dhcp6": {
     "client-classes": [
         {
             "name": "Client_enterprise",
             "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:0::1, 2001:db8:2::1"
                 }
             ]
         },
         ...
     ],
     ...
 }

14.5. Using Static Host Reservations In Classification

   Classes can be statically assigned to the clients using techniques
   described in Section 8.3.6, "Reserving Client Classes in DHCPv4" and
   Section 9.3.5, "Reserving Client Classes in DHCPv6".

14.6. Configuring Subnets With Class Information

   In certain cases it beneficial to restrict access to certain subnets only
   to clients that belong to a given class, using the "client-class" keyword
   when defining the subnet.

   Let's assume that the server is connected to a network segment that uses
   the 192.0.2.0/24 prefix. The Administrator of that network has decided
   that addresses from range 192.0.2.10 to 192.0.2.20 are going to be managed
   by the DHCP4 server. Only clients belonging to client class Client_foo are
   allowed to use this subnet. Such a configuration can be achieved in the
   following way:

 "Dhcp4": {
     "client-classes": [
         {
             "name": "Client_foo",
             "test": "substring(option[61].hex,0,3) == 'foo'",
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.1, 192.0.2.2"
                 }
             ]
         },
         ...
     ],
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [ { "pool": "192.0.2.10 - 192.0.2.20" } ],
             "client-class": "Client_foo"
         },
         ...
     ],,
     ...
 }

   The following example shows restricting access to a DHCPv6 subnet. This
   configuration will restrict use of the addresses 2001:db8:1::1 to
   2001:db8:1::FFFF to members of the "Client_enterprise" class.

 "Dhcp6": {
     "client-classes": [
         {
             "name": "Client_enterprise",
             "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:0::1, 2001:db8:2::1"
                 }
             ]
         },
         ...
     ],
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
             "client-class": "Client_enterprise"
         }
     ],
     ...
 }

14.7. Configuring Pools With Class Information

   Similar to subnets in certain cases access to certain address or prefix
   pools must be restricted to only clients that belong to a given class,
   using the "client-class" when defining the pool.

   Let's assume that the server is connected to a network segment that uses
   the 192.0.2.0/24 prefix. The Administrator of that network has decided
   that addresses from range 192.0.2.10 to 192.0.2.20 are going to be managed
   by the DHCP4 server. Only clients belonging to client class Client_foo are
   allowed to use this pool. Such a configuration can be achieved in the
   following way:

 "Dhcp4": {
     "client-classes": [
         {
             "name": "Client_foo",
             "test": "substring(option[61].hex,0,3) == 'foo'",
             "option-data": [
                 {
                     "name": "domain-name-servers",
                     "code": 6,
                     "space": "dhcp4",
                     "csv-format": true,
                     "data": "192.0.2.1, 192.0.2.2"
                 }
             ]
         },
         ...
     ],
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 {
                     "pool": "192.0.2.10 - 192.0.2.20",
                     "client-class": "Client_foo"
                 }
             ]
         },
         ...
     ],,

 }

   The following example shows restricting access to an address pool. This
   configuration will restrict use of the addresses 2001:db8:1::1 to
   2001:db8:1::FFFF to members of the "Client_enterprise" class.

 "Dhcp6": {
     "client-classes": [
         {
             "name": "Client_enterprise_",
             "test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
             "option-data": [
                 {
                     "name": "dns-servers",
                     "code": 23,
                     "space": "dhcp6",
                     "csv-format": true,
                     "data": "2001:db8:0::1, 2001:db8:2::1"
                 }
             ]
         },
         ...
     ],
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",

             "pools": [
                 {
                     "pool": "2001:db8:1::-2001:db8:1::ffff",
                     "client-class": "Client_foo"
                 }
             ]
         },
         ...
     ],
     ...
 }

14.8. Using Classes

   Currently classes can be used for two functions. They can supply options
   to the members of the class and they can be used to choose a subnet from
   which an address will be assigned to the class member.

   When supplying options, options defined as part of the class definition
   are considered "class globals". They will override any global options that
   may be defined and in turn will be overridden by any options defined for
   an individual subnet.

14.9. Classes and Hooks

   You may use a hook to classify your packets. This may be useful if the
   expression would either be complex or time consuming and be easier or
   better to write as code. Once the hook has added the proper class name to
   the packet the rest of the classification system will work as normal in
   choosing a subnet and selecting options. For a description of hooks see
   Chapter 15, Hooks Libraries, for a description on configuring classes see
   Section 14.4, "Configuring Classes" and Section 14.6, "Configuring Subnets
   With Class Information".

14.10. Debugging Expressions

   While you are constructing your classification expressions you may find it
   useful to enable logging see Chapter 19, Logging for a more complete
   description of the logging facility.

   To enable the debug statements in the classification system you will need
   to set the severity to "DEBUG" and the debug level to at least 55. The
   specific loggers are "kea-dhcp4.eval" and "kea-dhcp6.eval".

   In order to understand the logging statements, one must understand a bit
   about how expressions are evaluated; for a more complete description refer
   to the design document at
   https://gitlab.isc.org/isc-projects/kea/wikis/design%20documents. In brief
   there are two structures used during the evaluation of an expression: a
   list of tokens which represent the expressions and a value stack which
   represents the values being manipulated.

   The list of tokens is created when the configuration file is processed
   with most expressions and values being converted to a token. The list is
   organized in reverse Polish notation. During execution, the list will be
   traversed in order. As each token is executed it will be able to pop
   values from the top of the stack and eventually push its result on the top
   of the stack. Imagine the following expression:

        "test": "substring(option[61].hex,0,3) == 'foo'",


   This will result in the following tokens:

        option, number (0), number (3), substring, text ('foo'), equals


   In this example the first three tokens will simply push values onto the
   stack. The substring token will then remove those three values and compute
   a result that it places on the stack. The text option also places a value
   on the stack and finally the equals token removes the two tokens on the
   stack and places its result on the stack.

   When debug logging is enabled, each time a token is evaluated it will emit
   a log message indicating the values of any objects that were popped off of
   the value stack and any objects that were pushed onto the value stack.

   The values will be displayed as either text if the command is known to use
   text values or hexadecimal if the command either uses binary values or can
   manipulate either text or binary values. For expressions that pop multiple
   values off the stack, the values will be displayed in the order they were
   popped. For most expressions this won't matter but for the concat
   expression the values are displayed in reverse order from how they are
   written in the expression.

   Let us assume that the following test has been entered into the
   configuration. This example skips most of the configuration to concentrate
   on the test.

        "test": "substring(option[61].hex,0,3) == 'foo'",


   The logging might then resemble this:

        2016-05-19 13:35:04.163 DEBUG [kea.eval/44478] EVAL_DEBUG_OPTION Pushing option 61 with value 0x666F6F626172
        2016-05-19 13:35:04.164 DEBUG [kea.eval/44478] EVAL_DEBUG_STRING Pushing text string '0'
        2016-05-19 13:35:04.165 DEBUG [kea.eval/44478] EVAL_DEBUG_STRING Pushing text string '3'
        2016-05-19 13:35:04.166 DEBUG [kea.eval/44478] EVAL_DEBUG_SUBSTRING Popping length 3, start 0, string 0x666F6F626172 pushing result 0x666F6F
        2016-05-19 13:35:04.167 DEBUG [kea.eval/44478] EVAL_DEBUG_STRING Pushing text string 'foo'
        2016-05-19 13:35:04.168 DEBUG [kea.eval/44478] EVAL_DEBUG_EQUAL Popping 0x666F6F and 0x666F6F pushing result 'true'


  Note

   The debug logging may be quite verbose if you have a number of expressions
   to evaluate. It is intended as an aid in helping you create and debug your
   expressions. You should plan to disable debug logging when you have your
   expressions working correctly. You also may wish to include only one set
   of expressions at a time in the configuration file while debugging them in
   order to limit the log statements. For example when adding a new set of
   expressions you might find it more convenient to create a configuration
   file that only includes the new expressions until you have them working
   correctly and then add the new set to the main configuration file.

                          Chapter 15. Hooks Libraries

   Table of Contents

   15.1. Introduction

   15.2. Installing Hook packages

   15.3. Configuring Hooks Libraries

   15.4. Available Hooks Libraries

                15.4.1. user_chk: Checking User Access

                15.4.2. legal_log: Forensic Logging Hooks

                15.4.3. flex_id: Flexible Identifiers for Host Reservations

                15.4.4. host_cmds: Host Commands

                15.4.5. lease_cmds: Lease Commands

                15.4.6. subnet_cmds: Subnet Commands

                15.4.7. class_cmds: Class Commands

                15.4.8. ha: High Availability

                15.4.9. stat_cmds: Supplemental Statistics Commands

                15.4.10. radius: RADIUS server support

                15.4.11. host_cache: Caching Host Reservations

   15.5. User contexts

15.1. Introduction

   Although Kea offers a lot of flexibility, there may be cases where its
   behavior needs customization. To accommodate this possibility, Kea
   includes the idea of "Hooks". This feature lets Kea load one or more
   dynamically-linked libraries (known as "hooks libraries") and, at various
   points in its processing ("hook points"), call functions in them. Those
   functions perform whatever custom processing is required.

   The hooks concept also allows keeping the core Kea code reasonably small
   by moving features that some, but not all users find useful to external
   libraries. People who don't need specific functionality simply don't load
   the libraries.

   Hooks libraries are loaded by individual Kea processes, not to Kea as a
   whole. This means (for example) that it is possible to associate one set
   of libraries with the DHCP4 server and a different set to the DHCP6
   server.

   Another point to note is that it is possible for a process to load
   multiple libraries. When processing reaches a hook point, Kea calls the
   hooks library functions attached to it. If multiple libraries have
   attached a function to a given hook point, Kea calls all of them, in the
   order in which the libraries are specified in the configuration file. The
   order may be important: consult the documentation of the libraries to see
   if this is the case.

   The next section describes how to configure hooks libraries. If you are
   interested in writing your own hooks library, information can be found in
   the Kea Developer's Guide.

   Note that some libraries are available under different licenses.

   Note that some libraries may require additional dependencies and/or
   compilation switches to be enabled, e.g. Radius library introduced in Kea
   1.4 requires FreeRadius-client library to be present. If
   --with-free-radius option is not specified, the Radius library will not be
   built.

15.2. Installing Hook packages

  Note

   The installation procedure has changed in 1.4.0. Kea 1.3.0 and earlier
   needed special switches passed to configure script to detect the hook
   libraries. Please see this KB article: https://kb.isc.org/article/AA-01587
   .

   Some hook packages are included in the base Kea sources. There is no need
   to do anything special to compile or install them, they are covered by the
   usual building and installation procedure. ISC also provides several
   additional hooks in form of various packages. All of those packages follow
   the same installation procedure that is similar to base Kea, but has
   several additional steps. For your convenience, the whole procedure is
   described here. Please refer to Chapter 3, Installation for general
   overview.

   1. Download the package. You will receive detailed instructions how to get
   it separately. This will be a file with a name similar to
   kea-premium-1.5.0.tar.gz. Your name may differ depending on which package
   you got.

   2. If you have the sources for the corresponding version of the
   open-source Kea package still on your system (from when you installed
   Kea), skip this step. Otherwise extract the Kea source from the original
   tarball you downloaded. For example, if you downloaded Kea 1.5.0., you
   should have a tarball called kea-1.5.0.tar.gz on your system. Unpack this
   tarball:

 $ tar zxvf kea-1.5.0.tar.gz

   This will unpack the tarball into the kea-1.5.0 subdirectory of your
   current working directory.

   3. Unpack the Kea premium tarball into the directory into which Kea was
   unpacked. For example, assuming that you followed step 2 and that Kea
   1.5.0 has been unpacked into a kea-1.5.0 subdirectory and that the Kea
   premium tarball is in your current directory, the following steps will
   unpack the premium tarball into the correct location:

   $ cd kea-1.5.0
   $ tar xvf ../kea-premium-1.5.0.tar.gz

   Note that unpacking the Kea premium package will put the files into a
   directory named premium. Regardless of the name of your package, the
   directory will always be called premium, just its content may vary.

   4. Run autoreconf tools. This step is necessary to update Kea's build
   script to include additional directory. If this tool is not already
   available on your system, you need to install automake and autoconf tools.
   To generate configure script, please use:

   $ autoreconf -i

   5. Rerun configure, using the same configure options as you used when
   originally building Kea. You can check if configure has detected the
   premium package by inspecting the summary printed when it exits. The first
   section of the output should look something like:

 Package:
   Name:            kea
   Version:         1.5.0
   Extended version:1.5.0 (tarball)
   OS Family:       Linux
   Using GNU sed:   yes
   Premium package: yes
   Included Hooks:  forensic_log flex_id host_cmds

   The last line indicates which specific hooks were detected. Note that some
   hooks may require its own dedicated switches, e.g. radius hook requires
   extra switches for FreeRADIUS. Please consult later sections of this
   chapter for details.

   6. Rebuild Kea

   $ make

   If your machine has multiple CPU cores, interesting option to consider
   here is -j X, where X is the number of available cores.

   7. Install Kea sources together with hooks:

 $ sudo make install

   Note that as part of the installation procedure, the install script will
   eventually venture into premium/ directory and will install additional
   hook libraries and associated files.

   The installation location of the hooks libraries depends whether you
   specified --prefix parameter to the configure script. If you did not, the
   default location will be /usr/local/lib/hooks. You can verify the
   libraries are installed properly with this command:

 $ ls -l /usr/local/lib/hooks/*.so
 /usr/local/lib/hooks/libdhcp_class_cmds.so
 /usr/local/lib/hooks/libdhcp_flex_id.so
 /usr/local/lib/hooks/libdhcp_host_cmds.so
 /usr/local/lib/hooks/libdhcp_lease_cmds.so
 /usr/local/lib/hooks/libdhcp_legal_log.so
 /usr/local/lib/hooks/libdhcp_subnet_cmds.so

   The exact list you see will depend on the packages you have. If you
   specified directory via --prefix, the hooks libraries will be located in
   {prefix directory}/lib/hooks.

15.3. Configuring Hooks Libraries

   The hooks libraries for a given process are configured using the
   hooks-libraries keyword in the configuration for that process. (Note that
   the word "hooks" is plural). The value of the keyword is an array of map
   structures, each structure corresponding to a hooks library. For example,
   to set up two hooks libraries for the DHCPv4 server, the configuration
   would be:

 "Dhcp4": {
     :
     "hooks-libraries": [
         {
             "library": "/opt/charging.so"
         },
         {
             "library": "/opt/local/notification.so",
             "parameters": {
                 "mail": "spam@example.com",
                 "floor": 13,
                 "debug": false,
                 "users": [ "alice", "bob", "charlie" ],
                 "languages": {
                     "french": "bonjour",
                     "klingon": "yl'el"
                 }
             }
         }
     ]
     :
 }

  Note

   This is a change to the syntax used in Kea 0.9.2 and earlier, where
   hooks-libraries was a list of strings, each string being the name of a
   library. The change was made in Kea 1.0 to facilitate the specification of
   library-specific parameters, a capability available in Kea 1.1.0 onwards.
   Libraries should allow a parameter entry where to put comments as it is
   done for many configuration scopes with comment and user context.

  Note

   The library reloading behavior has changed in Kea 1.1.0. Libraries are
   reloaded, even if their list hasn't changed. Kea does that, because the
   parameters specified for the library (or the files those parameters point
   to) may have changed.

   Libraries may have additional parameters. Those are not mandatory in the
   sense that there may be libraries that don't require them. However, for
   specific library there is often specific requirement for specify certain
   set of parameters. Please consult the documentation for your library for
   details. In the example above, the first library has no parameters. The
   second library has five parameters, specifying mail (string parameter),
   floor (integer parameter), debug (boolean parameter) and even lists (list
   of strings) and maps (containing strings). Nested parameters could be used
   if the library supports it. This topic is explained in detail in the Hooks
   Developer's Guide in the "Configuring Hooks Libraries" section.

   Notes:

     * The full path to each library should be given.

     * As noted above, order may be important - consult the documentation for
       each library.

     * An empty list has the same effect as omitting the hooks-libraries
       configuration element all together.

  Note

       There is one case where this is not true: if Kea is running with a
       configuration that contains a hooks-libraries item, and that item is
       removed and the configuration reloaded, the removal will be ignored
       and the libraries remain loaded. As a workaround, instead of removing
       the hooks-libraries item, change it to an empty list. This will be
       fixed in a future version of Kea.

   At the present time, only the kea-dhcp4 and kea-dhcp6 processes support
   hooks libraries.

15.4. Available Hooks Libraries

   As described above, the hooks functionality provides a way to customize a
   Kea server without modifying the core code. ISC has chosen to take
   advantage of this feature to provide functions that may only be useful to
   a subset of Kea users. To this end ISC has created some hooks libraries;
   these discussed in the following sections.

  Note

   Some of these libraries will be available with the base code while others
   will be shared with organizations supporting development of Kea , possibly
   as a 'benefit' or 'thank you' for helping to sustain the larger Kea
   project. If you would like to get access to those libraries, please
   consider taking out a support contract: this includes professional
   support, advance security notifications, input into our roadmap planning,
   and many other benefits, while helping making Kea sustainable in the long
   term.

   The following table provides a list of libraries currently available from
   ISC. It is important to pay attention to which libraries may be loaded by
   which Kea processes. It is a common mistake to configure the
   kea-ctrl-agent process to load libraries that should, in fact, be loaded
   by the kea-dhcp4 or kea-dhcp6 processes. If a library from ISC doesn't
   work as expected, please make sure that it has been loaded by the correct
   process per the table below.

  Warning

   While the Kea Control Agent includes the "hooks" functionality, (i.e.
   hooks libraries can be loaded by this process), none of ISC's current
   hooks libraries should be loaded by the Control Agent.

   Table 15.1. List of available hooks libraries

+----------------------------------------------------------------------------------------+
|     Name     |Availability| Since | Load by |               Description                |
|              |            |       | process |                                          |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |Reads known users list from a file.       |
|              |            |       |         |Unknown users will be assigned a lease    |
|              |            |       |         |from the last subnet defined in the       |
|              |            |       |         |configuration file, e.g. to redirect them |
|user_chk      |Kea sources |Kea 0.8|kea-dhcp4|a captive portal. This demonstrates how an|
|              |            |       |kea-dhcp6|external source of information can be used|
|              |            |       |         |to influence the Kea allocation engine.   |
|              |            |       |         |This hook is part of the Kea source code  |
|              |            |       |         |and is available in the                   |
|              |            |       |         |src/hooks/dhcp/user_chk directory.        |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |This library provides hooks that record a |
|              |            |       |         |detailed log of lease assignments and     |
|              |            |       |         |renewals into a set of log files. In many |
|              |            |       |         |legal jurisdictions companies, especially |
|              |            |       |         |ISPs, must record information about the   |
|              |            |       |         |addresses they have leased to DHCP        |
|Forensic      |Support     |Kea    |kea-dhcp4|clients. This library is designed to help |
|Logging       |customers   |1.1.0  |kea-dhcp6|with that requirement. If the information |
|              |            |       |         |that it records is sufficient it may be   |
|              |            |       |         |used directly. If your jurisdiction       |
|              |            |       |         |requires that you save a different set of |
|              |            |       |         |information, you may use it as a template |
|              |            |       |         |or example and create your own custom     |
|              |            |       |         |logging hooks.                            |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |Kea software provides a way to handle host|
|              |            |       |         |reservations that include addresses,      |
|              |            |       |         |prefixes, options, client classes and     |
|              |            |       |         |other features. The reservation can be    |
|              |            |       |         |based on hardware address, DUID,          |
|              |            |       |         |circuit-id or client-id in DHCPv4 and     |
|              |            |       |         |using hardware address or DUID in DHCPv6. |
|              |            |       |         |However, there are sometimes scenarios    |
|              |            |       |         |where the reservation is more complex,    |
|Flexible      |Support     |Kea    |kea-dhcp4|e.g. uses other options that mentioned    |
|Identifier    |customers   |1.2.0  |kea-dhcp6|above, uses part of specific options or   |
|              |            |       |         |perhaps even a combination of several     |
|              |            |       |         |options and fields to uniquely identify a |
|              |            |       |         |client. Those scenarios are addressed by  |
|              |            |       |         |the Flexible Identifiers hook application.|
|              |            |       |         |It allows defining an expression, similar |
|              |            |       |         |to the one used in client classification, |
|              |            |       |         |e.g. substring(relay6[0].option[37],0,6). |
|              |            |       |         |Each incoming packet is evaluated against |
|              |            |       |         |that expression and its value is then     |
|              |            |       |         |searched in the reservations database.    |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |Kea provides a way to store host          |
|              |            |       |         |reservations in a database. In many larger|
|              |            |       |         |deployments it is useful to be able to    |
|              |            |       |         |manage that information while the server  |
|              |            |       |         |is running. This library provides         |
|              |            |       |         |management commands for adding, querying  |
|              |            |       |         |and deleting host reservations in a safe  |
|              |            |       |         |way without restarting the server. In     |
|Host Commands |Support     |Kea    |kea-dhcp4|particular, it validates the parameters,  |
|              |customers   |1.2.0  |kea-dhcp6|so an attempt to insert incorrect data,   |
|              |            |       |         |e.g. add a host with conflicting          |
|              |            |       |         |identifier in the same subnet will be     |
|              |            |       |         |rejected. Those commands are exposed via  |
|              |            |       |         |command channel (JSON over unix sockets)  |
|              |            |       |         |and Control Agent (JSON over RESTful      |
|              |            |       |         |interface). Additional commands and       |
|              |            |       |         |capabilities related to host reservations |
|              |            |       |         |will be added in the future.              |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |In deployments in which subnet            |
|              |            |       |         |configuration needs to be frequently      |
|              |            |       |         |updated, it is a hard requirement that    |
|              |            |       |         |such updates be performed without the need|
|              |            |       |         |for a full DHCP server reconfiguration or |
|              |            |       |         |restart. This hooks library allows for    |
|Subnet        |Support     |Kea    |kea-dhcp4|incremental changes to the subnet         |
|Commands      |customers   |1.3.0  |kea-dhcp6|configuration such as: adding a subnet,   |
|              |            |       |         |removing a subnet. It also allows for     |
|              |            |       |         |listing all available subnets and fetching|
|              |            |       |         |detailed information about a selected     |
|              |            |       |         |subnet. The commands exposed by this      |
|              |            |       |         |library do not affect other subnets or    |
|              |            |       |         |configuration parameters currently used by|
|              |            |       |         |the server.                               |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |The lease commands hook library offers a  |
|              |            |       |         |number of new commands used to manage     |
|              |            |       |         |leases. Kea provides a way to store lease |
|              |            |       |         |information in various backends: memfile, |
|              |            |       |         |MySQL, PostgreSQL and Cassandra. This     |
|              |            |       |         |library provides a unified interface that |
|              |            |       |         |can manipulate leases in an unified, safe |
|              |            |       |         |way. In particular, it allows: manipulate |
|              |            |Kea    |kea-dhcp4|leases in memfile while Kea is running,   |
|Lease Commands|Kea sources |1.3.0  |kea-dhcp6|sanity check changes, check lease         |
|              |            |       |         |existence and remove all leases belonging |
|              |            |       |         |to specific subnet. It can also catch more|
|              |            |       |         |obscure errors, like adding a lease with  |
|              |            |       |         |subnet-id that does not exist in the      |
|              |            |       |         |configuration or configuring a lease to   |
|              |            |       |         |use an address that is outside of the     |
|              |            |       |         |subnet to which it is supposed to belong. |
|              |            |       |         |It provides a way to manage user contexts |
|              |            |       |         |associated with leases.                   |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |Minimizing a risk of DHCP service         |
|              |            |       |         |unavailability is achieved by setting up a|
|              |            |       |         |pair of the DHCP servers in a network. Two|
|              |            |       |         |modes of operation are supported. The     |
|              |            |       |         |first one is called load balancing and is |
|              |            |       |         |sometimes referred to as active-active.   |
|              |            |       |         |Each server can handle selected group of  |
|              |            |       |         |clients in this network or all clients, if|
|              |            |       |         |it detects that its partner has became    |
|              |            |       |         |unavailable. It is also possible to       |
|              |            |       |         |designate one server to serve all DHCP    |
|              |            |       |         |clients, and leave another server as      |
|              |            |       |         |"standby". This mode is called hot standby|
|High          |Kea sources |Kea    |kea-dhcp4|and is sometimes referenced to as         |
|Availability  |            |1.4.0  |kea-dhcp6|active-passive. This server will activate |
|              |            |       |         |its DHCP function when it detects that its|
|              |            |       |         |partner is not available. Such cooperation|
|              |            |       |         |between the DHCP servers requires that    |
|              |            |       |         |these servers constantly communicate with |
|              |            |       |         |each other to send updates about allocated|
|              |            |       |         |leases and to periodically test whether   |
|              |            |       |         |their partners are still operational. The |
|              |            |       |         |hook library also provides an ability to  |
|              |            |       |         |send lease updates to external backup     |
|              |            |       |         |server, making it much easier to have a   |
|              |            |       |         |replacement that is almost up to date. The|
|              |            |       |         |"libdhcp_ha" library provides such        |
|              |            |       |         |functionality for Kea DHCP servers.       |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |The Statistics Commands library provides  |
|              |            |       |         |additional commmands for retrieving       |
|              |            |       |         |accurate DHCP lease statistics for Kea    |
|              |            |       |         |DHCP servers that share the same lease    |
|              |            |       |         |database. This setup is common in         |
|              |            |       |         |deployments where DHCP service redundancy |
|              |            |       |         |is required and a shared lease database is|
|Statistics    |Kea sources |Kea    |kea-dhcp4|used to avoid lease data replication      |
|Commands      |            |1.4.0  |kea-dhcp6|between the DHCP servers. A feature was   |
|              |            |       |         |introduced in Kea 1.4.0 that allows       |
|              |            |       |         |tracking lease allocations within the     |
|              |            |       |         |lease database, thus making the statistics|
|              |            |       |         |accessible to all connected DHCP servers. |
|              |            |       |         |The Statistics Commands hooks library     |
|              |            |       |         |utilizes this feature and returns lease   |
|              |            |       |         |statistics for all subnets respectively.  |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |The RADIUS Hook library allows Kea to     |
|              |            |       |         |interact with the RADIUS servers using    |
|              |            |       |         |access and accounting mechanisms. The     |
|              |            |       |         |access mechanism may be used for access   |
|              |Support     |Kea    |kea-dhcp4|control, assigning specific IPv4 or IPv6  |
|Radius        |customers   |1.4.0  |kea-dhcp6|addresses reserved by RADIUS, dynamically |
|              |            |       |         |assigning addresses from designated pools |
|              |            |       |         |chosen by RADIUS or rejecting the client's|
|              |            |       |         |messages altogether. The accounting       |
|              |            |       |         |mechanism allows RADIUS server to keep    |
|              |            |       |         |track of device activity over time.       |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |Some of the database backends, such as    |
|              |            |       |         |RADIUS, are considered slow and may take a|
|              |            |       |         |long time to respond. Since Kea in general|
|              |            |       |         |is synchronous, the backend performance   |
|              |            |       |         |directly affects the DHCP performance. To |
|Host Cache    |Support     |Kea    |kea-dhcp4|minimize the impact and improve           |
|              |customers   |1.4.0  |kea-dhcp6|performance, the Host Cache library       |
|              |            |       |         |provides a way to cache responses from    |
|              |            |       |         |other hosts. This includes negative       |
|              |            |       |         |caching, i.e. the ability to remember that|
|              |            |       |         |there is no client information in the     |
|              |            |       |         |database.                                 |
|--------------+------------+-------+---------+------------------------------------------|
|              |            |       |         |This Class Cmds hooks library allows for  |
|Class Commands|Support     |Kea    |kea-dhcp4|adding, updating deleting and fetching    |
|              |customers   |1.5.0  |kea-dhcp6|configured DHCP client classes without the|
|              |            |       |         |need to restart the DHCP server.          |
+----------------------------------------------------------------------------------------+

   ISC hopes to see more hooks libraries become available as time progresses,
   both developed internally and externally. Since this list may evolve
   dynamically, we decided to keep it on a wiki page, available at this link:
   https://gitlab.isc.org/isc-projects/kea/wikis/Hooks-available. If you are
   a developer or are aware of any hooks libraries not listed there, please
   send a note to the kea-users or kea-dev mailing lists and someone will
   update it.

   The libraries developed by ISC are described in detail in the following
   sections.

  15.4.1. user_chk: Checking User Access

   The user_chk library is the first hooks library published by ISC. It
   attempts to serve several purposes:

     * To assign "new" or "unregistered" users to a restricted subnet, while
       "known" or "registered" users are assigned to unrestricted subnets.

     * To allow DHCP response options or vendor option values to be
       customized based upon user identity.

     * To provide a real time record of the user registration activity which
       can be sampled by an external consumer.

     * To serve as a demonstration of various capabilities possible using the
       hooks interface.

   Once loaded, the library allows segregating incoming requests into known
   and unknown clients. For known clients, the packets are processed mostly
   as usual, except it is possible to override certain options being sent.
   That can be done on a per host basis. Clients that are not on the known
   hosts list will be treated as unknown and will be assigned to the last
   subnet defined in the configuration file.

   As an example of use, this behavior may be used to put unknown users into
   a separate subnet that leads to a walled garden, where they can only
   access a registration portal. Once they fill in necessary data, their
   details are added to the known clients file and they get a proper address
   after their device is restarted.

  Note

   This library was developed several years before the host reservation
   mechanism has become available. Currently host reservation is much more
   powerful and flexible, but nevertheless the user_chk capability to consult
   and external source of information about clients and alter Kea's behavior
   is useful and remains of educational value.

   The library reads the /tmp/user_chk_registry.txt file while being loaded
   and each time an incoming packet is processed. The file is expected to
   have each line contain a self-contained JSON snippet which must have the
   following two entries:

     * type, whose value is "HW_ADDR" for IPv4 users or "DUID" for IPv6 users

     * id, whose value is either the hardware address or the DUID from the
       request formatted as a string of hex digits, with or without ":"
       delimiters.

   and may have the zero or more of the following entries:

     * bootfile whose value is the pathname of the desired file

     * tftp_server whose value is the hostname or IP address of the desired
       server

   A sample user registry file is shown below:

 { "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:04", "bootfile" : "/tmp/v4bootfile" }
 { "type" : "HW_ADDR", "id" : "0c:0e:0a:01:ff:06", "tftp_server" : "tftp.v4.example.com" }
 { "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:04", "bootfile" : "/tmp/v6bootfile" }
 { "type" : "DUID", "id" : "00:01:00:01:19:ef:e6:3b:00:0c:01:02:03:06", "tftp_server" : "tftp.v6.example.com" }

   As with any other hooks libraries provided by ISC, internals of the
   user_chk code are well documented. You can take a look at the Kea
   Developer's Guide section dedicated to the user_chk library that discusses
   how the code works internally. That, together with our general entries in
   Hooks Framework section should give you some pointers how to extend this
   library and perhaps even write your own from scratch.

  15.4.2. legal_log: Forensic Logging Hooks

   This section describes the forensic log hooks library. This library
   provides hooks that record a detailed log of lease assignments and
   renewals into a set of log files. Currently this library is only available
   to ISC customers with a support contract.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   In many legal jurisdictions companies, especially ISPs, must record
   information about the addresses they have leased to DHCP clients. This
   library is designed to help with that requirement. If the information that
   it records is sufficient it may be used directly. If your jurisdiction
   requires that you save a different set of information you may use it as a
   template or example and create your own custom logging hooks.

   This logging is done as a set of hooks to allow it to be customized to any
   particular need. Modifying a hooks library is easier and safer than
   updating the core code. In addition by using the hooks features those
   users who don't need to log this information can leave it out and avoid
   any performance penalties.

    15.4.2.1. Log File Naming

   The names for the log files have the following form:

 path/base-name.CCYYMMDD.txt

   The "path" and "base-name" are supplied in the configuration as described
   below see Section 15.4.2.4, "Configuring the Forensic Log Hooks". The next
   part of the name is the date the log file was started, with four digits
   for year, two digits for month and two digits for day. The file is rotated
   on a daily basis.

  Note

   When running Kea servers for both DHCPv4 and DHCPv6 the log names must be
   distinct. See the examples in Section 15.4.2.4, "Configuring the Forensic
   Log Hooks".

    15.4.2.2. DHCPv4 Log Entries

   For DHCPv4 the library creates entries based on DHCPREQUEST messages and
   corresponding DHCPv4 leases intercepted by lease4_select (for new leases)
   and lease4_renew (for renewed leases) hooks.

   An entry is a single string with no embedded end-of-line markers, a
   prepended timestamp and has the following sections:

 timestamp address duration device-id {client-info} {relay-info} {user-context}

   Where:

     * timestamp - the current date and time the log entry was written in
       "%Y-%m-%d %H:%M:%S %Z" strftime format ("%Z" is the time zone name).

     * address - the leased IPv4 address given out and whether it was
       assigned or renewed.

     * duration - the lease lifetime expressed in days (if present), hours,
       minutes and seconds. A lease lifetime of 0xFFFFFFFF will be denoted
       with the text "infinite duration".

     * device-id - the client's hardware address shown as numerical type and
       hex digit string.

     * client-info - the DHCP client id option (61) if present, shown as a
       hex string.

     * relay-info - for relayed packets the giaddr and the RAI circuit-id,
       remote-id and subscriber-id options (option 82 sub options: 1, 2 and
       6) if present. The circuit id and remote id are presented as hex
       strings

     * user-context - the optional user context associated to the lease.

   For instance (line breaks added for readability, they would not be present
   in the log file).

 2018-01-06 01:02:03 CET Address: 192.2.1.100 has been renewed for 1 hrs 52 min 15 secs to a device with hardware address:
 hwtype=1 08:00:2b:02:3f:4e, client-id: 17:34:e2:ff:09:92:54 connected via relay at address: 192.2.16.33,
 identified by circuit-id: 68:6f:77:64:79 and remote-id: 87:f6:79:77:ef

   In addition to logging lease activity driven by DHCPv4 client traffic, it
   also logs entries for the following lease management control channel
   commands: lease4-add, lease4-update, and lease4-del. Each entry is a
   single string with no embedded end-of-line markers and they will typically
   have the following forms:

   lease4-add:

 *timestamp* Administrator added a lease of address: *address* to a device with hardware address: *device-id*

   Dependent on the arguments of the add command, it may also include the
   client-id and duration.

   Example:

 2018-01-06 01:02:03 CET Administrator added a lease of address: 192.0.2.202 to a device with hardware address:
 1a:1b:1c:1d:1e:1f for 1 days 0 hrs 0 mins 0 secs

   lease4-update:

 *timestamp* Administrator updated information on the lease of address: *address* to a device with hardware address: *device-id*

   Dependent on the arguments of the update command, it may also include the
   client-id and lease duration.

   Example:

 2018-01-06 01:02:03 CET Administrator updated information on the lease of address: 192.0.2.202 to a device
 with hardware address: 1a:1b:1c:1d:1e:1f, client-id: 1234567890

   lease4-del: Deletes have two forms, one by address and one by identifier
   and identifier type:

 *timestamp* Administrator deleted the lease for address: *address*

   or

 *timestamp* Administrator deleted a lease for a device identified by: *identifier-type* of *identifier*

   Currently only a type of @b hw-address (hardware address) is supported.

   Examples:

 2018-01-06 01:02:03 CET Administrator deleted the lease for address: 192.0.2.202

 2018-01-06 01:02:12 CET Administrator deleted a lease for a device identified by: hw-address of 1a:1b:1c:1d:1e:1f

    15.4.2.3. DHCPv6 Log Entries

   For DHCPv6 the library creates entries based on lease management actions
   intercepted by the lease6_select (for new leases), lease6_renew (for
   renewed leases) and lease6_rebind (for rebound leases).

   An entry is a single string with no embedded end-of-line markers, a
   prepended timestamp and has the following sections:

 timestamp address duration device-id {relay-info}* {user-context}

   Where:

     * timestamp - the current date and time the log entry was written in
       "%Y-%m-%d %H:%M:%S %Z" strftime format ("%Z" is the time zone name).

     * address - the leased IPv6 address or prefix given out and whether it
       was assigned or renewed.

     * duration - the lease lifetime expressed in days (if present), hours,
       minutes and seconds. A lease lifetime of 0xFFFFFFFF will be denoted
       with the text "infinite duration".

     * device-id - the client's DUID and hardware address (if present).

     * relay-info - for relayed packets the content of relay agent messages,
       remote-id (code 37), subscriber-id (code 38) and interface-id (code
       18) options if present. Note that interface-id option, if present,
       identifies the whole interface the relay agent received the message
       on. This typically translates to a single link in your network, but it
       depends on your specific network topology. Nevertheless, this is
       useful information to better scope down the location of the device, so
       it is being recorded, if present.

     * user-context - the optional user context associated to the lease.

   For instance (line breaks added for readability, they would not be present
   in the log file).

 2018-01-06 01:02:03 PST Address:2001:db8:1:: has been assigned for 0 hrs 11 mins 53 secs
 to a device with DUID: 17:34:e2:ff:09:92:54 and hardware address: hwtype=1 08:00:2b:02:3f:4e
 (from Raw Socket) connected via relay at address: fe80::abcd for client on link address: 3001::1,
 hop count: 1, identified by remote-id: 01:02:03:04:0a:0b:0c:0d:0e:0f and subscriber-id: 1a:2b:3c:4d:5e:6f

   In addition to logging lease activity driven by DHCPv6 client traffic, it
   also logs entries for the following lease management control channel
   commands: lease6-add, lease6-update, and lease6-del. Each entry is a
   single string with no embedded end-of-line markers and they will typically
   have the following forms:

   lease6-add:

 *timestamp* Administrator added a lease of address: *address* to a device with DUID: *DUID*

   Dependent on the arguments of the add command, it may also include the
   hardware address and duration.

   Example:

 2018-01-06 01:02:03 PST Administrator added a lease of address: 2001:db8::3 to a device with DUID:
 1a:1b:1c:1d:1e:1f:20:21:22:23:24 for 1 days 0 hrs 0 mins 0 secs

   lease6-update:

 *timestamp* Administrator updated information on the lease of address: *address* to a device with DUID: *DUID*

   Dependent on the arguments of the update command, it may also include the
   hardware address and lease duration.

   Example:

 2018-01-06 01:02:03 PST Administrator updated information on the lease of address: 2001:db8::3 to a device with
 DUID: 1a:1b:1c:1d:1e:1f:20:21:22:23:24, hardware address: 1a:1b:1c:1d:1e:1f

   lease6-del: Deletes have two forms, one by address and one by identifier
   and identifier type:

 *timestamp* Administrator deleted the lease for address: *address*

   or

 *timestamp* Administrator deleted a lease for a device identified by: *identifier-type* of *identifier*

   Currently only a type of DUID is supported.

   Examples:

 2018-01-06 01:02:03 PST Administrator deleted the lease for address: 2001:db8::3

 2018-01-06 01:02:11 PST Administrator deleted a lease for a device identified by: duid of 1a:1b:1c:1d:1e:1f:20:21:22:23:24

    15.4.2.4. Configuring the Forensic Log Hooks

   To use this functionality the hook library must be included in the
   configuration of the desired DHCP server modules. The legal_log library is
   installed alongside the Kea libraries in [kea-install-dir]/lib where
   kea-install-dir is determined by the "--prefix" option of the configure
   script. It defaults to /usr/local. Assuming the default value then,
   configuring kea-dhcp4 to load the legal_log library could be done with the
   following Kea4 configuration:

 "Dhcp4": {
     "hooks-libraries": [
         {
             "library": "/usr/local/lib/libdhcp_legal_log.so",
             "parameters": {
                 "path": "/var/kea/var",
                 "base-name": "kea-forensic4"
             }
         },
         ...
     ]
 }

   To configure it for kea-dhcp6, the commands are simply as shown below:

 "Dhcp6": {
     "hooks-libraries": [
         {
             "library": "/usr/local/lib/libdhcp_legal_log.so",
             "parameters": {
                 "path": "/var/kea/var",
                 "base-name": "kea-forensic6"
             }
         },
         ...
     ]
 }

   Two Hook Library parameters are supported:

     * path - the directory in which the forensic file(s) will be written.
       The default value is [prefix]/kea/var. The directory must exist.

     * base-name - an arbitrary value which is used in conjunction with the
       current system date to form the current forensic file name. It
       defaults to kea-legal.

   If it is desired to restrict forensic logging to certain subnets, the
   "legal-logging" boolean parameter can be specified within a user context
   of these subnets. For example:

 "Dhcpv4" {
     "subnet4": [
         {
             "subnet": "192.0.2.0/24",
             "pools": [
                 {
                      "pool": "192.0.2.1 - 192.0.2.200"
                 }
             ],
             "user-context": {
                 "legal-logging": false
             }
         }
     ]
 }

   disables legal logging for the subnet "192.0.2.0/24". If this parameter is
   not specified, it defaults to 'true', which enables legal logging for the
   subnet.

   The following example demonstrates how to selectively disable legal
   logging for an IPv6 subnet.

 "Dhcpv6": {
     "subnet6": [
         {
             "subnet": "2001:db8:1::/64",
             "pools": [
                  {
                      "pool": "2001:db8:1::1-2001:db8:1::ffff"
                  }
             ],
             "user-context": {
                 "legal-logging": false
             }
         }
     ]
 }

   See Section 8.11, "User contexts in IPv4" and Section 9.14, "User contexts
   in IPv6" to learn more about user contexts in Kea configuration.

    15.4.2.5. Database backend

   Log entries can be inserted into a database when Kea is configured with
   database backend support: a table named 'logs' is used with a timestamp
   (timeuuid for Cassandra CQL) generated by the database software and a text
   log with the same format than for files without the timestamp.

   Please refer to Section 4.3.2, "MySQL" for MySQL, to Section 4.3.3,
   "PostgreSQL" for PostgreSQL or to Section 4.3.4, "CQL (Cassandra)" for
   Cassandra CQL. The logs table is part of the Kea database schemas.

   Configuration parameters are extended by standard lease database
   parameters as defined in Section 8.2.2.2, "Lease Database Configuration".
   The "type" parameter should be "mysql", "postgresql", "cql" or be
   "logfile". When it is absent or set to "logfile" files are used.

   This database feature is experimental and will be likely improved, for
   instance to add an address / prefix index (currently the only index is the
   timestamp). No specific tools is provided to operate the database but
   standard tools are applicable, for instance to dump the logs table from a
   CQL database:

 $ echo 'SELECT dateOf(timeuuid), log FROM logs;' | cqlsh -k database-name

  system.dateof(timeuuid)         | log
 ---------------------------------+---------------------------------------
  2018-01-06 01:02:03.227000+0000 | Address: 192.2.1.100 has been renewed ...
  ...
 (12 rows)
 $

  15.4.3. flex_id: Flexible Identifiers for Host Reservations

   This section describes a hook application dedicated to generate flexible
   identifiers for host reservation. Kea software provides a way to handle
   host reservations that include addresses, prefixes, options, client
   classes and other features. The reservation can be based on hardware
   address, DUID, circuit-id or client-id in DHCPv4 and using hardware
   address or DUID in DHCPv6. However, there are sometimes scenarios where
   the reservation is more complex, e.g. uses other options that mentioned
   above, uses part of specific options or perhaps even a combination of
   several options and fields to uniquely identify a client. Those scenarios
   are addressed by the Flexible Identifiers hook application.

   Currently this library is only available to ISC customers with a support
   contract.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   The library allows for defining an expression, using notation initially
   used for client classification only. See Section 14.3, "Using Expressions
   In Classification" for detailed description of the syntax available. One
   notable difference is that for client classification the expression
   currently has to evaluate to either true or false, while the flexible
   identifier expression is expected to evaluate to a string that will be
   used as identifier. It is a valid case for the expression to evaluate to
   empty string (e.g. in cases where a client does not sent specific
   options). This expression is then evaluated for each incoming packet. This
   evaluation generates an identifier that is used to identify the client. In
   particular, there may be host reservations that are tied to specific
   values of the flexible identifier.

   The library can be loaded in similar way as other hook libraries. It takes
   a mandatory parameter identifier-expression and optional boolean parameter
   replace-client-id:

 "Dhcp6": {
     "hooks-libraries": [
         {
             "library": "/path/libdhcp_flex_id.so",
             "parameters": {
                 "identifier-expression": "expression",
                 "replace-client-id": "false"
             }
         },
         ...
     ]
 }

   The flexible identifier library supports both DHCPv4 and DHCPv6.

   EXAMPLE: Let's consider a case of an IPv6 network that has an independent
   interface for each of the connected customers. Customers are able to plug
   in whatever device they want, so any type of identifier (e.g. a client-id)
   is unreliable. Therefore the operator may decide to use an option inserted
   by a relay agent to differentiate between clients. In this particular
   deployment, the operator verified that the interface-id is unique for each
   customer facing interface. Therefore it is suitable for usage as
   reservation. However, only the first 6 bytes of the interface-id are
   interesting, because remaining bytes are either randomly changed or not
   unique between devices. Therefore the customer decided to use first 6
   bytes of the interface-id option inserted by the relay agent. After adding
   "flex-id" host-reservation-identifiers goal can be achieved by using the
   following configuration:

 "Dhcp6": {
     "subnet6": [{ ..., // subnet definition starts here
     "reservations": [
         "flex-id": "'port1234'", // value of the first 8 bytes of the interface-id
         "ip-addresses": [ "2001:db8::1" ]
     ],
     }], // end of subnet definitions
     "host-reservation-identifiers": ["duid", "flex-id"], // add "flex-id" to reservation identifiers
     "hooks-libraries": [
         {
             "library": "/path/libdhcp_flex_id.so",
             "parameters": {
                 "identifier-expression": "substring(relay6[0].option[18].hex,0,8)"
             }
         },
         ...
     ]
 }

   NOTE: Care should be taken when adjusting the expression. If the
   expression changes, then all the flex-id values may change, possibly
   rendering all reservations based on flex-id unusable until they're
   manually updated. Therefore it is strongly recommended to start with the
   expression and a handful reservations, adjust the expression as needed and
   only after it was confirmed the expression does exactly what is expected
   out of it go forward with host reservations on any broader scale.

   flex-id values in host reservations can be specified in two ways. First,
   they can be expressed as hex string, e.g. bar string can be represented as
   626174. Alternatively, it can be expressed as quoted value (using double
   and single quotes), e.g. "'bar'". The former is more convenient for
   printable characters, while hex string values are more convenient for
   non-printable characters and does not require the use of the hexstring
   operator.

 "Dhcp6": {
     "subnet6": [{ ..., // subnet definition starts here
     "reservations": [
         "flex-id": "01:02:03:04:05:06", // value of the first 8 bytes of the interface-id
         "ip-addresses": [ "2001:db8::1" ]
     ],
     }], // end of subnet definitions
     "host-reservation-identifiers": ["duid", "flex-id"], // add "flex-id" to reservation identifiers
     "hooks-libraries": [
         {
             "library": "/path/libdhcp_flex_id.so",
             "parameters": {
                 "identifier-expression": "vendor[4491].option[1026].hex"
             }
         },
         ...
     ]
 }

   When "replace-client-id" is set to false (which is the default setting),
   the flex-id hook library uses evaluated flexible identifier solely for
   identifying host reservations, i.e. searching for reservations within a
   database. This is a functional equivalent of other identifiers, similar to
   hardware address or circuit-id. However, this mode of operation has an
   implication that if a client device is replaced, it may cause a conflict
   between an existing lease (allocated for old device) and the new lease
   being allocated for the new device. The conflict arises because the same
   flexible identifier is computed for the replaced device and the server
   will try to allocate the same lease. The mismatch between client
   identifiers sent by new device and old device causes the server to refuse
   this new allocation until the old lease expires. A manifestation of this
   problem is dependant on specific expression used as flexible identifier
   and is likely to appear if you only use options and other parameters that
   are identifying where the device is connected (e.g. circuit-id), rather
   than the device identification itself (e.g. MAC address).

   The flex-id library offers a way to overcome the problem with lease
   conflicts by dynamically replacing client identifier (or DUID in DHCPv6
   case) with a value derived from flexible identifier. The server processes
   the client's query as if flexible identifier was sent in the client
   identifier (or DUID) option. This guarantees that returning client (for
   which the same flexible identifier is evaluated) will be assigned the same
   lease despite the client identifier and/or MAC address change.

   The following is a stub configuration that enables this behavior:

 "Dhcp4": {
     "hooks-libraries": [
         {
             "library": "/path/libdhcp_flex_id.so",
             "parameters": {
                 "identifier-expression": "expression",
                 "replace-client-id": "true"
             }
         },
         ...
     ]
 }

   In the DHCPv4 case, the value derived from the flexible identifier is
   formed by prepending 1 byte with a value of zero to flexible identifier.
   In the IPv6 case, it is formed by prepanding two zero bytes before the
   flexible identifier.

   Note that for this mechanism to take effect, the DHCPv4 server must be
   configured to respect the client identifier option value during lease
   allocation, i.e. "match-client-id" must be set to true. See
   Section 8.2.19, "Using Client Identifier and Hardware Address" for
   details. No additional settings are required for DHCPv6.

   If "replace-client-id" option is set to true, the value of
   "echo-client-id" parameter (that governs whether to send back a client-id
   option or not) is ignored.

   The Section 15.4.5, "lease_cmds: Lease Commands" section describes
   commands used to retrieve, update and delete leases using various
   identifiers, e.g. "hw-address", "client-id". The lease_cmds library
   doesn't natively support querying for leases by flexible identifier.
   However, when "replace-client-id" is set to true, it makes it possible to
   query for leases using a value derived from the flexible identifier. In
   the DHCPv4 case, the query will look similar to this:

 {
     "command": "lease4-get",
     "arguments": {
         "identifier-type": "client-id",
         "identifier": "00:54:64:45:66",
         "subnet-id": 44
     }
 }

   where hexadecimal value of "54:64:45:66" is a flexible identifier computed
   for the client.

   In the DHCPv6 case, the corresponding query will look similar to this:

 {
     "command": "lease6-get",
     "arguments": {
         "identifier-type": "duid",
         "identifier": "00:00:54:64:45:66",
         "subnet-id": 10
     }
 }

  15.4.4. host_cmds: Host Commands

   This section describes a hook application that offers a number of new
   commands used to query and manipulate host reservations. Kea provides a
   way to store host reservations in a database. In many larger deployments
   it is useful to be able to manage that information while the server is
   running. This library provides management commands for adding, querying
   and deleting host reservations in a safe way without restarting the
   server. In particular, it validates the parameters, so an attempt to
   insert incorrect data e.g. add a host with conflicting identifier in the
   same subnet will be rejected. Those commands are exposed via command
   channel (JSON over unix sockets) and Control Agent (JSON over RESTful
   interface). Additional commands and capabilities related to host
   reservations will be added in the future.

   Currently this library is only available to ISC customers with a support
   contract.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   Currently three commands are supported: reservation-add (which adds new
   host reservation), reservation-get (which returns existing reservation if
   specified criteria are matched) and reservation-del (which attempts to
   delete a reservation matching specified criteria). To use commands that
   change the reservation information (currently these are reservation-add
   and reservation-del, but this rule applies to other commands that may be
   implemented in the future), hosts database must be specified (see
   hosts-databases description in Section 8.2.3.1, "DHCPv4 Hosts Database
   Configuration" and Section 9.2.3.1, "DHCPv6 Hosts Database Configuration")
   and it must not operate in read-only mode. If the hosts-databases are not
   specified or are running in read-only mode, the host_cmds library will
   load, but any attempts to use reservation-add or reservation-del will
   fail.

   Additional host reservation commands are planned in the future. For a
   description of envisaged commands, see Control API Requirements document.

   All commands are using JSON syntax. They can be issued either using
   control channel (see Chapter 17, Management API) or via Control Agent (see
   Chapter 7, Kea Control Agent).

   The library can be loaded in similar way as other hook libraries. It does
   not take any parameters. It supports both DHCPv4 and DHCPv6 servers.

 "Dhcp6": {
     "hooks-libraries": [
         {
             "library": "/path/libdhcp_host_cmds.so"
         }
         ...
     ]
 }

    15.4.4.1. The subnet-id parameter

   Prior to diving into the individual commands, it is worth discussing the
   parameter, subnet-id. Currently it is mandatory for all of the commands
   supplied by this library. Prior to Kea 1.5.0, reservations had to belong
   to specific subnet. Beginning with Kea 1.5.0, reservations may now be
   specified globally. In other words, they are not specific to any subnet.
   When reservations are supplied via the configuration file, the ID of the
   containing subnet (or lack thereof) is implicit in the configuration
   structure. However, when managing reservations using the host commands, it
   is necessary to explicitly identify the scope to which the reservation
   belongs. This is done via the subnet-id parameter. For global
   reservations, use a value of zero (0). For reservations scoped to a
   specific subnet, use that subnet's ID.

    15.4.4.2. reservation-add command

   reservation-add allows for the insertion of a new host. It takes a set of
   arguments that vary depending on the nature of the host reservation. Any
   parameters allowed in the configuration file that pertain to host
   reservation are permitted here. For details regarding IPv4 reservations,
   see Section 8.3, "Host Reservation in DHCPv4" and Section 9.3, "Host
   Reservation in DHCPv6". The subnet-id is manadatory. Use a value of zero
   (0) to add a global reservation, or the id of the subnet to which the
   reservation should be added. An example command can be as simple as:

 {
     "command": "reservation-add",
     "arguments": {
         "reservation": {
             "subnet-id": 1,
             "hw-address": "1a:1b:1c:1d:1e:1f",
             "ip-address": "192.0.2.202"
         }
     }
 }

   but can also take many more parameters, for example:

 {
     "command": "reservation-add",
     "arguments": {
         "reservation":
             {
                 "subnet-id":1,
                 "client-id": "01:0a:0b:0c:0d:0e:0f",
                 "ip-address": "192.0.2.205",
                 "next-server": "192.0.2.1",
                 "server-hostname": "hal9000",
                 "boot-file-name": "/dev/null",
                 "option-data": [
                     {
                         "name": "domain-name-servers",
                         "data": "10.1.1.202,10.1.1.203"
                     }
                 ],
                 "client-classes": [ "special_snowflake", "office" ]
             }
     }
 }

   Here is an example of complex IPv6 reservation:

 {
     "command": "reservation-add",
     "arguments": {
         "reservation":
             {
                 "subnet-id":1,
                 "duid": "01:02:03:04:05:06:07:08:09:0A",
                 "ip-addresses": [ "2001:db8:1:cafe::1" ],
                 "prefixes": [ "2001:db8:2:abcd::/64" ],
                 "hostname": "foo.example.com",
                 "option-data": [
                     {
                         "name": "vendor-opts",
                         "data": "4491"
                     },
                     {
                         "name": "tftp-servers",
                         "space": "vendor-4491",
                         "data": "3000:1::234"
                     }
                 ]
             }
     }
 }

   The command returns a status that indicates either a success (result 0) or
   a failure (result 1). Failed command always includes text parameter that
   explains the cause of failure. Example results:

 { "result": 0, "text": "Host added." }

   Example failure:

 { "result": 1, "text": "Mandatory 'subnet-id' parameter missing." }

   As reservation-add is expected to store the host, hosts-databases
   parameter must be specified in your configuration and databases must not
   run in read-only mode. In the future versions it will be possible to
   modify the reservations read from a configuration file. Please contact ISC
   if you are interested in this functionality.

    15.4.4.3. reservation-get command

   reservation-get can be used to query the host database and retrieve
   existing reservations. There are two types of parameters this command
   supports: (subnet-id, address) or (subnet-id, identifier-type,
   identifier). The first type of query is used when the address (either IPv4
   or IPv6) is known, but the details of the reservation aren't. One common
   use case of this type of query is to find out whether a given address is
   reserved or not. The second query uses identifiers. For maximum
   flexibility, Kea stores the host identifying information as a pair of
   values: type and the actual identifier. Currently supported identifiers
   are "hw-address", "duid", "circuit-id", "client-id" and "flex-id", but
   additional types may be added in the future. If any new identifier types
   are defined in the future, reservation-get command will support them
   automatically. The subnet-id is manadatory. Use a value of zero (0) to
   fetch a global reservation, or the id of the subnet to which the
   reservation belongs.

   An example command for getting a host reservation by (subnet-id, address)
   pair looks as follows:

 {
     "command": "reservation-get",
     "arguments": {
         "subnet-id": 1,
         "ip-address": "192.0.2.202"
     }
 }

   An example query by (subnet-id, identifier-type, identifier) looks as
   follows:

 {
     "command": "reservation-get",
     "arguments": {
         "subnet-id": 4,
         "identifier-type": "hw-address",
         "identifier": "01:02:03:04:05:06"
     }
 }

   reservation-get typically returns result 0 when the query was conducted
   properly. In particular, 0 is returned when the host was not found. If the
   query was successful a number of host parameters will be returned. An
   example of a query that did not find the host looks as follows:

 { "result": 0, "text": "Host not found." }

   An example result returned when the host was found:

 {
   "arguments": {
     "boot-file-name": "bootfile.efi",
     "client-classes": [

     ],
     "hostname": "somehost.example.org",
     "hw-address": "01:02:03:04:05:06",
     "ip-address": "192.0.2.100",
     "next-server": "192.0.0.2",
     "option-data": [

     ],
     "server-hostname": "server-hostname.example.org"
   },
   "result": 0,
   "text": "Host found."
 }

   An example result returned when the query was malformed:

 { "result": 1, "text": "No 'ip-address' provided and 'identifier-type'
                         is either missing or not a string." }

    15.4.4.4. reservation-del command

   reservation-del can be used to delete a reservation from the host
   database. There are two types of parameters this command supports:
   (subnet-id, address) or (subnet-id, identifier-type, identifier). The
   first type of query is used when the address (either IPv4 or IPv6) is
   known, but the details of the reservation aren't. One common use case of
   this type of query is to remove a reservation (e.g. you want a specific
   address to no longer be reserved). The second query uses identifiers. For
   maximum flexibility, Kea stores the host identifying information as a pair
   of values: type and the actual identifier. Currently supported identifiers
   are "hw-address", "duid", "circuit-id", "client-id" and "flex-id", but
   additional types may be added in the future. If any new identifier types
   are defined in the future, reservation-get command will support them
   automatically. The subnet-id is manadatory. Use a value of zero (0) to
   delete a global reservation, or the id of the subnet from which the
   reservation should be deleted.

   An example command for deleting a host reservation by (subnet-id, address)
   pair looks as follows:

 {
     "command": "reservation-del",
     "arguments": {
         "subnet-id": 1,
         "ip-address": "192.0.2.202"
     }
 }

   An example deletion by (subnet-id, identifier-type, identifier) looks as
   follows:

 {
     "command": "reservation-del",
     "arguments":
         "subnet-id": 4,
         "identifier-type": "hw-address",
         "identifier": "01:02:03:04:05:06"
     }
 }

   reservation-del returns result 0 when the host deletion was successful or
   1 if it was not. A descriptive text is provided in case of error. Example
   results look as follows:

 {
     "result": 1,
     "text": "Host not deleted (not found)."
 }

 {
     "result": 0,
     "text": "Host deleted."
 }

 {
     "result": 1,
     "text": "Unable to delete a host because there is no hosts-database
              configured."
 }

  15.4.5. lease_cmds: Lease Commands

   This section describes the hook library that offers a number of new
   commands used to manage leases. Kea provides a way to store lease
   information in several backends (memfile, MySQL, PostgreSQL and
   Cassandra). This library provides a unified interface that can manipulate
   leases in an unified, safe way. In particular, it allows things previously
   impossible: manipulate leases in memfile while Kea is running, sanity
   check changes, check lease existence and remove all leases belonging to
   specific subnet. It can also catch more obscure errors, like adding a
   lease with subnet-id that does not exist in the configuration or
   configuring a lease to use an address that is outside of the subnet to
   which it is supposed to belong. It provides a non programmatic way to
   manage user contexts associated to leases.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   There are many use cases when an administrative command may be useful:
   during migration between servers (possibly even between different
   vendors), when a certain network is being retired, when a device has been
   disconnected and the sysadmin knows for sure that it will not be coming
   back. The "get" queries may be useful for automating certain management
   and monitoring tasks. They can also act as preparatory steps for lease
   updates and removals.

   This library provides the following commands:

     * lease4-add - adds new IPv4 lease;

     * lease6-add - adds new IPv6 lease;

     * lease4-get - checks if an IPv4 lease with the specified parameters
       exists and returns it if it does;

     * lease6-get - checks if an IPv6 lease with the specified parameters
       exists and returns it if it does;

     * lease4-get-all - returns all IPv4 leases or IPv4 leases for specified
       subnets;

     * lease6-get-all - returns all IPv6 leases or IPv6 leases for specified
       subnets;

     * lease4-get-page - returns a page of all IPv4 leases; by iterating over
       pages it is possible to retrieve all leases in chunks;

     * lease6-get-page - returns a page of all IPv6 leases; by iterating over
       pages it is possible to retrieve all leases in chunks;

     * lease4-del - attempts to delete an IPv4 lease with the specified
       parameters;

     * lease6-del - attempts to delete an IPv6 lease with the specified
       parameters;

     * lease4-update - updates an IPv4 lease;

     * lease6-update - updates an IPv6 lease;

     * lease4-wipe - removes all leases from a specific IPv4 subnet or all
       subnets;

     * lease6-wipe - removes all leases from a specific IPv6 subnet or all
       subnets;

   Lease commands library is part of the open source code and is available to
   every Kea user.

   All commands are using JSON syntax. They can be issued either using
   control channel (see Chapter 17, Management API) or via Control Agent (see
   Chapter 7, Kea Control Agent).

   The library can be loaded in the same way as other hook libraries. It does
   not take any parameters. It supports both DHCPv4 and DHCPv6 servers.

 "Dhcp6": {
     "hooks-libraries": [
         {
             "library": "/path/libdhcp_lease_cmds.so"
         }
         ...
     ]
 }

    15.4.5.1. lease4-add, lease6-add commands

   lease4-add and lease6-add commands allow for the creation of a new lease.
   Typically Kea creates a lease on its own, when it first sees a new device.
   However, sometimes it may be convenient to create the lease
   administratively. The lease4-add command requires at least two parameters:
   an IPv4 address, and an identifier: hardware (MAC) address. A third
   parameter, subnet-id, was mandatory in Kea 1.4.0, but is optional
   beginning with Kea 1.5.0.. If not specified or specified value is 0, Kea
   will try to determine the value by running a subnet selection procedure.
   If specified, however, its value must match the existing subnet. The
   simplest successful call might look as follows:

 {
     "command": "lease4-add",
     "arguments": {
         "ip-address": "192.0.2.202",
         "hw-address": "1a:1b:1c:1d:1e:1f"
     }
 }

   lease6-add command requires four parameters: an IPv6 address, and IAID
   value (identity association identifier, a value sent by clients) and a
   DUID. The same principle for subnet-id as in lease4-add applies. If not
   specified or specified value is 0, Kea will try to determine the value own
   by running a subnet selection procedure. If specified, however, its value
   must match the existing subnet. For example:

 {
     "command": "lease6-add",
     "arguments": {
         "subnet-id": 66,
         "ip-address": "2001:db8::3",
         "duid": "1a:1b:1c:1d:1e:1f:20:21:22:23:24",
         "iaid": 1234
     }
 }

   lease6-add can be also used to add leases for IPv6 prefixes. In this case
   there are three additional parameters that must be specified: subnet-id,
   type (set to value of "IA_PD") and a prefix length. The actual prefix is
   set using ip-address field. Note that Kea is not able to guess subnet-id
   values for prefixes, so it must be specified explicitly. For example, to
   configure a lease for prefix 2001:db8:abcd::/48, the following command can
   be used:

 {
     "command": "lease6-add",
     "arguments": {
         "subnet-id": 66,
         "type": "IA_PD",
         "ip-address": "2001:db8:abcd::",
         "prefix-len": 48,
         "duid": "1a:1b:1c:1d:1e:1f:20:21:22:23:24",
         "iaid": 1234
     }
 }

   The commands can take a number of additional optional parameters:

     * valid-lft - specifies the lifetime of the lease, expressed in seconds.
       If not specified, the value configured in the subnet related to
       specified subnet-id is used.

     * expire - timestamp of the lease expiration time, expressed in unix
       format (seconds since 1 Jan 1970). If not specified, the default value
       is now + valid lifetime.

     * fqdn-fwd - specifies whether the lease should be marked as if forward
       DNS update was conducted. Note this only affects the lease parameter
       and the actual DNS update will not be conducted at the lease insertion
       time. If configured, a DNS update to remove the A or AAAA records will
       be conducted when the lease is removed due to expiration or being
       released by a client. If not specified, the default value is false.
       Hostname parameter must be specified in fqdn-fwd is set to true.

     * fqdn-rev - specifies whether the lease should be marked as if reverse
       DNS update was conducted. Note this only affects the lease parameter
       and the actual DNS update will not be conducted at the lease insertion
       time. If configured, a DNS update to remove the PTR record will be
       conducted when the lease is removed due to expiration or being
       released by a client. If not specified, the default value is false.
       Hostname parameter must be specified in fqdn-fwd is set to true.

     * hostname - specifies the hostname to be associated with this lease.
       Its value must be non-empty if either fqdn-fwd or fwdn-rev are set to
       true. If not specified, the default value is an empty string.

     * hw-address - hardware (MAC) address can be optionally specified for
       IPv6 lease. It is mandatory parameter for IPv4 lease.

     * client-id - client identifier is an optional parameter that can be
       specified for IPv4 lease.

     * preferred-lft - Preferred lifetime is an optional parameter for IPv6
       leases. If not specified, the value configured for the subnet
       corresponding to the specified subnet-id is used. This parameter is
       not used in IPv4.

     * user-context - specifies the user context to be associated with this
       lease. It must be a JSON map.

   Here's an example of more complex lease addition:

 {
     "command": "lease6-add",
     "arguments": {
         "subnet-id": 66,
         "ip-address": "2001:db8::3",
         "duid": "01:02:03:04:05:06:07:08",
         "iaid": 1234,
         "hw-address": "1a:1b:1c:1d:1e:1f",
         "preferred-lft": 500,
         "valid-lft": 1000,
         "expire": 12345678,
         "fqdn-fwd": true,
         "fqdn-rev": true,
         "hostname": "urania.example.org",
         "user-context": { "version": 1 }
     }
 }

   The command returns a status that indicates either a success (result 0) or
   a failure (result 1). Failed command always includes text parameter that
   explains the cause of failure. Example results:

 { "result": 0, "text": "Lease added." }

   Example failure:

 { "result": 1, "text": "missing parameter 'ip-address' (<string>:3:19)" }

      15.4.5.1.1. lease4-get, lease6-get commands

   lease4-get or lease6-get can be used to query the lease database and
   retrieve existing leases. There are two types of parameters the lease4-get
   supports: (address) or (subnet-id, identifier-type, identifier). There are
   two types for lease6-get: (address,type) or (subnet-id, identifier-type,
   identifier, IAID, type). The first type of query is used when the address
   (either IPv4 or IPv6) is known, but the details of the lease aren't. One
   common use case of this type of query is to find out whether a given
   address is being used or not. The second query uses identifiers. Currently
   supported identifiers for leases are: "hw-address" (IPv4 only),
   "client-id" (IPv4 only) and "duid" (IPv6 only).

   An example lease4-get command for getting a lease by an IPv4 address looks
   as follows:

 {
     "command": "lease4-get",
     "arguments": {
         "ip-address": "192.0.2.1"
     }
 }

   An example of the lease6-get query looks as follows:

 {
   "command": "lease6-get",
   "arguments": {
     "ip-address": "2001:db8:1234:ab::",
     "type": "IA_PD"
   }
 }

   An example query by "hw-address" for IPv4 lease looks as follows:

 {
     "command": "lease4-get",
     "arguments": {
         "identifier-type": "hw-address",
         "identifier": "08:08:08:08:08:08",
         "subnet-id": 44
     }
 }

   An example query by "client-id" for IPv4 lease looks as follows:

 {
     "command": "lease4-get",
     "arguments": {
         "identifier-type": "client-id",
         "identifier": "01:01:02:03:04:05:06",
         "subnet-id": 44
     }
 }

   An example query by (subnet-id, identifier-type, identifier, iaid, type)
   for IPv6 lease looks as follows:

 {
     "command": "lease4-get",
     "arguments": {
         "identifier-type": "duid",
         "identifier": "08:08:08:08:08:08",
         "iaid": 1234567,
         "type": "IA_NA",
         "subnet-id": 44
     }
 }

   The type is an optional parameter. Supported values are: IA_NA
   (non-temporary address) and IA_PD (IPv6 prefix) are supported. If not
   specified, IA_NA is assumed.

   leaseX-get returns a result that indicates a result of the operation and
   lease details, if found. It has one of the following values: 0 (success),
   1 (error) or 2 (empty). The empty result means that a query has been
   completed properly, but the object (a lease in this case) has not been
   found. The lease parameters, if found, are returned as arguments.

   An example result returned when the host was found:

 {
   "arguments": {
     "client-id": "42:42:42:42:42:42:42:42",
     "cltt": 12345678,
     "fqdn-fwd": false,
     "fqdn-rev": true,
     "hostname": "myhost.example.com.",
     "hw-address": "08:08:08:08:08:08",
     "ip-address": "192.0.2.1",
     "state": 0,
     "subnet-id": 44,
     "valid-lft": 3600
   },
   "result": 0,
   "text": "IPv4 lease found."
 }

      15.4.5.1.2. lease4-get-all, lease6-get-all commands

   lease4-get-all and lease6-get-all are used to retrieve all IPv4 or IPv6
   leases or all leases for the specified set of subnets. All leases are
   returned when there are no arguments specified with the command as in the
   following example:

 {
     "command": "lease4-get-all"
 }

   If the arguments are provided, it is expected that they contain "subnets"
   parameter, being a list of subnet identifiers for which the leases should
   be returned. For example, in order to retrieve all IPv6 leases belonging
   to the subnets with identifiers 1, 2, 3 and 4:

 {
     "command": "lease6-get-all",
     "arguments": {
         "subnets": [ 1, 2, 3, 4 ]
     }
 }

   The returned response contains a detailed list of leases in the following
   format:

 {
     "arguments": {
         "leases": [
             {
                 "cltt": 12345678,
                 "duid": "42:42:42:42:42:42:42:42",
                 "fqdn-fwd": false,
                 "fqdn-rev": true,
                 "hostname": "myhost.example.com.",
                 "hw-address": "08:08:08:08:08:08",
                 "iaid": 1,
                 "ip-address": "2001:db8:2::1",
                 "preferred-lft": 500,
                 "state": 0,
                 "subnet-id": 44,
                 "type": "IA_NA",
                 "valid-lft": 3600
             },
             {
                 "cltt": 12345678,
                 "duid": "21:21:21:21:21:21:21:21",
                 "fqdn-fwd": false,
                 "fqdn-rev": true,
                 "hostname": "",
                 "iaid": 1,
                 "ip-address": "2001:db8:0:0:2::",
                 "preferred-lft": 500,
                 "prefix-len": 80,
                 "state": 0,
                 "subnet-id": 44,
                 "type": "IA_PD",
                 "valid-lft": 3600
             }
         ]
     },
     "result": 0,
     "text": "2 IPv6 lease(s) found."
 }

  Warning

   The lease4-get-all and lease6-get-all commands may result in very large
   responses. This may have negative impact on the DHCP server responsiveness
   while the response is generated and transmitted over the control channel,
   as the server imposes no restriction on the number of leases returned as a
   result of this command.

      15.4.5.1.3. lease4-get-page, lease6-get-page commands

   The lease4-get-all and lease6-get-all commands may result in very large
   responses. Generating such a response may consume CPU bandwith as well as
   memory. It may even cause the server to become unresponsive. In case of
   large lease databases it is usually better to retrieve leases in chunks,
   using paging mechanism. The lease4-get-page and lease6-get-page implement
   paging mechanism for DHCPv4 and DHCPv6 servers respectively. The following
   command retrieves first 1024 IPv4 leases:

 {
     "command": "lease4-get-page",
     "arguments": {
         "from": "start",
         "limit": 1024
     }
 }

   The keyword start denotes that the first page of leases should be
   retrieved. Alternatively, an IPv4 zero address can be specified to
   retrieve the first page:

 {
     "command": "lease4-get-page",
     "arguments": {
         "from": "0.0.0.0",
         "limit": 1024
     }
 }

   Similaraly, the IPv6 zero address can be specified in the lease6-get-page
   command:

 {
     "command": "lease6-get-page",
     "arguments": {
         "from": "::",
         "limit": 6
     }
 }

   The response has the following structure:

 {
     "arguments": {
         "leases": [
             {
                 "ip-address": "2001:db8:2::1",
                 ...
             },
             {
                 "ip-address": "2001:db8:2::9",
                 ...
             },
             {
                 "ip-address": "2001:db8:3::1",
                 ...
             },
             {
                 "ip-address": "2001:db8:5::3",
                 ...
             }
             {
                 "ip-address": "2001:db8:4::1",
                 ...
             },
             {
                 "ip-address": "2001:db8:2::7",
                 ...
             }

         ],
         "count": 6
     },
     "result": 0,
     "text": "6 IPv6 lease(s) found."
 }

   Note that the leases' details were excluded from the response above for
   brevity.

   Generally, the returned list isn't sorted in any particular order. Some
   lease database backends may sort leases in ascending order of addresses,
   but the controlling client must not rely on this behavior. In case of
   highly distributed databases, such as Cassandra, ordering may be
   inefficient or even impossible.

   The count parameter contains a number of returned leases on the page.

   In order to fetch next page the client must use the last address of the
   current page as an input to the next lease4-get-page or lease6-get-page
   command call. In this example it is going to be:

 {
     "command": "lease6-get-page",
     "arguments": {
         "from": "2001:db8:2::7",
         "count": 6
     }
 }

   because the 2001:db8:2::7 is the last address on the current page.

   The client may assume that it has reached the last page when the count
   value is lower than specified in the command, including the case when the
   count is equal to 0, which means that no leases were found.

      15.4.5.1.4. lease4-del, lease6-del commands

   leaseX-del can be used to delete a lease from the lease database. There
   are two types of parameters this command supports, similar to leaseX-get
   commands: (address) for both v4 and v6, (subnet-id, identifier-type,
   identifier) for v4 and (subnet-id, identifier-type, identifier, type,
   IAID) for v6. The first type of query is used when the address (either
   IPv4 or IPv6) is known, but the details of the lease are not. One common
   use case of this type of query is to remove a lease (e.g. you want a
   specific address to no longer be used, no matter who may use it). The
   second query uses identifiers. For maximum flexibility, this interface
   uses identifiers as a pair of values: type and the actual identifier.
   Currently supported identifiers are "hw-address" (IPv4 only), "client-id"
   (IPv4 only) and "duid" (IPv6 only), but additional types may be added in
   the future.

   An example command for deleting a host reservation by address looks as
   follows:

 {
     "command": "lease4-del",
     "arguments": {
         "ip-address": "192.0.2.202"
     }
 }

   An example IPv4 lease deletion by "hw-address" looks as follows:

 {
   "command": "lease4-del",
   "arguments": {
     "identifier": "08:08:08:08:08:08",
     "identifier-type": "hw-address",
     "subnet-id": 44
   }
 }

   leaseX-del returns a result that indicates a outcome of the operation. It
   has one of the following values: 0 (success), 1 (error) or 3 (empty). The
   empty result means that a query has been completed properly, but the
   object (a lease in this case) has not been found.

      15.4.5.1.5. lease4-update, lease6-update commands

   lease4-update and lease6-update commands can be used to update existing
   leases. Since all lease database backends are indexed by IP addresses, it
   is not possible to update an address. All other fields may be updated. If
   an address needs to be changed, please use leaseX-del followed by
   leaseX-add commands.

   Subnet-id parameter, used to be mandatory in Kea 1.4.0, but it is optional
   since 1.5.0. If not specified or specified value is 0, Kea will try to
   determine its value by running a subnet selection procedure. If specified,
   however, its value must match the existing subnet.

   The optional boolean parameter "force-create" specifies if the lease
   should be created if it doesn't exist in the database. It defaults to
   false, which indicates that the lease is not created if it doesn't exist.
   In such case, an error is returned as a result of trying to update a
   non-existing lease. If the "force-create" parameter is set to true and the
   updated lease doesn't exist, the new lease is created as a result of
   receiving the leaseX-update.

   An example command updating IPv4 lease looks as follows:

 {
   "command": "lease4-update",
   "arguments": {
     "ip-address": "192.0.2.1",
     "hostname": "newhostname.example.org",
     "hw-address": "1a:1b:1c:1d:1e:1f",
     "subnet-id": 44,
     "force-create": true
   }
 }

   An example command updating IPv6 lease looks as follows:

 {
   "command": "lease6-update",
   "arguments": {
     "ip-address": "2001:db8::1",
     "duid": "88:88:88:88:88:88:88:88",
     "iaid": 7654321,
     "hostname": "newhostname.example.org",
     "subnet-id": 66,
     "force-create": false
   }
 }

      15.4.5.1.6. lease4-wipe, lease6-wipe commands

   lease4-wipe and lease6-wipe are designed to remove all leases associated
   with a given subnet. This administrative task is expected to be used when
   existing subnet is being retired. Note that the leases are not properly
   expired, there are no DNS updates conducted, no log messages and hooks are
   not called for leases being removed.

   An example of lease4-wipe looks as follows:

 {
   "command": "lease4-wipe",
   "arguments": {
     "subnet-id": 44
   }
 }

   An example of lease6-wipe looks as follows:

 {
   "command": "lease6-wipe",
   "arguments": {
     "subnet-id": 66
   }
 }

   The commands return a textual description of the number of leases removed
   and 0 (success) status code if any leases were removed and 2 (empty) if
   there were no leases. Status code 1 (error) may be returned in case the
   parameters are incorrect or some other exception is encountered.

   The subnet-id 0 has special meaning. It tells Kea to delete leases from
   all configured subnets. Also, the subnet-id parameter may be omitted. If
   not specified, leases from all subnets are wiped.

   Note: not all backends support this command.

  15.4.6. subnet_cmds: Subnet Commands

   This section describes a hook application that offers a number of new
   commands used to query and manipulate subnet and shared network
   configurations in Kea. This application is very useful in deployments with
   a large number of subnets being managed by the DHCP servers and when the
   subnets are frequently updated. The commands offer lightweight approach
   for manipulating subnets without a need to fully reconfigure the server
   and without affecting existing servers' configurations. An ability to
   manage shared networks (listing, retrieving details, adding new ones,
   removing existing ones, adding subnets to and removing from shared
   networks) is also provided.

   Currently this library is only available to ISC customers with a support
   contract.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   The following commands are currently supported:

     * subnet4-list/subnet6-list: lists all configured subnets
     * subnet4-get/subnet6-get: retrieves detailed information about a
       specified subnet
     * subnet4-add/subnet6-add: adds new subnet into server's configuration
     * subnet4-del/subnet6-del: removes a subnet from the server's
       configuration
     * network4-list/network6-list: lists all configured shared networks
     * network4-get/network6-get: retrieves detailed information about
       specified shared network
     * network4-add/network6-add: adds a new shared network to the server's
       configuration
     * network4-del/network6-del: removes a shared network from the server's
       configuration
     * network4-subnet-add/network6-subnet-add: adds existing subnet to
       existing shared network
     * network4-subnet-del/network6-subnet-del: removes a subnet from
       existing shared network and demotes it to a plain subnet.

    15.4.6.1. subnet4-list command

   This command is used to list all currently configured subnets. The subnets
   are returned in a brief form, i.e. a subnet identifier and subnet prefix
   is included for each subnet. In order to retrieve the detailed information
   about the subnet the subnet4-get should be used.

   This command has the simple structure:

 {
     "command": "subnet4-list"
 }

   The list of subnets returned as a result of this command is returned in
   the following format:

 {
     "result": 0,
     "text": "2 IPv4 subnets found",
     "arguments": {
     "subnets": [
         {
             "id": 10,
             "subnet": "10.0.0.0/8"
         },
         {
             "id": 100,
             "subnet": "192.0.2.0/24"
         }
     ]
 }

   If no IPv4 subnets are found, an error code is returned along with the
   error description.

    15.4.6.2. subnet6-list command

   This command is used to list all currently configured subnets. The subnets
   are returned in a brief form, i.e. a subnet identifier and subnet prefix
   is included for each subnet. In order to retrieve the detailed information
   about the subnet the subnet6-get should be used.

   This command has the simple structure:

 {
     "command": "subnet6-list"
 }

   The list of subnets returned as a result of this command is returned in
   the following format:

 {
     "result": 0,
     "text": "2 IPv6 subnets found",
     "arguments": {
     "subnets": [
         {
             "id": 11,
             "subnet": "2001:db8:1::/64"
         },
         {
             "id": 233,
             "subnet": "3000::/16"
         }
     ]
 }

   If no IPv6 subnets are found, an error code is returned along with the
   error description.

    15.4.6.3. subnet4-get command

   This command is used to retrieve detailed information about the specified
   subnet. This command usually follows the subnet4-list, which is used to
   discover available subnets with their respective subnet identifiers and
   prefixes. Any of those parameters can be then used in subnet4-get to fetch
   subnet information:

 {
     "command": "subnet4-get",
     "arguments": {
         "id": 10
     }
 }

   or

 {
     "command": "subnet4-get",
     "arguments": {
         "subnet": "10.0.0.0/8"
     }
 }

   If the subnet exists the response will be similar to this:

 {
     "result": 0,
     "text": "Info about IPv4 subnet 10.0.0.0/8 (id 10) returned",
     "arguments": {
         "subnets": [
             {
                 "subnet": "10.0.0.0/8",
                 "id": 1,
                 "option-data": [
                     ....
                 ]
                 ...
             }
         ]
     }
 }


    15.4.6.4. subnet6-get command

   This command is used to retrieve detailed information about the specified
   subnet. This command usually follows the subnet6-list, which is used to
   discover available subnets with their respective subnet identifiers and
   prefixes. Any of those parameters can be then used in subnet6-get to fetch
   subnet information:

 {
     "command": "subnet6-get",
     "arguments": {
         "id": 11
     }
 }

   or

 {
     "command": "subnet6-get",
     "arguments": {
         "subnet": "2001:db8:1::/64"
     }
 }

   If the subnet exists the response will be similar to this:

 {
     "result": 0,
     "text": "Info about IPv6 subnet 2001:db8:1::/64 (id 11) returned",
     "arguments": {
         "subnets": [
             {
                 "subnet": "2001:db8:1::/64",
                 "id": 1,
                 "option-data": [
                     ...
                 ]
                 ....
             }
         ]
     }
 }

    15.4.6.5. subnet4-add

   This command is used to create and add new subnet to the existing server
   configuration. This operation has no impact on other subnets. The subnet
   identifier must be specified and must be unique among all subnets. If the
   identifier or a subnet prefix is not unique an error is reported and the
   subnet is not added.

   The subnet information within this command has the same structure as the
   subnet information in the server configuration file with the exception
   that static host reservations must not be specified within subnet4-add.
   The commands described in Section 15.4.4, "host_cmds: Host Commands"
   should be used to add, remove and modify static reservations.

 {
     "command": "subnet4-add",
     "arguments": {
         "subnets": [ {
             "id": 123,
             "subnet": "10.20.30.0/24",
             ...
         } ]
     }
 }

   The response to this command has the following structure:

 {
     "result": 0,
     "text": "IPv4 subnet added",
     "arguments": {
         "subnets": [
             {
                 "id": 123,
                 "subnet": "10.20.30.0/24"
             }
         ]
     }
 }

    15.4.6.6. subnet6-add

   This command is used to create and add new subnet to the existing server
   configuration. This operation has no impact on other subnets. The subnet
   identifier must be specified and must be unique among all subnets. If the
   identifier or a subnet prefix is not unique an error is reported and the
   subnet is not added.

   The subnet information within this command has the same structure as the
   subnet information in the server configuration file with the exception
   that static host reservations must not be specified within subnet6-add.
   The commands described in Section 15.4.4, "host_cmds: Host Commands"
   should be used to add, remove and modify static reservations.

 {
     "command": "subnet6-add",
     "arguments": {
         "subnet6": [ {
             "id": 234,
             "subnet": "2001:db8:1::/64",
             ...
         } ]
     }
 }

   The response to this command has the following structure:

 {
     "result": 0,
     "text": "IPv6 subnet added",
     "arguments": {
         "subnet6": [
             {
                 "id": 234,
                 "subnet": "2001:db8:1::/64"
             }
         ]
     }
 }

   It is recommended, but not mandatory to specify subnet id. If not
   specified, Kea will try to assign the next subnet-id value. This automatic
   ID value generator is simple. It returns a previously automatically
   assigned value increased by 1. This works well, unless you manually create
   a subnet with a value bigger than previously used. For example, if you
   call subnet4-add five times, each without id, Kea will assign IDs: 1,2,3,4
   and 5 and it will work just fine. However, if you try to call subnet4-add
   five times, with the first subnet having subnet-id of value 3 and
   remaining ones having no subnet-id, it will fail. The first command (with
   explicit value) will use subnet-id 3, the second command will create a
   subnet with id of 1, the third will use value of 2 and finally the fourth
   will have the subnet-id value auto-generated as 3. However, since there is
   already a subnet with that id, it will fail.

   The general recommendation is to either: never use explicit values (so the
   auto-generated values will always work) or always use explicit values (so
   the auto-generation is never used). You can mix those two approaches only
   if you understand how the internal automatic subnet-id generation works.

  Note

   Subnet IDs must be greater than zero and less than 4294967295.

    15.4.6.7. subnet4-del command

   This command is used to remove a subnet from the server's configuration.
   This command has no effect on other configured subnets but removing a
   subnet has certain implications which the server's administrator should be
   aware of.

   In most cases the server has assigned some leases to the clients belonging
   to the subnet. The server may also be configured with static host
   reservations which are associated with this subnet. The current
   implementation of the subnet4-del removes neither the leases nor host
   reservations associated with a subnet. This is the safest approach because
   the server doesn't loose track of leases assigned to the clients from this
   subnet. However, removal of the subnet may still cause configuration
   errors and conflicts. For example: after removal of the subnet, the server
   administrator may add a new subnet with the ID used previously for the
   removed subnet. This means that the existing leases and static
   reservations will be in conflict with this new subnet. Thus, we recommend
   that this command is used with extreme caution.

   This command can also be used to completely delete an IPv4 subnet that is
   part of a shared network. If you want to simply remove the subnet from a
   shared network and keep the subnet configuration, use network4-subnet-del
   command instead.

   The command has the following structure:

 {
     "command": "subnet4-del",
     "arguments": {
         "id": 123
     }
 }

   The example successful response may look like this:

 {
     "result": 0,
     "text": "IPv4 subnet 192.0.2.0/24 (id 123) deleted",
     "arguments": {
         "subnets": [
             {
                 "id": 123,
                 "subnet": "192.0.2.0/24"
             }
         ]
     }
 }

    15.4.6.8. subnet6-del command

   This command is used to remove a subnet from the server's configuration.
   This command has no effect on other configured subnets but removing a
   subnet has certain implications which the server's administrator should be
   aware of.

   In most cases the server has assigned some leases to the clients belonging
   to the subnet. The server may also be configured with static host
   reservations which are associated with this subnet. The current
   implementation of the subnet6-del removes neither the leases nor host
   reservations associated with a subnet. This is the safest approach because
   the server doesn't loose track of leases assigned to the clients from this
   subnet. However, removal of the subnet may still cause configuration
   errors and conflicts. For example: after removal of the subnet, the server
   administrator may add a new subnet with the ID used previously for the
   removed subnet. This means that the existing leases and static
   reservations will be in conflict with this new subnet. Thus, we recommend
   that this command is used with extreme caution.

   This command can also be used to completely delete an IPv6 subnet that is
   part of a shared network. If you want to simply remove the subnet from a
   shared network and keep the subnet configuration, use network6-subnet-del
   command instead.

   The command has the following structure:

 {
     "command": "subnet6-del",
     "arguments": {
         "id": 234
     }
 }

   The example successful response may look like this:

 {
     "result": 0,
     "text": "IPv6 subnet 2001:db8:1::/64 (id 234) deleted",
     "subnets": [
         {
             "id": 234,
             "subnet": "2001:db8:1::/64"
         }
     ]
 }

    15.4.6.9. network4-list, network6-list commands

   These commands are used to retrieve full list of currently configured
   shared networks. The list contains only very basic information about each
   shared network. If more details are needed, please use network4-get or
   network6-get to retrieve all information available. This command does not
   require any parameters and its invocation is very simple:

 {
     "command": "network4-list"
 }

   An example response for network4-list looks as follows:

 {
     "arguments": {
         "shared-networks": [
             { "name": "floor1" },
             { "name": "office" }
         ]
     },
     "result": 0,
     "text": "2 IPv4 network(s) found"
 }

   network6-list follows exactly the same syntax for both the query and the
   response.

    15.4.6.10. network4-get, network6-get commands

   These commands are used to retrieve detailed information about shared
   networks, including subnets currently being part of a given network. Both
   commands take one mandatory parameter name, which specify the name of
   shared network. An example command to retrieve details about IPv4 shared
   network with a name "floor13" looks as follows:

 {
     "command": "network4-get",
     "arguments": {
         "name": "floor13"
     }
 }

   An example response could look as follows:

 {
     "result": 0,
     "text": "Info about IPv4 shared network 'floor13' returned",
     "arguments": {
         "shared-networks": [
         {
             "match-client-id": true,
             "name": "floor13",
             "option-data": [ ],
             "rebind-timer": 90,
             "relay": {
                 "ip-address": "0.0.0.0"
             },
             "renew-timer": 60,
             "reservation-mode": "all",
             "subnet4": [
                 {
                     "subnet": "192.0.2.0/24",
                     "id": 5,
                     // many other subnet specific details here
                 },
                 {
                     "id": 6,
                     "subnet": "192.0.3.0/31",
                     // many other subnet specific details here
                 }
             ],
             "valid-lifetime": 120
         }
         ]
     }
 }

   Note that actual response contains many additional fields that are omitted
   here for clarity. The response format is exactly the same as used in
   config-get, just is limited to returning shared networks information.

    15.4.6.11. network4-add, network6-add commands

   These commands are used to add a new shared network. New network has to
   have unique name. This command requires one parameter shared-networks,
   which is a list and should contain exactly one entry that defines the
   network. The only mandatory element for a network is its name. Although it
   does not make operational sense, it is allowed to add an empty shared
   network that does not have any subnets in it. That is allowed for testing
   purposes, but having empty networks (or with only one subnet) is
   discouraged in production environments. For details regarding syntax, see
   Section 8.4, "Shared networks in DHCPv4" and Section 9.4, "Shared networks
   in DHCPv6".

  Note

   As opposed to parameter inheritance during full new configuration
   processing, this command does not fully handle parameter inheritance and
   any missing parameters will be filled with default values, rather than
   inherited from global scope.

   An example that showcases how to add a new IPv4 shared network looks as
   follows:

 {
     "command": "network4-add",
     "arguments": {
         "shared-networks": [ {
             "name": "floor13",
             "subnet4": [
             {
                 "id": 100,
                 "pools": [ { "pool": "192.0.2.2-192.0.2.99" } ],
                 "subnet": "192.0.2.0/24",
                 "option-data": [
                     {
                         "name": "routers",
                         "data": "192.0.2.1"
                     }
                 ]
             },
             {
                 "id": 101,
                 "pools": [ { "pool": "192.0.3.2-192.0.3.99" } ],
                 "subnet": "192.0.3.0/24",
                 "option-data": [
                     {
                         "name": "routers",
                         "data": "192.0.3.1"
                     }
                 ]
             } ]
         } ]
     }
 }

   Assuming there was no shared network with a name floor13 and no subnets
   with id 100 and 101 previously configured, the command will be successful
   and will return the following response:

 {
     "arguments": {
         "shared-networks": [ { "name": "floor13" } ]
     },
     "result": 0,
     "text": "A new IPv4 shared network 'floor13' added"
 }

   The network6-add uses the same syntax for both the query and the response.
   However, there are some parameters that are IPv4-only (e.g.
   match-client-id) and some are IPv6-only (e.g. interface-id). The same
   applies to subnets within the network.

    15.4.6.12. network4-del, network6-del commands

   These commands are used to delete existing shared networks. Both commands
   take exactly one parameter 'name' that specifies the name of the network
   to be removed. An example invocation of network4-del command looks as
   follows:

 {
     "command": "network4-del",
     "arguments": {
         "name": "floor13"
     }
 }

   Assuming there was such a network configured, the response will look
   similar to the following:

 {
     "arguments": {
         "shared-networks": [
             {
                 "name": "floor13"
             }
         ]
     },
     "result": 0,
     "text": "IPv4 shared network 'floor13' deleted"
 }

   The network6-del command uses exactly the same syntax for both the command
   and the response.

   If there are any subnets belonging to the shared network being deleted,
   they will be demoted to a plain subnet. There is an optional parameter
   called subnets-action that, if specified, takes one of two possible
   values: keep (which is the default) and delete. It controls whether the
   subnets be demoted to plain subnets or removed. An example usage in
   network6-del command that deletes the shared network and all subnets in it
   could looks like as follows:

 {
     "command": "network4-del",
     "arguments": {
         "name": "floor13",
         "subnets-action": "delete"
     }
 }

   Alternatively, if you want to completely remove the subnets, you may use
   subnet4-del or subnet6-del commands.

    15.4.6.13. network4-subnet-add, network6-subnet-add commands

   These commands are used to add existing subnets to existing shared
   networks. There are several ways to add new shared network. System
   administrator can add the whole shared network at once, either by editing
   a configuration file or by calling network4-add or network6-add commands
   with desired subnets in it. This approach works better for completely new
   shared subnets. However, there may be cases when an existing subnet is
   running out of addresses and needs to be extended with additional address
   space. In other words another subnet has to be added on top of it. For
   this scenario, a system administrator can use network4-add or network6-add
   and then add existing subnet to this newly created shared network using
   network4-subnet-add or network6-subnet-add.

   The network4-subnet-add and network6-subnet-add commands take two
   parameters: id, which is an integer and specifies subnet-id of existing
   subnet to be added to a shared network; and name, which specifies name of
   the shared network the subnet will be added to. The subnet must not belong
   to any existing network. In case you want to reassign a subnet from one
   shared network to another, please use network4-subnet-del or
   network6-subnet-del commands first.

   An example invocation of network4-subnet-add command looks as follows:

 {
     "command": "network4-subnet-add",
     "arguments": {
         "name": "floor13",
         "id": 5
     }
 }

   Assuming there is a network named 'floor13', there is a subnet with
   subnet-id 5 and it is not a part of existing network, the command will
   return a response similar to the following:

 {
     "result": 0,
     "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now part of shared network 'floor1'"
 }

   The network6-subnet-add command uses exactly the same syntax for both the
   command and the response.

  Note

   As opposed to parameter inheritance during full new configuration
   processing or when adding a new shared network with new subnets, this
   command does not fully handle parameter inheritance and any missing
   parameters will be filled with default values, rather than inherited from
   global scope or from the shared network.

    15.4.6.14. network4-subnet-del, network6-subnet-del commands

   These commands are used to remove a subnet that is part of existing shared
   network and demote it to a plain, stand-alone subnet. If you want to
   remove a subnet completely, use subnet4-del or subnet6-del commands
   instead. The network4-subnet-del and network6-subnet-del commands take two
   parameters: id, which is an integer and specifies subnet-id of existing
   subnet to be removed from a shared network; and name, which specifies name
   of the shared network the subnet will be removed from.

   An example invocation of the network4-subnet-del command looks as follows:

  {
     "command": "network4-subnet-del",
     "arguments": {
         "name": "floor13",
         "id": 5
     }
  }

   Assuming there was a subnet with subnet-id equal to 5 that was part of a
   shared network named 'floor13', the response would look similar to the
   following:

 {
     "result": 0,
     "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now removed from shared network 'floor13'"
 }

   The network6-subnet-del command uses exactly the same syntax for both the
   command and the response.

  15.4.7. class_cmds: Class Commands

   This section describes the Class Commands hooks library, which exposes
   several control commands for manipulating client classes, being a part of
   the Kea DHCP servers' configurations, without the need to restart those
   servers. Using these commands it is possible to add, update, delete and
   list client classes configured for a given server.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   The Class Commands hooks library is available to premium Kea customers
   only.

    15.4.7.1. class-add command

   The class-add command is used to add a new client class to the DHCP server
   configuration. This class is appended at the end of the list of classes
   used by the server, i.e. this class may depend on any of the already
   configured client classes.

   The following example demonstrates how to add a new client class to the
   DHCPv4 server configuration:

 {
     "command": "class-add",
     "arguments": {
         "client-classes": [
             {
                 "name": "ipxe_efi_x64",
                 "test": "option[93].hex == 0x0009",
                 "next-server": "192.0.2.254",
                 "server-hostname": "hal9000",
                 "boot-file-name": "/dev/null"
             }
         ]
     }
 }

   Note that the client-classes parameter is a JSON list, but it allows only
   a single client class to be present. In the future this hooks library may
   be extended to support specification of multiple client classes within a
   single class-add command.

   The following is the example response to the class-add command:

 {
     "result": 0,
     "text": "Class 'ipxe_efi_x64' added."
 }

    15.4.7.2. class-update command

   The class-update command is used to update an existing client class in the
   DHCP server configuration. If the client class with the given name doesn't
   exist, the server returns result code of 3. In such case, the server
   configuration is not modified (client class is not created). The class-add
   command must be used instead to create the new client class.

   The class-update command has the same arguments structure as class-add
   command:

 {
     "command": "class-update",
     "arguments": {
         "client-classes": [
             {
                 "name": "ipxe_efi_x64",
                 "test": "option[93].hex == 0x0017",
                 "next-server": "0.0.0.0",
                 "server-hostname": "xfce",
                 "boot-file-name": "/dev/null"
             }
         ]
     }
 }

   The following is the example response:

 {
     "result": 0,
     "text": "Class 'ipxe_efi_x64' updated."
 }

   Any parameter of the client class can be modified with this command,
   except name. There is currently no way to rename the class, because the
   class name is used as a key for searching the class to be updated. In
   order to achieve similar effect to renaming the class, an existing class
   should be removed with class-del command and then added again with a
   different name using class-add. Note however, that the class with the new
   name will be added at the end of the list of configured classes.

    15.4.7.3. class-del command

   The class-del is used to remove a particular class from the server
   configuration. The class to be removed is identified by name. The class
   won't be removed if there are other classes dependening on it. In order to
   remove such class, the dependent classes must be removed first.

   The following is the example command removing ipxe_efi_x64 class:

 {
     "command": "class-del",
     "arguments": {
         {
             "name": "ipxe_efi_x64"
         }
     }
 }

   The following is the sample response to the class-del command when the
   specified client class has been found:

 {
     "result": 0,
     "text": "Class 'ipxe_efi_x64' deleted."
 }

   If the class doesn't exist, the result of 3 is returned.

    15.4.7.4. class-list command

   The class-list is used to retrieve a list of all client classes. This
   command includes no arguments:

 {
     "command": "class-list"
 }

   The following is the example response of the server including the list of
   client classes:

 {
     "result": 0,
     "text": "2 classes found",
     "arguments": {
         "client-classes": [
             {
                 "name": "ipxe_efi_x64"
             },
             {
                 "name": "pxeclient"
             }
         ]
     }
 }

   Note that the returned list does not contain full class definitions, but
   merely class names. In order to retrieve full class information, the
   class-get command should be used.

    15.4.7.5. class-get command

   The class-get is used to retrieve detail information about specified
   class. The command structure is very simple:

 {
     "command": "class-get",
     "arguments": {
         "name": "pxeclient"
     }
 }

   If the class with the specified name doesn't exist, the status code of 3
   is returned. If the specified client class exists, the class details are
   returned in the following format:

 {
     "result": 0,
     "text": "Class 'pxeclient' definition returned",
     "arguments": {
         "client-classes": [
             {
                 "name": "pxeclient",
                 "only-if-required": true,
                 "test": "option[vendor-class-identifier].text == 'PXEClient'",
                 "option-def": [
                     {
                         "name": "configfile",
                         "code": 209,
                         "type": "string"
                     }
                 ],
                 "option-data": [ ],
                 "next-server": "0.0.0.0",
                 "server-hostname": "xfce",
                 "boot-file-name": "/dev/null"
             }
         ]
     }
 }

   Note that the example above is DHCPv4 specific. The last three parameters
   are only returned by the DHCPv4 server and never returned by the DHCPv6
   server. Also, some of the parameters provided in this example may not be
   returned if they are not specified for the class. Specifically,
   only-if-required, test and the option-def are not returned if they are not
   specified for the class.

  15.4.8. ha: High Availability

   This section describes the High Availability hooks library, which can be
   loaded on a pair of DHCPv4 or DHCPv6 servers to increase reliability of
   the DHCP service in case of outage of one of the servers. This library
   used to be only available to ISC customers, but is now part of the open
   source Kea, available to all users.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   High Availability (HA) of the DHCP service is provided by running multiple
   cooperating server instances. If any of these instances becomes
   unavailable for whatever reason (DHCP software crash, Control Agent
   software crash, power outage, hardware failure), a surviving server
   instance can continue providing the reliable service to the clients. Many
   DHCP servers implementations include "DHCP Failover" protocol, which most
   significant features are: communication between the servers, partner
   failure detection and leases synchronization between the servers. However,
   the DHCPv4 failover standardization process was never completed at IETF.
   The DHCPv6 failover standard (RFC 8156) was published, but it is complex,
   difficult to use, has significant operational constraints and is different
   than its v4 counterpart. Although it may be useful for some users to use a
   "standard" failover protocol, it seems that most of the Kea users are
   simply interested in a working solution which guarantees high availability
   of the DHCP service. Therefore, Kea HA hook library derives major concepts
   from the DHCP Failover protocol but uses its own solutions for
   communication, configuration and its own state machine, which greatly
   simplifies its implementation and generally better fits into Kea. Also, it
   provides the same features in both DHCPv4 and DHCPv6. This document
   purposely uses the term "High Availability" rather than "Failover" to
   emphasize that it is not the Failover protocol implementation.

   The following sections describe the configuration and operation of the Kea
   HA hook library.

    15.4.8.1. Supported Configurations

   The Kea HA hook library supports two configurations also known as HA
   modes: load balancing and hot standby. In the load balancing mode, there
   are two servers responding to the DHCP requests. The load balancing
   function is implemented as described in RFC3074, with each server
   responding to 1/2 of received DHCP queries. When one of the servers
   allocates a lease for a client, it notifies the partner server over the
   control channel (RESTful API), so as the partner can save the lease
   information in its own database. If the communication with the partner is
   unsuccessful, the DHCP query is dropped and the response is not returned
   to the DHCP client. If the lease update is successful, the response is
   returned to the DHCP client by the server which has allocated the lease.
   By exchanging the lease updates, both servers get a copy of all leases
   allocated by the entire HA setup and any of the servers can be switched to
   handle the entire DHCP traffic if its partner becomes unavailable.

   In the load balancing configuration, one of the servers must be designated
   as "primary" and the other server is designated as "secondary".
   Functionally, there is no difference between the two during the normal
   operation. This distniction is required when the two servers are started
   at (nearly) the same time and have to synchronize their lease databases.
   The primary server synchronizes the database first. The secondary server
   waits for the primary server to complete the lease database
   synchronization before it starts the synchronization.

   In the hot standby configuration one of the servers is designated as
   "primary" and the second server is designated as "secondary". During the
   normal operation, the primary server is the only one that responds to the
   DHCP requests. The secodary server receives lease updates from the primary
   over the control channel. However, it does not respond to any DHCP queries
   as long as the primary is running or, more accurately, until the secondary
   considers the primary to be offline. When the secondary server detects the
   failure of the primary, it starts responding to all DHCP queries.

   In the configurations described above, the primary, secondary and standby
   are referred to as "active" servers, because they receive lease updates
   and can automatically react to the partner's failures by responding to the
   DHCP queries which would normally be handled by the partner. The HA hook
   library supports another server type (role) - backup server. The use of
   the backup servers is optional. They can be used in both load balancing
   and hot standby setup, in addition to the active servers. There is no
   limit on the number of backup servers in the HA setup. However, the
   presence of the backup servers increases latency of the DHCP responses,
   because not only do active servers send lease updates to each other, but
   also to the backup servers.

    15.4.8.2. Clocks on Active Servers

   Synchronized clocks are essential for the HA setup to operate reliably.
   The servers share lease information via lease updates and during
   synchronization of the databases. The lease information includes the time
   when the lease has been allocated and when it expires. Some clock skew
   between the servers participating the HA setup would usually exist. This
   is acceptable as long as the clock skew is relatively low, comparing to
   the lease lifetimes. However, if the clock skew becomes too high, the
   different notions of time for the lease expiration by different servers
   may cause the HA system to malfuction. For example, one server may
   consider a valid lease to be expired. As a consequence, the lease
   reclamation process may remove a name associated with this lease from the
   DNS, even though the lease may later get renewed by a client.

   Each active server monitors the clock skew by comparing its current time
   with the time returned by its partner in response to the heartbeat
   command. This gives a good approximation of the clock skew, although it
   doesn't take into account the time between sending the response by the
   partner and receiving this response by the server which sent the heartbeat
   command. If the clock skew exceeds 30 seconds, a warning log message is
   issued. The administrator may correct this problem by synchronizing the
   clocks (e.g. using NTP). The servers should notice the clock skew
   correction and stop issuing the warning

   If the clock skew is not corrected and it exceeds 60 seconds, the HA
   service on each of the servers is terminated, i.e. the state machine
   enters the terminated state. The servers will continue to respond to the
   DHCP clients (as in the load-balancing or hot-standby mode), but will
   neither exchange lease updates nor heartbeats and their lease databases
   will diverge. In this case, the administrator should synchronize the
   clocks and restart the servers.

    15.4.8.3. Server States

   The DHCP server operating within an HA setup runs a state machine and the
   state of the server can be retrieved by its peers using the ha-heartbeat
   command sent over the RESTful API. If the partner server doesn't respond
   to the ha-heartbeat command longer than configured amount of time, the
   communication is considered interrupted and the server may (depending on
   the configuration) use additional measures (desribed further in this
   document) to verify if the partner is still operating. If it finds that
   the partner is not operating, the server transitions to the partner-down
   state to handle the entire DHCP traffic directed to the system.

   In this case, the surviving server continues to send the ha-heartbeat
   command to detect when the partner wakes up. The partner synchronizes the
   lease database and when it is finally ready to operate, the surviving
   server returns to the normal operation, i.e. load-balancing or hot-standby
   state.

   The following is the list of all possible states into which the servers
   may transition:

     * backup - normal operation of the backup server. In this state it
       receives lease updates from the active servers.

     * hot-standby - normal operation of the active server running in the hot
       standby mode. Both primary and standby server are in this state during
       their normal operation. The primary server is responding to the DHCP
       queries and sends lease updates to the standby server and to the
       backup servers, if any backup servers are present.

     * load-balancing - normal operation of the active server running in the
       load balancing mode. Both primary and secondary server are in this
       state during their normal operation. Both servers are responding to
       the DHCP queries and send lease updates to each other and to the
       backup servers, if any backup servers are present.

     * partner-down - an active server transitions to this state after
       detecting that its partner (another active server) is offline. The
       server doesn't transition to this state if any of the backup servers
       is unavailable. In the partner-down state the server responds to all
       DHCP queries, so also those queries which are normally handled by the
       active server which is now unavailable.

     * ready - an active server transitions to this state after synchronizing
       its lease database with an active partner. This state is to indicate
       to the partner (likely being in the partner-down state that it may
       return to the normal operation. When it does, the server being in the
       ready state will also start normal operation.

     * syncing - an active server transitions to this state to fetch leases
       from the active partner and update the local lease database. When it
       this state, it issues the dhcp-disable to disable the DHCP service of
       the partner from which the leases are fetched. The DHCP servie is
       disabled for the maximum time of 60 seconds, after which it is
       automatically enabled, in case the syncing partner has died again
       failing to re-enable the service. If the synchronization is completed
       the syncing server issues the dhcp-enable to re-enable the DHCP
       service of the partner. The syncing operation is synchronous. The
       server is waiting for an answer from the partner and is not doing
       anything else while the leases synchronization takes place. A server
       which is configured to not synchronize its database with the partner,
       i.e. when the sync-leases configuration parameter is set to false,
       will never transition to this state. Instead, it will transition
       directly from the waiting to ready state.

     * terminated - an active server transitions to this state when the High
       Availability hooks library is unable to further provide reliable
       service and a manual intervention of the administrator is required to
       correct the problem. It is envisaged that various issues with the HA
       setup may cause the server to transition to this state in the future.
       As of Kea 1.4.0 release, the only issue causing the HA service to
       terminate is unacceptably high clock skew between the active servers,
       i.e. if the clocks on respective servers are more than 60 seconds
       apart. While in this state, the server will continue responding to the
       DHCP clients based on the HA mode selected (load balancing or hot
       standby), but the lease updates won't be exchanged and the heartbeats
       won't be sent. Once a server has entered the "terminated" state it
       will remain in this state until it is restarted. The administrator
       must correct the issue which caused this situation prior to restarting
       the server (e.g. synchronize clocks). Otherwise, the server will
       return to the "terminated" state as soon as it finds that the clock
       skew is still too high.

     * waiting - each started server instance enters this state. The backup
       server will transition directly from this state to the backup state.
       An active server will send heartbeat to its partner to check its
       state. If the partner appears to be unavailable the server will
       transition to the partner-down, otherwise it will transition to the
       syncing or ready state (depending on the setting of the sync-leases
       configuration parameter). If both servers appear to be in the waiting
       state (concurrent startup) the primary server will transition to the
       next state first. The secondary or standby server will remain in the
       waiting state until the primary transitions to the ready state.

  Note

   Currently, restarting the HA service being in the terminated state
   requires restarting the DHCP server or reloading its configuration. In the
   future, we will provide a command to restart the HA service.

   Whether the server responds to the DHCP queries and which queries it
   responds to is a matter of the server's state, if no administrative action
   is performed to configure the server otherwise. The following table
   provides the default behavior for various states.

   The DHCP Server Scopes denotes what group of received DHCP queries the
   server responds to in the given state. The in-depth explanation what the
   scopes are can be found below.

   Table 15.2. Default behavior of the server in various HA states

   +------------------------------------------------------------------------+
   |     State      |   Server Type   | DHCP Service | DHCP Service Scopes  |
   |----------------+-----------------+--------------+----------------------|
   | backup         |  backup server  |   disabled   |         none         |
   |----------------+-----------------+--------------+----------------------|
   |                |   primary or    |              |    HA_server1 if     |
   | hot-standby    |  standby (hot   |   enabled    |    primary, none     |
   |                |  standby mode)  |              |      otherwise       |
   |----------------+-----------------+--------------+----------------------|
   |                |   primary or    |              |    HA_server1 or     |
   | load-balancing | secondary (load |   enabled    |      HA_server2      |
   |                | balancing mode) |              |                      |
   |----------------+-----------------+--------------+----------------------|
   | partner-down   |  active server  |   enabled    |      all scopes      |
   |----------------+-----------------+--------------+----------------------|
   | ready          |  active server  |   disabled   |         none         |
   |----------------+-----------------+--------------+----------------------|
   | syncing        |  active server  |   disabled   |         none         |
   |----------------+-----------------+--------------+----------------------|
   |                |                 |              |    same as in the    |
   | terminated     |  active server  |   enabled    |  load-balancing or   |
   |                |                 |              |  hot-standby state   |
   |----------------+-----------------+--------------+----------------------|
   | waiting        |   any server    |   disabled   |         none         |
   +------------------------------------------------------------------------+

   The DHCP service scopes require some explanation. The HA configuration
   must specify a unique name for each server within the HA setup. This
   document uses the following convention within provided examples: server1
   for a primary server, server2 for the secondary or standby server and
   server3 for the backup server. In the real life any names can be used as
   long as they remain unique.

   In the load balancing mode there are two scopes named after the active
   servers: HA_server1 and HA_server2. The DHCP queries load balanced to the
   server1 belong to the HA_server1 scope and the queries load balanced to
   the server2 belong to the HA_server2 scope. If any of the servers is in
   the partner-down state, it is responsible for serving both scopes.

   In the hot standby mode, there is only one scope HA_server1 because only
   the server1 is responding to the DHCP queries. If that server becomes
   unavailable, the server2 becomes responsible for this scope.

   The backup servers do not have their own scopes. In some cases they can be
   used to respond to the queries belonging to the scopes of the active
   servers. Also, a server which is neither in the partner-down state nor in
   the normal operation serves no scopes.

   The scope names can be used to associate pools, subnets and networks with
   certain servers, so as only these servers can allocate addresses or
   prefixes from those pools, subnets or network. This is done via the client
   classification mechanism (see below).

    15.4.8.4. Scope Transition in Partner Down Case

   When one of the servers finds that its partner is unavailble, it will
   start serving clients from its own scope and the scope of the partner
   which is considered unavailable. This is straight forward for the new
   clients, i.e. sending DHCPDISCOVER (DHCPv4) or Solicit (DHCPv6), because
   those requests are not sent to any particular server. The available server
   will respond to all such queries when it is in the partner-down state.

   When the client is renewing a lease, it will send its DHCPREQUEST (DHCPv4)
   or Renew (DHCPv6) message directly to the server which has allocated the
   lease being renewed. Because this server is unavailable, the client will
   not get any response. In that case, the client continues to use its lease
   and re-tries to renew until the rebind timer (T2) elapses. The client will
   now enter the rebinding phase, in which it will send DHCPREQUEST (DHCPv4)
   or Rebind (DHCPv6) message to any available server. The surviving server
   will receive the rebinding request and will (typically) extend the
   lifetime of the lease. The client will continue to contact that new server
   to renew its lease as appropriate.

   When the other server becomes available, both active servers will
   eventually transition to the load-balancing or hot-standby state, in which
   they will be responsible for their own scopes. Some clients belonging to
   the scope of the started server will be trying to renew their leases via
   the surviving server. This server will not respond to them anymore and the
   client will eventually transition back to the right server via rebinding
   mechanism again.

    15.4.8.5. Load Balancing Configuration

   The following is the configuration snippet which enables high availability
   on the primary server within the load balancing configuration. The same
   configuration should be applied on the secondary and the backup server,
   with the only difference that the this-server-name should be set to
   server2 and server3 on those servers respectively.

 {
 "Dhcp4": {

     ...

     "hooks-libraries": [
         {
             "library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
             "parameters": { }
         },
         {
             "library": "/usr/lib/hooks/libdhcp_ha.so",
             "parameters": {
                 "high-availability": [ {
                     "this-server-name": "server1",
                     "mode": "load-balancing",
                     "heartbeat-delay": 10000,
                     "max-response-delay": 10000,
                     "max-ack-delay": 5000,
                     "max-unacked-clients": 5,
                     "peers": [
                         {
                             "name": "server1",
                             "url": "http://192.168.56.33:8080/",
                             "role": "primary",
                             "auto-failover": true
                         },
                         {
                             "name": "server2",
                             "url": "http://192.168.56.66:8080/",
                             "role": "secondary",
                             "auto-failover": true
                         },
                         {
                             "name": "server3",
                             "url": "http://192.168.56.99:8080/",
                             "role": "backup",
                             "auto-failover": false
                         }
                     ]
                 } ]
             }
         }
     ],

     "subnet4": [
         {
             "subnet": "192.0.3.0/24",
             "pools": [
                 {
                     "pool": "192.0.3.100 - 192.0.3.150",
                     "client-class": "HA_server1"
                 },
                 {
                     "pool": "192.0.3.200 - 192.0.3.250",
                     "client-class": "HA_server2"
                 }
             ],

             "option-data": [
                 {
                     "name": "routers",
                     "data": "192.0.3.1"
                 }
             ],

             "relay": { "ip-address": "10.1.2.3" }
         }
     ],

     ...

 }

 }

   Two hook libraries must be loaded to enable HA: libdhcp_lease_cmds.so and
   libdhcp_ha.so. The latter provides the implemenation of the HA feature.
   The former enables control commands required by HA to fetch and manipulate
   leases on the remote servers. In the example provided above, it is assumed
   that Kea libraries are installed in the /usr/lib directory. If Kea is not
   installed in the /usr directory, the hook libraries locations must be
   updated accordingly.

   The HA configuration is specified within the scope of the libdhcp_ha.so.
   Note that the top level parameter high-availability is a list, even though
   it currently contains only one entry. In the future this configuration is
   likely to be extended to contain more entries, if the particular server
   can participate in more than one HA relationships.

   The following are the global parameters which control the server's
   behavior with respect to HA:

     * this-server-name - is a unique identifier of the server within this HA
       setup. It must match with one of the servers specified within peers
       list.

     * mode - specifies a HA mode of operation. Currently supported modes are
       load-balancing and hot-standby.

     * heartbeat-delay - specifies a duration in milliseconds between the
       last heartbeat (or other command sent to the partner) and sending the
       next heartbeat. The heartbeats are sent periodically to gather the
       status of the partner and to verify whether the partner is still
       operating. The default value of this parameter is 10000 ms.

     * max-response-delay - specifies a duration in milliseconds since the
       last successful communication with the partner, after which the server
       assumes that the communication with the partner is interrupted. This
       duration should be greater than the heartbeat-delay. Usually it is a
       greater than the duration of multiple heartbeat-delay values. When the
       server detects that the communication is interrupted, it may
       transition to the partner-down state (when max-unacked-clients is 0)
       or trigger failure detection procedure using the values of the two
       parameters below. The default value of this parameter is 60000.

     * max-ack-delay - is one of the parameters controlling partner failure
       detection. When the communication with the partner is interrupted, the
       server examines values of the secs field (DHCPv4) or Elapsed Time
       option (DHCPv6) which denote how long the DHCP client has been trying
       to communicate with the DHCP server. This parameter specifies the
       maximum time in milliseconds for the client to try to communicate with
       the DHCP server, after which this server assumes that the client
       failed to communicate with the DHCP server (is "unacked"). The default
       value of this parameter is 10000.

     * max-unacked-clients - specifies how many "unacked" clients are allowed
       (see max-ack-delay) before this server assumes that the partner is
       offline and transitions to the partner-down state. The special value
       of 0 is allowed for this parameter which disables failure detection
       mechanism. In this case, the server which can't communicate with the
       partner over the control channel assumes that the partner server is
       down and transitions to the partner-down state immediately. The
       default value of this parameter is 10.

   The values of max-ack-delay and max-unacked-clients must be selected
   carefully, taking into account specifics of the network in which DHCP
   servers are operating. Note that the server in question may not respond to
   some of the DHCP clients because these clients are not to be serviced by
   this server (per administrative policy). The server may also drop
   malformed queries from the clients. Therefore, selecting too low value for
   the max-unacked-clients may result in transitioning to the partner-down
   state even though the partner is still operating. On the other hand,
   selecting too high value may result in never transitioning to the
   partner-down state if the DHCP traffic in the network is very low (e.g.
   night time), because the number of distinct clients trying to communicate
   with the server could be lower than max-unacked-clients.

   In some cases it may be useful to disable the failure detection mechanism
   altogether, if the servers are located very close to each other and the
   network partitioning is unlikely, i.e. failure to respond to heartbeats is
   only possible when the partner is offline. In such cases, set the
   max-unacked-clients to 0.

   The peers parameter contains a list of servers within this HA setup. In
   this configuration it must contain at least one primary and one secondary
   server. It may also contain unlimited number of backup servers. In this
   example there is one backup server which receives lease updates from the
   active servers.

   There are the following parameters specified for each of the peers within
   this list:

     * name - specifies unique name for the server.

     * url - specifies URL to be used to contact this server over the control
       channel. Other servers use this URL to send control commands to that
       server.

     * role - denotes the role of the server in the HA setup. The following
       roles are supported in the load balancing configuration: primary,
       secondary and backup. There must be exactly one primary and one
       secondary server in the load balancing setup.

     * auto-failover - a boolean value which denotes whether the server
       detecting a partner's failure should automatically start serving
       partner's clients. The default value of this parameter is true.

   In our example configuration, both active servers can allocate leases from
   the subnet "192.0.3.0/24". This subnet contains two address pools:
   "192.0.3.100 - 192.0.3.150" and "192.0.3.200 - 192.0.3.250", which are
   associated with HA servers scopes using client classification. When the
   server1 processes a DHCP query it will use the first pool for the lease
   allocation. Conversely, when the server2 is processing the DHCP query it
   will use the second pool. When any of the servers is in the partner-down
   state, it can serve leases from both pools and it will select the pool
   which is appropriate for the received query. In other words, if the query
   would normally be processed by the server2, but this server is not
   available, the server1 will allocate the lease from the pool of
   "192.0.3.200 - 192.0.3.250".

    15.4.8.6. Load Balancing with Advanced Classification

   In the previous section we have provided an example which demonstrated the
   load balancing configuration with the client classification limited to the
   use of HA_server1 and HA_server2 classes, which are dynamically assigned
   to the received DHCP queries. In many cases it will be required to use HA
   in deployments which already use some client classification.

   Suppose there is a system which classifies devices into two groups: phones
   and laptops, based on some classification criteria specified in Kea
   configuration file. Both types of devices are allocated leases from
   different address pools. Introducing HA in the load balancing mode is
   expected to result in further split of each of those pools, so as each of
   the servers can allocate leases for some part of the phones and part of
   the laptops. This requires that each of the existing pools should be split
   between the HA_server1 and HA_server2, so we end up with the following
   classes:

     * phones_server1
     * laptops_server1
     * phones_server2
     * laptops_server2

   The corresponding server configuration using advanced classification (and
   member expression) is provided below. For brevity the HA hook library
   configuration has been removed from this example.

 {
 "Dhcp4": {

     "client-classes": [
         {
             "name": "phones",
             "test": "substring(option[60].hex,0,6) == 'Aastra'",
         },
         {
             "name": "laptops",
             "test": "not member('phones')"
         },
         {
             "name": "phones_server1",
             "test": "member('phones') and member('HA_server1')"
         },
         {
             "name": "phones_server2",
             "test": "member('phones') and member('HA_server2')"
         },
         {
             "name": "laptops_server1",
             "test": "member('laptops') and member('HA_server1')"
         },
         {
             "name": "laptops_server2",
             "test": "member('laptops') and member('HA_server2')"
         }
     ],

     "hooks-libraries": [
         {
             "library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
             "parameters": { }
         },
         {
             "library": "/usr/lib/hooks/libdhcp_ha.so",
             "parameters": {
                 "high-availability": [ {

                     ...

                 } ]
             }
         }
     ],

     "subnet4": [
         {
             "subnet": "192.0.3.0/24",
             "pools": [
                 {
                     "pool": "192.0.3.100 - 192.0.3.125",
                     "client-class": "phones_server1"
                 },
                 {
                     "pool": "192.0.3.126 - 192.0.3.150",
                     "client-class": "laptops_server1"
                 },
                 {
                     "pool": "192.0.3.200 - 192.0.3.225",
                     "client-class": "phones_server2"
                 },
                 {
                     "pool": "192.0.3.226 - 192.0.3.250",
                     "client-class": "laptops_server2"
                 }
             ],

             "option-data": [
                 {
                     "name": "routers",
                     "data": "192.0.3.1"
                 }
             ],

             "relay": { "ip-address": "10.1.2.3" }
         }
     ],

     ...

 }

 }

   The configuration provided above splits the address range into four pools.
   Two pools are dedicated to server1 and two are dedicated for server2. Each
   server can assign leases to both phones and laptops. Both groups of
   devices are assigned addresses from different pools. The HA_server1 and
   HA_server2 are builtin classes (see Section 14.2, "Builtin Client
   Classes") and they don't need to be declared. They are assigned
   dynamically by the HA hook library as a result of load balancing
   algorithm. The phones_* and laptop_* evaluate to "true" when the query
   belongs to a given combination of other classes, e.g. HA_server1 and
   phones. The pool will be selected accordingly as a result of such
   evaluation.

   Consult Chapter 14, Client Classification for details on how to use member
   expression and about class dependencies.

    15.4.8.7. Hot Standby Configuration

   The following is the example configuration of the primary server in the
   hot standby configuration:

 {
 "Dhcp4": {

     ...

     "hooks-libraries": [
         {
             "library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
             "parameters": { }
         },
         {
             "library": "/usr/lib/hooks/libdhcp_ha.so",
             "parameters": {
                 "high-availability": [ {
                     "this-server-name": "server1",
                     "mode": "hot-standby",
                     "heartbeat-delay": 10000,
                     "max-response-delay": 10000,
                     "max-ack-delay": 5000,
                     "max-unacked-clients": 5,
                     "peers": [
                         {
                             "name": "server1",
                             "url": "http://192.168.56.33:8080/",
                             "role": "primary",
                             "auto-failover": true
                         },
                         {
                             "name": "server2",
                             "url": "http://192.168.56.66:8080/",
                             "role": "standby",
                             "auto-failover": true
                         },
                         {
                             "name": "server3",
                             "url": "http://192.168.56.99:8080/",
                             "role": "backup",
                             "auto-failover": false
                         }
                     ]
                 } ]
             }
         }
     ],

     "subnet4": [
         {
             "subnet": "192.0.3.0/24",
             "pools": [
                 {
                     "pool": "192.0.3.100 - 192.0.3.250",
                     "client-class": "HA_server1"
                 }
             ],

             "option-data": [
                 {
                     "name": "routers",
                     "data": "192.0.3.1"
                 }
             ],

             "relay": { "ip-address": "10.1.2.3" }
         }
     ],

     ...

 }

 }

   This configuration is very similar to the load balancing configuration
   described Section 15.4.8.5, "Load Balancing Configuration", with a few
   notable differences.

   The mode is now set to hot-standby, in which only one server is responding
   to the DHCP clients. If the primary server is online, the primary server
   is responding to all DHCP queries. The standby server takes over the
   entire DHCP traffic when it discovers that the primary is unavailable.

   In this mode, the non-primary active server is called standby and that's
   what the role of the second active server is set to.

   Finally, because there is always one server responding to the DHCP
   queries, there is only one scope HA_server1 in use within pools
   definitions. In fact, the client-class parameter could be removed from
   this configuration without harm, because there are no conflicts in lease
   allocations by different servers as they do not allocate leases
   concurrently. The client-class is left in this example mostly for
   demonstration purposes, to highlight the differences between the hot
   standby and load balancing mode of operation.

    15.4.8.8. Lease Information Sharing

   An HA enabled server informs its active partner about allocated or renewed
   leases by sending appropriate control commands. The partner updates the
   lease information in its own database. When the server starts up for the
   first time or recovers after a failure it synchronizes its lease database
   with the partner. These two mechanisms guarantee consistency of the lease
   information between the servers and allow for designating one of the
   servers to handle the entire DHCP traffic in case the other server becomes
   unavailable.

   In some cases, though, it is desired to disable lease updates and/or
   database synchronization between the active servers if the exchange of
   information about the allocated leases is performed using some other
   mechanism. Kea supports various types of databases to be used as a storage
   for leases, e.g. MySQL, Postgres, Cassandra. Those databases include
   builtin solutions for data replication which are often used by Kea users
   to provide redundancy.

   The HA hook library supports such scenarios by allowing to disable lease
   updates over the control channel and/or lease database synchronization,
   leaving the server to rely on the database replication mechanism. This is
   controlled by the two boolean parameters: send-lease-updates and
   sync-leases, which values default to true:

 {
 "Dhcp4": {

     ...

     "hooks-libraries": [
         {
             "library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
             "parameters": { }
         },
         {
             "library": "/usr/lib/hooks/libdhcp_ha.so",
             "parameters": {
                 "high-availability": [ {
                     "this-server-name": "server1",
                     "mode": "load-balancing",
                     "send-lease-updates": false,
                     "sync-leases": false,
                     "peers": [
                         {
                             "name": "server1",
                             "url": "http://192.168.56.33:8080/",
                             "role": "primary"
                         },
                         {
                             "name": "server2",
                             "url": "http://192.168.56.66:8080/",
                             "role": "secondary"
                         }
                     ]
                 } ]
             }
         }
     ],

     ...

 }

   In the most typical use case, both parameters are set to the same value,
   i.e. both are false if the database replication is in use, or both are
   true otherwise. Introducing two separate parameters to control lease
   updates and lease database synchronization is aimed at possible special
   use cases, e.g. synchronization is performed by copying a lease file
   (therefore the sync-leases is set to false), but lease updates should be
   conducted as usual (send-lease-updates set to true). It should be noted
   that Kea doesn't natively support such use case, but users may develop
   their own scripts and tools around Kea to provide such mechanisms. The HA
   hooks library configuration is designed to maximize the administration
   flexibility.

    15.4.8.9. Controlling Lease Page Size Limit

   An HA enabled server initiates synchronization of the lease database after
   down time or upon receiving ha-sync command. The server uses commands
   described in Section 15.4.5.1.3, "lease4-get-page, lease6-get-page
   commands" to fetch leases from the partner server (lease queries). The
   size of the results page (maximum number of leases to be returned in a
   single response to one of these commands) can be controlled via HA hooks
   library configuration. Increasing the page size decreases the number of
   lease queries sent to the partner server, but it causes the partner server
   to generate larger responses, which lengthens transmission time as well as
   memory and CPU utilization on both servers. Decreasing the page size helps
   to decrease resources utilization but requires more lease queries to be
   issued to fetch the entire lease database.

   The default value of the sync-page-limit controlling the page size is
   10000. This means that the entire lease database can be fetched with a
   single command if the size of this database is equal or lower than 10000.

    15.4.8.10. Discussion about Timeouts

   In deployments with large number of clients connected to the network,
   lease database synchronization after the server failure may be a time
   consuming operation. The synchronizing server needs to gather all leases
   from the partner which yields a large response over the RESTful interface.
   The server receives leases using the paging mechanism described in
   Section 15.4.8.9, "Controlling Lease Page Size Limit". Before the page of
   leases is fetched, the synchronizing server sends a dhcp-disable command
   to disable the DHCP service on the partner server. If the service is
   already disabled, this command will reset the timeout for the DHCP service
   being disabled. This timeout value is by default set to 60 seconds. If
   fetching a single page of leases takes longer, the partner server will
   assume that the synchronizing server died and will resume its DHCP
   service. The connection of the synchronizing server with its partner is
   also guarded with the timeout. If the synchronization of a single page of
   leases takes longer than 60 seconds the synchronizing server terminates
   the connection and the synchronization fails. Both timeout values are
   controlled by a single configuration parameter sync-timeout. The following
   configuration snippet deminstrates how to modify the timeout for automatic
   re-enabling of the DHCP service on the partner server and the timeout for
   fetching a single page of leases from 60 seconds to 90 seconds:

 {
 "Dhcp4": {

     ...

     "hooks-libraries": [
         {
             "library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
             "parameters": { }
         },
         {
             "library": "/usr/lib/hooks/libdhcp_ha.so",
             "parameters": {
                 "high-availability": [ {
                     "this-server-name": "server1",
                     "mode": "load-balancing",
                     "sync-timeout": 90000,
                     "peers": [
                         {
                             "name": "server1",
                             "url": "http://192.168.56.33:8080/",
                             "role": "primary"
                         },
                         {
                             "name": "server2",
                             "url": "http://192.168.56.66:8080/",
                             "role": "secondary"
                         }
                     ]
                 } ]
             }
         }
     ],

     ...

 }

   It is important to note that extending this value may sometimes be
   insufficient to prevent issues with timeouts during lease database
   synchronization. The control commands travel via Control Agent, which also
   monitors incoming (with synchronizing server) and outgoing (with DHCP
   server) connections for timeouts. The DHCP server also monitors the
   connection from the Control Agent for timeouts. Those timeouts can't be
   currently modified via configuration. Extending these timeouts is only
   possible by modifing them in the Kea code and recompiling the server. The
   relevant constants are located in the Kea sources:
   src/lib/config/timeouts.h.

    15.4.8.11. Pausing HA State Machine

   The high availability state machine includes many different states
   described in detail in Section 15.4.8.3, "Server States". The server
   enters each state when certain conditions are met, most often taking into
   account the partner server's state. In some states the server performs
   specific actions, e.g. synchronization of the lease database in the
   syncing state or responding to DHCP queries according to the configured
   mode of operation in the load-balancing and hot-standby states.

   By default, transitions between the states are performed automatically and
   the server administrator has no direct control when the transitions take
   place and, in most cases, the administrator doesn't need such control. In
   some situations, however, the administrator may want to "pause" the HA
   state machine in a selected state to perform some additional
   administrative actions before the server transitions to the next state.

   Consider a server failure which results in a loss of the entire lease
   database. Typically, the server will rebuild its lease database when it
   enters the syncing state by querying the partner server for leases, but it
   is possible that the partner was also experiencing a failure and lacks
   lease information. In this case, it may be required to reconstruct lease
   databases on both servers from some external source, e.g. a backup server.
   If the lease database is going to be reconstructed via RESTful API, the
   servers should be started in the initial, i.e. waiting state and remain in
   this state while leases are being added. In particular, the servers should
   not attempt to synchronize their lease databases nor start serving DHCP
   clients.

   The HA hooks library provides configuration parameters and a command to
   control when the HA state machine should be paused and resumed. The
   following configuration will cause the HA state machine to pause in the
   waiting state after server startup.

 "Dhcp4": {

     ...

     "hooks-libraries": [
         {
             "library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
             "parameters": { }
         },
         {
             "library": "/usr/lib/hooks/libdhcp_ha.so",
             "parameters": {
                 "high-availability": [ {
                     "this-server-name": "server1",
                     "mode": "load-balancing",
                     "peers": [
                         {
                             "name": "server1",
                             "url": "http://192.168.56.33:8080/",
                             "role": "primary"
                         },
                         {
                             "name": "server2",
                             "url": "http://192.168.56.66:8080/",
                             "role": "secondary"
                         }
                     ],
                     "state-machine": {
                         "states":  [
                             {
                                 "state": "waiting",
                                 "pause": "once"
                             }
                         ]
                     }
                 } ]
             }
         }
     ],

     ...

 }

   The pause parameter value once denotes that the state machine should be
   paused upon the first transition to the waiting state. Later transitions
   to this state won't cause the state machine to pause. Two other supported
   values of the pause parameter are: always and never. The latter is the
   default value for each state, which instructs the server to never pause
   the state machine.

   In order to "unpause" the state machine the ha-continue command must be
   sent to the paused server. This command does not take any arguments. See
   Section 15.4.8.13, "Control Commands for High Availability" for details
   about commands specific for HA hooks library.

   It is possible to configure the state machine to pause in more than one
   state. Consider the following configuration.

 "Dhcp4": {

     ...

     "hooks-libraries": [
         {
             "library": "/usr/lib/hooks/libdhcp_lease_cmds.so",
             "parameters": { }
         },
         {
             "library": "/usr/lib/hooks/libdhcp_ha.so",
             "parameters": {
                 "high-availability": [ {
                     "this-server-name": "server1",
                     "mode": "load-balancing",
                     "peers": [
                         {
                             "name": "server1",
                             "url": "http://192.168.56.33:8080/",
                             "role": "primary"
                         },
                         {
                             "name": "server2",
                             "url": "http://192.168.56.66:8080/",
                             "role": "secondary"
                         }
                     ],
                     "state-machine": {
                         "states": [
                             {
                                 "state": "ready",
                                 "pause": "always"
                             },
                             {
                                 "state": "partner-down",
                                 "pause": "once"
                             }
                         ]
                     }
                 } ]
             }
         }
     ],

     ...

 }

   This configuration instructs the server to pause the state machine every
   time it transitions to the ready state and upon the first transition to
   the partner-down state.

   Refer to the Section 15.4.8.3, "Server States" for a complete of list of
   server states. The state machine can be paused in any of the supported
   states, however it is not practical for the backup and terminated states
   because the server never transitions out of these states anyway.

  Note

   In the syncing state the server is paused before it makes an attempt to
   synchronize lease database with a partner. In order to pause the state
   machine after lease database synchronization, use the ready state instead.

  Note

   The state of the HA state machine depends on the state of the cooperating
   server. Therefore, it must be taken into account that pausing the state
   machine of one server may affect the operation of the partner server. For
   example: if the primary server is paused in the waiting state the partner
   server will also remain in the waiting state until the state machine of
   the primary server is resumed and that server transitions to the ready
   state.

    15.4.8.12. Control Agent Configuration

   The Chapter 7, Kea Control Agent describes in detail the Kea deamon which
   provides RESTful interface to control Kea servers. The same functionality
   is used by High Availability hook library to establish communication
   between the HA peers. Therefore, the HA library requires that Control
   Agent is started for each DHCP instance within HA setup. If the Control
   Agent is not started the peers will not be able to communicate with the
   particular DHCP server (even if the DHCP server itself is online) and may
   eventually consider this server to be offline.

   The following is the example configuration for the CA running on the same
   machine as the primary server. This configuration is valid for both load
   balancing and hot standby cases presented in previous sections.

 {
 "Control-agent": {
     "http-host": "192.168.56.33",
     "http-port": 8080,

     "control-sockets": {
         "dhcp4": {
             "socket-type": "unix",
             "socket-name": "/tmp/kea-dhcp4-ctrl.sock"
         },
         "dhcp6": {
             "socket-type": "unix",
             "socket-name": "/tmp/kea-dhcp6-ctrl.sock"
         }
     }
 }
 }

    15.4.8.13. Control Commands for High Availability

   Even though the HA hook library is designed to automatically resolve
   issues with DHCP service interruptions by redirecting the DHCP traffic to
   a surviving server and synchronizing the lease database when required, it
   may be useful for the administrator to have control over the server
   behavior. In particular, it may be useful be able to trigger lease
   database synchronization on demand. It may also be useful to manually set
   the HA scopes that are being served.

   Note that the backup server can sometimes be used to handle the DHCP
   traffic in case if both active servers are down. The backup servers do not
   perform failover function automatically. Hence, in order to use the backup
   server to respond to the DHCP queries, the server administrator must
   enable this function manually.

   The following sections describe commands supported by the HA hook library
   which are available for the administrator.

      15.4.8.13.1. ha-sync command

   The ha-sync is issued to instruct the server to synchronize its local
   lease database with the selected peer. The server fetches all leases from
   the peer and updates those locally stored leases which are older comparing
   to those fetched. It also creates new leases when any of those fetched do
   not exist in the local database. All leases that are not returned by the
   peer but are in the local database are preserved. The database
   synchronization is unidirectional, i.e. only the database on the server to
   which the command has been sent is updated. In order to synchronize the
   peer's database a separate ha-sync has to be issued to that peer.

   The database synchronization may be triggered for both active and backup
   server type. The ha-sync has the following structure (DHCPv4 server case):

 {
     "command": "ha-sync",
     "service": [ "dhcp4 "],
     "arguments": {
         "server-name": "server2",
         "max-period": 60
     }
 }

   When the server receives this command it first disables the DHCP service
   of the server from which it will be fetching leases, i.e. sends
   dhcp-disable command to that server. The max-period parameter specifies
   the maximum duration (in seconds) for which the DHCP service should be
   disabled. If the DHCP service is successfully disabled, the synchronizing
   server will fetch leases from the remote server by issuing one or more
   lease4-get-page commands. When the lease database synchronization is
   complete, the synchronizing server sends the dhcp-enable to the peer to
   re-enable its DHCP service.

   The max-period value should be sufficiently long to guarantee that it
   doesn't elapse before the synchronization is completed. Otherwise, the
   DHCP server will automatically enable its DHCP function while the
   synchronization is still in progress. If the DHCP server subsequently
   allocates any leases during the synchronization, those new (or updated)
   leases will not be fetched by the synchronizing server leading to database
   inconsistencies.

      15.4.8.13.2. ha-scopes command

   This command allows for modifying the HA scopes that the server is
   serving. Consult Section 15.4.8.5, "Load Balancing Configuration" and
   Section 15.4.8.7, "Hot Standby Configuration" to learn what scopes are
   available for different HA modes of operation. The ha-scopes command has
   the following structure (DHCPv4 server case):

 {
     "command": "ha-scopes",
     "service": [ "dhcp4" ],
     "arguments": {
         "scopes": [ "HA_server1", "HA_server2" ]
     }
 }

   This command configures the server to handle traffic from both HA_server1
   and HA_server2 scopes. In order to disable all scopes specify an empty
   list:

 {
     "command": "ha-scopes",
     "service": [ "dhcp4 "],
     "arguments": {
         "scopes": [ ]
     }
 }

      15.4.8.13.3. ha-continue command

   This command is used to resume the operation of the paused HA state
   machine as described in the Section 15.4.8.11, "Pausing HA State Machine".
   It takes no arguments, so the command structure is as simple as:

 {
     "command": "ha-continue"
 }

  15.4.9. stat_cmds: Supplemental Statistics Commands

   This library provides additional statistics commands for retrieving lease
   statistics from Kea DHCP servers. These commands were added to address an
   issue with obtaining accurate lease statistics in deployments running
   multiple Kea servers that use shared lease back end. The in-memory
   statistics kept by individual servers only track lease changes made by
   that server. Thus in a deployment with multiple servers (e.g. two
   kea-dhcp6 servers using the same PostgreSQL database for lease storage),
   these statistics are incomplete. In Kea 1.4, the MySQL and PostgreSQL back
   ends were modified to track lease allocation changes as they occur via
   database triggers. Additionally, all four lease back ends were extended to
   support retrieving lease statistics for all subnets, a single subnet, or a
   range of subnets. Finally, this library was constructed to provide
   commands for retrieving these statistics. Additional statistics commands
   may be added to this library in future releases.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   The commands currently provided by this library are:

     * stat-lease4-get - fetches DHCPv4 lease statistics

     * stat-lease6-get - fetches DHCPv6 lease statistics

   The Stat commands library is part of the open source code and is available
   to every Kea user.

   All commands use JSON syntax and can be issued either directly to the
   servers via the control channel (see Chapter 17, Management API) or via
   Control Agent (see Chapter 7, Kea Control Agent).

   This library may be loaded by both kea-dhcp4 and kea-dhcp6 servers. It is
   loaded in the same way as other libraries and currently has no parameters:

 "Dhcp6": {
     "hooks-libraries": [
         {
             "library": "/path/libdhcp_stat_cmds.so"
         }
         ...
     ]
 }

   In a deployment with multiple Kea DHCP servers sharing a common lease
   storage, it may be loaded by any or all of the servers. However, one thing
   to keep in mind is that a server's response to a stat-lease{4/6}-get
   command will only contain data for subnets known to that server. In other
   words, if subnet does not appear in a server's configuration, it will not
   retrieve statistics for it.

    15.4.9.1. stat-lease4-get, stat-lease6-get commands

   The stat-lease4-get and stat-lease6-get commands fetch lease statistics
   for a range of known subnets. The range of subnets is determined through
   the use of optional command input parameters:

     * subnet-id - ID of the subnet for which lease statistics should be
       fetched. Use this to get statistics for a single subnet. If the subnet
       does not exist the command result code will be 3 (i.e.
       CONTROL_RESULT_EMPTY).

     * subnet-range - A pair of subnet IDs which describe an inclusive range
       of subnets for which statistics should be retrieved. Note that fuzzy
       values are supported thus allowing for a query for statistics using
       approximate ID values. If the range does not include any known
       subnets, the command result code will be 3 (i.e.
       CONTROL_RESULT_EMPTY).

          * first-subnet-id - ID of the first subnet in the range.

          * last-subnet-id - ID of the first subnet in the range.

   The use of subnet-id and subnet-range are mutually exclusive. If no
   parameters are given, the result will contain data for all known subnets.
   Note that in configurations with large numbers of subnets, this can be
   result in a large response.

   The following command would fetch lease statistics for all known subnets
   from kea-dhcp4 server:

 {
   "command": "stat-lease4-get"
 }

   The following command would fetch lease statistcis for subnet ID 10 from
   kea-dhcp6 server:

 {
   "command": "stat-lease6-get",
   "arguments": {
     "subnet-id" : 10
   }
 }

   The following command would fetch lease statistcis for all subnets from
   subnet ID 10 through 50 from kea-dhcp4 server:

 {
   "command": "stat-lease4-get",
   "arguments": {
     "subnet-range" {
       "first-subnet-id": 10,
       "last-subnet-id": 50,
     }
   }
 }

   The response to the either command will contain three elements:

     * result - numeric value indicating the outcome of the command where:

          * 0 - command was successful
          * 1 - an error occurred, an explanation will be the "text" element
          * 2 - indicates the fetch found no matching data

     * text - an explanation of the command outcome. When the command
       succeeds it will contain the command name along with the number of
       rows returned.

     * arguments - a map containing the data returned by the command as the
       element "result-set", which patterned after SQL statement responses:

          * columns - a list of text column labels. The columns returned for
            DHCPv4 are:

               * subnet-id - ID of the subnet
               * total-addresses - total number of addresses available for
                 DHCPv4 management in the subnet. In other words, this is the
                 sum of all addresses in all the configured pools in the
                 subnet.
               * assigned-addresses - number of addresses in the subnet that
                 are currently assigned to a client.
               * declined-addresses - number of addresses in the subnet that
                 are currently declined and are thus unavailable for
                 assignment.

          * The columns returned for DHCPv6 are:

               * subnet-id - ID of the subnet
               * total-nas - number of NA addresses available for DHCPv6
                 management in the subnet. In other words, this is the sum of
                 all the NA addresses in the all configured NA pools in the
                 subnet.
               * assigned-nas - number of NA addresses in a the subnet that
                 are currently assigned to a client.
               * declined-nas - number of NA addresses that are currently
                 declined and are thus unavailable for assignment.
               * total-pds - total number of prefixes available of DHCPv6
                 management in the subnet. In other words, this is the sum of
                 all prefixes in all the configured prefix pools in the
                 subnet.
               * assigned-pds - number of prefixes in the subnet that are
                 currently assigned to a client.

          * rows - a list of rows, one per subnet ID. Each row contains a
            data value for corresponding to and in the same order as each
            column listed in "columns" for a given subnet.

          * timestamp - textual date and time the data was fetched, expressed
            as GMT

   The response to a DHCPv4 command might look as follows:

   {
     "result": 0,
     "text": "stat-lease4-get: 2 rows found",
     "arguments": {
       "result-set": {
         "columns": [ "subnet-id", "total-addresses", "assigned-addresses", "declined-addresses" ]
         "rows": [
           [ 10, 256, 111, 0 ],
           [ 20, 4098, 2034, 4 ]
         ],
       "timestamp": "2018-05-04 15:03:37.000000"
       }
     }
   }

   The response to a DHCPv6 command might look as follows (subnet 10 has no
   prefix pools, subnet 20 has no NA pools, and subnet 30 has both NA and PD
   pools):

   {
     "result": 0,
     "text": "stat-lease6-get: 2 rows found",
     "arguments": {
       "result-set": {
         "columns": [ "subnet-id", "total-nas", "assigned-nas", "declined-nas", "total-pds", "assigned-pds" ]
         "rows": [
           [ 10, 4096, 2400, 3, 0, 0],
           [ 20, 0, 0, 0, 1048, 233 ]
           [ 30, 256, 60, 0, 1048, 15 ]
         ],
       "timestamp": "2018-05-04 15:03:37.000000"
       }
     }
   }

  15.4.10. radius: RADIUS server support

   The RADIUS hook library allows Kea to interact with two types of RADIUS
   servers: access and accounting. Although the most common DHCP and RADIUS
   integration is done on DHCP relay agent level (DHCP clients send DHCP
   packets to DHCP relays; relays contact RADIUS server and depending on the
   response either send the packet to the DHCP server or drop it), it does
   require a DHCP relay hardware to support RADIUS communication. Also, even
   if the relay has necessary support it is often not flexible enough to send
   and receive additional RADIUS attributes. As such, the alternative looks
   more appealing: to extend DHCP server to talk to RADIUS directly. That is
   the goal this library intends to fulfill.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   The major feature of the library is the ability to use RADIUS
   authorization. When a DHCP packet is received, the Kea server will send
   send Access-Request to the RADIUS server and will await a response. The
   server will then send back either Access-Accept with specific client
   attributes or Access-Reject. There are two cases supported here. First,
   the Access-Accept includes Framed-IP-Address (for DHCPv4) or
   Framed-IPv6-Address (for DHCPv6), which will be interpreted by Kea as an
   instruction to assign that specified IPv4 or IPv6 address. This
   effectively means RADIUS can act as address reservation database.

   The second case supported is the ability to assign clients to specific
   pools based on RADIUS response. In this case RADIUS server sends back
   Access-Accept with Framed-Pool (IPv4) or Framed-IPv6-Pool (IPv6). In both
   cases, Kea will interpret those attributes as client classes. With the
   recent addition of the ability to limit access to pools to specific
   classes (see Section 14.7, "Configuring Pools With Class Information"), it
   can be used to force client to be assigned a dynamic address from specific
   pool. Furthermore, the same mechanism can be used to control what kind of
   options the client will get (if there are DHCP options specified for a
   particular class).

    15.4.10.1. Compilation and Installation of RADIUS Hook

   The following section describes how to compile and install the software on
   CentOS 7.0. Other systems may differ slightly.

   STEP 1: Install dependencies

   Several tools are needed to build dependencies and Kea itself. The
   following commands should install them:

 $ sudo rpm -Uvh https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
 $ sudo yum install gcc-g++ openssl-devel log4cplus-devel wget git

   STEP 2: FreeRADIUS installation.

   Kea RADIUS hook library uses FreeRadius client library to conduct RADIUS
   communication. Unfortunately, the standard 1.1.7 release available from
   the project website http://freeradius.org/sub_projects/ has several
   serious deficiencies. ISC engineers observed a segmentation fault during
   testing. Also, the base version of the library does not offer asynchronous
   transmissions, which is essential for effective accounting implementation.
   Both of these issues were addressed by ISC engineers. The changes have
   been reported to FreeRadius client project. Acceptance of those changes is
   outside of ISC responsibilities. Until those are processed, it is strongly
   recommended to use FreeRadius client with ISC patches. To download and
   compile this version, please use the following steps:

 $ git clone https://github.com/fxdupont/freeradius-client.git
 $ cd freeradius-client/
 $ git checkout iscdev
 $ ./configure
 $ make
 $ sudo make install

   You may pass additional parameters to configure script, if you need to.
   Once installed, the FreeRADIUS client will be installed in /usr/local.
   This is the default path where Kea will be looking for it. You may install
   it in a different directory. If you choose to do so, make sure you pass
   that path to configure script when compiling kea.

   STEP 3: Install recent BOOST version

   Kea requires reasonably recent Boost version. Unfortunately, the version
   available in CentOS 7 is too old. Therefore a newer Boost version is
   necessary. Furthermore, CentOS 7 has an old version of g++ compiler that
   does not handle latest Boost versions. Fortunately, Boost 1.65 meets both
   requirements: is recent enough for Kea and is still able to be compiled
   using the g++ 4.8 version in CentOS.

   To download and compile Boost 1.65, please use the following commands:

 $ wget -nd https://dl.bintray.com/boostorg/release/1.65.1/source/boost_1_65_1.tar.gz
 $ tar zxvf boost_1_65_1.tar.gz
 $ cd boost_1_65_1/
 $ ./bootstrap.sh
 $ ./b2 --without-python
 $ sudo ./b2 install

   Note that b2 script may optionally take extra parameters. One of them
   specify the destination path where the sources are to be compiled.

   STEP 4: Compile and Install Kea

   Obtain Kea sources either by downloading it from git repository or extract
   the tarball:

 # Use one of those commands to obtain Kea sources:

 # Choice 1: get from github
 $ git clone https://github.com/isc-projects/kea

 # Get a tarball and extract it
 $ tar zxvf kea-1.5.0.tar.gz

   The next step is to extract premium Kea package that contains Radius
   repository into the Kea sources. After the tarball is extracted, the Kea
   sources should have a premium/ subdirectory.

   $ cd kea
   $ tar zxvf ../kea-premium-radius-1.5.0.tar.gz

   Once this is done, make sure the kea sources look similar to this:

 $ ls -l
 total 952
 -rw-r--r--   1 thomson  staff    6192 Apr 25 17:38 AUTHORS
 -rw-r--r--   1 thomson  staff   29227 Apr 25 17:38 COPYING
 -rw-r--r--   1 thomson  staff  360298 Apr 25 20:00 ChangeLog
 -rw-r--r--   1 thomson  staff     645 Apr 25 17:38 INSTALL
 -rw-r--r--   1 thomson  staff    5015 Apr 25 17:38 Makefile.am
 -rw-r--r--   1 thomson  staff     587 Apr 25 17:38 README
 drwxr-xr-x   5 thomson  staff     170 Apr 26 19:04 compatcheck
 -rw-r--r--   1 thomson  staff   62323 Apr 25 17:38 configure.ac
 -rw-r--r--   1 thomson  staff     300 Apr 25 17:38 dns++.pc.in
 drwxr-xr-x  12 thomson  staff     408 Apr 26 19:04 doc
 drwxr-xr-x   7 thomson  staff     238 Apr 25 17:38 examples
 drwxr-xr-x   5 thomson  staff     170 Apr 26 19:04 ext
 drwxr-xr-x   8 thomson  staff     272 Apr 26 19:04 m4macros
 drwxr-xr-x  20 thomson  staff     680 Apr 26 11:22 premium
 drwxr-xr-x  10 thomson  staff     340 Apr 26 19:04 src
 drwxr-xr-x  14 thomson  staff     476 Apr 26 19:04 tools

   The makefiles have to be regenerated using autoreconf.

   The next step is to configure Kea. There are several essential steps
   necessary here. Running autoreconf -if is necessary to compile premium
   package that contains RADIUS. Also, --with-freeradius option is necessary
   to tell Kea where the FreeRADIUS client sources can be found. Also, since
   the non-standard boost is used, the path to it has to be specified.

 $ autoreconf -i
 $ ./configure --with-freeradius=/path/to/freeradius --with-boost-include=/path/to/boost --with-boost-lib-dir=/path/to/boost/state/lib

   For example, assuming FreeRadius client was installed in the default
   directory (/usr/local) and Boost 1.65 sources were compiled in
   /home/thomson/devel/boost1_65_1, the configure path should look as
   follows:

 ./configure --with-freeradius=/usr/local \
             --with-boost-include=/home/thomson/devel/boost_1_65_1 \
             --with-boost-lib-dir=/home/thomson/devel/boost_1_65_1/stage/lib

   After some checks, the configure script should print a report similar to
   the following:


        Kea source configure results:
     -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

 Package:
   Name:              kea
   Version:           1.5.0
   Extended version:  1.5.0 (tarball)
   OS Family:         Linux

   Hooks directory:   /usr/local/lib/hooks
   Premium hooks:     yes
   Included Hooks:    forensic_log flex_id host_cmds subnet_cmds radius host_cache

 C++ Compiler:
   CXX:             g++ --std=c++11
   CXX_VERSION:     g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16)
   CXX_STANDARD:    201103
   DEFS:            -DHAVE_CONFIG_H
   CPPFLAGS:         -DOS_LINUX  -DBOOST_ASIO_HEADER_ONLY
   CXXFLAGS:        -g -O2
   LDFLAGS:          -lpthread
   KEA_CXXFLAGS:     -Wall -Wextra -Wnon-virtual-dtor -Wwrite-strings -Woverloaded-virtual -Wno-sign-compare -pthread -Wno-missing-field-initializers -fPIC

 Python:
   PYTHON_VERSION:  not needed (because kea-shell is disabled)

 Boost:
   BOOST_VERSION:   1.65.1
   BOOST_INCLUDES:  -I/home/thomson/devel/boost_1_65_1
   BOOST_LIBS:      -L/home/thomson/devel/boost_1_65_1/stage/lib  -lboost_system

 OpenSSL:
   CRYPTO_VERSION:  OpenSSL 1.0.2k  26 Jan 2017
   CRYPTO_CFLAGS:
   CRYPTO_INCLUDES:
   CRYPTO_LDFLAGS:
   CRYPTO_LIBS:     -lcrypto

 Botan: no

 Log4cplus:
   LOG4CPLUS_VERSION:  1.1.3
   LOG4CPLUS_INCLUDES: -I/usr/include
   LOG4CPLUS_LIBS:     -L/usr/lib -L/usr/lib64 -llog4cplus

 Flex/bison:
   FLEX:  flex
   BISON: bison -y

 MySQL:
   no

 PostgreSQL:
   no

 Cassandra CQL:
   no
 Google Test:
   no
 Google Benchmark:
   no

 FreeRADIUS client:
   FREERADIUS_INCLUDE:    -I/usr/local/include
   FREERADIUS_LIB:        -L/usr/local/lib -lfreeradius-client
   FREERADIUS_DICTIONARY: /usr/local/etc/radiusclient/dictionary

 Developer:
   Enable Debugging:       no
   Google Tests:           no
   Valgrind:               not found
   C++ Code Coverage:      no
   Logger checks:          no
   Generate Documentation: no
   Parser Generation:      no
   Kea-shell:              no

   Please make sure that your compilation has the following:

     * radius listed in Included Hooks
     * FreeRadius client directories printed and pointing to the right
       directories
     * Boost version is at least 1.65.1. The versions available in CentOS 7
       (1.48 and and 1.53) are too old.

   After that compile kea using make. If your system has more than one core,
   it is recommended to use -j N option.

     $ make -j5
     $ sudo make install

    15.4.10.2. RADIUS Hook Configuration

   The RADIUS Hook is a library that has to be loaded by either DHCPv4 or
   DHCPv6 Kea servers. Compared to other available hook libraries, this one
   takes many parameters to actually run. For example, this configuration
   could be used:

   "Dhcp4": {

   // Your regular DHCPv4 configuration parameters here.

   "hooks-libraries": [
   {
       // Note that RADIUS requires host-cache for proper operation,
       // so that library is loaded as well.
       "library": "/usr/local/lib/hooks/libdhcp_host_cache.so"
   },
   {
       "library": "/usr/local/lib/hooks/libdhc_radius.so",
       "parameters": {

           // Specify where FreeRADIUS dictionary could be located
           "dictionary": "/usr/local/etc/freeradius/dictionary",

           // Specify which address to use to communicate with RADIUS servers
           "bindaddr": "*",

           // more RADIUS parameters here
       }
   } ]

   Radius is a complicated environment. As such, it's not really possible to
   provide a default configuration that would work out of the box. However,
   we do have one example that showcases some of the more common features.
   Please see doc/examples/kea4/hooks-radius.json in your Kea sources.

   The RADIUS hook library supports the following global configuration flags,
   which corresponds to FreeRADIUS client library options:

     * bindaddr (default "*") specifies the address to be used by the hook
       library in communication with RADIUS servers. The "*" special value
       means to leave the kernel to choose it.
     * canonical-mac-address (default false) specifies whether MAC addresses
       in attributes follows the canonical Radius format (lowercase pairs of
       hexadecimal digits separated by '-').
     * client-id-pop0 (default false) used with flex-id removes the leading
       zero (or pair of zero in DHCPv6) type in client-id (aka duid in
       DHCPv6). Implied by client-id-printable.
     * client-id-printable (default false) checks if the client-id / duid
       content is printable and uses it as it instead of in hexadecimal.
       Implies client-id-pop0 and extract-duid as 0 and 255 are not
       printable.
     * deadtime (default 0) is a mechanism to try not responding servers
       after responding servers. Its value specifies the number of seconds
       the fact a server did not answer is kept, so 0 disables the mechanism.
       As the asynchronous communication does not use locks or atomics it is
       not recommended to use this feature with this mode.
     * dictionary (default set by configure at build time) is the attribute
       and value dictionary. Note it is a critical parameter.
     * extract-duid (default true) extracts from RFC 4361 compliant DHCPv4
       client-id the embedded duid. Implied by client-id-printable.
     * identifier-type4 (default client-id) specifies the identifier type to
       build the User-Name attribute. It should be the same than host
       identifier and when the flex-id hook library is used the
       replace-client-id must be set to true and client-id will be used with
       client-id-pop0.
     * identifier-type6 (default duid) specifies the identifier type to build
       the User-Name attribute. It should be the same than host identifier
       and when the flex-id hook librairy is used the replace-client-id must
       be set to true and duid will be used with client-id-pop0.
     * realm (default "") is the default realm.
     * reselect-subnet-address (default false) uses the Kea reserved address
       / RADIUS Framed-IP-Address or Framed-IPv6-Address to reselect subnets
       where the address is not in the subnet range.
     * reselect-subnet-pool (default false) uses the Kea client-class /
       RADIUS Frame-Pool to reselect subnets where no available pool can be
       found.
     * retries (default 3) is the number of retries before trying the next
       server. Note it is not supported for asynchronous communication.
     * session-history (default "") is the name of the file providing
       persistent storage for accounting session history.
     * timeout (default 10) is the number of seconds a response is waited
       for.

   When reselect-subnet-pool or reselect-subnet-address is set to true at the
   reception of RADIUS Access-Accept the selected subnet is checked against
   the client-class name or the reserved address and if it does not matched
   another subnet is selected among matching subnets.

   Two services are supported:

     * access - the authentication service
     * accounting - the accounting service

   Configuration of services is divided into two parts:

     * servers that define RADIUS servers the library is expected to contact.
       Each server may have the following items specified:

          * name which specifies the IP address of the server (it is allowed
            to use a name which will be resolved but it is not recommended).
          * port (default RADIUS authentication or accounting service) which
            specifies the UDP port of the server. Note that the FreeRADIUS
            client library by default uses ports 1812 (auth) and 1813 (acct).
            Some server implementations use 1645 (auth) ns 1646 (acct). You
            may use the "port" parameter to adjust as needed.
          * secret which authenticates messages.

       There may be up to 8 servers. Note when no server was specified the
       service is disabled.

     * attributes which define additional attributes that the Kea server will
       send to a RADIUS server. The parameter must be identified either by a
       name or type. Its value can be specified using one of three possible
       ways: data (which defines a plain text value), raw (which defines the
       value in hex) or expr (which defines an expression, which will be
       evaluated for each incoming packet independently).

          * name of the attribute.
          * type of the attribute. Type or name is required, and the
            attribute must be defined in the dictionary.
          * data is the first out of three ways to specify the attribute
            content. The data entry is parsed by the FreeRADIUS library so
            values defined in the dictionary of the attribute may be used.
          * raw is the second out of three way to specify the attribute
            content. It specifies the content in hexadecimal. Note it does
            not work with integer content attributes (date, integer and IPv4
            address), a string content attribute (string. IPv6 address and
            IPv6 prefix) is required.
          * expr is the last way to specify the attribute content. It
            specifies an evaluation expression which must return a not empty
            string when evaluated with the DHCP query packet. Currently this
            is restricted to the access service.

   For example, to specify a single access server available on localhost that
   uses "secret" as a secret and tell Kea to send three additional attributes
   (Password, Connect-Info and Configuration-Token), the following snipped
   could be used:

 "parameters": {

     // Other RADIUS parameters here

     "access": {

         // This starts the list of access servers
         "servers": [
         {
             // These are parameters for the first (and only) access server
             "server": "127.0.0.1",
             "port": 1812,
             "secret": "secret"
         }
         // Additional access servers could be specified here
         ],

         // This define a list of additional attributes Kea will send to each
         // access server in Access-Request.
         "attributes": [
         {
             // This attribute is identified by name (must be present in the
             // dictionary) and has static value (i.e. the same value will be
             // sent to every server for every packet)
             "name": "Password",
             "data": "mysecretpassword"
         },
         {
             // It's also possible to specify an attribute using its type,
             // rather than a name. 77 is Connect-Info. The value is specified
             // using hex. Again, this is a static value. It will be sent the
             // same for every packet and to every server.
             "type": 77,
             "raw": "65666a6a71"
         },
         {
             // This example shows how an expression can be used to send dynamic
             // value. The expression (see Section 13) may take any value from
             // the incoming packet or even its metadata (e.g. the interface
             // it was received over from)
             "name": "Configuration-Token",
             "expr": "hexstring(pkt4.mac,':')"
         }
         ] // End of attributes
     } // End of access

     // accounting could be specified here.

     }

   For the RADIUS Hook library to operate properly in DHCPv4, it is necessary
   to also load the Host Cache hook library. The reason for this is somewhat
   complex. In a typical deployment the DHCP clients send their packets via
   DHCP relay which inserts certain Relay Agent Information options, such are
   circuit-id or remote-id. The values of those options are then used by the
   Kea DHCP server to formulate necessary attributes in the Access-Request
   message sent to the RADIUS server. However, once the DHCP client gets its
   address, it then renews by sending packets directly to the DHCP server. As
   a result, the relays are not able to insert their RAI options and DHCP
   server can't send the Access-Request queries to the RADIUS server by using
   just the information from incoming packets. Kea needs to keep the
   information received during initial Discover/Offer exchanges and later use
   it when sending accounting messages.

   This mechanism is implemented based on user context in host reservations.
   (See Section 15.5, "User contexts" for details about user context). The
   host cache mechanism allows to retain the information retrieved by RADIUS
   to be stored and later used for sending accounting and access queries to
   the RADIUS server. In other words, the host-cache mechanism is mandatory,
   unless you don't want the RADIUS communication for messages other than
   Discover and the first Request from each client.

  15.4.11. host_cache: Caching Host Reservations

   Some of the database backends, such as RADIUS, are considered slow and may
   take a long time to respond. Since Kea in general is synchronous, the
   backend performance directly affects the DHCP performance. To minimize the
   impact and improve performance, the Host Cache library provides a way to
   cache responses from other hosts. This includes negative caching, i.e. the
   ability to remember that there is no client information in the database.

  Note

   This library may only be loaded by kea-dhcp4 or kea-dhcp6 process.

   In principle it can be used with any backend that may introduce
   performance degradation (MySQL, PostgreSQL, Cassandra, RADIUS). Host Cache
   is required to be loaded for the RADIUS accounting mechanism to work.

   Host Cache hook library is currently very simple. It takes only one
   optional parameter ("maximum") that defines the maximum number of hosts to
   be cached. If not specified the default value of 0 is used, which means
   there is no limit. The hook library can be loaded the same way as any
   other hook library. For example, this configuration could be used:

   "Dhcp4": {

   // Your regular DHCPv4 configuration parameters here.

   "hooks-libraries": [
   {
       "library": "/usr/local/lib/hooks/libdhc_host_cache.so",
       "parameters": {

           // Tells Kea to never cache more than 1000 hosts.
           "maximum: "1000"

       }
   } ]

   Once loaded, the Host Cache hook library makes available a number of new
   commands. Those commands can be used either over control channel (see
   Section 17.2, "Using the Control Channel") or REST API (see Section 7.1,
   "Overview"). An example REST API client is described in Section 20.1,
   "Overview". The following sections describe the commands available.

    15.4.11.1. cache-flush command

   This command allows removal of specified number of cached host entries. It
   takes one parameter which defines the number of hosts to be removed. An
   example usage looks as follows:

 {
     "command": "cache-flush",
     "arguments": 1000
 }

   This command will remove 1000 hosts. If you want to delete all cached
   hosts, please use cache-clear instead. The hosts are stored in FIFO order,
   so always the oldest entries are removed.

    15.4.11.2. cache-clear command

   This command allows removal of all cached host entries. An example usage
   looks as follows:

 {
     "command": "cache-clear"
 }

   This command will remove all hosts. If you want to delete only certain
   number of cached hosts, please use cache-flush instead.

    15.4.11.3. cache-write command

   In general case the cache content is considered a run-time state and the
   server can be shutdown or restarted as usual. The cache will then be
   repopulated after restart. However, there are some cases when it is useful
   to store contents of the cache. One such case is RADIUS (where the cached
   hosts also retain additional cached RADIUS attributes and there is no easy
   way to obtain this information again, because renewing clients send their
   packet to the DHCP server directly. As a result, packets never go through
   relay which doesn't insert relay options, which in turn are in some
   deployment to query the RADIUS server). Another use case is when you want
   to restart the server and for performance reasons you want it to start
   with a hot (populated) cache.

   This command allows writing the contents of in-memory cache to a file on
   disk. It takes one parameter which defines the filename. An example usage
   looks as follows:

 {
     "command": "cache-write",
     "arguments": "/tmp/kea-host-cache.json"
 }

   This command will store the contents to /tmp/kea-host-cache.json file.
   That file can then be loaded with cache-load command or processed by any
   other tool that is able to understand JSON format.

    15.4.11.4. cache-load command

   See previous section for a discussion regarding use cases where it may be
   useful to write and load contents of the host cache to disk.

   This command allows load the contents of a file on disk into an in-memory
   cache. It takes one parameter which defines the filename. An example usage
   looks as follows:

 {
     "command": "cache-load",
     "arguments": "/tmp/kea-host-cache.json"
 }

   This command will store the contents to /tmp/kea-host-cache.json file.
   That file can then be loaded with cache-load command or processed by any
   other tool that is able to understand JSON format.

    15.4.11.5. cache-get command

   This command is similar to cache-write, but instead of writing the cache
   contents to disk, it returns the contents to whoever sent the command.

   This command allows load the contents of a file on disk into an in-memory
   cache. It takes one parameter which defines the filename. An example usage
   looks as follows:

 {
     "command": "cache-get"
 }

   This command will return all the cached hosts. Note the response may be
   large.

    15.4.11.6. cache-insert command

   This command may be used to manually insert a host into the cache. There
   are very few use cases when this command could be useful. This command
   expects the arguments to follow the usual syntax for specifying host
   reservations (see Section 8.3, "Host Reservation in DHCPv4" or
   Section 9.3, "Host Reservation in DHCPv6") with one difference: the
   subnet-id value must be specified explicitly.

   An example command that will insert a IPv4 host into the host cache looks
   as follows:

 {
     "command": "cache-insert",
     "arguments": {
         "hw-address": "01:02:03:04:05:06",
         "subnet-id4": 4,
         "subnet-id6": 0,
         "ip-address": "192.0.2.100",
         "hostname": "somehost.example.org",
         "client-classes4": [ ],
         "client-classes6": [ ],
         "option-data4": [ ],
         "option-data6": [ ],
         "next-server": "192.0.0.2",
         "server-hostname": "server-hostname.example.org",
         "boot-file-name": "bootfile.efi",
         "host-id": 0
     }
 }

   An example command that will insert IPv6 host into the host cache looks as
   follows:

 {
     "command": "cache-insert",
     "arguments": {
         "hw-address": "01:02:03:04:05:06",
         "subnet-id4": 0,
         "subnet-id6": 6,
         "ip-addresses": [ "2001:db8::cafe:babe" ],
         "prefixes": [ "2001:db8:dead:beef::/64" ],
         "hostname": "",
         "client-classes4": [ ],
         "client-classes6": [ ],
         "option-data4": [ ],
         "option-data6": [ ],
         "next-server": "0.0.0.0",
         "server-hostname": "",
         "boot-file-name": "",
         "host-id": 0
     }
 }

    15.4.11.7. cache-remove command

   Sometimes it is useful to remove a single entry from the host cache. A
   good use case is a situation where the device is up, Kea already provided
   configuration and the host entry is in cache. As a result of
   administrative action (e.g. customer hasn't paid their bills or perhaps
   been upgraded to better service), the information in the backend (e.g.
   MySQL or RADIUS) is being updated. However, since cache is in use, Kea
   does not notice the change as the cached values are used. Cache-remove
   command can solve this problem by removing cached entry after
   administrative changes.

   The cache-remove command works similarly to reservation-get command. It
   allows querying by two parameters. One of them is either subnet-id4 or
   subnet-id6 and the other one is one of: ip-address (may be IPv4 or IPv6
   address), hw-address (specifies hardware/MAC address), duid, circuit-id,
   client-id or flex-id.

   An example command to remove an IPv4 host with reserved address 192.0.2.1
   from subnet with a subnet-id 123 looks as follows:

 {
     "command": "cache-remove",
     "arguments": {
         "ip-address": "192.0.2.1",
         "subnet-id": 123
     }
 }

   Another example that removes IPv6 host identifier by DUID and specific
   subnet-id is:

 {
     "command": "cache-remove",
     "arguments": {
         "duid": "00:01:ab:cd:f0:a1:c2:d3:e4",
         "subnet-id": 123
     }
 }

15.5. User contexts

   Hook libraries can have their own configuration parameters. That is
   convenient if the parameter applies to the whole library. However,
   sometimes it is very useful if certain configuration entities are extended
   with additional configuration data. This is where the concept of user
   contexts comes in. A sysadmin can define an arbitrary set of data and
   attach it to Kea structures, as long as the data is specified as JSON map.
   In particular, it is possible to define fields that are integers, strings,
   boolean, lists and maps. It is possible to define nested structures of
   arbitrary complexity. Kea does not use that data on its own, simply stores
   and makes it available for the hook libraries.

   Another use case for user contexts may be storing comments and other
   information that will be retained by Kea. Regular comments are discarded
   when configuration is loaded, but user contexts are retained. This is
   useful if you want your comments to survive config-set, config-get
   operations for example.

   If user context is supported in a given context, the parser translates
   "comment" entries into user context with a "comment" entry. The pretty
   print of a configuration does the opposite operation and puts "comment"
   entries at the beginning of maps as it seems to be the common usage.

   As of Kea 1.3, the structures that allow user contexts are pools of all
   types (addresses and prefixes) and subnets. Kea 1.4 extended user context
   support to the global scope, interfaces config, shared networks, subnets,
   client classes, option datas and definitions, host reservations, control
   socket, dhcp ddns, loggers and server id. These are supported in both
   DHCPv4 and DHCPv6 at the exception of server id which is DHCPv6 only.

                             Chapter 16. Statistics

   Table of Contents

   16.1. Statistics Overview

   16.2. Statistics Lifecycle

   16.3. Commands for Manipulating Statistics

                16.3.1. statistic-get command

                16.3.2. statistic-reset command

                16.3.3. statistic-remove command

                16.3.4. statistic-get-all command

                16.3.5. statistic-reset-all command

                16.3.6. statistic-remove-all command

16.1. Statistics Overview

   Both Kea DHCP servers support statistics gathering. A working DHCP server
   encounters various events that can cause certain statistics to be
   collected. For example, a DHCPv4 server may receive a packet
   (pkt4-received statistic increases by one) that after parsing was
   identified as a DHCPDISCOVER (pkt4-discover-received). The Server
   processed it and decided to send a DHCPOFFER representing its answer
   (pkt4-offer-sent and pkt4-sent statistics increase by one). Such events
   happen frequently, so it is not uncommon for the statistics to have values
   in high thousands. They can serve as an easy and powerful tool for
   observing a server's and network's health. For example, if pkt4-received
   statistic stops growing, it means that the clients' packets are not
   reaching the server.

   There are four types of statistics:

     * integer - this is the most common type. It is implemented as 64 bit
       integer (int64_t in C++), so it can hold any value between -2^63 to
       2^63 -1.
     * floating point - this type is intended to store floating point
       precision. It is implemented as double C++ type.
     * duration - this type is intended for recording time periods. It uses
       boost::posix_time::time_duration type, which stores hours, minutes,
       seconds and microseconds.
     * string - this type is intended for recording statistics in textual
       form. It uses std::string C++ type.

   During normal operation, DHCPv4 and DHCPv6 servers gather statistics. For
   a list of DHCPv4 and DHCPv6 statistics, see Section 8.8, "Statistics in
   the DHCPv4 Server" and Section 9.12, "Statistics in the DHCPv6 Server",
   respectively.

   To extract data from the statistics module, the control channel can be
   used. See Chapter 17, Management API for details. It is possible to
   retrieve a single or all statistics, reset statistics (i.e. set to neutral
   value, typically zero) or even remove completely a single or all
   statistics. See section Section 16.3, "Commands for Manipulating
   Statistics" for a list of statistic oriented commands.

16.2. Statistics Lifecycle

   It is useful to understand how the Statistics Manager module works. When
   the server starts operation, the manager is empty and does not have any
   statistics. When statistic-get-all is executed, an empty list is returned.
   Once the server performs an operation that causes a statistic to change,
   the related statistic will be created. In the general case, once a
   statistic is recorded even once, it is kept in the manager, until
   explicitly removed, by statistic-remove or statistic-remove-all being
   called or the server is shut down. Per subnet statistics are explicitly
   removed when reconfiguration takes place.

   Statistics are considered run-time properties, so they are not retained
   after server restart.

   Removing a statistic that is updated frequently makes little sense as it
   will be re-added when the server code next records that statistic. The
   statistic-remove and statistic-remove-all commands are intended to remove
   statistics that are not expected to be observed in the near future. For
   example, a misconfigured device in a network may cause clients to report
   duplicate addresses, so the server will report increasing values of
   pkt4-decline-received. Once the problem is found and the device is
   removed, the system administrator may want to remove the
   pkt4-decline-received statistic, so it won't be reported anymore. If a
   duplicate address is detected ever again, the server will add this
   statistic back.

16.3. Commands for Manipulating Statistics

   There are several commands defined that can be used for accessing (-get),
   resetting to zero or neutral value (-reset) or even removing a statistic
   completely (-remove). The difference between reset and remove is somewhat
   subtle. The reset command sets the value of the statistic to zero or
   neutral value. After this operation, the statistic will have a value of 0
   (integer), 0.0 (float), 0h0m0s0us (duration) or "" (string). When asked
   for, a statistic with the values mentioned will be returned. Remove
   removes a statistic completely, so the statistic will not be reported
   anymore. Please note that the server code may add it back if there's a
   reason to record it.

  Note

   The following sections describe commands that can be sent to the server:
   the examples are not fragments of a configuration file. For more
   information on sending commands to Kea, see Chapter 17, Management API.

  16.3.1. statistic-get command

   statistic-get command retrieves a single statistic. It takes a single
   string parameter called name that specifies the statistic name. An example
   command may look like this:

 {
     "command": "statistic-get",
     "arguments": {
         "name": "pkt4-received"
     }
 }

   The server will respond with details of the requested statistic, with
   result set to 0 indicating success and the specified statistic as the
   value of "arguments" parameter. If the requested statistic is not found,
   the response will contain an empty map, i.e. only { } as argument, but the
   status code will still be set to success (0).

  16.3.2. statistic-reset command

   statistic-reset command sets the specified statistic to its neutral value:
   0 for integer, 0.0 for float, 0h0m0s0us for time duration and "" for
   string type. It takes a single string parameter called name that specifies
   the statistic name. An example command may look like this:

 {
     "command": "statistic-reset",
     "arguments": {
         "name": "pkt4-received"
     }
 }

   If the specific statistic is found and reset was successful, the server
   will respond with a status of 0, indicating success and an empty
   parameters field. If an error is encountered (e.g. requested statistic was
   not found), the server will return a status code of 1 (error) and the text
   field will contain the error description.

  16.3.3. statistic-remove command

   statistic-remove command attempts to delete a single statistic. It takes a
   single string parameter called name that specifies the statistic name. An
   example command may look like this:

 {
     "command": "statistic-remove",
     "arguments": {
         "name": "pkt4-received"
     }
 }

   If the specific statistic is found and its removal was successful, the
   server will respond with a status of 0, indicating success and an empty
   parameters field. If an error is encountered (e.g. requested statistic was
   not found), the server will return a status code of 1 (error) and the text
   field will contain the error description.

  16.3.4. statistic-get-all command

   statistic-get-all command retrieves all statistics recorded. An example
   command may look like this:

 {
     "command": "statistic-get-all",
     "arguments": { }
 }

   The server will respond with details of all recorded statistics, with
   result set to 0 indicating that it iterated over all statistics (even when
   the total number of statistics is zero).

  16.3.5. statistic-reset-all command

   statistic-reset command sets all statistics to their neutral values: 0 for
   integer, 0.0 for float, 0h0m0s0us for time duration and "" for string
   type. An example command may look like this:

 {
     "command": "statistic-reset-all",
     "arguments": { }
 }

   If the operation is successful, the server will respond with a status of
   0, indicating success and an empty parameters field. If an error is
   encountered, the server will return a status code of 1 (error) and the
   text field will contain the error description.

  16.3.6. statistic-remove-all command

   statistic-remove-all command attempts to delete all statistics. An example
   command may look like this:

 {
     "command": "statistic-remove-all",
     "arguments": { }
 }

   If the removal of all statistics was successful, the server will respond
   with a status of 0, indicating success and an empty parameters field. If
   an error is encountered, the server will return a status code of 1 (error)
   and the text field will contain the error description.

                           Chapter 17. Management API

   Table of Contents

   17.1. Data Syntax

   17.2. Using the Control Channel

   17.3. Commands Supported by Both the DHCPv4 and DHCPv6 Servers

                17.3.1. build-report

                17.3.2. config-get

                17.3.3. config-reload

                17.3.4. config-test

                17.3.5. config-write

                17.3.6. leases-reclaim

                17.3.7. libreload

                17.3.8. list-commands

                17.3.9. config-set

                17.3.10. shutdown

                17.3.11. dhcp-disable

                17.3.12. dhcp-enable

                17.3.13. version-get

   17.4. Commands Supported by Control Agent

   A classic approach to daemon configuration assumes that the server's
   configuration is stored in configuration files and, when the configuration
   is changed, the daemon is restarted. This approach has the significant
   disadvantage of introducing periods of downtime, when client traffic is
   not handled. Another risk is that if the new configuration is invalid for
   whatever reason, the server may refuse to start, which will further extend
   the downtime period until the issue is resolved.

   To avoid such problems, both the DHCPv4 and DHCPv6 servers include support
   for a mechanism that allows on-line reconfiguration without requiring
   server shutdown. Both servers can be instructed to open control sockets,
   which is a communication channel. The server is able to receive commands
   on that channel, act on them and report back status.

   The DHCPv4 and DHCPv6 servers receive commands over the unix domain
   sockets. The details how to configure these sockets, see Section 8.9,
   "Management API for the DHCPv4 Server" and Section 9.13, "Management API
   for the DHCPv6 Server". While it is possible control the servers directly
   using unix domain sockets it requires that the controlling client be
   running on the same machine as the server. In order to connect remotely
   SSH is usually used to connect to the controlled machine.

   The network administrators usually prefer using some form of a RESTful API
   to control the servers, rather than using unix domain sockets directly.
   Therefore, as of Kea 1.2.0 release, Kea includes a new component called
   Control Agent (or CA) which exposes a RESTful API to the controlling
   clients and can forward commands to the respective Kea services over the
   unix domain sockets. The CA configuration has been described in
   Section 7.2, "Configuration".

   The HTTP requests received by the CA contain the control commands
   encapsulated within HTTP requests. Simply speaking, the CA is responsible
   for stripping the HTTP layer from the received commands and forwarding the
   commands in a JSON format over the unix domain sockets to respective
   services. Because the CA receives commands for all services it requires
   additional "forwarding" information to be included in the client's
   messages. This "forwarding" information is carried within the service
   parameter of the received command. If the service parameter is not
   included or if the parameter is a blank list the CA will assume that the
   control command is targetted at the CA itself and will try to handle it on
   its own.

   Control connections over both HTTP and unix domain sockets are guarded
   with timeouts. The default timeout value is set to 10s and is not
   configurable. The timeout configuration will be implemented in the future.

  Note

   Kea 1.2.0 release and earlier had a limitation of 64kB on the maximum size
   of a command and a response sent over the unix domain socket. This
   limitation has been removed in Kea 1.3.0 release.

17.1. Data Syntax

   Communication over the control channel is conducted using JSON structures.
   If configured, Kea will open a socket and listen for incoming connections.
   A process connecting to this socket is expected to send JSON commands
   structured as follows:

 {
     "command": "foo",
     "service": [ "dhcp4" ]
     "arguments": {
         "param1": "value1",
         "param2": "value2",
         ...
     }
 }

   The same command sent over the RESTful interface to the CA will have the
   following structure.

     POST / HTTP/1.1\r\n
     Content-Type: application/json\r\n
     Content-Length: 147\r\n\r\n
     {
         "command": "foo",
         "service": [ "dhcp4" ]
         "arguments": {
             "param1": "value1",
             "param2": "value2",
             ...
         }
     }

   command is the name of command to execute and is mandatory. arguments is a
   map of parameters required to carry out the given command. The exact
   content and format of the map is command specific.

   service is a list of the servers at which the control command is
   targetted. In the example above, the control command is targetted at the
   DHCPv4 server. In most cases, the CA will simply forward this command to
   the DHCPv4 server for processing via unix domain socket. Sometimes, the
   command including a service value may also be processed by the CA, if the
   CA is running a hooks library which handles such command for the given
   server. As an example, the hooks library loaded by the CA may perform some
   operations on the database (like adding host reservations, modifying
   leases etc.). An advantage of performing DHCPv4 specific administrative
   operations in the CA rather than forwarding it to the DHCPv4 server is the
   ability to perform these operations without disrupting the DHCPv4 service
   (DHCPv4 server doesn't have to stop processing DHCP messages to apply
   changes to the database). Nevertheless, these situations are rather rare
   and, in most cases, when the service parameter contains a name of the
   service the commands are simply forwarded by the CA. The forwarded command
   includes the service parameter but this parameter is ignored by the
   receiving server. This parameter is only meaningful to the CA.

   If the command received by the CA does not include a service parameter or
   this list is empty, the CA will simply process this message on its own.
   For example, the config-get command which doesn't include service
   parameter will return Control Agent's own configuration. The config-get
   including a service value "dhcp4" will be forwarded to the DHCPv4 server
   and will return DHCPv4 server's configuration and so on.

   The following list contains a mapping of the values carried within the
   service parameter to the servers to which the commands are forwarded:

     * dhcp4 - the command is forwarded to the kea-dhcp4 server,
     * dhcp6 - the command is forwarded to the kea-dhcp6 server,
     * d2 - the command is forwarded to the kea-d2 server.

   The server processing the incoming command will send a response of the
   form:

 {
     "result": 0|1|2|3,
     "text": "textual description",
     "arguments": {
         "argument1": "value1",
         "argument2": "value2",
         ...
     }
 }

   result indicates the outcome of the command. A value of 0 means success
   while any non-zero value designates an error or at least a failure to
   complete the requested action. Currently 1 is used as a generic error, 2
   means that a command is not supported and 3 means that the requested
   operation was completed, but the requested object was not found.
   Additional error codes may be added in the future. For example a well
   formed command that requests a subnet that exists in server's
   configuration would return result 0. If the server encounters an error
   condition, it would return 1. If the command was asking for IPv6 subnet,
   but was sent to DHCPv4 server, it would return 2. If the query was asking
   for a subnet-id and there is no subnet with such id, the result would be
   set to 3.

   The text field typically appears when result is non-zero and contains a
   description of the error encountered, but it often also appears for
   successful outcomes. The exact text is command specific, but in general
   uses plain English to describe the outcome of the command. arguments is a
   map of additional data values returned by the server which is specific to
   the command issued. The map is may be present, but that depends on
   specific command.

  Note

   When sending commands via Control Agent, it is possible to specify
   multiple services at which the command is targetted. CA will forward this
   command to each service individually. Thus, the CA response to the
   controlling client will contain an array of individual responses.

17.2. Using the Control Channel

   Kea development team is actively working on providing client applications
   which can be used to control the servers. These applications are, however,
   in the early stages of development and as of Kea 1.2.0 release have
   certain limitations. The easiest way to start interacting with the control
   API is to use common Unix/Linux tools such as socat and curl.

   In order to control the given Kea service via unix domain socket, use
   socat in interactive mode as follows:

 $ socat UNIX:/path/to/the/kea/socket -

   or in batch mode, include the "ignoreeof" option as shown below to ensure
   socat waits long enough for the server to respond:

 $ echo "{ some command...}" | socat UNIX:/path/to/the/kea/socket -,ignoreeof

   where /path/to/the/kea/socket is the path specified in the
   Dhcp4/control-socket/socket-name parameter in the Kea configuration file.
   Text passed to socat will be sent to Kea and the responses received from
   Kea printed to standard output. This approach communicates with the
   specific server directly and bypasses Control Agent.

   It is also easy to open UNIX socket programmatically. An example of such a
   simplistic client written in C is available in the Kea Developer's Guide,
   chapter Control Channel Overview, section Using Control Channel.

   In order to use Kea's RESTful API with curl you may use the following:

 $ curl -X POST -H "Content-Type: application/json" -d '{ "command": "config-get", "service": [ "dhcp4" ] }' http://ca.example.org:8000/

   This assumes that the Control Agent is running on host ca.example.org and
   runs RESTful service on port 8000.

17.3. Commands Supported by Both the DHCPv4 and DHCPv6 Servers

  17.3.1. build-report

   The build-report command returns on the control channel what the command
   line -W argument displays, i.e. the embedded content of the config.report
   file. This command does not take any parameters.

 {
     "command": "build-report"
 }

  17.3.2. config-get

   The config-get command retrieves the current configuration used by the
   server. This command does not take any parameters. The configuration
   returned is roughly equal to the configuration that was loaded using -c
   command line option during server start-up or later set using config-set
   command. However, there may be certain differences. Comments are not
   retained. If the original configuration used file inclusion, the returned
   configuration will include all parameters from all the included files.

   Note that returned configuration is not redacted, i.e. it will contain
   database passwords in plain text if those were specified in the original
   configuration. Care should be taken to not expose the command channel to
   unprivileged users.

   An example command invocation looks like this:

 {
     "command": "config-get"
 }

  17.3.3. config-reload

   The config-reload command instructs Kea to load again the configuration
   file that was used previously. This operation is useful if the
   configuration file has been changed by some external sources. For example,
   a sysadmin can tweak the configuration file and use this command to force
   Kea pick up the changes.

   Caution should be taken when mixing this with config-set commands. Kea
   remembers the location of the configuration file it was started with. This
   configuration can be significantly changed using config-set command. When
   config-reload is issued after config-set, Kea will attempt to reload its
   original configuration from the file, possibly losing all changes
   introduced using config-set or other commands.

   config-reload does not take any parameters. An example command invocation
   looks like this:

 {
     "command": "config-reload"
 }

  17.3.4. config-test

   The config-test command instructs the server to check whether the new
   configuration supplied in the command's arguments can be loaded. The
   supplied configuration is expected to be the full configuration for the
   target server along with an optional Logger configuration. As for the -t
   command some sanity checks are not performed so it is possible a
   configuration which successfully passes this command will still fail in
   config-set command or at launch time. The structure of the command is as
   follows:

 {
     "command": "config-test",
     "arguments":  {
         "<server>": {
         },
         "Logging": {
         }
      }
 }

   where <server> is the configuration element name for a given server such
   as "Dhcp4" or "Dhcp6". For example:

 {
     "command": "config-test",
     "arguments":  {
         "Dhcp6": {
             :
         },
         "Logging": {
             :
         }
      }
 }

   The server's response will contain a numeric code, "result" (0 for
   success, non-zero on failure), and a string, "text", describing the
   outcome:

     {"result": 0, "text": "Configuration seems sane..." }

     or

     {"result": 1, "text": "unsupported parameter: BOGUS (<string>:16:26)" }

  17.3.5. config-write

   The config-write command instructs Kea server to write its current
   configuration to a file on disk. It takes one optional argument called
   filename that specifies the name of the file to write configuration to. If
   not specified, the name used when starting Kea (passed as -c argument)
   will be used. If relative path is specified, Kea will write its files only
   in the directory it is running.

   An example command invocation looks like this:

 {
     "command": "config-write",
     "arguments": {
         "filename": "config-modified-2017-03-15.json"
     }
 }

  17.3.6. leases-reclaim

   The leases-reclaim command instructs the server to reclaim all expired
   leases immediately. The command has the following JSON syntax:

 {
     "command": "leases-reclaim",
     "arguments": {
         "remove": true
     }
 }

   The remove boolean parameter is mandatory and it indicates whether the
   reclaimed leases should be removed from the lease database (if true), or
   they should be left in the expired-reclaimed state (if false). The latter
   facilitates lease affinity, i.e. ability to re-assign expired lease to the
   same client which used this lease before. See Section 10.3, "Configuring
   Lease Affinity" for the details. Also, see Section 10.1, "Lease
   Reclamation" for the general information about the processing of expired
   leases (leases reclamation).

  17.3.7. libreload

   The libreload command will first unload and then load all currently loaded
   hook libraries. This is primarily intended to allow one or more hook
   libraries to be replaced with newer versions without requiring Kea servers
   to be reconfigured or restarted. Note the hook libraries will be passed
   the same parameter values (if any) they were passed when originally
   loaded.

 {
     "command": "libreload",
     "arguments": { }
 }

   The server will respond with a result of 0 indicating success, or 1
   indicating a failure.

  17.3.8. list-commands

   The list-commands command retrieves a list of all commands supported by
   the server. It does not take any arguments. An example command may look
   like this:

 {
     "command": "list-commands",
     "arguments": { }
 }

   The server will respond with a list of all supported commands. The
   arguments element will be a list of strings. Each string will convey one
   supported command.

  17.3.9. config-set

   The config-set command instructs the server to replace its current
   configuration with the new configuration supplied in the command's
   arguments. The supplied configuration is expected to be the full
   configuration for the target server along with an optional Logger
   configuration. While optional, the Logger configuration is highly
   recommended as without it the server will revert to its default logging
   configuration. The structure of the command is as follows:

 {
     "command": "config-set",
     "arguments":  {
         "<server>": {
         },
         "Logging": {
         }
      }
 }

   where <server> is the configuration element name for a given server such
   as "Dhcp4" or "Dhcp6". For example:

 {
     "command": "config-set",
     "arguments":  {
         "Dhcp6": {
             :
         },
         "Logging": {
             :
         }
      }
 }

   If the new configuration proves to be invalid the server will retain its
   current configuration. Please note that the new configuration is retained
   in memory only. If the server is restarted or a configuration reload is
   triggered via a signal, the server will use the configuration stored in
   its configuration file. The server's response will contain a numeric code,
   "result" (0 for success, non-zero on failure), and a string, "text",
   describing the outcome:

     {"result": 0, "text": "Configuration successful." }

     or

     {"result": 1, "text": "unsupported parameter: BOGUS (<string>:16:26)" }

  17.3.10. shutdown

   The shutdown command instructs the server to initiate its shutdown
   procedure. It is the equivalent of sending a SIGTERM signal to the
   process. This command does not take any arguments. An example command may
   look like this:

 {
     "command": "shutdown"
 }

   The server will respond with a confirmation that the shutdown procedure
   has been initiated.

  17.3.11. dhcp-disable

   The dhcp-disable command globally disables the DHCP service. The server
   continues to operate, but it drops all received DHCP messages. This
   command is useful when the server's maintenance requires that the server
   temporarily stops allocating new leases and renew existing leases. It is
   also useful in failover like configurations during a synchronization of
   the lease databases at startup or recovery after a failure. The optional
   parameter max-period specifies the time in seconds after which the DHCP
   service should be automatically re-enabled if the dhcp-enable command is
   not sent before this time elapses.

 {
     "command": "dhcp-disable",
     "arguments": {
         "max-period": 20
     }
 }

  17.3.12. dhcp-enable

   The dhcp-enable command globally enables the DHCP service.

 {
     "command": "dhcp-enable"
 }

  17.3.13. version-get

   The version-get command returns an extended information about Kea version.
   It is the same information as Kea caled with -V command line argument.
   This command does not take any parameters.

 {
     "command": "version-get"
 }

17.4. Commands Supported by Control Agent

   The following commands listed in Section 17.3, "Commands Supported by Both
   the DHCPv4 and DHCPv6 Servers" are also supported by the Control Agent,
   i.e. when the service parameter is blank the commands are handled by the
   CA and they relate to the CA process itself:

     * build-report
     * config-get
     * config-test
     * config-write
     * list-commands
     * shutdown
     * version-get

                       Chapter 18. The libdhcp++ Library

   Table of Contents

   18.1. Interface detection and Socket handling

   libdhcp++ is a library written in C++ that handles many DHCP-related
   tasks, including:

     * DHCPv4 and DHCPv6 packets parsing, manipulation and assembly
     * Option parsing, manipulation and assembly
     * Network interface detection
     * Socket operations such as creation, data transmission and reception
       and socket closing.

   While this library is currently used by Kea, it is designed to be a
   portable, universal library, useful for any kind of DHCP-related software.

18.1. Interface detection and Socket handling

   Both the DHCPv4 and DHCPv6 components share network interface detection
   routines. Interface detection is currently supported on Linux, all BSD
   family (FreeBSD, NetBSD, OpenBSD), Mac OS X and Solaris 11 systems.

   DHCPv4 requires special raw socket processing to send and receive packets
   from hosts that do not have IPv4 address assigned. Support for this
   operation is implemented on Linux, FreeBSD, NetBSD and OpenBSD. It is
   likely that DHCPv4 component will not work in certain cases on other
   systems.

                              Chapter 19. Logging

   Table of Contents

   19.1. Logging Configuration

                19.1.1. Loggers

                19.1.2. Logging Message Format

                19.1.3. Logging During Kea Startup

19.1. Logging Configuration

   During its operation Kea may produce many messages. They differ in
   severity (some are more important than others) and source (some are
   produced by specific components, e.g. hooks). It is useful to understand
   which log messages are needed and which are not, and configure your
   logging appropriately. For example, debug level messages can be safely
   ignored in a typical deployment. They are, however, very useful when
   debugging a problem.

   The logging system in Kea is configured through the Logging section in
   your configuration file. All daemons (e.g. DHCPv4 and DHCPv6 servers) will
   use the configuration in the Logging section to see what should be logged
   and to where. This allows for sharing identical logging configuration
   between daemons.

  19.1.1. Loggers

   Within Kea, a message is logged through an entity called a "logger".
   Different components log messages through different loggers, and each
   logger can be configured independently of one another. Some components, in
   particular the DHCP server processes, may use multiple loggers to log
   messages pertaining to different logical functions of the component. For
   example, the DHCPv4 server uses one logger for messages pertaining to
   packet reception and transmission, another logger for messages related to
   lease allocation and so on. Some of the libraries used by the Kea servers,
   e.g. libdhcpsrv, use their own loggers.

   Users implementing hooks libraries (code attached to the server at
   runtime) are responsible for creating the loggers used by those libraries.
   Such loggers should have unique names, different from the logger names
   used by Kea. In this way the messages output by the hooks library can be
   distinguished from messages issued by the core Kea code. Unique names also
   allow the loggers to be configured independently of loggers used by Kea.
   Whenever it makes sense, a hook library can use multiple loggers to log
   messages pertaining to different logical parts of the library.

   In the Logging section of a configuration file you can specify the
   configuration for zero or more loggers (including loggers used by the
   proprietary hooks libraries). If there are no loggers specified, the code
   will use default values: these cause Kea to log messages of INFO severity
   or greater to standard output. There is also a small time window after Kea
   has been started, but has not yet read its configuration. Logging in this
   short period can be controlled using environment variables. For details,
   see Section 19.1.3, "Logging During Kea Startup".

   The three main elements of a logger configuration are: name (the component
   that is generating the messages), the severity (what to log), and the
   output_commands (where to log). There is also a debuglevel element, which
   is only relevant if debug-level logging has been selected.

    19.1.1.1. name (string)

   Each logger in the system has a name, the name being that of the component
   binary file using it to log messages. For instance, if you want to
   configure logging for the DHCPv4 server, you add an entry for a logger
   named "kea-dhcp4". This configuration will then be used by the loggers in
   the DHCPv4 server, and all the libraries used by it (unless a library
   defines its own logger and there is specific logger configuration that
   applies to that logger).

   When tracking down an issue with the server's operation, use of DEBUG
   logging is required to obtain the verbose output needed for problems
   diagnosis. However, the high verbosity is likely to overwhelm the logging
   system in cases when the server is processing high volume traffic. To
   mitigate this problem, use can be made of the fact that Kea uses multiple
   loggers for different functional parts of the server and that each of
   these can be configured independently. If the user is reasonably confident
   that a problem originates in a specific function of the server, or that
   the problem is related to the specific type of operation, they may enable
   high verbosity only for the relevant logger, so limiting the debug
   messages to the required minimum.

   The loggers are associated with a particular library or binary of Kea.
   However, each library or binary may (and usually does) include multiple
   loggers. For example, the DHCPv4 server binary contains separate loggers
   for: packet parsing, for dropped packets, for callouts etc.

   The loggers form a hierarchy. For each program in Kea, there is a "root"
   logger, named after the program (e.g. the root logger for kea-dhcp (the
   DHCPv4 server) is named kea-dhcp4. All other loggers are children of this
   logger, and are named accordingly, e.g. the the allocation engine in the
   DHCPv4 server logs messages using a logger called kea-dhcp4.alloc-engine.

   This relationship is important as each child logger derives its default
   configuration from its parent root logger. In the typical case, the root
   logger configuration is the only logging configuration specified in the
   configuration file and so applies to all loggers. If an entry is made for
   a given logger, any attributes specified override those of the root
   logger, whereas any not specified are inherited from it.

   To illustrate this, suppose you are using the DHCPv4 server with the root
   logger "kea-dhcp4" logging at the INFO level. In order to enable DEBUG
   verbosity for the DHCPv4 packet drops, you must create configuration entry
   for the logger called "kea-dhcp4.bad-packets" and specify severity DEBUG
   for this logger. All other configuration parameters may be omitted for
   this logger if the logger should use the default values specified in the
   root logger's configuration.

   If there are multiple logger specifications in the configuration that
   might match a particular logger, the specification with the more specific
   logger name takes precedence. For example, if there are entries for both
   "kea-dhcp4" and "kea-dhcp4.dhcpsrv", the DHCPv4 server -- and all
   libraries it uses that are not dhcpsrv -- will log messages according to
   the configuration in the first entry ("kea-dhcp4").

   Currently defined loggers are defined in the following table. The
   "Software Package" column of this table specifies whether the particular
   loggers belong to the core Kea code (open source Kea binaries and
   libraries), or hook libraries (open source or premium).

   Table 19.1. List of loggers supported by Kea servers and hooks libraries
   shipped with Kea and premium packages

   +------------------------------------------------------------------------+
   | Logger Name                 |   Software Package   | Description       |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | The root logger   |
   |                             |                      | for the Control   |
   |                             |                      | Agent exposing    |
   |                             |                      | RESTful control   |
   | kea-ctrl-agent              |         core         | API. All          |
   |                             |                      | components used   |
   |                             |                      | by the Control    |
   |                             |                      | Agent inherit the |
   |                             |                      | settings from     |
   |                             |                      | this logger.      |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | A logger which    |
   |                             |                      | outputs log       |
   |                             |                      | messages related  |
   | kea-ctrl-agent.http         |         core         | to receiving,     |
   |                             |                      | parsing and       |
   |                             |                      | sending HTTP      |
   |                             |                      | messages.         |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | The root logger   |
   |                             |                      | for the DHCPv4    |
   |                             |                      | server. All       |
   | kea-dhcp4                   |         core         | components used   |
   |                             |                      | by the DHCPv4     |
   |                             |                      | server inherit    |
   |                             |                      | the settings from |
   |                             |                      | this logger.      |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | The root logger   |
   |                             |                      | for the DHCPv6    |
   |                             |                      | server. All       |
   | kea-dhcp6                   |         core         | components used   |
   |                             |                      | by the DHCPv6     |
   |                             |                      | server inherit    |
   |                             |                      | the settings from |
   |                             |                      | this logger.      |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used by the lease |
   |                             |                      | allocation        |
   |                             |                      | engine, which is  |
   |                             |                      | responsible for   |
   |                             |                      | managing leases   |
   |                             |                      | in the lease      |
   | kea-dhcp4.alloc-engine      |         core         | database, i.e.    |
   | kea-dhcp6.alloc-engine      |                      | create, modify    |
   |                             |                      | and remove DHCP   |
   |                             |                      | leases as a       |
   |                             |                      | result of         |
   |                             |                      | processing        |
   |                             |                      | messages from the |
   |                             |                      | clients.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used by the DHCP  |
   |                             |                      | servers for       |
   |                             |                      | logging inbound   |
   |                             |                      | client packets    |
   |                             |                      | that were dropped |
   |                             |                      | or to which the   |
   |                             |                      | server responded  |
   | kea-dhcp4.bad-packets       |         core         | with a DHCPNAK.   |
   | kea-dhcp6.bad-packets       |                      | It allows         |
   |                             |                      | administrators to |
   |                             |                      | configure a       |
   |                             |                      | separate log      |
   |                             |                      | output that       |
   |                             |                      | contains only     |
   |                             |                      | packet drop and   |
   |                             |                      | reject entries.   |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used to log       |
   |                             |                      | messages          |
   |                             |                      | pertaining to the |
   | kea-dhcp4.callouts          |         core         | callouts          |
   | kea-dhcp6.callouts          |                      | registration and  |
   |                             |                      | execution for the |
   |                             |                      | particular hook   |
   |                             |                      | point.            |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used to log       |
   |                             |                      | messages relating |
   |                             |                      | to the handling   |
   | kea-dhcp4.commands          |         core         | of commands       |
   | kea-dhcp6.commands          |                      | received by the   |
   |                             |                      | the DHCP server   |
   |                             |                      | over the command  |
   |                             |                      | channel.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used to log       |
   |                             |                      | messages relating |
   | kea-dhcp4.database          |                      | to general        |
   | kea-dhcp6.database          |         core         | operations on the |
   |                             |                      | relational        |
   |                             |                      | databases and     |
   |                             |                      | Cassandra.        |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used by the DHCP  |
   |                             |                      | server to log     |
   |                             |                      | messages related  |
   |                             |                      | to the Client     |
   | kea-dhcp4.ddns              |                      | FQDN and Hostname |
   | kea-dhcp6.ddns              |         core         | option            |
   |                             |                      | processing. It    |
   |                             |                      | also includes log |
   |                             |                      | messages related  |
   |                             |                      | to the relevant   |
   |                             |                      | DNS updates.      |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used by the       |
   | kea-dhcp4.dhcp4             |         core         | DHCPv4 server     |
   |                             |                      | daemon to log     |
   |                             |                      | basic operations. |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | The base loggers  |
   | kea-dhcp4.dhcpsrv           |         core         | for the           |
   | kea-dhcp6.dhcpsrv           |                      | libkea-dhcpsrv    |
   |                             |                      | library.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used to log       |
   |                             |                      | messages relating |
   | kea-dhcp4.eval              |         core         | to the client     |
   | kea-dhcp6.eval              |                      | classification    |
   |                             |                      | expression        |
   |                             |                      | evaluation code.  |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | used to log       |
   | kea-dhcp4.host-cache-hooks  |  libdhcp_host_cache  | messages related  |
   | kea-dhcp6.host-cache-hooks  | premium hook library | to operation of   |
   |                             |                      | the Host Cache    |
   |                             |                      | Hook Library.     |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | used to log       |
   | kea-dhcp4.flex-id-hooks     |   libdhcp_flex_id    | messages related  |
   | kea-dhcp6.flex-id-hooks     | premium hook library | to operation of   |
   |                             |                      | the Flexible      |
   |                             |                      | Identifiers Hook  |
   |                             |                      | Library.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | used to log       |
   | kea-dhcp4.ha-hooks          |   libdhcp_ha hook    | messages related  |
   | kea-dhcp6.ha-hooks          |       library        | to operation of   |
   |                             |                      | the High          |
   |                             |                      | Availability Hook |
   |                             |                      | Library.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used to log       |
   |                             |                      | messages related  |
   |                             |                      | to management of  |
   |                             |                      | hooks libraries,  |
   |                             |                      | e.g. registration |
   |                             |                      | and               |
   | kea-dhcp4.hooks             |                      | deregistration of |
   | kea-dhcp6.hooks             |         core         | the libraries,    |
   |                             |                      | and to the        |
   |                             |                      | initialization of |
   |                             |                      | the callouts      |
   |                             |                      | execution for     |
   |                             |                      | various hook      |
   |                             |                      | points within the |
   |                             |                      | DHCP server.      |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | used to log       |
   |                             |                      | messages related  |
   |                             |                      | to operation of   |
   |                             |                      | the Host Cmds     |
   |                             |                      | hooks library. In |
   | kea-dhcp4.host-cmds-hooks   |  libdhcp_host_cmds   | general these     |
   | kea-dhcp6.host-cmds-hooks   | premium hook library | will pertain to   |
   |                             |                      | loading and       |
   |                             |                      | unloading the     |
   |                             |                      | library and the   |
   |                             |                      | execution of      |
   |                             |                      | commands by the   |
   |                             |                      | library.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used within the   |
   |                             |                      | libdhcpsrv and it |
   |                             |                      | logs messages     |
   |                             |                      | related to the    |
   | kea-dhcp4.hosts             |                      | management of the |
   | kea-dhcp6.hosts             |         core         | DHCP host         |
   |                             |                      | reservations,     |
   |                             |                      | i.e. retrieval of |
   |                             |                      | the reservations  |
   |                             |                      | and adding new    |
   |                             |                      | reservations.     |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | used to log       |
   |                             |                      | messages related  |
   |                             |                      | to operation of   |
   |                             |                      | the Lease Cmds    |
   |                             |                      | hooks library. In |
   | kea-dhcp4.lease-cmds-hooks  |  libdhcp_lease_cmds  | general these     |
   | kea-dhcp6.lease-cmds-hooks  |     hook library     | will pertain to   |
   |                             |                      | loading and       |
   |                             |                      | unloading the     |
   |                             |                      | library and the   |
   |                             |                      | execution of      |
   |                             |                      | commands by the   |
   |                             |                      | library.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used by the DHCP  |
   |                             |                      | server to log     |
   |                             |                      | messages related  |
   |                             |                      | to the lease      |
   |                             |                      | allocation. The   |
   | kea-dhcp4.leases            |                      | messages include  |
   | kea-dhcp6.leases            |         core         | detailed          |
   |                             |                      | information about |
   |                             |                      | the allocated or  |
   |                             |                      | offered leases,   |
   |                             |                      | errors during the |
   |                             |                      | lease allocation  |
   |                             |                      | etc.              |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | used to log       |
   | kea-dhcp4.legal-log-hooks   |  libdhcp_legal_log   | messages related  |
   | kea-dhcp6.legal-log-hooks   | premium hook library | to operation of   |
   |                             |                      | the Forensic      |
   |                             |                      | Logging Hooks     |
   |                             |                      | Library.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used by the DHCP  |
   |                             |                      | server to log     |
   |                             |                      | messages related  |
   |                             |                      | to processing of  |
   |                             |                      | the options in    |
   |                             |                      | the DHCP          |
   | kea-dhcp4.options           |                      | messages, i.e.    |
   | kea-dhcp4.options           |         core         | parsing options,  |
   |                             |                      | encoding options  |
   |                             |                      | into on-wire      |
   |                             |                      | format and packet |
   |                             |                      | classification    |
   |                             |                      | using options     |
   |                             |                      | contained in the  |
   |                             |                      | received packets. |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | mostly used to    |
   |                             |                      | log messages      |
   |                             |                      | related to        |
   |                             |                      | transmission of   |
   |                             |                      | the DHCP packets, |
   |                             |                      | i.e. packet       |
   |                             |                      | reception and     |
   |                             |                      | sending a         |
   |                             |                      | response. Such    |
   |                             |                      | messages include  |
   |                             |                      | information about |
   |                             |                      | the source and    |
   |                             |                      | destination IP    |
   |                             |                      | addresses and     |
   |                             |                      | interfaces used   |
   |                             |                      | to transmit       |
   | kea-dhcp4.packets           |         core         | packets. The      |
   | kea-dhcp6.packets           |                      | logger is also    |
   |                             |                      | used to log       |
   |                             |                      | messages related  |
   |                             |                      | to subnet         |
   |                             |                      | selection, as     |
   |                             |                      | this selection is |
   |                             |                      | usually based on  |
   |                             |                      | the IP addresses, |
   |                             |                      | relay addresses   |
   |                             |                      | and/or interface  |
   |                             |                      | names, which can  |
   |                             |                      | be retrieved from |
   |                             |                      | the received      |
   |                             |                      | packet, even      |
   |                             |                      | before the DHCP   |
   |                             |                      | message carried   |
   |                             |                      | in the packet is  |
   |                             |                      | parsed.           |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | used to log       |
   | kea-dhcp4.radius-hooks      |    libdhcp_radius    | messages related  |
   | kea-dhcp6.radius-hooks      | premium hook library | to operation of   |
   |                             |                      | the Radius Hook   |
   |                             |                      | Library.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | used to log       |
   |                             |                      | messages related  |
   |                             |                      | to operation of   |
   |                             |                      | the Stats Cmds    |
   |                             |                      | hooks library. In |
   | kea-dhcp4.stat-cmds-hooks   |  libdhcp_stat_cmds   | general these     |
   | kea-dhcp6.stat-cmds-hooks   |     hook library     | will pertain to   |
   |                             |                      | loading and       |
   |                             |                      | unloading the     |
   |                             |                      | library and the   |
   |                             |                      | execution of      |
   |                             |                      | commands by the   |
   |                             |                      | library.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | This logger is    |
   |                             |                      | used to log       |
   |                             |                      | messages related  |
   |                             |                      | to operation of   |
   |                             |                      | the Subnet Cmds   |
   |                             |                      | hooks library. In |
   | kea-dhcp4.subnet-cmds-hooks | libdhcp_subnet_cmds  | general these     |
   | kea-dhcp6.subnet-cmds-hooks |     hook library     | will pertain to   |
   |                             |                      | loading and       |
   |                             |                      | unloading the     |
   |                             |                      | library and the   |
   |                             |                      | execution of      |
   |                             |                      | commands by the   |
   |                             |                      | library.          |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | The root logger   |
   |                             |                      | for the           |
   |                             |                      | kea-dhcp-ddns     |
   |                             |                      | daemon. All       |
   |                             |                      | components used   |
   | kea-dhcp-ddns               |         core         | by this daemon    |
   |                             |                      | inherit the       |
   |                             |                      | settings from     |
   |                             |                      | this logger if    |
   |                             |                      | there is no       |
   |                             |                      | specialized       |
   |                             |                      | logger provided.  |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | The logger used   |
   |                             |                      | by the            |
   |                             |                      | kea-dhcp-ddns     |
   |                             |                      | daemon for        |
   | kea-dhcp-ddns.dctl          |         core         | logging basic     |
   |                             |                      | information about |
   |                             |                      | the process,      |
   |                             |                      | received signals  |
   |                             |                      | and triggered     |
   |                             |                      | reconfigurations. |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | The logger used   |
   |                             |                      | by the            |
   |                             |                      | kea-dhcp-ddns     |
   | kea-dhcp-ddns.dhcpddns      |         core         | daemon for        |
   |                             |                      | logging events    |
   |                             |                      | related to DDNS   |
   |                             |                      | operations.       |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used by the       |
   |                             |                      | kea-dhcp-ddns     |
   |                             |                      | daemon for        |
   |                             |                      | logging           |
   |                             |                      | information about |
   | kea-dhcp-ddns.dhcp-to-d2    |         core         | events dealing    |
   |                             |                      | with receiving    |
   |                             |                      | messages from the |
   |                             |                      | DHCP servers and  |
   |                             |                      | adding them to    |
   |                             |                      | the queue for     |
   |                             |                      | processing.       |
   |-----------------------------+----------------------+-------------------|
   |                             |                      | Used by the       |
   |                             |                      | kea-dhcp-ddns     |
   |                             |                      | daemon for        |
   |                             |                      | logging           |
   | kea-dhcp-ddns.d2-to-dns     |         core         | information about |
   |                             |                      | events dealing    |
   |                             |                      | with sending and  |
   |                             |                      | receiving         |
   |                             |                      | messages with the |
   |                             |                      | DNS servers.      |
   +------------------------------------------------------------------------+

   Note that user-defined hook libraries should not use any of those loggers
   but should define new loggers with names that correspond to the libraries
   using them. Suppose that the user created the library called
   "libdhcp-packet-capture" to dump packets received and transmitted by the
   server to the file. The appropriate name for the logger could be
   kea-dhcp4.packet-capture-hooks. (Note that the hook library implementor
   only specifies the second part of this name, i.e. "packet-capture". The
   first part is a root logger name and is prepended by the Kea logging
   system.) It is also important to note that since this new logger is a
   child of a root logger, it inherits the configuration from the root
   logger, something that can be overridden by an entry in the configuration
   file.

   Additional loggers may be defined in future versions of Kea. The easiest
   way to find out the logger name is to configure all logging to go to a
   single destination and look for specific logger names. See Section 19.1.2,
   "Logging Message Format" for details.

    19.1.1.2. severity (string)

   This specifies the category of messages logged. Each message is logged
   with an associated severity which may be one of the following (in
   descending order of severity):

     * FATAL - associated with messages generated by a condition that is so
       serious that the server cannot continue executing.
     * ERROR- associated with messages generated by an error condition. The
       server will continue executing, but the results may not be as
       expected.
     * WARN - indicates an out of the ordinary condition. However, the server
       will continue executing normally.
     * INFO - an informational message marking some event.
     * DEBUG - messages produced for debugging purposes.

   When the severity of a logger is set to one of these values, it will only
   log messages of that severity and above (e.g. setting the logging severity
   to INFO will log INFO, WARN, ERROR and FATAL messages). The severity may
   also be set to NONE, in which case all messages from that logger are
   inhibited.

  Note

   The keactrl tool, described in Chapter 6, Managing Kea with keactrl, can
   be configured to start the servers in the verbose mode. If this is the
   case, the settings of the logging severity in the configuration file will
   have no effect, i.e. the servers will use logging severity of DEBUG
   regardless of the logging settings specified in the configuration file. If
   you need to control severity via configuration file, please make sure that
   the kea_verbose value is set to "no" within the keactrl configuration.

    19.1.1.3. debuglevel (integer)

   When a logger's severity is set to DEBUG, this value specifies what level
   of debug messages should be printed. It ranges from 0 (least verbose) to
   99 (most verbose). If severity for the logger is not DEBUG, this value is
   ignored.

    19.1.1.4. output_options (list)

   Each logger can have zero or more output_options. These specify where log
   messages are sent. These are explained in detail below.

      19.1.1.4.1. output (string)

   This value determines the type of output. There are several special values
   allowed here: stdout (messages are printed on standard output), stderr
   (messages are printed on stderr), syslog (messages are logged to syslog
   using default name, syslog:name (messages are logged to syslog using
   specified name). Any other value is interpreted as a filename to which
   messages should be written.

      19.1.1.4.2. flush (true of false)

   Flush buffers after each log message. Doing this will reduce performance
   but will ensure that if the program terminates abnormally, all messages up
   to the point of termination are output. The default is "true".

      19.1.1.4.3. maxsize (integer)

   Only relevant when the destination is a file. This is maximum size in
   bytes that a log file may reach. When the maximum size is reached, the
   file is renamed and a new file opened. For example, a ".1" is appended to
   the name -- if a ".1" file exists, it is renamed ".2", etc. This is
   referred to as rotation.

   The default value is 10240000 (10MB). The smallest value that may be
   specified without disabling rotation is 204800. Any value less than this,
   including 0, disables rotation.

  Note

   Due to a limitation of the underlying logging library (log4cplus), rolling
   over the log files (from ".1" to ".2", etc) may show odd results: There
   can be multiple small files at the timing of roll over. This can happen
   when multiple processes try to roll over the files simultaneously. Version
   1.1.0 of log4cplus solved this problem, so if this version or later of
   log4cplus is used to build Kea, it should not happen. Even for older
   versions it is normally expected to happen rarely unless the log messages
   are produced very frequently by multiple different processes.

      19.1.1.4.4. maxver (integer)

   Only relevant when the destination is file and rotation is enabled (i.e.
   maxsize is large enough). This is maximum number of rotated versions that
   will be kept. Once that number of files has been reached, the oldest file,
   "log-name.maxver", will be discarded each time the log rotates. In other
   words, at most there will be the active log file plus maxver rotated
   files. The minimum and default value is 1.

    19.1.1.5. Example Logger Configurations

   In this example we want to set the global logging to write to the console
   using standard output.

 "Logging": {
     "loggers": [
         {
             "name": "kea-dhcp4",
             "output_options": [
                 {
                     "output": "stdout"
                 }
             ],
             "severity": "WARN"
         }
     ]
 }

   In this second example, we want to store debug log messages in a file that
   is at most 2MB and keep up to 8 copies of old logfiles. Once the logfile
   grows to 2MB, it will be renamed and a new file file be created.

 "Logging": {
     "loggers": [
         {
             "name": "kea-dhcp6",
             "output_options": [
                 {
                     "output": "/var/log/kea-debug.log",
                     "maxver": 8,
                     "maxsize": 204800,
                     "flush": true
                 }
             ],
             "severity": "DEBUG",
             "debuglevel": 99
         }
    ]
 }

  19.1.2. Logging Message Format

   Each message written to the configured logging destinations comprises a
   number of components that identify the origin of the message and, if the
   message indicates a problem, information about the problem that may be
   useful in fixing it.

   Consider the message below logged to a file:

 2014-04-11 12:58:01.005 INFO  [kea-dhcp4.dhcpsrv/27456]
     DHCPSRV_MEMFILE_DB opening memory file lease database: type=memfile universe=4

   Note: the layout of messages written to the system logging file (syslog)
   may be slightly different. This message has been split across two lines
   here for display reasons; in the logging file, it will appear on one line.

   The log message comprises a number of components:

   2014-04-11 12:58:01.005

           The date and time at which the message was generated.

   INFO

           The severity of the message.

   [kea-dhcp4.dhcpsrv/27456]

           The source of the message. This comprises two elements: the Kea
           process generating the message (in this case, kea-dhcp4) and the
           component within the program from which the message originated
           (dhcpsrv, which is the name of the common library used by DHCP
           server implementations). The number after the slash is a process
           id (pid).

   DHCPSRV_MEMFILE_DB

           The message identification. Every message in Kea has a unique
           identification, which can be used as an index into the Kea
           Messages Manual
           (https://jenkins.isc.org/job/Kea_doc/messages/kea-messages.html)
           from which more information can be obtained.

   opening memory file lease database: type=memfile universe=4

           A brief description. Within this text, information relating to the
           condition that caused the message to be logged will be included.
           In this example, the information is logged that the in-memory
           lease database backend will be used to store DHCP leases.

  19.1.3. Logging During Kea Startup

   The logging configuration is specified in the configuration file. However,
   when Kea starts, the file is not read until some way into the
   initialization process. Prior to that, the logging settings are set to
   default values, although it is possible to modify some aspects of the
   settings by means of environment variables. Note that in the absence of
   any logging configuration in the configuration file, the settings of
   (possibly modified) default configuration will persist while the program
   is running.

   The following environment variables can be used to control the behavior of
   logging during startup:

   KEA_LOCKFILE_DIR

           Specifies a directory where the logging system should create its
           lock file. If not specified, it is prefix/var/run/kea, where
           prefix defaults to /usr/local. This variable must not end with a
           slash. There is one special value: "none", which instructs Kea to
           not create lock file at all. This may cause issues if several
           processes log to the same file.

   KEA_LOGGER_DESTINATION

           Specifies logging output. There are several special values.

                stdout

                        Log to standard output.

                stderr

                        Log to standard error.

                syslog[:fac]

                        Log via syslog. The optional fac (which is separated
                        from the word "syslog" by a colon) specifies the
                        facility to be used for the log messages. Unless
                        specified, messages will be logged using the facility
                        "local0".

           Any other value is treated as a name of the output file. If not
           specified otherwise, Kea will log to standard output.

                           Chapter 20. The Kea Shell

   Table of Contents

   20.1. Overview

   20.2. Shell Usage

20.1. Overview

   Kea 1.2.0 introduced the Control Agent (CA, see Chapter 7, Kea Control
   Agent) that provides a RESTful control interface over HTTP. That API is
   typically expected to be used by various IPAMs and similar management
   systems. Nevertheless, there may be cases when you want to send a command
   to the CA directly. The Kea Shell provides a way to do this. It is a
   simple command-line, scripting-friendly text client that is able connect
   to the CA, send it commands with parameters, retrieve the responses and
   display them.

   As the primary purpose of the Kea Shell is as a tool in scripting
   environment, it is not interactive. However, with simple tricks it can be
   run manually.

20.2. Shell Usage

   kea-shell is run as follows:

 kea-shell [--host hostname] [--port number] [--path path] [--timeout seconds] [--service service-name] [command]

   where:

     * --host hostname specifies the hostname of the CA. If not specified,
       "localhost" is used.
     * --port number specifies the TCP port on which the CA listens. If not
       specified, 8000 is used.
     * --path path specifies the path in the URL to connect to. If not
       specified, empty path is used. As CA listens at the empty path this
       parameter is useful only with a reverse proxy.
     * --timeout seconds specifies the timeout (in seconds) for the
       connection. If not given, 10 seconds is used.
     * --service service-name specifies the target of a command. If not
       given, CA will be used as target. May be used more than once to
       specify multiple targets.
     * command specifies the command to be sent. If not specified,
       list-commands command is used.

   Other switches are:

     * -h prints a help message.
     * -v prints the software version.

   Once started, the shell reads parameters for the command from standard
   input, which are expected to be in JSON format. When all have been read,
   the shell establishes a connection with the CA using HTTP, sends the
   command and awaits a response. Once that is received, it is printed on
   standard output.

   For a list of available commands, see Chapter 17, Management API.
   Additional commands may be provided by hook libraries. If unsure which
   commands are supported, use the list-commands command. It will instruct
   the CA to return a list of all supported commands.

   The following shows a simple example of usage:

 $ kea-shell --host 192.0.2.1 --port 8001 --service dhcp4 list-commands
 ^D

   After the command line is entered, the program waits for command
   parameters to be entered. Since list-commands does not take any arguments,
   CTRL-D (represented in the above example by "^D") is pressed to indicate
   end of file (and so terminate the parameter input). The Shell will then
   contact the CA and print out the list of available commands returned for
   the service named dhcp4.

   It is envisaged that Kea Shell will be most frequently used in scripts.
   The next example shows a simple scripted execution. It sends the command
   "config-write" to the CA ( --service parameter hasn't been used), along
   with the parameters specified in param.json. The result will be stored in
   result.json.

 $ cat param.json
 "filename": "my-config-file.json"
 $ cat param.json | kea-shell --host 192.0.2.1 config-write > result.json

   When a reverse proxy is used to de-multiplex requests to different servers
   the default empty path in the URL is not enough so the --path parameter
   should be used. For instance if requests to the "/kea" path are forwarded
   to the CA this can be used:

 $ kea-shell --host 192.0.2.1 --port 8001 --path kea ...

   Kea Shell requires Python to to be installed on the system. It was tested
   with Python 2.7 and various versions of Python 3, up to 3.5. Since not
   every Kea deployment uses this feature and there are deployments that do
   not have Python, the Kea Shell is not enabled by default. To use it, you
   must specify --enable-shell to when running "configure" during the
   installation of Kea.

   The Kea Shell is intended to serve more as a demonstration of the RESTful
   interface capabilities (and, perhaps, an illustration for people
   interested in integrating their management evironments with Kea) than as a
   serious management client. Do not expect it to be significantly expanded
   in the future. It is, and will remain, a simple tool.

                        Chapter 21. YANG/NETCONF Support

   Table of Contents

   21.1. Overview

   21.2. Installing NETCONF

                21.2.1. Installing NETCONF on Ubuntu 18.04

                21.2.2. Installing NETCONF on CentOS 7.5

   21.3. Quick sysrepo overview

   21.4. Supported YANG models

   21.5. Using the Netconf agent

   21.6. Configuration

   21.7. Kea-netconf Configuration Example

   21.8. Starting and Stopping the Netconf Agent

   21.9. Step by Step Netconf Operation Example

                21.9.1. Setup of Netconf Operation Example

                21.9.2. Error handling in Netconf Operation Example

                21.9.3. Netconf Operation Example with Two Pools

                21.9.4. Netconf Operation Example with Two Subnets

                21.9.5. Netconf Operation Example with Logging

21.1. Overview

   Kea 1.5.0 introduced an optional support for YANG/NETCONF interface with
   the new kea-netconf Netconf agent.

   This bare bones documentation is a work in progress. Its current purpose
   is to let engineers joining the project or perhaps advanced early adopters
   to get up to speed quickly.

21.2. Installing NETCONF

   Note that to get NETCONF capabilities Kea uses Sysrepo software, which has
   many dependencies. Unfortunately, some of them are not available as
   packages and need to be compiled manually.

   Please note that libyang building requires a gcc version at least 4.9 so
   on some environments like CentOS 7.5 the system compiler cannot be used.

   The following sections provide installation instructions for Ubuntu 18.04
   and CentOS 7.5. Due to more modern compiler and many available packages,
   the installation procedure is much simpler on Ubuntu.

  21.2.1. Installing NETCONF on Ubuntu 18.04

   For detailed installation instructions see Ubuntu installation notes page.

  21.2.2. Installing NETCONF on CentOS 7.5

   For detailed installation instructions see CentOS installation notes page.

   CentOS 7.5 has a very old gcc compiler 4.8.5. Some sysrepo dependencies
   require at least 4.9, which unfortunately means that a new compiler has to
   be installed. Also, many of the Sysrepo dependencies are not avalable in
   CentOS as packages, so for the time being they need to be installed from
   sources. The situation is expected to improve over time as more and more
   CentOS / RedHat packages become available.

21.3. Quick sysrepo overview

   This section covers a rather brief overview of a subset of available
   functionality in sysrepo. For more complete document, see sysrepo
   homepage. You may also want to take a look at notes made during a series
   of IETF Hackathons.

   In YANG configurations and state data are described in the YANG syntax in
   module files named: "module-name"[@"revision"].yang

   The revision part is optional and has YYYY-MM-DD format. An alternate XML
   syntax YIN is defined but less user friendly. Top level modules are named
   in kea models (short version of schema models).

   List currently installed YANG modules:

   $ sysrepoctl -l

   After installation the result should be similar to this:

 Sysrepo schema directory: /home/thomson/devel/sysrepo-0.7.6/build/repository/yang/
 Sysrepo data directory:   /home/thomson/devel/sysrepo-0.7.6/build/repository/data/
 (Do not alter contents of these directories manually)

 Module Name                | Revision   | Conformance | Data Owner          | Permissions | Submodules                    | Enabled Features
 -----------------------------------------------------------------------------------------------------------------------------------------------
 ietf-netconf-notifications | 2012-02-06 | Installed   | root:root           | 666         |                               |
 ietf-netconf               | 2011-06-01 | Imported    |                     |             |                               |
 ietf-netconf-acm           | 2012-02-22 | Imported    |                     |             |                               |
 nc-notifications           | 2008-07-14 | Installed   | root:root           | 666         |                               |
 notifications              | 2008-07-14 | Installed   | root:root           | 666         |                               |
 turing-machine             | 2013-12-27 | Installed   | root:root           | 666         |                               |
 iana-if-type               | 2014-05-08 | Installed   |                     |             |                               |
 ietf-interfaces            | 2014-05-08 | Installed   | root:root           | 666         |                               |
 ietf-ip                    | 2014-06-16 | Installed   |                     |             |                               |

   Installing Kea YANG modules. There are two major modules that Kea is able
   to support: kea-dhcp4-server and kea-dhcp6-server. Note that while there
   is an active effort at DHC working group at IETF to develop an DHCPv6 YANG
   model, similar initiative for DHCPv4 died long time ago. As such, Kea uses
   its own dedicated models for DHCPv4 and DHCPv6 but partially supports the
   IETF model for DHCPv6. Those three models have extra modules as
   dependencies. The dependency modules are also provided in
   src/share/yang/modules in sources and share/kea/yang/modules after
   installation.

   To install modules from sources, do the following:

 cd src/share/yang/modules
 sudo sysrepoctl -i -s /home/thomson/devel/sysrepo-0.7.6/build/repository/yang -s . -g ietf-dhcpv6-server*.yang
 sudo sysrepoctl -i -s /home/thomson/devel/sysrepo-0.7.6/build/repository/yang -s . -g kea-dhcp4-server*.yang
 sudo sysrepoctl -i -s /home/thomson/devel/sysrepo-0.7.6/build/repository/yang -s . -g kea-dhcp6-server*.yang
 ...

   Note the first -s parameter specifies the location of your YANG schema
   repository. You can check it with sysrepoctl -l. This is a parameter that
   is configured during sysrepo compilation and is detected by Kea configure
   under the SYSREPO_REPO name.

   The installation should look similar to the following:

 $ sudo sysrepoctl -i -s /home/thomson/devel/sysrepo-0.7.6/build/repository/yang -s . -g ietf-dhcpv6-server*.yang
 Installing a new module from file 'ietf-dhcpv6-server@2018-11-20.yang'...
 Installing the YANG file to '/home/thomson/devel/sysrepo-0.7.6/build/repository/yang/ietf-dhcpv6-server@2018-07-14.yang'...
 Resolving dependency: 'ietf-dhcpv6-server' imports 'ietf-dhcpv6-options'...
 Installing the YANG file to '/home/thomson/devel/sysrepo-0.7.6/build/repository/yang/ietf-dhcpv6-options@2018-07-14.yang'...
 Resolving dependency: 'ietf-dhcpv6-options' imports 'ietf-dhcpv6-types'...
 Installing the YANG file to '/home/thomson/devel/sysrepo-0.7.6/build/repository/yang/ietf-dhcpv6-types@2018-07-14.yang'...
 Resolving dependency: 'ietf-dhcpv6-server' imports 'ietf-dhcpv6-types'...
 Installing the YANG file to '/home/thomson/devel/sysrepo-0.7.6/build/repository/yang/ietf-dhcpv6-types@2018-07-14.yang'...
 Resolving dependency: 'ietf-dhcpv6-server' imports 'ietf-interfaces'...
 Schema of the module ietf-interfaces is already installed, skipping...
 Installing data files for module 'ietf-dhcpv6-server'...
 Resolving dependency: 'ietf-dhcpv6-server' imports 'ietf-dhcpv6-options'...
 Skipping installation of data files for module 'ietf-dhcpv6-options'...
 Resolving dependency: 'ietf-dhcpv6-options' imports 'ietf-dhcpv6-types'...
 Skipping installation of data files for module 'ietf-dhcpv6-types'...
 Resolving dependency: 'ietf-dhcpv6-server' imports 'ietf-dhcpv6-types'...
 Skipping installation of data files for module 'ietf-dhcpv6-types'...
 Resolving dependency: 'ietf-dhcpv6-server' imports 'ietf-interfaces'...
 Installing data files for module 'ietf-interfaces'...
 Notifying sysrepo about the change...
 Install operation completed successfully.

   You can confirm whether the models are imported correctly by using
   sysrepoctl -l

 $ sysrepoctl -l
 Sysrepo schema directory: /home/thomson/devel/sysrepo-0.7.6/build/repository/yang/
 Sysrepo data directory:   /home/thomson/devel/sysrepo-0.7.6/build/repository/data/
 (Do not alter contents of these directories manually)

 Module Name                | Revision   | Conformance | Data Owner          | Permissions | Submodules                    | Enabled Features
 -----------------------------------------------------------------------------------------------------------------------------------------------
 ietf-netconf-notifications | 2012-02-06 | Installed   | root:root           | 666         |                               |
 ietf-netconf               | 2011-06-01 | Imported    |                     |             |                               |
 ietf-netconf-acm           | 2012-02-22 | Imported    |                     |             |                               |
 nc-notifications           | 2008-07-14 | Installed   | root:root           | 666         |                               |
 notifications              | 2008-07-14 | Installed   | root:root           | 666         |                               |
 turing-machine             | 2013-12-27 | Installed   | root:root           | 666         |                               |
 iana-if-type               | 2014-05-08 | Installed   |                     |             |                               |
 ietf-interfaces            | 2014-05-08 | Installed   | root:root           | 666         |                               |
 ietf-ip                    | 2014-06-16 | Installed   |                     |             |                               |
 kea-dhcp4-server           | 2018-11-20 | Installed   | root:root           | 666         |                               |
 kea-dhcp6-server           | 2018-11-20 | Installed   | root:root           | 666         |                               |
 ietf-dhcpv6-server         | 2018-09-04 | Installed   | root:root           | 666         |                               |
 ietf-dhcpv6-options        | 2018-09-04 | Imported    |                     |             |                               |
 ietf-dhcpv6-types          | 2018-01-30 | Imported    |                     |             |                               |

   To install a new revision of a module it must be first uninstalled, e.g.
   by:

 sudo sysrepoctl -u -m kea-dhcp4-server

   If the module is used (i.e. imported) by other modules it can be unstalled
   only after modules using it. Installation and uninstallation must be done
   in dependency order and reverse dependency order accordingly.

21.4. Supported YANG models

   The currently the only supported models are kea-dhcp4-server and
   kea-dhcp6-server. There is partial support for ietf-dhcpv6-server, but the
   primary focus of testing was on Kea DHCP servers. Several other models
   (kea-dhcp-ddns and kea-ctrl-agent) are currently not supported. It is
   envisaged the situation to change in the future.

21.5. Using the Netconf agent

   The Netconf agent follows this algorithm:

     * For each managed server get the initial configuration from the server
       through the control scoket.
     * Open a connection with the sysrepo environment and establish two
       sessions with the startup and running datastores.
     * Check that used (not essential) and required (essential) modules are
       installed in the sysrepo repository at the right revision. If an
       essential module, i.e. a module where the configuration schema for a
       managed server is defined, is not installed then a fatal error is
       raised.
     * For each managed server get the YANG configuration from the startup
       datastore, translate it to JSON and load it onto the server being
       configured.
     * For each managed server subscribe a module change callback using its
       model name.
     * When a running configuration is changed, the callback tries to
       validate or load the updated configuration to the managed server.

21.6. Configuration

   The behavior described in Section 21.5, "Using the Netconf agent" is
   controlled by a few configuration flags which can be set in the global
   scope or in a specific managed server scope. In the second case the value
   defined in managed server scope takes precedence. These flags are:

     * The boot-update controls the initial configuration phase: when true
       (the default) the initial configuration retrieved from the classic Kea
       server JSON configuration file is loaded first, then the startup YANG
       model is loaded. This setting lets you define a control socket in your
       local JSON file and then download the configuration from YANG. When
       set to false, this phase is skipped.
     * The subscribe-changes controls the module change subscription: when
       true (the default) a module change callback is subscribed, when false
       the phase is skipped and running configuration updates are disabled.
       When set to true, the running datastore is used to subscribe for
       changes.
     * The validate-changes controls how Kea monitors the changes in Sysrepo
       configuration. Sysrepo offers two stages where Kea could interact:
       validation and application. The first one is called validation (or
       SR_EV_VERIFY event in Sysrepo naming convention). At this stage Kea
       will get the new configuration being committed and will verify it. If
       the configuration is incorrect for whatever reason, Kea servers will
       reject it, the error will be propagated back to the Sysrepo, which in
       will return an error to whoever tried to commit those changes. This
       step only takes place if validate-changes is set to true. There is
       also a second step called application (or SR_EV_APPLY event in Sysrepo
       naming convention), where the actual configuration is being applied.
       At this stage Kea can receive the configuration, but it is too late to
       signal back any errors, as the configuration has been comitted
       already.

   Other configuration flags are under study and may appear in future Kea
   versions. For instance for loading updated configurations directly in the
   validation callback so syntactically correct, but invalid configurations
   (such as overlapping subnets) can be rejected as soon as possible.

   The idea behind the initial configuration phase is to boot Kea servers
   with a minimal configuration which includes only a control socket making
   them manageable. For instance for the DHCPv4 server:

 {
     "Dhcp4": {
         "control-socket": {
             "socket-type": "unix",
             "socket-name": "/tmp/kea4-sock"
         }
     }
 }

   Note the alternative to boot with full configurations does not allow an
   easy track of changes or synchronization between the JSON and YANG sources
   of configurations. So it not really compatible with the YANG / Netconf
   configuration management paradigm where everything should be performed in
   YANG.

   With module change subscriptions enabled, the kea-netconf daemon will
   monitor any configuration changes as they appear in the sysrepo. Such
   changes can be done using sysrepocfg tool or remotely using any NETCONF
   client. For details, please see Sysrepo documentation or Section 21.9,
   "Step by Step Netconf Operation Example". Those tools can be used to
   modify YANG configurations in the running datastore. Note committed
   configurations are only updated in the running datastore: to keep them
   between server reboots they must be copied to the startup datastore.

   When module changes are tracked (using subscribe-changes set to true) and
   the running configuration has changed (e.g. using sysrepocfg or any
   NETCONF client) the callback is called to validate the modified
   configuration (if validate-changes was not set to false) and a second time
   to apply it. If the validation failed the callback is still called again
   but with an ABORT (vs APPLY) event with rollback changes.

   The returned code of the callback on an APPLY event is ignored, i.e. it is
   too late to refuse a bad configuration.

   There are four ways in which a modified YANG configuration could possibly
   be incorrect:

    1. It can be not compliant with the schema, e.g. unknown entry, missing
       mandatory entry, value with a bad type or not matching a constraint.
    2. It can fail to be translated from YANG to JSON, e.g. invalid user
       context.
    3. It can fail Kea server sanity checks, e.g. out of subnet pool range or
       unsupported database type.
    4. Syntax is correct and pass server sanity checks but the configuration
       fails to be run, e.g. the configuration specifies database
       credentials, but the database refuses connection.

   The first case is handled by sysrepo. The second and third cases are
   handled by Netconf in the validation phase (if not disabled by setting
   validate-changes to true). The last case makes the application phase to
   fail without a sensible report to sysrepo.

   The managed Kea servers or agents are described in the managed-servers
   section. Each sub-section begins by the service name: dhcp4, dhcp6, d2
   (the DHCP-DDNS server does not support the control channel feature yet),
   and ca (the control agent).

   Each managed server entry contains optionally:

     * boot-update, subscribe-changes and validate-changes control flags.
     * model specifies the YANG model / module name. For each service the
       default is the corresponding Kea YANG model, e.g. for "dhcp4" it is
       "kea-dhcp4-server".
     * control-socket specifies the control socket for managing the service
       configuration.

   A control socket is specified by:

     * socket-type: the socket type is either stdout (the default. It is not
       really a socket, but it allows to run kea-netconf in debugging mode
       where everything is printed on stdout. Can be also useful to redirect
       the commands easily.), unix (standard direct server control channel,
       which uses UNIX sockets), and http (using a control agent, which
       accepts HTTP connections).
     * socket-name: the local socket name for the unix socket type (default
       empty string).
     * socket-url: the HTTP URL for the http socket type (default
       http://127.0.0.1:8000/).

   User contexts can store arbitrary data as long as it is valid JSON syntax
   and its top level element is a map (i.e. the data must be enclosed in
   curly brackets). They are accepted at the Netconf entry, i.e. below the
   toplevel, managed service entry and control socket entry scopes.

   Hooks libraries can be loaded by the Netconf agent just like other servers
   or agents. It currently supports no hook point, however. This is expected
   to change in the upcoming Kea releases. The hooks-libraries list contains
   the list of hooks libraries that should be loaded by Netconf, along with
   their configuration information specified with parameters.

   Please consult Chapter 19, Logging for the details how to configure
   logging. The Netconf's root logger's name is kea-netconf as given in the
   example above.

21.7. Kea-netconf Configuration Example

   The following example demonstrates the basic Netconf configuration. More
   examples are available in doc/examples/netconf directory in Kea sources.

 // This is a simple example of a configuration for Netconf.
 // This server provides YANG interface for all Kea servers and agent.
 {
     "Netconf":
     {
         // Control flags can be defined in the global scope or
         // in a managed server scope. Precedence are:
         // - use the default value (true)
         // - use the global value
         // - use the local value.
         // So this overwrites the default value:
         "boot-update": false,

         // This map specifies how each server is managed. For each server there
         // is a name of the YANG model to be used and the control channel.
         //
         // Currently three control channel types are supported:
         // "stdout" which output the configuration on the standard output,
         // "unix" which uses the local control channel supported by
         // "dhcp4" and "dhcp6" servers ("d2" support is not yet available),
         // and "http" which uses the Control agent "ca" to manage itself or
         // to forward commands to "dhcp4" or "dhcp6" (in the future also
         // to d2).
         "managed-servers":
         {
             // This is how Netconf can communicate with the DHCPv4 server.
             "dhcp4":
             {
                 "comment": "DHCP4 server",
                 "model": "kea-dhcp4-server",
                 "control-socket":
                 {
                     "socket-type": "unix",
                     "socket-name": "/tmp/kea4-ctrl-socket"
                 }
             },

             // DHCPv6 parameters.
             "dhcp6":
             {
                 "model": "kea-dhcp6-server",
                 "control-socket":
                 {
                     "socket-type": "unix",
                     "socket-name": "/tmp/kea6-ctrl-socket"
                 }
             },

             // Currently the DHCP-DDNS (nicknamed D2) server does not support
             // command channel yet.
             "d2":
             {
                 "model": "kea-dhcp-ddns",
                 "control-socket":
                 {
                     "socket-type": "stdout",
                     "user-context": { "in-use": false }
                 }
             },

             // Of course the Control Agent (nicknamed CA) supports HTTP.
             "ca":
             {
                 "model": "kea-ctrl-agent",
                 "control-socket":
                 {
                     "socket-type": "http",
                     "socket-url": "http://127.0.0.1:8000/"
                 }
             }
         },

         // Netconf is able to load hook libraries that augment its operation.
         // Currently there are no hook points defined in kea-netconf
         // processing.
         "hooks-libraries": [
             // Hook libraries list may contain more than one library.
             {
                 // The only necessary parameter is the library filename.
                 "library": "/opt/local/netconf-commands.so",

                 // Some libraries may support parameters. Make sure you
                 // type this section carefully, as the kea-netconf does not
                 // validate it (because the format is library specific).
                 "parameters": {
                     "param1": "foo"
                 }
             }
         ]

     },

     // Similar to other Kea components, Netconf also uses logging.
     "Logging":
     {
         "loggers": [
             {
                 "name": "kea-netconf",
                 "output_options": [
                     {
                         "output": "/var/log/kea-netconf.log",
                         // Several additional parameters are possible in
                         // addition to the typical output.
                         // Flush determines whether logger flushes output
                         //  to a file.
                         // Maxsize determines maximum filesize before
                         // the file is being rotated.
                         // Maxver specifies the maximum number of
                         //  rotated files being kept.
                         "flush": true,
                         "maxsize": 204800,
                         "maxver": 4
                     }
                 ],
                 "severity": "INFO",
                 "debuglevel": 0
             }
         ]
     }
 }

21.8. Starting and Stopping the Netconf Agent

   Netconf accepts the following command-line switches:

     * -c file - specifies the configuration file.
     * -d - specifies whether the agent logging should be switched to
       debug/verbose mode. In verbose mode, the logging severity and
       debuglevel specified in the configuration file are ignored and "debug"
       severity and the maximum debuglevel (99) are assumed. The flag is
       convenient, for temporarily switching the server into maximum
       verbosity, e.g. when debugging.
     * -t file - specifies the configuration file to be tested. Kea-netconf
       will attempt to load it, and will conduct sanity checks. Note that
       certain checks are possible only while running the actual server. The
       actual status is reported with exit code (0 = configuration looks ok,
       1 = error encountered). Kea will print out log messages to standard
       output and error to standard error when testing configuration.
     * -v - prints out the Kea version and exits.
     * -V - prints out the Kea extended version with additional parameters
       and exits. The listing includes the versions of the libraries
       dynamically linked to Kea.
     * -W - prints out the Kea configuration report and exits. The report is
       a copy of the config.report file produced by ./configure: it is
       embedded in the executable binary.

21.9. Step by Step Netconf Operation Example

  Note

   Copies of example configurations presented within this section can be
   found in the Kea source code, under
   doc/examples/netconf/kea-dhcp6-operations.

  21.9.1. Setup of Netconf Operation Example

   The test box has an Ethernet interface named eth1. On some systems it is
   possible to rename interfaces, for instance on a Linux with an ens38
   interface:

  # ip link set down dev ens38
  # ip link set name eth1 dev ens38
  # ip link set up dev eth1

   The interface must have an address in the test prefix:

  # ip -6 addr add 2001:db8::1/64 dev eth1

   The Kea DHCPv6 server must be launched with the configuration specifying a
   control socket used to receive control commands. The kea-netconf process
   uses this socket to communicate with the DHCPv6 server, i.e. it pushes
   translated configurations to that server using control commands. The
   following is the example control socket specification for the Kea DHCPv6
   server:

 {
     "Dhcp6": {
         "control-socket": {
             "socket-type": "unix",
             "socket-name": "/tmp/kea6-sock"
         }
     }
 }

   In order to launch the Kea DHCPv6 server using configuration contained
   within boot.json file, run:

  # kea-dhcp6 -d -c boot.json

   The current configuration of the server can be fetched via control socket
   by running:

  # echo '{ "command": "config-get" }' | socat UNIX:/tmp/kea6-sock '-,ignoreeof'

   The following is the example netconf.json configuration for kea-netconf,
   to manage the Kea DHCPv6 server:

 {
     "Netconf":
     {
         "managed-servers":
         {
             "dhcp6":
             {
                 "control-socket":
                 {
                     "socket-type": "unix",
                     "socket-name": "/tmp/kea6-sock"
                 }
             }
         }
     },
     "Logging":
     {
         "loggers":
         [
             {
                 "name": "kea-netconf",
                 "output_options":
                 [
                     {
                         "output": "stderr"
                     }
                 ],
                 "severity": "DEBUG",
                 "debuglevel": 99
             }
         ]
     }
 }

   Note that in production you should not need to log at the DEBUG level.

   The Kea Netconf agent is lanched by:

  # kea-netconf -d -c netconf.json

   Now that both kea-netconf and kea-dhcp6 are running, it is possible to
   populate updated to configuration to the DHCPv6 server. The following is
   the configuration extracted from the startup.xml:

 <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
   <subnet6>
     <id>1</id>
     <pool>
       <start-address>2001:db8::1:0</start-address>
       <end-address>2001:db8::1:ffff</end-address>
       <prefix>2001:db8::1:0/112</prefix>
     </pool>
     <subnet>2001:db8::/64</subnet>
   </subnet6>
   <interfaces-config>
     <interfaces>eth1</interfaces>
   </interfaces-config>
   <control-socket>
     <socket-name>/tmp/kea6-sock</socket-name>
     <socket-type>unix</socket-type>
   </control-socket>
 </config>

   In order to populate this new configuration:

  # sysrepocfg -d startup -f xml -i startup.xml kea-dhcp6-server

   kea-netconf will push the configuration found in the sysrepo startup
   datastore to all Kea servers during its initialization phase, after it
   subscribes to module changes in the sysrepo running datastore. This action
   copies the configuration from the startup datastore to the running
   datastore and enables the running datastore making it available.

   Changes to the running datastore are applied after validation to the Kea
   servers. Note they are not by default copied back to the startup
   datastore, i.e. changes are not permanent.

  21.9.2. Error handling in Netconf Operation Example

   There are four classes of isssues with the configurations applied via
   netconf:

    1. The configuration does not comply with the YANG schema.
    2. The configuration cannot be translated from YANG to the Kea JSON.
    3. The configuration is rejected by the Kea server.
    4. The configuration was validated by the Kea server but cannot be
       applied.

   In the first case, the following BAD-schema.xml configuration file:

 <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
   <subnet4>
     <id>1</id>
     <pool>
       <start-address>2001:db8::1:0</start-address>
       <end-address>2001:db8::1:ffff</end-address>
       <prefix>2001:db8::1:0/112</prefix>
     </pool>
     <subnet>2001:db8::/64</subnet>
   </subnet6>
   <interfaces-config>
     <interfaces>eth1</interfaces>
   </interfaces-config>
   <control-socket>
     <socket-name>/tmp/kea6-sock</socket-name>
     <socket-type>unix</socket-type>
   </control-socket>
 </config>

   is directly rejected by sysrepocfg:

  # sysrepocfg -d running -f xml -i BAD-schema.xml kea-dhcp6-server

   In the second case, the configuration is rejected by kea-netconf. For
   example, the BAD-translator.xml file:

 <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
   <subnet6>
     <id>1</id>
     <pool>
       <start-address>2001:db8::1:0</start-address>
       <end-address>2001:db8::1:ffff</end-address>
       <prefix>2001:db8::1:0/112</prefix>
     </pool>
     <subnet>2001:db8::/64</subnet>
   </subnet6>
   <interfaces-config>
     <interfaces>eth1</interfaces>
   </interfaces-config>
   <control-socket>
     <socket-name>/tmp/kea6-sock</socket-name>
     <socket-type>unix</socket-type>
   </control-socket>
   <user-context>bad</user-context>
 </config>

   In the third case, the configuration is presented to the Kea DHCPv6 server
   and fails to validate as in the BAD-config.xml file:

 <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
   <subnet6>
     <id>1</id>
     <pool>
       <start-address>2001:db8:1::0</start-address>
       <end-address>2001:db8:1::ffff</end-address>
       <prefix>2001:db8:1::0/112</prefix>
     </pool>
     <subnet>2001:db8::/64</subnet>
   </subnet6>
   <interfaces-config>
     <interfaces>eth1</interfaces>
   </interfaces-config>
   <control-socket>
     <socket-name>/tmp/kea6-sock</socket-name>
     <socket-type>unix</socket-type>
   </control-socket>
 </config>

   In the last case, the misconfiguration is detected too late and the change
   must be reverted in sysrepo, e.g. using the startup datastore as a backup.
   For this reason, please use the sysrepocfg --permanent / -p option (or
   simlar feature of NETCONF clients) with care.

  21.9.3. Netconf Operation Example with Two Pools

   This example adds a second pool to the initial (i.e. startup)
   configuration in the twopools.xml file:

 <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
   <subnet6>
     <id>1</id>
     <pool>
       <start-address>2001:db8::1:0</start-address>
       <end-address>2001:db8::1:ffff</end-address>
       <prefix>2001:db8::1:0/112</prefix>
     </pool>
     <pool>
       <start-address>2001:db8::2:0</start-address>
       <end-address>2001:db8::2:ffff</end-address>
       <prefix>2001:db8::2:0/112</prefix>
     </pool>
     <subnet>2001:db8::/64</subnet>
   </subnet6>
   <interfaces-config>
     <interfaces>eth1</interfaces>
   </interfaces-config>
   <control-socket>
     <socket-name>/tmp/kea6-sock</socket-name>
     <socket-type>unix</socket-type>
   </control-socket>
 </config>

   This configuration is installed by:

  # sysrepocfg -d running -f xml -i twopools.xml kea-dhcp6-server

  21.9.4. Netconf Operation Example with Two Subnets

   This example specifies two subnets in the twosubnets.xml file:

 <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
   <subnet6>
     <id>1</id>
     <pool>
       <start-address>2001:db8:1::</start-address>
       <end-address>2001:db8:1::ffff</end-address>
       <prefix>2001:db8:1::/112</prefix>
     </pool>
     <subnet>2001:db8:1::/64</subnet>
   </subnet6>
   <subnet6>
     <id>2</id>
     <pool>
       <start-address>2001:db8:2::</start-address>
       <end-address>2001:db8:2::ffff</end-address>
       <prefix>2001:db8:2::/112</prefix>
     </pool>
     <subnet>2001:db8:2::/64</subnet>
   </subnet6>
   <interfaces-config>
     <interfaces>eth1</interfaces>
   </interfaces-config>
   <control-socket>
     <socket-name>/tmp/kea6-sock</socket-name>
     <socket-type>unix</socket-type>
   </control-socket>
 </config>

   This configuration is installed by:

  # sysrepocfg -d running -f xml -i twosubnets.xml kea-dhcp6-server

  21.9.5. Netconf Operation Example with Logging

   This example adds a Logging section to the initial (i.e. startup)
   configuration in the logging.xml file:

 <config xmlns="urn:ietf:params:xml:ns:yang:kea-dhcp6-server">
   <interfaces-config>
     <interfaces>eth1</interfaces>
   </interfaces-config>
   <subnet6>
     <id>1</id>
     <pool>
       <start-address>2001:db8::1:0</start-address>
       <end-address>2001:db8::1:ffff</end-address>
       <prefix>2001:db8::1:0/112</prefix>
     </pool>
     <subnet>2001:db8::/64</subnet>
   </subnet6>
   <control-socket>
     <socket-name>/tmp/kea6-sock</socket-name>
     <socket-type>unix</socket-type>
   </control-socket>
   <logger>
     <name>kea-dhcp6</name>
     <output-option>
       <output>stderr</output>
     </output-option>
     <debuglevel>99</debuglevel>
     <severity>DEBUG</severity>
   </logger>
 </config>

   The corresponding Kea configuration in JSON is:

 {
   "Dhcp6": {
     "control-socket": {
       "socket-name": "/tmp/kea6-sock",
       "socket-type": "unix"
     },
     "interfaces-config": {
       "interfaces": [ "eth1" ]
     },
     "subnet6": [
       {
         "id": 1,
         "pools": [
           {
             "pool": "2001:db8::1:0/112"
           }
         ],
         "subnet": "2001:db8::/64"
       }
     ]
   },
   "Logging": {
     "loggers": [
       {
         "name": "kea-dhcp6",
         "output_options": [
           {
             "output": "stderr"
           }
         ],
         "severity": "DEBUG",
         "debuglevel": 99
       }
    ]
  }
 }

   Finally, any of the previous examples can be replayed using sysrepocfg in
   edit mode as follows:

  # sysrepocfg -d running -f xml -e vi kea-dhcp6-server

   or of course using a netconf client like netopeer2-cli from the Netopeer2
   NETCONF Toolset.

                           Appendix A. API Reference

   Table of Contents

   A.1. build-report reference

   A.2. cache-clear reference

   A.3. cache-get reference

   A.4. cache-insert reference

   A.5. cache-load reference

   A.6. cache-remove reference

   A.7. cache-write reference

   A.8. class-add reference

   A.9. class-del reference

   A.10. class-get reference

   A.11. class-list reference

   A.12. class-update reference

   A.13. config-get reference

   A.14. config-reload reference

   A.15. config-set reference

   A.16. config-test reference

   A.17. config-write reference

   A.18. dhcp-disable reference

   A.19. dhcp-enable reference

   A.20. ha-continue reference

   A.21. ha-heartbeat reference

   A.22. ha-scopes reference

   A.23. ha-sync reference

   A.24. lease4-add reference

   A.25. lease4-del reference

   A.26. lease4-get reference

   A.27. lease4-get-all reference

   A.28. lease4-update reference

   A.29. lease4-wipe reference

   A.30. lease6-add reference

   A.31. lease6-del reference

   A.32. lease6-get reference

   A.33. lease6-get-all reference

   A.34. lease6-update reference

   A.35. lease6-wipe reference

   A.36. leases-reclaim reference

   A.37. libreload reference

   A.38. list-commands reference

   A.39. network4-add reference

   A.40. network4-del reference

   A.41. network4-get reference

   A.42. network4-list reference

   A.43. network4-subnet-add reference

   A.44. network4-subnet-del reference

   A.45. network6-add reference

   A.46. network6-del reference

   A.47. network6-get reference

   A.48. network6-list reference

   A.49. network6-subnet-add reference

   A.50. network6-subnet-del reference

   A.51. reservation-add reference

   A.52. reservation-del reference

   A.53. reservation-get reference

   A.54. shutdown reference

   A.55. stat-lease4-get reference

   A.56. stat-lease6-get reference

   A.57. statistic-get reference

   A.58. statistic-get-all reference

   A.59. statistic-remove reference

   A.60. statistic-remove-all reference

   A.61. statistic-reset reference

   A.62. statistic-reset-all reference

   A.63. subnet4-add reference

   A.64. subnet4-del reference

   A.65. subnet4-get reference

   A.66. subnet4-list reference

   A.67. subnet6-add reference

   A.68. subnet6-del reference

   A.69. subnet6-get reference

   A.70. subnet6-list reference

   A.71. version-get reference

   Kea currently supports 71 commands: build-report , cache-clear , cache-get
   , cache-insert , cache-load , cache-remove , cache-write , class-add ,
   class-del , class-get , class-list , class-update , config-get ,
   config-reload , config-set , config-test , config-write , dhcp-disable ,
   dhcp-enable , ha-continue , ha-heartbeat , ha-scopes , ha-sync ,
   lease4-add , lease4-del , lease4-get , lease4-get-all , lease4-update ,
   lease4-wipe , lease6-add , lease6-del , lease6-get , lease6-get-all ,
   lease6-update , lease6-wipe , leases-reclaim , libreload , list-commands ,
   network4-add , network4-del , network4-get , network4-list ,
   network4-subnet-add , network4-subnet-del , network6-add , network6-del ,
   network6-get , network6-list , network6-subnet-add , network6-subnet-del ,
   reservation-add , reservation-del , reservation-get , shutdown ,
   stat-lease4-get , stat-lease6-get , statistic-get , statistic-get-all ,
   statistic-remove , statistic-remove-all , statistic-reset ,
   statistic-reset-all , subnet4-add , subnet4-del , subnet4-get ,
   subnet4-list , subnet6-add , subnet6-del , subnet6-get , subnet6-list ,
   version-get .

   Commands supported by kea-ctrl-agent daemon: build-report , config-get ,
   config-test , config-write , list-commands , shutdown , version-get .

   Commands supported by kea-dhcp4 daemon: build-report , cache-clear ,
   cache-get , cache-insert , cache-load , cache-remove , cache-write ,
   class-add , class-del , class-get , class-list , class-update , config-get
   , config-reload , config-set , config-test , config-write , dhcp-disable ,
   dhcp-enable , ha-continue , ha-heartbeat , ha-scopes , ha-sync ,
   lease4-add , lease4-del , lease4-get , lease4-get-all , lease4-update ,
   lease4-wipe , leases-reclaim , libreload , list-commands , network4-add ,
   network4-del , network4-get , network4-list , network4-subnet-add ,
   network4-subnet-del , reservation-add , reservation-del , reservation-get
   , shutdown , stat-lease4-get , statistic-get , statistic-get-all ,
   statistic-remove , statistic-remove-all , statistic-reset ,
   statistic-reset-all , subnet4-add , subnet4-del , subnet4-get ,
   subnet4-list , version-get .

   Commands supported by kea-dhcp6 daemon: build-report , cache-clear ,
   cache-get , cache-insert , cache-load , cache-remove , cache-write ,
   class-add , class-del , class-get , class-list , class-update , config-get
   , config-reload , config-set , config-test , config-write , dhcp-disable ,
   dhcp-enable , ha-continue , ha-heartbeat , ha-scopes , ha-sync ,
   lease6-add , lease6-del , lease6-get , lease6-get-all , lease6-update ,
   lease6-wipe , leases-reclaim , libreload , list-commands , network6-add ,
   network6-del , network6-get , network6-list , network6-subnet-add ,
   network6-subnet-del , reservation-add , reservation-del , reservation-get
   , shutdown , stat-lease6-get , statistic-get , statistic-get-all ,
   statistic-remove , statistic-remove-all , statistic-reset ,
   statistic-reset-all , subnet6-add , subnet6-del , subnet6-get ,
   subnet6-list , version-get .

   Commands supported by class_cmds hook library: class-add , class-del ,
   class-get , class-list , class-update .

   Commands supported by high_availability hook library: ha-continue ,
   ha-heartbeat , ha-scopes , ha-sync .

   Commands supported by host_cache hook library: cache-clear , cache-get ,
   cache-insert , cache-load , cache-remove , cache-write .

   Commands supported by host_cmds hook library: reservation-add ,
   reservation-del , reservation-get .

   Commands supported by lease_cmds hook library: lease4-add , lease4-del ,
   lease4-get , lease4-get-all , lease4-update , lease4-wipe , lease6-add ,
   lease6-del , lease6-get , lease6-get-all , lease6-update , lease6-wipe .

   Commands supported by stat_cmds hook library: stat-lease4-get ,
   stat-lease6-get .

   Commands supported by subnet_cmds hook library: network4-add ,
   network4-del , network4-get , network4-list , network4-subnet-add ,
   network4-subnet-del , network6-add , network6-del , network6-get ,
   network6-list , network6-subnet-add , network6-subnet-del , subnet4-add ,
   subnet4-del , subnet4-get , subnet4-list , subnet6-add , subnet6-del ,
   subnet6-get , subnet6-list .

A.1. build-report reference

   build-report - Returns a list of compilation options that this particular
   binary was built with

   Supported by: kea-dhcp4, kea-dhcp6, kea-ctrl-agent

   Availability: 1.2.0 (built-in)

   Description and examples: See Section 17.3.1, "build-report"

   Command syntax:

 {
     "command": "build-report"
 }

   Response syntax:

 {
     "result": 0,
     "text": <string with build details>
 }

A.2. cache-clear reference

   cache-clear - This command removes all cached host reservations.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (host_cache hook)

   Description and examples: See Section 15.4.11.2, "cache-clear command"

   Command syntax:

 {
     "command": "cache-clear"
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.3. cache-get reference

   cache-get - Returns full content of the host cache.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (host_cache hook)

   Description and examples: See Section 15.4.11.5, "cache-get command"

   Command syntax:

 {
     "command": "cache-get"
 }

   Response syntax:

 {
     "result": 0
     "text": "123 entries returned."
     "arguments": <list of cashed host>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.4. cache-insert reference

   cache-insert - This command may be used to manually insert a host into the
   cache.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (host_cache hook)

   Description and examples: See Section 15.4.11.6, "cache-insert command"

   Command syntax:

 {
     "command": "cache-insert",
     "arguments": {
         "hw-address": "01:02:03:04:05:06",
         "subnet-id4": 4,
         "subnet-id6": 0,
         "ip-address": "192.0.2.100",
         "hostname": "somehost.example.org",
         "client-classes4": [ ],
         "client-classes6": [ ],
         "option-data4": [ ],
         "option-data6": [ ],
         "next-server": "192.0.0.2",
         "server-hostname": "server-hostname.example.org",
         "boot-file-name": "bootfile.efi",
         "host-id": 0
     }
 },
 {
     "command": "cache-insert",
     "arguments": {
         "hw-address": "01:02:03:04:05:06",
         "subnet-id4": 0,
         "subnet-id6": 6,
         "ip-addresses": [ "2001:db8::cafe:babe" ],
         "prefixes": [ "2001:db8:dead:beef::/64" ],
         "hostname": "",
         "client-classes4": [ ],
         "client-classes6": [ ],
         "option-data4": [ ],
         "option-data6": [ ],
         "next-server": "0.0.0.0",
         "server-hostname": "",
         "boot-file-name": "",
         "host-id": 0
     }
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.5. cache-load reference

   cache-load - This command allows load the contents of a file on disk into
   an in-memory cache.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (host_cache hook)

   Description and examples: See Section 15.4.11.4, "cache-load command"

   Command syntax:

 {
     "command": "cache-load",
     "arguments": "/tmp/kea-host-cache.json"
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.6. cache-remove reference

   cache-remove - The cache-remove command works similarly to reservation-get
   command.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (host_cache hook)

   Description and examples: See Section 15.4.11.7, "cache-remove command"

   Command syntax:

 {
     "command": "cache-remove",
     "arguments": {
         "ip-address": "192.0.2.1",
         "subnet-id": 123
     }
 }

 Another example that removes IPv6 host identifier by DUID and specific subnet-id is:
 {
     "command": "cache-remove",
     "arguments": {
         "duid": "00:01:ab:cd:f0:a1:c2:d3:e4",
         "subnet-id": 123
     }
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.7. cache-write reference

   cache-write - Instructs Kea to write its host cache content to disk.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (host_cache hook)

   Description and examples: See Section 15.4.11.3, "cache-write command"

   Command syntax:

 {
     "command": "cache-write",
     "arguments": "/path/to/the/file.json"
 }

   The command takes one mandatory argument that specifies a filename path of
   a file to be written.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.8. class-add reference

   class-add - This command is used to create and add a new class to the
   existing server configuration.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.5.0 (class_cmds hook)

   Description and examples: See Section 15.4.7.1, "class-add command"

   Command syntax:

 {
     "command": "class-add",
     "arguments": {
         "client-classes": [ {
            "name": <name of the class>,
            "test": <test expression to be evaluated on incoming packets>,
            "option-data": [ <option values here> ],
            "option-def": [ <option defintions here> ],
            "next-server": <ipv4 address>,
            "server-hostname": <string>,
            "boot-file-name": <name of the boot file>
         } ]
     }
 }

   The next-server, server-hostname and boot-file-name are DHCPv4 specific.
   Only one client class can be added with a single command.

   Response syntax:

 {
     "result": 0,
     "text": "Class '<class-name>' added.",
 }

   The command will be successful (result 0), unless the class name is a
   duplicate or another error occurs (result 1).

A.9. class-del reference

   class-del - This command is used to remove a client class from the server
   configuration.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.5.0 (class_cmds hook)

   Description and examples: See Section 15.4.7.3, "class-del command"

   Command syntax:

 {
     "command": "class-del",
     "arguments": {
         "name": <name of the class>
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "Class '<class-name>' deleted."
 }

   The command will return a result of 3 (empty) if the client class doesn't
   exist. If the client class exists, the retured result is 0 if the deletion
   was successful and the result is 1 if the deletion is unsuccessful.

A.10. class-get reference

   class-get - This command is used to return detailed information about an
   existing client class.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.5.0 (class_cmds hook)

   Description and examples: See Section 15.4.7.5, "class-get command"

   Command syntax:

 {
     "command": "class-get",
     "arguments": {
         "name": <name of the class>
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "Class '<class-name>' definition returned",
     "arguments": {
         "client-classes": [
             {
                 "name": <name of the class>,
                 "only-if-required": <only if required boolean value>,
                 "test": <test expression to be evaluated on incoming packets>,
                 "option-data": [ <option values here> ],
                 "option-def": [ <option defintions here> ],
                 "next-server": <ipv4 address>,
                 "server-hostname": <string>,
                 "boot-file-name": <name of the boot file>
             }
         ]
     }
 }

   The returned information depends on the DHCP server type, i.e. some
   parameters are specific to DHCPv4 server. Also, some parameters may not be
   returned if they are not set for the client class. If the class with
   specified name doesn't exist a result of 3 (empty) is returned. If the
   client class is found, the result of 0 is returned. If there is an error
   while processing the command, the result of 1 is returned.

A.11. class-list reference

   class-list - This command is used to retrieve a list of all client classes
   from the server configuration.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.5.0 (class_cmds hook)

   Description and examples: See Section 15.4.7.4, "class-list command"

   Command syntax:

 {
     "command": "class-list"
 }

   This command includes no arguments.

   Response syntax:

 {
     "result": 0,
     "text": "<number of> classes found",
     "arguments": {
         "client-classes": [
             {
                 "name": <first class name>
             },
             {
                 "name": <second class name>
             }
         ]
     }
 }

   The returned list of classes merely contains their names. In order to
   retrieve full information about one of these classes use Section 15.4.7.5,
   "class-get command". The returned result is 3 (empty) if no classes are
   found. If the command is processed successfully and the list of client
   classes is not empty, the result of 0 is returned. If there is an error
   while processing the command, the result of 1 is returned.

A.12. class-update reference

   class-update - This command is used to update an existing client class in
   the server configuration.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.5.0 (class_cmds hook)

   Description and examples: See Section 15.4.7.2, "class-update command"

   Command syntax:

 {
     "command": "class-update",
     "arguments": {
         "client-classes": [ {
            "name": <name of the class>,
            "test": <test expression to be evaluated on incoming packets>,
            "option-data": [ <option values here> ],
            "option-def": [ <option defintions here> ],
            "next-server": <ipv4 address>,
            "server-hostname": <string>,
            "boot-file-name": <name of the boot file>
         } ]
     }
 }

   The next-server, server-hostname and boot-file-name are DHCPv4 specific.
   Only one client class can be updated with a single command.

   Response syntax:

 {
     "result": 0,
     "text": "Class '<class-name>' updated.",
 }

   The command will return the result of 3 (empty) if the client class
   doesn't exist. If the client class exists, the retured result is 0 if the
   update was successful and the result is 1 if the update is unsuccessful.

A.13. config-get reference

   config-get - Retrieves the current configuration used by the server. The
   configuration is roughtly equal to the configuration file, but includes
   additional changes made by other commands and due to parameters
   inheritance.

   Supported by: kea-dhcp4, kea-dhcp6, kea-ctrl-agent

   Availability: 1.2.0 (built-in)

   Description and examples: See Section 17.3.2, "config-get"

   Command syntax:

 {
     "command": "config-get"
 }

   This command takes no parameters.

   Response syntax:

 {
     "result": <integer>,
     "arguments": {
         <JSON configuration here, starting with Dhcp4, Dhcp6, or Control-agent object>
     }
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.14. config-reload reference

   config-reload - The config-reload command instructs Kea to load again the
   configuration file that was used previously.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.2.0 (built-in)

   Description and examples: See Section 17.3.3, "config-reload"

   Command syntax:

 {
     "command": "config-reload"
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.15. config-set reference

   config-set - The config-set command instructs the server to replace its
   current configuration with the new configuration supplied in the command's
   arguments.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.2.0 (built-in)

   Description and examples: See Section 17.3.9, "config-set"

   Command syntax:

 {
     "command": "config-set",
     "arguments":  {
         "<server>": {
         },
         "Logging": {
         }
      }
 }

   where <server> is the configuration element name for a given server such
   as "Dhcp4" or "Dhcp6"

   Response syntax:

     {"result": 0, "text": "Configuration successful." }

     or

     {"result": 1, "text": "unsupported parameter: BOGUS (<string>:16:26)" }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.16. config-test reference

   config-test - The config-test command instructs the server to check
   whether the new configuration supplied in the command's arguments can be
   loaded.

   Supported by: kea-dhcp4, kea-dhcp6, kea-ctrl-agent

   Availability: 1.2.0 (built-in)

   Description and examples: See Section 17.3.4, "config-test"

   Command syntax:

 {
     "command": "config-test",
     "arguments":  {
         "<server>": {
         },
         "Logging": {
         }
      }
 }

   where <server> is the configuration element name for a given server such
   as "Dhcp4" or "Dhcp6"

   Response syntax:

 {"result": 0, "text": "Configuration seems sane..." }

     or

     {"result": 1, "text": "unsupported parameter: BOGUS (<string>:16:26)" }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.17. config-write reference

   config-write - The config-write command instructs the Kea server to write
   its current configuration to a file on disk.

   Supported by: kea-dhcp4, kea-dhcp6, kea-ctrl-agent

   Availability: 1.2.0 (built-in)

   Description and examples: See Section 17.3.5, "config-write"

   Command syntax:

 {
     "command": "config-write",
     "arguments": {
         "filename": "config-modified-2017-03-15.json"
     }
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.18. dhcp-disable reference

   dhcp-disable - The dhcp-disable command globally disables the DHCP
   service.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (built-in)

   Description and examples: See Section 17.3.11, "dhcp-disable"

   Command syntax:

 {
     "command": "dhcp-disable",
     "arguments": {
         "max-period": 20
     }
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.19. dhcp-enable reference

   dhcp-enable - The dhcp-enable command globally enables the DHCP service.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (built-in)

   Description and examples: See Section 17.3.12, "dhcp-enable"

   Command syntax:

 {
     "command": "dhcp-enable"
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.20. ha-continue reference

   ha-continue - This command is used to resume the operation of the paused
   HA state machine.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (high_availability hook)

   Description and examples: See Section 15.4.8.13.3, "ha-continue command"

   Command syntax:

 {
     "command": "ha-continue"
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.21. ha-heartbeat reference

   ha-heartbeat - This command is sent internally by Kea partner when
   operating in High Availability (HA) mode. It will retrieve the server HA
   state and clock value.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (high_availability hook)

   Description and examples: See Section 15.4.8.3, "Server States"

   Command syntax:

 {
     "command": "ha-heartbeat"
     }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   The response to this command is different from the typical command
   response. The response will include server state (see Section 15.4.8.3,
   "Server States" plus the current clock value.

A.22. ha-scopes reference

   ha-scopes - This command modifies the scope that the server is responsible
   for serving when operating in High Availability (HA) mode.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (high_availability hook)

   Description and examples: See Section 15.4.8.13.2, "ha-scopes command"

   Command syntax:

 {
     "command": "ha-scopes",
     "service": [ <service, typically "dhcp4" or "dhcp6"> ],
     "arguments": {
         "scopes": [ "HA_server1", "HA_server2" ]
     }
 }

   In the example given, the arguments configure the server to handle traffic
   from both HA_server1 and HA_server2 scopes.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.23. ha-sync reference

   ha-sync - The command is issued to instruct the server running in HA mode
   to synchronize its local lease database with the selected peer.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.4.0 (high_availability hook)

   Description and examples: See Section 15.4.8.13.1, "ha-sync command"

   Command syntax:

 {
     "command": "ha-sync",
     "service": [ <service affected: "dhcp4" or "dhcp6" ],
     "arguments": {
         "server-name": <name of the partner server>,
         "max-period": <integer, in seconds>
     }
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.24. lease4-add reference

   lease4-add - The lease4-add command adds a new IPv4 lease
   administratively.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1, "lease4-add, lease6-add
   commands"

   Command syntax:

 {
     "command": "lease4-add",
     "arguments": {
         "ip-address": "192.0.2.202",
         "hw-address": "1a:1b:1c:1d:1e:1f"
     }
 }

   Note that Kea 1.4 requires an additional argument, subnet-ID, which is
   optional as of Kea 1.5. A number of other more detailed optional arguments
   are also supported.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.25. lease4-del reference

   lease4-del - lease4-del can be used to delete a lease from the lease
   database.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.4, "lease4-del, lease6-del
   commands"

   Command syntax:

 {
     "command": "lease4-del",
     "arguments": {
         "ip-address": "192.0.2.202"
     }
 }

   Specify the lease to be deleted either by IP address, or by
   identifier-type and identifier value. Currently supported identifiers are
   "hw-address" and "client-id".

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.26. lease4-get reference

   lease4-get - lease4-get can be used to query the lease database and
   retrieve existing leases.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.1, "lease4-get, lease6-get
   commands"

   Command syntax:

 {
     "command": "lease4-get",
     "arguments": {
         "ip-address": "192.0.2.1"
     }
 }

   Response syntax:

 {
   "arguments": {
     "client-id": "42:42:42:42:42:42:42:42",
     "cltt": 12345678,
     "fqdn-fwd": false,
     "fqdn-rev": true,
     "hostname": "myhost.example.com.",
     "hw-address": "08:08:08:08:08:08",
     "ip-address": "192.0.2.1",
     "state": 0,
     "subnet-id": 44,
     "valid-lft": 3600
   },
   "result": 0,
   "text": "IPv4 lease found."
 }

   lease4-get returns a result that indicates a result of the operation and
   lease details, if found. It has one of the following values: 0 (success),
   1 (error) or 2 (empty).

A.27. lease4-get-all reference

   lease4-get-all - lease4-get-all is used to retrieve all IPv4 leases or all
   leases for the specified set of subnets.

   Supported by: kea-dhcp4

   Availability: 1.4.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.2, "lease4-get-all,
   lease6-get-all commands"

   Command syntax:

 {
     "command": "lease4-get-all",
     "arguments": "subnets"
 }

   The lease4-get-all command may result in very large responses.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.28. lease4-update reference

   lease4-update - The lease4-update command can be used to update existing
   leases.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.5, "lease4-update,
   lease6-update commands"

   Command syntax:

 {
   "command": "lease4-update",
   "arguments": {
     "ip-address": "192.0.2.1",
     "hostname": "newhostname.example.org",
     "hw-address": "1a:1b:1c:1d:1e:1f",
     "subnet-id": 44,
     "force-create": true
   }
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.29. lease4-wipe reference

   lease4-wipe - lease4-wipe is designed to remove all leases associated with
   a given subnet.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.6, "lease4-wipe,
   lease6-wipe commands"

   Command syntax:

 {
   "command": "lease4-wipe",
   "arguments": {
     "subnet-id": 44
   }
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.30. lease6-add reference

   lease6-add - The lease6-add command creates a new lease administratively.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1, "lease4-add, lease6-add
   commands"

   Command syntax:

 {
     "command": "lease6-add",
     "arguments": {
         "subnet-id": 66,
         "ip-address": "2001:db8::3",
         "duid": "1a:1b:1c:1d:1e:1f:20:21:22:23:24",
         "iaid": 1234
     }
 }

   lease6-add can be also used to add leases for IPv6 prefixes..

   Response syntax:

 { "result": 0,
             "text": "Lease added." }

           { "result": 1,
             "text": "missing parameter 'ip-address' (<string>:3:19)" }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.31. lease6-del reference

   lease6-del - lease6-del can be used to delete a lease from the lease
   database.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.4, "lease4-del, lease6-del
   commands"

   Command syntax:

 {
     "command": "lease6-del",
     "arguments": {
         "ip-address": "192.0.2.202"
     }
 }

   lease6-del returns a result that indicates a outcome of the operation. It
   has one of the following values: 0 (success), 1 (error) or 3 (empty).

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.32. lease6-get reference

   lease6-get - lease6-get can be used to query the lease database and
   retrieve existing leases.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.1, "lease4-get, lease6-get
   commands"

   Command syntax:

 {
   "command": "lease6-get",
   "arguments": {
     "ip-address": "2001:db8:1234:ab::",
     "type": "IA_PD"
   }
 }

   lease6-get returns a result that indicates a result of the operation and
   lease details, if found. It has one of the following values: 0 (success),
   1 (error) or 2 (empty).

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.33. lease6-get-all reference

   lease6-get-all - lease6-get-all is used to retrieve all IPv6 leases or all
   leases for the specified set of subnets.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.2, "lease4-get-all,
   lease6-get-all commands"

   Command syntax:

 {
     "command": "lease6-get-all",
     "arguments": {
         "subnets": [ 1, 2, 3, 4 ]
     }
 }

   Response syntax:

 {
     "arguments": {
         "leases": [
             {
                 "cltt": 12345678,
                 "duid": "42:42:42:42:42:42:42:42",
                 "fqdn-fwd": false,
                 "fqdn-rev": true,
                 "hostname": "myhost.example.com.",
                 "hw-address": "08:08:08:08:08:08",
                 "iaid": 1,
                 "ip-address": "2001:db8:2::1",
                 "preferred-lft": 500,
                 "state": 0,
                 "subnet-id": 44,
                 "type": "IA_NA",
                 "valid-lft": 3600
             },
             {
                 "cltt": 12345678,
                 "duid": "21:21:21:21:21:21:21:21",
                 "fqdn-fwd": false,
                 "fqdn-rev": true,
                 "hostname": "",
                 "iaid": 1,
                 "ip-address": "2001:db8:0:0:2::",
                 "preferred-lft": 500,
                 "prefix-len": 80,
                 "state": 0,
                 "subnet-id": 44,
                 "type": "IA_PD",
                 "valid-lft": 3600
             }
         ]
     },
     "result": 0,
     "text": "2 IPv6 lease(s) found."
 }

   The lease6-get-all command may result in very large responses.

A.34. lease6-update reference

   lease6-update - The lease6-update command can be used to update existing
   leases.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.5, "lease4-update,
   lease6-update commands"

   Command syntax:

 {
   "command": "lease6-update",
   "arguments": {
     "ip-address": "2001:db8::1",
     "duid": "88:88:88:88:88:88:88:88",
     "iaid": 7654321,
     "hostname": "newhostname.example.org",
     "subnet-id": 66,
     "force-create": false
   }
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.35. lease6-wipe reference

   lease6-wipe - lease6-wipe is designed to remove all leases associated with
   a given subnet.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (lease_cmds hook)

   Description and examples: See Section 15.4.5.1.6, "lease4-wipe,
   lease6-wipe commands"

   Command syntax:

 {
   "command": "lease6-wipe",
   "arguments": {
     "subnet-id": 66
   }
 }

   Note: not all backends support this command.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.36. leases-reclaim reference

   leases-reclaim - The leases-reclaim command instructs the server to
   reclaim all expired leases immediately.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.0.0 (built-in)

   Description and examples: See Section 17.3.6, "leases-reclaim"

   Command syntax:

 {
     "command": "leases-reclaim",
     "arguments": {
         "remove": true
     }
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.37. libreload reference

   libreload - The libreload command will first unload and then load all
   currently loaded hook libraries.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.2.0 (built-in)

   Description and examples: See Section 17.3.7, "libreload"

   Command syntax:

 {
     "command": "libreload",
     "arguments": { }
 }

   The server will respond with a result of 0 indicating success, or 1
   indicating a failure.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.38. list-commands reference

   list-commands - The list-commands command retrieves a list of all commands
   supported by the server.

   Supported by: kea-dhcp4, kea-dhcp6, kea-ctrl-agent

   Availability: 1.0.0 (built-in)

   Description and examples: See Section 17.3.8, "list-commands"

   Command syntax:

 {
     "command": "list-commands",
     "arguments": { }
 }

   The server will respond with a list of all supported commands.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.39. network4-add reference

   network4-add - The network4-add command is used to add a new shared
   network.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.11, "network4-add,
   network6-add commands"

   Command syntax:

 {
     "command": "network4-add",
     "arguments": {
         "shared-networks": [ {
             "name": "floor13",
             "subnet4": [
             {
                 "id": 100,
                 "pools": [ { "pool": "192.0.2.2-192.0.2.99" } ],
                 "subnet": "192.0.2.0/24",
                 "option-data": [
                     {
                         "name": "routers",
                         "data": "192.0.2.1"
                     }
                 ]
             },
             {
                 "id": 101,
                 "pools": [ { "pool": "192.0.3.2-192.0.3.99" } ],
                 "subnet": "192.0.3.0/24",
                 "option-data": [
                     {
                         "name": "routers",
                         "data": "192.0.3.1"
                     }
                 ]
             } ]
         } ]
     }
 }

   Response syntax:

 {
     "arguments": {
         "shared-networks": [ { "name": "floor13" } ]
     },
     "result": 0,
     "text": "A new IPv4 shared network 'floor13' added"
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.40. network4-del reference

   network4-del - The network4-del command is used to delete existing shared
   networks.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.12, "network4-del,
   network6-del commands"

   Command syntax:

 {
     "command": "network4-del",
     "arguments": {
         "name": "floor13"
     }
 }

   Response syntax:

 {
     "arguments": {
         "shared-networks": [
             {
                 "name": "floor13"
             }
         ]
     },
     "result": 0,
     "text": "IPv4 shared network 'floor13' deleted"
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.41. network4-get reference

   network4-get - The network4-get command is used to retrieve detailed
   information about shared networks, including subnets currently being part
   of a given network.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.10, "network4-get,
   network6-get commands"

   Command syntax:

 {
     "command": "network4-get",
     "arguments": {
         "name": "floor13"
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "Info about IPv4 shared network 'floor13' returned",
     "arguments": {
         "shared-networks": [
         {
             "match-client-id": true,
             "name": "floor13",
             "option-data": [ ],
             "rebind-timer": 90,
             "relay": {
                 "ip-address": "0.0.0.0"
             },
             "renew-timer": 60,
             "reservation-mode": "all",
             "subnet4": [
                 {
                     "subnet": "192.0.2.0/24",
                     "id": 5,
                     // many other subnet specific details here
                 },
                 {
                     "id": 6,
                     "subnet": "192.0.3.0/31",
                     // many other subnet specific details here
                 }
             ],
             "valid-lifetime": 120
         }
         ]
     }
 }

   Note that the actual response contains many additional fields that are
   omitted here for clarity.

A.42. network4-list reference

   network4-list - The network4-list command is used to retrieve full list of
   currently configured shared networks.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.9, "network4-list,
   network6-list commands"

   Command syntax:

 {
     "command": "network4-list"
 }

   Response syntax:

 {
     "arguments": {
         "shared-networks": [
             { "name": "floor1" },
             { "name": "office" }
         ]
     },
     "result": 0,
     "text": "2 IPv4 network(s) found"
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.43. network4-subnet-add reference

   network4-subnet-add - The network4-subnet-add command is used to add
   existing subnets to existing shared networks.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.13, "network4-subnet-add,
   network6-subnet-add commands"

   Command syntax:

 {
     "command": "network4-subnet-add",
     "arguments": {
         "name": "floor13",
         "id": 5
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now part of shared network 'floor1'"
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.44. network4-subnet-del reference

   network4-subnet-del - The network4-subnet-del command is used to remove a
   subnet that is part of an existing shared network and demote it to a
   plain, stand-alone subnet.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.14, "network4-subnet-del,
   network6-subnet-del commands"

   Command syntax:

 {
     "command": "network4-subnet-del",
     "arguments": {
         "name": "floor13",
         "id": 5
     }
  }

   Response syntax:

 {
     "result": 0,
     "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now removed from shared network 'floor13'"
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.45. network6-add reference

   network6-add - The network6-add command is used to add a new shared
   network.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.11, "network4-add,
   network6-add commands"

   Command syntax:

 {
     "command": "network4-add",
     "arguments": {
         "shared-networks": [ {
             "name": "floor13",
             "subnet4": [
             {
                 "id": 100,
                 "pools": [ { "pool": "192.0.2.2-192.0.2.99" } ],
                 "subnet": "192.0.2.0/24",
                 "option-data": [
                     {
                         "name": "routers",
                         "data": "192.0.2.1"
                     }
                 ]
             },
             {
                 "id": 101,
                 "pools": [ { "pool": "192.0.3.2-192.0.3.99" } ],
                 "subnet": "192.0.3.0/24",
                 "option-data": [
                     {
                         "name": "routers",
                         "data": "192.0.3.1"
                     }
                 ]
             } ]
         } ]
     }
 }

   The network6-add uses the same syntax for both the query and the response.
   However, there are some parameters that are IPv4-only (e.g.
   match-client-id) and some are IPv6-only (e.g. interface-id).

   Response syntax:

 {
     "arguments": {
         "shared-networks": [ { "name": "floor13" } ]
     },
     "result": 0,
     "text": "A new IPv4 shared network 'floor13' added"
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.46. network6-del reference

   network6-del - The network6-del command is used to delete existing shared
   networks.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.12, "network4-del,
   network6-del commands"

   Command syntax:

 {
     "command": "network4-del",
     "arguments": {
         "name": "floor13"
     }
 }

   The network6-del command uses exactly the same syntax for both the command
   and the response.

   Response syntax:

 {
     "command": "network4-del",
     "arguments": {
         "name": "floor13",
         "subnets-action": "delete"
     }
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.47. network6-get reference

   network6-get - The network6-get command is used to retrieve detailed
   information about shared networks, including subnets currently being part
   of a given network.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.10, "network4-get,
   network6-get commands"

   Command syntax:

 {
     "command": "network4-get",
     "arguments": {
         "name": "floor13"
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "Info about IPv4 shared network 'floor13' returned",
     "arguments": {
         "shared-networks": [
         {
             "match-client-id": true,
             "name": "floor13",
             "option-data": [ ],
             "rebind-timer": 90,
             "relay": {
                 "ip-address": "0.0.0.0"
             },
             "renew-timer": 60,
             "reservation-mode": "all",
             "subnet4": [
                 {
                     "subnet": "192.0.2.0/24",
                     "id": 5,
                     // many other subnet specific details here
                 },
                 {
                     "id": 6,
                     "subnet": "192.0.3.0/31",
                     // many other subnet specific details here
                 }
             ],
             "valid-lifetime": 120
         }
         ]
     }
 }

   Note that the actual response contains many additional fields that are
   omitted here for clarity.

A.48. network6-list reference

   network6-list - The network6-list command is used to retrieve full list of
   currently configured shared networks.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.9, "network4-list,
   network6-list commands"

   Command syntax:

 {
     "command": "network4-list"
 }

   network6-list follows exactly the same syntax for both the query and the
   response.

   Response syntax:

 {
     "arguments": {
         "shared-networks": [
             { "name": "floor1" },
             { "name": "office" }
         ]
     },
     "result": 0,
     "text": "2 IPv4 network(s) found"
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.49. network6-subnet-add reference

   network6-subnet-add - The network6-subnet-add command is used to add
   existing subnets to existing shared networks.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.13, "network4-subnet-add,
   network6-subnet-add commands"

   Command syntax:

 {
     "command": "network4-subnet-add",
     "arguments": {
         "name": "floor13",
         "id": 5
     }
 }

   The network6-subnet-add command uses exactly the same syntax for both the
   command and the response.

   Response syntax:

 {
     "result": 0,
     "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now part of shared network 'floor1'"
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.50. network6-subnet-del reference

   network6-subnet-del - The network6-subnet-del command is used to remove a
   subnet that is part of existing shared network and demote it to a plain,
   stand-alone subnet.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.14, "network4-subnet-del,
   network6-subnet-del commands"

   Command syntax:

 {
     "command": "network4-subnet-del",
     "arguments": {
         "name": "floor13",
         "id": 5
     }
  }

   The network6-subnet-del command uses exactly the same syntax for both the
   command and the response.

   Response syntax:

 {
     "result": 0,
     "text": "IPv4 subnet 10.0.0.0/8 (id 5) is now removed from shared network 'floor13'"
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.51. reservation-add reference

   reservation-add - adds a new host reservation. The reservation may include
   IPv4 address, IPv6 addresses, IPv6 prefixes, various identifiers, a class
   the client will be assigned to, DHCPv4 and DHCPv6 options and more.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.2.0 (host_cmds hook)

   Description and examples: See Section 15.4.4.2, "reservation-add command"

   Command syntax:

 {
     "command": "reservation-add",
     "arguments": {
         "reservation": {
             "boot-file-name": <string>,
             "comment": <string>
             "client-id": <string>,
             "circuit-id": <string>,
             "duid": <string>,
             "flex-id": <string>,
             "ip-address": <string (IPv4 address)>,
             "ip-addresses": [ <comma separated strings> ],
             "hw-address": <string>,
             "hostname": <string>,
             "next-server": <string (IPv4 address)>,
             "option-data-list": [ <comma separated structures defining options> ],
             "prefixes": [ <comma separated IPv6 prefixes> ],
             "reservation-client-classes": [ <comma separated strings> ],
             "server-hostname": <string>,
             "subnet-id": <integer>,
             "user-context": <any valid JSON>,
         }
     }
 }

   Note the ip-address, client-id, next-server, server-hostname and
   boot-file-name are IPv4 specific. duid, ip-addresses and prefixes are IPv6
   specific.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.52. reservation-del reference

   reservation-del - Deletes an existing host reservation.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.2.0 (host_cmds hook)

   Description and examples: See Section 15.4.4.4, "reservation-del command"

   Command syntax:

 {
     "command": "reservation-del",
     "arguments": {
         "subnet-id": <integer>,
         "ip-address": <string>,
         "identifier-type": <one of "hw-address", "duid", "circuit-id", "client-id" and "flex-id">,
         "identifier": <string>
     }
 }

   The host reservation can be identified by either (subnet-id, ip-address)
   pair or a triplet of (subnet-id, identifier-type, identifier).

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.53. reservation-get reference

   reservation-get - Attempts to retrieve an existing host reservation

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.2.0 (host_cmds hook)

   Description and examples: See Section 15.4.4.3, "reservation-get command"

   Command syntax:

 {
     "command": "reservation-get",
     "arguments": {
         "subnet-id": <integer>,
         "identifier-type": <string with one value out of: hw-address|duid|circuit-id|client-id|flex-id>,
         "identifier": <string>;
     }
 }

   The host reservation can be identified by either (subnet-id, ip-address)
   pair or a triplet of (subnet-id, identifier-type, identifier).

   Response syntax:

 {
     "result": <integer>,
     "text": <string>,
     "arguments": {
         "boot-file-name": <string>,
         "comment": <string>
         "client-id": <string>,
         "circuit-id": <string>,
         "duid": <string>,
         "flex-id": <string>,
         "ip-address": <string (IPv4 address)>,
         "ip-addresses": [ <comma separated strings> ],
         "hw-address": <string>,
         "hostname": <string>,
         "next-server": <string (IPv4 address)>,
         "option-data-list": [ <comma separated structures defining options> ],
         "prefixes": [ <comma separated IPv6 prefixes> ],
         "reservation-client-classes": [ <comma separated strings> ],
         "server-hostname": <string>,
         "subnet-id": <integer>,
         "user-context": <any valid JSON>,
     }
 }

   Arguments object appear only if a host is found. Many fields in the
   arguments object appear only if specific field is set.

A.54. shutdown reference

   shutdown - The shutdown command instructs the server to initiate its
   shutdown procedure.

   Supported by: kea-dhcp4, kea-dhcp6, kea-ctrl-agent

   Availability: 1.0.0 (built-in)

   Description and examples: See Section 17.3.10, "shutdown"

   Command syntax:

 {
     "command": "shutdown"
 }

   The server will respond with a confirmation that the shutdown procedure
   has been initiated.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.55. stat-lease4-get reference

   stat-lease4-get - The stat-lease4-get command fetches lease statistics for
   a range of known IPv4 subnets.

   Supported by: kea-dhcp4

   Availability: 1.4.0 (stat_cmds hook)

   Description and examples: See Section 15.4.9.1, "stat-lease4-get,
   stat-lease6-get commands"

   Command syntax:

 {
   "command": "stat-lease4-get"
 }

   Response syntax:

 {
     "result": 0,
     "text": "stat-lease4-get: 2 rows found",
     "arguments": {
       "result-set": {
         "columns": [ "subnet-id",
                        "total-addresses",
                        "assigned-addresses",
                        "declined-addresses" ]
         "rows": [
           [ 10, 256, 111, 0 ],
           [ 20, 4098, 2034, 4 ]
         ],
       "timestamp": "2018-05-04 15:03:37.000000"
       }
     }
   }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.56. stat-lease6-get reference

   stat-lease6-get - The stat-lease6-get command fetches lease statistics for
   a range of known IPv6 subnets.

   Supported by: kea-dhcp6

   Availability: 1.4.0 (stat_cmds hook)

   Description and examples: See Section 15.4.9.1, "stat-lease4-get,
   stat-lease6-get commands"

   Command syntax:

 {
   "command": "stat-lease6-get",
   "arguments": {
     "subnet-id" : 10
   }
 }

   Response syntax:

 {
     "result": 0,
     "text": "stat-lease6-get: 2 rows found",
     "arguments": {
       "result-set": {
         "columns": [ "subnet-id", "total-nas", "assigned-nas", "declined-nas", "total-pds", "assigned-pds" ]
         "rows": [
           [ 10, 4096, 2400, 3, 0, 0],
           [ 20, 0, 0, 0, 1048, 233 ]
           [ 30, 256, 60, 0, 1048, 15 ]
         ],
       "timestamp": "2018-05-04 15:03:37.000000"
       }
     }
   }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.57. statistic-get reference

   statistic-get - The statistic-get command retrieves a single statistic. It
   takes a single string parameter called name that specifies the statistic
   name.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.0.0 (built-in)

   Description and examples: See Section 16.3.1, "statistic-get command"

   Command syntax:

 {
     "command": "statistic-get",
     "arguments": {
         "name": "pkt4-received"
     }
 }

   The server will respond with details of the requested statistic, with a
   result set to 0 indicating success and the specified statistic as the
   value of the "arguments" parameter.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.58. statistic-get-all reference

   statistic-get-all - The statistic-get-all command retrieves all statistics
   recorded.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.0.0 (built-in)

   Description and examples: See Section 16.3.4, "statistic-get-all command"

   Command syntax:

 {
     "command": "statistic-get-all",
     "arguments": { }
 }

   The server will respond with details of all recorded statistics, with
   result set to 0 indicating that it iterated over all statistics (even when
   the total number of statistics is zero).

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.59. statistic-remove reference

   statistic-remove - The statistic-remove command attempts to delete a
   single statistic. It takes a single string parameter called name that
   specifies the statistic name.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.0.0 (built-in)

   Description and examples: See Section 16.3.3, "statistic-remove command"

   Command syntax:

 {
     "command": "statistic-remove",
     "arguments": {
         "name": "pkt4-received"
     }
 }

   If the specific statistic is found and its removal was successful, the
   server will respond with a status of 0, indicating success and an empty
   parameters field. If an error is encountered (e.g. requested statistic was
   not found), the server will return a status code of 1 (error) and the text
   field will contain the error description.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.60. statistic-remove-all reference

   statistic-remove-all - The statistic-remove-all command attempts to delete
   all statistics.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.0.0 (built-in)

   Description and examples: See Section 16.3.6, "statistic-remove-all
   command"

   Command syntax:

 {
     "command": "statistic-remove-all",
     "arguments": { }
 }

   If the removal of all statistics was successful, the server will respond
   with a status of 0, indicating success and an empty parameters field. If
   an error is encountered, the server will return a status code of 1 (error)
   and the text field will contain the error description.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.61. statistic-reset reference

   statistic-reset - The statistic-reset command sets the specified statistic
   to its neutral value: 0 for integer, 0.0 for float, 0h0m0s0us for time
   duration and "" for string type. It takes a single string parameter called
   name that specifies the statistic name.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.0.0 (built-in)

   Description and examples: See Section 16.3.2, "statistic-reset command"

   Command syntax:

 {
     "command": "statistic-reset",
     "arguments": {
         "name": "pkt4-received"
     }
 }

   If the specific statistic is found and reset was successful, the server
   will respond with a status of 0, indicating success and an empty
   parameters field. If an error is encountered (e.g. requested statistic was
   not found), the server will return a status code of 1 (error) and the text
   field will contain the error description.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.62. statistic-reset-all reference

   statistic-reset-all - The statistic-reset command sets all statistics to
   their neutral values: 0 for integer, 0.0 for float, 0h0m0s0us for time
   duration and "" for string type.

   Supported by: kea-dhcp4, kea-dhcp6

   Availability: 1.0.0 (built-in)

   Description and examples: See Section 16.3.5, "statistic-reset-all
   command"

   Command syntax:

 {
     "command": "statistic-reset-all",
     "arguments": { }
 }

   If the operation is successful, the server will respond with a status of
   0, indicating success and an empty parameters field. If an error is
   encountered, the server will return a status code of 1 (error) and the
   text field will contain the error description.

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.63. subnet4-add reference

   subnet4-add - This command is used to create and add a new subnet to the
   existing server configuration.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.5, "subnet4-add"

   Command syntax:

 {
     "command": "subnet4-add",
     "arguments": {
         "subnets": [ {
             "id": 123,
             "subnet": "10.20.30.0/24",
             ...
         } ]
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "IPv4 subnet added",
     "arguments": {
         "subnets": [
             {
                 "id": 123,
                 "subnet": "10.20.30.0/24"
             }
         ]
     }
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.64. subnet4-del reference

   subnet4-del - This command is used to remove a subnet from the server's
   configuration. This command has no effect on other configured subnets but
   removing a subnet has certain implications which the server's
   administrator should be aware of.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.7, "subnet4-del command"

   Command syntax:

 {
     "command": "subnet4-del",
     "arguments": {
         "id": 123
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "IPv4 subnet 192.0.2.0/24 (id 123) deleted",
     "arguments": {
         "subnets": [
             {
                 "id": 123,
                 "subnet": "192.0.2.0/24"
             }
         ]
     }
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.65. subnet4-get reference

   subnet4-get - This command is used to retrieve detailed information about
   the specified subnet. This command usually follows the subnet4-list, which
   is used to discover available subnets with their respective subnet
   identifiers and prefixes.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.3, "subnet4-get command"

   Command syntax:

 {
     "command": "subnet4-get",
     "arguments": {
         "id": 10
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "Info about IPv4 subnet 10.0.0.0/8 (id 10) returned",
     "arguments": {
         "subnets": [
             {
                 "subnet": "10.0.0.0/8",
                 "id": 1,
                 "option-data": [
                     ....
                 ]
                 ...
             }
         ]
     }
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.66. subnet4-list reference

   subnet4-list - This command is used to list all currently configured
   subnets. The subnets are returned in a brief form, i.e. a subnet
   identifier and subnet prefix is included for each subnet.

   Supported by: kea-dhcp4

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.1, "subnet4-list command"

   Command syntax:

 {
     "command": "subnet4-list"
 }

   Response syntax:

 {
     "result": 0,
     "text": "2 IPv4 subnets found",
     "arguments": {
     "subnets": [
         {
             "id": 10,
             "subnet": "10.0.0.0/8"
         },
         {
             "id": 100,
             "subnet": "192.0.2.0/24"
         }
     ]
 }

   If no IPv4 subnets are found, an error code is returned along with the
   error description.

A.67. subnet6-add reference

   subnet6-add - This command is used to create and add new subnet to the
   existing server configuration. This operation has no impact on other
   subnets.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.6, "subnet6-add"

   Command syntax:

 {
     "command": "subnet6-add",
     "arguments": {
         "subnet6": [ {
             "id": 234,
             "subnet": "2001:db8:1::/64",
             ...
         } ]
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "IPv6 subnet added",
     "arguments": {
         "subnet6": [
             {
                 "id": 234,
                 "subnet": "2001:db8:1::/64"
             }
         ]
     }
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.68. subnet6-del reference

   subnet6-del - This command is used to remove a subnet from the server's
   configuration. This command has no effect on other configured subnets but
   removing a subnet has certain implications which the server's
   administrator should be aware of.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.8, "subnet6-del command"

   Command syntax:

 {
     "command": "subnet6-del",
     "arguments": {
         "id": 234
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "IPv6 subnet 2001:db8:1::/64 (id 234) deleted",
     "subnets": [
         {
             "id": 234,
             "subnet": "2001:db8:1::/64"
         }
     ]
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.69. subnet6-get reference

   subnet6-get - This command is used to retrieve detailed information about
   the specified subnet. This command usually follows the subnet6-list, which
   is used to discover available subnets with their respective subnet
   identifiers and prefixes.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.4, "subnet6-get command"

   Command syntax:

 {
     "command": "subnet6-get",
     "arguments": {
         "id": 11
     }
 }

   Response syntax:

 {
     "result": 0,
     "text": "Info about IPv6 subnet 2001:db8:1::/64 (id 11) returned",
     "arguments": {
         "subnets": [
             {
                 "subnet": "2001:db8:1::/64",
                 "id": 1,
                 "option-data": [
                     ...
                 ]
                 ....
             }
         ]
     }
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

A.70. subnet6-list reference

   subnet6-list - This command is used to list all currently configured
   subnets. The subnets are returned in a brief form, i.e. a subnet
   identifier and subnet prefix is included for each subnet.

   Supported by: kea-dhcp6

   Availability: 1.3.0 (subnet_cmds hook)

   Description and examples: See Section 15.4.6.2, "subnet6-list command"

   Command syntax:

 {
     "command": "subnet6-list"
 }

   Response syntax:

 {
     "result": 0,
     "text": "2 IPv6 subnets found",
     "arguments": {
     "subnets": [
         {
             "id": 11,
             "subnet": "2001:db8:1::/64"
         },
         {
             "id": 233,
             "subnet": "3000::/16"
         }
     ]
 }

   If no IPv6 subnets are found, an error code is returned along with the
   error description.

A.71. version-get reference

   version-get - The version-get command returns extended information about
   Kea version. The returned string is the same as if Kea would be run with
   -V command line option.

   Supported by: kea-dhcp4, kea-dhcp6, kea-ctrl-agent

   Availability: 1.2.0 (built-in)

   Description and examples: See Section 17.3.13, "version-get"

   Command syntax:

 {
     "command": "version-get"
 }

   Response syntax:

 {
     "result": <integer>,
     "text": <string>
 }

   Result is an integer representation of the status. Currently supported
   statuses are:

     * 0 - success

     * 1 - error

     * 2 - unsupported

     * 3 - empty (command was completed successfully, but no data was
       affected or returned)

                          Appendix B. Acknowledgments

   Kea is an open source project designed, developed, and maintained by
   Internet Systems Consortium, Inc, a 501(c)3 non-profit organization. ISC
   is primarily funded by revenues from support subscriptions for our open
   source and we encourage all professional users to consider this option. To
   learn more, see *https://www.isc.org/support/.

   If you would like to contribute to ISC to assist us in continuing to make
   quality open source software, please visit our donations page at
   *http://www.isc.org/donate/.

   We thank all the organizations and individuals who have helped to make Kea
   possible. Comcast and the Comcast Innovation Fund provided major support
   for the development of Kea's DHCPv4, DHCPv6 and DDNS modules. Mozilla
   funded initial work on the REST API via a MOSS award.

   Kea was initially implemented as a collection of applications within the
   BIND 10 framework. We thank the founding sponsors of the BIND10 project:
   Afilias, IIS.SE, Nominet, SIDN, JPRS, CIRA; and additional sponsors AFNIC,
   CNNIC, CZ.NIC, DENIC eG, Google, RIPE NCC, Registro.br, .nz Registry
   Services, and Technical Center of Internet .
