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dhcpd is the older Internet Systems Consortium (ISC) DHCP server. Be aware that dhcpd is no longer maintained as of January 2023; ISC promotes Kea as its official replacement.

Note: dhcpd (DHCP server daemon) is not the same as dhcpcd (DHCP client daemon).

## Installation

Install the dhcp package.

## Usage

dhcpd includes two unit files, `dhcpd4.service` and `dhcpd6.service`, which can be used to control the daemon. They start the daemon on all network interfaces for IPv4 and IPv6 respectively. See #Listening on only one interface for an alternative.

## Configuration

Assign a static IPv4 address to the interface you want dhcpd to listen on (here `eth0`). The specified subnet should not overlap with that of other interfaces.

    # ip link set up dev eth0
    # ip addr add 139.96.30.100/24 dev eth0 # arbitrary address

Tip: To have a static IP address assigned at boot, see Network configuration#Static IP address.
Tip: The following subnets are usually reserved for private networks and will not conflict with hosts on the internet:

- `192.168/16` (subnet `192.168.0.0`, netmask `255.255.0.0`)
- `172.16/12` (subnet `172.16.0.0`, netmask `255.240.0.0`)
- `10/8` (for large networks; subnet `10.0.0.0`, netmask `255.0.0.0`)

See also RFC 1918.

The default configuration file `dhcpd.conf` contains many uncommented examples, so relocate it:

    # cp /etc/dhcpd.conf /etc/dhcpd.conf.example

To only listen on the subnet `139.96.30.0/24`, you may create the following minimal configuration file:

    /etc/dhcpd.conf

    option domain-name-servers 8.8.8.8, 8.8.4.4;
    option subnet-mask 255.255.255.0;
    option routers 139.96.30.100;
    subnet 139.96.30.0 netmask 255.255.255.0 {
      range 139.96.30.150 139.96.30.250;
    }

The options used in this configuration file are:

`domain-name-servers` which contains addresses of DNS servers supplied to the clients. Here we use Google's public DNS servers. If you have configured your own DNS server on a local machine, specify its address in your subnet (here `139.96.30.0/24`).

`subnet-mask` and `routers` which define a subnet mask and a list of available routers on the subnet; `routers` also defines the default gateway served to the client. For small networks, you can usually use `255.255.255.0` as a mask and specify an IP address of the machine on which you are running dhcpd (here `139.96.30.100`).

`subnet` which defines options for separate subnets that are applied to the network interfaces on which dhcpd is listening. Here we have defined the range of available IP addresses for a single subnet `139.96.30.0/24` (on a single interface `eth0`).

For a complete list of options, consult dhcpd.conf(5).

### Listening on only one interface

This article or section is out of date.

Reason: While the man page dhcpd(8) suggests the behavior described below, in practice `dhcpd` only listens on interfaces with subnets declared in its configuration file. (Discuss in Talk:Dhcpd)

If your computer is already part of one or several networks, it could be a problem if your computer starts giving ip addresses to machines from the other networks. It can be done by either configuring dhcpd or starting it as a daemon with systemctl.

#### Configuring dhcpd

The factual accuracy of this article or section is disputed.

Reason: `dhcpd` does not listen on interfaces whose subnets are not declared in its configuration file. (Discuss in Talk:Dhcpd)

In order to exclude an interface, you must create an empty declaration for the subnet that will be configured on that interface.

This is done by editing the configuration file (for example):

    /etc/dhcpd.conf

    # No DHCP service in DMZ network (192.168.2.0/24)
    subnet 192.168.2.0 netmask 255.255.255.0 {
    }

#### Service file

The factual accuracy of this article or section is disputed.

Reason: Does not work with systemd 251. (Discuss in Talk:Dhcpd)

The default service file provided by dhcpd does not specify an interface. Use a drop-in unit file for the `dhcpd4.service` as follows:

    /etc/systemd/system/dhcpd4.service.d/override.conf

    [Service]
    ExecStart=
    ExecStart=/usr/bin/dhcpd -4 -q -cf /etc/dhcpd.conf -pf /run/dhcpd4/dhcpd.pid %I

This allows using `dhcpd4.service` as a template unit, binding dhcpd to a particular interface; for example `dhcpd4@eth0.service`, where eth0 is the first enumerated Ethernet device.

### Use for PXE

PXE Configuration is done with the following two options:

    /etc/dhcpd.conf

    next-server 192.168.0.2;
    filename "/pxelinux.0";

This section can either be in an entire `subnet` or just in a `host` definition. `next-server` is the IP of the TFTP Server, and `filename` is the filename of the image to boot. For more information see PXE.

## See also

- ISC DHCP Documentation

Category:

- DHCP

Hidden categories:

- Pages or sections flagged with Template:Out of date
- Pages or sections flagged with Template:Accuracy