systemd-networkd
Related articles
As of version 210, systemd supports basic network configuration through udev and networkd.
systemd-networkd is a system daemon that manages network configuration. It detects and configures network devices as they appear, as well as creates virtual network devices. This service can run alongside your usual network management tool like netctl or even replace it for some configurations when it comes to virtualization. This service can especially be very useful to setup basic or more complex network settings (static IP, bridge,vlan...) for a container managed by systemd-nspawn.
It is not intended to configure low-level settings of network interfaces as this remains udev's job.
networkd is intended for simple setups such as VMs or containers, but also works fine on Ethernet connections. It has no support for WiFi but can be used with wpa_supplicant to manage wireless connections.
Installation
The service is available with systemd >= 210. You will want to enable and start the systemd-networkd.service
on the host and container.
For debugging purposes, it is strongly advised to install the bridge-utils, net-tools and iproute2 packages.
If you are using systemd-nspawn, you may need to modify the systemd-nspawn@.service
and append boot options to the ExecStart
line. Please refer to man 1 systemd-nspawn
for an exhaustive list of options.
Note that if you want to take advantage of automatic DNS configuration from DHCP, you need to enable systemd-resolved
and symlink /run/systemd/resolve/resolv.conf
to /etc/resolv.conf
. See systemd-resolved.service(8)
for more details.
Configuration files
Configuration files will be read from /usr/lib/systemd/network
, the volatile runtime network directory /run/systemd/network
and the local administration network directory /etc/systemd/network
. Files in /etc/systemd/network
have the highest priority.
There are three types of configuration files.
- .network files. They will apply a network configuration for a matching device
- .netdev files. They will create a virtual network device for a matching environment
- .link files. When a network device appears, udev will look for the first matching .link file
They all follow the same rules:
- If all conditions in the
[Match]
section are matched, the profile will be activated - an empty
[Match]
section means the profile will apply in any case (can be compared to the*
joker) - each entry is a key with the
NAME=VALUE
syntax - all configuration files are collectively sorted and processed in lexical order, regardless of the directory in which they live
- files with identical name replace each other
network files
These files are aimed at setting network configuration variables, especially for servers and containers.
Below is a basic structure of a MyProfile.network file:
/etc/systemd/network/MyProfile.network
[Match] a vertical list of keys [Network] a vertical list of keys [Address] a vertical list of keys [Route] a vertical list of keys
[Match] section
Most common keys are:
-
Name=
the device name (e.g Br0, enp4s0) -
Host=
the machine hostname -
Virtualization=
check whether the system is executed in a virtualized environment or not. AVirtualization=no
key will only apply on your host machine, whileVirtualization=yes
apply to any container or VM.
[Network] section
Most common keys are:
-
DHCP=
enables DHCPv4 and/or DHCPv6 support. Acceptsboth
,none
,v4
orv6
-
DNS=
is a DNS server address. You can specify this option more than once -
Bridge=
is the name of the bridge to add the link to
[Address] section
Most common key in the [Address]
section is:
-
Address=
is a static IPv4 or IPv6 address and its prefix length, separated by a/
character (e.g192.168.1.90/24
). This option is mandatory unless DHCP is used.
[Route] section
Most common key in the [Route]
section is:
-
Gateway=
is the address of your machine gateway. This option is mandatory unless DHCP is used.
For an exhaustive key list, please refer to systemd.network(5)
netdev files
These files will create virtual network devices.
Below is a basic structure of a Mydevice.netdev file:
/etc/systemd/network/MyDevice.netdev
[Match] a vertical list of keys [Netdev] a vertical list of keys
[Match] section
Most common keys are Host=
and Virtualization=
[Netdev] section
Most common keys are:
-
Name=
is the interface name used when creating the netdev. This option is compulsory -
Kind=
is the netdev kind. Currently, bridge, bond, vlan and macvlan are supported. This option is compulsory
For an exhaustive key list, please refer to systemd.netdev(5)
link files
These files are an alternative to custom udev rules and will be applied by udev as the device appears.
Below is a basic structure of a Mydevice.link file:
/etc/systemd/network/MyDevice.link
[Match] a vertical list of keys [Link] a vertical list of keys
The [Match]
section will determine if a given link file may be applied to a given device, when the [Link]
section specifies the device configuration.
[Match] section
Most common keys are MACADRESS=
, Host=
and Virtualization=
.
Type=
is the device type (e.g. vlan)
[Link] section
Most common keys are:
MACAddressPolicy=
is either persistent when the hardware has a persistent MAC address (as most hardware should) or random , which allows to give a random MAC address when the device appears.
MACAddress=
shall be used when no MACAddressPoicy=
is specified.
Usage
Basic DHCP network
This set up will enable a DHCP IP for host and container. In this case, both systems will share the same IP as they share the same interfaces.
/etc/systemd/network/MyDhcp.network
[Match] Name=en* [Network] DHCP=v4
Then, enable and start systemd-networkd.service
on your container.
You can of course replace en*
by the full name of your ethernet device given by the output of the ip link
command.
- on host and container:
$ ip a
2: enp7s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether 14:da:e9:b5:7a:88 brd ff:ff:ff:ff:ff:ff inet 192.168.1.72/24 brd 192.168.1.255 scope global enp7s0 valid_lft forever preferred_lft forever inet6 fe80::16da:e9ff:feb5:7a88/64 scope link valid_lft forever preferred_lft forever
By default hostname received from the DHCP server will be used as the transient hostname.
To change it add UseHostname=false
in section [DHCPv4]
/etc/systemd/network/MyDhcp.network
[DHCPv4] UseHostname=false
If you did not want configure a DNS in /etc/resolv.conf
and want to rely on DHCP for setting it up, you need to enable systemd-resolved
and symlink /run/systemd/resolve/resolv.conf
to /etc/resolv.conf
. See systemd-resolved.service(8)
for more details.
$ systemctl enable systemd-resolved $ ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
DHCP with two distinct IP
Bridge interface
Create a virtual bridge interface
/etc/systemd/network/MyBridge.netdev
[NetDev] Name=br0 Kind=bridge
- on host and container:
$ ip a
3: br0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default link/ether ae:bd:35:ea:0c:c9 brd ff:ff:ff:ff:ff:ff
Note that the interface br0 is listed but is DOWN.
Bind ethernet to bridge
Modify the /etc/systemd/network/MyDhcp.network
to remove the DHCP, as the bridge requires an interface to bind to with no IP, and add a key to bind this device to br0. Let's change its name to a more relevant one.
/etc/systemd/network/MyEth.network
[Match] Name=en* [Network] Bridge=br0
Bridge network
Create a network profile for the Bridge
/etc/systemd/network/MyBridge.network
[Match] Name=br0 [Network] DHCP=v4
Add option to boot the container
As we want to give a separate IP for host and container, we need to Disconnect networking of the container from the host. To do this, add this option --network-bridge=br0
to your container boot command.
# systemd-nspawn --network-bridge=br0 -bD /path_to/my_container
Result
- on host
$ ip a
3: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default link/ether 14:da:e9:b5:7a:88 brd ff:ff:ff:ff:ff:ff inet 192.168.1.87/24 brd 192.168.1.255 scope global br0 valid_lft forever preferred_lft forever inet6 fe80::16da:e9ff:feb5:7a88/64 scope link valid_lft forever preferred_lft forever 6: vb-MyContainer: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP group default qlen 1000 link/ether d2:7c:97:97:37:25 brd ff:ff:ff:ff:ff:ff inet6 fe80::d07c:97ff:fe97:3725/64 scope link valid_lft forever preferred_lft forever
- on container
$ ip a
2: host0: <BROADCAST,MULTICAST,ALLMULTI,AUTOMEDIA,NOTRAILERS,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether 5e:96:85:83:a8:5d brd ff:ff:ff:ff:ff:ff inet 192.168.1.73/24 brd 192.168.1.255 scope global host0 valid_lft forever preferred_lft forever inet6 fe80::5c96:85ff:fe83:a85d/64 scope link valid_lft forever preferred_lft forever
Notice
- we have now one IP address for Br0 on the host, and one for host0 in the container
- two new interfaces have appeared:
vb-MyContainer
in the host andhost0
in the container. This comes as a result of the--network-bridge=br0
option. This option implies another option,--network-veth
. This means a virtual Ethernet link has been created between host and container. - the DHCP address on
host0
comes from the system/usr/lib/systemd/network/80-container-host0.network
file. - on host
$ brctl show
bridge name bridge id STP enabled interfaces br0 8000.14dae9b57a88 no enp7s0 vb-MyContainer
the above command output confirms we have a bridge with two interfaces binded to.
- on host
$ ip route
default via 192.168.1.254 dev br0 192.168.1.0/24 dev br0 proto kernel scope link src 192.168.1.87
- on container
$ ip route
default via 192.168.1.254 dev host0 192.168.1.0/24 dev host0 proto kernel scope link src 192.168.1.73
the above command outputs confirm we have activated br0
and host0
interfaces with an IP address and Gateway 192.168.1.254. The gateway address has been automatically grabbed by systemd-networkd
$ cat /run/systemd/resolve/resolv.conf
nameserver 192.168.1.254
Static IP network
Setting a static IP for each device can be helpful in case of deployed web services (e.g FTP, http, SSH). Each device will keep the same MAC address across reboots if your system /usr/lib/systemd/network/99-default.link
file has the MACAddressPolicy=persistent
option (it has by default). Thus, you will easily route any service on your Gateway to the desired device.
First, we shall get rid of the system /usr/lib/systemd/network/80-container-host0.network
file. To do it in a permanent way (e.g even after upgrades), do the following on both host and container. This will mask the file /usr/lib/systemd/network/80-container-host0.network
since files of the same name in /etc/systemd/network
take priority over /usr/lib/systemd/network
.
# ln -sf /dev/null /etc/systemd/network/80-container-host0.network
Then, enable and start systemd-networkd
on your container.
The needed configuration files:
- on host
/etc/systemd/network/MyBridge.netdev /etc/systemd/network/MyEth.network
A modified MyBridge.network
/etc/systemd/network/MyBridge.network
[Match] Name=br0 [Network] DNS=192.168.1.254 Address=192.168.1.87/24 Gateway=192.168.1.254
- on container
/etc/systemd/network/MyVeth.network
[Match] Name=host0 [Network] DNS=192.168.1.254 Address=192.168.1.94/24 Gateway=192.168.1.254