systemd-networkd

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systemd-networkd is a system daemon that manages network configurations. It detects and configures network devices as they appear; it can also create virtual network devices. This service can be especially useful to set up complex network configurations for a container managed by systemd-nspawn or for virtual machines. It also works fine on simple connections.

Basic usage

The systemd package is part of the default Arch installation and contains all needed files to operate a wired network. Wireless adapters can be setup by other services, such as wpa_supplicant, which are covered later in this article.

Required services and setup

To use systemd-networkd, start the following two services and enable them to run on system boot:

  • systemd-networkd.service
  • systemd-resolved.service
Note: systemd-resolved is actually required only if you are specifying DNS entries in .network files or if you want to obtain DNS addresses from networkd's DHCP client.

For compatibility with resolv.conf, delete or rename the existing file and create the following symbolic link:

# ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf

Optionally, if you wish to use the local DNS stub resolver of systemd-resolved (and thus use LLMNR and DNS merging per interface), replace dns with resolve in /etc/nsswitch.conf:

hosts: files resolve myhostname

See man systemd-resolved and man resolved.conf and Systemd README.

Note: Systemd's resolve may not search the local domain when given just the hostname, even when UseDomains=yes or Domains=[domain-list] is present in the appropriate .network file, and that file produces the expected search [domain-list] in resolv.conf. If you run into this problem:
  • Switch to using fully-qualified domain names
  • Use /etc/hosts to resolve hostnames
  • Fall back to using glibc's dns instead of using systemd's resolve

Configuration examples

All configurations in this section are stored as foo.network in /etc/systemd/network. For a full listing of options and processing order, see #Configuration files and the systemd.network man page.

Systemd/udev automatically assigns predictable, stable network interface names for all local Ethernet, WLAN, and WWAN interfaces. Use networkctl list to list the devices on the system.

After making changes to a configuration file, restart systemd-networkd.service.

Note: In the examples below, enp1s0 is the wired adapter and wlp2s0 is the wireless adapter. These names can be different on different systems.

Wired adapter using DHCP

/etc/systemd/network/wired.network
[Match]
Name=enp1s0

[Network]
DHCP=ipv4

Wired adapter using a static IP

/etc/systemd/network/wired.network
[Match]
Name=enp1s0

[Network]
Address=10.1.10.9/24
Gateway=10.1.10.1

See the systemd.network(5) man page for more network options such as specifying DNS servers and a broadcast address.

Wireless adapter

In order to connect to a wireless network with systemd-networkd, a wireless adapter configured with another service such as wpa_supplicant is required. In this example, the corresponding systemd service file that needs to be enabled is wpa_supplicant@wlp2s0.service.

/etc/systemd/network/wireless.network
[Match]
Name=wlp2s0

[Network]
DHCP=ipv4

If the wireless adapter has a static IP address, the configuration is the same (except for the interface name) as in a wired adapter.

Wired and wireless adapters on the same machine

This setup will enable a DHCP IP for both a wired and wireless connection making use of the metric directive to allow the kernel the decide on-the-fly which one to use. This way, no connection downtime is observed when the wired connection is unplugged.

The kernel's route metric (same as configured with ip) decides which route to use for outgoing packets, in cases when several match. This will be the case when both wireless and wired devices on the system have active connections. To break the tie, the kernel uses the metric. If one of the connections is terminated, the other automatically wins without there being a gap with nothing configured (ongoing transfers may still not deal with this nicely but that is at a different OSI layer).

Note: The Metric option is for static routes while the RouteMetric option is for setups not using static routes.
/etc/systemd/network/wired.network
[Match]
Name=enp1s0

[Network]
DHCP=ipv4

[DHCP]
RouteMetric=10
/etc/systemd/network/wireless.network
[Match]
Name=wlp2s0

[Network]
DHCP=ipv4

[DHCP]
RouteMetric=20

IPv6 privacy extensions

If you are using IPv6 you might also want to set the IPv6PrivacyExtensions option as settings placed in /etc/sysctl.d/40-ipv6.conf are not honored.

/etc/systemd/network/wireless.network
[Match]
Name=wlp2s0

[Network]
DHCP=yes
IPv6PrivacyExtensions=true

[DHCP]
RouteMetric=20

Configuration files

Configuration files are located in /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
Tip:
  • to override a system-supplied file in /usr/lib/systemd/network in a permanent manner (i.e even after upgrade), place a file with same name in /etc/systemd/network and symlink it to /dev/null
  • the * joker can be used in VALUE (e.g en* will match any Ethernet device)
  • following this Arch-general thread, the best practice is to setup specific container network settings inside the container with networkd configuration files.

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, en*)
  • Host= the machine hostname
  • Virtualization= check whether the system is executed in a virtualized environment or not. A Virtualization=no key will only apply on your host machine, while Virtualization=yes apply to any container or VM.

[Link] section

Most common keys are:

  • MACAddress= useful for MAC address spoofing
  • MTUBytes= the maximum transmission unit in bytes (suffixes K, M, G, are supported and are understood to the base of 1024). Using a larger MTU value (Jumbo frames) can significantly speed up your network transfers.

[Network] section

Most common keys are:

  • DHCP= enables DHCPv4 and/or DHCPv6 support. Accepts yes, no, ipv4 or ipv6
  • 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
  • IPForward= defaults to no. It enables IP forwarding, performing the forwarding according to the routing table and is required for setting up Internet sharing. Note that turning IPForward= on applies to all network interfaces.
  • Domains= a list of the domains used for DNS host name resolution.

Please see systemd.network(5) for details.

[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.g 192.168.1.90/24). 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)

Tip: you can put the Address= and Gateway= keys in the [Network] section as a short-hand if Address= contains only an Address key and Gateway= section contains only a Gateway key

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. For example, bridge, bond, vlan, veth, sit, etc. 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 MACAddress=, 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 MACAddressPolicy= is specified.

Note: the system /usr/lib/systemd/network/99-default.link is generally sufficient for most of the basic cases.

Usage with containers

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.

Tango-edit-clear.pngThis article or section needs language, wiki syntax or style improvements.Tango-edit-clear.png

Reason: Too many points for a tip, some of them are very similar so they could be merged. (Discuss in Talk:Systemd-networkd#)
Tip: Before you start to configure your container network, it is useful to:
  • disable all your netctl services. This will avoid any potential conflicts with systemd-networkd and make all your configurations easier to test. Furthermore, odds are high you will end with few or even no netctl activated profiles. The netctl list command will output a list of all your profiles, with the activated one being starred.
  • disable the systemd-nspawn@.service and use the systemd-nspawn -bnD /path_to/your_container/ command as root to boot the container. To log off and shutdown inside the container systemctl poweroff is used as root. Once the network setting meets your requirements, enable and start systemd-nspawn@.service
  • disable the dhcpcd.service if enabled on your system, since it activates dhcpcd on all interfaces
  • make sure you have no netctl profiles activated in the container, and ensure that systemd-networkd.service is neither enabled nor started
  • make sure you do not have any iptables rules which can block traffic
  • make sure packet forwarding is enabled if you want to let containers access the internet. Make sure that your .network file does not accidentally turn off forwarding because if you do not have a IPForward=1 setting in it, systemd-networkd will turn off forwarding on this interface, even if you have it enabled globally.
  • when the daemon is started the systemd networkctl command displays the status of network interfaces.
Note: For the set-up described below,
  • we will limit the output of the ip a command to the concerned interfaces
  • we assume the host is your main OS you are booting to and the container is your guest virtual machine
  • all interface names and IP addresses are only examples

Basic DHCP network

This setup 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=ipv4

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 to configure a DNS in /etc/resolv.conf and want to rely on DHCP for setting it up, you need to enable systemd-resolved.service and symlink /run/systemd/resolve/resolv.conf to /etc/resolv.conf

# ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf

See systemd-resolved.service(8) for more details.

DHCP with two distinct IP

Bridge interface

Create a virtual bridge interface

/etc/systemd/network/MyBridge.netdev
[NetDev]
Name=br0
Kind=bridge

Restart systemd-networkd.service to have systemd create the 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 us 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=ipv4

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 and host0 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 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

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: In the listing of configuration files, /etc/systemd/network/MyBridge.netdev has the .netdev extension. But, the MyBridge.network example file has the .network extension. (Discuss in Talk:Systemd-networkd#)
/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

See also