Difference between revisions of "Systemd-networkd"
m (→[Route]: typo fix)
(→Wired adapter using a static IP: Added DNS keys to example)
|Line 61:||Line 61:|
Revision as of 08:00, 17 November 2017
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.
- 1 Basic usage
- 2 Configuration files
- 3 Usage with containers
- 4 Management and desktop integration
- 5 Troubleshooting
- 6 See also
The wpa_supplicant, which are covered later in this article.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
Required services and setup
To use systemd-networkd, start/enable both
For compatibility with resolv.conf, delete or rename the existing file and create the following symbolic link when using systemd-resolved:
# ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf
See Systemd README., , and
All configurations in this section are stored as
/etc/systemd/network. For a full listing of options and processing order, see #Configuration files and .
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
- In the examples below,
enp1s0is the wired adapter and
wlp2s0is the wireless adapter. These names can be different on different systems. It is also possible to use a wildcard, e.g.
- If you want to disable IPv6, see IPv6#systemd-networkd.
DHCP=yesto accept an IPv4 and IPv6 DHCP request to the
Wired adapter using DHCP
[Match] Name=enp1s0 [Network] DHCP=ipv4
Wired adapter using a static IP
[Match] Name=enp1s0 [Network] Address=10.1.10.9/24 Gateway=10.1.10.1 DNS=10.1.10.1 #DNS=126.96.36.199
Address= can be used more than once to configure multiple IPv4 or IPv6 addresses. See #network files or for more options.
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
email@example.com. This service will run wpa_supplicant with the configuration file
/etc/wpa_supplicant/wpa_supplicant-wlp2s0.conf. If this file does not exist, the service will not start.
[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 to 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).
[Match] Name=enp1s0 [Network] DHCP=ipv4 [DHCP] RouteMetric=10
[Match] Name=wlp2s0 [Network] DHCP=ipv4 [DHCP] RouteMetric=20
Renaming an interface
Instead of editing udev rules, a .link file can be used to rename an interface. A useful example is to set a predictable interface name for a USB-to-Ethernet adapter based on its MAC address, as those adapters are usually given different names depending on which USB port they are plugged into.
[Match] MACAddress=12:34:56:78:90:ab [Link] Description=USB to Ethernet Adapter Name=ethusb0
99-default.linkin order to be considered at all. For example, name the file
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. They all use a format similar to systemd unit 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
- 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
- to override a system-supplied file in
/usr/lib/systemd/networkin a permanent manner (i.e even after upgrade), place a file with same name in
/etc/systemd/networkand symlink it to
*joker can be used in
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.
These files are aimed at setting network configuration variables, especially for servers and containers.
.network files have the following sections:
[DHCP]. Below are commonly configured keys for each section. See for more information and examples.
Name=the device name
Host=the machine hostname
Virtualization=check whether the system is executed in a virtualized environment or not. A
Virtualization=nokey will only apply on your host machine, while
Virtualization=yesapply to any container or VM.
MACAddress=useful for MAC address spoofing
MTUBytes=setting a larger MTU value (jumbo frames) can significantly speed up your network transfers
DHCP=enables the DHCP client
DHCPServer=enables the DHCP server
DNS=DNS server address
Bridge=the bridge name
IPForward=enables IP packet forwarding
Domains=a list of domains to be resolved on this link
Address=this option is mandatory unless DHCP is used
Gateway=this option is mandatory unless DHCP is used
Destination=the destination prefix of the route, possibly followed by a slash and the prefix length
Destination is not present in
[Route] section this section is treated as a default route.
Gateway=keys in the
[Network]section as a short-hand if
[Address]section contains only an Address key and
[Route]section contains only a Gateway key.
UseDomains=truecan sometimes fix local name resolving when using systemd-resolved
These files will create virtual network devices. They have two sections:
[NetDev]. Below are commonly configured keys for each section. See for more information and examples.
Virtualization=check if running in a VM
Most common keys are:
Name=the interface name. mandatory
Kind=e.g. bridge, bond, vlan, veth, sit, etc. mandatory
These files are an alternative to custom udev rules and will be applied by udev as the device appears. They have two sections:
[Link]. Below are commonly configured keys for each section. See for more information and examples.
udevadm test-builtin net_setup_link /sys/path/to/network/deviceto diagnose problems with
MACAddress=the MAC address
Host=the host name
Type=the device type e.g. vlan
MACAddressPolicy=persistent or random addresses, or
MACAddress=a specific address
/usr/lib/systemd/network/99-default.linkis generally sufficient for most of the basic cases.
Usage with containers
For debugging purposes, it is strongly advised to install the , , and 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 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
/etc/resolv.conf. See for more details.
- disable all your netctl (host and container), dhcpcd (host and container), systemd-networkd (container only) and
systemd-nspawn@.service(host only) services to avoid potential conflicts and to ease debugging
- make sure packet forwarding is enabled if you want to let containers access the internet. Make sure that your
.networkfile does not accidentally turn off forwarding because if you do not have a
IPForward=1setting in it,
systemd-networkdwill turn off forwarding on this interface, even if you have it enabled globally.
- make sure you do not have any iptables rules which can block traffic
- when the daemon is started the systemd
networkctlcommand displays the status of network interfaces.
- we will limit the output of the
ip acommand 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.
[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
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
# ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
Seefor more details.
/usr/bin/arch-chrootfrom , will need to create the symlink outside of the chroot, on the mounted partition. This is due to arch-chroot linking the file to the live environment.
DHCP with two distinct IP
Create a virtual bridge interface
[NetDev] Name=br0 Kind=bridge
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
/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.
[Match] Name=en* [Network] Bridge=br0
Create a network profile for the Bridge
[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
- 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
- we have now one IP address for
br0on the host, and one for
host0in the container
- two new interfaces have appeared:
vb-MyContainerin the host and
host0in the container. This comes as a result of the
--network-bridge=br0option. This option implies another option,
--network-veth. This means a virtual Ethernet link has been created between host and container.
- the DHCP address on
host0comes from the system
- 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
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
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
# 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
A modified MyBridge.network
[Match] Name=br0 [Network] DNS=192.168.1.254 Address=192.168.1.87/24 Gateway=192.168.1.254
- on container
[Match] Name=host0 [Network] DNS=192.168.1.254 Address=192.168.1.94/24 Gateway=192.168.1.254
Management and desktop integration
systemd-networkd doesn't have a proper interactive management interface via either command-line or GUI. networkctl (via CLI) just offers a simple dump of the network interface states.
When networkd is configured with wpa_supplicant, both wpa_cli and wpa_gui offer the ability to associate and reconfigure WLAN interfaces dynamically.
networkd-notify can generate simple notifications in response to network interface state changes (such as connection/disconnection and re-association).
TheAUR daemon allows executing scripts in response to network interface state changes, similar to NetworkManager-dispatcher.
resolve not searching the local domain
resolve may not search the local domain when given just the hostname, even when
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:
hostsdatabase (e.g., by removing
- Switch to using fully-qualified domain names
/etc/hoststo resolve hostnames
- Fall back to using glibc's
dnsinstead of using systemd's
- systemd.networkd man page
- Tom Gundersen, main systemd-networkd developer, G+ home page
- Tom Gundersen posts on Core OS blog
- How to set up systemd-networkd with wpa_supplicant (WonderWoofy's walkthrough on Arch forums)