# systemd-networkd

Related articles

- systemd
- systemd-nspawn
- Bridge with netctl
- Network configuration
- Wireless network configuration
- Category:Network managers

As of version 210, systemd now includes support for 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 connection.

## 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.

Depending on your networking set-up, you will need to modify the `systemd-nspawn@.service` and append to the `ExecStart` line some boot options. Please refer to `systemd-nspawn(1)` 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

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)
- `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.

#### [Network] section

Most common keys are:

- `DHCP=` is a Boolean. When set to `true` it enables a basic DHCPv4 support.
- `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.g `192.168.1.90/24`). This option is mandatory

#### [Route] section

Most common key in the `[Route]` section is:

- `Gateway=` is the address of your machine gateway. This option is mandatory

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. 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.

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

## Usage

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 `systemd-nspawn@.service` and use the `# systemd-nspawn -bD /path_to/your_container/` command with some more options to boot the container. To log off and shutdown, run inside the container `# systemctl poweroff`. Once your network setting met your requirements, enable and start `systemd-nspawn@.service`
- disable `dhcpcd.service` if enabled on your system. This service apply dhcpcd on all interfaces
- make sure you have no netctl profiles activated on your container, nor the `systemd-networkd.service` enabled and started
- make sure you don't have any iptables rules which can block traffic
- make sure packet forwarding is enabled if you plan to set up a private network on your container
- after any configuration files, reload the networkd daemon when running `# systemctl restart systemd-networkd`

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 adresses are only examples

### 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=yes

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=yes

#### 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 `MACAdressPolicy=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

Et voila!

## See also

- systemd.networkd man page
- Tom Gundersen, main systemd-networkd developer, G+ home page
- Tom Gundersen posts on Core OS blog

Categories:

- Network managers
- Virtualization