Network Configuration

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.

Configuration Examples

All configurations are stored as foo.network in the /etc/systemd/network/, /lib/systemd/network/ and /run/systemd/network/ folder. Use the networkctl list command to list all the devices on the system.

After making changes to a configuration file, restart the systemd-networkd.service if version is < 245, for other version run the following commands:

root@photon [ /home/sus ]# networkctl reload
root@photon [ /home/sus ]# networkctl reconfigure eth0

Note:

• The options mentioned in the configuration files are case sensitive.
• Set DHCP=yes to accept IPv4 and IPv6 DHCP requests.
• Set DHCP=ipv4 to accept IPv4 DHCP requests.
• Set LinkLocalAddressing=no to disable IPv6. Please do not disable IPv6 via sysctl. When LinkLocalAddressing=no in the .network file, the kernel drops addresses starting with fe80, for example fe80::20c:29ff:fe4c:7eca. If IPv6LL address is not available networkd will not start IPv6 configurations.

To link network configurations using DHCPv4 (IPv6 disabled), run the following command:

/etc/systemd/network/20-eth0.network
[Match]
Name=eth0

[Network]
LinkLocalAddressing=no

DHCP=ipv4

To link network configurations using DHCPv6, run the following command:

/etc/systemd/network/20-eth0.network
[Match]
Name=eth0

[Network]
IPv6AcceptRA=yes

DHCP=ipv6

To link network configurations using a static IP address, run the following command:

/etc/systemd/network/20-wired.network
[Match]
Name=enp1s0

[Network]
Address=10.1.10.9/24
Gateway=10.1.10.1
DNS=10.1.10.1

Here Address= can be used more than once to configure multiple IPv4 or IPv6 addresses.

A .link file can be used to rename an interface. For example, set a predictable interface name for a Ethernet adapter based on its MAC address by running the following command:

/etc/systemd/network/10-test0.link
[Match]
MACAddress=12:34:56:78:90:ab

[Link]
Description=my custom name
Name=test123

Configuration Files

Configuration files are located in /usr/lib/systemd/network/ folder, the volatile runtime network directory in /run/systemd/network/ folder and the local administration network directory in /etc/systemd/network/ folder. Configuration files in /etc/systemd/network/ folder have the highest priority.

There are three types of configuration files and they use a format similar to systemd unit files.

• .network : These files apply a network configuration to a matching device.
• .netdev : These files are used to create a virtual network device for a matching environment.

• .link : When a network device appears, udev looks for the first matching .link file. These link files follow the following rules:

• Only if all conditions in the [Match] section are matched, the profile will be activated.

• An empty [Match] section means the profile can apply to any case (can be compared to the * wild card)
• All configuration files are collectively sorted and processed in lexical order, regardless of the directory it resides in.
• Files with identical names replace each other.

Dupliate Matches

If we have multiple configuration files matching an interface, the first (in lexical order) network file matching a given device is applied. All other files are ignored even if they match. The following is an example of matching configuration files:

builder@localhost [ ~ ]$ cat /etc/systemd/network/10-eth0.network
[Match]
Name=eth0
[Network]
DHCP=yes

builder@localhost [ ~ ]$ cat /etc/systemd/network/99-dhcp-en.network
[Match]
Name=e*

[Network]
DHCP=yes
IPv6AcceptRA=no

Network Files

These files are used to set network configuration variables for servers and containers. .network files have the following sections:

[Match]

[Link]

• MACAddress= : Used to spoof MAC address.
• MTUBytes= : Setting a larger MTU value (For example: when using jumbo frames) can significantly speed up your network transfers.
• Multicast : Enables the use of multicast on interface(s).

[Network]

[Address]

Address= option is mandatory unless DHCP is used.

[Route]

• Gateway= option is mandatory unless DHCP is used.
• Destination= option defines the destination prefix of the route, possibly followed by a slash and the prefix length. If Destination is not present in [Route] section it is treated as a default route. Note: You can add the Address= and Gateway= keys in the [Network] section as a short-hand, if the [Address] section contains only an Address key and [Route] section contains only a Gateway key.

DHCP

[DHCPServer]

The following is an example of a DHCP server configuration which works well with hostapd to create a wireless hotspot. IPMasquerade adds the firewall rules for NAT and IPForward enables packet forwarding.

/etc/systemd/network/wlan0.network
[Match]
Name=wlan0

[Network]
Address=10.1.1.1/24
DHCPServer=true
IPMasquerade=true
IPForward=true

[DHCPServer]
PoolOffset=100
PoolSize=20
EmitDNS=yes
DNS=9.9.9.9

Netdev Files

These files create virtual network devices. They have the following two sections:

[Match]

• Host= : The host name.
• Virtualization= : Checks if it is running in a virtual environment.

[NetDev]

• Name= : The interface's name. This is a mandatory field.
• Kind= : For example: bridge, bond, vlan, veth, sit, etc. This is a mandatory field.

Link Files

These files are an alternative to custom udev rules and will be applied by udev as the device appears. They have the following two sections:

[Match]

• MACAddress= : The MAC address.
• Host= : The host name.
• Virtualization= : Checks if it is running in a virtual environment.
• Type= : the device type. For example: vlan.

[Link]

• MACAddressPolicy= : Persistent or random addresses.
• MACAddress= : The MAC address. Note: The system /usr/lib/systemd/network/99-default.link file is sufficient for most cases.

Debugging Systemd-networkd

The log can be generated by creating a drop-in config. For example:

# /etc/systemd/system/systemd-networkd.service.d/override.conf
[Service]
Environment=SYSTEMD_LOG_LEVEL=debug