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.

##Duplicate 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