/etc/systemd/network/*.network

The /etc/systemd/network/*.network files are used for configuring network interfaces with systemd-networkd, a system service in systemd that manages network configurations. These .network files define how network interfaces should behave, including network addresses, routes, and other networking-related settings.

Overview of /etc/systemd/network/*.network files

These configuration files are typically stored in the /etc/systemd/network/ directory, and each file typically corresponds to a network interface or a specific configuration group. The .network files allow administrators to configure various networking options for both Ethernet and Wi-Fi interfaces, such as IP addressing, routes, and DNS settings.

Basic Structure of a .network File

A .network file typically consists of multiple sections that define different aspects of the network interface.

Here is the basic structure of a .network file:

[Match]
Name=eth0

[Network]
DHCP=yes

[DHCP]
ClientIdentifier=mac

Common Sections in a .network File

1. [Match]

   • This section specifies the criteria to match the network interface. You can match by interface name, MAC address, or other attributes.

   • Common keys in this section:

     • Name: Specifies the name of the network interface (e.g., eth0, enp0s3).

     • MACAddress: Matches based on the MAC address.

     • Driver: Matches based on the network driver used.

   Example:

   [Match]
   Name=enp0s3

2. [Network]

   • This section defines the network configuration for the matched interface. You specify settings like IP addressing, routes, DNS, etc.

   • Common keys in this section:

     • DHCP: Enable or disable DHCP (set to yes or no).

     • Address: Assign static IP addresses.

     • Gateway: Define the default gateway.

     • DNS: Define DNS servers.

     • Routes: Add specific routes to be used.

   Example:

   [Network]
   DHCP=yes

   Or for static IP configuration:

   [Network]
   Address=192.168.1.100/24
   Gateway=192.168.1.1
   DNS=8.8.8.8

3. [DHCP]

   • This section provides specific DHCP client settings. It is only relevant when DHCP=yes in the [Network] section.

   • Common keys in this section:

     • ClientIdentifier: The identifier used by the DHCP client (usually MAC address or a custom identifier).

     • Hostname: The hostname assigned by DHCP.

     • UseDNS: Whether to use DNS information provided by DHCP.

   Example:

   [DHCP]
   ClientIdentifier=mac

4. [Link]

   • This section provides settings that control the interface link properties.

   • Common keys in this section:

     • MTUBytes: Set the Maximum Transmission Unit (MTU).

     • WakeOnLan: Enable or disable Wake-on-LAN.

   Example:

   [Link]
   MTUBytes=1500

5. [VLAN]

   • Used to configure VLAN interfaces.

   • Common keys in this section:

     • VLANId: The VLAN ID for this interface.

   Example:

   [VLAN]
   VLANId=10

Example .network File Configurations

Example 1: Using DHCP for Network Configuration

[Match]
Name=enp0s3

[Network]
DHCP=yes

• This configuration automatically assigns an IP address to the enp0s3 interface using DHCP.

Example 2: Static IP Configuration

[Match]
Name=enp0s3

[Network]
Address=192.168.1.100/24
Gateway=192.168.1.1
DNS=8.8.8.8

• This configuration assigns a static IP address 192.168.1.100/24 to enp0s3, with a gateway at 192.168.1.1 and a DNS server at 8.8.8.8.

Example 3: Using Static IP with Multiple Addresses

[Match]
Name=enp0s3

[Network]
Address=192.168.1.100/24
Address=192.168.2.100/24
Gateway=192.168.1.1
DNS=8.8.8.8

• This configuration assigns two IP addresses to the interface enp0s3, 192.168.1.100/24 and 192.168.2.100/24, and uses the same gateway and DNS.

Example 4: VLAN Configuration

[Match]
Name=enp0s3

[VLAN]
VLANId=10

[Network]
Address=192.168.1.100/24
Gateway=192.168.1.1

• This configuration creates a VLAN interface with the ID 10 on the enp0s3 interface and assigns it a static IP address.

File Naming Convention

Network configuration files in /etc/systemd/network/ typically follow a naming convention like XX-<interface>.network, where XX is a numeric prefix to control the order in which configurations are applied, and <interface> is the network interface name. Files with more specific names will override more generic configurations.

For example:

• 10-eth0.network

• 20-wlan0.network

Applying Changes

To apply the changes made to .network files, you need to restart the systemd-networkd service:

sudo systemctl restart systemd-networkd

Alternatively, to reload the configurations without fully restarting:

sudo networkctl reload

Conclusion

The .network files under /etc/systemd/network/ are used to configure various aspects of network interfaces, such as IP addressing, DNS, and routes, using systemd-networkd. These files are an alternative to traditional network management tools like ifup/ifdown or NetworkManager, and are especially useful in server environments or minimal installations where you prefer direct control over network configurations.