#### Beyond Linux® From Scratch (systemd Edition) - Version r13.0-491

### Chapter 14. Connecting to a Network

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# Advanced Network Setup

## Network Bridge

### Kernel Configuration

Enable the following options in the kernel configuration and recompile the kernel if necessary:

    Networking support: Y
      Networking options:
        802.1d Ethernet Bridging: M or Y

### Setting up a Network Bridge

In this section we are going to discuss how to set up a network bridge using systemd-networkd. In the examples below, `eth0` represents the external interface that is being bridged, while `br0` represents the bridge interface.

To create a bridge interface, create the following configuration file by running the following command as the `root` user:

    cat > /etc/systemd/network/50-br0.netdev << EOF
    [NetDev]
    Name=br0
    Kind=bridge
    EOF

To assign a network interface to a bridge, create the following configuration file by running the following command as the `root` user:

    cat > /etc/systemd/network/51-eth0.network << EOF
    [Match]
    Name=eth0

    [Network]
    Bridge=br0
    EOF

Repeat the process for any other interfaces that need to be bridged. Note that it is important that nothing assigns any addresses to the bridged interfaces. If you are using NetworkManager-1.56.0, make sure you configure them to ignore the bridged interfaces, as well as the bridge interface itself.

If you are on a network which uses DHCP for assigning ip addresses, create the following configuration file by running the following command as the `root` user:

    cat > /etc/systemd/network/60-br0.network << EOF
    [Match]
    Name=br0

    [Network]
    DHCP=yes
    EOF

Alternatively, if using a static ip setup, create the following configuration file by running the following command as the `root` user:

    cat > /etc/systemd/network/60-br0.network << EOF
    [Match]
    Name=br0

    [Network]
    Address=192.168.0.2/24
    Gateway=192.168.0.1
    DNS=192.168.0.1
    EOF

If you want to contact another system connected to the bridge, for example a qemu instance, then you also need to enable IP forwarding. Again as the `root` user, do:

    echo 'IPForward=ipv4' >> /etc/systemd/network/60-br0.network

To bring up the bridge interface, simply restart the systemd-networkd daemon by running the following command as the `root` user:

    systemctl restart systemd-networkd

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