Build your own bridge

Estimated reading time: 2 minutes

This section explains how to build your own bridge to replace the Docker default bridge. This is a bridge network named bridge created automatically when you install Docker.

Note: The Docker networks feature allows you to create user-defined networks in addition to the default bridge network.

You can set up your own bridge before starting Docker and configure Docker to use your bridge instead of the default docker0 bridge.

  1. Configure the new bridge.

    $ sudo brctl addbr bridge0

$ sudo ip addr add 192.168.5.1/24 dev bridge0

$ sudo ip link set dev bridge0 up

    Confirm the new bridge’s settings.

    $ ip addr show bridge0

4: bridge0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state UP group default
    link/ether 66:38:d0:0d:76:18 brd ff:ff:ff:ff:ff:ff
    inet 192.168.5.1/24 scope global bridge0
       valid_lft forever preferred_lft forever

  2. Configure Docker to use the new bridge by setting the option in the daemon.json file, which is located in /etc/docker/ on Linux or C:\ProgramData\docker\config\ on Windows Server. On Docker for Mac or Docker for Windows, click the Docker icon, choose Preferences, and go to Daemon.

    If the daemon.json file does not exist, create it. Assuming there are no other settings in the file, it should have the following contents:

    {
  "bridge": "bridge0"
}

    Restart Docker for the changes to take effect.

  3. Confirm that the new outgoing NAT masquerade is set up.

    $ sudo iptables -t nat -L -n

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
MASQUERADE  all  --  192.168.5.0/24      0.0.0.0/0

  4. Remove the now-unused docker0 bridge.

    $ sudo ip link set dev docker0 down

$ sudo brctl delbr docker0

$ sudo iptables -t nat -F POSTROUTING

  5. Create a new container, and verify that it is in the new IP address range.

You can use the brctl show command to see Docker add and remove interfaces from the bridge as you start and stop containers, and can run ip addr and ip route inside a container to confirm that it has an address in the bridge’s IP address range and uses the Docker host’s IP address on the bridge as its default gateway to the rest of the Internet.

docker, bridge, docker0, network