Changing default subnet for docker custom networks

Question

Our internal network has the range 172.20.0.0/16 reserved for internal purposes and docker uses the 172 range by default for its internal networking. I can reset the bridge to live in 192.168 by providing the bip setting to the daemon:

➜  ~ sudo cat /etc/docker/daemon.json
{
  "bip": "192.168.2.1/24"
}

➜  ~ ifconfig                        
docker0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
    inet 192.168.2.1  netmask 255.255.255.0  broadcast 0.0.0.0

However, when creating new custom networks via docker network create or by defining them in the networks sections of the docker-compose.yaml these are still created in 172, thus eventually clashing with 172.20:

➜  ~ docker network create foo
610fd0b7ccde621f87d40f8bcbed1699b22788b70a75223264bb14f7e63f5a87
➜  ~ docker network inspect foo | grep Subnet
                "Subnet": "172.17.0.0/16",
➜  ~ docker network create foo1              
d897eab31b2c558517df7fb096fab4af9a4282c286fc9b6bb022be7382d8b4e7
➜  ~ docker network inspect foo1 | grep Subnet
                "Subnet": "172.18.0.0/16",

I understand I can provide the subnet value to docker network create, but I rather want all such subnets created under 192.168.*.

How can one configure dockerd to do this automatically?

Answer 1

For anyone who found this question. Now it is possible.

$ docker -v
Docker version 18.06.0-ce, build 0ffa825

Edit or create config file for docker daemon:

# nano /etc/docker/daemon.json

Add lines:

{
  "default-address-pools":
  [
    {"base":"10.10.0.0/16","size":24}
  ]
}

Restart dockerd:

# service docker restart

Check the result:

$ docker network create foo
$ docker network inspect foo | grep Subnet
                    "Subnet": "10.10.1.0/24"

It works for docker-compose too.

Your "bip": "192.168.2.1/24" works for bridge0 only. It means that any container which run without --network will use this default network.