Overlapping subnetworks or how to change Docker default subnet size?

Several services already running were no longer available from subnets after a new container was created using docker-compose.
The control of the IP addresses showed that a new network 192.168.X.0/20 was created, which overlapped the existing networks and therefore the communication did not work anymore.

By default, Docker uses the following subnet areas for creating new networks:


Also docker-compose uses these network areas when creating new networks, this can lead to problems in larger networks.

To prevent this, you can specify in the /etc/docker/daemon.json the network areas to be used, so that there are no overlaps with your own networks.


base = Network area from which a subnet of size is selected for the new network.

To test the configuration, 50 networks were created and their subnet displayed and deleted.

for i in {1..50}; do docker network create net-$i; done
for i in $(docker network ls -q); do docker network inspect --format='{{.Name}} {{.IPAM.Config}}' $i; done
for i in {1..50}; do docker network rm net-$i; done

This option is only available since version 18.06!