Default Bridge
When containers are ran using docker run without specifying the network name, the default bridge will be used.
Finding default bridge
# to show all the networks
docker network ls
# in the networks, "bridge" is the default bridge
# you can get more info of the bridge
docker inspect bridge
# you can find the network interface name of the bridge as follows
docker inspect bridge | grep com.docker.network.bridge.name
# shows network interface info
ip addr show docker0
Inspect the links
# by default, there will be no links to the docker0 bridge when no containers are running
bridge link | grep docker0 # this will be empty
# when container is started, the network will be connected to the default bridge when no other network is spicified
docker run -itd --rm busybox sh
# now there will be a new interface that connects to docker0 bridge
bridge link | grep docker0
User Defined Bridge
Works similar to the default bridge but containers will be linked only when the network is specified to use the user defined bridge
Creating a user defined bridge
# first create a network
docker network create some_nework_name
# to find the network interface name, first find the network id in the docker
docker network ls --filter 'name=some_nework_name' --format '{{.ID}}'
# network interface should be created using be 'br-' prefix
ip addr show | grep 'br-<network_id>'
Create a new network withing the network
# use the --network flag to pass the network of the container
docker run -it --rm --network test some_nework_name sh
# now a new interface should be linked to the new bridge
bridge link | grep 'br-<network_id>'
Host
Host network runs a container but it's similar to running an application in the host network.
Run a container in the host
docker run -it --rm --network host busybox sh