# User-defined Bridge vs Default Bridge networking

Paul Tomoiu

●

Docker,

networking

●

Published 2022-12-03

This tutorial explains the differences between a user-defined bridge and a default bridge in Docker.

User-defined bridges provide automatic DNS resolution between containers

Containers on the default bridge network can only access each other by IP addresses, unless you use the --link option, which is considered legacy. On a user-defined bridge network, containers can resolve each other by name or alias.

User-defined bridges provide better isolation

All containers without a --network specified, are attached to the default bridge network. This can be a risk, as unrelated stacks/services/containers are then able to communicate. Using a user-defined network provides a scoped network in which only containers attached to that network are able to communicate.

Containers can be attached and detached from user-defined networks on the fly

During a container’s lifetime, you can connect or disconnect it from user-defined networks on the fly. To remove a container from the default bridge network, you need to stop the container and recreate it with different network options.

Each user-defined network creates a configurable bridge

If your containers use the default bridge network, you can configure it, but all the containers use the same settings. In addition, configuring the default bridge network happens outside of Docker itself, and requires a restart of Docker.

Create a user-defined bridge:

linux
docker network create my-bridged-net

List the networks on Docker host:

linux
docker network ls

and the result is like this:

linux
NETWORK ID     NAME             DRIVER    SCOPE
db8e765f1473   bridge           bridge    local
ddd7c07f5878   host             host      local
b9a7e3793d41   my-bridged-net   bridge    local
9b6e685952f6   none             null      local

List only the bridged networks on Docker host:

linux
docker network ls --filter driver=bridge

Remove a user-defined network from Docker host:

linux
docker network rm my-bridged-net