As we mentioned earlier, Docker comes with a set of sensible defaults to get your containers communicating on the network. From a network perspective, the Docker default is to attach any spawned container to the docker0 bridge. In this recipe, we'll show how to connect containers in the default bridge mode and explain how network traffic leaving and destined for the container is handled.
You'll need access to a Docker host and an understanding of how your Docker host is connected to the network. In our example, we'll be using a Docker host that has two physical network interfaces, like the one shown in the following diagram:
You'll want to make sure that you have access to view iptables rules to verify netfilter policies. If you wish to download and run example containers, your Docker host will also need access to the Internet. In some cases, the changes we make may require you to have root-level access to the system.