Inspecting container network settings in Docker - Commands & Configuration

Introduction

Sometimes you need to see how your Docker containers connect to networks. This helps you understand IP addresses, ports, and network modes used by containers.

When you want to find the IP address assigned to a running container to connect to it.

When you need to check which network a container is connected to for troubleshooting.

When you want to verify port mappings between the host and the container.

When you want to confirm if a container is using the default bridge network or a custom network.

When you want to inspect network settings before connecting containers together.

Commands

This command lists all Docker networks on your system so you can see available networks.

Terminal

docker network ls

Expected Output

NETWORK ID     NAME      DRIVER    SCOPE

b1f3a2c4d5e6   bridge    bridge    local

c7d8e9f0a1b2   host      host      local

f3e4d5c6b7a8   none      null      local

This shows all running containers so you can find the container ID or name to inspect.

Terminal

docker ps

Expected Output

CONTAINER ID   IMAGE          COMMAND                  CREATED        STATUS        PORTS                    NAMES

7a8b9c0d1e2f   nginx:1.23     "/docker-entrypoint.…"   2 minutes ago  Up 2 minutes  0.0.0.0:8080->80/tcp     my-nginx

This command shows detailed network settings of the container named 'my-nginx' in JSON format for easy reading.

Terminal

docker inspect my-nginx --format '{{json .NetworkSettings}}'

Expected Output

{"Bridge":"bridge","SandboxID":"a1b2c3d4e5f6g7h8i9j0","HairpinMode":false,"LinkLocalIPv6Address":"","LinkLocalIPv6PrefixLen":0,"Ports":{"80/tcp":[{"HostIp":"0.0.0.0","HostPort":"8080"}]},"SandboxKey":"/var/run/docker/netns/a1b2c3d4e5f6","SecondaryIPAddresses":null,"SecondaryIPv6Addresses":null,"EndpointID":"1234567890abcdef","Gateway":"172.17.0.1","GlobalIPv6Address":"","GlobalIPv6PrefixLen":0,"IPAddress":"172.17.0.2","IPPrefixLen":16,"IPv6Gateway":"","MacAddress":"02:42:ac:11:00:02","Networks":{"bridge":{"IPAMConfig":null,"Links":null,"Aliases":null,"NetworkID":"b1f3a2c4d5e6","EndpointID":"1234567890abcdef","Gateway":"172.17.0.1","IPAddress":"172.17.0.2","IPPrefixLen":16,"IPv6Gateway":"","GlobalIPv6Address":"","GlobalIPv6PrefixLen":0,"MacAddress":"02:42:ac:11:00:02","DriverOpts":null}}}

→

--format - Formats the output to show only network settings in JSON for clarity

This command shows details about the 'bridge' network including connected containers and their IP addresses.

Terminal

docker network inspect bridge

Expected Output

[

    {

        "Name": "bridge",

        "Id": "b1f3a2c4d5e6",

        "Created": "2024-06-01T12:00:00.000000000Z",

        "Scope": "local",

        "Driver": "bridge",

        "EnableIPv6": false,

        "IPAM": {

            "Driver": "default",

            "Options": null,

            "Config": [

                {

                    "Subnet": "172.17.0.0/16",

                    "Gateway": "172.17.0.1"

                }

            ]

        },

        "Containers": {

            "7a8b9c0d1e2f": {

                "Name": "my-nginx",

                "EndpointID": "1234567890abcdef",

                "MacAddress": "02:42:ac:11:00:02",

                "IPv4Address": "172.17.0.2/16",

                "IPv6Address": ""

            }

        },

        "Options": {},

        "Labels": {}

    }

]

Key Concept

If you remember nothing else from this pattern, remember: docker inspect lets you see exactly how a container connects to networks including IPs and ports.

Common Mistakes

Using 'docker inspect' without specifying the container name or ID.

The command will fail or show too much unrelated information making it hard to find network details.

Always specify the container name or ID after 'docker inspect' to focus on the container you want.

Not using the --format flag to filter output.

The full inspect output is very long and hard to read, especially for beginners.

Use --format '{{json .NetworkSettings}}' to get clear, focused network info.

Summary

Use 'docker network ls' to list all Docker networks on your system.

Use 'docker ps' to find running containers and their names or IDs.

Use 'docker inspect <container>' with --format to see detailed network settings like IP address and port mappings.

Use 'docker network inspect <network>' to see which containers are connected and their network details.