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Docker simplifies container networking by providing built-in networks and easy-to-use commands for creating custom networks. Whether you need isolated environments or seamless inter-container communication, this guide covers everything from default networks to user-defined bridges, inspection commands, and internal mechanics.

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Built-in Docker Networks

Docker creates three networks upon installation:
Network NameDescriptionTypical Use Case
bridgeDefault private internal network on the hostGeneral container communication
hostShares host’s network namespace—no isolationHigh-performance networking, host apps
noneNo network interfaces except loopbackSecurity-isolated or self-managed setups
You can attach containers to any network using the --network flag: 
docker run --network=<network_name> ubuntu

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1. Bridge Network

The bridge network is Docker’s default. Each container on this network gets an internal IP (typically in 172.17.x.x). Containers on the same bridge can communicate directly.

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Port Mapping

Expose container ports to the host with -p: 
docker run -d -p 8080:80 nginx
This maps port 80 in the container to port 8080 on your Docker host.
If you omit -d, the container runs in the foreground.

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2. Host Network

Running with --network=host makes the container share your host’s network stack: 
docker run --network=host ubuntu
Key points:
  • No port mapping needed
  • Ports in the container are the same as on the host
  • Cannot run multiple containers on the same host port
Using the host network removes isolation. Only use this when you trust the container’s network behavior.

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3. None Network

The none network disables all external interfaces, leaving only the loopback: 
docker run --network=none ubuntu
Use this for maximum network isolation when no connectivity is desired.

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Creating a User-Defined Bridge Network

Custom bridge networks let you isolate groups of containers and define subnets: 
docker network create \
  --driver bridge \
  --subnet 182.18.0.0/16 \
  custom-isolated-network
List all available networks: 
docker network ls
Example output: 
NETWORK ID          NAME                         DRIVER    SCOPE
dba0fb9370fe        bridge                       bridge    local
4d60768bc9          custom-isolated-network      bridge    local
6de6865ce1c6        docker_gwbridge              bridge    local
e29d81be47          host                         host      local
mmrho7vb9rm         ingress                      overlay   swarm
d371b4009142        simplewebappdocker_default   bridge    local
The image illustrates a user-defined network setup with Docker containers, showing IP addresses and connections between them.

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Inspecting a Container’s Network Settings

To retrieve a container’s IP address and network details: 
docker inspect <container_id_or_name>
Search for the NetworkSettings section in the JSON output: 
"NetworkSettings": {
  "Gateway": "172.17.0.1",
  "IPAddress": "172.17.0.6",
  "MacAddress": "02:42:ac:11:00:06",
  "Networks": {
    "bridge": {
      "Gateway": "172.17.0.1",
      "IPAddress": "172.17.0.6",
      "MacAddress": "02:42:ac:11:00:06"
    }
  }
}
Use jq to filter output:
docker inspect <id> | jq '.[0].NetworkSettings'

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Name-Based Container Communication

Docker’s embedded DNS (at 127.0.0.11) lets containers resolve each other by name: 
mysql.connect(mysql)
Here, mysql refers to the target container’s name. No static IPs required.

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Under the Hood: Namespaces & veth Pairs

Docker uses Linux network namespaces to isolate containers. Communication between a container and the host bridge relies on veth (virtual Ethernet) pairs:
  • One end lives in the container’s namespace
  • The other end attaches to the host bridge
This setup ensures both isolation and connectivity.

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