Docker Networking Overview

What is Docker networking?

Every container gets a virtual network interface (NIC) when it starts. Docker connects that NIC to a network — a software-defined layer that controls which containers can talk to each other and to the outside world.

Without Docker networking, containers would be completely isolated islands. With it, you can wire together microservices, expose ports to the host, and segment traffic by environment — all without touching the host’s physical network configuration.

Network drivers

Docker ships with four built-in network drivers. Each one trades off isolation, performance, and ease of use differently.

Driver	Scope	Description
bridge	Single host	Default driver. Creates a virtual switch (docker0) on the host. Containers on the same bridge can communicate; containers on different bridges cannot.
host	Single host	Removes network isolation — the container shares the host’s network stack directly. Highest performance, zero port mapping needed, but no isolation.
none	Single host	Disables all networking. The container gets only a loopback interface. Useful for batch jobs that need no network access.
overlay	Multi-host	Spans multiple Docker daemons (Docker Swarm). Used for distributed services that need to communicate across physical machines.

Default networks

Docker creates three networks automatically when the daemon starts. You can see them with docker network ls:

docker network ls

Expected output:

NETWORK ID     NAME      DRIVER    SCOPE
abc123def456   bridge    bridge    local
def456abc789   host      host      local
ghi789jkl012   none      null      local

The bridge network (backed by the docker0 virtual switch) is where every container lands by default when you omit --network. The host and none networks are special-purpose.

Inspecting the default bridge

docker network inspect shows detailed configuration — subnet, gateway, and which containers are currently attached:

docker network inspect bridge

What this module covers

Lesson	Topic
The Default Bridge Network	How docker0 works, container IPs, and the DNS limitation
Container DNS and User-Defined Networks	How user-defined bridges provide automatic name resolution
Publishing and Exposing Ports	-p vs EXPOSE, port binding syntax, ephemeral ports
Custom Networks and Container Isolation	Creating, connecting, inspecting, and removing networks

Hands-on: inspect the defaults

# List all networks
docker network ls

# Inspect the default bridge in detail
docker network inspect bridge

Inspect default networks ↗

🐳 Three networks exist by default

Docker creates bridge, host, and none networks automatically. Every container that omits —network starts on the default bridge.

Which Docker network driver is used by default when you run a container without specifying --network?

host overlay bridge none

What does the 'host' network driver do?

Creates a virtual switch that isolates containers from the host Disables all networking for the container Spans containers across multiple Docker daemons Shares the host's network stack directly with the container, removing isolation

Which command lists all Docker networks on the current host?

docker network show docker network ls docker ps --networks docker inspect networks

Which network driver should you use when you need containers to communicate across multiple physical machines in a Docker Swarm?

bridge none host overlay

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