How Docker0 Veth And Eth0 Works Docker Bridge Networking

Docker bridge networking has a few names that look strange at first: docker0, veth, and eth0.

You do not need to become a network engineer to use Docker, but knowing the basic idea helps you understand how containers connect to the host and each other.

The simple picture

On a Linux host, Docker creates a bridge interface called docker0.

Think of docker0 as a small virtual switch on your machine. Containers can connect to this switch.

container eth0
-> veth pair
-> docker0 bridge
-> host network

eth0 inside the container

Inside a container, the network interface is usually named eth0.

From the container's point of view, eth0 is its network card.

You can inspect it by entering a container and running network commands, depending on what tools are installed in the image.

veth pair

A veth pair is like a virtual cable with two ends.

One end appears inside the container as eth0. The other end stays on the host and connects to the Docker bridge.

This is how traffic moves between the container and the host network.

docker0 bridge

The docker0 bridge connects containers on the default bridge network.

It can forward traffic between containers and help route traffic out to the host network.

When containers need internet access, Docker also uses NAT rules on the host to send traffic outward.

Port mapping in this picture

When you run:

docker run -p 8080:80 nginx

Docker makes host port 8080 forward traffic to port 80 inside the container.

The browser talks to the host. Docker forwards the traffic through the networking layer to the container.

Why this matters

If networking fails, this model gives you places to check:

• Is the container running?
• Is the app listening on the expected container port?
• Did you publish the port with -p?
• Is the host firewall or AWS security group allowing the host port?
• Are containers on the same Docker network?

Written By: Shiva Srivastava