Explore networking features

Estimated reading time: 5 minutes

Docker Desktop provides several networking features to make it easier to use.

Features for all platforms

VPN Passthrough

Docker Desktop networking can work when attached to a VPN. To do this, Docker Desktop intercepts traffic from the containers and injects it into the host as if it originated from the Docker application.

Port Mapping

When you run a container with the -p argument, for example:

$ docker run -p 80:80 -d nginx

Docker Desktop makes whatever is running on port 80 in the container (in this case, nginx) available on port 80 of localhost. In this example, the host and container ports are the same. If, for example, you already have something running on port 80 of your host machine, you can connect the container to a different port:

$ docker run -p 8000:80 -d nginx

Now, connections to localhost:8000 are sent to port 80 in the container. The syntax for -p is HOST_PORT:CLIENT_PORT.

HTTP/HTTPS Proxy Support

See:

Features for Mac and Linux

SSH agent forwarding

Docker Desktop on Mac and Linux allows you to use the host’s SSH agent inside a container. To do this:

  1. Bind mount the SSH agent socket by adding the following parameter to your docker run command:

    --mount type=bind,src=/run/host-services/ssh-auth.sock,target=/run/host-services/ssh-auth.sock

  2. Add the SSH_AUTH_SOCK environment variable in your container:

    -e SSH_AUTH_SOCK="/run/host-services/ssh-auth.sock"

To enable the SSH agent in Docker Compose, add the following flags to your service:

services:
  web:
    image: nginx:alpine
    volumes:
      - type: bind
        source: /run/host-services/ssh-auth.sock
        target: /run/host-services/ssh-auth.sock
    environment:
      - SSH_AUTH_SOCK=/run/host-services/ssh-auth.sock

Known limitations for all platforms

Changing internal IP addresses

The internal IP addresses used by Docker can be changed from the Settings, if you’re a Windows user, or Preferences, if you use Mac or Linux. After changing IPs, it is necessary to reset the Kubernetes cluster and to leave any active Swarm.

There is no docker0 bridge on the host

Because of the way networking is implemented in Docker Desktop, you cannot see a docker0 interface on the host. This interface is actually within the virtual machine.

I cannot ping my containers

Docker Desktop can’t route traffic to Linux containers. However if you’re a Windows user, you can ping the Windows containers.

Per-container IP addressing is not possible

The docker bridge network is not reachable from the host. However if you are a Windows user, it works with Windows containers.

Use cases and workarounds for all platforms

I want to connect from a container to a service on the host

The host has a changing IP address (or none if you have no network access). We recommend that you connect to the special DNS name host.docker.internal which resolves to the internal IP address used by the host. This is for development purpose and does not work in a production environment outside of Docker Desktop.

You can also reach the gateway using gateway.docker.internal.

If you have installed Python on your machine, use the following instructions as an example to connect from a container to a service on the host:

  1. Run the following command to start a simple HTTP server on port 8000.

    python -m http.server 8000

    If you have installed Python 2.x, run python -m SimpleHTTPServer 8000.

  2. Now, run a container, install curl, and try to connect to the host using the following commands:

     $ docker run --rm -it alpine sh
     # apk add curl
     # curl http://host.docker.internal:8000
     # exit
    

I want to connect to a container from the host

Port forwarding works for localhost; --publish, -p, or -P all work. Ports exposed from Linux are forwarded to the host.

Our current recommendation is to publish a port, or to connect from another container. This is what you need to do even on Linux if the container is on an overlay network, not a bridge network, as these are not routed.

For example, to run an nginx webserver:

$ docker run -d -p 80:80 --name webserver nginx

To clarify the syntax, the following two commands both publish container’s port 80 to host’s port 8000:

$ docker run --publish 8000:80 --name webserver nginx

$ docker run -p 8000:80 --name webserver nginx

To publish all ports, use the -P flag. For example, the following command starts a container (in detached mode) and the -P flag publishes all exposed ports of the container to random ports on the host.

$ docker run -d -P --name webserver nginx

See the run command for more details on publish options used with docker run.

networking, docker desktop