IPv6 in a Docker container on a non-ipv6 network

12-04-2016 | Remy van Elst

Table of Contents

At work and at home my ISP's have native IPv6. I recently was at a clients location where they had no IPv6 at all and had to set up and demonstrate an application in a Docker container with IPv6 functionality. They said the had IPv6 but on location it appeared that IPv6 wasn't working. Since IPv6 was required for the demo the container needed a workaround. This article describes the workaround I used to add IPv6 to a Docker container on a non IPv6 network. It was tested on an Ubuntu 14.04 container, but should work for other Linux distro's as well.

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The workaround involes installing miredo in the container to get a tunnel and an IPv6 connection that way. Extremely simple, but it required some extra parameters in the Docker workflow.

Miredo is a client for the teredo protocol. On Ubuntu it is an easy way to add IPv6 to an IPv4 only system. Installing miredo and starting the service is enough.

First I started the docker container with docker run, and added an extra parameter, the --privileged one, like so:

docker run --privileged --name "$APPNAME" "$IMAGENAME"

This gives the container the ability to create a /dev/net/tun device required for miredo. Otherwise you will get an error like below when starting miredo:

/dev/net/tun does not exist.

A Docker container is (to be) used for a single process (as opposed to for example an LXD or OpenVZ container, which are more suited for VPS-like operation) and therefore there is no SSH access or a service manager like systemd or init. Installing software should be done via the Dockerfile in a new container. I needed a way to install and start the miredo service outside of the Dockerfile for this one instance.

Since this container was to be used only that occasion I used a rather dirty hack to get a shell in the container, install and start the service. It works, but it's not the best way (that would involve setting IPv6 up on the host and configuring the Docker network to also use that in the bridge).

Get the container ID with docker ps:

docker ps


CONTAINER ID        IMAGE                      COMMAND                CREATED             STATUS              PORTS               NAMES
7522a5aedc8b        7.0-apache-openssl-1.1.0   "apache2-foreground"   About an hour ago   Up About an hour    80/tcp              testapp

Open a shell inside of the container, replacing the ID with your container ID:

docker exec -i -t 7522a5aedc8b bash

This gives you a bash prompt in the container. Install the miredo package:

apt-get update && apt-get install miredo

Start the service:

service miredo start

Check if the new interface (miredo) exists and is up:

2: teredo: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1280 qdisc noqueue state UNKNOWN group default qlen 500
    inet6 2001:0:53aa:64c:1089:2f63:6e89:5ffc/32 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::ffff:ffff:ffff/64 scope link 
       valid_lft forever preferred_lft forever

You can now close the prompt and continue the container, which has IPv6 connectivity now via this tunnel.

Do note that these changes are temporary. If you stop the container the changes are gone, so on a new run of the container you need to execute these steps again if needed.

Tags: containers, docker, ipv6, lxc, miredo, teredo,