Docker IPv6 Support

By default, IPv6 support is disabled in Docker / Docker containers. This results in any IPv6 only resources (e.g., internet pages, Git repositories, etc.) not being available inside a container.
However, enabling IPv6 support is very easy.

Enable IPv6 Support — Docker Daemon

First, you must determine the IPv6 prefix assigned to your network. If you are behind a private internet connection, you can obtain this information easily from your router administration page.
Now, determine a fixed CIDR subnet/range that your docker daemon may use. For example, if your prefix is 2001:1:1:1::/64, you can simply add 1234 and use an /80 subnet for docker: 2001:1:1:1:1234::/80.

This information has to be added to the /etc/docker/daemon.json file (create it if it does not already exist), along with the setting to enable IPv6 at all:

{
  "ipv6": true,
  "fixed-cidr-v6": "2001:1:1:1:1234::/80"
}

Finally, reload the docker daemon to apply the changes:

systemctl reload docker

Docker will now assign the containers an IPv6 address from within the defined CIDR subnet.

Test IPv6

Simply try to ping/reach an IPv6 resource, e.g. by using curl:

# run following command inside a docker container
curl --ipv6 google.com

# for example, like so (replace google.com by the domain you need access to)
docker run -it --rm curlimages/curl:latest --ipv6 google.com

Automated Update of the Config File

You can use the python script from this Gist to update the config file either manually or via a cronjob or something similar.
Configure the three config variables according to your needs:

• PREFIX_LENGTH: length of the IPv6 prefix of your internet connection (this information should be shown on your routers admin/configuration interface)
• TARGET_SUBNET_LENGTH: length of the subnet you want to assign to the docker daemon
• FILL_WITH: Hexadecimal digits to fill the CIDR range (between network and target-prefix) with

Run the script with at least python version 3:

# put this in a cronjob or run it manually
/usr/bin/python3 dockeripv6update.py

Feel free to use the concepts of the python script to create your own script in any other language or adjust it according to your specific needs!