added example for a docker compse file using IPv6 config.

[murphy83]

If you want to use IPv6 in Docker with Power-DNS, this example file is a good starting point.
Added fields to docker compose (best placed in an .env-file):

• NETWORK_NAME="my_dns_network"
• NETWORK_IPV6_PREFIX="any valid IPv6-prefix you like to assign - use one of the ULA-Range for testing, should be a global unique one for production"
• NETWORK_IPV6_PREFIX_LENGTH="prefix-length that matches your defined prefix" (keep in mind, you regularly get a /64 by your ISP/Hosting provider, which you need to subsegment => using a value between /80 and /120 is reasonable)

Be advised, that you may also need to adjust your docker host to allow IPv6 routing and that you should think about securing access to your services (eg. by setting firewall rules on the host system, this is not done automatically by docker or docker compose).

[pschiffe]

Thank you.