Docker-IPv6-HowTo

a straight-forward approach

Background: Local IPv6, Docker subnets, Subnetting IPv6

Define a local (private) IPv6 subnet

https://dnschecker.org/ipv6-address-generator.php

This example input:

Global ID: 0000000000
Subnet ID: 0000

will result in:

Name	Value
Prefix / L	fd
Global ID	0000000000
Subnet ID	0000
Network	fd00::
CIDR	fd00::/64
IPv6 Address Format	fd00:0000:0000:0000:XXXX:XXXX:XXXX:XXXX
Start Range	fd00:0000:0000:0000:0000:0000:0000:0000
End Range	fd00:0000:0000:0000:ffff:ffff:ffff:ffff
Block Size	18446744073709551616

That is 2^64 addresses

Define Docker subnets / Subnetting IPv6

https://subnettingpractice.com/ipv6-subnet-calculator.html

Goal is to split the /64 subnet to smaller subnets

My personal split logic:

IPv6	Total IP Addresses	Split
/64	2^64 (18,446,744,073,709,551,616)	64k subnets of size /80
/80	2^48 (281,474,976,710,656)	64k subnets of size /96
/96	2^32 (4,294,967,296)	-

IPv6	IPv4	Total IP Addresses	Split
/96	*	2^32 (4,294,967,296)	256 subnets of size /104 (IPv4:/8)
/104	/8 (x.*)	2^24 (16,777,216)	256 subnets of size /112 (IPv4:/16)
/112	/16 (x.x.*)	2^16 (65,536)	256 subnets of size /120 (IPv4:/24)
/120	/24 (x.x.x.*)	2^8 (256)	-

Setup

https://docs.docker.com/config/daemon/ipv6/

Check: Local subnets should all be unique and not overlapping!

Important: At the moment this document is released IPv6 is still experimental

Hint "mixed environments":
I personally encountered problems in mixed environments.
Example: Traefik Network IPv6 with other networks still running in IPv4.
Above resulted in containers (sometimes/random!) not being able to reach each other.
Declaring all networks to v6 seems to do the trick!

/etc/docker/daemon.json

{
  "ipv6": true,
  "fixed-cidr": "172.16.0.0/16",
  "fixed-cidr-v6": "fd00::16:0/112",
  "experimental": true,
  "ip6tables": true,
  "default-address-pools": [
    {
      "base": "172.17.0.0/16",
      "size": 24
    },
    {
      "base": "fd00::17:0/112",
      "size": 120
    }
  ]
}

Default bridge (fixed-cidr)

1 subnet - 65,636 addresses in total

172.16.0.0/16 (65,536 addresses)  
fd00::16:0/112 (65,536 addresses)  

Default address pools (default-address-pools)

256 subnets x 256 addresses (65,636 addresses in total)

172.17.0.0/16 (65,536 addresses) split to /24 (256 addresses)  
fd00::17:0/112 (65,536 addresses) split to /120 (256 addresses)  

docker-compose.yml

networks:
  name:
    enable_ipv6: true

Additional networks

1 subnet - 65,636 addresses in total

example:

172.18.0.0/16
fd00::18:0/112

docker network create --ipv6 --subnet 172.18.0.0/16 --subnet fd00::18:0/112 networkname

256 subnets x 256 addresses (65,636 addresses in total)

example:

  172.18.0.0/24,   172.18.1.0/24,     172.18.2.0/24 ...
fd00::18:0/120,  fd00::18:100/120,  fd00::18:200/120 ...

docker network create --ipv6 --subnet 172.18.0.0/24 --subnet fd00::18:0/120 networkname
docker network create --ipv6 --subnet 172.18.1.0/24 --subnet fd00::18:100/120 networkname
docker network create --ipv6 --subnet 172.18.2.0/24 --subnet fd00::18:200/120 networkname
...

Links

Reserved IP addresses

https://en.wikipedia.org/wiki/Reserved_IP_addresses

Docker IPv6 Official Documentation

https://docs.docker.com/config/daemon/ipv6/

Local IPv6 Address Generator

https://dnschecker.org/ipv6-address-generator.php

IPv6 Subnetting

https://docs.netgate.com/pfsense/en/latest/network/ipv6/subnets.html

IPv6 Subnet Calculator

https://subnettingpractice.com/ipv6-subnet-calculator.html

IP(v4) Subnet Calculator

https://www.calculator.net/ip-subnet-calculator.html