No IPv6 connectivity from docker container

Question

i'm having serious problems enabling IPv6 in docker.

Environment

• The host is running Debian Jessie.
• It's a virtual Server (KVM).
• eth0 has a statically configured address like w:x:y:z::1 in a network like w:x.y:z::/64, which is assigned to my by my hosting company.
• My host is capable of using IPv6 without any problem: Pinging the outside world works, a website running on a container (Port 80 bound to host:80) is accessible via ipv6.

Problem

I cannot however access the outside world from within the containers! My docker0 bridge does NOT have a IPv6 address after restarting docker with the parameters below. There's no route and no gateway either (doesn't makes sense without an ipv6 address).

My Docker setup: Docker is started with these parameters in DOCKER_OPTS

DOCKER_OPTS="--dns 8.8.8.8 --dns 8.8.4.4 --ipv6 --fixed-cidr-v6=w:x:y:z:a::/80"

Some ipv6 host configuration parameters:

net.ipv6.conf.all.forwarding = 1
net.ipv6.conf.default.forwarding = 1

here's One of the networks i created myself:

root@wopr:~# docker network inspect wopr6
[
    {
        "Name": "wopr6",
        "Id": "ddc192d4af2a8edc809975e84cf3e4cb82c24d4cfe970dd8e3fc7d6ff31e20ee",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": true,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.23.0.0/16",
                    "Gateway": "172.23.0.1/16"
                },
                {
                    "Subnet": "w:x:y:z:a:0:0:0/80",
                    "Gateway": "w:x:y:z:a::1"
                }
            ]
        },
        "Internal": false,
        "Containers": {
            "dff30ab1496a4c3689ad6da0837fdb6cf7ea1a5b32312116214313b5b14ed07e": {
                "Name": "happy_varahamihira",
                "EndpointID": "8cd4ed4b91d8421171ec8cc771bbe7b7d81f05dc9f4679f20c642c2e828ec475",
                "MacAddress": "02:42:ac:17:00:02",
                "IPv4Address": "172.23.0.2/16",
                "IPv6Address": "w:x:y:z:a::2/80"
            }
        },
        "Options": {},
        "Labels": {}
    }
]

Here's some information from inside the container, which is mentioned above:

Addresses

root@dff30ab1496a:/# ip -6 a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
332: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500
    inet6 2a03:4000:6:2158:a::2/80 scope global nodad
       valid_lft forever preferred_lft forever
    inet6 fe80::42:acff:fe17:2/64 scope link
       valid_lft forever preferred_lft forever

Routes

root@dff30ab1496a:/# ip -6 r
2a03:4000:6:2158:a::/80 dev eth0  proto kernel  metric 256
fe80::/64 dev eth0  proto kernel  metric 256
default via 2a03:4000:6:2158:a::1 dev eth0  metric 1024

Ping

PING ipv6.l.google.com (2a00:1450:4001:811::200e): 56 data bytes, id 0x0011 = 17
--- ipv6.l.google.com ping statistics ---
1 packets transmitted, 0 packets received, 100% packet loss

What am i missing?

Solution

So after waiting two weeks for an answer and researching another few hours after opening up a bounty i found the solution.

1. Set up a new IPv6 enabled network and assign a subnet available to me (a /80 of my /64)

   docker network create --ipv6 --subnet=w:x:y:z:aaaa::/80 myfancynetwork
   

   Now start a container and connect it to the new network. Find out it's IP address. Let's say it's w:x:y:z:aaaa::5 in this example.

2. Enable proxy_ndp

   sysctl net.ipv6.conf.eth0.proxy_ndp=1
   

   You may also configure this setting via /etc/sysctl.conf, to make it persistent.

3. Add proxy to make my host (IPv6 enable) to respond to Neighbour Sollicitation messages from my router (like: "hey, who's hosting w:x:y:z:aaaa::5?") with Neighbour Advertisement messages ("that would be me!").

   ip -6 neigh add proxy w:x:y:z:aaaa::5 dev eth0
   

   ndppd may help you to automatically advertize any hosts on your network.

Bam, that's it.

Comments

[Michael Hampton]

You can install the ndppd daemon to automate this.

[Bogdan Perian]

@MichaelHampton: That's exactly what i suggested.