I'm trying to run a container with a static IPv4 and IPv6 address (specifically a DNS server that will be propagated by the router, thus the requirement for static IP addresses). For this I'm trying to create a Docker macvlan network so I can run containers, reachable from other VLANs via the router. The network itself is set up correctly and works as every other VLAN I have:

root@noatun:~# ip addr show dev br0.8
17: br0.8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether b4:2e:99:ad:6c:51 brd ff:ff:ff:ff:ff:ff
    inet 10.100.80.4/24 brd 10.100.80.255 scope global dynamic noprefixroute br0.8
       valid_lft 41348sec preferred_lft 35948sec
    inet6 fd3b:2815:be50::967/128 scope global dynamic noprefixroute
       valid_lft 42615sec preferred_lft 42615sec
    inet6 2003:e5:d730:6200::967/128 scope global dynamic noprefixroute
       valid_lft 13644sec preferred_lft 1044sec
    inet6 fd3b:2815:be50:0:9f84:ac1a:9cea:ee0d/64 scope global mngtmpaddr noprefixroute
       valid_lft forever preferred_lft forever
    inet6 2003:e5:d730:6200:9834:1760:1142:e4a0/64 scope global dynamic mngtmpaddr noprefixroute
       valid_lft 13645sec preferred_lft 1045sec
    inet6 fe80::e8c5:16ff:fe3d:3d8a/64 scope link
       valid_lft forever preferred_lft forever

The Docker network doesn't have any IPv6 support enabled:

root@noatun:~# docker network inspect br0.8
[
    {
        "Name": "br0.8",
        "Id": "ba9083ca9744046029a93b5d170beede78f348852830a1ff225d1cee29a19adb",
        "Created": "2020-09-16T14:49:38.714737243+02:00",
        "Scope": "local",
        "Driver": "macvlan",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "10.100.80.0/24",
                    "IPRange": "10.100.80.128/25",
                    "Gateway": "10.100.80.1",
                    "AuxiliaryAddresses": {
                        "server": "10.100.80.4"
                    }
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {},
        "Options": {
            "parent": "br0.8"
        },
        "Labels": {}
    }
]

IPv6 is enabled in the Docker settings:

 

It seems like I'm missing something here, but I don't know what else to try.

I fixed this for now by creating the Docker network manually and not checking the custom networks in the Unraid Docker settings.

docker network create -d macvlan \
  --subnet=10.100.80.0/24 --gateway=10.100.80.1 \
  --subnet=fd3b:2815:be50::8/64 --gateway=fd3b:2815:be50::8 \
  --ipv6 \
  --aux-address='dhcp2=10.100.80.2' \
  --aux-address='dhcp3=10.100.80.3' \
  --aux-address='dhcp4=10.100.80.4' \
  --aux-address='dhcp5=10.100.80.5' \
  -o parent=br0.8 \
  vlan8

Nice side effect is that I can now use the full address range and tell Docker to not do something with the very small DHCP range at the start of the subnet.