IPv6 addresses with more than two groups set cause address collision

[hellt]

Consider the following topo:

---
name: c

mgmt:
  network: clab-mgmt
  ipv4_subnet: 172.30.0.0/16
  ipv6_subnet: fd1a:b128:5901::/32

topology:
  defaults:
    kind: linux
    image: alpine

  nodes:
    l1:
      mgmt_ipv4: 172.30.1.1
      mgmt_ipv6: fd1a:b128:5901::101
    l2:
      mgmt_ipv4: 172.30.1.2
      mgmt_ipv6: fd1a:b128:5902::101

Nodes l1 and l2 has different IPV6 addresses set, but they are not parsed either by clab or docker and cause address collision:

❯ clab dep -c -t test.clab.yml     
INFO[0000] Containerlab v0.38.0 started                 
INFO[0000] Parsing & checking topology file: test.clab.yml 
INFO[0000] Removing /tmp/clab-c directory...            
INFO[0000] Creating lab directory: /tmp/clab-c          
INFO[0000] Creating docker network: Name="clab-mgmt", IPv4Subnet="172.30.0.0/16", IPv6Subnet="fd1a:b128:5901::/32", MTU="1450" 
INFO[0000] Creating container: "l2"                     
INFO[0000] Creating container: "l1"                     
ERRO[0001] failed deploy phase for node "l2": Error response from daemon: Address already in use 
ERRO[0001] failed to run postdeploy task for node l2: failed to Statfs "": no such file or directory 

This is because the address that gets configured for the first node only has two groups set:

❯ docker inspect clab-mgmt
[
    {
        "Name": "clab-mgmt",
        "Id": "b301768abab95b091bd22f7d2720900efaaccc17c9c3e1441e068c5f5a36a408",
        "Created": "2023-03-21T15:00:49.717101046+01:00",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": true,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.30.0.0/16"
                },
                {
                    "Subnet": "fd1a:b128:5901::/32"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "1027b8dbe0df2b768d1283160aa1827f6d4128e740bb793a3c634fd8def76093": {
                "Name": "clab-c-l1",
                "EndpointID": "08f0a9da0dc45321e5c3b903f95c26b0516e1af78dc958406299368c8fc4a35f",
                "MacAddress": "02:42:ac:1e:01:01",
                "IPv4Address": "172.30.1.1/16",
                "IPv6Address": "fd1a:b128::101/32"
            }
        },
        "Options": {
            "com.docker.network.driver.mtu": "1450"
        },
        "Labels": {
            "containerlab": ""
        }
    }
]

[steiler]

Reported to docker
moby/moby#45402

[hellt]

Thanks @steiler for digging all the way to moby, as explained in moby/moby#45402 (comment) this is an implementation detail in moby that truncates makes an address fd1a:b128:a:b:c:d:e:f to be truncated as fd1a:b128::c:d:e:f.

We have to make a note in the docs about it for ipv6 addresses