Problems with network connectivity and docker on Synology

  docker, networking, ping, synology

I run docker containers on a Synology NAS. All container using the host driver have network connection but none of the containers using the bridge driver have. In the past it worked but some months ago one of my experimental containers experienced network problems

Environment:
Synology DS218+
DSM 6.2.3-25426 Update 2
10 GB internal memory

To simplify the description of the problem I have followed the tutorial from docker:

docker run –dit --name alpine1 alpine ash
docker run –dit --name alpine2 alpine ash

The containers have 172.17.0.2 and172.17.0.3 as IP addresses. When I attached to alpine1 I wasn’t able to ping to alpine2 using its IP-address (since the default bridge doesn’t do name resolution)

I also tried to use a user defined bridge:

docker network create –driver bridge test

and connected the containers to this network (and disconnected them from the default bridge network)

bash-4.3# docker network inspect test
[
    {
        "Name": "test",
        "Id": "e0e203000f5cfae8103ed9b80dce113633e0e198c542f943ac2e7026cb684784",
        "Created": "2020-12-22T22:47:08.331525073+01:00",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.22.0.0/16",
                    "Gateway": "172.22.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "3da4fda1508743b36540d6848c5334c84c3c9c02df88170e617d08f15e85999b": {
                "Name": "alpine1",
                "EndpointID": "ccf4be3f89c45dc73183210fafcfdafee9bbe30309ef15cf27e37bbb3783ea58",
                "MacAddress": "02:42:ac:16:00:03",
                "IPv4Address": "172.22.0.3/16",
                "IPv6Address": ""
            },
            "c024024eb5a0e57720f7c2abe76ea5f5396a29eb02addd1f60d23075fcfcad78": {
                "Name": "alpine2",
                "EndpointID": "d4a8cf285d6dae7e8b7f96426a390b73ea800a72bf1739b0ea88c122de975650",
                "MacAddress": "02:42:ac:16:00:02",
                "IPv4Address": "172.22.0.2/16",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {}
    }

Also in this case I wasn’t able to ping one container from the other.
Apart from updates of DSM I also upgraded the internal memory. Don’t think this has anything to do with the problem but you never know

Source: Docker Questions

LEAVE A COMMENT