Problems with network connectivity and docker on Synology - docker

Question

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

Answer 1

I had a similar issue, have you tried disabling the firewall rules on the NAS?