Docker Swarm Network Overlay DNS Resolv not working (Docker 1.11.1)

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Docker Swarm Network Overlay DNS Resolv not working (Docker 1.11.1)

I was running a docker swarm network overlay. It was using the company internal dns to resolv (10.0.0.1)

I created the network using:

docker -H :4000 network create test

 docker -H :4000 network inspect test 
[
    {
        "Name": "test",
        "Id": "29b9a2cb98de53fb48c2233c91ed364b27db49c2718dd9be6b9da70ac8f9c48a",
        "Scope": "global",
        "Driver": "overlay",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "10.0.0.0/24",
                    "Gateway": "10.0.0.1/24"
                }
            ]
        },
        "Internal": false,
        "Containers": {},
        "Options": {},
        "Labels": {}
    }
]

Now, when starting a container using the network, DNS resolution failed.

docker -H :4000 run -it --net=test busybox bash

ping google.com.... failed

Solution:

The docker network test has the same subnet ip address as our company wide network (both 10.0.0/24) Therefore, the docker network (Docker embedded DNS server) could not resolv to the correct 10.0.0.1 DNS Nameserver

Our Solution was, to create another network with a different subnet adress thaan 10.0.0/24:

docker -H :4000 network create test2
docker -H :4000 network inspect test2
[
    {
        "Name": "test2",
        "Id": "b1e4a1c046e78eb0db54d6bac153be798551a148462d3d73db44d47ab5072c27",
        "Scope": "global",
        "Driver": "overlay",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "10.0.1.0/24",
                    "Gateway": "10.0.1.1/24"
                }
            ]
        },
        "Internal": false,
        "Containers": {},
        "Options": {},
        "Labels": {}
    }
]

Now, when starting a container using the network, DNS resolution works :).

docker -H :4000 run -it --net=test busybox bash

ping google.com.... failed

How Did I debug?

On the host, I ran tcpdump to intercept all DNS traffic:

tcpdump -vvv -s 0 -l -n port 53 | tee /tmp/dns.cap

When trying to ping google.com, it did not show up in the host DNS tcpdump logs. Therefore I was sure, docker was the issue.