Docker Networking (Connect, Disconnect)

In this guide, we will see how we can connect multiple networks to a container and how to disconnect them.

Create a container with the bridge network-

gaurav@learning-ocean:~$ docker container run -it --network bridge ubuntu:14.04 bash
root@1a5752e79f47:/# ifconfig
eth0      Link encap:Ethernet  HWaddr 02:42:ac:11:00:02
          inet addr:172.17.0.2  Bcast:172.17.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:7 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:606 (606.0 B)  TX bytes:0 (0.0 B)
lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
root@1a5752e79f47:/#

It has been allocated with eht0 NIC. If we want to allocate it with one more NIC interface, create one more network with

Let's create a network with name ‘test’-

gaurav@learning-ocean:~$ docker network create test
348f7295d3cac9a633c0a8619879a55c0371691c454139f3b9f3f5e7693a239d

By default, a bridge network is created.

gaurav@learning-ocean:~$ docker network ls
NETWORK ID     NAME      DRIVER    SCOPE
6c51373f78ac   bridge    bridge    local
3a33f83c3663   host      host      local
e4ebd601732c   none      null      local
348f7295d3ca   test      bridge    local
gaurav@learning-ocean:~$

To attach this network to the container, use below command -

$ docker network connect <network_name> <container_name>

example:

gaurav@learning-ocean:~$ docker container ls
CONTAINER ID   IMAGE          COMMAND   CREATED         STATUS          PORTS     NAMES
1a5752e79f47   ubuntu:14.04   "bash"    3 minutes ago   Up 23 seconds             focused_heisenberg
gaurav@learning-ocean:~$ docker network connect test 1a5752e79f47
gaurav@learning-ocean:~$

Another network has been attached to the container with name as eth1-

gaurav@learning-ocean:~$ docker container exec -it 1a bash
root@1a5752e79f47:/# ifconfig
eth0      Link encap:Ethernet  HWaddr 02:42:ac:11:00:02
          inet addr:172.17.0.2  Bcast:172.17.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:12 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:976 (976.0 B)  TX bytes:0 (0.0 B)
eth2      Link encap:Ethernet  HWaddr 02:42:ac:13:00:02
          inet addr:172.19.0.2  Bcast:172.19.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:906 (906.0 B)  TX bytes:0 (0.0 B)
lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
root@1a5752e79f47:/#

Now to disconnect this network, you can simply replace the connect with disconnect-

$ docker network disconnect <network_name> <container_name>

Example:

gaurav@learning-ocean:~$ docker network disconnect test 1a5752e79f47
gaurav@learning-ocean:~$

Verifying the same by running ifconfig command on the container-

gaurav@learning-ocean:~$ docker container exec -it 1a bash
root@1a5752e79f47:/# ifconfig
eth0      Link encap:Ethernet  HWaddr 02:42:ac:11:00:02
          inet addr:172.17.0.2  Bcast:172.17.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:12 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:976 (976.0 B)  TX bytes:0 (0.0 B)
lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
root@1a5752e79f47:/#

Note: Connecting a container with none network with another network

You cannot connect a container with none network with another network. You will below error even you try to-

Error response from daemon: Container cannot be connected to multiple networks with one of the networks in private (none) mode

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