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
:/
 
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
:/
 
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
:/
 
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