Changing the IP range for docker0

Lately, I’ve been tinkering a lot with docker. Mostly, I’ve been doing it for work at The Linux Foundation. But I do have a desire to have docker instances on my local box for distros which I do not run.

While doing some testing for work on my personal laptop, I noticed that the network which docker uses for it’s bridge, aptly named docker0, was in the same network as one of our VPNs.

# ip a s docker0
7: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 ...
 link/ether fe:54:00:18:1a:fd brd ff:ff:ff:ff:ff:ff
 inet 172.17.41.1/16 brd 10.100.72.255 scope global docker0
 ..snip..

# ip a s tun0
139: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1412 ...
    link/none 
    inet 172.17.123.32/24 brd 172.17.224.255 scope global tun0
       valid_lft forever preferred_lft forever

As you can tell, the docker0 network bridge covers all of the tun0 network. Any time I would attempt to ssh into one of the systems inside the VPN, it would time out. I was left wondering why for a few moments.

Luckily, it’s very easy to fix this problem. All that is needed is a defined bridge for docker0 and to restart the docker service. Here’s what to do:

First, stop docker:

# service docker stop
Redirecting to /bin/systemctl stop  docker.service

Next, create the network bridge file. You can choose any IP range you like. On Fedora 19, it looks like this:

# cat /etc/sysconfig/network-scripts/ifcfg-docker0 
DEVICE="docker0"
TYPE="Bridge"
ONBOOT="yes"
NM_CONTROLLED="no"
BOOTPROTO="static"
IPADDR=10.100.72.254
NETMASK=255.255.255.0

Restart your network services.  NOTE: service network restart may be needed.

# service NetworkManager restart
Redirecting to /bin/systemctl restart  NetworkManager.service

The docker0 bridge should now be in a range outside the VPN.

# ip a s docker0
7: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 ...
    link/ether fe:54:00:18:1a:fd brd ff:ff:ff:ff:ff:ff
    inet 10.100.72.254/24 brd 10.100.72.255 scope global docker0

Starting new containers with docker should get IP addesses in the above range:

# service docker start
Redirecting to /bin/systemctl start  docker.service

# docker run -i -t herlo/fedora:20 /bin/bash
bash-4.2# ip a s eth0
141: eth0: <BROADCAST,UP,LOWER_UP> mtu 1412 ...
    link/ether fa:5f:e3:8d:61:f2 brd ff:ff:ff:ff:ff:ff
    inet 10.100.72.2/24 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::f85f:e3ff:fe8d:61f2/64 scope link 
       valid_lft forever preferred_lft forever

SUCCESS!

Cheers,

herlo