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Set up a network bridge – Ubuntu 12.04 LTS +

1. Installation

In order to set up a network bridge, the package bridge-utils needs to be installed. Install it with:

sudo apt-get install bridge-utils

The output should look similar to below:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
  bridge-utils
0 upgraded, 1 newly installed, 0 to remove and 16 not upgraded.
Need to get 28.6 kB of archives.
[...]
Preparing to unpack .../bridge-utils_1.5-9ubuntu1_amd64.deb ...
Unpacking bridge-utils (1.5-9ubuntu1) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up bridge-utils (1.5-9ubuntu1) ...

This is mandatory

If bridge-utils isn’t installed before moving on, it won’t be possible to bring up the new bridge and will likely result in loss of network access entirely.

2. Configuration

With the bridge-utils package installed, begin by opening /etc/network/interfaces in a text editor. I like vim:

sudo vim /etc/network/interfaces

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

This is the default interfaces file. Within this file add a new bridge named br0. The simplest edit to make is as follows (note the emphasis):

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto br0
iface br0 inet dhcp
    bridge_ports eth0

iface eth0 inet manual

This will set the eth0 interface to manual and create a new bridge that piggybacks directly off it.
If you wish to create a static interface while you’re editing this file, the following may help you:

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto br0 
iface br0 inet static
        address 192.168.0.44
        netmask 255.255.255.0
        network 192.168.0.0
        broadcast 192.168.0.255
        gateway 192.168.0.1
        # dns-* options are implemented by the resolvconf package, if installed
        dns-nameservers 8.8.8.8 8.8.4.4 #google-dns
        dns-search localdomain.local #optional-line
        # bridge options
        bridge_ports eth0
iface eth0 inet manual

Following any edits, it’s a good idea to restart the interfaces to force the changes to take place. Obviously if you’re connected via SSH this will disconnect your session. You’ll need to have physical access to the machine/VM.

sudo ifdown eth0 && sudo ifup eth0 && sudo ifup br0

Running ifconfig on the CLI will now confirm the changes have been applied:

jason@ubuntu-lxdzfs:~$ ifconfig
br0       Link encap:Ethernet  HWaddr 00:0c:29:2f:cd:30  
          inet addr:192.168.0.44  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe2f:cd30/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2235187 errors:0 dropped:37359 overruns:0 frame:0
          TX packets:111487 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:2108302272 (2.1 GB)  TX bytes:8296995 (8.2 MB)

eth0      Link encap:Ethernet  HWaddr 00:0c:29:2f:cd:30  
          inet6 addr: fe80::20c:29ff:fe2f:cd30/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:161568870 errors:0 dropped:0 overruns:0 frame:0
          TX packets:132702 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:185204051222 (185.2 GB)  TX bytes:23974566 (23.9 MB)

[...]

If for any reason no changes have applied, or ifconfig returns no IPv4 addresses at all, please double check the configuration and optionally give the host a reboot.

3. Conclusion

Congratulations, you now have a bridged network with which to provide direct LAN access to your virtualised guests!

I hope this has been helpful, as always I’m @jasonbayton on Twitter, @bayton.org on Facebook and will also respond to comments below if you have any questions.

If you spot any errors in the above, or have suggestions on how to improve this guide, feel free to reach out.

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