Bridging made easy

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This page covers how to set up a simple bridge. This is probably the most common way to set up bridging in a small home or office network. Let's start with what is needed.

We'll need:

After having checked these prerequisites identify the ethx names of the ethernet NICs that will comprise the bridge. Let's say we have a scenario where eth0 is our external interface and eth1 and eth2 will be our internal bridge. First, "null" these interfaces by editing their respective configuration files in /etc/sysconfig/network-scripts:

ifcfg-eth1

  DEVICE=eth1
  BOOTPROTO=none
  ONBOOT=yes

ifcfg-eth2

  DEVICE=eth2
  BOOTPROTO=none
  ONBOOT=yes

The interfaces will now get "empty" adresses on boot. Now let's edit the bridge interface:

ifcfg-br0

  brctl addbr br0 2&> /dev/null
  brctl addif br0 eth1 2&> /dev/null
  brctl addif br0 eth2 2&> /dev/null
  brctl stp br0 off 2&> /dev/null
  DEVICE=br0
  ONBOOT=yes
  BOOTPROTO=static
  IPADDR=192.168.0.1
  NETMASK=255.255.255.0

Now just run /etc/rc.d/init.d/network restart to bring up your bridge, and reconfigure filtering and routing scripts to act on the interface "br0" instead of what you had there earlier.

It's actually that simple. If you have more interfaces just list them after brctl addif br0 eth2. The redirect to /dev/null is because this is actually an ugly hack and as such will spew some errors when the network is restarted or stopped. The command brctl stp br0 off disables spanning tree protocol because we only need the simple switching functions of the bridge in this case.

See also