how-to Create Virtual Bridge
This is kinda old, but pretty helpful. I find myself referring to these notes often so I thought I would share
1. Create Virtual Bridge
# brctl addbr br0
verify with: brctl show
2. Create network script, edit /etc/sysconfig/network-scripts/ifcfg-br0
DEVICE=br0
TYPE=Bridge
BOOTPROTO=dhcp
ONBOOT=yes
3. Edit eth0 network script add…
BRIDGE=br0
4. Add your physical interface to the bridge
# brctl addif br0 eth0
verify with: brctl show
5. Restart your network services
# service network restart
References:
http://www.linux-kvm.com/content/using-bridged-networking-virt-manager
huffisland.wordpress.com 
Was talking with my friend Gareth Jenkins today and he was experiencing an unexpected issues where once the bridge is set up doing a “ifup br0” failed because eth0 was down. We both expected that once the bridge is set up “ifup br0” would also bring up eth0 which looks not to be the case.
TO fix this either set both eth0 and br0 to “onboot=yes” and restart networking “service network restart”
or if you’re using RHEL or Fedora, you can use “virsh iface-start br0”, which, under the covers, calls netcf, and netcf ifup’s all the subordinate interfaces before bringing up the main interface.
05/16/2012 at 10:11 AM