Setting Up a Bridged Network Interface for KVM in Ubuntu

The process for setting up a network bridge for KVM in Ubuntu is actually fairly simple. For the purposes of this demo, we will assume that you already have KVM/QEMU installed from the Ubuntu Repos and that you are not using Network Manager. If you are using Network Manager, you must disable it prior to following these instructions. I am using  Ubuntu Server 11.10 (Oneiric Ocelot), but this should work for 10.04 (Lucid Lynx), 10.10 (Maverick Meerkat) and 11.04 (Natty Narwhal).