For everybody who has trouble setting up bridged networking for virtual machines with kvm, qemu, libvirt on ubuntu 11.10 (oneiric ocelot).

There are a few important settings to take care of.

  1. Set up a bridge on your host system 
    Setting up virtualization on Ubuntu with KVM

  2. Disable filtering on your host system
    As can be found on libvirt networking

    The final step is to disable netfilter on the bridge:
    # cat >> /etc/sysctl.conf <<EOF
    net.bridge.bridge-nf-call-ip6tables = 0
    net.bridge.bridge-nf-call-iptables = 0
    net.bridge.bridge-nf-call-arptables = 0
    # sysctl -p /etc/sysctl.conf
  3. Configure your VM
    Setting up virtualization on Ubuntu with KVM

  4. Take care that bridged networking ist enabled on your vm:

    • change interface description to:
      <interface type='bridge'>
      <mac address='[vm-iface-mac-address]'/>
      <source bridge='br0'/>
    • edit your vm-settings:
      sudo virsh edit [vm_name]