ubuntu add bridge network with libvirt

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_Installation_Guide/sect-Virtualization_Host_Configuration_and_Guest_Installation_Guide-Network_Configuration-Network_Configuration-Bridged_networking_with_libvirt.html

Bridged networking (also known as physical device sharing) is used to dedicate a physical device to a virtual machine. Bridging is often used for more advanced setups and on servers with multiple network interfaces.

To create a bridge ( br0) based on the  eth0 interface, execute the following command on the host:

# virsh iface-bridge eth0 br0

Important

NetworkManager does not support bridging. NetworkManager must be disabled to use networking with the network scripts (located in the  /etc/sysconfig/network-scripts/ directory).

# chkconfig NetworkManager off
# chkconfig network on
# service NetworkManager stop
# service network start

If you do not want to disable  NetworkManager entirely, add " NM_CONTROLLED=no" to the  ifcfg-* network script being used for the bridge.

if there is error:

libvirtError: this function is not supported by the connection driver: virInterfaceDefineXML

That's because you've libvirt compiled with udev rather than netcf. The  netcf is the only one backend that knows how to create a new interface.

Install netcf and rebuild libvirt and you should be able to create  interfaces via libvirt.

https://www.redhat.com/archives/libvirt-users/2014-March/msg00091.html