[libvirt] device type 'interface' cannot be attached

I'm using libvirt 0.6.2 on F11 x86_64 and CPU supports hw virtualization. When I try to do 'virsh attach-interface ...' I get an error that the function is not supported by the hypervisor device type 'interface' cannot be attached. Is this command not supported? Or is there something special I need to do? I found it in the man page. -Gerry