I endend up doing the same, I configured the bridge manually and (risking to be a bit OT) if you try to setup BONDING at the same time this post helped me out HUGELY:
http://forum.proxmox.com/threads/2676-bonding-bridging-freez -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/520386 Title: libvirt-bin hypervisor does not support virConnectNumOfInterfaces / unable to create domain with virt-manager using network bridge To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/520386/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs