I'm using Xen with libvirt and trying to set it up on a bridged interface. I am able to install an OS and everything works as I would expect. If I save the xml output from "virsh dumpxml guest", edit the mac address for the interface, and then define the domU with this new xml file I find that traffic is no longer forwarded from the vif0.0 interface to br0. The ifcfg-eth0 file on the guest was automatically updated to reflect the new mac address and the ifconfig output looks the same. Does anyone know why this is happening or how to properly change the mac address for a libvirt configuration?
udev manages devices and you changed the network device. so the kernel can't recognize it because the old mac address doesn't exist.
Remove the file
/etc/udev/rules.d/70-persistent-net.rules then reboot.