Comment 12 for bug 865515

From my experience I think there was a time when libvirt would only allow the use of networks defined with libvirt. Nowadays (at least starting with Trusty/12.04) it is picking up and allowing the use of network interfaces outside the control of libvirt. So I am not sure this is still in need.

Not sure whether the creation of the NAT bridge is challenged as something that should not be done on server. It can be "not used". In addition there appear to be choices for macvtap on host network devices or when the host defines bridges (/etc/network/interfaces style) those can be used. Also not really sure about a script. Maybe an example of how to define a bridge manually. But mostly it seems like admins are rather expected to want to do it on their own.