Comment 4 for bug 588731

There seems to be an issue with kvm virtual network interface being connected to a in-kernel bridge implementation.

When you configure networking that way the bridge port comes up when the kvm instance is started.

As the time from the kvm start to entering the netboot rom is minimal and the timeout before the bridge starts forwarding on new ports is long this may cause the machine never getting an address.

If you are using a bridge try setting the forwarding delay to a small value like:

iface vmbridge inet static
 bridge_ports <probably should put some network interface name here - undocumented>
 address 10.10.10.1
 netmask 255.255.255.0
 post-up brctl setfd vmbridge 3