libvirt users - Apr 2010 - Allowing incoming traffic to a virtual network

Hello!

I have some virtual networks defined on a virtualization host (using
libvirt 0.7.7 and kvm 0.12.3) with some virtual bridges (virbr1, virbr2)
which are all plugged into a phisical bridge br0. Now I would like to
allow external hosts to connect to guest machines, but the automatically
created iptables rules forbid it.
I have found this rather old post on the mailing list
http://www.redhat.com/archives/libvir-list/2007-January/msg00048.html
which suggests a "forwarding" element for the network configuration,
but
this seem to be unimplemented.

cheers
Mathias