xen network problem

[Geert Hendrickx <ghen%netbsd.org@localhost>]

Hi, 

I've started playing a bit with Xen, and it mostly seems to work well,
except for networking.  The domain0 kernel detects the network card, I can
ifconfig it, it can even see when the network cable is (un)plugged, but
there is no traffic.  The network interface is up, I can ping myself, but
when I try to ping others, tcpdump shows ARP requests, but no replies.
Networking between domains doesn't work either.  

Any clues?  

        Geert

PS: please CC me any replies, thanks.