Network trouble with bridges

[Andreas Neth <ane+netbsd%n3th.de@localhost>]

Hello together,

I'm running NetBSD 3.0 along with xen2, and today I ran into trouble  
with my setup.

Up to now, I had dom0 export a disk via nfs to the domUs. I now  
charged one of the domU's with being the nfs-server.
I have two bridges configured, bridge0 shares an external wm0 with  
all domUs and bridge1 creates a private lan with dom0's tap0.

Traffic passing from other physical machines passes just fine to the  
domU's, but anything between 2 domUs has a delay of about 20 seconds.  
ICMP works, but does not even show the latency, instead reportint an  
RTT of 0,4ms.
The delay even happens when pinging the domU by itself

Sadly, nfs and everything else now times out with

mount_nfs: bad MNT RPC: RPC: Timed out

This even happens with the GENERIC XEN0 Kernel.
I have ruled out the MACs being the troublemakers, all begin with aa.

Any clues?

Thanks in advance,
Andreas