guest <-> guest communication problem

Very sorry for bugin' you all, but I have an issue someone may be able to fix.

I have 3 guests on a single host. This host is using bridged networking. The guest VMs can talk to the host and any other computer on the hosts network. They can even get outside to the internet.

Likewise,
the host - and any other computer on the hosts network can communicate to the guests fine and without problem.

However, none of the guests can talk
to another guest. I have checked and they are all on the same bridge (each machine using it's own tap interface) and all use the same vnet.

Heres an
example command I am using:

kvm -drive file=disk.qcow2,index=0,media=disk,if=virtio,boot=on -m 512 -net tap,vlan=0,script=no,ifname=tap0,downscript=no -net nic,vlan=0,model=virtio
-net tap,vlan=1,script=no,ifname=tap1,downscript=no -net nic,vlan=1,model=virtio -smp 1 -monitor unix:/monitor,server,nowait -vnc 0.0.0.0:2 -name ns1 -pidfile pid -no-shutdown -daemonize

I have ensured
that iptables is correct:

iptables -A INPUT -i tap0 -j ACCEPT

iptables
-A INPUT -i tap0 -j ACCEPT

Note: this is Debian Lenny. Strangely enough,
this worked fine under my desktop tests (Ubuntu 9.10) using the same exact config.

Dean M. Rantala
Programmer / Server Administrator
Cell: (931) 284-7384
Home: (931) 268-4763