Subject: mrouted and unicast tunnels
To: None <>
From: Stephen Borrill <>
List: tech-net
Date: 03/07/2006 20:21:12
I'm trying to get mrouted working between two 3.0 hosts which are linked 
with an OpenVPN tunnel. Both hosts are running as NAT gateways for their 
respective internal networks. Routing is set up over the OpenVPN tunnel 
correctly (i.e. any machine on on one site can talk to on the other).

One end has:
name LOCAL
phyint ex0 boundary LOCAL

The other:
name LOCAL
phyint fxp0 boundary LOCAL

mrouted -d 3 at each end shows they are speaking:
20:12:58.881 SENT neighbor probe     from   to
20:12:58.881 SENT neighbor probe     from   to
20:13:01.796 RECV route report       from   to
20:13:01.796 Updating 4 routes from to
20:13:01.832 RECV neighbor probe     from   to

tcpdump -ni tun0 (i.e. the OpenPVN link) shows the multicast traffic is 
being forwarded over the link each way:
20:09:44.687152 IP > IP > UDP, length: 417 (ipip-proto-4)
20:09:44.688759 IP > IP > UDP, length: 1023 (ipip-proto-4)

However, on the local networks only the local multicast traffic is seen, 
the tunnelled packets are not forwarded. There's probably just some silly 
step I'm missing. Any ideas?