Subject: interconnecting pim clouds with ipip tunneling

From: Pekka Savola <[email-masked]>
Date: Mon, 26 Mar 2001 22:23:11 +0300 (EEST)

Hello all,

Sorry if this is a wrong forum for this -- please tell of a better one if
this is the case.

DVMRP is not that good a solution for Internet multicasting; people rather
use PIM.  However, every upstream router has to be able to handle rather
recent versions of PIM for this to be an option.  Sometimes this just
can't happen.

Therefore I thought of using IPIP tunneling to establish virtual
connection with the PIM-enabled multicast domain.  This tunnel would only
be used for multicast traffic; no unicast routing would be done through
it.

Are there some flaws to this logic?  Has this kind of thing been done?
Successfully?  Any pointers?

As it is, I tried this quickly with FreeBSD 4.2 and pimd (PIMv2
sparse-mode) vs. Cisco 12.0; the link was established fine, I got
bootstrap and hello messages to flow in both directions but not much
else happened on the wire;  behind the tunnel, no multicast groups were
seen.

Please Cc: as I'm not on the list.  Thanks,
-- 
Pekka Savola                  "Tell me of difficulties surmounted,
Netcore Oy                    not those you stumble over and fall"
Systems. Networks. Security.   -- Robert Jordan: A Crown of Swords

---

From: Pavlin Ivanov Radoslavov <[email-masked]>
Date: Mon, 26 Mar 2001 17:30:19 -0800

> Successfully?  Any pointers?

If you use a virtual connection/tunnel between two routers, this
virtual interface that corresponds to that tunnel must be in the
unicast routing table. To be more specific, the RPF (Reverse unicast
Path Forwarding) check toward the RPs or sources that are in the
other cloud must return that vif. Well, you don't really have to run
unicast routing protocol over that tunnel, or send the unicast pkts
over it; it is that the RPF check has to return the tunnel
vif. Otherwise, all mcast pkts received over that tunnel will be
dropped.
This could be simple with a single tunnel, but the situation gets
more complicated if you have two or more tunnels configured in a
router: how do you know when the RPF check should return tunnel_1 or
tunnel_2?

> else happened on the wire;  behind the tunnel, no multicast groups were

Maybe you have the RPF check problem I described above?

Regards,
Pavlin