Subject: directly connected sources

From: Tom Pusateri <[email-masked]>
Date: Tue, 04 Sep 2001 14:10:20 -0700

There is a case when a source is directly connected to two or more
RP's that I wanted to bring up. These two or more RP's are running
PIM sparse mode and MSDP peering with each other (as in the Anycast
RP case).

In this case, it isn't necessary to register to the RP since the source
is directly connected to the RP. Currently, the MSDP spec doesn't
say anything regarding originating SA's for directly connected sources,
it only mentions generating an SA based on receiving a register.

If, internally, an RP registers to itself, then we should see only one
register (from the DR) and only one MSDP speaker will originate the SA
and everything should work as expected.

I don't know how other implementations work but internally, we don't
send registers for sources directly connected to the RP.

So if there are two RP's on a shared network with a source also attached,
then one of the RP's will be the DR and it should be originating the MSDP
SA but the other shouldn't. This gets trickier when other PIM routers are on
the shared network as well but aren't RPs. Using the DR election rules,
it is possible to select either a DR that is also an RP that will originate
the SA or another  PIM router that is the DR but isn't an RP that will register
to the RP. The important part is for an RP that isn't a DR on a shared
network to not originate SA's for directly connected sources on that shared
network.

While I think most implementors would figure this out, it was not obvious
to me at first and so I thought I would mention it in case either spec
wants to include this discussion.

Thanks,
Tom

---

From: Toerless Eckert <[email-masked]>
Date: Tue, 4 Sep 2001 23:43:00 -0700

What's the problem of duplicate SA announcements for these, hmmm... either
local issues (anycast-RP configs) or pathetic setups (sources on MIX
or ISP-peering-link) ? I particularily don't see a bad thing in a source
being registered for by all RPs on a LAN. What am i missing here ?

Cheers
	Toerless