Subject: RP on a stick scenario

From: Mathur Sonum-CSM109 <[email-masked]>
Date: Thu, 21 Jun 2001 16:29:06 -0500

When RP has an (S,G) entry with Null OIF and IIF is on a shared link,  which has some other recievers, there is a possibility of data hole. This was one of the issues in RFC 2362 as specified in PIM-SM issue #27: Turnaround rules incompletely specified

	---------------------------------LAN
	|	|	|
	R1	RP	R2----Rcvr
	|
	R3---Sender
	|
	Rcvr

R2 never sends (S,G) Join directly to source (as it never goes to shortest path tree) and RP doesn't send periodic (S,G) Join as its OIF is Null and is not forwarding. This may lead to no data on LAN.

RP needs to have some state (or special flag in (S,G) entry) which indicates that it has to send periodic (S,G) Joins to source to get data on LAN. If this issue has already been resolved in the new spec, please explain how.

Thanks
--
Sonum

---

From: John Zwiebel <[email-masked]>
Date: Thu, 21 Jun 2001 15:26:48 -0700

Mathur Sonum-CSM109 wrote:

If R2 doesn't send (S,G) joins (which you would have had to specifically
configure it to do because even though the IIF for the RPT and the SPT
may
be the same, that has nothing to do with which tree that router is
joined to).

-- then it must be sending (*,G) joins, which means that the RP should 
have a non-NULL olist for the (*,G).

An RP that is receiving a (*,G) join without a (S,G,RP) prune (and R2
has
to be sending the (*,G) join part as long as there is a member and if
it "never joins the shortest-path" as you said then it doens't include
the (S,G,RP-bit) prune in the message) should know that it must continue
to send (S,G) joins for the group.  The specifics on you you want to
make this 
happen are up to you.

[NOTE: any router that receives a JOIN/PRUNE message with only a (*,G)
part
and no (S,G,rp-bit)prune part has received some very important
information
that it should act on.]

Let me say again that if you are looking at RFC2362, you're wasting your
time.

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