Subject: [pim] RP behaviour on a LAN

From: viorel peca <[email-masked]>
Date: Mon, 19 May 2003 15:45:14 +0200

Hi,

Please consider the following configuration:
On a LAN there are RP, S-DR and IR.

                  RP
                    |
------------------------------------
          |                        |      ^
      S-DR                  IR     | (*,G) Join
         |                        |       |
     Source            Reciever

The receiver behind the IR Sends a *,G join. Then the source start
sending, S-DR sends registers and RP sends S,G join and register stop.
Mcast traffic flows natively on LAN. In RP mcast routing table has an
entry for *.G with no iif (Null) and 1 oif and an S,G entry with one iif
(the same as oif of *,G of course ) and no oif.
From now on consider 2 scenarios:
1) there is a ddr behind IR, who has to send S,G joins to trigger the
spt switch over.

2) there is no S,G join to trigger the spt switch over.

What RP should do: send S,G prune towards source because the oif=iif or
not?

Best Regards,

Viorel Peca

---

From: John Zwiebel <[email-masked]>
Date: Mon, 19 May 2003 10:46:39 -0700

> On a LAN there are RP, S-DR and IR.

An implementation may choose to say that the (*,G) has a NULL IIF, but
that may cause problems for you.  Even the RP has to choose which 
interface
is the RP address -- which would be the IIF.

You have a classic "turn-around" router case here.
As long as the RP is getting (*,G) joins without an (S,G,RP-bit) prune,
it needs to continue sending (S,G) joins toward the source.

Whether you realize this with the X-flag (as cisco does) or by placing
the IIF in the OIF list, is up to the implementor.

> <viorel.peca.vcf>

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