Subject: PR-bit and (S,G) Poison-Reverse Message

From: [email-masked]
Date: Tue, 27 Mar 2001 12:39:08 -0800

Hi all,

     Can someone explain to me the purpose of PR-bit in (S,G) state and the use
of Poison-Reverse messages in the current BGMP spec?  Some example scenarios
will definitely help.

Thx,
James Huang

---

From: [email-masked]
Date: Thu, 29 Mar 2001 10:54:28 -0800

From:  James Huang@MITEL on 03/29/2001 10:54 AM PST
Hi ALL,

     Consider the following scenario where X, Y, Z, S, G are domains.  S is the
domain where the source s of (s, g) traffic resides.  G is the root domain
containing g.  Domain Y has receivers for (*, g) traffic and runs DVMRP as its
M-IGP.

                G ======= Y
                |         |
                |         |
                X         Z
                |         |
                |         |
                S --------+

Lets use the notation of BR(A,B) to denote the boarder router in domain A which
connects to domain B.

Suppose the best route from Y to S is through Z and the best route from S to G
is through X.  Then the boarder router BR(Y,Z) will send a join(s, g) toward s
and establish a source-specific branch.  When (s, g) starts arriving through the
source-specific branch, BR(Y,Z) will send a prune(s, g) to BR(Y,G).  When
BR(Y,G) receives the prune message, it will stop sending (s,g) traffic it
receives from the shared tree into domain Y.

Here is my question.
When BR(Y,G) receives the (s, g) traffic injected into domain Y by BR(Y,Z), what
prevent it from forwarding the traffic up toward G?  If it does that, receivers
in G will receive duplicate copies of (s, g) traffic, one copy from S - X - G,
another copy from S - Z - Y - G.

Thanks for answering this question for me.

-- James Huang

[email-masked] on 03/27/2001 01:39:08 PM

To:   [email-masked]
cc:   [email-masked], [email-masked], [email-masked], James
      Huang/USA/Mitel@Mitel

Subject:  PR-bit and (S,G) Poison-Reverse Message

Hi all,

Thx,
James Huang