Subject: [pim] Regarding the scenarios which would trigger the assert cancel message

From: deepa ramar <[email-masked]>
Date: Fri, 23 Sep 2011 18:21:45 +0530

Hi,

I am a little confused regarding the scenarios which would trigger the
Assert Cancel message.

Please consider the attached topology.
Let us assume that R3 is the assert winner for (S,G). We have created a
static route
at R3 with R4 as the next hop RPF(S). As per my understanding, the Assert
Cancel could
be triggered if

 (a) R3(I32) becomes that RPF(S) as per RFC 3973 Sec 4.6.4

 The state machine uses the following macro : CouldAssert(S,G,I) = (RPF
Interface (S) != I)

(b) R3( Assert Winner) changes the state to NO-INFO as per RFC 3973 Sec
4.6.4.2

            CouldAssert(S,G,I) -> FALSE

       This router's RPF interface changed, making CouldAssert(S,G,I)
       false.  This router can no longer perform the actions of the
       Assert winner, so the Assert state machine MUST transition to
       NoInfo (NI) state, send an AssertCancel(S,G) to interface I,
       cancel the Assert Timer (AT(S,G,I)), and remove itself as the
       Assert Winner.

(and)

 (c) Router R3 is going down and is going to stop forwarding data for (S,G)
as per RFC 3973
      Sec 4.6.5

      An Assert winner for (S,G) sends a cancelling assert when it is
      about to stop forwarding on an (S,G) entry.  Example: If a router
      is being taken down, then a canceling assert is sent.

My doubt is .... what would happen if the static route to reach S is
removed at R3. Would this trigger an
Assert Cancel? If not, How would the Assert Loser R2 come to know that
the R3 does not have unicast route
to R5 anymore and that he needs to start forwarding traffic for (S,G)?

Any light on this concept would be greatly appreciated.

Regards,
Dheepa P R

---

From: deepa ramar <[email-masked]>
Date: Fri, 23 Sep 2011 18:23:26 +0530

Hi,

(and)

Regards,
Dheepa P R

---

From: Rishabh Parekh <[email-masked]>
Date: Fri, 23 Sep 2011 14:40:18 -0700

Deepa,
Removal of static route on R3 could result in RPF_Interface(S) change from
I31 to I32 (if R5 is reachable via R2) . CouldAssert(S,G,I32) would
transition from TRUE to FALSE and AssertCancel(S,G) would be originated on
I32.
However, if R5 is no longer reachable from R3, the CouldAssert(S,G,I) macro
condition check should really be CouldAssert(S,G,I) = (RPF_Interface(S) !=
NULL && RPF_Interface(S) != I) for CouldAssert(S,G,I32) to transition to
FALSE (and therefore originate AssertCancel(S,G) ).

My 2 cents,
-Rishabh.

On Fri, Sep 23, 2011 at 5:51 AM, deepa ramar <[email-masked]> wrote:

> My doubt is .... what would happen if the static route to reach S is removed at R3. Would this trigger an
> Assert Cancel? If not, How would the Assert Loser R2 come to know that the R3 does not have unicast route
>
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