Subject: [pim] draft-hemige-pim-improved-assert

From: "Venu Hemige" <[email-masked]>
Date: Fri, 11 Nov 2005 10:56:25 -0800

Bill,

I wanted to better understand the (S,G)/(*,G) problem you pointed out in
the meeting yesterday. The scenario talks about a (*,G) tree and an
(S,G) tree in the network. There is a policy configured on some upstream
router to not forward (S,G) traffic down the (S,G) tree (or sub-tree).
But the objective is still to forward (S,G) traffic via the shared tree
to those receivers that have joined the (*,G) tree. Because of such a
policy in place and current PIM-SM behavior, the (S,G) traffic would
flow down the (*,G) tree for the life of the stream. Is that the
intended behavior? Why is such a behavior desired?

Thanks,

-Venu

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From: "Venu Hemige" <[email-masked]>
Date: Tue, 22 Nov 2005 13:45:38 -0800

Hi Bill, 

<Resending email with additional comments>

The behavior in PIM-SM is completely different depending on whether such
a policy is configured before SPTBit(S,G) becomes true on a router vs if
such a policy is configured after SPTBit(S,G) becomes true on a router.

1.       If the policy is configured *before* SPTBit(S,G) becomes true,
then the traffic is forwarded down the shared tree for the life of the
stream.

2.       If the policy is configured *after* SPTBit(S,G) becomes true,
then the traffic is black-holed for the remaining life of the stream.
This is because the (*,G) receivers would have switched to the SPT tree
and sent (S,G,rpt) prunes on the shared tree. SPTBit(S,G) will only
become false if JoinDesired(S,G) becomes false. 

Given this conflicting behavior in PIM-SM, I fail to understand what the
desired behavior is. And why it is bad to elect an assert winner before
SPTBit becomes true. Could you please correct me if I am missing
something?

Regards,

-Venu

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Venu Hemige
Sent: Friday, November 11, 2005 10:56 AM
To: 'Bill Fenner'
Cc: [email-masked]
Subject: [pim] draft-hemige-pim-improved-assert

Bill,

Thanks,

-Venu