Subject: [pim] Regarding (s,g) and (*,g) assert mechanism...

From: snibad <[email-masked]>
Date: Fri, 05 Oct 2007 10:02:05 +0530

Hi all , I have a doubt in assert mechanism ... why is the following
paragraph specified

in PIM RFC is needed ... anyone pls shed some light on it ...

"It is important to note that NO TRANSITION CAN OCCUR in the (*,G) state

machine as a result of receiving an Assert message unless the (S,G)

assert state machine for the relevant S and G is in the "NoInfo" state

after the (S,G) state machine has processed the message.  Also NO

TRANSITION CAN OCCUR in the (*,G) state machine as a result of receiving

an assert message if that message triggers any change of state in the

(S,G) state machine.

For example, if both the (S,G) and (*,G) assert state machines where in

the NoInfo state when an Assert message arrives, and the message causes

the (S,G) state machine to transition to either "W" or "L" state, then

the assert would not be processed by the (*,G) assert state machine.

Another example: if the (S,G) assert state machine is in "L" state when

an assert message is received, and the assert metric in the message is

worse than my_assert_metric(S,G,I), then the (S,G) assert state machine

will transition to NoInfo state.  In such a case if the (*,G) assert

state machine were in NoInfo state, it might appear that it would

transition to "W" state, but this is not the case because this message

already triggered a transition in the (S,G) assert state machine."

thanks

sinbad

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From: Christopher Thomas Brown <[email-masked]>
Date: Mon, 8 Oct 2007 20:55:39 -0700

> an assert message if that message triggers any change of state in the

If the (S,G) assert winner sends a (*,G) assert then the losers will
see the assert as inferior and transition to No Info. Additionally,
you only want to cause churn to the (*,G) tree if there are two or more
routers actually forwarding active traffic on the (*,G) tree. In the loser
transition, this may not be the case.

On receiving such and it causes a transition in the (S,G) state machine
its one of the following:
a) no info -> winner
b) winner -> winner
c) loser -> no info (if the winner sent it)

So you don't process it if the router transitions to winner, is the winner,
or the winner sent the assert.

> the assert would not be processed by the (*,G) assert state machine.

This is case a from above.

This is misleading there is no transition to "L" from No Info.

> already triggered a transition in the (S,G) assert state machine."

This is case c from above.

This is misstated. It will only transition to No Info if the assert
is worse than my_assert_metric(S,G,I) and it is received from the
current assert winner.

Chris