Subject: Re: Asserts in PIM-DM

From: Bill Fenner <[email-masked]>
Date: Wed, 4 Nov 1998 21:18:51 PST

I redirected to the PIM mailing list, where this probably belongs.

In message <[email-masked]>you write:
>1. Are the assert messages sent periodically? That is, as and when a   
>   Multicast datagram is received on a outgoing interface,even if
>   the interface is pruned for some reason, should an assert
>   message be sent?

Interfaces that are pruned are not considered to be outgoing interfaces,
so interfaces that are pruned due to Asserts (or any other reason) will
not send Assert packets until the prune times out.  This should probably
be more explicit in the spec.

>2. Ref. section 5.5 in draft-ietf-pim-v2-dm-00.txt . In paragraph titled,   
>   'Asserts received on incoming interface' why should we revert
>   back to the RPF lookup neigbor when the Assert Timer expires.
>   The draft doesn't specify why an Assert timer needs to be
>   started even though it has been recommended to start one.

This may not be the only reason, but when Asserts happen due to
multiple unicast routing protocols, timeouts are necessary to adapt
to changes in unicast routing.  Since the two routers are participating
in different routing protcols, the only way for PIM to adapt to changes
in the underlying routing is to periodically time out and re-resolve
any conflicts.

  Bill