Re: [pim] Simple join failure notification for PIM-SM multicast routing

[Beau Williamson <bwilliam at cisco.com>]

Hoerdt, et al,

I did a quick review of the draft as well as reading some of Pekka's
and Toerless' comments.

It seems to me that what you are calling for would best be served by a
PIM-NACK message.  We've talked about doing PIM-ACK's to do reliable
PIM signalling for years but most of this has centered on the use of
PIM-ACK messages.

While I like the fundament concept of being able to signal tree failure,
I would agree with Pekka and Toerless that we have a ways to go to put
all the items in place to do this and make it effective.  

For example, let's say that there is a temporary outage or topology
change that results in a Periodic Join failing to be processed. If we
send this PIM-NACK message down the tree, is the last hop router supposed
to send a Prune and delete the mroute state in order to tear down the now
useless tree?  What if the outage has been rectified a short time
later.  How does the last hop router know to "try
again".

Having said the above, I don't want to discourage you from pursuing this.
All I wanted to point out is that it seems to me that a new PIM control
packet would be better served to accomplish this.  Ergo, the
PIM-NACK that is propagated down the tree. That and (like Toerless) I'm
not sure exactly how existing hosts and networks would make use of this
information.

Beau Williamson


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