Subject: [pim] TTL value of 1 for some PIM-SM messages

From: "" <[email-masked]>
Date: Thu, 2 Sep 2004 07:00:52 -0400 (EDT)

Hi All,

I would like to know why a TTL value of 1 is used for Register and

C-RP ADV mesgs. whereas, a gretaer TTL value is used for other control mesgs.

Also 

- why is the upstream neighbor addr. included in JOIN-PRUNE messages ?

- Normally, the PIM router knows whom it is targetting the message to

  For e.g it knows that it should forward Join message to the next 

  router in the path to the RP. So, what is the need to have a 

  multicast addr. in the dest . addr. Can't we just restrict 

  multicast addresses to IGMP hosts ?

Regards,

Arut

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From: "Rajesh Babu Nataraja" <[email-masked]>
Date: Thu, 2 Sep 2004 17:21:51 +0530

On your first point  Its been a while I read the draft. But arut, Are you
sure you did not read it the other way.
Though I coult not understand your Also query .it is necessary for the
over-ride and suppression scenarios.

-rajesh.

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From: Christopher Thomas Brown <[email-masked]>
Date: Thu, 02 Sep 2004 15:42:14 -0400

On Thu, 02 Sep 2004 07:00:52 EDT
>C-RP ADV mesgs. whereas, a gretaer TTL value is used for other control mesgs.

You have this reversed. Register messages and C-RP Advertisement messages
(as well as Register STop) are unicasted and may travel multiple hop to
reach the distination so the TTL should be greater than 1. Other control
messages are multicast to the link local group ALL-PIM-ROUTERS. Since
they are not intended to be forwarded (and should not be forwarded)
they are given a TTL of 1.

>- why is the upstream neighbor addr. included in JOIN-PRUNE messages ?

PIM does not require that a router keep track of all interested downstream
routers. So when a router sends a prune to the upstsream its other neighbors
need to be able to process the prune so that they may override the prune
by sending a join. So this message must be multicasted for all neighbors
to process it. As such it needs a field to indicate for which neighbor the
message it intended.

Chris