Subject: DVMRP Prune question

From: Magesh Kannan <[email-masked]>
Date: Wed, 27 Jun 2001 17:54:24 -0500 (CDT)

Hi All,

I have a question regarding the transmission of DVMRP prune messages. I
refer to the Internet draft 'draft-ietf-idmr-dvmrp-v3-10.txt'

Is it correct to say that prune messages are sent only in response to the
following two events? (Pl. ignore prune retransmissions)
1. Arrival of a multicast datagram (for which there are no interested
listeners).
2. Arrival of a prune message from a dependent downstream router.

This question is meant to clarify this scenario: Some hosts in a network
have subscribed to a multicast group to which no source is sending
traffic. After some time, all these hosts leave this group (and still no
source is sending traffic to this group). When the last member leaves this
group, will the DVMRP router for this network send a prune message
upstream?

Thanks,
Magesh

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From: Tom Pusateri <[email-masked]>
Date: Wed, 27 Jun 2001 16:33:26 -0700

No, there are more conditions that cause prune messages to be generated.
For instance, all of your downstream dependent neighbors could either
timeout or their routing information could change which would cause them
to stop being dependents. I'm sure there other scenarios as well.

Tom

In message <[email-masked]> you wri

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From: Christopher Thomas Brown <[email-masked]>
Date: Wed, 27 Jun 2001 20:32:03 -0400

On Wed, 27 Jun 2001 17:54:24 CDT
>2. Arrival of a prune message from a dependent downstream router.

Not quite correct.
2 should be: If the forwarding cache entry to transitions to a NULL
outgoing interface list. This implies recent s,g data flow or else you
would not have a forwarding cache entry.

>group, will the DVMRP router for this network send a prune message

If data has never flowed then you do not have a forwarding cache entry
for s,g. So, you do not send a prune.

Chris Brown
NextHop Technologies