Subject: DVMRP Prunning on routers unable to forward

From: Panos GEVROS <[email-masked]>
Date: Fri, 22 Aug 1997 21:11:01 +0100

-Hi, 
the scenario is as follows:

Source   starts sending,
Packets  get flooded,
Packets  reach a router through an interface
Router   tries to flood (send packets on all other tunnels) 
But ..
because of the TTL value at that point and the thresholds configured in the 
tunnels packets cannot get forwarded any further.

The router will never hear "prune" from these downstream neighbors
because the neighbors never learned about the group (traffic never reached 
them)
Consequently it will never send prune upstream (or not?) 
the same his upstream neighbor (for this source) and this will be propagated..

How things actually work in such a case?

Thanks,
Panos

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From: Ajit Thyagarajan <[email-masked]>
Date: Fri, 22 Aug 1997 20:21:33 -0400

>How things actually work in such a case?

You don't want the router to send prunes because the source may be using
the ttl in an expanding ring manner to search for resources.
If the router had pruned the source, then subsequent packets wouldn't be 
forwarded properly.  The use of ttl is useful for applications which make 
use of an expanding ring type of search.  If used as a scoping mechanism,
it has its limitations.  Thats why it is preferable to use scoped groups 
to limit the range of multicast traffic.

Ajit