Subject: PIM group aggregation

From: Ian Walker <[email-masked]>
Date: Tue, 13 Jul 1999 12:12:30 +0100

Can anybody clarify some confusion I have over group aggregation.

RFC2362 (PIM-SM) specifies that an encoded group address consists of a
multicast address and a mask length.

I can see why aggregating group addresses is useful in CandidateRP and
Bootstrap messages, but cannot see how it is so useful in routing
messages such as JoinPrune, Register and Assert messages without
increasing the complexity of the route maintenance.

All other multicast protocols that I've read about (DVMRP, MOSPF, IGMP)
only ever manipulate 32-bit (ipv4) group addresses. So if there is to be
any aggregation of groups within the route database it must be PIM that
is aggregating these routes. To do route aggregation would need careful
management as if different levels of aggregation were made in different
parts of the network then route maintenance becomes much more
complicated.

Was it ever the intention that (S,G) and (*,G) route entries ever
specified aggregated groups ? If yes, has anybody implemented this. 

regards, ian.