From: jongsoo.kim@intelsat.com
Date: Sat Aug 07 2004 - 16:51:36 GMT-3
Andy
Regrading your question " Does the group interpret this requirement to also include instanceswhere the source is closer than the RP and SPT uses (S,G) instead of(*,G)? IOW, if I have (S,G) mroutes would that violate the requirement?"
My answer is "No it didn't violate"
Based on my study,
PIM SM process depends upon both of source tree and share tree.
a) from receiver to RP, Shared tree( *,G) by SM definision
b) from RP to Source, Source doesn't know PIM but will just forward multicast traffic. The first PIM router that receives the traffic from source will do the following. 1) if group address has RP in SM or SD, it will send PIM registeration via Unicast to RP, or 2) if group address doesn't have RP in SD or DM( always), it will flood traffic to all PIM interafce except for incoming interface. After PIM registeration process, RP will preform source tree toward source to convert the traffic from "unicast tunnel" to pure multicast based on SPT. Finally, RP and all the PIM router on SPR path from RP to source will have SPT.
Now,like your question, PIM routers on SPT path from source to RP will have both shared tree(*, G) by a) and source tree(S,G) by b) for the same group. But RPF check process(loop-free process, independent from SM, SD, or DM) on each router will choose interface toward source( source tree incoming interface) for valid incoming interface and cause interface toward RP( shared tree incoming interface) to block multicast traffic receiving from RP.
I hope this is correct as I am not a multicast expert.
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