Subject: [pim] [PIM-BIDIR]: upstream forwarding using only RPA state ?

From: "Srikanth Rao" <[email-masked]>
Date: Wed, 20 Apr 2005 13:52:13 -0700

In section 3.3.2 on source only branches of the draft (pim-bidir-07), it mentions that 
upstream forwarding can happen "only on RPA state". This may not work when there 
are multiple RPs of the same priority in the RP-set announced by a PIM-BSR, for 
the same multicast group range. Some of the vendors are sampling data to do
upstream forwarding., but the question is can you make it data event independent ?

For instance, consider a first hop router attached to a sender only branch where
a group range GR-1 is served by RP1 & RP2 with RPF interfaces to RP1 and RP2 
being different (from the MRIB). A multicast group G1 in the range GR-1 may either 
map to RP1 or RP2 depending on the hash function. In this scenario, if router sees 
traffic for G1 on the sender-only branch that it has to upstream forward towards RP, 
then will it forward towards RP1 or RP2 ?
 
Actually this problem is not limited to sender-only branch, it can happen on
any intermediate router where it hasn't learnt the group apriori.

If this has been already discussed, please point me to the outcome.
thanks,
Srikanth
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