[Xorp-users] IGMP/PIM question ?

[Vikram KAUL]

Thanks for the reply. My comments interspersed...


pavlin>The PIM-SM spec <draft-ietf-pim-sm-v2-new-12.txt, Section 4.2.  Data
pavlin>Packet Forwarding Rules) mandates that the iif is always excluded
pavlin>from the oiflist:
pavlin>
pavlin><QUOTE>
pavlin>On receipt of data from S to G on interface iif:
pavlin>...
pavlin> oiflist = oiflist (-) iif
pavlin> forward packet on all interfaces in oiflist
pavlin></QUOTE>
pavlin>
pavlin>The reason for excluding the iif from the oiflist is because
pavlin>forwarding multcast data back on the interface it came from can
pavlin>result in multicast loops, and such loops can bring down a whole
pavlin>network.

Loops and duplicates can be avoided with filtering based on the IP ID 
field for UDP packets and maintaining a state for either a two-tuple 
(Source, ID) or a three-tuple (Source, DestGroup, ID). Of course, the IP 
ID has been designed for for support of packet fragmentation, so one has 
to be careful
Several multicast ad-hoc implementations use IP ID. I intend to insert 
the mechanism as a module in the kernel or as part of the kernel itself. 

pavlin>
pavlin>In addition, if we take into account the PIM assert mechanism,
pavlin>then the iif might be excluded anyway from the oiflist.
pavlin>

Is there some more information you (or anyone else) can give me about 
this. 

Thanks again for the help

regards..
Vikram