[Xorp-users] Need Help for pimsm multicasting join or any message modification

[Bruce Simpson]

bhavin81 at iitb.ac.in wrote:
> Hello friends,
>
>          I want to do some modification in standard pim-sm multicasting.
> I want to modify either join or some other message such that whenever
> any user wants to join any group it(user) specifies some sort of choice by
> some flag which is part of pim-sm message field.
OK...
>  Is there any field in
> the message which i can modify means any optional field? If yes then which
> code out of pim-sm in xorp i need to modify?

Not really, unless you modify the reserved bits in the PIM-SM fixed 
header (which are supposed to be ignored on receive).

A better bet would be the source address tuple, where a number of bits 
are already allocated in the first 18 bits of the tuple. Pick up a copy 
of RFC 2362 (in PostScript format preferably, I cannot seem to find the 
original) or refer to Interdomain Multicast Routing 
(Edwards/Giuliano/Wright, Addison-Wesley).

See PimJpHeader::network_send() here, where encoding actually happens, 
work your way back up the call graph:
    
http://cvsweb.xorp.org/cgi-bin/cvsweb.cgi/xorp/pim/pim_proto_join_prune_message.cc?rev=1.33

P.S. I would advise testing very carefully if you plan to run this 
modification in a production network with standards-compliant equipment.

thanks,
BMS