1.I have read that join/prune message are sent periodically as keepalive in PIM-SM mode.Is that periodically sent on PIM-DM also,i dont see any reason for it,but just to know if anything such is there???
2. why is graft message sent???can't join message be used instead ,b'cas the message format of both join and graft message is same,except the type.(6 for graft and 3 for join).Is there any reason for that???
In PIM DM it's not sent periodically but intially after the flooding is done. PIM floods packets out to all routers in the network and then prunes routers that do not support members of that particular multicast group.