http://www.enterprisenetworkingplanet.com/netsp/article.php/3623181/Networking-101--Understanding-Multicast-Routing.htm
DVMP dense mode
PIM dense mode just like DVMP, flood anywhere first then prune by the router when on one want to have that multicast stream (by IGMP)
PIM sparse mode, use RP to inform who like to have the stream and where to pass it (join, or graft, the opposite of join).
RFP (Reverse Path Forwarding) is used to prevent routing loop, by looking and choosing the shortest path to the sender.
MOSFP, BGMP rarely used.
