PIM-SSM: no RP
RP, FHR(closest to the source), LHR(closest to the receiver), Shared tree to SPT(shorted path tree) fallback
Bi-DR (phantom RP): no source tree (S,G), only shared tree; DF-closest to RP
RPF check — prevent duplicate of multicast packets. When a router receives duplicate streams from different incoming intfs, it performs the RPF-check against the source(sender) IP to see which incoming interface is the closest to the sender based on its unicast routing table. The incoming intf that leads to the closest route towards the sender will be accepted for the multicast stream. The steam(s) from other intf(s) will be droped.
anycast RP — multiple RPs with the same IP address. The sources and receivers find the nearest RP based on routing protocol.
MSDP– multicast source discovery protocol. Used in anycast RP, to solve the problem when sender and receiver are registered to different RPs. When this happens, on the sender’s RP, there is (S,G) but nexthop is null, because there is no receiver. On the sender’s RP, there is only (*,G) because sender is not found. MSDP is used between RPs to sync the sender/receiver info.
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