Multicast RPs: The Truth Unveiled

D.

Multicast RPs (Rendezvous Points) are used in multicast routing protocols to forward multicast traffic to receivers. The correct answer to the question is B: RPs are required for protocol independent multicast sparse mode and dense mode.

In Protocol Independent Multicast Sparse Mode (PIM-SM), multicast traffic is forwarded to receivers on the basis of a shared tree or a source tree. The RP is a central point that all routers use to join the multicast tree. The RP maintains the state of the multicast group and is responsible for forwarding multicast traffic to the multicast group members. The RP is required in PIM-SM to determine the root of the multicast distribution tree.

In Protocol Independent Multicast Dense Mode (PIM-DM), multicast traffic is forwarded to all routers in the network. Routers that do not have any receivers for the multicast group can then prune the traffic to save bandwidth. The RP is required in PIM-DM to determine the root of the multicast distribution tree.

Option A is incorrect because RPs are required in PIM-SM and PIM-DM, not just PIM-DM.

Option C is incorrect because the RP does not need to periodically maintain sessions with sources and receivers.

Option D is incorrect because the RP is needed not only to start new sessions but also to maintain existing sessions.

In conclusion, the correct answer is B: RPs are required for protocol independent multicast sparse mode and dense mode.