About RP, which of the following statement is correct? (Multiple choice)

Question

Options

• AAll routers in the PIM-SM network need to know the location of the RP
• BThe RP is dynamically elected or can only be specified manually
• CRP is elected by the BSR router
• DRP is the root of the RPT tree

• A
  81% (44)
• B
  11% (6)
• C
  6% (3)
• D
  2% (1)

Explanation

In PIM-SM (Protocol Independent Multicast - Sparse Mode), the RP (Rendezvous Point) is the central junction where multicast sources register and receivers converge. Every router in the domain must know the RP's address to build the shared tree - without it, no router can send PIM Join messages toward the RP or forward multicast traffic, making A fundamentally correct.

B is wrong because the "can only be specified manually" clause is false. RP can be statically configured or dynamically discovered via mechanisms like BSR (Bootstrap Router) or Cisco's Auto-RP - there is no "only one way" restriction.

C is wrong because the BSR does not directly elect the RP. The BSR is itself elected among Candidate BSRs, and then it distributes Candidate RP (C-RP) advertisements across the network. Routers independently apply a hash algorithm to select the active RP from those candidates - the BSR facilitates discovery, not election.

D is wrong because while the RP does serve as the root of the initial shared tree (RPT), PIM-SM routers can switch to a Shortest Path Tree (SPT) rooted at the source, bypassing the RP entirely. Calling the RP "the root of the RPT tree" overstates its permanent role in the forwarding path.

Memory tip: Think of the RP as a post office - every router in town must know where the post office is (A), even if some letters eventually get delivered directly house-to-house (SPT switchover, which is why D is incomplete).

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