Which of the following descriptions about RP is incorrect?

Question

Options

• AIn PIM-SM, multicast data traffic does not necessarily have to be forwarded through RP.
• BFor a multicast group, there can be multiple RP addresses at the same time to improve network reliability.
• CUnicast data packets converge C-RPs are used at the same time to improve the full availability of the RP.
• DAll multicast streams in the shared tree are forwarded to the receiver through the RP.

• A
  7% (2)
• B
  10% (3)
• C
  3% (1)
• D
  80% (24)

Explanation

Option D is incorrect because in PIM-SM, receivers can switch from the shared tree (rooted at the RP) to a Shortest Path Tree (SPT) that goes directly from the source to the receiver, completely bypassing the RP - so it is false that all multicast streams in the shared tree must pass through the RP to reach receivers. Option A is therefore a true statement, directly contradicting D: PIM-SM explicitly allows SPT switchover so that traffic no longer traverses the RP once the switch occurs. Option B is also correct, as mechanisms like Anycast RP allow multiple physical routers to serve as RP for the same group simultaneously, providing redundancy. Option C, though awkwardly worded, correctly describes how multiple Candidate RPs (C-RPs) advertise themselves via unicast to the Bootstrap Router (BSR), allowing the network to select an RP and improve availability.

Memory tip: Think of the RP as a mandatory relay only during the initial shared-tree phase - PIM-SM is designed to let routers "shortcut" past the RP once they know the source, which is the whole point of SPT switchover. Any answer claiming the RP is always in the forwarding path is wrong.

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