What mechanism does PIM use to forward multicast traffic?

Question

Options

• APIM sparse mode uses a pull model to deliver multicast traffic.
• BPIM dense mode uses a pull model to deliver multicast traffic.
• CPIM sparse mode uses receivers to register with the RP.
• DPIM sparse mode uses a flood and prune model to deliver multicast traffic.

• A
  88% (29)
• B
  3% (1)
• C
  3% (1)
• D
  6% (2)

Explanation

PIM Multicast Forwarding Mechanisms

Option A is correct because PIM Sparse Mode (PIM-SM) operates on a pull model, meaning traffic is only forwarded to routers that have explicitly requested it by joining a multicast group - traffic flows toward receivers on demand, not by default.

Why the distractors are wrong:

• Option B is incorrect because it's PIM Dense Mode (PIM-DM) that uses flood and prune (a push model), not a pull model - PIM-DM floods traffic everywhere first, then prunes branches with no receivers.
• Option C is partially true (sources register with the RP, not receivers), but the statement is misleading - sources register with the Rendezvous Point (RP), while receivers join using IGMP; this alone doesn't describe the forwarding mechanism.
• Option D is incorrect because flood and prune describes PIM Dense Mode, not Sparse Mode.

Memory Tip: Think of the words themselves - "Sparse" means few/scattered, so routers only pull traffic where needed (pull = sparse). "Dense" means packed/everywhere, so traffic floods everywhere first (flood = dense). Sparse = Pull; Dense = Push (flood & prune).

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