How does Protocol Independent Multicast function?

Question

Options

• AIn sparse mode it establishes neighbor adjacencies and sends hello messages at 5-second intervals.
• BIt uses the multicast routing table to perform the multicast forwarding function.
• CIt uses unicast routing information to perform the multicast forwarding function.
• DIt uses broadcast routing information to perform the multicast forwarding function.

• A
  2% (1)
• C
  93% (40)
• D
  5% (2)

Explanation

Protocol Independent Multicast (PIM) Explained

PIM is called "Protocol Independent" precisely because it relies on the unicast routing table (populated by whatever unicast routing protocol is running, such as OSPF, EIGRP, or static routes) to make its multicast forwarding decisions through a mechanism called Reverse Path Forwarding (RPF). This independence from any specific routing protocol is the defining characteristic of PIM, making option C correct.

Why the distractors are wrong:

• Option A is partially true (PIM sparse mode does send hello messages), but the interval is 30 seconds, not 5 seconds - making this a classic "almost right" trap answer
• Option B is incorrect because PIM does not use a separate multicast routing table; it leverages the existing unicast routing table, not a dedicated multicast one
• Option D is incorrect because PIM has no relationship with broadcast routing information whatsoever

Memory Tip: Focus on the name itself - "Protocol Independent" means it doesn't care which routing protocol you use, as long as there's a unicast routing table to reference. Think: "PIM borrows from unicast, regardless of who built the table."

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