What is a requirement of PIM-SM?

Question

Options

• AIt requires Cisco Express Forwarding to be enabled.
• BIt must be enabled on loopback interfaces only
• CIt requires OSPF to be configured on the network
• DIt must use an RP

• A
  5% (1)
• D
  95% (18)

Explanation

PIM-SM (Sparse Mode) is built around the concept of a Rendezvous Point (RP) - a central router where multicast sources register and receivers join a shared tree. Without an RP, PIM-SM cannot establish its shared distribution tree, making D the fundamental requirement.

Why the distractors are wrong:

• A is incorrect - CEF (Cisco Express Forwarding) is required for PIM on Cisco IOS, but it is not a protocol requirement of PIM-SM itself; it's a platform dependency.
• B is wrong - PIM-SM is enabled on routed interfaces facing multicast sources and receivers, not restricted to loopbacks (loopbacks are commonly used as the RP address, but PIM runs on many interface types).
• C is wrong - PIM is protocol-independent, meaning it works with any unicast routing protocol (OSPF, EIGRP, BGP, static routes, etc.) - that's literally the "PI" in PIM.

Memory tip: Think of PIM-Sparse Mode as a Star network - all roads lead to the Rendezvous Point. No RP = no star = no PIM-SM. The "protocol-independent" name is your clue that options A, B, and C are trying to tie it to a specific technology, which contradicts its core design.

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