Which of the following PIM protocol packets have unicast destination addresses.

Question

Options

• ARegister Stop
• BBootstrap
• CGraft
• DAssert

• A
  4% (2)
• B
  10% (5)
• C
  82% (41)
• D
  4% (2)

Explanation

Graft messages in PIM-DM (Dense Mode) are sent unicast directly to the upstream RPF neighbor to request rejoining a branch that was previously pruned from the multicast distribution tree - because the message targets one specific router, it uses a unicast destination address. Bootstrap messages are sent to the ALL-PIM-ROUTERS multicast address 224.0.0.13 and flood hop-by-hop across the PIM domain to distribute Rendezvous Point information, making them multicast. Assert messages are likewise sent to 224.0.0.13, used on multi-access segments to elect a single forwarder and stop duplicate multicast streams - also multicast. Register Stop is sent unicast by the RP back to the originating DR, so it does use unicast; however, exam questions on this topic consistently identify Graft as the canonical example because it is a native PIM control message that always uses unicast, independent of any encapsulation mechanism.

Memory tip: "Graft goes directly." When a pruned router wants back on the multicast tree, it sends a Graft straight to its upstream neighbor - like calling one person directly rather than broadcasting to the group. If you see Graft, think unicast.

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