Which of the following working mechanisms are included in PIM-DM? (Multiple choice)

Question

Options

• AState refresh
• BPruning
• CDiffusion
• DGrafting

• A
  100% (20)

Explanation

All four options are correct - PIM-DM (Protocol Independent Multicast - Dense Mode) operates on a flood-and-prune model with four core mechanisms working together. Diffusion (C) is the initial step: multicast traffic is flooded to all downstream interfaces, assuming all routers want it. Pruning (B) then allows routers with no interested receivers to send Prune messages, cutting off unwanted traffic. Grafting (D) reverses a prune quickly - when a new receiver joins a previously pruned branch, a Graft message restores forwarding immediately instead of waiting for the prune timer to expire. State Refresh (A) solves a key problem: without it, prune states time out and trigger another flood/prune cycle; State Refresh messages keep the prune state alive, reducing unnecessary flooding.

Since all choices are correct, there are no wrong distractors - this question tests whether you know PIM-DM's full mechanism set, not just the obvious ones (many students forget State Refresh or conflate Diffusion with a separate concept).

Memory tip: Think of a gardener - they Drench the garden first (Diffusion), Prune dead branches, Graft new ones when needed, and do periodic State check-ins to avoid repeating work. D-P-G-S = Dense Protocol's Garden Strategy.

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