Which types of multicast distribution tree can PIM-SM use?

Question

Options

• AOnly shared tree rooted at the source
• BOnly shared tree rooted at the RP
• COnly shortest path tree rooted at the RP
• DShared tree rooted at the source and shortest path tree switchover
• EShared tree rooted at the RP and shortest path tree switchover
• FShared tree rooted at the first-hop router and shortest path tree rooted at the RP

• B
  6% (2)
• D
  3% (1)
• E
  88% (29)
• F
  3% (1)

Explanation

PIM-SM (Protocol Independent Multicast – Sparse Mode) operates using two types of distribution trees. It begins by building a shared tree (also called the RPT, Rendezvous Point Tree) rooted at the RP. When a last-hop router determines that traffic flow warrants a more optimal path, it can trigger an SPT (Shortest Path Tree) switchover, building a source-rooted tree directly between the last-hop router and the multicast source. This SPT switchover improves efficiency by eliminating the RP as a transit point. Option E correctly describes both tree types used in PIM-SM: the initial shared tree rooted at the RP and the subsequent SPT switchover. Options A, C, and F are wrong because they either misidentify the root of the shared tree or describe unsupported combinations. Option D is wrong because the shared tree in PIM-SM is rooted at the RP, not the source.

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