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350-401 Practice Question: Which two statements about PIM sparse mode are…
Which two statements about PIM sparse mode are true? (Choose two.)
⚠ Common exam trap
350-401 often tests the difference between PIM sparse and dense modes, so candidates must remember that sparse mode uses explicit joins and a shared tree, while dense mode uses flood-and-prune.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
PIM sparse mode uses an explicit join model to receive multicast traffic.
Option A is correct because PIM-SM is fundamentally an explicit-join protocol: receivers send IGMP joins, the last-hop router sends a PIM (*,G) Join toward the RP, and traffic only flows where joins have been explicitly requested, unlike dense mode's implicit-join/push model. Option C is correct because PIM-SM first builds a shared distribution tree rooted at the rendezvous point (RP), known as the RPT or (*,G) tree, which all sources and receivers initially use before any switch to a source-specific SPT. Option B is wrong because after the first packet arrives via the shared tree, the last-hop router may switch to the shortest path tree only if the SPT threshold is met (default is typically 0, but it is not automatic or immediate in all cases, and the shared tree is used first). Option D is wrong because flood-and-prune is the mechanism used by PIM dense mode, not sparse mode. Option E is wrong because BSR is only one of several ways to distribute RP information (static RP, Auto-RP, and BSR are all valid); PIM-SM can operate with a statically configured RP and does not require BSR.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
PIM sparse mode uses an explicit join model to receive multicast traffic.
Why this is correct
Receivers must explicitly send PIM joins toward the rendezvous point to be added to the distribution tree; traffic is only delivered where requested. This explicit join model is the defining mechanism of sparse mode, contrasting with dense mode's flood-and-prune approach.
- ✗
PIM sparse mode routers always use the shortest path tree (SPT) immediately after the first packet is received.
Why it's wrong here
Routers initially forward via the shared tree and switch to the shortest path tree only after the threshold is crossed or traffic justifies it. It is tempting because SPT switching does occur, but it is the correct choice only when describing the switchover trigger, not immediate post-first-packet behaviour.
- ✓
PIM sparse mode builds a shared tree rooted at the rendezvous point (RP).
Why this is correct
Sparse mode receivers join a shared distribution tree whose root is the rendezvous point, so traffic initially flows via the RP before switching to the shortest-path tree. This shared-tree construction is the defining mechanism distinguishing sparse mode from dense mode flooding.
- ✗
PIM sparse mode uses a flood-and-prune mechanism to distribute multicast traffic.
Why it's wrong here
Flood-and-prune is dense-mode behaviour; sparse mode forwards only after an explicit join toward the rendezvous point. It is tempting because both modes deliver multicast, but flood-and-prune is the correct choice only when the question concerns dense mode or a small, densely populated multicast domain.
- ✗
PIM sparse mode requires the use of a bootstrap router (BSR) to operate.
Why it's wrong here
Sparse mode can build shared trees using statically configured rendezvous points; BSR is one dynamic RP-discovery method, not a prerequisite. It is tempting because BSR is genuinely required in some vendor designs, but it is the correct choice only when the question asks how rendezvous points are advertised dynamically.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.