hardMultiple Select
CCNP Practice Question: Which three statements about RPF check in IP…
Which three statements about RPF check in IP multicast are true? (Choose three.)
⚠ Common exam trap
350-401 often tests the misconception that RPF is only checked on the first packet or that it uses the multicast routing table exclusively; candidates must remember RPF is per-packet and based on the unicast route to the source.
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
✓
The RPF check ensures that multicast packets are forwarded only if they arrive on the interface that the router would use to send unicast traffic back to the source.
Option A is correct because the RPF check verifies that a multicast packet arrives on the interface the router would use to reach the source via the unicast routing table (or the MRIB derived from it), which is the fundamental definition of the RPF check in IP multicast. Option B is correct because when the incoming interface does not match the RPF interface, the router considers the packet to have arrived via a suboptimal or looped path and silently drops it. Option E is correct because the RPF check compares the actual arrival interface against the RPF interface; even if a valid unicast route to the source exists, a packet arriving on any other interface fails the check and is discarded. Option C is not correct because the RPF check is performed on every multicast packet, not just the first packet of a stream, to continuously guard against loops and suboptimal paths. Option D is not correct because the RPF check can use the unicast routing table (or the MRIB, which is populated from unicast routing information) and, in some implementations, static mroutes, so it does not rely solely on the multicast routing table.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The RPF check ensures that multicast packets are forwarded only if they arrive on the interface that the router would use to send unicast traffic back to the source.
Why this is correct
The router consults its unicast routing table for the source address and derives the outgoing interface toward it. Multicast packets are accepted only when received on that same interface, which builds the shortest-path distribution tree and prevents forwarding loops in the topology.
- ✓
If the RPF check fails, the multicast packet is dropped by the router.
Why this is correct
RPF verification compares the packet's incoming interface against the interface in the unicast routing table for the source. When they differ, the router discards the packet, preventing loops and duplicate delivery. This drop behaviour is the mechanism that enforces the loop-free multicast distribution tree.
- ✗
The RPF check is performed only on the first packet of a multicast stream to determine the forwarding path.
Why it's wrong here
The RPF check runs on every multicast packet, not just the first, so a topology change mid-stream is caught immediately. It is tempting because the first packet does establish the initial forwarding state, and some vendors log only that event.
- ✗
The RPF check relies solely on the multicast routing table (MRIB) to determine the incoming interface.
Why it's wrong here
The RPF check consults the unicast routing table to find the outgoing interface toward the source, then verifies the packet arrived on that interface; the MRIB is not the sole reference. It is tempting because MRIB does carry multicast route state.
- ✓
A multicast packet can fail the RPF check even if the unicast route to the source exists, if the packet arrives on a different interface than the one used for unicast return traffic.
Why this is correct
RPF checks the incoming interface, not merely route existence. A valid unicast route to the source may point out a different interface than the one the multicast packet arrived on, so the check fails and the packet is discarded. This distinguishes RPF from simple reachability.
About these practice questions
One of 1,923 original 350-401 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
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.