hardMultiple Choice
300-410 Practice Question: Runs the following command to troubleshoot BFD…
A network engineer runs the following command to troubleshoot BFD session flapping:
R1# debug bfd packet *Mar 1 00:15:23.456: BFD: [R1-to-R3] received async packet from 10.5.5.2, state UP, diag 0 *Mar 1 00:15:23.457: BFD: [R1-to-R3] sending async packet, state UP *Mar 1 00:15:23.458: BFD: [R1-to-R3] received echo packet from 10.5.5.2, state UP *Mar 1 00:15:23.459: BFD: [R1-to-R3] echo packet lost, no echo received for 300 ms *Mar 1 00:15:23.460: BFD: [R1-to-R3] state UP -> DOWN (echo failure)
What does this output indicate?
⚠ Common exam trap
Watch out — candidates often confuse async control packet failure with echo packet failure — candidates see 'BFD session down' and assume the control packets are the problem, when the log clearly shows async packets succeeding and only echo packets failing.
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
✓
BFD session went DOWN because of echo timeout, indicating possible path issue.
The debug output shows the BFD session transitioning from UP to DOWN specifically due to an echo failure — the echo packet sent to 10.5.5.2 was not returned within the 300 ms echo interval. This indicates the forwarding path for echo packets is broken even though async control packets are still being received, which is the classic signature of a unidirectional or return-path forwarding problem. The session is not stable and the cause is echo timeout, not async packet loss or multiplier misconfiguration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
BFD session is UP and stable.
Why it's wrong here
The final line records the state transitioning UP to DOWN on echo failure, so the session is not stable. It is tempting because the first three lines show UP states and successful packet exchange, which would indicate a healthy session if the echo loss and transition lines were absent.
- ✓
BFD session went DOWN because of echo timeout, indicating possible path issue.
Why this is correct
The debug shows echo packets failing while async control packets remain UP, so the session transitions UP to DOWN specifically on echo timeout. That points to a forwarding-path problem affecting echo traffic rather than a control-plane failure.
- ✗
BFD async packets are failing, causing session down.
Why it's wrong here
The log shows async packets arriving and being sent successfully with diag 0; the failure is the missing echo reply, which trips the echo detection timer. It is tempting because the session does indeed go down, and async failure would be the cause if no hello packets were received within the detection interval.
- ✗
BFD session is flapping due to misconfigured multiplier.
Why it's wrong here
The log attributes the transition to echo failure after 300 ms without a reply, not to a detection multiplier mismatch, which would show missed async hellos across the negotiated detection interval. It is tempting because flapping often stems from multiplier tuning, and that would fit if async packets were being dropped.
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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 300-410 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 300-410 exam.