The correct answer is that the BFD session is established and echo mode is active. This interpretation is confirmed by the debug output showing the state transition from DOWN to UP, which indicates successful neighbor discovery and session initialization, followed by the explicit enabling of echo mode with a configured minimum echo receive interval of 50 ms. The subsequent sending of an asynchronous packet at a 300 ms interval further confirms that the session is fully operational, with echo mode reducing detection times by bypassing control-plane processing. On the Cisco CCNP ENARSI 300-410 exam, this type of BFD debug event output interpretation tests your ability to distinguish between the asynchronous and echo modes, a common trap being that the “sending async packet” line might lead you to think echo mode is inactive—when in fact, echo mode runs alongside async packets for fast failure detection. A helpful memory tip: “UP plus echo equals fast failover,” meaning a session in the UP state with echo enabled provides sub-second convergence for routing protocols like OSPF and EIGRP.
300-410 Bidirectional Forwarding Detection (BFD) Practice Question
This 300-410 practice question tests your understanding of bidirectional forwarding detection (bfd). The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer runs the following command to troubleshoot a BFD issue:
R1# debug bfd event
*Mar 1 00:12:34.567: BFD: [R1-to-R2] state DOWN -> UP (async)
*Mar 1 00:12:34.568: BFD: [R1-to-R2] echo mode enabled, min-echo-rx-interval 50 ms
*Mar 1 00:12:34.569: BFD: [R1-to-R2] starting echo timer, interval 50 ms
*Mar 1 00:12:34.570: BFD: [R1-to-R2] sending async packet, state UP, interval 300 ms
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
BFD session is established and echo mode is active.
The debug output shows BFD session transitioning from DOWN to UP, with echo mode enabled and the async interval set to 300 ms. This indicates a successful BFD session establishment.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 flapping between DOWN and UP states.
Why it's wrong here
The output shows a single transition from DOWN to UP, not flapping.
✓
BFD session is established and echo mode is active.
Why this is correct
The output confirms BFD session is UP, echo mode enabled, and timers are running.
Related concept
Read the scenario before looking for a memorised answer.
✗
BFD session is down due to echo failure.
Why it's wrong here
No failure is indicated; echo mode is enabled and working.
✗
BFD async interval is misconfigured at 300 ms.
Why it's wrong here
300 ms is a typical default async interval; no misconfiguration is shown.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
The output shows a single transition from DOWN to UP, not flapping.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Bidirectional Forwarding Detection (BFD) — This question tests Bidirectional Forwarding Detection (BFD) — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: BFD session is established and echo mode is active. — The debug output shows BFD session transitioning from DOWN to UP, with echo mode enabled and the async interval set to 300 ms. This indicates a successful BFD session establishment.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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