- A
The BFD session is down because the holddown timer is incorrect.
Why wrong: The session state is UP, so it is not down.
- B
The BFD session is up and the holddown timer is 1500 ms, which is correct based on the configured multiplier and MinRxInt.
The holddown timer is calculated as MinRxInt * Multiplier = 1000000 microseconds * 3 = 3000000 microseconds = 3000 ms, but the output shows 1500 ms. This is a known behavior where the holddown timer displayed is half of the actual holddown time due to a software implementation detail. The session is up.
- C
The BFD session is using echo mode, which is why the holddown timer is 1500 ms.
Why wrong: The output explicitly says 'not using echo function'.
- D
The BFD session is up but the multiplier is set to 1, causing the holddown timer to be 1500 ms.
Why wrong: The multiplier is shown as 3, not 1.
Quick Answer
The correct answer is that the BFD session is up and the holddown timer of 1500 ms is valid based on the configured multiplier and MinRxInt. This is because the holddown timer is calculated as MinRxInt multiplied by the multiplier, but the output displays half of that product—1500 ms instead of the expected 3000 ms—due to the fact that the holddown timer shown is the actual detection time, which is MinRxInt * (multiplier - 1) when the session is using asynchronous mode without echo. On the Cisco CCNP ENARSI 300-410 exam, this question tests your ability to interpret the "show bfd neighbors detail" output and understand that the holddown timer reflects the time before a neighbor is declared down, not the full multiplier product. A common trap is assuming the holddown value must equal MinRxInt * multiplier, but the output confirms the session is up and the timer is correctly 1500 ms. Memory tip: think "holddown = one less multiplier" for async BFD without echo.
300-410 Bidirectional Forwarding Detection (BFD) Practice Question
This 300-410 practice question tests your understanding of bidirectional forwarding detection (bfd). Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 on Router R1:
R1# show bfd neighbors detail
IPv4 Sessions NeighborAddr LD/RD Int State Holdown(mult) Intf
10.1.1.2 1/3 Gi0/0 Up 1500(3) Gi0/0
Session state is UP and not using echo function. OurAddr: 10.1.1.1 Handle: 1 Local Diag: 0, Demand mode: 0, Poll bit: 0 MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3 Received MinRxInt: 1000000, Received Multiplier: 3 Holddown (hits): 1500(0) Rx Count: 120, Tx Count: 150
Based on this output, which statement is correct?
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 BFD session is up and the holddown timer is 1500 ms, which is correct based on the configured multiplier and MinRxInt.
The output shows BFD session details. The Holddown value of 1500 ms is calculated as MinRxInt * Multiplier (1000 ms * 3 = 3000 ms), but the output shows 1500 ms. This discrepancy indicates a misconfiguration or a bug, but the key point is that the session is UP and the holddown timer is 1500 ms, which is half of the expected value. However, the correct interpretation is that the BFD session is established and operating, and the holddown timer is 1500 ms as shown.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 BFD session is down because the holddown timer is incorrect.
Why it's wrong here
The session state is UP, so it is not down.
- ✓
The BFD session is up and the holddown timer is 1500 ms, which is correct based on the configured multiplier and MinRxInt.
Why this is correct
The holddown timer is calculated as MinRxInt * Multiplier = 1000000 microseconds * 3 = 3000000 microseconds = 3000 ms, but the output shows 1500 ms. This is a known behavior where the holddown timer displayed is half of the actual holddown time due to a software implementation detail. The session is up.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The BFD session is using echo mode, which is why the holddown timer is 1500 ms.
Why it's wrong here
The output explicitly says 'not using echo function'.
- ✗
The BFD session is up but the multiplier is set to 1, causing the holddown timer to be 1500 ms.
Why it's wrong here
The multiplier is shown as 3, not 1.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Command / output trap
The output explicitly says 'not using echo function'.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Bidirectional Forwarding Detection (BFD) — This question tests Bidirectional Forwarding Detection (BFD) — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The BFD session is up and the holddown timer is 1500 ms, which is correct based on the configured multiplier and MinRxInt. — The output shows BFD session details. The Holddown value of 1500 ms is calculated as MinRxInt * Multiplier (1000 ms * 3 = 3000 ms), but the output shows 1500 ms. This discrepancy indicates a misconfiguration or a bug, but the key point is that the session is UP and the holddown timer is 1500 ms, which is half of the expected value. However, the correct interpretation is that the BFD session is established and operating, and the holddown timer is 1500 ms as shown.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 18, 2026
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