The answer is that the BFD session is operating in async mode with intervals at 1 second. This is confirmed by the output showing "not using echo function" and consistent MinTxInt and MinRxInt values of 1000000 microseconds, which translate to 1000 ms intervals, alongside a multiplier of 3. In BFD async mode, both peers independently send control packets at the negotiated interval without relying on echo packets for faster failure detection, and the absence of echo function here directly indicates async operation. On the Cisco CCNP ENARSI 300-410 exam, this question tests your ability to interpret "show bfd neighbors detail" output and differentiate between async and echo modes—a common trap is confusing the "Demand mode: 0" field with async mode, but remember that demand mode is a separate feature that disables periodic hellos. For a quick memory tip, think "No echo = async, intervals in microseconds divide by 1000 for milliseconds."
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 to verify BFD operation:
R1# show bfd neighbors detail
IPv4 Sessions
NeighAddr LD/RD RH/RS State Int
10.1.1.2 1/2 Up Up Gi0/0
Session state is UP and not using echo function.
Session type: single-hop
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
Received MinRxInt: 1000000, Received Multiplier: 3
Holddown (hits): 0 (0), Hello (hits): 1000/5
Rx Count: 1000, Rx Interval (ms) min/max/avg: 900/1100/1000
Tx Count: 1000, Tx Interval (ms) min/max/avg: 900/1100/1000
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 operating with async mode, intervals at 1 second.
The output shows a BFD session in UP state with consistent transmit and receive intervals around 1000 ms, no echo function, and a multiplier of 3. The session is healthy.
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.
✗
BFD session is using echo mode for fast failure detection.
Why it's wrong here
The output explicitly states 'not using echo function'.
✗
BFD session is down and not sending hellos.
Why it's wrong here
State is UP and hello counts are incrementing.
✓
BFD session is operating with async mode, intervals at 1 second.
Why this is correct
MinTxInt and MinRxInt are 1,000,000 microseconds (1 second), no echo, and session is UP.
Holddown is 0; the multiplier is 3, but holddown hits are 0.
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 states '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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
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: BFD session is operating with async mode, intervals at 1 second. — The output shows a BFD session in UP state with consistent transmit and receive intervals around 1000 ms, no echo function, and a multiplier of 3. The session is healthy.
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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