- A
Increase the BFD minimum interval and multiplier values on both routers.
Correct. Higher intervals and multipliers make BFD less sensitive to minor delays, reducing the chance of false failure detection.
- B
Disable BFD on the routing protocol and rely solely on the routing protocol's own hello timers.
Correct. Removing BFD from the routing protocol eliminates BFD as a cause of flapping, though it also removes fast convergence.
- C
Set the BFD minimum interval to 50 ms and the multiplier to 3 on both sides.
Why wrong: Incorrect. Aggressive timers (50 ms) are more likely to cause flapping if there is any jitter or delay; this is not a preventative measure.
- D
Configure BFD echo mode on both routers to reduce control packet processing overhead.
Why wrong: Incorrect. Echo mode reduces CPU load but does not directly prevent flapping caused by timer mismatches or network delays.
- E
Ensure that the BFD timers are identical on both routers.
Why wrong: Incorrect. BFD timers are negotiated; they do not need to be identical. Forcing identical timers is unnecessary and does not prevent flapping.
Quick Answer
The correct actions are increasing the BFD timers or disabling BFD on the routing protocol, as both directly address the root causes of session flapping. BFD flapping typically occurs when detection intervals are too aggressive for the network’s current CPU load or link stability; raising the BFD interval or multiplier creates a larger tolerance window for transient delays, while disabling BFD removes the protocol’s dependency on rapid failure detection entirely, reverting to the routing protocol’s own hello timers. On the Cisco CCNP ENARSI 300-410 exam, this question tests your understanding of BFD tuning under the “Troubleshoot BFD” objective, and a common trap is assuming that lowering timers or enabling echo mode will fix flapping—echo mode reduces CPU overhead but does not prevent timer-induced flaps. Remember the memory tip: “When BFD flaps, give it more slack—raise the interval or take it off the track.”
300-410 Bidirectional Forwarding Detection (BFD) Practice Question
This 300-410 practice question tests your understanding of bidirectional forwarding detection (bfd). This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Which TWO actions will prevent a BFD session from flapping when a routing protocol (e.g., OSPF or EIGRP) is configured to use BFD? (Choose TWO.)
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
Increase the BFD minimum interval and multiplier values on both routers.
BFD session flapping can be caused by mismatched timers, high CPU load, or aggressive detection multipliers. Increasing the BFD interval or multiplier makes the session more tolerant to transient issues. Disabling BFD for the routing protocol removes BFD dependency. Lowering timers or using default values can actually increase flapping. Echo mode helps reduce CPU load but does not directly prevent flapping due to timer mismatches.
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.
- ✓
Increase the BFD minimum interval and multiplier values on both routers.
Why this is correct
Correct. Higher intervals and multipliers make BFD less sensitive to minor delays, reducing the chance of false failure detection.
Related concept
OSPF neighbours must agree on key parameters.
- ✓
Disable BFD on the routing protocol and rely solely on the routing protocol's own hello timers.
Why this is correct
Correct. Removing BFD from the routing protocol eliminates BFD as a cause of flapping, though it also removes fast convergence.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
Set the BFD minimum interval to 50 ms and the multiplier to 3 on both sides.
Why it's wrong here
Incorrect. Aggressive timers (50 ms) are more likely to cause flapping if there is any jitter or delay; this is not a preventative measure.
- ✗
Configure BFD echo mode on both routers to reduce control packet processing overhead.
Why it's wrong here
Incorrect. Echo mode reduces CPU load but does not directly prevent flapping caused by timer mismatches or network delays.
- ✗
Ensure that the BFD timers are identical on both routers.
Why it's wrong here
Incorrect. BFD timers are negotiated; they do not need to be identical. Forcing identical timers is unnecessary and does not prevent flapping.
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.
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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Bidirectional Forwarding Detection (BFD) — study guide chapter
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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: Increase the BFD minimum interval and multiplier values on both routers. — BFD session flapping can be caused by mismatched timers, high CPU load, or aggressive detection multipliers. Increasing the BFD interval or multiplier makes the session more tolerant to transient issues. Disabling BFD for the routing protocol removes BFD dependency. Lowering timers or using default values can actually increase flapping. Echo mode helps reduce CPU load but does not directly prevent flapping due to timer mismatches.
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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