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300-410 Practice Question: Which TWO actions will prevent a BFD session from…
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.
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.
- ✓
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.
- ✗
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.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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