N10-009 BFD provides sub-second failure detection. Practice Question
An organization uses OSPF as its interior gateway protocol in a multi-area design. After a core router failure, the network takes several seconds to reconverge. Which technology can be implemented to improve convergence speed?
⚠ Common exam trap
The N10-009 exam often tests the distinction between OSPF fast hello timers (which still rely on seconds-based dead intervals) and BFD (which provides true sub-second detection), leading candidates to mistakenly choose fast hello timers as the faster solution.
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
✓
Configure BFD (Bidirectional Forwarding Detection)
BFD provides sub-second failure detection times (as low as 50 ms) independent of the routing protocol, allowing OSPF to reconverge much faster than relying on its default dead timer intervals. By detecting link failures in milliseconds, BFD triggers OSPF to immediately recalculate routes, drastically reducing the convergence delay after a core router failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Implement LSA throttling
Why it's wrong here
LSA throttling is a mechanism designed to prevent excessive LSA generation and flooding during periods of network instability, thereby protecting router CPUs and preventing network meltdown. It works by imposing minimum intervals between consecutive LSA updates for the same LSA type or instance. While it helps stabilize a flapping network by rate-limiting updates, it deliberately delays the propagation of new topology information, which is counterproductive to the goal of achieving faster convergence after a failure.
When this WOULD be correct
In a scenario where OSPF routers are experiencing excessive LSA flooding causing CPU spikes and instability, LSA throttling would be correct to stabilize the network by limiting LSA generation rates.
- ✗
Enable OSPF fast hello timers
Why it's wrong here
Enabling OSPF fast hello timers involves reducing the default hello and dead timer intervals, allowing OSPF to detect a lost neighbor more quickly than with standard settings. While this does accelerate neighbor failure detection, it relies on the OSPF process itself for monitoring, which can be CPU-intensive and less precise at sub-second intervals. BFD, operating at a lower layer and with dedicated lightweight packets, offers superior sub-second detection capabilities and is generally more robust and less resource-intensive for extremely rapid failure detection compared to simply shortening OSPF hello timers.
When this WOULD be correct
A question asks: 'An organization wants to reduce OSPF neighbor dead timer detection from 40 seconds to 10 seconds without changing the hello interval. Which feature should be configured?' In this scenario, enabling OSPF fast hello timers (or adjusting hello/dead intervals) would be correct.
- ✓
Configure BFD (Bidirectional Forwarding Detection)
Why this is correct
Configuring BFD (Bidirectional Forwarding Detection) establishes a lightweight, independent detection mechanism that rapidly monitors the forwarding path between two routers. By sending small, periodic BFD control packets at sub-second intervals, it can detect link or neighbor failures significantly faster than OSPF's default hello/dead timers. This rapid detection allows OSPF to be immediately notified of a topology change, triggering a much quicker recalculation of routes and thus accelerating network convergence after a failure.
- ✗
Convert all areas to stub areas
Why it's wrong here
Converting all areas to stub areas primarily aims to reduce the size of the OSPF routing table and the frequency of LSA flooding within those areas by blocking Type 4 and Type 5 LSAs. While this can improve router resource utilization and potentially reduce the impact of external route changes, it does not inherently speed up the detection of local link or neighbor failures within an area. The core mechanisms for detecting such failures (like hello timers) remain unchanged, thus not directly improving convergence time.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓Configure BFD (Bidirectional Forwarding Detection)Correct answer▾
Why this is correct
Configuring BFD (Bidirectional Forwarding Detection) establishes a lightweight, independent detection mechanism that rapidly monitors the forwarding path between two routers. By sending small, periodic BFD control packets at sub-second intervals, it can detect link or neighbor failures significantly faster than OSPF's default hello/dead timers. This rapid detection allows OSPF to be immediately notified of a topology change, triggering a much quicker recalculation of routes and thus accelerating network convergence after a failure.
✗Implement LSA throttlingWrong answer — click to see why▾
Why this is wrong here
LSA throttling controls the rate of LSA generation and flooding, which can reduce CPU load during instability but does not speed up failure detection or convergence; it may actually delay convergence.
★ When this WOULD be the correct answer
In a scenario where OSPF routers are experiencing excessive LSA flooding causing CPU spikes and instability, LSA throttling would be correct to stabilize the network by limiting LSA generation rates.
Why candidates choose this
Candidates may confuse throttling with optimization, thinking that reducing LSA overhead will speed up convergence, but throttling primarily prevents router overload, not faster detection.
✗Enable OSPF fast hello timersWrong answer — click to see why▾
Why this is wrong here
OSPF fast hello timers reduce the time to detect a neighbor failure, but they do not speed up the overall reconvergence process after a core router failure, which involves LSA flooding, SPF calculation, and routing table updates. BFD provides faster failure detection than fast hello timers and integrates with OSPF to trigger quicker reconvergence.
★ When this WOULD be the correct answer
A question asks: 'An organization wants to reduce OSPF neighbor dead timer detection from 40 seconds to 10 seconds without changing the hello interval. Which feature should be configured?' In this scenario, enabling OSPF fast hello timers (or adjusting hello/dead intervals) would be correct.
Why candidates choose this
Candidates may think that faster hello timers directly speed up convergence, but they only improve failure detection time; the overall reconvergence still depends on OSPF's LSA propagation and SPF calculation, which BFD addresses more effectively.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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.
Go deeper
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Key term
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Key term
Router
A router is a networking device that connects different networks together and directs data traffic between them by choosing the best path for data to travel.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.