The answer is to configure BFD (Bidirectional Forwarding Detection). BFD improves OSPF convergence speed by providing sub-second failure detection, as low as 50 milliseconds, independent of the routing protocol itself. Instead of waiting for OSPF’s default dead timer intervals—which can take 40 seconds or more—BFD immediately alerts OSPF to a link or neighbor failure, triggering an instant recalculation of routes. On the CompTIA Network+ N10-009 exam, this question tests your understanding that BFD is a lightweight, protocol-agnostic mechanism designed specifically to accelerate convergence, and a common trap is confusing it with OSPF’s own hello or dead timers. Remember that BFD works in tandem with OSPF, not as a replacement for it. A useful memory tip: BFD stands for “Bypass the Four-second Dead timer”—it slashes detection time from seconds to milliseconds.
N10-009 BFD provides sub-second failure detection. Practice Question
This N10-009 practice question tests your understanding of network implementation. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: bFD provides sub-second failure detection.. 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.
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?
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.
BFD provides sub-second failure detection, allowing OSPF to converge much faster than with default timers.
Related concept
BFD provides sub-second failure detection.
✗
Convert all areas to stub areas
Why it's wrong here
Stub areas reduce the types of LSAs but do not directly improve convergence speed after a failure.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco 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.
Detailed technical explanation
How to think about this question
BFD operates as a lightweight, independent protocol that sends rapid echo or control packets between adjacent routers, with detection times configurable down to 50 ms. When BFD detects a failure, it signals the routing protocol (e.g., OSPF) via a callback, causing OSPF to immediately transition the neighbor to DOWN state and trigger SPF recalculation, bypassing the slower hello/dead timer mechanism. In real-world deployments, BFD is often used in conjunction with OSPF or BGP to achieve carrier-grade convergence under 200 ms.
KKey Concepts to Remember
BFD provides sub-second failure detection.
BFD operates independently of the routing protocol.
BFD can be used with OSPF, EIGRP, BGP, and IS-IS.
BFD offloads failure detection from the routing protocol's CPU.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
BFD provides sub-second failure detection.
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 N10-009 question in full detail.
The correct answer is: 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.
What should I do if I get this N10-009 question wrong?
Review bFD provides sub-second failure detection., then practise related N10-009 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
BFD provides sub-second failure detection.
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Variation 1. An organization uses OSPF as its interior gateway protocol in a multi-area design. After a core router failure, the network takes a long time to reconverge. Which technology can be implemented to improve convergence speed?
Why C: BFD provides sub-second failure detection by sending rapid, lightweight hello packets independently of OSPF's own hello mechanism. When a core router fails, BFD detects the link down in milliseconds and immediately signals OSPF to trigger reconvergence, drastically reducing the time OSPF would otherwise spend waiting for its own dead timer to expire.
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