NSE7 Advanced Networking and SD-WAN Practice Question
An administrator configures BFD on a FortiGate to improve convergence time for OSPF. What is the primary purpose of BFD in this context?
⚠ Common exam trap
Candidates often confuse BFD's fast detection with OSPF's own hello mechanism, thinking BFD replaces or modifies OSPF timers, when in fact BFD works in parallel and triggers OSPF state changes only after a failure is detected.
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
✓
To detect link failures faster than OSPF hello timers
BFD (Bidirectional Forwarding Detection) provides sub-second link failure detection, typically in the range of 50-300 milliseconds, which is significantly faster than OSPF's default hello/dead intervals (e.g., 10/40 seconds for broadcast networks). By integrating BFD with OSPF, the FortiGate can trigger OSPF neighbor state changes and route convergence almost immediately upon a link failure, without waiting for OSPF's own hello timer expiration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
To reduce the number of OSPF neighbors
Why it's wrong here
BFD detects link or path failure faster; it neither forms nor removes OSPF adjacencies, which OSPF hello and dead timers govern. Reducing neighbour counts is achieved by area design or passive interfaces, not by enabling BFD.
- ✗
To encrypt OSPF packets
Why it's wrong here
BFD is a lightweight hello protocol that detects path failures in milliseconds so OSPF can tear down and reconverge faster; it carries no cryptographic payload. Encryption of OSPF packets is provided by OSPF authentication (MD5 or SHA hashing) or IPsec, which is the correct control when the requirement is protecting routing updates from tampering.
- ✓
To detect link failures faster than OSPF hello timers
Why this is correct
BFD sends rapid sub-second hello packets between neighbours, detecting path failures far sooner than OSPF's slower hello and dead intervals. This satisfies the convergence-time goal by triggering immediate OSPF neighbour teardown, allowing faster route recalculation and failover.
- ✗
To load balance OSPF traffic across multiple links
Why it's wrong here
BFD provides rapid liveness detection of the forwarding path so OSPF can tear down failed adjacencies quickly; it does not distribute traffic. Load balancing is the role of ECMP or OSPF equal-cost paths, not BFD.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE7 practice question is part of Courseiva's free Fortinet 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 NSE7 exam.