NSE4 High Availability and Diagnostics Practice Question
A company has two remote sites connected via an SD-WAN overlay. The headquarters uses a FortiGate with two WAN links: Fiber (priority 1) and LTE (priority 2). The SD-WAN rule for business-critical traffic uses the 'best quality' strategy with SLA targets for latency and jitter. The fiber link occasionally experiences high jitter but low latency. The engineer notices that traffic is not failing over to LTE even when jitter exceeds the threshold. What is the most likely reason?
⚠ Common exam trap
Many candidates assume jitter is automatically monitored in SD-WAN SLA, but FortiGate requires explicit configuration of each metric (latency, jitter, packet loss) in the performance SLA; otherwise, unconfigured metrics are ignored for failover decisions.
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
✓
The performance SLA for jitter is not configured, only latency.
The SD-WAN rule uses the 'best quality' strategy, which selects the best link based on configured SLA metrics. If only latency is configured in the performance SLA, jitter exceeding the threshold will not trigger a failover, as the SLA only evaluates the configured metrics. The fiber link may still meet the latency SLA, so traffic remains on it despite high jitter.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The performance SLA for jitter is not configured, only latency.
Why this is correct
The 'best quality' strategy only fails over when the configured SLA performance criteria are breached. If the performance SLA monitors latency alone, high jitter never triggers a member failure, so traffic stays on the fiber link despite exceeding the jitter threshold.
- ✗
The SD-WAN rule has SLA match set to 'either' instead of 'all'.
Why it's wrong here
With 'either', the link passes the SLA if latency OR jitter meets target, so low latency masks the jitter breach and no failover occurs. 'All' would require both targets, triggering failover. It is tempting because 'either' is a valid setting, but it suits scenarios where only one metric must hold.
- ✗
The LTE link has a higher cost and is not considered for failover.
Why it's wrong here
Cost is a routing attribute for cost-based strategies, not an exclusion from 'best quality' SLA evaluation; LTE remains a candidate when fiber breaches jitter. Cost is tempting because it does steer path selection, but it would be the correct choice under a lowest-cost strategy, not best quality.
- ✗
The fiber link has a higher interface weight.
Why it's wrong here
Interface weight only influences load-balancing distribution among links that already satisfy the SLA; it cannot keep a jitter-breaching link in the rule. Weight is tempting because it appears to govern link preference, but it is the correct choice for weighting traffic across healthy members, not for SLA enforcement.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE4 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 NSE4 exam.