NSE4 System and Network Administration Practice Question
A FortiGate is configured with two WAN interfaces in an SD-WAN zone. The administrator wants to ensure voice traffic uses the interface with the lowest latency. Which SD-WAN configuration should be used?
⚠ Common exam trap
Test-takers frequently confuse policy-based routing (PBR) with SD-WAN rules, not realizing that PBR lacks dynamic SLA-based path selection and cannot automatically adapt to changing network conditions.
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 an SD-WAN rule with a performance SLA that monitors latency and set strategy to 'Best Quality'
SD-WAN rules with a performance SLA allow the FortiGate to monitor real-time latency on each WAN interface and dynamically route voice traffic to the interface with the lowest latency. The 'Best Quality' strategy selects the best-performing interface based on the SLA metrics, ensuring optimal voice quality.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Set the strategy to 'Manual'
Why it's wrong here
Manual strategy in SD-WAN requires the administrator to explicitly select an outbound interface for each rule; it does not use real-time SLA probes or latency measurements. With a Manual setting, the FortiGate will keep sending voice traffic over the designated interface even if that link's latency has degraded, so it fails the requirement to dynamically select the lowest-latency WAN path.
- ✗
Set the strategy to 'Load Balance'
Why it's wrong here
Load Balance strategy in SD-WAN distributes sessions across members based on configured weights or volume, not on real-time link quality. While it may spread voice traffic across multiple WAN links, it does not continuously measure latency via performance SLA probes, so it cannot guarantee that voice traffic is sent over the lowest-latency path at any given moment.
- ✓
Configure an SD-WAN rule with a performance SLA that monitors latency and set strategy to 'Best Quality'
Why this is correct
This is correct because a performance SLA defines the latency threshold and probing mechanism, and the Best Quality strategy inspects those live SLA results to choose the WAN interface with the lowest measured latency. When the SLA detects that a WAN link's latency exceeds the threshold, the FortiGate dynamically fails over voice traffic to the best-performing member, ensuring optimal real-time voice quality.
- ✗
Use policy-based routing with a higher priority for voice traffic
Why it's wrong here
Policy-based routing with a higher priority for voice traffic uses static routing rules to define the preferred path based on source/destination or service, but it does not evaluate current link latency. Even with high priority, the FortiGate will continue sending voice traffic over the configured interface until that policy is manually changed; it cannot automatically react to rising latency or select a better path in real time.
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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.