NSE7 Advanced Networking and SD-WAN Practice Question
An administrator is configuring an SD-WAN rule to route VoIP traffic over the most reliable link. They have two WAN members: port1 (MPLS) and port2 (Internet). They create a performance SLA that monitors latency and jitter, and set the SLA target to 150 ms latency and 30 ms jitter. They apply the SLA to both members. The SD-WAN rule is set to 'Best Quality' strategy. After applying the configuration, they notice that VoIP traffic is sometimes routed over port2 even though port1 has lower latency and jitter. What is the most likely reason?
⚠ Common exam trap
The trap here is thinking that 'Best Quality' always selects the member with the lowest latency and jitter, ignoring SLA thresholds; in reality, a member must meet the SLA to be considered, and intermittent violations cause temporary failover.
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
✓
Port1 is intermittently failing the SLA due to jitter spikes, causing the FortiGate to temporarily select port2 until port1 meets the SLA again.
With the 'Best Quality' strategy, the FortiGate continuously evaluates member health against the SLA. If port1 experiences jitter spikes that exceed the configured threshold, it is considered to have failed the SLA, and the rule will select the next best member, which is port2. This can cause VoIP traffic to temporarily switch to port2. Once port1's jitter returns below the threshold, it will be preferred again. This behavior ensures that traffic only uses links that meet the required 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.
- ✓
Port1 is intermittently failing the SLA due to jitter spikes, causing the FortiGate to temporarily select port2 until port1 meets the SLA again.
Why this is correct
The 'Best Quality' strategy continuously monitors SLA metrics. If port1 experiences jitter spikes that exceed the configured 30 ms threshold, it fails the SLA, and the FortiGate selects port2, which may meet the SLA. Once port1 recovers, it will be preferred again. This intermittent behavior is expected when SLA thresholds are tight and link quality fluctuates.
- ✗
The performance SLA is not enabled on the SD-WAN rule, so the FortiGate falls back to a default load balancing method.
Why it's wrong here
If the SLA were not enabled, the rule would not consider SLA status, but the scenario states the SLA is applied to both members and the rule uses 'Best Quality'. The issue is more likely due to intermittent SLA failures on port1, causing the rule to temporarily select port2.
- ✗
The 'Best Quality' strategy selects the member with the lowest cost, not the best quality, so port2 is chosen because it has a lower cost.
Why it's wrong here
The 'Best Quality' strategy selects the member with the best measured quality based on the SLA metrics, not cost. Cost is used by the 'Lowest Cost' strategy. Therefore, the selection of port2 is not due to cost but likely due to SLA violations or measurement fluctuations.
- ✗
The SD-WAN rule is configured with a source IP-based load balancing method, which overrides the 'Best Quality' strategy.
Why it's wrong here
The scenario states the rule uses 'Best Quality' strategy, not source IP-based load balancing. Source IP-based methods are different algorithms and would not override the strategy unless explicitly configured. The intermittent routing is due to SLA violations on port1, not an override.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Fortinet exam blueprint
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