SD-WAN Best Quality Not Using Lowest Latency
A network administrator configures SD-WAN on a FortiGate with two WAN members (port1, port2). They set up a performance SLA to measure latency to 8.8.8.8. The SLA shows both members are 'alive'. However, traffic matching an SD-WAN rule with 'best quality' strategy is not using the lowest-latency link. What is the MOST likely cause?
Quick Answer
The answer is that the performance SLA does not have latency as the first metric in the priority order. The 'best quality' strategy selects the WAN member with the highest priority metric, and by default, jitter and packet loss are evaluated before latency. Even if the SLA shows both members as alive, the FortiGate will prefer a link with lower jitter or packet loss over one with lower latency unless latency is explicitly moved to the top of the metric priority list. This question tests your understanding of SD-WAN rule strategy logic on the Fortinet NSE 7 Advanced Security NSE7 exam, where a common trap is assuming 'best quality' automatically equals lowest latency. To avoid this, remember that the SLA priority order dictates the tiebreaker—latency is not king unless you crown it. A useful memory tip: "First in the list, first in the link."
⚠ Common exam trap
Many candidates assume 'best quality' always means lowest latency, but FortiGate's implementation uses a configurable metric priority order, so the first metric in the list determines the 'best' link, not latency by default.
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 does not have 'latency' as the first metric in the priority order
The 'best quality' strategy selects the link with the highest priority based on the performance SLA's metric order. If latency is not the first metric in the priority list (e.g., jitter or packet loss is first), the algorithm will prefer the link that best satisfies the first metric, not necessarily the lowest latency. Thus, even though both links are alive, the link with lower latency may be deprioritized if it performs worse on the first metric.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Both WAN members have the same cost in the SD-WAN configuration
Why it's wrong here
Cost is used for lowest-cost strategy, not best quality.
- ✗
The SD-WAN rule is configured with 'manual' strategy
Why it's wrong here
Manual strategy requires explicit interface selection, not best quality.
- ✗
The SD-WAN rule has 'set-match' enabled for source IP
Why it's wrong here
Set-match is for load balancing, not best quality; it doesn't affect metric-based selection.
- ✓
The performance SLA does not have 'latency' as the first metric in the priority order
Why this is correct
Best quality uses the configured metric order; if latency is not first, another metric determines the selection.
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Variation 1. An administrator configures SD-WAN with two members (port1 and port2). A performance SLA monitors latency to 8.8.8.8. The SD-WAN rule uses 'Best Quality' strategy based on latency. When the link on port1 becomes slow, the FortiGate continues using port1 even though port2 has lower latency. What is the most likely cause?
medium- A.The FortiGate is not receiving ICMP replies from 8.8.8.8
- B.The SD-WAN rule is configured with 'Manual' strategy
- ✓ C.The performance SLA is not associated with the SD-WAN members
- D.The load balancing algorithm is set to 'volume' instead of 'lowest-latency'
Why C: The performance SLA must be explicitly associated with the SD-WAN members (port1 and port2) for the 'Best Quality' strategy to use latency measurements. Without this association, the FortiGate cannot compare the SLA results per interface and defaults to using the current active member, even if its latency is higher. The SLA monitors 8.8.8.8, but the SD-WAN rule has no link to those measurements, so port1 continues to be used.
JA
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.