SD-WAN Best Quality Strategy: Automatic Failover on SLA Failure
A company has two internet connections: a primary fiber link (port1, 100 Mbps) and a backup DSL link (port2, 20 Mbps). They are using SD-WAN to load balance traffic based on volume, with a rule that sends 70% of traffic to port1 and 30% to port2. Recently, users report that video conferencing applications are experiencing high latency and jitter. The network team finds that the SD-WAN performance SLA for the fiber link shows 80% packet loss and high latency. The SD-WAN rule action is set to 'best quality' with a latency threshold of 150 ms. The current latency on port1 is 200 ms, and on port2 is 40 ms. What should the administrator do to ensure that video conferencing traffic uses the DSL link while the fiber link is degraded?
Quick Answer
The answer is that no changes are needed, because the SD-WAN best quality strategy with automatic failover on SLA failure will handle this scenario. When the SD-WAN rule action is set to 'best quality', the FortiGate continuously monitors performance SLA metrics like latency and packet loss; if an interface fails the threshold—here, port1 exceeds the 150 ms latency limit and shows 80% packet loss—new sessions are automatically steered to the best-performing link, which is port2 with 40 ms latency. This tests your understanding of how SD-WAN best quality differs from other strategies like volume-based load balancing, a key concept in the Fortinet NSE 7 Advanced Security NSE7 exam. A common trap is assuming manual intervention is required, but the automatic failover is built into the 'best quality' action. Memory tip: think "best quality = best path per session, not per packet"—the SLA failure triggers a seamless switch for new flows only.
⚠ Common exam trap
Test-takers frequently assume manual configuration (like changing thresholds or ratios) is required to fix a degraded link, when in fact the 'best quality' action with performance SLA already provides automatic failover to the best-performing link.
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
✓
No changes are needed; the SD-WAN rule with 'best quality' will automatically use port2 for new sessions because port1 does not meet the SLA.
The SD-WAN rule action is set to 'best quality', which means the FortiGate will automatically steer new sessions away from any interface that fails the performance SLA. Since port1 has 80% packet loss and 200 ms latency (exceeding the 150 ms threshold), it is considered degraded, and new video conferencing traffic will be directed to port2 (40 ms latency) without manual intervention.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the SLA latency threshold to 250 ms so that the fiber link is considered acceptable.
Why it's wrong here
Incorrect. This would allow the degraded link to be used, which would not solve the performance issue.
- ✗
Change the SD-WAN rule action to 'lowest cost' to favor the DSL link.
Why it's wrong here
Incorrect. 'Lowest cost' ignores SLA status and uses cost-based selection, which would still prefer the fiber link if its cost is lower.
- ✗
Adjust the volume ratio to send 100% of traffic to port2 until the fiber link recovers.
Why it's wrong here
Incorrect. This is a manual workaround but not necessary; the SLA mechanism already redirects traffic based on performance.
- ✓
No changes are needed; the SD-WAN rule with 'best quality' will automatically use port2 for new sessions because port1 does not meet the SLA.
Why this is correct
Correct. With 'best quality' action, if a member fails SLA, new sessions will be directed to the best performing member.
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Same concept, more angles
1 more way this is tested on NSE7
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company with a hub-and-spoke SD-WAN topology uses FortiGates at each site. The hub has two WAN links: MPLS (10 Mbps) and broadband (100 Mbps). The spokes connect only via MPLS. The company deploys a new real-time application that requires low latency and low jitter. The network administrator creates an SD-WAN rule for this application with 'best quality' strategy and both MPLS and broadband as members. The SLA for MPLS is configured with latency < 10 ms and jitter < 5 ms. The SLA for broadband is configured with latency < 50 ms and jitter < 20 ms. The actual measured latency on MPLS is 12 ms, and jitter is 4 ms. The broadband latency is 25 ms, jitter 10 ms. Which path will the application traffic take?
medium- ✓ A.The traffic will use the broadband link because MPLS SLA fails and broadband SLA is met.
- B.The traffic will be load-balanced between MPLS and broadband.
- C.The traffic will use the MPLS link because it is the preferred member.
- D.The traffic will be dropped because no link meets the SLA.
Why A: The SD-WAN rule uses the 'best quality' strategy, which selects the member with the best SLA performance. The MPLS link fails its SLA because its measured latency of 12 ms exceeds the configured threshold of 10 ms, even though jitter is within limits. The broadband link meets both its latency (25 ms < 50 ms) and jitter (10 ms < 20 ms) thresholds, so it becomes the active path for the application traffic.
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.