SD-WAN Lowest-Cost Strategy Not Load Balancing
An administrator configures an SD-WAN rule to steer traffic from a specific subnet to an SD-WAN member with the lowest cost. Which load balancing algorithm should be selected in the SD-WAN rule to achieve this behavior?
⚠ Common exam trap
Many exam-takers confuse 'Lowest-cost' with dynamic path selection algorithms like 'Best Quality' or 'SLA-based' routing, assuming cost implies real-time performance metrics, whereas in Fortinet SD-WAN, cost is a static administrative value unrelated to link quality.
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
✓
Lowest-cost
The 'Lowest-cost' algorithm is correct because it directs traffic to the SD-WAN member with the lowest configured cost metric, which directly matches the administrator's requirement to steer traffic from a specific subnet to the member with the lowest cost. In Fortinet SD-WAN, the cost is a static metric assigned per SD-WAN member interface, and the Lowest-cost algorithm selects the member with the smallest cost value for each new session, ensuring traffic follows the least-cost path.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Lowest-cost
Why this is correct
Lowest-cost selects the member with the cheapest path metric, matching the stem's requirement to steer the subnet's traffic to the lowest-cost SD-WAN member. Other algorithms (such as weighted round-robin or source-IP based) ignore cost, so they cannot guarantee this outcome.
- ✗
Volume
Why it's wrong here
Volume balances traffic by measured byte throughput across members, so it distributes load rather than selecting the single lowest-cost member. It is tempting because volume is the correct algorithm when you want to spread traffic proportionally across links according to their capacity.
- ✗
Sessions
Why it's wrong here
Sessions distributes new sessions across members based on session counts, which spreads load instead of pinning traffic to the lowest-cost member. It is tempting because session-based balancing is the correct choice when you want even distribution of connection load across multiple WAN links.
- ✗
Source-dest-IP
Why it's wrong here
Source-dest-IP hashes each flow to a member for session stickiness, ignoring cost entirely, so traffic will not consistently use the cheapest link. It is tempting because this algorithm is correct when you need a given source-destination pair to remain on one member for the session's lifetime.
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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.