NSE4 System and Network Administration Practice Question
A FortiGate is configured with two ISPs (WAN1 and WAN2) and uses SD-WAN for load balancing. The administrator notices that traffic to a critical SaaS application is being sent over the slower link. What should the administrator do to ensure this traffic uses the faster link?
⚠ Common exam trap
Watch out — candidates often confuse SD-WAN rules with policy-based routing, thinking PBR can achieve the same result, but PBR lacks SD-WAN's application awareness, SLA monitoring, and seamless failover integration.
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
✓
Create an SD-WAN rule to match the SaaS application's destination and set preferred member to the faster link.
SD-WAN rules allow you to define traffic steering policies based on application or destination, and setting a preferred member explicitly directs matching traffic to the faster link. This overrides the default load-balancing algorithm, ensuring critical SaaS traffic uses the optimal path without affecting other traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create an SD-WAN rule to match the SaaS application's destination and set preferred member to the faster link.
Why this is correct
An SD-WAN rule configured with an application match for the SaaS traffic and a preferred member set to the faster link is the correct approach because SD-WAN rules can steer traffic based on Layer 7 application signatures and dynamic link performance metrics. The preferred member acts as a tie-breaker, forcing the traffic to use the specified interface as long as it meets the SD-WAN health-check SLA (latency, jitter, packet loss), while still allowing automatic failover to the backup link if the preferred link degrades. This preserves redundancy and ensures the SaaS application consistently uses the best-performing path.
- ✗
Remove the slower link from the SD-WAN interface.
Why it's wrong here
Removing the slower link from the SD-WAN interface eliminates the ability to load balance and creates a single point of failure, which defeats the inherent redundancy of a dual-WAN design. Even if the remaining link is faster, this approach does not provide seamless failover if that link drops, causing SaaS sessions to blackhole rather than being dynamically re-routed. In an SD-WAN zone, all WAN members should remain active so that health-check probes and SLA-based steering can maintain optimal path selection while keeping resilience.
- ✗
Increase the bandwidth on the slower link.
Why it's wrong here
Increasing the bandwidth on the slower link merely raises its capacity but does not influence which interface the FortiGate selects for the SaaS application, because traffic steering is performed by SD-WAN rules and SLA metrics, not by raw interface speed alone. A higher-bandwidth link can still exhibit higher latency or jitter, which would make it ineligible against a faster, lower-latency link under the SD-WAN health-check algorithm. Moreover, this option is costly and does not address the requirement to explicitly route the SaaS traffic to the faster link; only an SD-WAN rule with a preferred member can enforce that behavior based on the application's destination.
- ✗
Configure policy-based routing for the SaaS application.
Why it's wrong here
Policy-based routing operates on source/destination IP and port, not on real-time link performance metrics; SD-WAN rules evaluate latency, jitter, and bandwidth to dynamically select the faster link. This option is tempting because PBR can direct traffic by application protocol, and in a static multi-WAN setup without SD-WAN, it would be the correct method to force SaaS traffic to a specific egress interface.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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