NSE7 Advanced Networking and SD-WAN Practice Question
An administrator wants to load-balance traffic across two WAN links using ECMP. The routes have equal distances and metrics. However, traffic is only using one of the links. What could be the cause?
⚠ Common exam trap
Candidates often assume equal metrics are sufficient for ECMP, overlooking that administrative distance (AD) is the primary tiebreaker in route selection, and different routing protocols inherently assign different ADs unless manually overridden.
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 routes are learned via different routing protocols with different administrative distances.
ECMP (Equal-Cost Multi-Path) requires routes to have identical administrative distances (AD) to be considered equal-cost. If routes are learned via different routing protocols (e.g., OSPF with AD 110 and static with AD 1), the FortiGate will prefer the route with the lower AD, even if metrics are equal. This causes traffic to use only the preferred link, as the other route is not installed in the routing table for ECMP selection.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The routes are learned via different routing protocols with different administrative distances.
Why this is correct
ECMP requires equal distances; if one route has a lower distance, it will be preferred.
- ✗
ECMP is not enabled globally under config system settings.
Why it's wrong here
ECMP is enabled by default; disabling it would cause this.
- ✗
The firewall policy is configured to use a specific egress interface.
Why it's wrong here
Policy can override routing, but typically routing decides.
- ✗
The traffic is session-based and ECMP uses per-packet load balancing.
Why it's wrong here
FortiGate ECMP is per-session by default.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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