NSE4 System and Network Administration Practice Question
An administrator is configuring ECMP (Equal-Cost Multi-Path) on a FortiGate. Which TWO conditions are required for ECMP to load balance traffic across multiple routes?
⚠ Common exam trap
It's easy for candidates to confuse 'priority' with 'administrative distance' or assume ECMP requires different next-hop IPs, but FortiGate actually requires both priority and administrative distance to be identical, and next-hop IPs can be the same if interfaces differ.
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
✓
Routes must have the same priority setting
ECMP requires that multiple routes have the same priority (also known as 'distance' in some contexts) to be considered equal-cost. In FortiGate, priority is a metric that determines route preference; only routes with identical priority can be used simultaneously for load balancing. Option C is also correct because administrative distance must be the same for routes to be considered equal; if administrative distances differ, the route with the lower distance is preferred, and ECMP will not apply.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Routes must use different next-hop IP addresses
Why it's wrong here
ECMP does not require routes to use different next-hop IP addresses as a separate configuration condition. In FortiGate, multiple routes to the same destination with equal administrative distance and priority are automatically considered for ECMP; whether the next-hop IPs differ is a natural outcome of having distinct paths. If two routes share the same next-hop, they are duplicates and only one is retained, so the distinguishing factor is equality of cost, not the next-hop address. Thus, this statement is incorrect because it misidentifies a consequence as a prerequisite.
- ✓
Routes must have the same priority setting
Why this is correct
The route priority setting, also known as the metric, must be identical for all routes to be eligible for ECMP in FortiGate. FortiGate evaluates routes by administrative distance first, then priority, and only when both values match are the routes considered equal cost and installed simultaneously. If one route has a lower priority, it will always be preferred, and the higher-priority route will be ignored, preventing load balancing. Therefore, ensuring the same priority is a correct and essential condition for ECMP.
- ✓
Routes must have the same administrative distance
Why this is correct
Equal administrative distance is a fundamental requirement for ECMP because it ensures all candidate paths are equally trusted. FortiGate uses administrative distance to rank route sources; if distances differ, the route with the lower distance is selected as the sole best path, and no multi-path behavior occurs. Only when the administrative distances are identical, along with priority, will the routes be treated as equal cost and installed in the routing table. Thus, matching administrative distance is a correct and necessary condition for ECMP.
- ✗
Routes must be static routes only
Why it's wrong here
ECMP is not restricted to static routes; it fully supports dynamic routing protocols such as OSPF, BGP, and RIP. For instance, OSPF natively computes multiple equal-cost paths when the same destination is reachable via several next hops, and FortiGate automatically installs up to the configured number of ECMP routes. Static routes are only one example, so claiming ECMP requires static routes is false. Dynamic protocols are often used to create ECMP paths, making this statement incorrect.
- ✗
Routes must be through different interfaces
Why it's wrong here
ECMP does not require the routes to traverse different physical interfaces; it only requires equal cost, and the paths can use the same interface or different interfaces. For example, two static routes with equal distance and priority might point to different next-hop addresses reachable through the same physical port, and FortiGate will still perform ECMP. The interface alone does not determine path identity; the combination of next-hop IP and egress interface matters. Since same-interface multi-path is possible, this statement is incorrect.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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