Troubleshooting FortiGate Policy Route Issues
An administrator configures a policy route to direct traffic from subnet 10.1.1.0/24 to the internet via ISP1 with a gateway of 203.0.113.1. However, traffic from that subnet is still using the default route via ISP2. What is the MOST likely cause?
Quick Answer
The answer is that the source interface is not specified in the policy route. Policy routes in FortiGate require both a source interface and a source address to match incoming traffic; without the source interface defined, the firewall cannot determine which physical or VLAN interface the traffic from subnet 10.1.1.0/24 is arriving on, so it skips the policy route entirely and falls back to the default route via ISP2. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this scenario tests your understanding of the policy route evaluation order and the critical role of the source interface field—a common trap is assuming a source address alone is sufficient, or confusing policy routes with static routes that only need a destination. Remember the memory tip: “No interface, no match—policy routes need a source to catch.”
⚠ Common exam trap
Many candidates assume policy routes are evaluated after the routing table or that administrative distance affects policy route matching, when in fact policy routes are processed first and require explicit source interface matching.
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 source interface is not specified in the policy route
Policy routes in FortiGate are evaluated based on the source interface and source address. If the source interface is not specified, the policy route may not match the incoming traffic because the firewall does not know which interface the traffic is arriving on. Without a matching source interface, the policy route is skipped, and the default route (via ISP2) is used instead.
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 source interface is not specified in the policy route
Why this is correct
Policy routes require a source interface to match. If not set, the policy route may not apply.
- ✗
The default route has a lower administrative distance
Why it's wrong here
Policy routes override static routes regardless of distance.
- ✗
The policy route's destination is set to 'all' which conflicts with the default route
Why it's wrong here
Destination 'all' should match any destination; it would not cause a conflict.
- ✗
The policy route is configured after the default route in the routing table
Why it's wrong here
Policy routes are evaluated before the routing table; order does not matter.
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Same concept, more angles
3 more ways this is tested on NSE4
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. An administrator configures a policy route to force traffic from a specific source subnet to use a particular WAN interface. After applying the configuration, the traffic still uses the default route. What is the most likely cause?
medium- A.The static default route has a lower administrative distance than the policy route
- B.The FortiGate's VDOM is enabled and the policy route is in the wrong VDOM
- ✓ C.The policy route's incoming interface is incorrectly configured
- D.The policy route has a lower priority than the static default route
Why C: Policy routes are evaluated based on the incoming interface specified in the rule. If the incoming interface is misconfigured (e.g., set to 'any' or the wrong physical interface), the FortiGate will not match the traffic against the policy route, causing it to fall through to the routing table and use the default route. The policy route must explicitly match the interface on which the traffic enters the FortiGate.
Variation 2. An administrator configures a policy route to send all traffic from a specific subnet to a different next-hop. However, traffic from that subnet is still using the default route. Which configuration could be causing this?
hard- A.The firewall policy denies the traffic before policy routing
- ✓ B.The policy route is applied to the wrong incoming interface
- C.The default route has a higher administrative distance
- D.The policy route destination is set to all
Why B: Policy routes are evaluated based on the incoming interface of the traffic. If the policy route is applied to the wrong incoming interface, traffic from the specified subnet arriving on a different interface will not match the policy and will instead follow the default route. This is a common misconfiguration where the administrator assumes the policy applies globally rather than per-interface.
Variation 3. An administrator configures a policy route to send all traffic from subnet 172.16.1.0/24 to a specific next-hop 10.0.0.2. However, the traffic is still using the default route. What could be the reason?
medium- ✓ A.The policy route has a lower priority than the default route.
- B.The policy route does not have a destination interface set.
- C.The policy route must be configured before the default route.
- D.The source subnet is not correctly defined in the policy route.
Why A: Policy routes in FortiGate are evaluated based on their priority value, where a lower number indicates higher priority. If the policy route has a higher priority value (e.g., 10) than the default route (which is implicitly 0), the default route will be preferred. The administrator must ensure the policy route's priority is lower than the default route's priority to override it.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE4 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 NSE4 exam.