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.”
NSE4 System and Network Administration Practice Question
This NSE4 practice question tests your understanding of system and network administration. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that 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.
Detailed technical explanation
How to think about this question
FortiGate policy routes are processed in the order they appear in the configuration, and they require a source interface to be explicitly defined unless the policy route is applied globally. The firewall performs a policy route lookup before the routing table lookup; if the source interface is omitted, the policy route may not be triggered for traffic arriving on a specific interface, causing the traffic to fall through to the default route. In real-world scenarios, this often happens when an administrator configures a policy route for a subnet but forgets to bind it to the correct ingress interface, such as 'internal' or 'lan'.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
System and Network Administration — This question tests System and Network Administration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this NSE4 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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.
Last reviewed: Jun 24, 2026
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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.
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