Question 1hardmultiple choice
Review the full subnetting walkthrough →Question 965 of 1,000
Quick Answer
The answer is a mismatch in the PBR rule’s source address configuration. Policy-based routing on FortiGate overrides the default route only when traffic matches every defined criterion, including the source IP and subnet mask; if the rule specifies 192.168.1.0/24 but the actual traffic originates from a slightly different subnet or a typo exists in the mask, the traffic does not match and falls through to the routing table, defaulting to ISP2. On the Fortinet NSE 4 exam, this scenario tests your understanding that PBR is evaluated before the routing table but is strictly conditional—a common trap is assuming PBR applies globally, when in fact it requires exact source, destination, and interface matches. Remember the memory tip: “PBR is picky—if the source doesn’t match, the route dispatches.”
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.
A FortiGate administrator configures policy-based routing (PBR) to direct traffic from subnet 192.168.1.0/24 to the internet via ISP1. 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 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 PBR rule's source address does not match the traffic correctly.
Policy-based routing (PBR) on FortiGate overrides the routing table only when the traffic matches all configured criteria, including the source address. If the source address in the PBR rule does not match 192.168.1.0/24 exactly (e.g., a typo, wrong subnet mask, or missing entry), the traffic falls through to the default route via ISP2. This is the most likely cause because PBR rules are evaluated before the routing table, but only for matching traffic.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse PBR with static routing and assume the default route's administrative distance or priority can override PBR, but PBR is evaluated before the routing table and is not subject to route metrics.
Detailed technical explanation
How to think about this question
FortiGate PBR uses a policy-based approach where each rule has a sequence number (priority) and is evaluated in order; the first match determines the gateway. Under the hood, PBR creates a separate forwarding decision that bypasses the FIB (Forwarding Information Base) for matched packets, but unmatched packets still use the routing table. A common real-world scenario is misconfiguring the source subnet mask (e.g., /24 vs /32) or using an interface IP instead of the subnet, causing the PBR rule to never match.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this NSE4 question test?
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 PBR rule's source address does not match the traffic correctly. — Policy-based routing (PBR) on FortiGate overrides the routing table only when the traffic matches all configured criteria, including the source address. If the source address in the PBR rule does not match 192.168.1.0/24 exactly (e.g., a typo, wrong subnet mask, or missing entry), the traffic falls through to the default route via ISP2. This is the most likely cause because PBR rules are evaluated before the routing table, but only for matching traffic.
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 →
Same concept, more angles
2 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 is troubleshooting why traffic from a specific source IP is not being matched by a policy route. Which THREE steps should the administrator take to diagnose the issue?
medium- A.Disable all firewall policies to test routing.
- B.Change the administrative distance of the default route to 0.
- ✓ C.Verify the source address object in the policy route matches the traffic's source IP.
- ✓ D.Check the policy route list order and ensure the matching condition is above the default route.
- ✓ E.Use the 'diagnose debug flow' command to trace packet flow.
Why C: Option C is correct because the most fundamental step in troubleshooting a policy route mismatch is to verify that the source address object defined in the policy route exactly matches the source IP of the traffic. If the object is misconfigured (e.g., wrong subnet mask, incorrect IP range, or a typo), the traffic will never hit the policy route, regardless of other settings.
Variation 2. An administrator notices that traffic to a particular subnet is being load-balanced across two WAN links, but they want all traffic to that subnet to use a single link. Which feature should be configured?
medium- ✓ A.Policy routing
- B.ECMP routing
- C.Static route with higher distance
- D.Route summarization
Why A: Policy routing (also called PBR) allows you to override the routing table based on criteria such as source/destination IP, protocol, or port. By configuring a policy route that matches traffic to the specific subnet and sets the output interface to a single WAN link, you can force all that traffic to use one link instead of being load-balanced.
Last reviewed: Jun 24, 2026
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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