- A
The firewall policy is disabled
Why wrong: A disabled policy would not match, but debug flow would not show 'no policy matched' until after evaluating that policy.
- B
The debug flow filter is not configured correctly
Why wrong: A misconfigured filter would not capture traffic, but the output would be empty or show other matches.
- C
The source IP is not in the routing table
Why wrong: Routing is for destination; source IP does not need to be in the routing table.
- D
The traffic is being blocked by an implicit deny or a different policy before reaching the expected policy
In FortiGate, the first matching policy is applied. If an earlier policy denies the traffic, debug flow shows 'no policy matched' from the perspective of the correct policy, but actually a preceding policy matched.
NSE4 High Availability and Diagnostics Practice Question
This NSE4 practice question tests your understanding of high availability and diagnostics. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 runs 'diagnose debug flow' with a filter for a specific source IP. The output shows 'no policy matched' for the traffic. The administrator verifies that a firewall policy exists with that source IP. What is the most likely reason for the 'no policy matched' message?
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 traffic is being blocked by an implicit deny or a different policy before reaching the expected policy
Option B is correct. Debug flow may show 'no policy matched' when traffic hits an implicit deny before reaching the explicit policy, e.g., due to inter-VDOM routing or policy order where an earlier policy with a broader match blocks it.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 firewall policy is disabled
Why it's wrong here
A disabled policy would not match, but debug flow would not show 'no policy matched' until after evaluating that policy.
- ✗
The debug flow filter is not configured correctly
Why it's wrong here
A misconfigured filter would not capture traffic, but the output would be empty or show other matches.
- ✗
The source IP is not in the routing table
Why it's wrong here
Routing is for destination; source IP does not need to be in the routing table.
- ✓
The traffic is being blocked by an implicit deny or a different policy before reaching the expected policy
Why this is correct
In FortiGate, the first matching policy is applied. If an earlier policy denies the traffic, debug flow shows 'no policy matched' from the perspective of the correct policy, but actually a preceding policy matched.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Trap categories for this question
Command / output trap
A disabled policy would not match, but debug flow would not show 'no policy matched' until after evaluating that policy.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
- Standard ACLs match source addresses.
- Extended ACLs can match source, destination, protocol and ports.
- The first matching ACL entry is used.
- There is usually an implicit deny at the end.
TExam Day Tips
- Check inbound versus outbound direction.
- Read the ACL from top to bottom.
- Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related NSE4 ACL questions on filtering logic and placement.
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High Availability and Diagnostics — study guide chapter
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FAQ
Questions learners often ask
What does this NSE4 question test?
High Availability and Diagnostics — This question tests High Availability and Diagnostics — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The traffic is being blocked by an implicit deny or a different policy before reaching the expected policy — Option B is correct. Debug flow may show 'no policy matched' when traffic hits an implicit deny before reaching the explicit policy, e.g., due to inter-VDOM routing or policy order where an earlier policy with a broader match blocks it.
What should I do if I get this NSE4 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related NSE4 ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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Last reviewed: Jun 21, 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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