The answer is that the firewall policy action is set to DENY, which directly causes the traffic drop. When a FortiGate firewall policy is configured with an action of DENY, any traffic matching that policy’s source, destination, and service criteria will be discarded at that point in the policy evaluation, even if the intended rule was to allow the traffic. In the scenario described, the debug flow shows packets hitting the policy but being dropped because the policy itself is instructing the firewall to deny the HTTP traffic, overriding any implicit allow logic. On the Fortinet NSE 4 Network Security Professional exam, this question tests your understanding of policy evaluation order and the critical difference between explicit deny and implicit deny—a common trap is assuming a policy that matches must be allowing traffic. Remember the memory tip: “If it hits but gets dropped, check the action—allow or deny, don’t get stopped.”
NSE4 Firewall Policies and NAT Practice Question
This NSE4 practice question tests your understanding of firewall policies and nat. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 admin configures a firewall policy to allow HTTP traffic from the internal network (10.0.0.0/8) to the internet. Users report that they cannot access web pages. The admin runs 'diagnose debug flow' and sees packets hitting the policy but being dropped. 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.
The interface is not configured as a WAN interface
Why wrong: Interface type does not affect policy matching; the policy references specific interfaces.
B
The policy is disabled
Why wrong: A disabled policy would not show hits in debug flow.
C
The firewall policy action is set to DENY
If the policy action is set to DENY, even though the traffic matches the source/destination/service, it will be dropped. This is a common misconfiguration.
D
The traffic is being processed by a higher priority deny policy
Why wrong: If a higher priority deny policy matched, the debug flow would not show the packet hitting this allow policy.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The firewall policy action is set to DENY
The implicit deny policy at the end of the policy list will drop traffic that does not match any explicit policy. If the policy is not the last matching policy or if there is a deny policy above it, traffic could be denied. But the most common issue is that the policy is not correctly ordered, and a deny policy above it is matching. However, the stem says packets hit the policy but are dropped. This typically indicates that the policy matched but another factor (like security profile action) dropped it, or the policy's action is set to DENY by mistake. Given the options, the admin likely set the policy action to DENY.
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 interface is not configured as a WAN interface
Why it's wrong here
Interface type does not affect policy matching; the policy references specific interfaces.
✗
The policy is disabled
Why it's wrong here
A disabled policy would not show hits in debug flow.
✓
The firewall policy action is set to DENY
Why this is correct
If the policy action is set to DENY, even though the traffic matches the source/destination/service, it will be dropped. This is a common misconfiguration.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The traffic is being processed by a higher priority deny policy
Why it's wrong here
If a higher priority deny policy matched, the debug flow would not show the packet hitting this allow policy.
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 show hits in debug flow.
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.
Firewall Policies and NAT — This question tests Firewall Policies and NAT — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The firewall policy action is set to DENY — The implicit deny policy at the end of the policy list will drop traffic that does not match any explicit policy. If the policy is not the last matching policy or if there is a deny policy above it, traffic could be denied. But the most common issue is that the policy is not correctly ordered, and a deny policy above it is matching. However, the stem says packets hit the policy but are dropped. This typically indicates that the policy matched but another factor (like security profile action) dropped it, or the policy's action is set to DENY by mistake. Given the options, the admin likely set the policy action to DENY.
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.
About these practice questions
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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 firewall policy with source address 'internal_net' (10.0.0.0/16) and destination address 'server_farm' (10.10.10.0/24). The action is set to ACCEPT with NAT enabled. However, traffic from 10.0.1.100 to 10.10.10.50 is being denied. What is the most likely cause?
medium
A.The destination address 'server_farm' does not include 10.10.10.50
✓ B.There is a deny policy above this policy that matches the traffic
C.The NAT translation is causing the traffic to be dropped
D.The source address 'internal_net' does not include 10.0.1.100
Why B: Policy order must be checked; another policy higher in the list with a DENY action might match before this policy. Also, the source/destination must match exactly.
Variation 2. A FortiGate admin configures a firewall policy to allow outbound HTTP traffic and applies a web filter profile. The admin notices that some users can access a known malicious URL while others are blocked. All users are in the same source subnet (10.0.1.0/24). What is the MOST likely cause of this inconsistent behavior?
hard
A.The FortiGate is using a proxy server that caches different results for different users
B.The web filter profile is configured to 'allow' but the FortiGuard rating is inconsistent
C.The firewall policy has an FQDN destination that resolves to different IPs for different users due to DNS load balancing
✓ D.Some users have a different web filter profile applied due to a policy ordering issue where a higher-priority policy matches their traffic
Why D: Option D is correct because when multiple firewall policies match traffic from the same source subnet, FortiGate uses the first matching policy in order (lowest policy ID). If a higher-priority policy with a different web filter profile matches some users' traffic (e.g., based on source port or application), those users will have different filtering behavior. This is a classic policy ordering issue where the intended web filter profile is not applied consistently to all users in the same subnet.
Last reviewed: Jun 21, 2026
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