The correct answer is to rely on the implicit deny policy at the end of the policy list, which will block all traffic not explicitly allowed. This is the recommended security posture because the implicit deny is a default, hidden rule on FortiGate that automatically denies any traffic not matched by a preceding explicit allow policy. By creating only a single policy to permit HTTP traffic from the internal network (10.0.1.0/24) to the DMZ web server (192.168.1.10), the implicit deny ensures all other traffic—such as SSH, RDP, or any unsolicited inbound connections—is blocked without additional configuration. On the Fortinet NSE 4 Network Security Professional exam, this concept tests your understanding of firewall policy order and the principle of least privilege; a common trap is thinking you need to add an explicit deny rule at the bottom, which is unnecessary and can introduce misconfiguration. Memory tip: “Implicit deny does the denying for you—just allow what’s needed, and the rest is history.”
NSE4 Firewall Policies and NAT Practice Question
This NSE4 practice question tests your understanding of firewall policies and nat. 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 is creating firewall policies for a FortiGate that separates the internal network (10.0.1.0/24) from a DMZ (192.168.1.0/24). The goal is to allow HTTP traffic from the internal network to the DMZ web server (192.168.1.10) but deny all other traffic. What is the recommended security posture for the implicit deny policy?
Set the allow policy to also deny all other traffic using security profiles
Why wrong: Security profiles do not replace policy deny actions.
B
Disable the implicit deny policy and create a catch-all deny policy
Why wrong: Implicit deny cannot be disabled; it is always present.
C
Create an explicit deny policy with logging enabled before the allow policy
Why wrong: An explicit deny is not necessary; implicit deny already blocks unmatched traffic. However, logging is not enabled by default on implicit deny.
D
Rely on the implicit deny policy at the end of the policy list, which will block all traffic not explicitly allowed
Implicit deny provides a default-deny posture, which aligns with least privilege.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Rely on the implicit deny policy at the end of the policy list, which will block all traffic not explicitly allowed
The implicit deny policy is a default, hidden policy at the end of the FortiGate policy list that denies all traffic not explicitly allowed by preceding policies. Since the administrator wants to allow only HTTP traffic from internal to the DMZ web server and deny all other traffic, relying on the implicit deny is the correct and recommended security posture. It automatically blocks everything else without requiring manual configuration, ensuring no unintended traffic is permitted.
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.
✗
Set the allow policy to also deny all other traffic using security profiles
Why it's wrong here
Security profiles do not replace policy deny actions.
✗
Disable the implicit deny policy and create a catch-all deny policy
Why it's wrong here
Implicit deny cannot be disabled; it is always present.
✗
Create an explicit deny policy with logging enabled before the allow policy
Why it's wrong here
An explicit deny is not necessary; implicit deny already blocks unmatched traffic. However, logging is not enabled by default on implicit deny.
✓
Rely on the implicit deny policy at the end of the policy list, which will block all traffic not explicitly allowed
Why this is correct
Implicit deny provides a default-deny posture, which aligns with least privilege.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think they need to create an explicit deny policy with logging to block unwanted traffic, not realizing that the implicit deny already performs this function and that placing a deny policy before the allow policy would break the intended traffic flow.
Detailed technical explanation
How to think about this question
The implicit deny policy is a built-in, hidden policy that exists at sequence number 0 in the policy list, after all user-defined policies. It cannot be deleted or modified, and it logs denied traffic only if global logging for implicit deny is enabled under system settings. In a real-world scenario, if an administrator mistakenly places an explicit deny policy before the allow policy, all traffic would be blocked, highlighting the importance of policy order and the reliance on the implicit deny for default blocking.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Firewall Policies and NAT — This question tests Firewall Policies and NAT — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Rely on the implicit deny policy at the end of the policy list, which will block all traffic not explicitly allowed — The implicit deny policy is a default, hidden policy at the end of the FortiGate policy list that denies all traffic not explicitly allowed by preceding policies. Since the administrator wants to allow only HTTP traffic from internal to the DMZ web server and deny all other traffic, relying on the implicit deny is the correct and recommended security posture. It automatically blocks everything else without requiring manual configuration, ensuring no unintended traffic is permitted.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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