- A
Configure a VIP with restricted source
Why wrong: VIP is for destination NAT, not access control.
- B
Use a local-in policy to block the server IP
Why wrong: Local-in policies apply to traffic destined to the FortiGate itself, not through traffic.
- C
Create a deny policy from internet to server with any source, then an allow policy from source 203.0.113.50 to the server above it
This ensures only the specific IP is allowed, and everything else is denied by the explicit deny policy.
- D
Create a single allow policy from source 203.0.113.50 to the server and rely on implicit deny for all other traffic
Why wrong: Implicit deny only applies after all policies are evaluated; but the allow policy would match only that source, other traffic would hit implicit deny, effectively working, but not following least privilege because the allow policy is not explicitly denying first. However, it works, but best practice is explicit deny. The question expects explicit deny for least privilege.
Quick Answer
The correct answer is to create a deny policy from the internet to the server with any source, then place an allow policy from source 203.0.113.50 to the server above it. This configuration adheres to the principle of least privilege by explicitly blocking all traffic first—since the implicit deny at the end of the policy list is a last resort—and then permitting only the specific required IP address. On the Fortinet NSE 4 Network Security Professional exam, this scenario tests your understanding of policy order and the explicit deny rule, often appearing as a trap where candidates mistakenly rely on the implicit deny alone. A common memory tip is “deny first, allow second” or think of it as building a wall with a single door: you must close everything before unlocking the one entry point.
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 admin wants to block all traffic from the internet to a specific internal server except for the IP address 203.0.113.50. Which firewall policy configuration achieves this using the principle of least privilege?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"least"Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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
Create a deny policy from internet to server with any source, then an allow policy from source 203.0.113.50 to the server above it
The principle of least privilege dictates blocking all first (implicit deny is last, so explicit deny needed) then allowing only required traffic. Option A does that.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure a VIP with restricted source
Why it's wrong here
VIP is for destination NAT, not access control.
- ✗
Use a local-in policy to block the server IP
Why it's wrong here
Local-in policies apply to traffic destined to the FortiGate itself, not through traffic.
- ✓
Create a deny policy from internet to server with any source, then an allow policy from source 203.0.113.50 to the server above it
Why this is correct
This ensures only the specific IP is allowed, and everything else is denied by the explicit deny policy.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Authentication checks who the user is.
- ✗
Create a single allow policy from source 203.0.113.50 to the server and rely on implicit deny for all other traffic
Why it's wrong here
Implicit deny only applies after all policies are evaluated; but the allow policy would match only that source, other traffic would hit implicit deny, effectively working, but not following least privilege because the allow policy is not explicitly denying first. However, it works, but best practice is explicit deny. The question expects explicit deny for least privilege.
Common exam traps
Common exam trap: authentication is not authorization
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
How to think about this question
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
KKey Concepts to Remember
- Authentication checks who the user is.
- Authorization controls what the user is allowed to do after login.
- Privilege levels affect access to EXEC and configuration commands.
- AAA, TACACS+ and RADIUS can separate login success from command access.
TExam Day Tips
- Do not assume successful login means full administrative access.
- Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
- Separate login problems from permission problems before choosing the answer.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
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 Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related NSE4 questions on access control and AAA configuration.
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Firewall Policies and NAT — study guide chapter
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FAQ
Questions learners often ask
What does this NSE4 question test?
Firewall Policies and NAT — This question tests Firewall Policies and NAT — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: Create a deny policy from internet to server with any source, then an allow policy from source 203.0.113.50 to the server above it — The principle of least privilege dictates blocking all first (implicit deny is last, so explicit deny needed) then allowing only required traffic. Option A does that.
What should I do if I get this NSE4 question wrong?
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related NSE4 questions on access control and AAA configuration.
Are there clue words in this question I should notice?
Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
What is the key concept behind this question?
Authentication checks who the user is.
About these practice questions
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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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