The correct configuration is to create a deny policy for source 10.0.0.99 to destination 'all' on the WAN interface, then an allow policy for all other traffic. This works because FortiGate firewall policies are evaluated sequentially from top to bottom, and the first matching policy is applied; by placing the specific deny rule first, traffic from that IP is blocked before it can match a broader allow rule. On the Fortinet NSE 4 Network Security Professional exam, this scenario tests your understanding of policy order and implicit deny logic—a common trap is placing the allow policy first, which would permit the specific IP before the deny rule is ever reached. Remember the memory tip: "specific deny first, general allow last" to ensure the exception is enforced before the blanket permission. This sequential evaluation is a core concept for controlling traffic flow in FortiGate environments, especially when you need to block specific IP and allow all other traffic without disrupting normal access.
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 wants to create a firewall policy that blocks all traffic from a specific IP address (10.0.0.99) to the internet, but allows all other traffic. Which policy configuration is correct?
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 for source 10.0.0.99 to destination 'all' on the WAN interface, then an allow policy for all other traffic
Option A is correct because FortiGate firewall policies are evaluated sequentially from top to bottom, and the first matching policy is applied. By placing a deny policy for source 10.0.0.99 to destination 'all' on the WAN interface first, traffic from that IP is blocked. Then a subsequent allow policy for all other traffic (source 'all') permits everything else, ensuring the specific IP is blocked while all other traffic is allowed.
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.
✓
Create a deny policy for source 10.0.0.99 to destination 'all' on the WAN interface, then an allow policy for all other traffic
Why this is correct
The deny policy should be placed above the allow policy.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create an allow policy for source 'all' and then a deny policy for 10.0.0.99
Why it's wrong here
The deny policy must come before the allow policy to be effective.
✗
Use a local-in policy to block the IP
Why it's wrong here
Local-in policy is for traffic destined to the FortiGate itself.
✗
Create a policy that denies all traffic from 10.0.0.99 to any destination
Why it's wrong here
This would block all traffic, not just internet.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think a deny policy alone is sufficient, forgetting that FortiGate requires an explicit allow policy for other traffic to pass, or they misorder policies, placing the allow before the deny, which causes the deny to be ineffective due to first-match logic.
Detailed technical explanation
How to think about this question
FortiGate firewall policies use a first-match logic with an implicit deny at the end. The order of policies is critical; placing the deny policy before the allow policy ensures the specific source is blocked. In real-world scenarios, administrators often mistakenly place broad allow policies first, causing specific deny rules to never be evaluated. Additionally, the destination 'all' in the deny policy matches any destination, including the internet, while the allow policy for 'all' sources ensures all other IPs are permitted.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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: Create a deny policy for source 10.0.0.99 to destination 'all' on the WAN interface, then an allow policy for all other traffic — Option A is correct because FortiGate firewall policies are evaluated sequentially from top to bottom, and the first matching policy is applied. By placing a deny policy for source 10.0.0.99 to destination 'all' on the WAN interface first, traffic from that IP is blocked. Then a subsequent allow policy for all other traffic (source 'all') permits everything else, ensuring the specific IP is blocked while all other traffic is allowed.
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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