The answer is that NAT is not enabled on the policy, which is the most likely issue. Without NAT configured, the FortiGate allows the outbound session from the private 10.0.1.0/24 network to the web server at 192.168.1.10, but the server’s return traffic is routed directly back to the private source IP, which is non-routable across the public internet or external networks. This means the client never receives the server’s response, even though the FortiGate logs the session as allowed. On the Fortinet NSE 4 Network Security Professional exam, this scenario tests your understanding of why NAT is required for private IP traffic in FortiGate policies—specifically, that source NAT (SNAT) must translate the private source to the FortiGate’s interface IP so return traffic flows back through the firewall. A common trap is assuming a policy that logs “allowed” means successful communication; remember that a logged allow only confirms the forward path. Memory tip: “No NAT, no return path—private IPs can’t swim upstream without a translation.”
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.
Exhibit
config firewall policy
edit 1
set name "Allow-HTTP"
set srcintf "internal"
set dstintf "dmz"
set srcaddr "10.0.1.0/24"
set dstaddr "192.168.1.10"
set action accept
set schedule "always"
set service "HTTP"
set logtraffic all
next
end
Refer to the exhibit. A FortiGate has this policy configured. Traffic from 10.0.1.0/24 to 192.168.1.10 on HTTP is being logged as allowed. However, users report that they cannot access the web server. What is the most likely issue?
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.
config firewall policy
edit 1
set name "Allow-HTTP"
set srcintf "internal"
set dstintf "dmz"
set srcaddr "10.0.1.0/24"
set dstaddr "192.168.1.10"
set action accept
set schedule "always"
set service "HTTP"
set logtraffic all
next
end
A
NAT is not enabled on the policy
Without NAT, the server may send replies directly to the client's private IP, which is not routable.
B
The policy is placed below a deny policy
Why wrong: If traffic is allowed, the policy must be hit before any deny policy.
C
The service is set to HTTP but the server uses HTTPS
Why wrong: The logs show HTTP traffic is allowed, so the server must be listening on HTTP.
D
The policy is disabled
Why wrong: Logs show traffic is allowed, so the policy is enabled.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
NAT is not enabled on the policy
The correct answer is A because the policy allows traffic from 10.0.1.0/24 to 192.168.1.10 on HTTP, but without NAT enabled, the return traffic from the web server will be sent directly to the source IP (10.0.1.x) without going through the FortiGate. Since the source is a private IP, the server cannot route back to it unless the FortiGate performs source NAT (SNAT) to translate the source IP to its own interface IP. Without NAT, the session is logged as allowed but the client never receives the server's response, resulting in a connectivity failure.
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.
✓
NAT is not enabled on the policy
Why this is correct
Without NAT, the server may send replies directly to the client's private IP, which is not routable.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The policy is placed below a deny policy
Why it's wrong here
If traffic is allowed, the policy must be hit before any deny policy.
✗
The service is set to HTTP but the server uses HTTPS
Why it's wrong here
The logs show HTTP traffic is allowed, so the server must be listening on HTTP.
✗
The policy is disabled
Why it's wrong here
Logs show traffic is allowed, so the policy is enabled.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates see 'allowed' in the logs and assume connectivity is working, overlooking the fact that NAT is required for return traffic when the source is a private IP destined for a different subnet or the internet.
Trap categories for this question
Command / output trap
The logs show HTTP traffic is allowed, so the server must be listening on HTTP.
Detailed technical explanation
How to think about this question
In FortiGate, when NAT is disabled on a policy, the firewall performs route-based forwarding without altering the source IP. For traffic from a private RFC 1918 address to a public or different subnet destination, the return traffic must traverse the FortiGate to be statefully inspected. Without SNAT, the server's response is sent directly to the private IP, which is unreachable across the internet or different routing domain, causing asymmetric routing and session failure. Enabling NAT (typically to the egress interface IP) ensures the server replies to the FortiGate, which then forwards the response to the original client.
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: NAT is not enabled on the policy — The correct answer is A because the policy allows traffic from 10.0.1.0/24 to 192.168.1.10 on HTTP, but without NAT enabled, the return traffic from the web server will be sent directly to the source IP (10.0.1.x) without going through the FortiGate. Since the source is a private IP, the server cannot route back to it unless the FortiGate performs source NAT (SNAT) to translate the source IP to its own interface IP. Without NAT, the session is logged as allowed but the client never receives the server's response, resulting in a connectivity failure.
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.
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?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.