The answer is that NAT is enabled on the policy, which replaces the original source IP with the public IP before logging occurs. This happens because FortiGate performs Network Address Translation (NAT) on the packet as it traverses the policy, and logging is executed after the translation step, so the log captures the translated source address rather than the internal client’s IP. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this concept tests your understanding of the order of operations in the FortiGate packet flow—specifically that NAT processing precedes log generation. A common trap is assuming logs record pre-NAT information, but the key is remembering that logging reflects the packet as it exits the interface. To avoid confusion, remember the memory tip: “NAT first, log last—the source you see is the one that passed.”
NSE4 System and Network Administration Practice Question
This NSE4 practice question tests your understanding of system and network administration. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 srcintf "internal"
set dstintf "wan1"
set srcaddr "all"
set dstaddr "all"
set action accept
set schedule "always"
set service "ALL"
set logtraffic all
set nat enable
next
end
Refer to the exhibit. The administrator notices that traffic from internal to wan1 is being logged, but the logs do not show the original source IP. What is the most likely reason?
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 srcintf "internal"
set dstintf "wan1"
set srcaddr "all"
set dstaddr "all"
set action accept
set schedule "always"
set service "ALL"
set logtraffic all
set nat enable
next
end
A
The schedule is set to 'always', causing no time-based logging.
Why wrong: Schedule does not affect logging content.
B
NAT is enabled, so the source IP is replaced with the public IP.
NAT hides the original source IP.
C
Logging is set to 'all' but only 'utma' events are logged.
Why wrong: Logging all should capture everything.
D
The policy action is 'accept' without authentication.
Why wrong: Authentication not related to source IP logging.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
NAT is enabled, so the source IP is replaced with the public IP.
When NAT is enabled on a FortiGate policy, the source IP of internal traffic is translated to the public IP of the FortiGate's WAN interface before the packet is logged. Since logging occurs after NAT processing, the log entries will show the translated (public) IP instead of the original internal source IP. This is the most likely reason the administrator sees logs without the original source IP.
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.
✗
The schedule is set to 'always', causing no time-based logging.
Why it's wrong here
Schedule does not affect logging content.
✓
NAT is enabled, so the source IP is replaced with the public IP.
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Logging is set to 'all' but only 'utma' events are logged.
Why it's wrong here
Logging all should capture everything.
✗
The policy action is 'accept' without authentication.
Why it's wrong here
Authentication not related to source IP logging.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think logging settings or policy actions (like authentication) affect the source IP in logs, when in fact NAT translation is the direct cause of the original source IP being replaced.
Detailed technical explanation
How to think about this question
FortiGate performs NAT before logging when the policy has NAT enabled, as per the order of operations in the FortiOS data plane: routing, NAT, then logging. This means the log entry captures the post-NAT source IP (the public IP of the egress interface). In real-world scenarios, this can complicate forensic analysis if the administrator expects to see internal IPs; enabling 'log-traffic-quota' or using identity-based policies can help preserve original source information.
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.
System and Network Administration — This question tests System and Network Administration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: NAT is enabled, so the source IP is replaced with the public IP. — When NAT is enabled on a FortiGate policy, the source IP of internal traffic is translated to the public IP of the FortiGate's WAN interface before the packet is logged. Since logging occurs after NAT processing, the log entries will show the translated (public) IP instead of the original internal source IP. This is the most likely reason the administrator sees logs without the original source IP.
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.
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