Quick Answer
The answer is the diagnose sniffer packet command. This is the correct choice because it allows an administrator to perform a real-time packet capture directly on a FortiGate interface, displaying live traffic as it traverses the device, which is essential for identifying where packets are being dropped or misrouted. On the Fortinet NSE 4 Network Security Professional exam, this command tests your practical troubleshooting skills under the "System Diagnostics" domain, often appearing in scenario-based questions where you must distinguish it from other diagnostic tools like the packet sniffer in the GUI or the fnsysctl dump. A common trap is confusing it with the execute packet-capture command, which is used for offline captures saved to a file, not for live viewing. To remember: think of "diagnose" as the doctor's toolkit for live symptoms, and "sniffer" as the nose that smells the traffic in real time.
This NSE4 practice question tests your understanding of high availability and diagnostics. 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.
An administrator wants to troubleshoot a traffic flow issue on a FortiGate. They suspect packets are being dropped. Which command should they use to perform a real-time packet capture on an interface?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
diagnose sniffer packet
This is the standard command for packet capture on FortiGate.
get system performance status
Why wrong: This shows system performance metrics, not packet-level data.
diagnose sys session list
Why wrong: This command lists current sessions, not packet captures.
diagnose debug flow
Why wrong: This command traces the flow of packets through the FortiGate, but it is not a packet capture.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
diagnose sniffer packet
Option A is correct. The 'diagnose sniffer packet' command is used to capture packets in real time on FortiGate interfaces.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
diagnose sniffer packet
Why this is correct
This is the standard command for packet capture on FortiGate.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
get system performance status
Why it's wrong here
This shows system performance metrics, not packet-level data.
diagnose sys session list
Why it's wrong here
This command lists current sessions, not packet captures.
diagnose debug flow
Why it's wrong here
This command traces the flow of packets through the FortiGate, but it is not a packet capture.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
This shows system performance metrics, not packet-level data.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the NSE4 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Identify which NSE4 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
High Availability and Diagnostics — study guide chapter
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FAQ
High Availability and Diagnostics — This question tests High Availability and Diagnostics — Read the scenario before looking for a memorised answer..
The correct answer is: diagnose sniffer packet — Option A is correct. The 'diagnose sniffer packet' command is used to capture packets in real time on FortiGate interfaces.
Identify which NSE4 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Read the scenario before looking for a memorised answer.
About these practice questions
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An administrator wants to monitor real-time traffic flows on a FortiGate, specifically to see packet details for traffic matching certain criteria. Which command should the administrator use to capture live packets on an interface?
easyWhy A: The 'diagnose sniffer packet' command is the built-in packet capture tool on FortiGate. It allows capturing packets on interfaces with filters for IP, port, protocol, etc. Example: 'diagnose sniffer packet any "host 10.0.0.1" 4'.
Variation 2. Which FortiGate diagnostic command allows you to capture packets on an interface for troubleshooting network connectivity issues?
easyWhy B: The 'diagnose sniffer packet' command captures packets in real-time on a specified interface, similar to tcpdump. It is the primary tool for packet-level troubleshooting.
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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