The answer is that the FortiGate's CA certificate is not installed in the Trusted Root Certification Authorities store on the clients. This is the most likely cause because when deep SSL inspection is enabled, the FortiGate acts as a man-in-the-middle, decrypting HTTPS traffic and re-encrypting it with its own local CA certificate. For clients to trust these decrypted connections, that CA certificate must be present in their trusted root store; without it, the browser sees an untrusted issuer and blocks the site, leading to HTTPS sites not loading after deep SSL inspection. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this scenario tests your understanding of SSL inspection trust chains and certificate deployment—a common trap is assuming the FortiGate itself handles client trust automatically. Remember the memory tip: "No root, no route"—without the CA in the client's trusted root, traffic gets blocked.
NSE4 Security Profiles Practice Question
This NSE4 practice question tests your understanding of security profiles. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
A company uses deep SSL inspection to filter traffic. Users report that some HTTPS sites are not loading. The administrator checks the FortiGate and sees that the certificate for the sites is not trusted on the client machines. What is the most likely cause?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The FortiGate's CA certificate is not installed in the Trusted Root Certification Authorities store on the clients.
When deep SSL inspection is enabled, the FortiGate acts as a man-in-the-middle by decrypting HTTPS traffic using a local CA certificate. For clients to trust the decrypted connections, the FortiGate's CA certificate must be installed in the Trusted Root Certification Authorities store on each client machine. If it is missing, the browser will display a certificate trust error and may block the site, causing the reported loading failures.
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 FortiGate's CA certificate is not installed in the Trusted Root Certification Authorities store on the clients.
Why this is correct
Without the CA certificate, the browser cannot verify the inspection certificate.
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 FortiGate is using a self-signed certificate for the SSL inspection policy.
Why it's wrong here
Self-signed certificates are common; the issue is trust, not the type of certificate.
✗
The SSL inspection policy is set to 'no-inspection' for the affected sites.
Why it's wrong here
'no-inspection' would bypass inspection and sites would load normally.
✗
The FortiGate's web filter profile is blocking the certificate.
Why it's wrong here
Web filter does not block certificates; it blocks URLs or content.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse the FortiGate's self-signed certificate used for its own web interface with the CA certificate required for deep inspection, or assume that 'no-inspection' would cause loading failures rather than bypassing inspection entirely.
Detailed technical explanation
How to think about this question
Under the hood, deep SSL inspection requires the FortiGate to generate a new certificate for each HTTPS session, signed by its own CA. The client validates this certificate against its trusted root store; if the FortiGate's CA is not present, the validation fails, and the browser displays a warning or blocks the connection. In real-world deployments, administrators often use Group Policy or MDM to push the CA certificate to all domain-joined clients, and forgetting this step is a common oversight.
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 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
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.
Security Profiles — This question tests Security Profiles — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The FortiGate's CA certificate is not installed in the Trusted Root Certification Authorities store on the clients. — When deep SSL inspection is enabled, the FortiGate acts as a man-in-the-middle by decrypting HTTPS traffic using a local CA certificate. For clients to trust the decrypted connections, the FortiGate's CA certificate must be installed in the Trusted Root Certification Authorities store on each client machine. If it is missing, the browser will display a certificate trust error and may block the site, causing the reported loading failures.
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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Question Discussion
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