Configuring SSL Inspection for Self-Signed Certificates on Non-Standard Ports
An administrator wants to inspect SSL traffic to a specific finance application that uses a custom port (9443) and a self-signed certificate. Which configuration is required?
Quick Answer
The correct answer is to use deep inspection and add the application's self-signed certificate to the FortiGate's trusted CA list. This is required because deep inspection performs full SSL/TLS decryption, allowing the FortiGate to inspect the payload of traffic on a non-standard port like 9443, whereas certificate inspection only validates metadata without decrypting. When a self-signed certificate is used, the FortiGate’s proxy cannot validate it against a public CA, so you must explicitly import that certificate into the trusted CA store to avoid connection drops. On the Fortinet NSE 4 exam, this scenario tests your understanding of the difference between certificate inspection and deep inspection, and it often appears as a trap where candidates mistakenly choose certificate inspection for non-standard ports. Remember the key distinction: certificate inspection is for metadata only, deep inspection is for full decryption. A helpful memory tip is “Deep for decrypt, self-signed needs trust.”
⚠ Common exam trap
Many exam-takers confuse certificate inspection with deep inspection, assuming certificate inspection can decrypt traffic, when in fact only deep inspection performs full decryption and is required for self-signed certificates on non-standard ports.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use deep inspection and add the application's self-signed certificate to the FortiGate's trusted CA list.
Deep inspection is required to decrypt and inspect SSL traffic using a self-signed certificate on a non-standard port. The FortiGate must trust the application's self-signed certificate by adding it to the trusted CA list; otherwise, the deep inspection proxy will fail to validate the certificate and drop the connection. Certificate inspection (Option A) only checks the certificate metadata without decrypting the payload, so it cannot inspect the actual application traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure certificate inspection on the policy.
Why it's wrong here
Certificate inspection does not decrypt traffic.
- ✗
Disable SSL inspection for that application.
Why it's wrong here
That would bypass inspection.
- ✓
Use deep inspection and add the application's self-signed certificate to the FortiGate's trusted CA list.
Why this is correct
Deep inspection decrypts and re-encrypts; trusted CA list allows self-signed certs.
- ✗
Use flow-based inspection with certificate inspection.
Why it's wrong here
Flow-based inspection does not decrypt deep.
Go deeper
Related to this question
About these practice questions
This NSE4 question is part of Courseiva's 282-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more way this is tested on NSE4
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. A network administrator notices that HTTP traffic is being scanned by the antivirus profile, but HTTPS traffic to the same web server is not being scanned. The firewall policy has the antivirus profile applied and SSL inspection is set to 'certificate-inspection'. What is the most likely reason HTTPS traffic is not being scanned?
medium- ✓ A.Certificate inspection does not decrypt the traffic, so the antivirus scanner cannot inspect the payload.
- B.The antivirus profile is configured in flow mode, which does not support scanning HTTPS traffic.
- C.The web server is not using a cipher supported by the FortiGate.
- D.The FortiGate is using proxy-based inspection, which does not support HTTPS scanning.
Why A: Certificate inspection only validates the SSL/TLS certificate without decrypting the traffic. Since the antivirus scanner requires access to the plaintext payload to detect threats, it cannot scan HTTPS traffic when only certificate inspection is configured. This is why HTTP traffic is scanned but HTTPS traffic is not.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.