The answer is that the service 'HTTPS' only allows TCP 443, but some websites use other ports. This is the most likely cause because when a FortiGate policy applies deep inspection using the default 'HTTPS' service object, it strictly matches traffic only on TCP port 443; any HTTPS traffic on non-standard ports like 8443 or 9443 bypasses the inspection engine entirely, causing the connection to fail when deep inspection is required. On the Fortinet NSE 4 Network Security Professional exam, this tests your understanding that deep inspection is service-aware and that the service definition must match the actual destination port for inspection to occur—a common trap is assuming the FortiGate CA certificate alone guarantees inspection. A useful memory tip is "Port must match policy; deep inspection won't fix a mismatched service."
NSE4 Security Profiles Practice Question
This NSE4 practice question tests your understanding of security profiles. 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
Refer to the exhibit.
config firewall policy
edit 1
set name "Web Access"
set srcintf "internal"
set dstintf "wan"
set srcaddr "all"
set dstaddr "all"
set action accept
set schedule "always"
set service "HTTPS"
set ssl-ssh-profile "deep-inspection"
set utm-status enable
set av-profile "default"
set webfilter-profile "strict"
next
end
Refer to the exhibit. The policy applies deep inspection, but users cannot access any HTTPS websites. The FortiGate CA certificate is installed on clients. 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.
Refer to the exhibit.
config firewall policy
edit 1
set name "Web Access"
set srcintf "internal"
set dstintf "wan"
set srcaddr "all"
set dstaddr "all"
set action accept
set schedule "always"
set service "HTTPS"
set ssl-ssh-profile "deep-inspection"
set utm-status enable
set av-profile "default"
set webfilter-profile "strict"
next
end
A
The deep inspection profile is misconfigured.
Why wrong: No evidence of misconfiguration.
B
The antivirus profile is blocking the traffic.
Why wrong: Antivirus would not block all HTTPS.
C
The web filter profile 'strict' is blocking all sites.
Why wrong: The profile would block some, not all.
D
The service 'HTTPS' only allows TCP 443, but some websites use other ports.
If non-standard ports are used, they are not allowed.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The service 'HTTPS' only allows TCP 443, but some websites use other ports.
Option D is correct because the policy uses the service 'HTTPS', which by default only matches TCP port 443. If any HTTPS websites are hosted on non-standard ports (e.g., 8443, 9443), the FortiGate will not apply deep inspection to that traffic, causing the connection to fail when deep inspection is required. The FortiGate CA certificate being installed on clients ensures trust, but the service definition must match the actual destination port for inspection to occur.
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 web filter profile 'strict' is blocking all sites.
Why it's wrong here
The profile would block some, not all.
✓
The service 'HTTPS' only allows TCP 443, but some websites use other ports.
Why this is correct
If non-standard ports are used, they are not allowed.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume 'HTTPS' covers all secure web traffic, but FortiGate service objects are port-specific, and deep inspection requires the policy to match the exact destination port used by the website.
Detailed technical explanation
How to think about this question
FortiGate service objects define the protocol and port range for policy matching; the default 'HTTPS' service only includes TCP/443. When deep inspection is enabled, the FortiGate must intercept the TLS handshake on the exact port the client uses; if a website uses a non-standard port (e.g., TCP 8443), the traffic will not match the HTTPS service and will bypass inspection, potentially causing a TCP reset or no decryption. In real-world scenarios, administrators often need to create custom service objects (e.g., 'HTTPS-ALT' for ports 443, 8443, 9443) to ensure all HTTPS traffic is inspected.
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.
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 service 'HTTPS' only allows TCP 443, but some websites use other ports. — Option D is correct because the policy uses the service 'HTTPS', which by default only matches TCP port 443. If any HTTPS websites are hosted on non-standard ports (e.g., 8443, 9443), the FortiGate will not apply deep inspection to that traffic, causing the connection to fail when deep inspection is required. The FortiGate CA certificate being installed on clients ensures trust, but the service definition must match the actual destination port for inspection to occur.
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.