This NSE4 practice question tests your understanding of firewall policies and nat. 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.
Which of the following is the default action of a FortiGate firewall policy if no policy matches the traffic?
Log and drop
Why wrong: Logging requires explicit configuration; implicit deny does not log by default.
Redirect to authentication
Why wrong: Authentication is not a default action.
Accept
Why wrong: Accept is not the default; it must be explicitly configured.
Deny
Traffic that does not match any policy is implicitly denied.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Deny
FortiGate firewall policies operate on a 'first-match' basis, and if no policy matches the traffic, the default action is to deny the traffic. This is a fundamental security principle to ensure that only explicitly permitted traffic is allowed through the firewall. The implicit deny rule is automatically applied at the end of the policy list and cannot be removed or modified.
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.
Log and drop
Why it's wrong here
Logging requires explicit configuration; implicit deny does not log by default.
Redirect to authentication
Why it's wrong here
Authentication is not a default action.
Accept
Why it's wrong here
Accept is not the default; it must be explicitly configured.
Deny
Why this is correct
Traffic that does not match any policy is implicitly denied.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates may confuse the default action of a firewall with the default action of a router (which forwards traffic) or assume that FortiGate logs all denied traffic by default, but neither is true; the implicit deny is silent unless explicitly configured to log.
Detailed technical explanation
The implicit deny rule is implemented as a hidden policy with an ID of 0, which has a source and destination of 'all' and an action of 'deny'. This rule is evaluated after all user-defined policies, and it does not generate log entries unless a global 'deny-log' setting is enabled under config system global. In real-world scenarios, if a FortiGate is misconfigured with an 'accept' action on a catch-all policy, it could lead to unauthorized access, which is why the default deny is critical for security compliance.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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FAQ
Firewall Policies and NAT — This question tests Firewall Policies and NAT — Read the scenario before looking for a memorised answer..
The correct answer is: Deny — FortiGate firewall policies operate on a 'first-match' basis, and if no policy matches the traffic, the default action is to deny the traffic. This is a fundamental security principle to ensure that only explicitly permitted traffic is allowed through the firewall. The implicit deny rule is automatically applied at the end of the policy list and cannot be removed or modified.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 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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