The answer is to block DNS queries to known malicious domains. This is correct because the DNS filter security profile on a FortiGate operates by inspecting outgoing DNS requests in real time, comparing them against FortiGuard’s threat intelligence database of malicious or unwanted domains. When a match is found, the FortiGate can drop the query, redirect it to a sinkhole, or return a forged response, effectively preventing the client from resolving the domain and thus stopping the connection before it begins. On the Fortinet NSE 4 Network Security Professional exam, this concept tests your understanding of how FortiGate enforces security at the DNS layer, often appearing in scenario-based questions where you must choose the correct profile to block command-and-control traffic. A common trap is confusing DNS filter with web filter—remember that DNS filter acts before the HTTP request, blocking the resolution itself. A useful memory tip: DNS filter is the “first gatekeeper” for domain-based threats, stopping the lookup before any data exchange can occur.
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.
What is the purpose of the DNS filter security profile on a FortiGate?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
To block DNS queries to known malicious domains
DNS filter inspects DNS queries to block access to malicious or unwanted domains.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
To block DNS queries to known malicious domains
Why this is correct
DNS filter uses FortiGuard DNS categories and custom domain lists to block malicious DNS queries.
Related concept
Static NAT maps one inside address to one outside address.
✗
To inspect DNS traffic for virus signatures
Why it's wrong here
Virus scanning is done by antivirus profiles.
✗
To filter spam emails based on DNS blacklists
Why it's wrong here
Spam filtering is done by email filter profiles.
✗
To prevent DNS tunneling attacks
Why it's wrong here
While DNS filter can help, its primary purpose is domain blocking based on categories.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related NSE4 NAT questions on configuration and troubleshooting.
Security Profiles — This question tests Security Profiles — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: To block DNS queries to known malicious domains — DNS filter inspects DNS queries to block access to malicious or unwanted domains.
What should I do if I get this NSE4 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related NSE4 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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 →
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. What is the purpose of enabling 'DNS filter' in a security profile?
easy
A.To cache DNS responses for faster browsing
B.To prevent DNS tunneling attacks
C.To enforce safe search on search engines
✓ D.To block DNS queries to known malicious domains
Why D: Option A is correct: DNS filter blocks malicious domains based on FortiGuard category or custom lists by inspecting DNS queries and responses.
Variation 2. What is the purpose of the 'DNS Filter' feature on a FortiGate?
easy
✓ A.To block DNS queries to malicious domains based on FortiGuard category and allow/block lists.
B.To cache DNS queries for faster resolution.
C.To encrypt DNS traffic to prevent eavesdropping.
D.To filter the content of DNS responses from legitimate servers.
Last reviewed: Jun 21, 2026
Question Discussion
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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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