- A
The VIP is configured with port forwarding only for external interface
Why wrong: VIP works regardless of incoming interface; but internal traffic typically goes through internal interface.
- B
The firewall policy for internal users does not have NAT disabled
For internal users accessing the VIP, the source NAT (overload) must be disabled so that the server sees the real client IP; otherwise, FortiGate may attempt to NAT again and break the session. Additionally, a policy from internal to the VIP interface (often a loopback or internal) is needed.
- C
The internal server is not configured to respond to requests on port 8080
Why wrong: External users succeed, so server is working.
- D
The internal users are using a different DNS server
Why wrong: DNS resolution does not affect connectivity after IP is reached.
Quick Answer
The answer is that the firewall policy for internal users does not have NAT disabled. This is the most likely reason because FortiGate, by default, blocks hairpin NAT—where internal users try to access a VIP’s public IP from inside the network—unless a specific policy is created to allow it. Without a policy that disables NAT on the source interface, the traffic gets caught in a double NAT loop or is dropped, as the FortiGate sees the source and destination as both internal. On the Fortinet NSE 4 exam, this scenario tests your understanding of VIP traffic flows and the necessity of a dedicated policy from internal to internal (or with source NAT disabled) to enable hairpin access. A common trap is assuming internet-facing policies suffice, but internal users require a separate rule. Remember the tip: “Hairpin needs a policy with NAT off—internal to internal, don’t get caught in the loop.”
NSE4 Firewall Policies and NAT Practice Question
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.
An admin configures a VIP to map public IP 203.0.113.10:80 to internal server 10.0.0.10:8080. Users on the internet can reach the server. However, internal users trying to access the public IP from inside the network fail. What is the MOST likely reason?
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 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
The firewall policy for internal users does not have NAT disabled
By default, FortiGate does not allow hairpin NAT (internal users accessing the VIP from inside). A policy with source NAT and the VIP as destination is required, and often NAT needs to be disabled on that policy to avoid double NAT. The common solution is to add a policy from internal to internal (or use NAT with source translation) but the core issue is that traffic from internal to VIP is not handled without a specific policy.
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.
- ✗
The VIP is configured with port forwarding only for external interface
Why it's wrong here
VIP works regardless of incoming interface; but internal traffic typically goes through internal interface.
- ✓
The firewall policy for internal users does not have NAT disabled
Why this is correct
For internal users accessing the VIP, the source NAT (overload) must be disabled so that the server sees the real client IP; otherwise, FortiGate may attempt to NAT again and break the session. Additionally, a policy from internal to the VIP interface (often a loopback or internal) is needed.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
The internal server is not configured to respond to requests on port 8080
Why it's wrong here
External users succeed, so server is working.
- ✗
The internal users are using a different DNS server
Why it's wrong here
DNS resolution does not affect connectivity after IP is reached.
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.
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Firewall Policies and NAT — study guide chapter
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FAQ
Questions learners often ask
What does this NSE4 question test?
Firewall Policies and NAT — This question tests Firewall Policies and NAT — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The firewall policy for internal users does not have NAT disabled — By default, FortiGate does not allow hairpin NAT (internal users accessing the VIP from inside). A policy with source NAT and the VIP as destination is required, and often NAT needs to be disabled on that policy to avoid double NAT. The common solution is to add a policy from internal to internal (or use NAT with source translation) but the core issue is that traffic from internal to VIP is not handled without a specific policy.
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.
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?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 21, 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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