- A
The firewall policy does not have NAT enabled
If Central SNAT fails to match, the policy must have NAT enabled for policy-based NAT to apply. Without it, no translation occurs.
- B
The IP Pool is configured for one-to-one NAT instead of overload
Why wrong: One-to-one NAT would still translate the IP, just differently. The symptom here is no translation at all.
- C
The Central SNAT rule's source interface is set to 'wan1' instead of 'internal'
Why wrong: This would cause the rule to not match, but the fallback would be policy-based NAT, not no NAT — unless the policy also lacks NAT.
- D
The IP Pool is configured with 'Fixed Port Range' which conflicts with overload
Why wrong: While this would cause a configuration error, it would likely prevent the rule from being created or cause a different behavior.
Quick Answer
The answer is that the firewall policy does not have NAT enabled. This is the most likely cause when Central SNAT is not working because FortiGate evaluates Central SNAT rules first, and if they fail to match the traffic—due to an incorrect source interface, destination, or IP Pool configuration—the device falls back to policy-based NAT. If the firewall policy itself has NAT disabled, no translation occurs, leaving the source IP as 10.0.0.10. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this scenario tests your understanding of the NAT evaluation order: Central SNAT overrides policy NAT only when it matches; otherwise, the policy’s NAT setting takes over. A common trap is assuming Central SNAT alone guarantees translation, but the policy must also permit NAT as a fallback. Memory tip: “Central first, policy last—if Central misses, policy’s NAT is your last chance.”
NSE4 Firewall Policies and NAT Practice Question
This NSE4 practice question tests your understanding of firewall policies and nat. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 administrator configures Central SNAT for traffic going from internal network (10.0.0.0/8) to the internet. The rule uses an IP Pool with overload (PAT) and the pool address is 203.0.113.10. However, traffic from 10.0.0.10 to a public server is not being NATed; the source IP remains 10.0.0.10. The firewall policy allows the traffic. 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.
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 does not have NAT enabled
Central SNAT rules are evaluated before policy-based NAT. If a Central SNAT rule exists but does not match the traffic (e.g., wrong source interface, destination, or pool), FortiGate falls back to policy-based NAT. If the firewall policy has no NAT enabled, the traffic is not translated. The admin likely has Central SNAT configured incorrectly or the policy has NAT disabled.
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 firewall policy does not have NAT enabled
Why this is correct
If Central SNAT fails to match, the policy must have NAT enabled for policy-based NAT to apply. Without it, no translation occurs.
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 IP Pool is configured for one-to-one NAT instead of overload
Why it's wrong here
One-to-one NAT would still translate the IP, just differently. The symptom here is no translation at all.
- ✗
The Central SNAT rule's source interface is set to 'wan1' instead of 'internal'
Why it's wrong here
This would cause the rule to not match, but the fallback would be policy-based NAT, not no NAT — unless the policy also lacks NAT.
- ✗
The IP Pool is configured with 'Fixed Port Range' which conflicts with overload
Why it's wrong here
While this would cause a configuration error, it would likely prevent the rule from being created or cause a different behavior.
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 does not have NAT enabled — Central SNAT rules are evaluated before policy-based NAT. If a Central SNAT rule exists but does not match the traffic (e.g., wrong source interface, destination, or pool), FortiGate falls back to policy-based NAT. If the firewall policy has no NAT enabled, the traffic is not translated. The admin likely has Central SNAT configured incorrectly or the policy has NAT disabled.
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.
About these practice questions
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Same concept, more angles
1 more ways 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. An administrator configures a Central SNAT policy to translate traffic from the internal network (10.0.0.0/8) to the internet using the IP pool 'pool1'. The administrator also has a firewall policy that uses policy-based NAT with an IP pool 'pool2'. Both policies match the same traffic. Which NAT will be applied?
hard- ✓ A.Central SNAT using pool1
- B.Both NAT rules are applied in sequence
- C.The traffic is dropped due to conflicting NAT configurations
- D.Policy-based NAT using pool2
Why A: When Central SNAT is enabled, it overrides policy-based NAT for matching traffic. The firewall policies are still used for access control, but the NAT is determined by the central NAT rules. Central NAT has higher precedence than policy-based NAT.
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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