The answer is to configure a firewall policy with NAT enabled and the outbound interface set to port1. This works because in NAT/Route mode, enabling NAT on a policy automatically performs source NAT (SNAT) using the IP address of the specified outbound interface—in this case, 203.0.113.1—without needing an IP pool or static route for the translation itself. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this scenario tests your understanding of policy-based NAT behavior, where the default action is to translate all internal source addresses (like 192.168.1.0/24) to the interface IP when NAT is checked. A common trap is assuming you must create a separate IP pool or configure Central NAT, but the exam emphasizes that the interface IP is the default translation target for a policy with NAT enabled and an outbound interface set. Remember the memory tip: “NAT on the policy, interface IP is the trick”—if the outbound interface is defined, the FortiGate uses its IP automatically, no pool required.
NSE4 System and Network Administration Practice Question
This NSE4 practice question tests your understanding of system and network administration. 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.
A FortiGate in NAT/Route mode has a policy with NAT enabled. The admin needs the source IP of traffic from internal users (192.168.1.0/24) to be translated to the interface IP of port1 (203.0.113.1) when accessing the internet. Which configuration is necessary?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure a firewall policy with NAT enabled and the outbound interface set to port1
Option D is correct because in NAT/Route mode, enabling NAT on a firewall policy with the outbound interface set to port1 causes the FortiGate to translate the source IP of traffic from the internal network (192.168.1.0/24) to the IP address of that interface (203.0.113.1) by default. This is the standard method for source NAT (SNAT) in a policy-based configuration, requiring no additional IP pool or static route for the translation itself.
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.
✗
Add a static route for 192.168.1.0/24 with next-hop 203.0.113.1
Create a central NAT rule with source 192.168.1.0/24 and IP pool 203.0.113.2-203.0.113.10
Why it's wrong here
This uses a pool, not the interface IP.
✓
Configure a firewall policy with NAT enabled and the outbound interface set to port1
Why this is correct
By default, NAT on a policy uses the egress interface IP as the translated source.
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 may confuse the need for an IP pool or static route with the simple policy-based NAT, assuming that translating to the interface IP requires additional configuration beyond enabling NAT on the policy.
Detailed technical explanation
How to think about this question
When NAT is enabled on a firewall policy without an IP pool, FortiGate performs dynamic NAT using the egress interface's primary IP address as the translated source. This behavior is governed by the session table, where the FortiGate creates a NAT session entry mapping the original source IP and port to the interface IP and a random high port (1024-65535). In a real-world scenario, this is commonly used for small office internet access where a single public IP is shared among multiple internal hosts.
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.
System and Network Administration — This question tests System and Network Administration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure a firewall policy with NAT enabled and the outbound interface set to port1 — Option D is correct because in NAT/Route mode, enabling NAT on a firewall policy with the outbound interface set to port1 causes the FortiGate to translate the source IP of traffic from the internal network (192.168.1.0/24) to the IP address of that interface (203.0.113.1) by default. This is the standard method for source NAT (SNAT) in a policy-based configuration, requiring no additional IP pool or static route for the translation itself.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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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. A FortiGate is set to NAT/Route mode. The admin wants traffic from internal users to the internet to use an IP address on the WAN interface for source NAT. Which configuration is required?
medium
A.Set the FortiGate to transparent mode
B.Configure a policy route to force traffic through a specific interface
C.Configure a virtual IP mapping internal IPs to the WAN IP
✓ D.Enable NAT on the policy from internal to WAN and set the outgoing interface to the WAN interface
Why D: In NAT/Route mode, source NAT (SNAT) is configured by enabling NAT on the firewall policy that governs traffic from the internal network to the WAN interface. When NAT is enabled on the policy and the outgoing interface is set to the WAN interface, FortiGate automatically translates the source IP of internal users to the primary IP address of that WAN interface (or a configured IP pool). This is the standard method for allowing internal users to access the internet with a public IP address.
Last reviewed: Jun 24, 2026
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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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