The answer is to enable NAT on the firewall policy from the internal network to the internet. This is correct because source NAT outbound traffic on a FortiGate is configured at the firewall policy level, not on the interface or via a static route; when NAT is enabled on the policy, the FortiGate automatically translates the source IP of traffic leaving port1 to the interface’s primary public IP address. On the Fortinet NSE 4 Network Security Professional exam, this concept tests your understanding that SNAT is a policy-based function in FortiOS, and a common trap is assuming you must configure NAT on the interface or add a separate IP pool for basic outbound translation. Remember the memory tip: “NAT lives on the policy, not the port”—if you need to source NAT traffic to the internet, always check the firewall policy’s NAT checkbox, as that is the standard and required step for outbound connectivity.
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 network administrator is configuring a new FortiGate and needs to ensure that all traffic from the internal network to the internet is source NATed to the public IP address on port1. The default route points to port1. Which configuration step is required to achieve this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable NAT on the firewall policy from internal to internet
Option B is correct because source NAT (SNAT) on a FortiGate is configured at the firewall policy level, not on the interface or via a static route. By enabling NAT on the firewall policy from the internal network to the internet, the FortiGate automatically translates the source IP of traffic egressing port1 to the interface's primary IP address (the public IP). This is the standard method for implementing source NAT in FortiOS, as defined in the FortiGate Administration Guide.
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.
✗
Configure a static route to the internet with NAT enabled
Why it's wrong here
NAT is not configured on static routes; it is configured on firewall policies.
✓
Enable NAT on the firewall policy from internal to internet
Why this is correct
In a firewall policy, enabling NAT performs source NAT (masquerade) using the egress interface IP.
Related concept
Read the scenario before looking for a memorised answer.
✗
Set the interface port1 to NAT mode in its settings
Why it's wrong here
There is no NAT mode setting on interfaces; NAT is applied via policies.
✗
Create an IP pool with the public IP and reference it in the policy
Why it's wrong here
An IP pool is only needed if you want to use a specific IP other than the interface IP, or for PAT with multiple IPs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse NAT configuration with interface settings or static routes, mistakenly thinking NAT must be enabled on the egress interface or as part of the route, whereas FortiOS applies NAT exclusively at the firewall policy level.
Detailed technical explanation
How to think about this question
When NAT is enabled on a firewall policy, FortiGate performs Port Address Translation (PAT) by default, using the egress interface's primary IP as the source address. This behavior is governed by the 'set nat enable' command in the policy configuration, and it automatically handles translation for all sessions matching the policy. In a real-world scenario, if the public IP is on port1 and the default route points there, enabling NAT on the policy is the only step needed; adding an IP pool would be redundant unless you need to translate to a different IP (e.g., for policy-based routing or multiple public IPs).
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: Enable NAT on the firewall policy from internal to internet — Option B is correct because source NAT (SNAT) on a FortiGate is configured at the firewall policy level, not on the interface or via a static route. By enabling NAT on the firewall policy from the internal network to the internet, the FortiGate automatically translates the source IP of traffic egressing port1 to the interface's primary IP address (the public IP). This is the standard method for implementing source NAT in FortiOS, as defined in the FortiGate Administration Guide.
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.
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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.
Question Discussion
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