The answer is to create two firewall policies, each with its own IP pool, for the respective subnets. This is correct because FortiGate’s IP pool feature allows you to assign a specific public IP address for source NAT on a per-policy basis, meaning you can map the engineering subnet (192.168.10.0/24) to one pool and the marketing subnet (192.168.20.0/24) to a different pool by simply applying each pool to its own firewall policy. On the Fortinet NSE 4 Network Security Professional exam, this scenario tests your understanding of how to achieve different source NAT IP per subnet without using Central SNAT, which cannot differentiate subnets within a single rule. A common trap is assuming one Central SNAT rule with a single IP pool can handle multiple subnets, but that would force all traffic through the same public IP. Memory tip: think “one policy, one pool, one subnet” — if you need different public IPs, you need separate policies.
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 administrator wants to ensure that traffic from the engineering department (subnet 192.168.10.0/24) to the internet uses a specific public IP address for source NAT. Additionally, traffic from the marketing department (192.168.20.0/24) should use a different public IP. Which method should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create two firewall policies, each with its own IP pool, for the respective subnets
Option B is correct because the requirement is to map specific source subnets to different public IP addresses. In FortiGate, this is achieved by creating separate firewall policies for each subnet, each with its own IP pool configured for source NAT. A single Central SNAT rule with one IP pool cannot differentiate between subnets to assign different public IPs.
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 single Central SNAT rule with multiple source subnets and a single IP pool
Why it's wrong here
A single IP pool cannot assign different IPs per subnet.
✓
Create two firewall policies, each with its own IP pool, for the respective subnets
Why this is correct
This allows granular control over which IP is used for each subnet.
Related concept
Read the scenario before looking for a memorised answer.
Use a single policy with a dynamic IP pool that randomly assigns IPs
Why it's wrong here
Random assignment would not guarantee different IPs per subnet.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse IP pools (used for source NAT) with Virtual IPs (used for destination NAT), leading them to incorrectly select VIP for source NAT.
Detailed technical explanation
How to think about this question
Under the hood, FortiGate IP pools are referenced in firewall policies and perform source NAT by replacing the original source IP with an IP from the pool. When using a static IP pool (with a single IP), all traffic matching that policy will use that IP. For granular control per subnet, separate policies with distinct IP pools are required. In real-world scenarios, this is common for compliance or logging reasons, such as ensuring all outbound traffic from a sensitive subnet appears to originate from a dedicated public IP for audit trails.
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.
Firewall Policies and NAT — This question tests Firewall Policies and NAT — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create two firewall policies, each with its own IP pool, for the respective subnets — Option B is correct because the requirement is to map specific source subnets to different public IP addresses. In FortiGate, this is achieved by creating separate firewall policies for each subnet, each with its own IP pool configured for source NAT. A single Central SNAT rule with one IP pool cannot differentiate between subnets to assign different public IPs.
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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Question Discussion
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