The correct answer is to create an IP Pool with 203.0.113.2 and reference it in the policy. This works because a standard firewall policy with NAT enabled uses the egress interface IP for source translation, but when you need a specific source NAT IP for traffic from a particular host, you must define an IP Pool object containing that exact address and then apply it within the policy’s NAT settings. On the Fortinet NSE 4 exam, this scenario tests your understanding of Dynamic IP Pool versus Fixed Port Address Translation, and the common trap is confusing the pool with the interface IP or assuming a secondary IP on the interface will suffice. Remember that IP Pools override the default interface IP for NAT, and the pool must be explicitly referenced in the policy—simply adding the IP to the interface does not change the translated source. A useful memory tip: “Pool for a specific rule, not for the whole interface.”
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 has configured a firewall policy that allows outbound traffic from a subnet to the internet, with NAT enabled. The external IP is 203.0.113.1. However, the administrator wants all traffic from a specific internal server (10.0.0.10) to appear with source IP 203.0.113.2. What should the administrator do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create an IP Pool with 203.0.113.2 and reference it in the policy
To use a specific source IP for NAT, an IP Pool object must be created with the desired IP (203.0.113.2) and then referenced in the firewall policy. Option C is correct.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Create a VIP with the external IP and apply it to the policy
Route-based NAT is not a standard term; policy-based NAT is used.
✗
Set the NAT to 'Use Outgoing Interface Address'
Why it's wrong here
That uses the egress interface IP (203.0.113.1), not 203.0.113.2.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related NSE4 subnetting questions on CIDR, address ranges, and subnet selection.
Firewall Policies and NAT — This question tests Firewall Policies and NAT — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create an IP Pool with 203.0.113.2 and reference it in the policy — To use a specific source IP for NAT, an IP Pool object must be created with the desired IP (203.0.113.2) and then referenced in the firewall policy. Option C is correct.
What should I do if I get this NSE4 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related NSE4 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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 administrator needs to create a firewall policy that allows traffic from the internal network (10.0.0.0/8) to a public web server (203.0.113.10) on port 443. The policy must also perform source NAT using the FortiGate's external IP (198.51.100.1). Which NAT configuration should be applied?
medium
A.Create an IP pool with the external IP and reference it in the firewall policy
✓ B.Enable NAT on the firewall policy without specifying an IP pool
C.Create a VIP for the web server and reference it in the firewall policy
D.Configure Central SNAT and a matching rule
Why B: When 'NAT' is enabled on a firewall policy, FortiGate performs source NAT using the egress interface IP by default. Option A correctly states this default behavior for outbound traffic.
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.