The answer is policy-based NAT, because it is evaluated first and takes precedence over Central SNAT when both are configured for the same traffic. This happens because policy-based NAT is directly tied to the firewall policy that matches the session, so it is checked before any Central SNAT rules are considered, regardless of rule IDs or global settings. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this concept tests your understanding of NAT evaluation order, a common trap where candidates assume Central SNAT overrides everything due to its centralized nature. Remember that policy-based NAT is always the first to apply for traffic matching its associated policy, making it the winner in any precedence conflict. A simple memory tip: “Policy first, Central later—if a policy has NAT, Central won’t matter.”
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.
A FortiGate has a policy-based NAT rule that translates source IPs from subnet 192.168.1.0/24 to 203.0.113.10 when accessing the internet. The admin also enables Central SNAT with a rule that translates the same subnet to 203.0.113.20. If both are configured, which translation will be applied to traffic from 192.168.1.0/24 to the internet?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Policy-based NAT because it is evaluated first
Policy-based NAT is evaluated before Central SNAT because it is directly tied to the firewall policy that matches the traffic. When a policy-based NAT rule exists for the same traffic, it takes precedence over Central SNAT rules, regardless of any global settings or rule IDs. Therefore, the source IPs from 192.168.1.0/24 will be translated to 203.0.113.10.
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.
✗
Both translations will be applied, causing an error
Why it's wrong here
Only one translation is applied; they do not stack.
✗
Central SNAT because it is a global setting
Why it's wrong here
Policy-based NAT is more specific and takes precedence.
✗
The FortiGate will use the translation from the policy with the highest ID
Why it's wrong here
Policy ID does not determine precedence between policy-based and central NAT.
✓
Policy-based NAT because it is evaluated first
Why this is correct
Policy-based NAT rules are evaluated before Central SNAT rules.
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 often assume Central SNAT, being a centralized feature, overrides all other NAT rules, but FortiGate explicitly gives policy-based NAT higher precedence for traffic matching a firewall policy.
Detailed technical explanation
How to think about this question
Under the hood, FortiGate processes NAT in a specific order: first policy-based NAT (configured directly in the firewall policy's 'NAT' tab), then Central SNAT (configured under Policy & Objects > Central SNAT). This precedence is hardcoded in the FortiOS kernel and cannot be altered by rule IDs or administrative distance. In real-world scenarios, an admin might inadvertently create conflicting NAT rules when migrating from legacy policy-based NAT to Central SNAT, leading to unexpected translation behavior if the old policy-based rules are not removed.
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: Policy-based NAT because it is evaluated first — Policy-based NAT is evaluated before Central SNAT because it is directly tied to the firewall policy that matches the traffic. When a policy-based NAT rule exists for the same traffic, it takes precedence over Central SNAT rules, regardless of any global settings or rule IDs. Therefore, the source IPs from 192.168.1.0/24 will be translated to 203.0.113.10.
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
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 →
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.