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.
Which of the following FortiGate operating modes allows the firewall to act as a Layer 3 device, performing NAT and routing between interfaces?
Flow-based inspection mode
Why wrong: Flow-based is a security profile processing mode, not an operating mode.
NAT/Route mode
Correct. NAT/Route mode enables routing and NAT.
VLAN mode
Why wrong: VLAN mode is not an operating mode; VLANs are sub-interfaces.
Transparent mode
Why wrong: Transparent mode is Layer 2, no routing or NAT.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
NAT/Route mode
NAT/Route mode (option B) is correct because it configures the FortiGate as a Layer 3 device with distinct interfaces in different subnets, enabling it to perform routing (forwarding packets based on routing table entries) and Network Address Translation (NAT) to translate private IP addresses to public IP addresses. This mode is the default and most common operational mode for perimeter firewalls, allowing policy-based routing and NAT rules to be applied between zones.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Flow-based inspection mode
Why it's wrong here
Flow-based is a security profile processing mode, not an operating mode.
NAT/Route mode
Why this is correct
Correct. NAT/Route mode enables routing and NAT.
Related concept
Read the scenario before looking for a memorised answer.
VLAN mode
Why it's wrong here
VLAN mode is not an operating mode; VLANs are sub-interfaces.
Transparent mode
Why it's wrong here
Transparent mode is Layer 2, no routing or NAT.
Common exam traps
The trap here is confusing operational modes (NAT/Route vs. Transparent) with inspection modes (Flow-based vs. Proxy-based), leading candidates to incorrectly select Flow-based inspection mode as the answer for Layer 3 routing and NAT capabilities.
Detailed technical explanation
In NAT/Route mode, each FortiGate interface is assigned an IP address and belongs to a separate subnet, allowing the firewall to act as a router using static or dynamic routing protocols (e.g., OSPF, BGP). NAT is performed at the session level using the FortiGate's session table, where source IP addresses are rewritten based on IP pool or outgoing interface address, and the firewall maintains stateful inspection to track return traffic. A real-world scenario is a branch office FortiGate using NAT/Route mode to connect internal 192.168.1.0/24 users to the internet via a public IP on the WAN interface, while routing between VLANs on the internal side.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
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FAQ
System and Network Administration — This question tests System and Network Administration — Read the scenario before looking for a memorised answer..
The correct answer is: NAT/Route mode — NAT/Route mode (option B) is correct because it configures the FortiGate as a Layer 3 device with distinct interfaces in different subnets, enabling it to perform routing (forwarding packets based on routing table entries) and Network Address Translation (NAT) to translate private IP addresses to public IP addresses. This mode is the default and most common operational mode for perimeter firewalls, allowing policy-based routing and NAT rules to be applied between zones.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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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