Quick Answer
The correct answer is that the FortiGate routes traffic between different subnets and can perform NAT. This is accurate because NAT/Route mode is the default Layer 3 operational mode where the FortiGate acts as a router, forwarding packets between distinct subnets based on its routing table, while also capable of translating source or destination IP addresses through NAT policies when configured. On the Fortinet NSE 4 Network Security Professional exam, this concept tests your understanding of how the FortiGate combines routing and NAT in a single mode, often appearing in questions that contrast it with Transparent mode or that ask about traffic flow between internal and external networks. A common trap is assuming NAT is mandatory in this mode—it is not; NAT is only applied when explicitly configured, so routing alone is the core function. Memory tip: think of NAT/Route as “Route first, NAT if needed”—the device always routes, but NAT is an optional overlay.
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 FortiGate is configured in NAT/Route mode. Which statement is correct about this mode?
Only one interface can be used for traffic.
Why wrong: Multiple interfaces are supported.
The FortiGate routes traffic between different subnets and can perform NAT.
NAT/Route mode is the default, routing Layer 3 traffic.
VLAN interfaces are not supported in this mode.
Why wrong: VLANs are supported.
The FortiGate acts as a Layer 2 bridge.
Why wrong: That is transparent mode.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The FortiGate routes traffic between different subnets and can perform NAT.
In NAT/Route mode, the FortiGate operates as a Layer 3 router, forwarding traffic between different subnets while also performing Network Address Translation (NAT) when configured. This is the default operational mode for most FortiGate deployments, enabling both routing and NAT capabilities on the same device.
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.
Only one interface can be used for traffic.
Why it's wrong here
Multiple interfaces are supported.
The FortiGate routes traffic between different subnets and can perform NAT.
Why this is correct
NAT/Route mode is the default, routing Layer 3 traffic.
Related concept
Read the scenario before looking for a memorised answer.
VLAN interfaces are not supported in this mode.
Why it's wrong here
VLANs are supported.
The FortiGate acts as a Layer 2 bridge.
Why it's wrong here
That is transparent mode.
Common exam traps
The trap here is that candidates often confuse NAT/Route mode with Transparent mode, assuming that NAT implies bridging or that only one interface can be used, but FortiGate explicitly supports multiple routed interfaces and VLANs in this mode.
Detailed technical explanation
Under the hood, NAT/Route mode uses the kernel routing table to make forwarding decisions based on destination IP addresses, and NAT is applied via policy-based rules using the session table. A real-world scenario is a branch office FortiGate that routes internal traffic between VLANs (e.g., 10.0.1.0/24 and 10.0.2.0/24) while performing source NAT for internet-bound traffic to a single public IP. This mode also supports advanced features like policy-based routing and BGP, which are unavailable in Transparent mode.
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.
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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: The FortiGate routes traffic between different subnets and can perform NAT. — In NAT/Route mode, the FortiGate operates as a Layer 3 router, forwarding traffic between different subnets while also performing Network Address Translation (NAT) when configured. This is the default operational mode for most FortiGate deployments, enabling both routing and NAT capabilities on the same device.
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
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