Quick Answer
The answer is Source NAT. This feature is unavailable in transparent mode because a FortiGate operating as a Layer 2 bridge does not perform routing; Source NAT requires Layer 3 forwarding to translate source IP addresses, and transparent mode interfaces lack routable IP addresses. On the Fortinet NSE 4 Network Security Professional exam, this question tests your understanding of how transparent mode strips away routing-dependent functions, often appearing as a trap where candidates confuse transparent mode with NAT mode. A common memory tip is to remember that transparent mode is “invisible” at Layer 3—if a feature needs to route or change IP headers, it won’t work here. Think of it as a bump-in-the-wire: it can filter and bridge traffic, but it cannot masquerade or redirect packets at the network layer.
This NSE4 practice question tests your understanding of system and network administration. 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 is configuring a FortiGate in a transparent mode. Which of the following features is NOT available in transparent mode?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "NOT"
Why it matters: Negative qualifier — you are looking for the one option that does NOT apply. Most options will be true; only one is false for this scenario.
Source NAT
NAT is not available because transparent mode does not route IP packets.
VLAN tagging
Why wrong: VLAN tagging is supported.
Intrusion Prevention System (IPS)
Why wrong: IPS is available in transparent mode.
Security profiles (AV, web filter)
Why wrong: Security profiles are available.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Source NAT
In transparent mode, the FortiGate operates as a Layer 2 bridge without routing capabilities, meaning it cannot perform Source NAT (SNAT) because SNAT requires Layer 3 routing to translate source IP addresses. Transparent mode does not have an IP address on its interfaces for routing, so features dependent on Layer 3 forwarding, such as NAT, are unavailable.
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.
Source NAT
Why this is correct
NAT is not available because transparent mode does not route IP packets.
Clue confirmation
The clue word "NOT" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
VLAN tagging
Why it's wrong here
VLAN tagging is supported.
Intrusion Prevention System (IPS)
Why it's wrong here
IPS is available in transparent mode.
Security profiles (AV, web filter)
Why it's wrong here
Security profiles are available.
Common exam traps
The trap here is that candidates often assume security features like IPS or AV require Layer 3 routing, but they actually operate at higher layers and work in transparent mode, while NAT is the only option that explicitly depends on Layer 3 functionality.
Detailed technical explanation
Transparent mode uses a bridge group where all interfaces share a single management IP (for administrative access) but no routed IPs for traffic, so NAT operations that rewrite source IPs in the IP header are impossible. Under the hood, the FortiGate uses a flow-based or proxy-based inspection engine that can still apply security profiles and IPS by examining packets at the bridge level, but any feature that modifies the IP header (like SNAT) is blocked because the device does not participate in IP routing. In real-world deployments, transparent mode is often used for inline security without changing the existing network topology, such as between a router and a switch.
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: Source NAT — In transparent mode, the FortiGate operates as a Layer 2 bridge without routing capabilities, meaning it cannot perform Source NAT (SNAT) because SNAT requires Layer 3 routing to translate source IP addresses. Transparent mode does not have an IP address on its interfaces for routing, so features dependent on Layer 3 forwarding, such as NAT, are unavailable.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "NOT". Negative qualifier — you are looking for the one option that does NOT apply. Most options will be true; only one is false for this scenario.
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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