PCNSE Core Concepts and Architecture Practice Question
This PCNSE practice question tests your understanding of core concepts and architecture. 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 company is deploying a Palo Alto Networks firewall in an existing Layer 2 switched environment. They need to inspect traffic between VLAN 10 and VLAN 20 without changing the IP addresses of hosts and without performing any routing. Which firewall mode should be used?
Why wrong: Virtual Wire mode is used for transparent inline inspection on the same subnet; it cannot handle multiple VLANs without additional configuration like subinterfaces, but it does not perform routing between VLANs.
B
Tap mode
Why wrong: Tap mode is passive monitoring only; traffic flows through the firewall but no inspection or control is applied.
C
Transparent (Layer 2)
Correct. Transparent mode bridges VLANs at Layer 2, enabling inspection without IP changes.
D
Layer 3
Why wrong: Layer 3 mode requires IP addresses on interfaces and performs routing, which changes the network topology.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Transparent (Layer 2)
Option C is correct because Transparent (Layer 2) mode allows the firewall to operate as a Layer 2 bridge, inspecting traffic between VLAN 10 and VLAN 20 without requiring any IP address changes or routing. The firewall forwards frames based on MAC addresses, preserving the existing IP subnet and host configurations, which is ideal for inserting security into an existing switched environment.
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.
✗
Virtual Wire
Why it's wrong here
Virtual Wire mode is used for transparent inline inspection on the same subnet; it cannot handle multiple VLANs without additional configuration like subinterfaces, but it does not perform routing between VLANs.
✗
Tap mode
Why it's wrong here
Tap mode is passive monitoring only; traffic flows through the firewall but no inspection or control is applied.
✓
Transparent (Layer 2)
Why this is correct
Correct. Transparent mode bridges VLANs at Layer 2, enabling inspection without IP changes.
Related concept
Read the scenario before looking for a memorised answer.
✗
Layer 3
Why it's wrong here
Layer 3 mode requires IP addresses on interfaces and performs routing, which changes the network topology.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Virtual Wire mode with Transparent mode, assuming Virtual Wire can handle VLANs, but Virtual Wire does not support VLAN subinterfaces or inter-VLAN inspection, making it unsuitable for this requirement.
Detailed technical explanation
How to think about this question
In Transparent (Layer 2) mode, the firewall uses a virtual wire-like bridge group but with full Layer 2 forwarding capabilities, including VLAN tagging and MAC address learning. It can inspect inter-VLAN traffic by placing the firewall as a Layer 2 device between the VLANs, often using subinterfaces to terminate each VLAN, while the firewall itself remains unnumbered on the Layer 3 side. A real-world scenario is deploying the firewall in a data center to enforce security between server VLANs without re-IPing the servers, leveraging features like ARP inspection and DHCP snooping.
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 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
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.
Core Concepts and Architecture — This question tests Core Concepts and Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Transparent (Layer 2) — Option C is correct because Transparent (Layer 2) mode allows the firewall to operate as a Layer 2 bridge, inspecting traffic between VLAN 10 and VLAN 20 without requiring any IP address changes or routing. The firewall forwards frames based on MAC addresses, preserving the existing IP subnet and host configurations, which is ideal for inserting security into an existing switched environment.
What should I do if I get this PCNSE 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.
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Question Discussion
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