PCNSE Deploy and Configure Firewalls Practice Question
This PCNSE practice question tests your understanding of deploy and configure firewalls. 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.
Exhibit
Refer to the exhibit.
admin@PA-500> show interface ethernet1/2.10
Interface ethernet1/2.10
VLAN: 20
Virtual router: default
IP netmask: 192.168.10.1/24
Zone: VLAN10
State: up
The administrator intended to create a sub-interface for VLAN 10 with IP 192.168.10.1/24. However, traffic from VLAN 10 is not being routed through this interface. Based on the exhibit, what is the cause?
Refer to the exhibit.
admin@PA-500> show interface ethernet1/2.10
Interface ethernet1/2.10
VLAN: 20
Virtual router: default
IP netmask: 192.168.10.1/24
Zone: VLAN10
State: up
A
The VLAN ID is misconfigured as 20 instead of 10.
The sub-interface expects VLAN tag 20, but traffic from VLAN 10 uses tag 10.
B
The IP netmask is /24 but should be /16.
Why wrong: The /24 netmask is appropriate for the intended 192.168.10.0/24 subnet.
C
The zone is incorrectly named 'VLAN10'.
Why wrong: The zone name is for administrative purposes and does not affect routing.
D
The virtual router is not correctly set.
Why wrong: The virtual router is set to 'default' and no routing issue is indicated.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VLAN ID is misconfigured as 20 instead of 10.
The exhibit shows the sub-interface is configured with VLAN ID 20, but the administrator intended VLAN 10. In Palo Alto Networks firewalls, sub-interfaces use 802.1Q VLAN tagging, and the VLAN ID must match the tag on incoming frames. Mismatched VLAN IDs cause the firewall to drop or ignore traffic because the sub-interface only processes frames with the configured tag.
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.
✓
The VLAN ID is misconfigured as 20 instead of 10.
Why this is correct
The sub-interface expects VLAN tag 20, but traffic from VLAN 10 uses tag 10.
Related concept
Read the scenario before looking for a memorised answer.
✗
The IP netmask is /24 but should be /16.
Why it's wrong here
The /24 netmask is appropriate for the intended 192.168.10.0/24 subnet.
✗
The zone is incorrectly named 'VLAN10'.
Why it's wrong here
The zone name is for administrative purposes and does not affect routing.
✗
The virtual router is not correctly set.
Why it's wrong here
The virtual router is set to 'default' and no routing issue is indicated.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the VLAN ID on the sub-interface with the IP subnet or zone name, assuming a mismatch in IP addressing or zone naming is the root cause, when in fact the VLAN tag mismatch is the direct and immediate reason traffic is not processed.
Detailed technical explanation
How to think about this question
Palo Alto Networks sub-interfaces rely on the IEEE 802.1Q standard, where each sub-interface is bound to a specific VLAN ID (1-4094). The firewall's dataplane inspects the VLAN tag in the Ethernet frame header and matches it to the sub-interface's configured tag; if no match, the frame is dropped. This is distinct from Cisco IOS sub-interfaces, where the encapsulation dot1Q command explicitly ties the VLAN ID to the sub-interface, but the underlying principle is identical.
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.
Deploy and Configure Firewalls — This question tests Deploy and Configure Firewalls — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The VLAN ID is misconfigured as 20 instead of 10. — The exhibit shows the sub-interface is configured with VLAN ID 20, but the administrator intended VLAN 10. In Palo Alto Networks firewalls, sub-interfaces use 802.1Q VLAN tagging, and the VLAN ID must match the tag on incoming frames. Mismatched VLAN IDs cause the firewall to drop or ignore traffic because the sub-interface only processes frames with the configured tag.
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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This PCNSE practice question is part of Courseiva's free Palo Alto Networks 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 PCNSE exam.
Question Discussion
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