PCNSE Deploy and Configure Firewalls Practice Question
This PCNSE practice question tests your understanding of deploy and configure firewalls. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 uses a custom application definition for a proprietary application that runs on UDP port 12345. The security rule allowing the application is configured, but traffic logs show the application as 'unknown' instead of matching the custom app. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The traffic is not matching the app's protocol or port in the signature.
Option C is correct because the custom application definition specifies UDP port 12345, but if the actual traffic uses a different port or does not match the protocol (UDP) defined in the signature, the firewall will classify it as 'unknown'. The security rule allows the application, but the traffic must first be identified by the App-ID engine based on the signature's protocol and port criteria; a mismatch here prevents proper classification.
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 custom application signature is not associated with the security rule.
Why it's wrong here
The rule already uses the custom application definition.
✗
The firewall is running in L2 mode.
Why it's wrong here
App-ID works in L2 mode as well.
✓
The traffic is not matching the app's protocol or port in the signature.
Why this is correct
If the actual traffic uses a different port or protocol than defined, App-ID will not match.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The application timeout is too short.
Why it's wrong here
Timeout affects session duration, not application identification.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a security rule referencing a custom application will automatically classify all traffic on that rule as the application, but App-ID requires the traffic to match the signature's protocol and port criteria first.
Detailed technical explanation
How to think about this question
App-ID uses a multi-stage classification process: it first checks the protocol and port defined in the application signature, then applies deeper inspection (e.g., pattern matching, behavioral analysis) if needed. If the traffic's port does not match the signature's port (UDP 12345), the firewall skips further inspection for that app and marks it as 'unknown'. In real-world scenarios, a common mistake is defining the application with a specific port but then allowing the rule on a different port, causing the App-ID engine to never attempt to match the custom signature.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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 traffic is not matching the app's protocol or port in the signature. — Option C is correct because the custom application definition specifies UDP port 12345, but if the actual traffic uses a different port or does not match the protocol (UDP) defined in the signature, the firewall will classify it as 'unknown'. The security rule allows the application, but the traffic must first be identified by the App-ID engine based on the signature's protocol and port criteria; a mismatch here prevents proper classification.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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