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.
An administrator needs to allow FTP traffic from the internal network to an external server. The firewall is configured with a security policy that has the application 'ftp' and service 'service-http'. What is the most likely cause of the traffic being denied?
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 service object in the rule is set to service-http, which does not match FTP traffic.
The correct answer is D because the security policy's service object is set to 'service-http' (TCP port 80), but FTP traffic uses TCP port 21 for control and TCP port 20 for data. In Palo Alto Networks firewalls, the service object defines the destination port for the traffic; if it does not match the actual port used by the application, the firewall will deny the session even if the application is correctly identified. The mismatch between the service and the application's expected port causes the traffic to be blocked.
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 source address is wrong.
Why it's wrong here
The source address is likely correct; the issue is service mismatch.
If enabled, the rule would still not match due to service mismatch.
✓
The service object in the rule is set to service-http, which does not match FTP traffic.
Why this is correct
FTP uses TCP ports 20 and 21, not HTTP port 80. The service must match the traffic.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think the application field alone is sufficient to allow traffic, but the service object must also match the destination port; Palo Alto Networks often tests this by pairing a correct application with an incorrect service to see if you understand the dual-layer check.
Detailed technical explanation
How to think about this question
Palo Alto Networks firewalls use a 'service' object to define the destination port for a security policy, which must match the port used by the application's traffic. For FTP, the control channel uses TCP port 21, and the data channel uses TCP port 20; setting the service to 'service-http' (TCP 80) creates a port mismatch that causes the firewall to deny the session, as the firewall performs a port-based check even when application identification is enabled. In a real-world scenario, this often occurs when administrators copy a policy from an HTTP rule without updating the service object, leading to silent drops that are only visible in the traffic logs with a 'deny' reason of 'service mismatch'.
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.
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: The service object in the rule is set to service-http, which does not match FTP traffic. — The correct answer is D because the security policy's service object is set to 'service-http' (TCP port 80), but FTP traffic uses TCP port 21 for control and TCP port 20 for data. In Palo Alto Networks firewalls, the service object defines the destination port for the traffic; if it does not match the actual port used by the application, the firewall will deny the session even if the application is correctly identified. The mismatch between the service and the application's expected port causes the traffic to be blocked.
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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Question Discussion
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