PCNSE Core Concepts and Architecture Practice Question
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?
⚠ Common exam trap
It's easy for candidates to 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.
Answer choices
Why each option matters
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 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.
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
An incorrect source address would block traffic from the internal subnet, but the stem's stated policy already pairs application 'ftp' with service 'service-http'. It tempts because address objects are frequently misconfigured, and it would be the cause if the source zone or address object excluded the sending hosts.
- ✗
The application is incorrectly set to ftp.
Why it's wrong here
Setting the application to 'ftp' is correct for FTP traffic, so it cannot explain the denial. It tempts because application identification errors do cause drops, and it would be the cause if the policy listed an unrelated application such as 'ssl' or 'web-browsing' instead of 'ftp'.
- ✗
The rule is not enabled.
Why it's wrong here
A disabled rule would deny all matching traffic, but the stem already identifies a specific mismatch between the application and service defined in the policy. It tempts because disabled rules are a common oversight, and it would be the cause if the policy matched the traffic correctly yet still dropped it.
- ✓
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, whereas service-http matches TCP 80. Because the security policy's service object is service-http, the firewall drops the FTP session on port 21 before the ftp application can be identified, so the traffic is denied.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.