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.
An administrator adds a new security rule to allow outbound 'web-browsing' and 'ssl' traffic. After committing, users report that some HTTPS sites are still blocked. Traffic logs show that the traffic matches the new rule but is denied. 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.
The service 'application-default' does not match the port used by the site.
Application-default restricts matching to the standard port for the application, so sites on non-standard ports do not match.
B
A decryption policy is required for HTTPS traffic.
Why wrong: Decryption is not required for the rule to allow traffic, but it may affect URL filtering; however, the traffic is being denied, not just filtered.
C
The application filter does not include 'ssl'.
Why wrong: The rule allows 'ssl', so the filter includes it.
D
The rule is placed too low in the rulebase.
Why wrong: If the traffic matches the rule, placement is not the issue.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The service 'application-default' does not match the port used by the site.
The correct answer is A because when a security rule uses the 'application-default' service, the firewall only allows traffic that matches the default port for the specified application. For 'web-browsing' (HTTP), the default port is TCP 80, and for 'ssl' (HTTPS), the default port is TCP 443. If an HTTPS site uses a non-standard port (e.g., TCP 8443), the traffic matches the rule based on the application but is denied because the service 'application-default' does not recognize that port as valid for the application.
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 service 'application-default' does not match the port used by the site.
Why this is correct
Application-default restricts matching to the standard port for the application, so sites on non-standard ports do 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.
✗
A decryption policy is required for HTTPS traffic.
Why it's wrong here
Decryption is not required for the rule to allow traffic, but it may affect URL filtering; however, the traffic is being denied, not just filtered.
If the traffic matches the rule, placement is not the issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume 'application-default' allows any port for the application, when in reality it strictly enforces the default port, causing denial for HTTPS on non-standard ports.
Detailed technical explanation
How to think about this question
Under the hood, Palo Alto Networks firewalls use App-ID to identify traffic and then enforce security rules based on the application and service. The 'application-default' service setting restricts traffic to the IANA-assigned default ports for each application (e.g., TCP 443 for SSL). If a web server hosts HTTPS on a non-standard port like TCP 8443, the firewall still identifies the application as 'ssl' but denies the session because the port does not match the default. This behavior is defined in the firewall's application signatures and can be overridden by using a custom service object that includes the non-standard port.
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 practitioner preparing for the PCNSE exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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 service 'application-default' does not match the port used by the site. — The correct answer is A because when a security rule uses the 'application-default' service, the firewall only allows traffic that matches the default port for the specified application. For 'web-browsing' (HTTP), the default port is TCP 80, and for 'ssl' (HTTPS), the default port is TCP 443. If an HTTPS site uses a non-standard port (e.g., TCP 8443), the traffic matches the rule based on the application but is denied because the service 'application-default' does not recognize that port as valid for the application.
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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