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.
A security administrator notices that traffic to a specific website is being denied. The traffic log shows that the application is 'ssl' and the action is 'deny' with the rule being 'Allow-SSL'. 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 security rule 'Allow-SSL' has 'service' set to 'application-default' but the website uses port 8443.
The security rule 'Allow-SSL' is configured with 'service' set to 'application-default', which means it only permits traffic on the default port for SSL (TCP 443). Since the website uses port 8443, the traffic is denied because the rule does not match the non-standard port. The firewall's application identification still correctly identifies the traffic as 'ssl', but the service constraint prevents the rule from applying, resulting in a deny action.
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 destination IP is in a blacklist.
Why it's wrong here
There is no mention of a blacklist; the rule is named 'Allow-SSL'.
✗
The security rule is placed too low in the rulebase.
Why it's wrong here
The traffic matches the rule, so rule order is not the issue; it is being matched but denied due to service mismatch.
✓
The security rule 'Allow-SSL' has 'service' set to 'application-default' but the website uses port 8443.
Why this is correct
Application-default restricts matching to the default port (443 for ssl), so port 8443 traffic does 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 SSL certificate is expired.
Why it's wrong here
An expired certificate would cause a browser warning but not a firewall denial.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume the 'Allow-SSL' rule should match all SSL traffic regardless of port, but Cisco tests the nuance that 'application-default' restricts the rule to only the default port for that application, causing a deny on non-standard ports like 8443.
Detailed technical explanation
How to think about this question
When a security rule has 'service' set to 'application-default', the firewall checks both the application (ssl) and the destination port. If the port differs from the default (443 for ssl), the rule does not match, even if the application is correctly identified. This is because the firewall enforces a strict port-application binding for default services; to allow SSL on a non-standard port, you must either set 'service' to 'any' or create a custom service object for port 8443. In real-world scenarios, this often catches administrators who assume application-based rules are port-agnostic.
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 security rule 'Allow-SSL' has 'service' set to 'application-default' but the website uses port 8443. — The security rule 'Allow-SSL' is configured with 'service' set to 'application-default', which means it only permits traffic on the default port for SSL (TCP 443). Since the website uses port 8443, the traffic is denied because the rule does not match the non-standard port. The firewall's application identification still correctly identifies the traffic as 'ssl', but the service constraint prevents the rule from applying, resulting in a deny action.
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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