PCNSE Core Concepts and Architecture Practice Question
This PCNSE practice question tests your understanding of core concepts and architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Exhibit
admin@PA-3020# show running security-policy
set security-policy rule 1 from zone internal to zone external source 10.0.0.0/8 destination 0.0.0.0/0 application web-browsing service service-http action deny
set security-policy rule 2 from zone internal to zone external source 10.1.0.0/16 destination 0.0.0.0/0 application web-browsing service service-http action allow
Refer to the exhibit. A user with IP 10.1.1.100 from the internal zone is trying to access http://203.0.113.1. What will the firewall do?
admin@PA-3020# show running security-policy
set security-policy rule 1 from zone internal to zone external source 10.0.0.0/8 destination 0.0.0.0/0 application web-browsing service service-http action deny
set security-policy rule 2 from zone internal to zone external source 10.1.0.0/16 destination 0.0.0.0/0 application web-browsing service service-http action allow
A
Drop the traffic because no rule matches.
Why wrong: The source 10.1.1.100 falls within 10.0.0.0/8 in rule 1, so a rule matches.
B
Allow the traffic because rule 2 matches.
Why wrong: Rule 2 matches the source subnet, but rule 1 matches first because it is listed first and has a broader source that includes 10.1.1.100.
C
Reset the traffic because of rule 1.
Why wrong: The action is deny, not reset.
D
Deny the traffic because rule 1 matches first.
Rule 1 has source 10.0.0.0/8 which includes 10.1.1.100, so it matches first and denies the traffic.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deny the traffic because rule 1 matches first.
Option D is correct because the firewall processes security rules in top-down order. Rule 1 explicitly denies traffic from the internal zone to the destination zone 'untrust-L3' for destination IP 203.0.113.1, which matches the user's traffic. Since rule 1 is matched first, the firewall denies the traffic and does not evaluate subsequent rules.
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.
✗
Drop the traffic because no rule matches.
Why it's wrong here
The source 10.1.1.100 falls within 10.0.0.0/8 in rule 1, so a rule matches.
✗
Allow the traffic because rule 2 matches.
Why it's wrong here
Rule 2 matches the source subnet, but rule 1 matches first because it is listed first and has a broader source that includes 10.1.1.100.
✗
Reset the traffic because of rule 1.
Why it's wrong here
The action is deny, not reset.
✓
Deny the traffic because rule 1 matches first.
Why this is correct
Rule 1 has source 10.0.0.0/8 which includes 10.1.1.100, so it matches first and denies the traffic.
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 often assume the firewall will continue to evaluate subsequent rules (like rule 2) after a match, but the first-match logic means rule 1's deny action is applied immediately, preventing any further rule evaluation.
Detailed technical explanation
How to think about this question
Palo Alto Networks firewalls use a first-match model for security rules, meaning the firewall evaluates rules from top to bottom and applies the action of the first matching rule. The 'deny' action in rule 1 silently drops the packet without sending a TCP reset or ICMP unreachable, which is the default behavior for deny rules unless explicitly configured otherwise. In real-world scenarios, this top-down evaluation can lead to unintended blocks if rules are not ordered correctly, especially when using broad destination zones like 'untrust-L3'.
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: Deny the traffic because rule 1 matches first. — Option D is correct because the firewall processes security rules in top-down order. Rule 1 explicitly denies traffic from the internal zone to the destination zone 'untrust-L3' for destination IP 203.0.113.1, which matches the user's traffic. Since rule 1 is matched first, the firewall denies the traffic and does not evaluate subsequent rules.
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.
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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