PCNSE Core Concepts and Architecture Practice Question
This PCNSE practice question tests your understanding of core concepts and architecture. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 network engineer is troubleshooting why traffic from the 10.0.1.0/24 subnet to the internet is being dropped. The firewall has the following security policies (in order): 1) Allow from 10.0.1.0/24 to 10.0.2.0/24, 2) Allow from any to any, 3) Deny from 10.0.1.0/24 to any. What is the most likely cause of the traffic being dropped?
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 traffic matches the 'Deny from 10.0.1.0/24 to any' rule first.
Option C is correct because the firewall evaluates security policies in top-down order, and the traffic from 10.0.1.0/24 to the internet (any destination) matches the first rule (10.0.1.0/24 to 10.0.2.0/24) only if the destination is 10.0.2.0/24. Since the internet is not in that subnet, the traffic proceeds to the second rule (allow any to any), which permits it. However, the third rule (deny from 10.0.1.0/24 to any) is then evaluated and matches, causing the traffic to be dropped. The key is that the deny rule is placed after the allow any rule, but because it is more specific to the source, it still applies after the broader allow rule is checked.
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 'Allow from 10.0.1.0/24 to 10.0.2.0/24' rule is blocking the traffic.
Why it's wrong here
That rule allows traffic to a different subnet, not the internet.
✗
The firewall's implicit deny rule is applied before any security rules.
Why it's wrong here
Implicit deny is at the end, not before explicit rules.
✓
The traffic matches the 'Deny from 10.0.1.0/24 to any' rule first.
Why this is correct
The deny rule is listed first and matches the traffic, so it is dropped before reaching the allow rule.
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 traffic matches the 'Allow from any to any' rule first.
Why it's wrong here
That would allow the traffic, not drop it.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the 'Allow from any to any' rule will permit all traffic and stop further evaluation, but Palo Alto firewalls continue to check subsequent rules, and a later deny rule can override an earlier allow rule if it matches.
Detailed technical explanation
How to think about this question
In Palo Alto Networks firewalls, security rules are evaluated in a top-down order, and the first matching rule determines the action. However, if a rule is configured with a 'deny' action, it will drop the traffic even if a previous rule allowed it, because the firewall processes rules sequentially and applies the action of the first match. This behavior is distinct from some other firewalls that use a 'first match wins' model where the first rule that matches the traffic is the final decision; here, the order is critical, and the deny rule at position 3 will match after the allow rule at position 2, causing the drop. A common real-world scenario is misplacing a deny rule after a broad allow rule, leading to unexpected drops for specific sources.
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 traffic matches the 'Deny from 10.0.1.0/24 to any' rule first. — Option C is correct because the firewall evaluates security policies in top-down order, and the traffic from 10.0.1.0/24 to the internet (any destination) matches the first rule (10.0.1.0/24 to 10.0.2.0/24) only if the destination is 10.0.2.0/24. Since the internet is not in that subnet, the traffic proceeds to the second rule (allow any to any), which permits it. However, the third rule (deny from 10.0.1.0/24 to any) is then evaluated and matches, causing the traffic to be dropped. The key is that the deny rule is placed after the allow any rule, but because it is more specific to the source, it still applies after the broader allow rule is checked.
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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