- A
The 'Allow from 10.0.1.0/24 to 10.0.2.0/24' rule is blocking the traffic.
Why wrong: Incorrect. Rule 1 allows traffic from 10.0.1.0/24 to 10.0.2.0/24 only, so it does not block traffic to the internet. It does not match because the destination is not 10.0.2.0/24.
- B
The firewall's implicit deny rule is applied before any security rules.
Why wrong: Incorrect. The implicit deny is applied only after all security rules are evaluated and no match is found. Here, rule 2 matches first, so the implicit deny is not applied.
- C
The traffic matches the 'Deny from 10.0.1.0/24 to any' rule first.
Why wrong: Incorrect. The traffic does not match the deny rule first; it matches rule 2 (Allow any to any) first. In a first-match system, rule 2 is applied and permits the traffic, so the deny rule is never reached.
- D
The traffic matches the 'Allow from any to any' rule first.
Correct. The traffic from 10.0.1.0/24 to the internet matches rule 2 (Allow from any to any) first because rule 1's destination is specific to 10.0.2.0/24. Since rule 2 is first match, the traffic should be allowed. If it is being dropped, the cause is not any of these rules.
Security Policy Evaluation Order — Last Matching Rule
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. A key principle to apply: rule evaluation order. 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 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 traffic matches the 'Allow from any to any' rule first.
Palo Alto firewalls use first-match logic: rules are evaluated top-down and the first matching rule is applied. Traffic from 10.0.1.0/24 to the internet does not match rule 1 (destination 10.0.2.0/24). Rule 2 (Allow from any to any) matches first and would permit the traffic. Therefore, the traffic should not be dropped by this rule set. Among the options, D is the only factually correct statement about which rule matches first. The drop must be due to another factor not listed, but D correctly identifies the first-match behavior.
Key principle: Rule evaluation order
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
Incorrect. Rule 1 allows traffic from 10.0.1.0/24 to 10.0.2.0/24 only, so it does not block traffic to the internet. It does not match because the destination is not 10.0.2.0/24.
- ✗
The firewall's implicit deny rule is applied before any security rules.
Why it's wrong here
Incorrect. The implicit deny is applied only after all security rules are evaluated and no match is found. Here, rule 2 matches first, so the implicit deny is not applied.
- ✗
The traffic matches the 'Deny from 10.0.1.0/24 to any' rule first.
Why it's wrong here
Incorrect. The traffic does not match the deny rule first; it matches rule 2 (Allow any to any) first. In a first-match system, rule 2 is applied and permits the traffic, so the deny rule is never reached.
- ✓
The traffic matches the 'Allow from any to any' rule first.
Why this is correct
Correct. The traffic from 10.0.1.0/24 to the internet matches rule 2 (Allow from any to any) first because rule 1's destination is specific to 10.0.2.0/24. Since rule 2 is first match, the traffic should be allowed. If it is being dropped, the cause is not any of these rules.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Rule evaluation order
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume last-match behavior, but Palo Alto uses first-match. In a first-match system, an earlier allow rule (rule 2) would permit the traffic before reaching the later deny rule (rule 3). Thus, the traffic would not be dropped by these rules.
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
- Rule evaluation order
- First-match behavior
- Specificity vs position
- Default deny
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
Rule evaluation order
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review rule evaluation order, then practise related PCNSE questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this PCNSE question test?
Core Concepts and Architecture — This question tests Core Concepts and Architecture — Rule evaluation order.
What is the correct answer to this question?
The correct answer is: The traffic matches the 'Allow from any to any' rule first. — Palo Alto firewalls use first-match logic: rules are evaluated top-down and the first matching rule is applied. Traffic from 10.0.1.0/24 to the internet does not match rule 1 (destination 10.0.2.0/24). Rule 2 (Allow from any to any) matches first and would permit the traffic. Therefore, the traffic should not be dropped by this rule set. Among the options, D is the only factually correct statement about which rule matches first. The drop must be due to another factor not listed, but D correctly identifies the first-match behavior.
What should I do if I get this PCNSE question wrong?
Review rule evaluation order, then practise related PCNSE questions on the same topic to reinforce the concept.
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?
Rule evaluation order
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Last reviewed: Jun 25, 2026
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