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Question 470 of 529

Core Concepts →hardMultiple ChoiceObjective-mapped

Why Traffic Is Blocked by Implicit Deny on Palo Alto Firewall

This PCNSA practice question tests your understanding of core concepts. 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 company has a Palo Alto Networks firewall in a data center, connecting internal users (zone: Internal) to the internet (zone: Untrust). Recently, users report that they cannot access the corporate HR portal hosted on a server in the DMZ (zone: DMZ, IP 10.10.10.10) using HTTPS. The firewall has a security policy that allows traffic from Internal to DMZ with application web-browsing and service https-ssl. The policy is in place and committed. The administrator verifies that the web server is running and reachable from within the DMZ. From the firewall, a ping from the management interface to the server is successful. However, when a user tries to access https://10.10.10.10, the connection times out. Traffic logs show no sessions logged for that traffic. 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.

A
The policy is missing the source zone; the traffic is being blocked by an implicit deny rule before any policy match.
If the source zone is not correctly configured, the policy won't match, and the traffic will hit the implicit deny rule, resulting in no log entries.
B
There is a routing issue preventing return traffic from reaching the firewall.
Why wrong: A routing issue would typically cause sessions to be created but with no return traffic, resulting in partially logged sessions, not zero sessions.
C
The policy has the wrong destination zone; the server is actually in the Internal zone.
Why wrong: If the destination zone were wrong, the traffic might match a different policy, but the absence of any sessions suggests no policy match at all.
D
The firewall is not configured to perform SSL decryption; thus HTTPS traffic is being blocked.
Why wrong: SSL decryption is optional; the firewall can allow HTTPS traffic without decryption if the policy permits the application and service.

Full breakdown with real-world context →

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 policy is missing the source zone; the traffic is being blocked by an implicit deny rule before any policy match.

Option A is correct. Since there are no sessions in the traffic log, the traffic is being dropped by the implicit deny rule, meaning no security policy matched. The most likely reason is that the policy's source zone is not set to Internal; if it were set to another zone (e.g., Untrust), the traffic from Internal would not match. Option B would likely produce sessions if matched by another policy. Option C would show sessions but no return traffic. Option D is incorrect because SSL decryption is not required for HTTPS to be allowed through the firewall.

Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

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 policy is missing the source zone; the traffic is being blocked by an implicit deny rule before any policy match.
Why this is correct
If the source zone is not correctly configured, the policy won't match, and the traffic will hit the implicit deny rule, resulting in no log entries.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
There is a routing issue preventing return traffic from reaching the firewall.
Why it's wrong here
A routing issue would typically cause sessions to be created but with no return traffic, resulting in partially logged sessions, not zero sessions.
✗
The policy has the wrong destination zone; the server is actually in the Internal zone.
Why it's wrong here
If the destination zone were wrong, the traffic might match a different policy, but the absence of any sessions suggests no policy match at all.
✗
The firewall is not configured to perform SSL decryption; thus HTTPS traffic is being blocked.
Why it's wrong here
SSL decryption is optional; the firewall can allow HTTPS traffic without decryption if the policy permits the application and service.

Common exam traps

Common exam trap: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

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.

What to study next

Got this wrong? Here's your next step.

Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related PCNSA ACL questions on filtering logic and placement.

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FAQ

Questions learners often ask

What does this PCNSA question test?

Core Concepts — This question tests Core Concepts — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: The policy is missing the source zone; the traffic is being blocked by an implicit deny rule before any policy match. — Option A is correct. Since there are no sessions in the traffic log, the traffic is being dropped by the implicit deny rule, meaning no security policy matched. The most likely reason is that the policy's source zone is not set to Internal; if it were set to another zone (e.g., Untrust), the traffic from Internal would not match. Option B would likely produce sessions if matched by another policy. Option C would show sessions but no return traffic. Option D is incorrect because SSL decryption is not required for HTTPS to be allowed through the firewall.

What should I do if I get this PCNSA question wrong?

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?

Standard ACLs match source addresses.

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This PCNSA practice question is part of Courseiva's free Palo Alto Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCNSA exam.