This PCNSA practice question tests your understanding of core concepts. 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.
During a security audit, it is discovered that some traffic from the 'guest' zone to the 'untrust' zone is not being inspected by Threat Prevention profiles. The security rule that matches this traffic has a Threat Prevention profile applied. What is a likely reason for the lack of inspection?
The Threat Prevention profile is disabled on the rule
Why wrong: The administrator confirmed the profile is applied, so it is not disabled.
B
An earlier rule with action 'allow' is matching the traffic before reaching this rule
If a higher-priority rule matches and allows traffic without a threat profile, the later rule's profile is not used.
C
The traffic uses a service that is not supported by the Threat Prevention profile
Why wrong: Threat Prevention profiles inspect all supported protocols; unsupported ones are passed without inspection but this would not affect supported services.
D
The security rule action is set to 'deny'
Why wrong: If action is deny, the traffic is blocked, not allowed without inspection.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An earlier rule with action 'allow' is matching the traffic before reaching this rule
Option D is correct because if the rule's action is 'allow', the threat profile is applied; but if the traffic matches an earlier rule with action 'allow' and no threat profile, the later rule's profile is not applied. Option A is wrong because if the profile is applied, it should be active. Option B is wrong because threat profiles apply to all sessions that match the rule, regardless of service. Option C is wrong because the action 'deny' would block traffic entirely, not allow without inspection.
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 Threat Prevention profile is disabled on the rule
Why it's wrong here
The administrator confirmed the profile is applied, so it is not disabled.
✓
An earlier rule with action 'allow' is matching the traffic before reaching this rule
Why this is correct
If a higher-priority rule matches and allows traffic without a threat profile, the later rule's profile is not used.
Related concept
Standard ACLs match source addresses.
✗
The traffic uses a service that is not supported by the Threat Prevention profile
Why it's wrong here
Threat Prevention profiles inspect all supported protocols; unsupported ones are passed without inspection but this would not affect supported services.
✗
The security rule action is set to 'deny'
Why it's wrong here
If action is deny, the traffic is blocked, not allowed without inspection.
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.
Core Concepts — This question tests Core Concepts — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: An earlier rule with action 'allow' is matching the traffic before reaching this rule — Option D is correct because if the rule's action is 'allow', the threat profile is applied; but if the traffic matches an earlier rule with action 'allow' and no threat profile, the later rule's profile is not applied. Option A is wrong because if the profile is applied, it should be active. Option B is wrong because threat profiles apply to all sessions that match the rule, regardless of service. Option C is wrong because the action 'deny' would block traffic entirely, not allow without inspection.
What should I do if I get this PCNSA question wrong?
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.
What is the key concept behind this question?
Standard ACLs match source addresses.
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