- A
Remove the new rule and implement the blocking via a Threat Prevention profile instead.
Threat Prevention profiles are more efficient for blocking known applications and offload processing from the policy engine.
- B
Move the new rule to the bottom of the rulebase to reduce matching frequency.
Why wrong: Moving the rule does not reduce the number of sessions that must be evaluated; it may increase latency for matching rules above.
- C
Convert the new rule to use a simplified service-based filter instead of application-based to reduce processing overhead.
Why wrong: Service-based filters are not effective for blocking modern applications that use arbitrary ports.
- D
Increase the session table size and adjust the TCP timewait timeout to reduce session setup overhead.
Why wrong: These adjustments address session capacity but not the CPU utilization caused by application identification.
Mitigate CPU Spike from App-ID Rule with Threat Prevention Profile
This PCNSE practice question tests your understanding of manage, monitor and operate. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 large enterprise has deployed two Palo Alto Networks PA-5250 firewalls in active/passive HA mode with Panorama for centralized management. The network contains over 10,000 users across multiple sites. Recently, the security team deployed a new security policy rule to block a set of high-risk applications. After the commit, the firewall's CPU utilization spiked to 95% and sessions started to drop intermittently. The firewall logs show a high number of session setup failures and timeouts. The existing security policy contains over 5,000 rules. The new rule uses application-based filtering and is placed near the top of the rulebase. What is the most effective course of action to reduce CPU load while maintaining security?
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
Remove the new rule and implement the blocking via a Threat Prevention profile instead.
The correct answer is A because the CPU spike is caused by the firewall having to perform application identification (App-ID) on every packet matching the new rule, which is placed near the top of a 5,000-rule policy. By moving the blocking logic to a Threat Prevention profile, the firewall can block the applications at the security profile stage after a faster initial match, reducing the per-session processing overhead. This approach offloads the heavy App-ID processing from the rulebase to a profile that is applied only to relevant traffic, thus lowering CPU utilization while still blocking the high-risk applications.
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.
- ✓
Remove the new rule and implement the blocking via a Threat Prevention profile instead.
Why this is correct
Threat Prevention profiles are more efficient for blocking known applications and offload processing from the policy engine.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Move the new rule to the bottom of the rulebase to reduce matching frequency.
Why it's wrong here
Moving the rule does not reduce the number of sessions that must be evaluated; it may increase latency for matching rules above.
- ✗
Convert the new rule to use a simplified service-based filter instead of application-based to reduce processing overhead.
Why it's wrong here
Service-based filters are not effective for blocking modern applications that use arbitrary ports.
- ✗
Increase the session table size and adjust the TCP timewait timeout to reduce session setup overhead.
Why it's wrong here
These adjustments address session capacity but not the CPU utilization caused by application identification.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume moving a rule to the bottom (Option B) reduces CPU load by reducing matching frequency, but in reality, App-ID processing is triggered per session regardless of rule position, and the firewall must still evaluate all rules above it, so the CPU spike persists.
Detailed technical explanation
How to think about this question
Under the hood, App-ID performs deep packet inspection (DPI) using multiple mechanisms such as protocol decoders, SSL decryption, and behavioral analysis, which is CPU-intensive, especially for the first few packets of a session. In a large rulebase with over 5,000 rules, the firewall must evaluate each rule sequentially until a match is found, and if the new rule is near the top, every session that matches it triggers full App-ID processing. By using a Threat Prevention profile with an application filter, the firewall can apply the block after a simpler rule match (e.g., based on source/destination zones or IP addresses), reducing the per-session CPU cost because the profile is evaluated only after a rule match and can leverage cached application signatures.
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 practitioner preparing for the PCNSE exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Questions learners often ask
What does this PCNSE question test?
Manage, Monitor and Operate — This question tests Manage, Monitor and Operate — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Remove the new rule and implement the blocking via a Threat Prevention profile instead. — The correct answer is A because the CPU spike is caused by the firewall having to perform application identification (App-ID) on every packet matching the new rule, which is placed near the top of a 5,000-rule policy. By moving the blocking logic to a Threat Prevention profile, the firewall can block the applications at the security profile stage after a faster initial match, reducing the per-session processing overhead. This approach offloads the heavy App-ID processing from the rulebase to a profile that is applied only to relevant traffic, thus lowering CPU utilization while still blocking the high-risk applications.
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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Last reviewed: Jul 4, 2026
This PCNSE 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 PCNSE exam.
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