PCNSE Manage, Monitor and Operate Practice Question
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?
⚠ Common exam trap
Test-takers frequently 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.
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 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.
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.
- ✗
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.