This PCNSE practice question tests your understanding of troubleshoot. 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 large enterprise uses a PA-5250 as a perimeter firewall with multiple virtual systems (vsys). One vsys is for the DMZ, and it is logging high amounts of dropped traffic. The administrator notices that the firewall's dataplane CPU is consistently above 80%. The logs show many 'application-id timeout' drops. The DMZ hosts are running custom applications on non-standard ports. What is the first step to mitigate the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a custom application signature for the custom applications.
Option C is correct because creating custom application signatures reduces the need for heuristic analysis of unknown traffic, lowering CPU load.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Disable application identification for the DMZ zone.
Why it's wrong here
Disabling app-id entirely would break security policy that depends on application matching.
✗
Reduce the number of security rules in the DMZ.
Why it's wrong here
Fewer rules do not directly address the app-id processing overhead.
✓
Use a custom application signature for the custom applications.
Why this is correct
Custom app signatures allow the firewall to identify traffic without deep packet inspection, reducing CPU.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Increase the application identification timeout for the custom applications.
Why it's wrong here
Increasing timeout would not reduce CPU; it may even allow more analysis time.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNSE NAT questions on configuration and troubleshooting.
Troubleshoot — This question tests Troubleshoot — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use a custom application signature for the custom applications. — Option C is correct because creating custom application signatures reduces the need for heuristic analysis of unknown traffic, lowering CPU load.
What should I do if I get this PCNSE question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNSE NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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