PCNSE Securing Traffic and App-ID Practice Question
This PCNSE practice question tests your understanding of securing traffic and app-id. 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.
Which THREE of the following can cause App-ID to incorrectly identify traffic?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Asymmetric routing causes the firewall to see only one direction of traffic.
Asymmetric routing causes App-ID to see only one direction of traffic (e.g., SYN but no SYN-ACK). App-ID relies on bidirectional flow inspection to identify applications; without seeing both directions, the firewall cannot complete the application signature match or protocol handshake, leading to incorrect or failed identification.
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.
✗
Multiple security rules are configured for the same traffic.
Why it's wrong here
Multiple rules do not affect App-ID identification.
✓
Asymmetric routing causes the firewall to see only one direction of traffic.
Why this is correct
Asymmetric routing can prevent the firewall from seeing the full session, causing inaccurate identification.
Related concept
Read the scenario before looking for a memorised answer.
✓
SSL decryption is not enabled for the traffic.
Why this is correct
Without decryption, App-ID cannot inspect encrypted payloads, leading to potential incorrect identification.
Related concept
Read the scenario before looking for a memorised answer.
✓
IP fragmentation occurs before the firewall.
Why this is correct
Fragmentation can obscure application signatures, leading to misidentification.
Related concept
Read the scenario before looking for a memorised answer.
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think IP fragmentation is a rare or non-impactful scenario, but it directly prevents App-ID from seeing complete application headers, making it a common cause of misidentification in real-world networks.
Detailed technical explanation
How to think about this question
App-ID uses a multi-pass approach: first, it performs protocol decoding (e.g., HTTP, SSL) and then applies application signatures. Asymmetric routing breaks this because the firewall must see the full TCP three-way handshake and subsequent data in both directions to correctly associate the flow with an application; without the return path, the firewall may classify traffic as 'incomplete' or fall back to a generic protocol like TCP. IP fragmentation before the firewall (Option D) can cause App-ID to misidentify traffic because fragmented packets may not contain complete application-layer headers, preventing signature matching or protocol decoding.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Securing Traffic and App-ID — This question tests Securing Traffic and App-ID — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Asymmetric routing causes the firewall to see only one direction of traffic. — Asymmetric routing causes App-ID to see only one direction of traffic (e.g., SYN but no SYN-ACK). App-ID relies on bidirectional flow inspection to identify applications; without seeing both directions, the firewall cannot complete the application signature match or protocol handshake, leading to incorrect or failed identification.
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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Question Discussion
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