- A
Verify that the port range in the custom application is correct.
Why wrong: Port is already configured; dynamic ports may be used.
- B
Update the App-ID signature database.
Why wrong: Custom apps do not depend on signature updates.
- C
Check for asymmetric routing on the firewall.
Why wrong: Asymmetric routing is less likely for internal traffic.
- D
Ensure a protocol decoder (e.g., SIP) is enabled for the application.
VoIP often uses dynamic ports; a protocol decoder is needed for full identification.
Question 209 of 516
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.
A company uses a custom application for internal VoIP traffic. The custom App-ID signature is configured with the correct protocol and port, but traffic is still not matching. The firewall shows the application as 'unknown-tcp'. What should the administrator check next?
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
✓
Ensure a protocol decoder (e.g., SIP) is enabled for the application.
Custom App-ID signatures require a protocol decoder to inspect application-layer payloads. Even if the port and protocol are correctly defined, without an enabled decoder (e.g., SIP for VoIP), the firewall cannot identify the application and falls back to 'unknown-tcp'. Enabling the appropriate decoder allows the firewall to parse the traffic and match the custom signature.
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.
- ✗
Verify that the port range in the custom application is correct.
Why it's wrong here
Port is already configured; dynamic ports may be used.
- ✗
Update the App-ID signature database.
Why it's wrong here
Custom apps do not depend on signature updates.
- ✗
Check for asymmetric routing on the firewall.
Why it's wrong here
Asymmetric routing is less likely for internal traffic.
- ✓
Ensure a protocol decoder (e.g., SIP) is enabled for the application.
Why this is correct
VoIP often uses dynamic ports; a protocol decoder is needed for full identification.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a custom App-ID only needs correct port/protocol definitions, overlooking that protocol decoders are mandatory for application-layer identification of VoIP and other complex protocols.
Detailed technical explanation
How to think about this question
Protocol decoders (e.g., SIP, H.323, MGCP) are essential for VoIP traffic because they parse the control channel to extract dynamic port information and application-layer details. Without the decoder, the firewall sees only TCP or UDP packets and cannot correlate them to the custom App-ID, even if the static port matches. In real-world scenarios, VoIP applications often use dynamic ports negotiated via SIP or H.225, so the decoder must be enabled to track these secondary channels.
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
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.
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Securing Traffic and App-ID — study guide chapter
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FAQ
Questions learners often ask
What does this PCNSE question test?
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: Ensure a protocol decoder (e.g., SIP) is enabled for the application. — Custom App-ID signatures require a protocol decoder to inspect application-layer payloads. Even if the port and protocol are correctly defined, without an enabled decoder (e.g., SIP for VoIP), the firewall cannot identify the application and falls back to 'unknown-tcp'. Enabling the appropriate decoder allows the firewall to parse the traffic and match the custom signature.
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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