- A
The application's timeout value is too short.
Why wrong: Timeout values affect session keepalive, not identification.
- B
The application is defined with the wrong protocol (TCP vs UDP).
If the custom application uses TCP but is defined as UDP, App-ID will not match.
- C
Content-ID is disabled on the security policy.
Why wrong: Content-ID handles data filtering, not application identification.
- D
The application requires URL categorization to be enabled.
Why wrong: URL categorization is separate from App-ID.
Question 311 of 516
Why Custom Application App-ID Fails: Incorrect Protocol Assignment
This PCNSE practice question tests your understanding of core concepts and architecture. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 firewall is using App-ID to identify applications running on non-standard ports. The administrator has configured a custom application with a default port of 8080, but traffic on port 8080 is still not being identified correctly. The application uses multiple connections on different ports. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
✓
The application is defined with the wrong protocol (TCP vs UDP).
Custom applications require both a default port and a protocol type (TCP/UDP). If the protocol is not specified correctly (e.g., TCP instead of UDP or vice versa), App-ID may fail to identify the traffic even if the port matches. Option A (timeout setting) affects session termination but not identification. Option C (Content-ID disabled) affects file analysis and threat detection, not basic App-ID identification. Option D (URL categorization required) is only relevant for HTTP-based applications and not for general application identification. Therefore, the most likely cause is that the application is defined with the wrong protocol.
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.
- ✗
The application's timeout value is too short.
Why it's wrong here
Timeout values affect session keepalive, not identification.
- ✓
The application is defined with the wrong protocol (TCP vs UDP).
- ✗
Content-ID is disabled on the security policy.
Why it's wrong here
Content-ID handles data filtering, not application identification.
- ✗
The application requires URL categorization to be enabled.
Why it's wrong here
URL categorization is separate from App-ID.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 PCNSE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Questions learners often ask
What does this PCNSE question test?
Core Concepts and Architecture — This question tests Core Concepts and Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The application is defined with the wrong protocol (TCP vs UDP). — Custom applications require both a default port and a protocol type (TCP/UDP). If the protocol is not specified correctly (e.g., TCP instead of UDP or vice versa), App-ID may fail to identify the traffic even if the port matches. Option A (timeout setting) affects session termination but not identification. Option C (Content-ID disabled) affects file analysis and threat detection, not basic App-ID identification. Option D (URL categorization required) is only relevant for HTTP-based applications and not for general application identification. Therefore, the most likely cause is that the application is defined with the wrong protocol.
What should I do if I get this PCNSE question wrong?
Identify which PCNSE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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