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.
Exhibit
Refer to the exhibit.
> show app-app-id counter
Application Packets Flags
web-browsing 1000
ssl 500
my-custom-app 0
> show app-override rule
Name: Override-SSH
Source: 10.0.0.0/24
Destination: 10.1.0.0/24
Application: my-custom-app
An engineer checks the application counter and sees that my-custom-app has zero packets, but they expected traffic from 10.0.0.0/24 to 10.1.0.0/24 to be identified as my-custom-app. What is the most likely reason?
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.
Refer to the exhibit.
> show app-app-id counter
Application Packets Flags
web-browsing 1000
ssl 500
my-custom-app 0
> show app-override rule
Name: Override-SSH
Source: 10.0.0.0/24
Destination: 10.1.0.0/24
Application: my-custom-app
A
The traffic is being identified as ssl instead.
Why wrong: Counter shows ssl packets, but this could be unrelated traffic. The issue is the missing port in the override rule.
B
The application override rule does not have the correct port.
Correct: Without a port, the override rule does not trigger, and traffic is identified normally.
C
The security policy does not allow the traffic.
Why wrong: Security policy is about allowing or denying, but identification happens before that. Even if denied, it would still be counted in the application counter.
D
The custom application my-custom-app is not committed.
Why wrong: If not committed, the application would still appear in the configuration, but the counter shows zero. The commit status is not the issue here.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The application override rule does not have the correct port.
The application override rule does not specify a port or service. By default, app override rules require a port to match; without it, the rule fails to match, and traffic is identified by default signatures.
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.
✗
The traffic is being identified as ssl instead.
Why it's wrong here
Counter shows ssl packets, but this could be unrelated traffic. The issue is the missing port in the override rule.
✓
The application override rule does not have the correct port.
Why this is correct
Correct: Without a port, the override rule does not trigger, and traffic is identified normally.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The security policy does not allow the traffic.
Why it's wrong here
Security policy is about allowing or denying, but identification happens before that. Even if denied, it would still be counted in the application counter.
✗
The custom application my-custom-app is not committed.
Why it's wrong here
If not committed, the application would still appear in the configuration, but the counter shows zero. The commit status is not the issue here.
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.
Trap categories for this question
Command / output trap
Counter shows ssl packets, but this could be unrelated traffic. The issue is the missing port in the override rule.
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.
Securing Traffic and App-ID — This question tests Securing Traffic and App-ID — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The application override rule does not have the correct port. — The application override rule does not specify a port or service. By default, app override rules require a port to match; without it, the rule fails to match, and traffic is identified by default signatures.
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: "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?
Static NAT maps one inside address to one outside address.
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