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 security policy has an application list with 'facebook-chat' and 'facebook-base'. A user reports that Facebook messages are being blocked. The firewall logs show the application as 'facebook-base' but not as 'facebook-chat'. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The application 'facebook-chat' is a dependency that is not allowed in the policy.
Option A is correct because 'facebook-chat' is a dependent application of 'facebook-base'; if the policy only allows 'facebook-base', the dependency may not be automatically included. Option B is wrong because signature updates are not the cause. Option C is wrong because ports are not the issue. Option D is wrong because blocking is not causing missing application.
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The App-ID signature for 'facebook-chat' is outdated.
Why it's wrong here
Outdated signatures would cause misidentification, but the log shows correct app.
✓
The application 'facebook-chat' is a dependency that is not allowed in the policy.
Why this is correct
Dependent apps must be allowed explicitly or using application group.
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 firewall is blocking the application 'facebook-chat' due to content filtering.
Why it's wrong here
Blocking would show dropped sessions, not missing appID.
✗
The traffic is using a non-standard port for chat.
Why it's wrong here
Facebook uses standard ports.
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
Outdated signatures would cause misidentification, but the log shows correct app.
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 'facebook-chat' is a dependency that is not allowed in the policy. — Option A is correct because 'facebook-chat' is a dependent application of 'facebook-base'; if the policy only allows 'facebook-base', the dependency may not be automatically included. Option B is wrong because signature updates are not the cause. Option C is wrong because ports are not the issue. Option D is wrong because blocking is not causing missing application.
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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Question Discussion
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