The answer is an incorrectly configured application override. When a Palo Alto Networks firewall terminates a session with a 'tcp-fin' reason, it indicates the firewall completed the TCP handshake but then gracefully closed the connection because the actual traffic payload did not match the expected application signature. In this scenario, the application is set to 'web-browsing', which expects HTTP traffic, but the application override forces the firewall to ignore deep packet inspection and trust the override; if the actual payload is non-HTTP, such as SSH or a custom protocol, the firewall detects the mismatch and sends a TCP FIN to terminate the session. On the PCNSE exam, this tests your understanding of how application overrides bypass App-ID and why a graceful FIN, rather than a reset or drop, occurs when the override conflicts with real traffic. A common trap is confusing this with a security policy deny or a TCP RST, but remember: a FIN is a polite goodbye, not a forceful rejection. Memory tip: "Override mismatch equals FINish."
PCNSE Core Concepts and Architecture Practice Question
This PCNSE practice question tests your understanding of core concepts and architecture. 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 administrator is troubleshooting a traffic drop between two internal zones. The firewall shows that the session is being terminated with a 'tcp-fin' reason. The administrator verifies that the application is set to 'web-browsing' and the service is 'application-default'. What is the most likely cause of the session termination?
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 override is incorrectly configured for the traffic.
When an application override is incorrectly configured, the firewall terminates the session with a 'tcp-fin' reason because it cannot match the expected application signature. The 'web-browsing' application expects HTTP traffic, but the actual payload may be non-HTTP (e.g., SSH or custom protocol), causing the firewall to send a TCP FIN to close the session gracefully. This is distinct from a reset (RST) or drop, as the firewall completes the TCP handshake but then terminates due to application mismatch.
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 security policy has a deny action for the traffic.
Why it's wrong here
A deny policy would show a 'deny' reason, not 'tcp-fin'.
✓
The application override is incorrectly configured for the traffic.
Why this is correct
Application override can cause the firewall to terminate the session if the traffic does not match the expected application.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The traffic is being asymmetrically routed.
Why it's wrong here
Asymmetric routing would show 'tcp-rst-from-server' or 'tcp-rst-from-client'.
✗
The zone protection profile is dropping the session.
Why it's wrong here
Zone protection drops would show 'zone-protect' reason.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Palo Alto Networks often tests the distinction between 'tcp-fin' (graceful close by firewall) and 'tcp-rst' (abrupt termination) to confuse candidates into thinking a deny policy or zone protection is responsible, when the real cause is an application mismatch due to incorrect override configuration.
Trap categories for this question
Command / output trap
A deny policy would show a 'deny' reason, not 'tcp-fin'.
Detailed technical explanation
How to think about this question
The 'tcp-fin' reason indicates the firewall itself sent a FIN packet to close the session, which occurs when the application override forces a specific App-ID but the traffic does not match that App-ID's signatures. Under the hood, the firewall performs TCP termination by sending a FIN after detecting the mismatch, which is different from a session that times out or is reset. In real-world scenarios, this often happens when administrators configure application overrides for custom ports without verifying the actual application behavior, leading to dropped connections that appear as graceful closes in logs.
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.
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 override is incorrectly configured for the traffic. — When an application override is incorrectly configured, the firewall terminates the session with a 'tcp-fin' reason because it cannot match the expected application signature. The 'web-browsing' application expects HTTP traffic, but the actual payload may be non-HTTP (e.g., SSH or custom protocol), causing the firewall to send a TCP FIN to close the session gracefully. This is distinct from a reset (RST) or drop, as the firewall completes the TCP handshake but then terminates due to application mismatch.
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.
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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Question Discussion
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