The answer is a missing return policy, because even when UDP traffic is allowed outbound, the Palo Alto Networks firewall treats each session as stateful and requires a corresponding security rule to permit the return traffic from the application server back to the internal client. Without this return policy, the firewall silently drops the response packets, so the outbound UDP traffic appears allowed in the logs while the application fails to function. On the PCNSE exam, this scenario tests your understanding of stateful inspection and the fact that UDP, despite being connectionless, still relies on bidirectional policy rules—a common trap is assuming that allowing one direction is sufficient for stateless protocols. Remember the memory tip: “UDP needs a round-trip ticket—outbound allowance alone won’t bring the reply back.”
PCNSE Troubleshoot Practice Question
This PCNSE practice question tests your understanding of troubleshoot. 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 deploys a new application that uses UDP on port 12345. The security policy is configured to allow UDP traffic from the internal network to the application server. However, users report that the application does not work. The firewall logs show that the traffic is allowed. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The firewall is dropping the return traffic due to a missing policy
Option D is correct because even though the outbound UDP traffic is allowed by the security policy, the firewall must also have a corresponding policy to allow the return traffic from the application server back to the internal clients. Without a return policy, the firewall drops the response packets, breaking the UDP communication. The logs show the outbound traffic as allowed, but the return traffic is silently dropped, which is why users report the application not working.
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 is using asymmetric routing
Why it's wrong here
Asymmetric routing is possible but less common than a missing return policy.
✗
The security policy is not logging the traffic correctly
Why it's wrong here
Logs show allowed, so logging is fine.
✗
The firewall is not inspecting UDP traffic correctly
Why it's wrong here
UDP inspection is not required for basic forwarding.
✓
The firewall is dropping the return traffic due to a missing policy
Why this is correct
The application may require responses; if the return traffic is not allowed by policy, the application breaks.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume that because the outbound traffic is allowed and logged, the application should work, but they overlook the requirement for a return policy in stateful firewall operation, especially for UDP which is connectionless and does not have a built-in handshake like TCP.
Trap categories for this question
Command / output trap
Logs show allowed, so logging is fine.
Detailed technical explanation
How to think about this question
In Palo Alto Networks firewalls, security policies are stateful and require both forward and return traffic to match a policy for the session to be established. For UDP, the firewall creates a session for the outbound flow, but if the return traffic does not match any security policy, the session is not completed and the packets are dropped. This is a common misconfiguration when administrators only create a policy for the initial traffic direction, forgetting that stateful inspection requires policies for both directions unless using a 'any' zone for the destination.
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.
Troubleshoot — This question tests Troubleshoot — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The firewall is dropping the return traffic due to a missing policy — Option D is correct because even though the outbound UDP traffic is allowed by the security policy, the firewall must also have a corresponding policy to allow the return traffic from the application server back to the internal clients. Without a return policy, the firewall drops the response packets, breaking the UDP communication. The logs show the outbound traffic as allowed, but the return traffic is silently dropped, which is why users report the application not working.
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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