- A
The firewall failed to properly synchronize the TCP sessions before the failover
Incomplete sync leads to half-closed sessions.
- B
The HA2 link failover timer is set too low
Why wrong: Timer settings affect failover speed, not session state.
- C
The ARP timeout on the next-hop router is too short
Why wrong: ARP timeout affects MAC resolution, not session state.
- D
Asymmetric routing is causing the firewall to see only one direction of traffic
Why wrong: That would cause new session setup issues, not half-closed state.
Question 95 of 516
PCNSE Practice Question: Managing Troubleshooting and High Availability
This PCNSE practice question tests your understanding of managing troubleshooting and high availability. 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.
During a network incident, an engineer notices that after an HA failover, some sessions are not active on the new active firewall. The 'show session all' command shows the sessions with state 'half-closed'. 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 firewall failed to properly synchronize the TCP sessions before the failover
Option A is correct because the 'half-closed' session state indicates that the firewall has only one side of the TCP handshake (FIN or RST) recorded, which typically occurs when session synchronization fails during an HA failover. In an active/passive HA pair, TCP session state information is synchronized via the HA2 link; if synchronization is incomplete or interrupted before the failover, the new active firewall will have partial session data, leading to half-closed sessions. This is a common symptom of a synchronization failure, not a timeout or routing issue.
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 firewall failed to properly synchronize the TCP sessions before the failover
Why this is correct
Incomplete sync leads to half-closed sessions.
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 HA2 link failover timer is set too low
Why it's wrong here
Timer settings affect failover speed, not session state.
- ✗
The ARP timeout on the next-hop router is too short
Why it's wrong here
ARP timeout affects MAC resolution, not session state.
- ✗
Asymmetric routing is causing the firewall to see only one direction of traffic
Why it's wrong here
That would cause new session setup issues, not half-closed state.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'half-closed' with 'incomplete' or 'asymmetric routing' symptoms, but 'half-closed' specifically indicates a TCP state where one side has initiated closure, which in an HA context points to incomplete session synchronization rather than a routing or ARP issue.
Detailed technical explanation
How to think about this question
In PAN-OS, session synchronization uses the HA2 link to replicate session state information, including TCP sequence numbers, window sizes, and state machine transitions. If the HA2 link is congested, misconfigured, or the synchronization process is interrupted (e.g., due to a sudden power loss or link failure), the passive firewall may have only partial session data, resulting in sessions appearing as 'half-closed' (TCP state FIN_WAIT or CLOSE_WAIT) after failover. This is distinct from 'incomplete' sessions, which occur when only the initial SYN is seen. In real-world scenarios, this often happens when the HA pair is under heavy traffic load and the synchronization queue overflows, or when the HA2 keepalive timer is misaligned with the session timeout.
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.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this PCNSE question test?
Managing Troubleshooting and High Availability — This question tests Managing Troubleshooting and High Availability — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The firewall failed to properly synchronize the TCP sessions before the failover — Option A is correct because the 'half-closed' session state indicates that the firewall has only one side of the TCP handshake (FIN or RST) recorded, which typically occurs when session synchronization fails during an HA failover. In an active/passive HA pair, TCP session state information is synchronized via the HA2 link; if synchronization is incomplete or interrupted before the failover, the new active firewall will have partial session data, leading to half-closed sessions. This is a common symptom of a synchronization failure, not a timeout or routing issue.
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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Last reviewed: Jul 4, 2026
This PCNSE practice question is part of Courseiva's free Palo Alto Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCNSE exam.
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