PCNSE Practice Question: Managing Troubleshooting and High Availability
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?
⚠ Common exam trap
A common mix-up: 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.
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
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.
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.
- ✗
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.