The answer is an HA1 link failure, as this is the most common cause of an active/active split brain state in a Palo Alto Networks high availability pair. When the dedicated HA1 keepalive link fails, both firewalls lose the heartbeat signal from their peer and independently assume the other unit is dead. As a fail-safe mechanism, each firewall transitions to active state to maintain traffic continuity, creating a dangerous scenario where duplicate IP addresses and traffic loops can occur. On the PCNSE exam, this concept tests your understanding of HA control link dependencies and the fail-safe logic that prioritizes uptime over consistency. A common trap is confusing HA1 failure with HA2 (data link) failure—HA2 failure does not trigger split brain because keepalives still flow over HA1. Remember the memory tip: “HA1 is the heartbeat; lose the beat, both feet hit the street as active.”
PCNSE Practice Question: Managing Troubleshooting and High Availability
This PCNSE practice question tests your understanding of managing troubleshooting and high availability. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which TWO conditions can cause an HA pair to enter an 'active/active' state? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Loss of HA keepalive on both sides
A is correct because when both firewalls lose the HA keepalive (sent over HA1 link), each firewall assumes the peer is dead and transitions to active state to ensure traffic continuity. This is a fail-safe mechanism: without keepalive, each unit independently becomes active, resulting in an active/active condition that can cause duplicate IP addresses and traffic loops.
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.
✓
Loss of HA keepalive on both sides
Why this is correct
If keepalives are lost, each firewall assumes the other is dead and becomes active.
Related concept
Read the scenario before looking for a memorised answer.
✗
License expiration on one firewall
Why it's wrong here
License expiration does not cause active/active.
✗
Session synchronization failure
Why it's wrong here
Session sync failure does not affect HA state.
✗
Configuration mismatch between peers
Why it's wrong here
Configuration mismatch does not cause active/active state.
✓
HA1 link failure
Why this is correct
If HA1 fails, firewalls cannot exchange heartbeats and may both become active.
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 often think only a complete HA1 link failure (option E) causes active/active, but they overlook that loss of keepalive on both sides (option A) is the underlying mechanism—and both conditions are correct because HA1 link failure directly causes loss of keepalive on both sides.
Detailed technical explanation
How to think about this question
The HA keepalive is sent every 1 second (default) over the HA1 link using UDP port 2925; if three consecutive keepalives are missed (3-second hold timer), the peer is considered dead. In active/passive mode, the passive firewall transitions to active only if it detects the active peer is unreachable, but if both lose keepalive simultaneously (e.g., HA1 link failure), each firewall independently becomes active. This is why redundant HA1 links (HA1 backup) are critical in production to avoid split-brain scenarios.
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.
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: Loss of HA keepalive on both sides — A is correct because when both firewalls lose the HA keepalive (sent over HA1 link), each firewall assumes the peer is dead and transitions to active state to ensure traffic continuity. This is a fail-safe mechanism: without keepalive, each unit independently becomes active, resulting in an active/active condition that can cause duplicate IP addresses and traffic loops.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer is troubleshooting an HA pair where both firewalls show as 'active' in the HA state. What is this condition called?
easy
A.Link failure
✓ B.Active/Active
C.Passive/Passive
D.Split brain
Why B: In an active/passive HA pair, only one firewall should be active at a time. When both firewalls show as 'active', this is known as a split-brain condition. It occurs when the HA heartbeat link fails and each firewall assumes the other is down, causing both to transition to the active state and process traffic independently.
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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.
Question Discussion
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