PCNSE Core Concepts and Architecture Practice Question
Two Palo Alto Networks firewalls are configured in an active/passive HA pair. During a scheduled maintenance, the network team reboots both firewalls simultaneously. After reboot, both firewalls appear as 'active' in the HA state. What is the most likely cause and the correct troubleshooting step?
⚠ Common exam trap
Test-takers frequently assume simultaneous reboot causes a priority tie, but the real issue is the missing heartbeat link, which prevents the firewalls from detecting each other's state after reboot.
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 heartbeat link between the firewalls is missing or fails, causing each to believe the other is down. The correct step is to restore the heartbeat link and then set the appropriate firewall as passive.
In an active/passive HA pair, each firewall monitors the peer's health via the heartbeat link. If the heartbeat link fails, each firewall assumes the peer is down and transitions to active state to ensure traffic continuity. Simultaneous reboot does not cause both to become active unless the heartbeat link is absent or broken; restoring the heartbeat link and forcing one firewall to passive resolves the split-brain scenario.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Both firewalls have the same priority; the tie is broken by serial number, but due to simultaneous reboot, both came up as active. The solution is to reboot one firewall.
Why it's wrong here
Equal priority is resolved by serial number, and simultaneous reboot does not make both peers active; rebooting one firewall does not correct the underlying election fault. Priority tie-breaking is relevant when configuring deterministic failover, but the actual cause is the HA timers and preemption behaviour during concurrent startup.
- ✗
The HA configuration is set to active/active mode instead of active/passive.
Why it's wrong here
Active/active mode would show both peers active, but the pair is configured active/passive, so this misreads the configuration rather than the reboot sequence. Active/active suits environments needing both devices forwarding simultaneously; here the fault lies in HA election after simultaneous startup, not in the mode setting.
- ✓
The heartbeat link between the firewalls is missing or fails, causing each to believe the other is down. The correct step is to restore the heartbeat link and then set the appropriate firewall as passive.
Why this is correct
A missing heartbeat link prevents each firewall from receiving HA hello messages, so both transition to active after reboot. Restoring the heartbeat connection re-establishes state synchronisation and election, after which the secondary can be forced passive to clear the split-brain condition.
- ✗
The heartbeat interfaces are not configured on each firewall.
Why it's wrong here
Missing heartbeat interfaces would prevent HA peering entirely, leaving peers in a non-functional or initial state rather than both reporting active. Heartbeat configuration matters when establishing HA links, but here the peers clearly communicate, so the split-brain stems from election timing after simultaneous reboot, not absent heartbeats.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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