Hi @jirasith (Firewall A = currently active firewall, firewall B = currently passive firewall) Download PAN-OS 8.1.19 to both firewalls Install 8.1.19 and reboot firewall B Download PAN-OS 9.0.0 to firewall B Download PAN-OS 9.0.13, install it and reboot firewall B Install PAN-OS 8.1.19 on firewall A and reboot (when you click reboot a failover is done to firewall B) Download PAN-OS 9.0.0 to firewall A Download PAN-OS 9.0.13, install it and reboot firewall A Download PAN-OS 9.1.0 to both firewalls Download PAN-OS 9.1.10 to both firewalls Install PAN-OS 9.1.10 on firewall A and reboot (when you click reboot a failover is done to firewall B) Install PAN-OS 9.1.10 on firewall B and reboot To make sure that you can downgrade in case of any problems export the configuration at all of the following steps on both firewalls: Installation of 8.1.19 Installation of 9.0.13
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