When Panorama is configured in a high availability (HA) setup, the managed firewalls are connected to both the active and passive Panorama HA peers. When the connection between the active and the passive Panorama peers fails, before the passive Panorama takes over as the active peer it checks whether any firewall is connected to both the active and the passive peer. If even one firewall is connected to both peers, the failover is not triggered.
In the rare event that a failover is triggered when a set of firewalls are connected to the active peer and a set of firewalls are connected to the passive peer, but none of the firewalls are connected to both peers, it is called a split brain. When a split brain occurs, the following conditions occur: