When replacing a Cisco Secure Firewall high-availability (HA) device due to a failure, the first step the engineer must take is to unregister the secondary (failed) device from the Cisco Secure Firewall Management Center (FMC). This action separates the HA pair and ensures that the new replacement device can be registered and configured correctly.

Steps:

Access the FMC and navigate to the device management section.

Unregister the failed secondary device to remove it from the HA pair.

Register the replacement device to the FMC.

Reconfigure the HA settings to restore the high-availability configuration.

By unregistering the failed device first, the engineer ensures a clean setup for the replacement device, avoiding potential conflicts or issues in the HA configuration.