A network administrator is setting up a new highly available Cisco Secure Firewall Threat Defense (FTD) pair. The administrator wants to monitor that the interfaces on the secondary Secure FTD are reachable not just up. What must the administrator configure?
To monitor that the interfaces on the secondary Cisco Secure Firewall Threat Defense (FTD) are not just up but also reachable, the network administrator must configure a secondary IP address. This allows the primary FTD to perform network tests to ensure the secondary interfaces are reachable, providing better failover functionality.
Although recommended, the standby address is not required. Without a standby IP address, the active unit cannot perform network tests to check the standby interface health; it can only track the link state. You also cannot connect to the standby unit on that interface for management purposes. https://www.cisco.com/c/en/us/td/docs/security/firepower/610/configuration/guide/fpmc-config-guide-v61/firepower_threat_defense_high_availability.html
Yes, (B) is correct.
B is the correct answer. ...What @Kris92 said.