Explanation
The security method that would be used to authenticate targets and initiators in an ISCSI environment is CHAP. CHAP stands for Challenge Handshake Authentication Protocol, and it is a method that validates the identity of targets and initiators during the initial link. CHAP uses a shared secret (a password) that is exchanged between the target and the initiator in a challenge-response manner. CHAP can be used in both one-way and mutual modes, depending on whether both parties need to authenticate each other or not. The other options are not valid for this scenario because:
NIS is a network information service that provides centralized management of user accounts and host names, but it does not provide authentication for ISCSI devices.
LDAP is a protocol for accessing and managing directory services, such as user and group information, but it does not provide authentication for ISCSI devices.
/etc/hosts is a file that maps host names to IP addresses, but it does not provide authentication for ISCSI devices. References :- How iSCSI authentication works, Securing iSCSI Devices, Configure iSCSI authentication