One means of securing iSCSI devices from unwanted intrusion is to require that the host, or initiator, be authenticated by the iSCSI device, or target, whenever the host attempts to access data on the target LUN.
The goal of authentication is to prove that the initiator has the right to access a target, a right granted when you configure authentication.
ESXi does not support Kerberos, Secure Remote Protocol (SRP), or public-key authentication methods for iSCSI. Additionally, it does not support IPsec authentication and encryption.
Use the vSphere Web Client to determine whether authentication is being performed and to configure the authentication method.