Data ONTAP supports two methods for authenticating NDMP access to a storage system: plaintext and challenge. You can use the options ndmpd.authtype command to specify whether a storage system will accept plaintext, challenge, or both to authenticate NDMP session requests.
challenge sets the challenge authentication method, generally the preferred and more secure authentication method.
plaintext sets the plaintext authentication method, in which the login password is transmitted as clear text.
plaintext,challenge sets both challenge and plaintext authentication methods.