None: No authentication.

Kerberos: Authentication is performed using a Kerberos server.

Kerberos/Local: Kerberos authentication is tried first, switching to Local if unsuccessful.

KerberosDownLocal: Local authentication is performed only when the Kerberos server is down.

LDAP: Authentication is performed against an LDAP database using an LDAP server.

LDAP/Local: LDAP authentication is tried first, switching to Local if unsuccessful.

LDAPDownLocal: Local authentication is performed only when the LDAP server is down.

Local: Authentication is performed locally. For example, using the /etc/passwd file.
Local/Radius: Authentication is performed locally first, switching to Radius if unsuccessful.

Local/TACACS+: Authentication is performed locally first, switching to TACACS+ if unsuccessful.

Local/NIS: Authentication is performed locally first, switching to NIS if unsuccessful.

NIS: NIS authentication is performed.

NIS/Local: NIS authentication is tried first, switching to Local if unsuccessful.

NISDownLocal: Local authentication is performed only when the NIS server is down.

Radius: Authentication is performed using a Radius authentication server.

Radius/Local: Radius authentication is tried first, switching to Local if unsuccessful.

RadiusDownLocal: Local authentication is performed only when the Radius server is down.

TACACS+: Authentication is performed using a TACACS+ authentication server.

TACACS+/Local: TACACS+ authentication is tried first, switching to Local if unsuccessful.

TACACS+DownLocal: Local authentication is tried only when the TACACS+ server is down.