Allied Telesis AT-S63 - Manual (Page 429)

AT-S63 Management Software Features Guide
Section IX: Management Security 429
Note
If no authentication server responds or if no servers have been
defined, the AT-S63 Management Software defaults to the standard
manager and operator accounts.
Note
For more information on TACACS+, refer to the RFC 1492 standard.
For more information on RADIUS, refer to the RFC 2865 standard.