|  |  | CiscoSecure ACS supports TACACS+ and RADIUS independently or at the same time, and can use the Windows NT user database to enable a single login. CiscoSecure ACS can be installed on the NT primary domain controller (PDC), backup domain controller (BDC), or a standalone server. CiscoSecure ACS 2.1 supports the leading authentication protocols: PAP, CHAP, AppleTalk Remote Access (ARAP), Token card servers, Windows NT user database, and Novell NDS. It also has a callback feature for added security.