TACACS
Terminal Access Controller Access Control System (TACACS) is a remote authentication protocol that is used to communicate with an authentication server commonly used in UNIX networks. TACACS allows a remote access server to communicate with an authentication server in order to determine if the user has access to the network.
A later version of TACACS was called XTACACS (Extended). These two versions have generally been replaced by TACACS+ and RADIUS in newer or updated networks. TACACS+ is a completely new protocol and is therefore not compatible with TACACS or XTACACS.
TACACS is defined in RFC 1492, uses port UDP 49