"Terminal Access Controller Access-Control System, or TACACS, is a remote authentication protocol used to communicate with an authentication server commonly used in UNIX networks. TACACS allows a remote access server to communicate with an authentication server to determine if the user is authorized to access the network. Remote Authentication Dial-In User Service (RADIUS) is also a protocol for controlling access to a network. Internet service providers and companies commonly use RADIUS to manage access to internal networks across several technologies, including modem, DSL, wireless, and VPNs."
