TACACS+ is a security application that provides centralized validation of users attempting to gain access to a router or network access server. TACACS+ services are maintained in a database on a TACACS+ daemon running, typically, on a UNIX or Windows NT workstation. You must have access to and must configure a TACACS+ server before the configured TACACS+ features on your network access server are available.
TACACS+ provides for separate and modular authentication, authorization, and accounting facilities. TACACS+ allows for a single access control server (the TACACS+ daemon) to provide each service—authentication, authorization, and accounting—independently. Each service can be tied into its own database to take advantage of other services available on that server or on the network, depending on the capabilities of the daemon.
The goal of TACACS+ is to provide a methodology for managing multiple network access points from a single management service. The Cisco family of access servers and routers and the Cisco IOS user interface (for both routers and access servers) can be network access servers.
Terminal Access Controller Access-Control System
Terminal Access Controller Access-Control System (TACACS, usually pronounced like tack-axe) refers to a family of related protocols handling remote authentication and related services for networked access control through a centralized server. The original TACACS protocol, which dates back to 1984, was used for communicating with an authentication server, common in older UNIX networks; it spawned related protocols:
- Extended TACACS (XTACACS) is a proprietary extension to TACACS introduced by Cisco Systems in 1990 without backwards compatibility to the original protocol. TACACS and XTACACS both allow a remote access server to communicate with an authentication server in order to determine if the user has access to the network.
- Terminal Access Controller Access-Control System Plus (TACACS+) is a protocol developed by Cisco and released as an open standard beginning in 1993. Although derived from TACACS, TACACS+ is a separate protocol that handles authentication, authorization, and accounting (AAA) services. TACACS+ and other flexible AAA protocols have largely replaced their predecessors.
TACACS was originally developed in 1984 by BBN Technologies for administering MILNET, which ran unclassified network traffic for DARPA at the time and would later evolve into the U.S. Department of Defense‘s NIPRNet. Originally designed as a means to automate authentication – allowing someone who was already logged into one host in the network to connect to another on the same network without needing to re-authenticate – it was first formally described by BBN’s Brian Anderson in December 1984 in IETF RFC 927. Cisco Systems began supporting TACACS in its networking products in the late 1980s, eventually adding several extensions to the protocol. In 1990, Cisco’s extensions on the top of TACACS became a proprietary protocol called Extended TACACS (XTACACS). Although TACACS and XTACACS are not open standards, Craig Finseth of the University of Minnesota, with Cisco’s assistance, published a description of the protocols in 1993 in IETF RFC 1492 for informational purposes.