TACACS is a security application that provides centralized validation of users attempting to gain access to a router or network
access server. 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 facilities. TACACS allows for a single access control server (the
TACACS) to provide each service--authentication. 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 and Cisco IOS XE user interface (for both routers and access
servers) can be network access servers.
Network access points enable traditional “dumb” terminals, terminal emulators, workstations, personal computers (PCs), and
routers in conjunction with suitable adapters (for example, modems or ISDN adapters) to communicate using protocols such as
Point-to-Point Protocol (PPP), Serial Line Internet Protocol (SLIP), Compressed SLIP (CSLIP), or AppleTalk Remote Access (ARA)
protocol. In other words, a network access server provides connections to a single user, to a network or subnetwork, and to
interconnected networks. The entities connected to the network through a network access server are called network access clients;
for example, a PC running PPP over a voice-grade circuit is a network access client. TACACS, administered through the AAA
security services, can provide the following services:
• Authentication--Provides complete control of authentication through login and password dialog, challenge and response, messaging
support.
The authentication facility provides the ability to conduct an arbitrary dialog with the user (for example, after a login
and password are provided, to challenge a user with a number of questions, like home address, mother’s maiden name, service
type, and social security number). In addition, the TACACS authentication service supports sending messages to user screens.
For example, a message could notify users that their passwords must be changed because of the company’s password aging policy.
The TACACS protocol provides authentication between the network access server and the TACACS, and it ensures confidentiality
because all protocol exchanges between a network access server and a TACACS are encrypted.
You need a system running TACACS software to use the TACACS functionality on your network access server.
Cisco makes the TACACS protocol specification available as a draft RFC for those customers interested in developing their
own TACACS software.