An Access Control Protocol, Sometimes Called TACACS (RFC1492)
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2019-Feb-10
Internet Society Requests For Comment (RFCs)
This RFC documents the extended TACACS protocol use by the Cisco Systems terminal servers. This same protocol is used by the University of Minnesota's distributed authentication system. This memo provides information for the Internet community. It does not specify an Internet standard.
Network Working Group C. Finseth Request for Comments: 1492 University of Minnesota July 1993
An Access Control Protocol, Sometimes Called TACACS
Status of this Memo
This memo provides information for the Internet community. It does not specify an Internet standard. Distribution of this memo is unlimited.
There used to be a network called ARPANET. This network consisted of end nodes (hosts), routing nodes (IMPs) and links. There were (at least) two types of IMPs: those that connected dedicated lines only and those that could accept dial up lines. The latter were called "TIPs."
People being what they were, there was a desire to control who could use the dial up lines. Someone invented a protocol, called "TACACS" (Terminal Access Controller Access Control System?), which allowed a TIP to accept a username and password and send a query to a TACACS authentication server, sometimes called a TACACS daemon or simply TACACSD. This server was normally a program running on a host. The host would determine whether to accept or deny the request and sent a response back. The TIP would then allow access or not, based upon the response.
While TIPs are -- shall we say? -- no longer a major presence on the Internet, terminal servers are. Cisco Systems terminal servers implement an extended version of this TACACS protocol. Thus, the access control decision is delegated to a host. In this way, the process of making the decision is "opened up" and the algorithms and data used to make the decision are under the complete control of whoever is running the TACACS daemon. For example, "anyone with a first name of Joe can only login after 10:00 PM Mon-Fri, unless his last name is Smith or there is a Susan already logged in."
The extensions to the protocol provide for more types of authentication requests and more types of response codes than were in the original specification.
The original TACACS protocol specification does exist. However, due to copyright issues, I was not able to obtain a copy of this document
Finseth [Page 1]
RFC 1492 TACACS July 1993
and this lack of access is the main reason for the writing of this document. This version of the specification was developed with the assistance of Cisco Systems, who has an implementation of the TACACS protocol that is believed to be compatible with the original specification. To be precise, the Cisco Systems implementation supports both the simple (non-extended) and extended versions. It is the simple version that would be compatible with the original.
Please keep in mind that this is an informational RFC and does not specify a standard, and that more information may be uncovered in the future (i.e., the original specification may become available) that could cause parts of this document to be known to be incorrect.
This RFC documents the extended TACACS protocol use by the Cisco Systems terminal servers. This same protocol is used by the University of Minnesota’s distributed authentication system.