RFC 1492 (rfc1492) - Page 1 of 21

An Access Control Protocol, Sometimes Called TACACS

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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


   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

   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


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