ROAMOPS Working Group                                    Bernard Aboba
     INTERNET-DRAFT                                               Microsoft
     Category: Standards Track
     14 June 1997
                         The Network Access Identifier
     1.  Status of this Memo
     This document is an Internet-Draft.  Internet-Drafts are working docu-
     ments of the Internet Engineering Task Force (IETF),  its  areas,  and
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     The  distribution  of  this memo is unlimited.  It is filed as <draft-
     ietf-roamops-nai-05.txt> and  expires January 1,  1998.   Please  send
     comments to the authors.
     2.  Abstract
     In order to enhance the interoperability of roaming and tunneling ser-
     vices, it is desirable to have a standardized method  for  identifying
     users.   This  document proposes syntax for the Network Access Identi-
     fier (NAI). It is expected that this will be of interest  for  support
     of  roaming as well as tunneling.  "Roaming capability" may be loosely
     defined as the ability to use any one  of  multiple  Internet  service
     providers  (ISPs),  while  maintaining a formal, customer-vendor rela-
     tionship with only one.  Examples of cases  where  roaming  capability
     might be required include ISP "confederations" and ISP-provided corpo-
     rate network access support.
     3.  Introduction
     Considerable interest has arisen recently in a set  of  features  that
     fit  within  the  general  category of "roaming capability" for dialup
     Internet users.  Interested parties have included:
          Regional Internet Service Providers  (ISPs)  operating  within  a
          particular  state  or  province, looking to combine their efforts
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     INTERNET-DRAFT                                            14 June 1997
          with those of other regional providers to  offer  dialup  service
          over a wider area.
          National  ISPs  wishing to combine their operations with those of
          one or more ISPs in another nation to  offer  more  comprehensive
          dialup service in a group of countries or on a continent.
          Businesses  desiring  to  offer  their  employees a comprehensive
          package of dialup services on a global basis.  Those services may
          include  Internet  access  as  well as secure access to corporate
          intranets via a Virtual Private Network (VPN), enabled by tunnel-
          ing protocols such as PPTP, L2F and L2TP.
     In order to enhance the interoperability of roaming and tunneling ser-
     vices, it is desirable to have a standardized method  for  identifying
     users.   This  document proposes syntax for the Network Access Identi-
     fier (NAI). Methods for authentication  routing  or  determination  of
     tunnel server endpoints will be addressed in future documents.
     3.1.  Terminology
     This document frequently uses the following terms:
     Network Access Identifier
               The  Network Access Identifier (NAI) is the userID submitted
               by the client during PPP  authentication.  In  roaming,  the
               purpose  of  the  NAI  is to identify the user as well as to
               assist in the routing of the authentication request.  Please
               note  that  the  NAI  may not necessarily be the same as the
               user's e-mail address or the userID submitted in an applica-
               tion layer authentication.
     Network Access Server
               The  Network  Access Server (NAS) is the device that clients
               dial in order to get access to the network. In  PPTP  termi-
               nology  this  is referred to as the PPTP Access Concentrator
               (PAC), and in L2TP terminology, it is  referred  to  as  the
               L2TP Access Concentrator (LAC).
     3.2.  Purpose
     As described in [1], there are now at least five services implementing
     dialup roaming, and the number of Internet Service Providers  involved
     in roaming consortia is increasing rapidly.
     In  order  to be able to offer roaming capability, one of the require-
     ments is to be able to identify the user's home authentication server.
     For  use  in  roaming,  this  function is accomplished via the Network
     Access Identifier (NAI) submitted by the user to the NAS in  the  ini-
     tial  PPP  authentication. It is also expected that PACs and LACs will
     use the NAI as part of the process of opening a new tunnel,  in  order
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     INTERNET-DRAFT                                            14 June 1997
     to determine the tunnel endpoint.
     As  proposed  in this document, the Network Access Identifer is of the
     form user@realm. Please note that while the realm is typically a Fully
     Qualified Domain Name (FQDN) it is not required that this be the case,
     and use of an FQDN as the realm does not imply use of DNS for location
     of the RADIUS server or authentication routing.
     Since  to  date  roaming  has  been  implemented on a relatively small
     scale, existing implementations  handle  location  of  RADIUS  servers
     within  a  domain  and  perform  authentication routing based on local
     knowledge expressed in proxy configuration files. To date  implementa-
     tions  have not found a need for use of DNS for location of the RADIUS
     server within a domain, although this can be accomplished via  use  of
     the  DNS SRV record.  Similarly, existing implementions have not found
     a need for dynamic routing protocols, or propagation of global routing
     Please note that NAS vendors may need to modify their devices so as to
     support the NAI as described in this document. Devices  handling  NAIs
     MUST support an NAI length of at least 72 octets.
     4.  Formal Definition of the NAI
     The  grammar for the NAI is given below, using the augmented BNF nota-
     tion described in reference [4].
     NAI      = USERNAME ["@" REALM]
     REALM    = token "."  token *[ "." token ]
     USERNAME = token
     Examples of valid Network Access Identifiers include:

     Examples of invalid Network Access Identifiers include:


     5.  Acknowledgements
     Thanks to Glen Zorn of Microsoft for many useful discussions  of  this
     problem space.
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     INTERNET-DRAFT                                            14 June 1997
     6.  References
     [1]   B. Aboba, J. Lu, J. Alsop, J. Ding, W. Wang.  "Review of Roaming
     Implementations."  Internet  draft  (work  in  progress),  draft-ietf-
     roamops-imprev-04.txt,  Microsoft,  Aimnet, i-Pass Alliance, Asiainfo,
     Merit, June 1997.
     [2]  C. Rigney, A. Rubens, W. Simpson, S. Willens.  "Remote  Authenti-
     cation  Dial  In  User Service (RADIUS)." RFC 2058, Livingston, Merit,
     Daydreamer, January, 1997.
     [3]  C. Rigney.  "RADIUS Accounting." RFC 2059,  Livingston,  January,
     [4] R. Fielding, et al.  "Hypertext Transfer Protocol - HTTP/1.1." RFC
     2068, UC Irvine, January, 1997.
     7.  Authors' Addresses
     Bernard Aboba
     Microsoft Corporation
     One Microsoft Way
     Redmond, WA 98052
     Phone: 206-936-6605
     Aboba                                                         [Page 4]