ROAMOPS Working Group                                    Bernard Aboba
     INTERNET-DRAFT                                               Microsoft
     Category: Standards Track                              Mark A. Beadles
     <draft-ietf-roamops-nai-06.txt>                       CompuServe, Inc.
     22 July 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
     its  working groups.  Note that other groups may also distribute work-
     ing documents as Internet-Drafts.
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     and  may  be updated, replaced, or obsoleted by other documents at any
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     The  distribution  of  this memo is unlimited.  It is filed as <draft-
     ietf-roamops-nai-06.txt> and  expires February 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                                            22 July 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).
     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 NASes will  use  the
     NAI as part of the process of opening a new tunnel, in order to deter-
     mine the tunnel endpoint.
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     INTERNET-DRAFT                                            22 July 1997
     As proposed in this document, the Network Access Identifier is of  the
     form  user@realm.  Please  note that while the user portion of the NAI
     conforms to the BNF described in [5], and the realm  conforms  to  the
     BNF  described  in  [4],  the  NAI need not be a valid e-mail address.
     While the realm is typically a Fully Qualified Domain Name (FQDN),  it
     is  not required that this be the case. As a result, use of an FQDN as
     the realm does not imply use of DNS for location of the RADIUS  server
     or for 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, described in [6].  Similarly, existing implementa-
     tions have not found a need for dynamic routing protocols, or propaga-
     tion of global routing information.
     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. The grammar for the username
     is taken from [5], and the grammar for the realm is based on [4].
     <nai>         ::= <username> | <username> "@" <realm>
     <username>    ::= <dot-string>
     <realm>       ::= <label> | <realm> "." <label>
     <label>       ::= <letter> [ [ <ldh-str> ] <let-dig> ]
     <ldh-str>     ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str>
     <let-dig-hyp> ::= <let-dig> | "-"
     <dot-string>  ::= <string> | <string> "." <dot-string>
     <string>      ::= <char> | <char> <string>
     <char>        ::= <c> | "
     <let-dig>     ::= <letter> | <digit>
     <letter>      ::= any one of the 52 alphabetic characters A through Z
                       in upper case and a through z in lower case
     <digit>       ::= any one of the ten digits 0 through 9
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     INTERNET-DRAFT                                            22 July 1997
     <c>           ::= any one of the 128 ASCII characters, but not any
                      <special> or <SP>
     <x>           ::= any one of the 128 ASCII characters (no exceptions)
     <SP>          ::= the space character (ASCII code 32)
     <special>     ::= "<" | ">" | "(" | ")" | "[" | "]" | "
                       | "," | ";" | ":" | "@"  """ | the control
                       characters (ASCII codes 0 through 31 inclusive and
     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.
     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 2138, Livingston, Merit,
     Daydreamer, April, 1997.
     [3]  C. Rigney.  "RADIUS Accounting."  RFC  2139,  Livingston,  April,
     [4]  P.  Mockapetris.   "Domain  Names - Implementation and Specifica-
     tion."  RFC 883, Information Sciences Institute, University of  South-
     ern California, November, 1983.
     [5]  Jonathan  B.  Postel.  "Simple Mail Transfer Protocol."  RFC 821,
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     INTERNET-DRAFT                                            22 July 1997
     Information Sciences Institute,  University  of  Southern  California,
     August, 1982
     [6]  A.  Gulbrandsen, P. Vixie.  "A DNS RR for specifying the location
     of services (DNS SRV)." RFC 2052,  Troll  Technologies,  Vixie  Enter-
     prises, October 1996.
     7.  Authors' Addresses
     Bernard Aboba
     Microsoft Corporation
     One Microsoft Way
     Redmond, WA 98052
     Phone: 425-936-6605
     Mark A. Beadles
     CompuServe, Inc.
     5000 Britton Rd.
     Hilliard, OH 43026
     Phone: 614-723-1941
     Aboba                                                         [Page 5]