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Network Working Group                                         B. AbobaRequest for Comments: 2486                                   MicrosoftCategory: Standards Track                                   M. Beadles                                            WorldCom Advanced Networks                                                          January 1999The Network Access IdentifierStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1999).  All Rights Reserved.1.  Abstract   In order to enhance the interoperability of roaming and tunneling   services, it is desirable to have a standardized method for   identifying users.  This document proposes syntax for the Network   Access Identifier (NAI), the userID submitted by the client during   PPP authentication. 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   relationship with only one.  Examples of where roaming capabilities   might be required include ISP "confederations" and ISP-provided   corporate network access support.2.  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        with those of other regional providers to offer dialup service        over a wider area.Aboba & Beadles             Standards Track                     [Page 1]

RFC 2486             The Network Access Identifier          January 1999        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 tunneling protocols such as PPTP, L2F, L2TP, and IPSEC tunnel        mode.   In order to enhance the interoperability of roaming and tunneling   services, it is desirable to have a standardized method for   identifying users.  This document proposes syntax for the Network   Access Identifier (NAI).  Examples of implementations that use the   NAI, and descriptions of its semantics, can be found in [1].2.1.  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             application 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             terminology this is referred to as the PPTP Access             Concentrator (PAC), and in L2TP terminology, it is referred             to as the L2TP Access Concentrator (LAC).   Roaming Capability             Roaming capability can be loosely defined as the ability to             use any one of multiple Internet service providers (ISPs),             while maintaining a formal, customer-vendor relationship             with only one. Examples of cases where roaming capability             might be required include ISP "confederations" and ISP-             provided corporate network access support.Aboba & Beadles             Standards Track                     [Page 2]

RFC 2486             The Network Access Identifier          January 1999   Tunneling Service             A tunneling service is any network service enabled by             tunneling protocols such as PPTP, L2F, L2TP, and IPSEC             tunnel mode.  One example of a tunneling service is secure             access to corporate intranets via a Virtual Private Network             (VPN).2.2.  Requirements language   In this document, the key words "MAY", "MUST, "MUST NOT", "optional",   "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as   described in [9].2.3.  Purpose   As described in [1], there are now a number of 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   requirements 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 initial 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 determine the tunnel endpoint.2.4.  Notes for Implementors   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], the BNF of the realm portion   allows the realm to begin with a digit, which is not permitted by the   BNF described in [4]. This change was made to reflect current   practice; although not permitted by the BNF described in [4], FQDNs   such as 3com.com are commonly used, and accepted by current software.   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.3.  Formal definition of the NAI   The grammar for the NAI is given below, described in ABNF as   documented in [7].  The grammar for the username is taken from [5],   and the grammar for the realm is an updated version of [4].   nai         = username / ( username "@" realm )Aboba & Beadles             Standards Track                     [Page 3]

RFC 2486             The Network Access Identifier          January 1999   username    = dot-string   realm       = realm "." label   label       = let-dig * (ldh-str)   ldh-str     = *( Alpha / Digit / "-" ) let-dig   dot-string  = string / ( dot-string "." string )   string      = char / ( string char )   char        = c / ( "\" x )   let-dig     = Alpha / Digit   Alpha       = %x41-5A / %x61-7A   ; A-Z / a-z   Digit       = %x30-39  ;0-9   c           = < any one of the 128 ASCII characters, but                  not any special or SP >   x           = %x00-7F                 ; all 127 ASCII characters, no exception   SP          = %x20 ; Space character   special     = "<" / ">" / "(" / ")" / "[" / "]" / "\" / "."                  / "," / ";" / ":" / "@" / %x22  / Ctl   Ctl         = %x00-1F / %x7F                 ; the control characters (ASCII codes 0 through 31                 ; inclusive and 127)   Examples of valid Network Access Identifiers include:        fred@3com.com        fred@foo-9.com        fred_smith@big-co.com        fred=?#$&*+-/^smith@bigco.com        fred@bigco.com        nancy@eng.bigu.edu        eng!nancy@bigu.edu        eng%nancy@bigu.eduAboba & Beadles             Standards Track                     [Page 4]

RFC 2486             The Network Access Identifier          January 1999   Examples of invalid Network Access Identifiers include:        fred@foo        fred@foo_9.com        @howard.edu        fred@bigco.com@smallco.com        eng:nancy@bigu.edu        eng;nancy@bigu.edu        <nancy>@bigu.edu4.  References   [1]  Aboba, B., Lu J., Alsop J., Ding J. and W. Wang, "Review of        Roaming Implementations",RFC 2194, September 1997.   [2]  Rigney C., Rubens A., Simpson W. and S. Willens, "Remote        Authentication Dial In User Service (RADIUS)",RFC 2138, April        1997.   [3]  Rigney C., "RADIUS Accounting",RFC 2139, April 1997.   [4]  Mockapetris, P., "Domain Names  -  Implementation  and        Specification", STD 13,RFC 1035, November 1987.   [5]  Postel, J., "Simple Mail Transfer Protocol", STD 10,RFC 821,        August 1982.   [6]  Gulbrandsen A. and P. Vixie, "A DNS RR for specifying the        location of services (DNS SRV)",RFC 2052, October 1996.   [7]  Crocker, D. and P. Overrell, "Augmented BNF for Syntax        Specifications: ABNF",RFC 2234, November 1997.   [8]  Kent, S. and R. Atkinson, "Security Architecture for the        Internet Protocol",RFC 2401, November 1998.   [9]  Bradner,  S., "Key words for use in RFCs to Indicate Requirement        Levels",BCP 14,RFC 2119, March 1997.5.  Security Considerations   Since an NAI reveals the home affiliation of a user, it may assist an   attacker in further probing the username space. Typically this   problem is of most concern in protocols which transmit the user name   in clear-text across the Internet, such as in RADIUS, described in   [2] and [3].  In order to prevent snooping of the user name,   protocols may use confidentiality services provided by IPSEC,   described in [8].Aboba & Beadles             Standards Track                     [Page 5]

RFC 2486             The Network Access Identifier          January 19996.  IANA Considerations   This document defines a new namespace that will need to be   administered, namely the NAI realm namespace. In order to to avoid   creating any new administrative procedures, administration of the NAI   realm namespace will piggyback on the administration of the DNS   namespace.   NAI realm names are required to be unique and the rights to use a   given NAI realm for roaming purposes are obtained coincident with   acquiring the rights to use a particular fully qualified domain name   (FQDN).  Those wishing to use an NAI realm name should first acquire   the rights to use the corresponding FQDN. Using an NAI realm without   ownership of the corresponding FQDN creates the possibility of   conflict and therefore is to be discouraged.   Note that the use of an FQDN as the realm name does not imply use of   the DNS for location of the authentication server or for   authentication routing.  Since to date roaming has been implemented   on a relatively small scale, existing implementations typically   handle location of authentication servers within a domain and perform   authentication routing based on local knowledge expressed in proxy   configuration files. The implementations described in [1] have not   found a need for use of DNS for location of the authentication server   within a domain, although this can be accomplished via use of the DNS   SRV record, described in [6].  Similarly, existing implementations   have not found a need for dynamic routing protocols, or propagation   of global routing information.  Note also that there is no   requirement that the NAI represent a valid email address.7.  Acknowledgements   Thanks to Glen Zorn of Microsoft for many useful discussions  of   this problem space.Aboba & Beadles             Standards Track                     [Page 6]

RFC 2486             The Network Access Identifier          January 19998.  Authors' Addresses   Bernard Aboba   Microsoft Corporation   One Microsoft Way   Redmond, WA 98052   Phone: 425-936-6605   EMail: bernarda@microsoft.com   Mark A. Beadles   WorldCom Advanced Networks   5000 Britton Rd.   Hilliard, OH 43026   Phone: 614-723-1941   EMail: mbeadles@wcom.netAboba & Beadles             Standards Track                     [Page 7]

RFC 2486             The Network Access Identifier          January 19999.  Full Copyright Statement   Copyright (C) The Internet Society (1999).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Aboba & Beadles             Standards Track                     [Page 8]