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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 4284

Network Working Group                                         F. Adrangi
Internet-Draft                                                  V. Lortz
Expires: June 16, 2005                                             Intel
                                                                 F. Bari
                                                           AT&T Wireless
                                                               P. Eronen
                                                                   Nokia
                                                       December 16, 2004


 Identity selection hints for Extensible Authentication Protocol (EAP)
                 draft-adrangi-eap-network-discovery-07

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
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   RFC 3668.

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   This Internet-Draft will expire on June 16, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   The Extensible Authentication Protocol (EAP) is defined in RFC 3748.
   This document defines a mechanism that allows an access network to
   provide identity selection hints to an EAP peer.  The purpose is to



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   assist the EAP peer in selecting an appropriate Network Access
   Identifier (NAI).  This is especially useful when the access network
   does not have a direct roaming relationship with the peer's home
   network, so that a mediating network, such as a roaming consortium or
   broker, is used.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1   Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Implementation requirements  . . . . . . . . . . . . . . . . .  4
     2.1   Packet format  . . . . . . . . . . . . . . . . . . . . . .  4
   3.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  5
   4.  Security considerations  . . . . . . . . . . . . . . . . . . .  5
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Appendix A (informative) - Delivery Options  . . . . . . . . .  6
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1   Normative references . . . . . . . . . . . . . . . . . . .  9
     7.2   Informative references . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
   Intellectual Property and Copyright Statements . . . . . . . . . . 12






























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1.  Introduction

   An EAP peer (hereafter, also referred to as the peer) can have
   several sets of credentials, and its home network may have roaming
   relationships with several mediating networks.  As a result, the peer
   may be unclear about the appropriate Network Access Identity (NAI) to
   include in an EAP-Response/Identity.

   The Extensible Authentication Protocol (EAP) is defined in [RFC3748].
   This document defines a mechanism that allows the access network to
   provide identity selection hints, including information about its
   roaming relationships, to an EAP peer.  This information is sent to
   the peer in an EAP-Request/Identity message by appending it after the
   displayable message and a NUL character.

   Exactly how the identity hint information is used by the peer depends
   largely on the peer's local policy and configuration, and is outside
   the scope of this document.

   In many roaming situations, an access network can have several
   roaming relationships, either with several home networks, or with
   mediating networks such as roaming consortiums and brokers, or both.

   One possible application for this mechanism is to help in selecting
   what kind of NAI decoration [rfc2486bis] must be applied to allow
   proper routing of AAA messages to the home AAA server.  If there are
   several possible mediating networks, the peer can choose which one to
   use.  However, exactly how the selection is made is beyond the scope
   of this document.  See [netsel-problem] for more detailed discussion
   about this problem space.

   Section 2 describes the required behavior of implementations of this
   specification, as well as the packet format for structuring and
   presenting identity hint information to an EAP peer.  The appendix A
   describes the delivery options that can be implemented by an access
   network to deliver identity hint information to an EAP peer.

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   NAI             Network Address Identifier [rfc2486bis].







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   Decorated NAI   An NAI with additional information for influencing
                   AAA routing.  Please refer to section 2.7 of
                   [rfc2486bis] for its construction.

   NAI Realm       Realm portion of an NAI [rfc2486bis].

2.  Implementation requirements

   An EAP peer implementing this specification MUST be able to receive
   an identity hint in an initial EAP-Request/Identity, or in a
   subsequent EAP-Request/Identity.

   The EAP authenticator MAY send an identity hint to the peer in the
   initial EAP-Request/Identity.  If the identity hint is not sent
   initially (such as when the authenticator does not support this
   specification), then if the EAP server receives an
   EAP-Response/Identity with an unacceptable NAI Realm, EAP servers
   implementing this specification SHOULD reply with an
   EAP-Request/Identity containing an identity hint.

   If after the EAP server sends an EAP-Request/Identity containing an
   identity hint, the peer responds with an EAP-Response/Identity
   containing an unacceptable NAI Realm, then the EAP server MAY respond
   immediately with an EAP Failure packet, or it MAY first send an
   EAP-Notification providing the reason for the failure.

   As noted in [RFC3748], Section 3.1, the minimum EAP MTU size is 1020
   octets.  EAP does not support fragmentation of EAP-Request/Identity
   messages, so that the maximum length of the identity hint information
   is limited by the link MTU.

2.1  Packet format

   The Identity hint information is placed after the displayable string
   and a NUL character in the EAP-Request/Identity.  The following ABNF
   [RFC2234] defines an NAIRealms attribute for presenting the identity
   hint information.  The attribute's value consists of a set of realm
   names separated by a semicolon.


      identity-request-data = [ displayable-string ] "%x00" [ Network-Info ]

      displayable-string    = *CHAR

      Network-Info     =   "NAIRealms=" realm-list
      Network-Info     =/  1*OCTET ",NAIRealms=" realm-list
      Network-Info     =/  "NAIRealms=" realm-list "," 1*OCTET
      Network-Info     =/  1*OCTET ",NAIRealms=" realm-list "," 1*OCTET



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      realm-list            = realm /
                              ( realm-list ";" realm )

   The "OCTET" and "CHAR" rules are defined in [RFC2234] and the "realm"
   rule is defined in [rfc2486bis].

   A sample hex dump of an EAP-Request/Identity packet is shown below.

      01                        ; Code: Request
      00                        ; Identifier: 0
      00 43                     ; Length: 67 octets
      01                        ; Type: Identity
      48 65 6c 6c 6f 21 00 4e   ; "Hello!\0NAIRealms=example.com;mnc014.
      41 49 52 65 61 6c 6d 73   ; mcc310.3gppnetwork.org"
      3d 69 73 70 2e 65 78 61
      6d 70 6c 65 2e 63 6f 6d
      3b 6d 6e 63 30 31 34 2e
      6d 63 63 33 31 30 2e 33
      67 70 70 6e 65 74 77 6f
      72 6b 2e 6f 72 67

   The Network-Info can contain NAIRealms list in addition to
   proprietary information.  The proprietary information can be placed
   before or after NAIRealms list.  To extract NAIRealms list, an
   implementation either finds the "NAIRealms=" immediately after the
   NUL or seeks forward to find ",NAIRealms" somewhere in the string.
   The realms data ends either at first "," or at the end of the string,
   whichever comes first.

3.  IANA Considerations

   This document does not define any new namespaces to be managed by
   IANA, and does not require any assignments in existing namespaces.

4.  Security considerations

   Identity hint information is delivered inside an EAP-Request/Identity
   before the authentication conversation begins, and therefore can be
   modified by an attacker.  The NAIRealms attribute therefore MUST be
   treated as a hint by the peer

   Unauthenticated hints may result in peers inadvertently revealing
   additional identities, compromising privacy.  Since the
   EAP-Response/Identity is sent in the clear,  this vulnerability
   already exists.  This vulnerability can be addressed via
   method-specific identity exchanges.

   Similarly, in a situation where the peer has multiple identities to



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   choose from, an attacker can use a forged hint to convince the peer
   to choose an identity bound to a weak EAP method.  Requiring the use
   of strong EAP methods can protect against this.  A similar issue
   already exists with respect to unprotected link layer advertisements
   such as 802.11 SSIDs.

   Where the identity hint is used to select a mediating network, with
   existing EAP methods there may not be a way for the home AAA server
   to verify that the mediating network selected by the peer was
   actually used.

5.  Acknowledgements

   The authors would specially like to thank Jari Arkko and Bernard
   Aboba for their help in scoping the problem, for reviewing the draft
   work in progress and for suggesting improvements to it.

   The authors would also like to acknowledge and thank Adrian Buckley,
   Blair Bullock, Jose Puthenkulam, Johanna Wild, Joe Salowey, Marco
   Spini, Simone Ruffino, Mark Grayson, Mark Watson, and Avi Lior for
   their support, feedback and guidance during the various stages of
   this work.

6.  Appendix A (informative) - Delivery Options

   Although the delivery options are described in the context of IEEE
   802.11 access networks, they are applicable to other access networks
   that use EAP [RFC3748] for authentication and use the NAI format
   [rfc2486bis] for identifying users.  Also, the options assume that
   the AAA protocol in use is RADIUS [RFC2865].  Diameter [RFC3588]
   could also be used instead of RADIUS without introducing significant
   architectural differences.

   The main difference amongst the options is which entity in the access
   network creates the EAP-Request/Identity.  For example, the role of
   EAP server may be played by the EAP authenticator (where an initial
   EAP-Request/Identity is sent with an identity hint), or a RADIUS
   proxy/server (where the NAI Realm is used for forwarding).

   When an Identity hint is sent by a RADIUS proxy/server, a RADIUS
   State (24) attribute can be used to help the RADIUS proxy/server
   determine if an identity hint had previously been sent by it to the
   EAP peer.

   The RADIUS proxy/server acts only on the RADIUS UserName(1) attribute
   and does not have to parse the EAP-Message attribute.

   Option 1: Initial EAP-Request/Identity from access point



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   In typical IEEE 802.11 wireless LANs, the initial
   EAP-Request/Identity is sent by the access point (i.e., EAP
   authenticator).  In the simplest case, the identity hint information
   is simply included in this request, as shown below.


     EAP          Access Point        local RADIUS           home RADIUS
     Peer                               proxy/server            server
     |     1. EAP        |                    |                    |
     |  Request/Identity |                    |                    |
     |   (NAIRealms)     |                    |                    |
     |<------------------|                    |                    |
     |     2. EAP        |                    |                    |
     |  Response/Identity|                    |                    |
     |------------------>|                    |                    |
     |                   | 3. Access-Request  |                    |
     |                   |      (EAP          |                    |
     |                   |  Response/Identity)|                    |
     |                   |------------------->|                    |
     |                   |                    | 4.Access-Request   |
     |                   |                    |      (EAP          |
     |                   |                    | Response/Identity) |
     |                   |                    |------------------->|
     |                   |                    |                    |
     |<-------------------EAP conversation ----------------------->|



   Current access points do not support this mechanism, so other options
   may be preferable.  This option can also require configuring the
   identity hint information in a potentially large number of access
   points, which may be problematic if the information changes often.

   Option 2: Initial EAP-Request/Identity from local RADIUS proxy/server

   This is similar to Option 1, but the initial EAP-Request/Identity is
   created by the local RADIUS proxy/server instead of the access point.
   Once a peer associates with an access network AP using IEEE 802.11
   procedures, the AP sends an EAP-Start message [RFC3579] within a
   RADIUS Access-Request.  The access network RADIUS server can then
   send the EAP-Request/Identity containing the identity hint
   information.









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     EAP          Access Point          local RADIUS           home RADIUS
     Peer                                proxy/server            server
     |                   | 1. Access-Request  |                    |
     |                   |    (EAP-Start)     |                    |
     |                   |------------------->|                    |
     |                   | 2.Access-Challenge |                    |
     |                   |       (EAP         |                    |
     |                   |  Request/Identity  |                    |
     |                   |   with NAIRealms)  |                    |
     |                   |<-------------------|                    |
     |     3. EAP        |                    |                    |
     | Request/Identity  |                    |                    |
     |   (NAIRealms)     |                    |                    |
     |<------------------|                    |                    |
     |     4. EAP        |                    |                    |
     | Response/Identity |                    |                    |
     |------------------>|                    |                    |
     |                   | 5. Access-Request  |                    |
     |                   |       (EAP         |                    |
     |                   | Response/Identity) |                    |
     |                   |------------------->|                    |
     |                   |                    | 6. Access-Request  |
     |                   |                    |        (EAP        |
     |                   |                    | Response/Identity) |
     |                   |                    |------------------->|
     |                   |                    |                    |
     |<------------------- EAP conversation ---------------------->|



   This option can work with current access points if they support the
   EAP-Start message.

   Option 3: Subsequent EAP-Request/Identity from local RADIUS
   proxy/server

   In the third option, the access point sends the initial
   EAP-Request/Identity without any hint information.  The peer then
   responds with an EAP-Response/Identity, which is forwarded to the
   local RADIUS proxy/server.  If the RADIUS proxy/server cannot route
   the message based on the identity provided by the peer, it sends a
   second EAP-Request/Identity containing the identity hint information.









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     EAP            Access Point       local RADIUS           home RADIUS
     Peer                              Proxy/Server             server
     |                   |                    |                    |
     |     1. EAP        |                    |                    |
     | Request/Identity  |                    |                    |
     | (w/o NAIRealms)   |                    |                    |
     |<------------------|                    |                    |
     |     2. EAP        |                    |                    |
     | Response/Identity |                    |                    |
     |------------------>|                    |                    |
     |                   | 3. Access-Request  |                    |
     |                   |      (EAP          |                    |
     |                   | Response/Identity) |                    |
     |                   |------------------->|                    |
     |                   | 4.Access-Challenge |                    |
     |                   |      (EAP          |                    |
     |                   |  Request/Identity  |                    |
     |                   |  with NAIRealms)   |                    |
     |                   |<-------------------|                    |
     |     5. EAP        |                    |                    |
     | Request/Identity  |                    |                    |
     |   (NAIRealms)     |                    |                    |
     |<------------------|                    |                    |
     |     6. EAP        |                    |                    |
     | Response/Identity |                    |                    |
     |------------------>|                    |                    |
     |                   | 7. Access-Request  |                    |
     |                   |      (EAP          |                    |
     |                   | Response/Identity) |                    |
     |                   |------------------->|                    |
     |                   |                    | 8. Access-Request  |
     |                   |                    |       (EAP         |
     |                   |                    | Response/Identity) |
     |                   |                    |------------------->|
     |                   |                    |                    |
     |<-------------------- EAP conversation --------------------->|


   This option does not require changes to existing NASes, so it may be
   preferable in many environments.

7.  References

7.1  Normative references

   [rfc2486bis]
              Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The
              Network Access Identifier",



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              draft-arkko-roamops-rfc2486bis-02 (work in progress), July
              2004.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H.
              Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
              3748, June 2004.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

7.2  Informative references

   [RFC3579]  Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
              Dial In User Service) Support For Extensible
              Authentication Protocol (EAP)", RFC 3579, September 2003.

   [netsel-problem]
              Arkko, J. and B. Aboba, "Network Discovery and Selection
              Problem", draft-ietf-eap-netsel-problem-01 (work in
              progress), July 2004.

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A. and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)", RFC
              2865, June 2000.


Authors' Addresses

   Farid Adrangi
   Intel Corporation
   2111 N.E. 25th Avenue
   Hillsboro, OR  97124
   USA

   Phone: +1 503-712-1791
   EMail: farid.adrangi@intel.com









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   Victor Lortz
   Intel Corporation
   2111 N.E. 25th Avenue
   Hillsboro, OR  97124
   USA

   Phone: +1 503-264-3253
   EMail: victor.lortz@intel.com


   Farooq Bari
   AT&T Wireless
   7277 164th Avenue N.E.
   Redmond, WA  98052
   USA

   Phone: +1 425-580-5526
   EMail: farooq.bari@attws.com


   Pasi Eronen
   Nokia Research Center
   P.O. Box 407
   FIN-00045 Nokia Group
   Finland

   EMail: pasi.eronen@nokia.com
























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