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Versions: (draft-korhonen-dime-nai-routing) 00 01 02 03 04 RFC 5729

Diameter Maintenance and                                J. Korhonen, Ed.
Extensions (DIME)                                 Nokia Siemens Networks
Internet-Draft                                                  M. Jones
Updates: 3588, 3588bis                               Bridgewater Systems
(if approved)                                                  L. Morand
Intended status: Standards Track                             Orange Labs
Expires: November 11, 2009                                       T. Tsou
                                                                  Huawei
                                                            May 10, 2009


   Diameter User-Name and Realm Based Request Routing Clarifications
                   draft-ietf-dime-nai-routing-02.txt

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Abstract

   This specification defines the behavior required of Diameter agents
   to route requests when the User-Name Attribute Value Pair contains a
   Network Access Identifier formatted with multiple realms.  These
   multi-realm or "Decorated" Network Access Identifiers are used in
   order to force the routing of request messages through a predefined
   list of mediating realms.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology and Abbreviations . . . . . . . . . . . . . . . . . 3
   3.  Problem Overview  . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Solution Overview . . . . . . . . . . . . . . . . . . . . . . . 6
     4.1.  Interpretation of Decorated NAIs  . . . . . . . . . . . . . 6
     4.2.  Ensuring Backwards Compatibility  . . . . . . . . . . . . . 6
     4.3.  Enhanced Request Routing Solution . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

























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1.  Introduction

   This specification defines the behavior required of Diameter agents
   to route requests when the User-Name Attribute Value Pair (AVP)
   contains a Network Access Identifier (NAI) formatted with multiple
   realms (hereafter referred to as Decorated NAI).  Decorated NAIs are
   used in order to force the routing of request messages through a
   predefined list of mediating realms.  This specification does not
   define a new Diameter application but instead defines behaviour that
   would be common across all Diameter applications which require
   request routing based on Decorated NAI.

   At the time of publication of the Diameter Base Protocol [RFC3588],
   the NAI definition was based on [RFC2486] in which a NAI could only
   contain a single realm.  The NAI definition has since been updated in
   [RFC4282] to define Decorated NAIs that contain multiple realms.
   However, RFC 4282 does not define how the Decorated NAIs should be
   handled by Diameter agents so this specification was written to
   capture those requirements.


2.  Terminology and Abbreviations

   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].

   Network Access Identifier (NAI):

      The Network Access Identifier (NAI) is the user identity submitted
      by the client during access 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.

   Decorated NAI:

      A NAI containing multiple realms used to specify a source route
      and formatted according to Section 2.7 in RFC 4282.

   Network Access Provider (NAP):

      A business entity that provides network access infrastructure to
      one or more realms.  A NAP infrastructure constitutes of one or
      more NASes.







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   Network Access Server (NAS):

      The device that peers connect to in order to obtain access to the
      network.



3.  Problem Overview

   The Diameter Base Protocol RFC 3588 Section 6.1 defines the request
   routing in detail.  This specification concerns only those cases
   where a Destination-Realm AVP is included in a request message.  A
   Diameter peer originating a request message MAY retrieve the realm
   information from the User-Name AVP and use that realm to populate the
   Destination-Realm AVP.  In that case, the User-Name AVP is in form of
   a NAI including the realm part.

   Decorated NAIs are used to force routing of messages through a
   predefined list of realms and in that way e.g., force certain inter-
   realm roaming arrangements, see Section 2.7. of RFC 4282.  For
   example, a terminal (e.g. a mobile host) may learn based on some
   application or implementation specific manner that its network access
   authentication signaling must traverse through certain realms in
   order to reach the home realm.  In this case the terminal would
   decorate its NAI during the network access authentication with the
   list of intermediating realms and the home realm.  As a result, the
   network access server (NAS) and intermediating Diameter agents would
   make sure that all subsequent request messages traverse through the
   desired realms as long as the request messages contain the User-Name
   AVP with a Decorated NAI.

   NAI decoration has previously been used in RADIUS [RFC2865] based
   roaming networks using RFC 2486 NAIs in a proprietary manner.  There
   is a need to replicate the same NAI based routing enforcement
   functionality also in Diameter based roaming networks.  There are
   also publicly available specifications (e.g., see [3GPP.23.234],
   [3GPP.24.234], [3GPP.23.003], [3GPP.29.273] and [WiMAX]) that assume
   NAI decoration based request routing enforcement is fully supported
   by RFC 3588.  The same assumption is carried over to NASREQ [RFC4005]
   and EAP [RFC4072] Diameter applications.

   Figure 1 illustrates an example deployment scenario where Decorated
   NAIs would be used to force a certain route through desired realms.
   A roaming terminal (e.g. a mobile host) discovers a number of Network
   Access Providers (NAP): NAP A and NAP B. None of the NAPs are able to
   provide direct connectivity to roaming terminals home realm (i.e.
   Realm-H).  However, the roaming terminal learns, somehow, that NAP B
   is able to provide connectivity to the Realm-H through the Realm-X



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   (i.e. the visited realm from the roaming terminal point of view).
   During the network access authentication, the roaming terminal would
   decorate its NAI as Realm-H!username@Realm-X.  The roaming terminal
   has also an alternative route to its home realm through NAP A,
   Realm-Z and Realm-X.  If the roaming terminal were to choose to use
   NAP A, then it would decorate its NAI as Realm-X!Realm-H!username@
   Realm-Z.  Diameter agents should now be able to route the request
   message through desired realms using the Decorated NAI originally
   found in the User-Name AVP.


         .--.                 .--.                   .--.
       _(.   `)             _(.   `)               _(.   `)
     _(Visited`)_         _(Visited`)_           _(  Home `)_
    (   Realm-Z  `)<---->(   Realm-X  `)<------>(   Realm-H  `)
   ( `  .       )  )    ( `  .       )  )      ( `  .       )  )
    `--(_______)--'      `--(_______)--'        `--(_______)--'
          |                 __ /
          |               /
         .--.          .--.
       _(    `.      _(    `.
      (  NAP A )    (  NAP B )
     ( `  .  )  )  ( `  .  )  )
      `--(___.-'    `--(___.-'
                     )
            (  (   )
              (  |
                 +-+
                 |M|
                 +-+

    Figure 1: Example roaming scenario with intermediating realms. The
      mobile host authenticates to the home realm through one or more
                              visited realms.

   NAI decoration is not limited to the network access authentication
   and authorization procedures.  It can be used with any Diameter
   application whose commands are proxiable and include the User-Name
   AVP with a NAI.  Generally, the NAI decoration can be used to force a
   certain route for all request messages at a realm granularity.

   As a problem summary we have two main issues:

   o  Updating both Destination-Realm and User-Name AVPs based on the
      Decorated NAI extracted from the User-Name AVP.  The update would
      be done by intermediating Diameter agents that participate to
      realm based request routing.  Specifically, this would concern
      Diameter proxies.



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   o  How Diameter agents could implement the handling of the NAI
      decoration based routing enforcement in a way that is still
      backwards compatible with RFC 3588.

   [RFC5113] Section 2.3. also discusses NAI decoration related issues
   with EAP [RFC3748] in general.


4.  Solution Overview

   This specification defines a solution for Diameter realm based
   request routing with routing enforcement using the User-Name AVP NAI
   decoration.  Diameter proxy agent implementations can claim
   compliance using the solution described in this specification.

4.1.  Interpretation of Decorated NAIs

   Implementations compliant to this specification MUST have an uniform
   way of interpreting decorated NAIs.  That is, in the case of
   decoration, the character '!' is used to separate realms in the list
   of decorated realms in the NAI (as shown in examples in [RFC4282]).

4.2.  Ensuring Backwards Compatibility

   Implementations compliant to this specification MUST define a new
   Diameter application.  This requirement is set to guarantee backwards
   compatibility with existing Diameter implementations, applications
   and deployments.  Diameter agents not compliant with this
   specification will not advertise support for these new applications
   that implement the enhanced routing solution based on Decorated NAIs
   and will therefore be bypassed.

4.3.  Enhanced Request Routing Solution

   When a Diameter client originates a request message, the Destination-
   Realm AVP is populated with the realm part of the NAI available in
   the User-Name AVP (realm given after the '@' character of the NAI).
   The NAI in the User-Name AVP may or may not be decorated.

   When a Diameter agent receives a request message containing the
   Destination-Realm AVP with a realm that the agent is configured to
   process locally (and in the case of proxies the Diameter application
   is locally supported), it MUST do the following further processing
   before handling the message locally:

   o  If the User-Name AVP is available in the request message, then the
      Diameter agent MUST inspect whether the User-Name AVP contains a
      Decorated NAI.  If the NAI is not decorated then the Diameter



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      agent proceeds with a normal RFC 3588 message processing.

   o  If the User-Name AVP contains a Decorated NAI, then the Diameter
      agent MUST process the NAI as defined in RFC 4282 and update the
      value of the User-Name AVP accordingly.  Furthermore, the Diameter
      agent MUST update the Destination-Realm AVP to match the new realm
      in the User-Name AVP.

   o  The request message is then sent to the next hop using the normal
      request routing rules as defined in RFC 3588.

   Figure 2 illustrates an example of a roaming terminal originated
   signaling with the home realm (Realm-H) through a NAP and two
   intermediating realms (Realm-Z, Realm-X) before reaching the home
   realm (Realm-H).  The example shows how the User-Name AVP and the
   Destination-Realm AVP change at each realm before reaching the final
   destination.  If the signaling were originated from the NAS/NAP only,
   then the step 1) can be omitted.

   1) Roaming Terminal -> NAS/NAP
          Identity/NAI = realm-X!realm-H!username@realm-Z

   2) NAS/NAP -> Realm-Z
          User-Name = realm-X!realm-H!username@realm-Z
          Destination-Realm = realm-Z

   3) Realm-Z -> realm-X
          User-Name = realm-H!username@realm-X
          Destination-Realm = realm-X

   4) Realm-X -> Realm-H
          User-Name = username@realm-H
          Destination-Realm = realm-H

     Figure 2: The roaming terminal decides that the Diameter messages
             must be routed via Realm-Z, Realm- X and Realm-H.


5.  IANA Considerations

   This specification has no actions to IANA.


6.  Security Considerations

   A malicious node initiating (or indirectly causing initiation of) a
   Diameter request may purposely create malformed list of realms in the
   NAI.  This may cause the routing of requests through realms that



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   would normally have nothing to do with the initiated Diameter message
   exchange.  Furthermore, a malformed list of realms may contain non-
   existing realms causing the routing of Diameter messages that cannot
   ultimately be routed anywhere.  However, the request message might
   get routed several hops before such non-existent realms are
   discovered and thus creating unnecessary overhead to the routing
   system in general.

   The NAI decoration is used in AAA infrastructures where the Diameter
   messages are transported between the NAS and the Diameter server via
   one or more AAA brokers or Diameter proxies.  In this case the NAS to
   the Diameter server AAA communication rely on the security properties
   of the intermediate AAA brokers and Diameter proxies.


7.  Acknowledgements

   The authors would like to thank Victor Fajardo, Stefan Winter and Avi
   Lior for their detailed comments on this document.

   Jouni Korhonen would like to thank TEKES WISEciti project for
   providing funding to work on this document while he was at
   TeliaSonera's employ.


8.  References

8.1.  Normative References

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

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

   [RFC4282]  Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
              Network Access Identifier", RFC 4282, December 2005.

8.2.  Informative References

   [3GPP.23.003]
              3GPP, "Numbering, addressing and identification", 3GPP
              TS 23.003 3.15.0, October 2006.

   [3GPP.23.234]
              3GPP, "3GPP system to Wireless Local Area Network (WLAN)
              interworking; System description", 3GPP TS 23.234 6.10.0,
              October 2006.



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   [3GPP.24.234]
              3GPP, "3GPP system to Wireless Local Area Network (WLAN)
              interworking; WLAN User Equipment (WLAN UE) to network
              protocols; Stage 3", 3GPP TS 24.234 6.7.0, October 2006.

   [3GPP.29.273]
              3GPP, "Evolved Packet System (EPS); 3GPP EPS AAA
              interfaces", 3GPP TS 29.273 8.1.0, March 2009.

   [RFC2486]  Aboba, B. and M. Beadles, "The Network Access Identifier",
              RFC 2486, January 1999.

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

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

   [RFC4005]  Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
              "Diameter Network Access Server Application", RFC 4005,
              August 2005.

   [RFC4072]  Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
              Authentication Protocol (EAP) Application", RFC 4072,
              August 2005.

   [RFC5113]  Arkko, J., Aboba, B., Korhonen, J., and F. Bari, "Network
              Discovery and Selection Problem", RFC 5113, January 2008.

   [WiMAX]    WiMAX Forum, "WiMAX Forum Network Architecture (Stage 2:
              Architecture Tenets, Reference Model and Reference
              Points)", Release 1 Version 1.2, January 2008.


Authors' Addresses

   Jouni Korhonen (editor)
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  FIN-02600
   Finland

   Email: jouni.nospam@gmail.com






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   Mark Jones
   Bridgewater Systems
   303 Terry Fox Drive
   Ottawa,  Ontario  K2K 3J1
   Canada

   Email: Mark.Jones@bridgewatersystems.com


   Lionel Morand
   Orange Labs
   38-40 rue du general Leclerc
   Issy-moulineaux Cedex 9,  92794
   France

   Email: Lionel.morand@orange-ftgroup.com


   Tina Tsou
   Huawei
   R&D Center, Huawei Technologies Co., Ltd
   Bantian,  Shenzhen
   P.R. China

   Email: tena@huawei.com


























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