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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: 3588bis                                     Bridgewater Systems
(if approved)                                                  L. Morand
Intended status: Standards Track                             Orange Labs
Expires: August 9, 2009                                          T. Tsou
                                                                  Huawei
                                                        February 5, 2009


   Diameter User-Name and Realm Based Request Routing Clarifications
                   draft-ietf-dime-nai-routing-01.txt

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Abstract

   This specification clarifies the Diameter realm based request
   routing.  We focus on the case where a Network Access Identifier in
   the User-Name AVP is used to populate the Destination-Realm AVP and
   the Network Access Identifier contains more than one realm.  This
   particular case is possible when the Network Access Identifier
   decoration is used to force a routing of request messages through a
   predefined list of realms.  However, this functionality is not
   unambiguously specified in the Diameter Base Protocol specification.


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.  Enhanced Request Routing Solution  . . . . . . . . . . . .  6
     4.3.  Backwards Compatibility Considerations . . . . . . . . . .  7
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     8.1.  Normative References . . . . . . . . . . . . . . . . . . .  8
     8.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10























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1.  Introduction

   This specification clarifies the Diameter realm based request routing
   defined in RFC 3588 [RFC3588].  We focus on the case where the
   Network Access Identifier (NAI) [RFC4282] in the User-Name AVP is
   used to populate the Destination-Realm AVP and the NAI contains more
   than one realm.  This particular case is possible when the NAI
   decoration is used to force a routing of request messages through a
   predefined list of realms.

   According to the Diameter request routing processing rules in RFC
   3588, the request originator may populate the Destination-Realm AVP
   with the realm part of the NAI available in the User-Name AVP.
   Unfortunately, there is no unambiguous mandatory language in RFC 3588
   how Diameter agents participating to the request routing should
   update the Destination-Realm AVP at each realm based on the content
   of the decorated NAI..

   This specification presents both the issue regarding to the Diameter
   realm based request routing with NAI decoration and also a solution
   for the problem.  The solution would only apply to Diameter Base
   Protocol implementations that take the solution presented in this
   specification into account.  The solution, however, is fully
   backwards compatible with the RFC 3588 Diameter Base Protocol.


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 [RFC2119].

   Network Access Identifier (NAI):

      The Network Access Identifier (NAI) is the user identity submitted
      by the client during access authentication.  In roaming case, 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 specifying a source route.  See Section 2.7 of RFC 4282 for
      more information.








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   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 Network Access Servers (NAS).

   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 in
   which 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 contains a
   NAI in the form of "username@realm".  The realm based request
   routing, as described in RFC 3588, does not discuss how to handle
   Decorated NAIs.  The original NAI RFC 2486 [RFC2486] that RFC 3588
   references to, does not defined how to construct a NAI with multiple
   realms.  Since then RFC 2486 has been obsoleted by RFC 4282 which in
   turn defines how to construct Decorated NAIs.

   Decorated NAIs are used to force routing of messages to the home
   realm through a predefined list of realms and in that way enable
   certain inter-realm roaming arrangements, see Section 2.7. of RFC
   4282 [RFC4282].  For example, a terminal (e.g., a mobile host) learns
   based on some application or implementation specific manner that its
   network access authentication signaling must go through certain
   realms in order to reach the home realm.  In this case the terminal
   decorates 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 will
   ensure that all subsequent request messages go through the desired
   realms as long as the request messages contain the User-Name AVP with
   a Decorated NAI.

   NAI Decoration has been previously used, for example, 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



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   [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 of deployment scenario where
   Decorated NAIs is 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 (i.e. the visited realm from the roaming terminal
   point of view).  Therefore, for the network access authentication,
   the roaming terminal decorates 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 had
   chosen to use NAP A, it would have decorated 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



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   application in which commands are proxiable and include the User-Name
   AVP with a NAI.  Generally NAI Decoration can be used to force a
   certain route for all request messages at a realm granularity.

   As a problem summary there are two main issues with the handling of
   Decorated NAI:

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

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

   RFC 5113 [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 a uniform
   way of interpreting decorated NAIs.  That is, in this case, the
   character '!' is used to separate realms in the list of decorated
   realms in the NAI (as shown in examples in [RFC4282]).

4.2.  Enhanced Request Routing Solution

   When a Diameter agent receives a request message containing a
   Destination-Realm AVP with a realm that the agent is configured to
   process locally (and, for Diameter 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
      agent proceeds with a normal RFC 3588 message processing.




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   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
      part of the NAI 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 originating
   signaling with the home realm (Realm-H) through a NAP A and two
   intermediating realms (Realm-Z, Realm-X).  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 to reach Realm-H.

4.3.  Backwards Compatibility Considerations

   Obviously, the functionality described in Section 4.2 cannot be
   guaranteed to work with implementations based on RFC 3588 or any
   Diameter application strictly based on RFC 3588 (such as NASREQ and
   EAP).  An implementation not compliant with the present specification
   would automatically fall back to the normal RFC 3588 request routing
   behavior that, unfortunately, cannot offer desired enhanced request
   routing functionality.  Therefore, it is RECOMMENDED that the
   solution defined in this specification is only applied to newly
   specified Diameter applications.  A Diameter agent MAY implement the
   solution defined in this specification also for the existing
   application.  A Diameter client SHOULD NOT assume the functionality
   described in Section 4.2 from Diameter applications that do not



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   comply with this specification.


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
   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 relies on the security
   properties of the intermediate AAA brokers and Diameter proxies.


7.  Acknowledgements

   The authors would like to thank Victor Fajardo and Stefan Winter for
   their comments on this draft.

   Jouni Korhonen would like to thank the TEKES GIGA Program 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.




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   [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.

   [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 8.0.0, December 2008.

   [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.



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Authors' Addresses

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

   Email: jouni.nospam@gmail.com


   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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