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Versions: (draft-tsou-dime-realm-based-redirect) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 7075

Internet Engineering Task Force                                  T. Tsou
Internet-Draft                                 Huawei Technologies (USA)
Updates: 6733 (if approved)                                       R. Hao
Intended status: Standards Track                           Comcast Cable
Expires: May 9, 2013                                      T. Taylor, Ed.
                                                     Huawei Technologies
                                                        November 5, 2012

                  Realm-Based Redirection In Diameter


   The Diameter protocol allows a Diameter redirect agent to specify one
   or more individual hosts to which a Diameter message may be
   redirected by an upstream Diameter node.  However, in some
   circumstances an operator may wish to redirect messages to an
   alternate domain without specifying individual hosts.  This document
   specifies a mechanism by which this can be achieved.  New
   applications may incorporate this capability by reference to the
   present document.

   This memo updates Sections 6.13 and 6.14 of RFC6733 with respect to
   the usage of the Redirect-Host-Usage and Redirect-Max-Cache-Time

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 9, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . . . 3
   2.  Support of Realm-Based Redirection Within Applications  . . . . 3
   3.  Realm-Based Redirection . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Configuration of the Redirecting Server . . . . . . . . . . 4
     3.2.  Behaviour of Diameter Nodes . . . . . . . . . . . . . . . . 5
       3.2.1.  Behaviour at the Redirecting Server . . . . . . . . . . 5
       3.2.2.  Proxy Behaviour . . . . . . . . . . . . . . . . . . . . 5
       3.2.3.  Client Behaviour  . . . . . . . . . . . . . . . . . . . 6
     3.3.  The Redirect-Realm AVP  . . . . . . . . . . . . . . . . . . 6
     3.4.  DIAMETER_REDIRECT_INDICATION Error Code . . . . . . . . . . 7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8

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1.  Introduction

   The usual redirect indication, as described in Section 6.1.8 and
   Sections 6.12-6.14 of [RFC6733], returns one or more individual host
   names to the upstream Diameter node.  However, consider the case
   where an operator has offered a specific service but no longer wishes
   to do so.  The operator has arranged for an alternative domain to
   provide the service.  To aid in the transition to the new
   arrangement, the original operator maintains a redirect server to
   indicate the alternative destination to upstream nodes.  However, the
   original operator has no interest in configuring a list of hosts in
   the alternative operator's domain, and would prefer simply to provide
   redirect indications to the domain as a whole.

   As an example of another use case, consider a 3GPP IMS deployment
   where subscriber data is provisioned in a geo-redundant Home
   Subscriber Server (HSS) cluster for reliability.  Each Application
   Server (AS) needs to maintain redundant Diameter Sh links to both
   cluster nodes for scalability.  It is preferable that the AS should
   go to the local HSS cluster node when it is available.  It would be
   useful for a cluster node to be able to redirect an AS request to its
   partner node in the cluster without specifying the individual Sh link
   to that alternate node.  This could be accomplished by identifying
   each cluster node with a separate realm and individual Sh links with
   separate servers, and redirecting on the basis of realm rather than
   individual server.  There can be multiple geo-redundant HSS clusters,
   in which case the Subscriber Location Function (SLF) performs the

   Within this specification, the term "realm-based redirection" is used
   to refer to a mode of operation where the redirect indication
   specifies a realm and the upstream Diameter node reroutes the message
   to the realm rather than an individual host.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Support of Realm-Based Redirection Within Applications

   Because realm-based redirection is not part of base Diameter
   behaviour, support for realm-based redirection by the agent MUST be
   specified as part of particular applications.  In this way,
   Diameter's capability negotiation mechanism can be used indirectly to
   indicate support for realm-based redirection by indicating support

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   for the applications concerned.  Designers of new applications can
   incorporate the mechanism specified here into their application by
   normative reference to this document.

   The result of making realm-based redirection an application-specific
   behaviour is that it cannot be performed by a redirect agent, but
   instead must be performed by a Diameter server.  However, despite the
   change in executing role, the behaviour itself is a slight
   modification of the behaviour of a redirect agent as described in
   Section 2.8.3 of [RFC6733].

   An application can specify that realm-based redirection operates only
   on the initial message of a session, or on any message of a session.
   In the former case, existing sessions will not be disrupted by the
   deployment of realm-based redirection.  In the latter case, existing
   sessions will be disrupted if they are stateful.

3.  Realm-Based Redirection

   This section specifies an extension to [RFC6733] to achieve realm-
   based redirection.  The elements of this solution are:

   o  a new result code, DIAMETER_REALM_REDIRECT_INDICATION (3xxx TBD);

   o  one new attribute-value pair (AVP), Redirect-Realm; and

   o  associated behaviour at Diameter nodes implementing this
      specification.  This behaviour includes the optional use of the
      Redirect-Host-Usage and Redirect-Max-Cache-Time AVPs.  In this
      document, these AVPs apply to the peer discovered by a node acting
      on the server's response, an extension to their normal usage as
      described in Sections 6.13 and 6.14 of [RFC6733].

   Section 3.2.2 and Section 3.2.3 describe how a proxy or client may
   update its routing table for the application and initial realm, as a
   result of selecting a peer in the new realm.  Note that as a result,
   the proxy or client will automatically route subsequent requests for
   that application to the new realm (with the possible exception of
   requests within sessions already established with the initial realm)
   until the cached routing entry expires.  This should be borne in mind
   if the rerouting is intended to be temporary.

3.1.  Configuration of the Redirecting Server

   A Diameter server MUST be configured as follows to execute realm-
   based redirection:

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   o  configured with an application that incorporates realm-based

   o  the Local Action field of the routing table described in Section
      2.7 of [RFC6733] is set to LOCAL;

   o  an application-specific field is set to indicate that the required
      local action is to perform realm-based redirection;

   o  an associated application-specific field is configured with the
      identities of one or more realms to which the request should be

3.2.  Behaviour of Diameter Nodes

3.2.1.  Behaviour at the Redirecting Server

   As mentioned in Section 2, an application incorporating realm-based
   redirection may specify that redirection applies for any request or
   only for the initial request of a session (i.e., to prevent
   disruption of established sessions).

   If a server configured as described in Section 3.1 receives a request
   to which realm-based redirection applies, the server MUST reply with
   an answer message with the 'E' bit set, while maintaining the Hop-by-
   Hop Identifier in the header.  The server MUST include the Result-
   also include the alternate realm identifier(s) with which it has been
   configured, each in a separate Redirect-Realm AVP instance.

   The server MAY include a copy of the Redirect-Host-Usage AVP, which
   SHOULD be set to REALM_AND_APPLICATION.  If this AVP is added, the
   Redirect-Max-Cache-Time AVP MUST also be included.  Note that these
   AVPs apply to the peer discovered by a node acting on the server's
   response, as described in the next section.  This is an extension of
   their normal usage as described by Sections 6.13 and 6.14 of

      If the redirected request contained a Destination-Host AVP, that
      AVP is ignored by the server.

3.2.2.  Proxy Behaviour

   A proxy conforming to this specification that receives an answer
   message with the Result-Code AVP set to
   original request to a server in a realm identified by a Redirect-
   Realm AVP instance in the answer message, or MAY simply forward the

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   message to the upstream peer.  If it chooses to reroute the request,
   it MUST take the following steps:

   1.  Select a specific realm from amongst those identified in
       instances of the Redirect-Realm AVP in the answer message.

   2.  If successful, locate and establish a route to a peer in the
       realm given by the Redirect-Realm AVP, using normal discovery
       procedures as described in Section 5.2 of [RFC6733].

   3.  If again successful:

       A.  update its cache of routing entries for the realm and
           application to which the original request was directed,
           taking into account the Redirect-Host-Usage and Redirect-Max-
           Cache-Time AVPs, if present in the answer.

       B.  Remove the Destination-Host (if present) and Destination-
           Realm AVPs from the original request and add a new
           Destination-Realm AVP containing the realm selected in the
           initial step.

       C.  Forward the modified request.

   4.  If either of the preceding steps 2-3 fail and additional realms
       have been identified in the original answer, select another
       instance of the Redirect-Realm AVP in that answer and repeat
       steps 2-3 for the realm that it identifies.

3.2.3.  Client Behaviour

   A client conforming to this specification MUST be prepared to receive
   either an answer message containing a Result-Code AVP set to
   DIAMETER_REALM_REDIRECT_INDICATION, or, as the result of proxy
   action, some other result from a realm differing from the one to
   which it sent the original request.  In the case where it receives
   steps prescribed in the previous section for a proxy, in order both
   to update its routing table and to obtain service for the original

3.3.  The Redirect-Realm AVP

   The Redirect-Realm AVP (code TBD) is of type DiameterIdentity.  It
   specifies a realm to which a node receiving a redirect indication
   containing the result code value DIAMETER_REALM_REDIRECT_INDICATION
   and the Redirect-Realm AVP SHOULD route the original request.  The M
   flag for the Redirect-Realm AVP MUST be set, and the V flag MUST NOT

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   be set.


   The DIAMETER_REDIRECT_INDICATION (3xxx TBD) error code indicates that
   a server has determined that the request within an application
   supporting realm-based redirection could not be satisfied locally and
   the initiator of the request SHOULD direct the request directly to a
   peer within a realm that has been identified in the response.  When
   set, the Redirect-Realm AVP MUST be present.

4.  Security Considerations

   Realm-based redirection implies a potential change in business
   relationships, the authorization checks described in Section 2.9 of

5.  IANA Considerations

   This specification adds a new AVP code [TBD] Redirect-Realm in the
   AVP Code registry under Authentication, Authorization, and Accounting
   (AAA) Parameters.

   This specification allocates a new Result-Code value
   Values (code 268) - Protocol Errors registry under Authentication,
   Authorization, and Accounting (AAA) Parameters.

6.  Acknowledgements

   Glen Zorn, Sebastien Decugis, Wolfgang Steigerwald, Mark Jones,
   Victor Fajardo, Jouni Korhonen, Avi Lior, and Lionel Morand
   contributed comments that helped to shape this document.

7.  Normative References

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

   [RFC6733]  Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", RFC 6733, October 2012.

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Authors' Addresses

   Tina Tsou
   Huawei Technologies (USA)
   2330 Central Expressway
   Santa Clara, CA  95050

   Phone: +1 408 330 4424
   Email: Tina.Tsou.Zouting@huawei.com
   URI:   http://tinatsou.weebly.com/contact.html

   Ruibing Hao
   Comcast Cable
   One Comcast Center
   Philadelphia, PA  19103

   Phone: +1 215 286 3991(O)
   Email: Ruibing_Hao@cable.comcast.com

   Tom Taylor (editor)
   Huawei Technologies

   Email: tom.taylor.stds@gmail.com

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