Internet Engineering Task Force (IETF)                           K. Jiao
Request for Comments: 6737                                        Huawei
Category: Standards Track                                        G. Zorn
ISSN: 2070-1721                                              Network Zen
                                                            October 2012

              The Diameter Capabilities Update Application

Abstract

   This document defines a new Diameter application and associated
   Command Codes.  The Capabilities Update application is intended to
   allow the dynamic update of certain Diameter peer capabilities while
   the peer-to-peer connection is in the open state.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6737.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Specification of Requirements . . . . . . . . . . . . . . . . . 2
   3.  Diameter Protocol Considerations  . . . . . . . . . . . . . . . 3
   4.  Capabilities Update . . . . . . . . . . . . . . . . . . . . . . 3
     4.1.  Command Code Values . . . . . . . . . . . . . . . . . . . . 4
       4.1.1.  Capabilities-Update-Request . . . . . . . . . . . . . . 4
       4.1.2.  Capabilities-Update-Answer  . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
     6.1.  Application Identifier  . . . . . . . . . . . . . . . . . . 5
     6.2.  Command Codes . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 6

1.  Introduction

   Capabilities exchange is an important component of the Diameter base
   protocol [RFC6733], allowing peers to exchange identities and
   Diameter capabilities (protocol version number, supported Diameter
   applications, security mechanisms, etc.).  As defined in RFC 3588,
   however, the capabilities exchange process takes place only once, at
   the inception of a transport connection between a given pair of
   peers.  Therefore, if a peer's capabilities change (due to a software
   update, for example), the existing connection(s) must be torn down
   (along with all of the associated user sessions) and restarted before
   the modified capabilities can be advertised.

   This document defines a new Diameter application intended to allow
   the dynamic update of a subset of Diameter peer capabilities over an
   existing connection.  Because the Capabilities Update application
   specified herein operates over an existing transport connection,
   modification of certain capabilities is prohibited.  Specifically,
   modifying the security mechanism in use is not allowed; if the
   security method used between a pair of peers is changed, the affected
   connection MUST be restarted.

2.  Specification of Requirements

   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 RFC 2119 [RFC2119].

3.  Diameter Protocol Considerations

   This section details the relationship of the Diameter Capabilities
   Update application to the Diameter base protocol.

   This document specifies Diameter Application-Id 10.  Diameter nodes
   conforming to this specification MUST advertise support by including
   the value 10 in the Auth-Application-Id of the Capabilities-Exchange-
   Request (CER) and Capabilities-Exchange-Answer (CEA) commands
   [RFC6733].

4.  Capabilities Update

   When the capabilities of a Diameter node conforming to this
   specification change, the node MUST notify all of the nodes with
   which it has an open transport connection and which have also
   advertised support for the Capabilities Update application using the
   Capabilities-Update-Request (CUR) message (Section 4.1.1).  This
   message allows the update of a peer's capabilities (supported
   Diameter applications, etc.).

   A Diameter node only issues a given command to those peers that have
   advertised support for the Diameter application that defines the
   command; a Diameter node must cache the supported applications in
   order to ensure that unrecognized commands and/or Attribute-Value
   Pairs (AVPs) are not unnecessarily sent to a peer.

   The receiver of the CUR MUST determine common applications by
   computing the intersection of its own set of supported Application
   Ids against all of the Application-Id AVPs (Auth-Application-Id,
   Acct-Application-Id, and Vendor-Specific-Application-Id) present in
   the CUR.  The value of the Vendor-Id AVP in the Vendor-Specific-
   Application-Id MUST NOT be used during computation.

   If the receiver of a CUR does not have any applications in common
   with the sender, then it MUST return a Capabilities-Update-Answer
   (CUA) (Section 4.1.2) with the Result-Code AVP set to
   DIAMETER_NO_COMMON_APPLICATION [RFC6733], and it SHOULD disconnect
   the transport-layer connection.  However, if active sessions are
   using the connection, peers MAY delay disconnection until the
   sessions can be redirected or gracefully terminated.  Note that
   receiving a CUA from a peer advertising itself as a relay (see
   [RFC6733], Section 2.4) MUST be interpreted as having common
   applications with the peer.

   As for CER/CEA messages, the CUR and CUA messages MUST NOT be
   proxied, redirected, or relayed.

   Even though the CUR/CUA messages cannot be proxied, it is still
   possible for an upstream agent to receive a message for which there
   are no peers available to handle the application that corresponds to
   the Command Code.  This could happen if, for example, the peers are
   too busy or down.  In such instances, the 'E' bit MUST be set in the
   answer message with the Result-Code AVP set to
   DIAMETER_UNABLE_TO_DELIVER to inform the downstream peer to take
   action (e.g., re-routing requests to an alternate peer).

4.1.  Command Code Values

   This section defines Command Code [RFC6733] values that MUST be
   supported by all Diameter implementations conforming to this
   specification.  The following Command Codes are defined in this
   document: Capabilities-Update-Request (CUR, Section 4.1.1), and
   Capabilities-Update-Answer (CUA, Section 4.1.2).  The Diameter
   Command Code Format (CCF) ([RFC6733], Section 3.2) is used in the
   definitions.

4.1.1.  Capabilities-Update-Request

   The Capabilities-Update-Request (CUR), indicated by the Command Code
   set to 328 and the Command Flags' 'R' bit set, is sent to update
   local capabilities.  Upon detection of a transport failure, this
   message MUST NOT be sent to an alternate peer.

   When Diameter is run over the Stream Control Transmission Protocol
   (SCTP) [RFC4960], which allows connections to span multiple
   interfaces and multiple IP addresses, the Capabilities-Update-Request
   message MUST contain one Host-IP-Address AVP for each potential IP
   address that may be locally used when transmitting Diameter messages.

   Message Format

      <CUR> ::= < Diameter Header: 328, REQ >
                { Origin-Host }
                { Origin-Realm }
             1* { Host-IP-Address }
                { Vendor-Id }
                { Product-Name }
                [ Origin-State-Id ]
              * [ Supported-Vendor-Id ]
              * [ Auth-Application-Id ]
              * [ Acct-Application-Id ]
              * [ Vendor-Specific-Application-Id ]
                [ Firmware-Revision ]
              * [ AVP ]

4.1.2.  Capabilities-Update-Answer

   The Capabilities-Update-Answer, indicated by the Command Code set to
   328 and the Command Flags' 'R' bit cleared, is sent in response to a
   CUR message.

                     Message Format

                     <CUA> ::= < Diameter Header: 328 >
                               { Origin-Host }
                               { Origin-Realm }
                               { Result-Code }
                               [ Error-Message ]
                             * [ AVP ]

5.  Security Considerations

   The security considerations applicable to the Diameter base protocol
   [RFC6733] are also applicable to this document.

6.  IANA Considerations

   This section explains the criteria to be used by the IANA for
   assignment of numbers within namespaces used within this document.

6.1.  Application Identifier

   This specification assigns the value 10 (Diameter Capabilities
   Update) from the Application Identifiers namespace [RFC6733].  See
   Section 3 for the assignment of the namespace in this specification.

6.2.  Command Codes

   This specification assigns the value 328 (Capabilities-Update-
   Request/Capabilities-Update-Answer (CUR/CUA)) from the Command Codes
   namespace [RFC6733].  See Section 4.1 for the assignment of the
   namespace in this specification.

7.  Contributors

   This document is based upon work done by Tina Tsou.

8.  Acknowledgements

   Thanks to Sebastien Decugis, Niklas Neumann, Subash Comerica, Lionel
   Morand, Dan Romascanu, Dan Harkins, and Ravi for helpful review and
   discussion.

9.  References

9.1.  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.

9.2.  Informative References

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

Authors' Addresses

   Jiao Kang
   Huawei Technologies
   Section F1, Huawei Industrial Base
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   EMail: kangjiao@huawei.com

   Glen Zorn
   Network Zen
   227/358 Thanon Sanphawut
   Bang Na, Bangkok  10260
   Thailand

   Phone: +66 (0) 909-201060
   EMail: glenzorn@gmail.com