





Network Working Group                                          V. Sastry
Request for Comments: 4917                           Samsung Electronics
Category: Standards Track                                       K. Leung
                                                                A. Patel
                                                           Cisco Systems
                                                               June 2007


                  Mobile IPv4 Message String Extension

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document specifies a new extension for use in Mobile IPv4.  This
   extension can be added by the Home Agent and the Foreign Agent to
   Registration Reply messages.  This extension carries a text string
   that is intended for the user of the Mobile Node.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................2
   3. Mobile IPv4 Message String Extension Format .....................2
   4. Operation and Use of the Message String Extension ...............3
   5. Security Considerations .........................................4
   6. IANA Considerations .............................................4
   7. Acknowledgements ................................................5
   8. Normative References ............................................5












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1.  Introduction

   This document specifies a new skippable extension that can be added
   by the Foreign Agent and Home Agent in any registration message
   targeted for the Mobile Node.  Such a message may be either a
   Registration Reply or Registration Revocation (i.e., co-located
   Care-of Address mode).  For the Registration Reply message, this
   extension can be added regardless of whether the registration has
   succeeded or failed.

   The content of the text string in this extension and its usage by the
   Mobile Node is implementation specific.  The text string in this
   extension is intended for the user of the Mobile Node.  For example,
   this message can be displayed on the Mobile Node's user interface,
   logged, or handled in any other implementation dependent way,
   depending on the form of the Mobile Node.

   Typical contents of the text string will indicate a registration
   failure reason, or give a welcome message on successful registration.
   This is important, as the failure reason code gives very limited
   information for interpretation by the user of the Mobile Node.  For
   example, a string like "registration failed : Prepaid Quota for the
   user is exhausted" can give a human readable description of the
   result of Mobile IP registration.

2.  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 RFC 2119 [RFC2119].

3.  Mobile IPv4 Message String Extension Format

   The Message String Extension conforms to the Short Extension format
   specified for Mobile IPv4 [RFC3344].  The Message String Extension is
   a skippable extension.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |   Length      |    Sub-Type   |    Text ....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:

      145: An 8-bit identifier of the type mobility option.





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   Length:

      An 8-bit unsigned integer.  Length of the extension, in bytes,
      excluding the extension Type and the extension Length fields.
      This field MUST be set to 1 plus the total length of the Text
      field.

   Sub-Type:

      1: Extension comes from the Home Agent

      2: Extension comes from the Foreign Agent

   Text:

      The Text field is one or more octets, and its contents are
      implementation dependent.  It is intended to be human readable,
      and MUST NOT affect the operation of the protocol.  The message
      MUST be in UTF-8 encoded ISO-10646 [RFC3629] characters.  The
      number of octets in the encoded representation of the message is
      always exactly the value of the Length field minus one.  (The
      number of unicode characters represented by this octet sequence
      may be smaller than the number of octets.)

4.  Operation and Use of the Message String Extension

   The Message String Extension is only valid for use within Mobile IPv4
   Registration Reply and Registration Revocation messages.  The Message
   String Extension is a skippable extension.  Either the Home Agent or
   Foreign Agent or both can add the Message String Extension to
   registration messages.  The usage of Text field of the Message String
   Extension is implementation dependent.  For example, the message can
   be displayed on the Mobile Node's user interface, logged, or handled
   in an implementation dependent way, depending on the form of the
   Mobile Node.  The Mobile Node may throttle how often the user is
   notified of the message.

   As an example, the Home Agent may reject the first Registration
   Request because the prepaid quota for the user is reached and may
   attach a Message String Extension with the text "Prepaid quota
   reached.  Please contact www.paymore.example.com to update balance".
   The Mobile Node could display this on the user interface.  As a
   response, the user of the Mobile Node may take the required action to
   update the prepaid account and retry the registration process.  The
   Home Agent may accept this Registration Request and attach a Message






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   String Extension with the text "Welcome to
   www.serviceprovider.example.com".  The Mobile Node could display this
   on the user interface, thus confirming a successful creation of
   binding on Home Agent.

   In the case that the message is not originated by the Home Agent
   itself, but for instance, is received from a RADIUS server [RFC2865],
   it could be received in some other encoding than UTF-8.  If so, the
   Home Agent MUST convert the message to UTF-8 encoded ISO-10646
   [RFC3629] characters.

5.  Security Considerations

   The Message String Extension can be added by the Home Agent or
   Foreign Agent or both.  The protection of the extension is based on
   the ordering method specified for message authentication in RFC 3344
   [RFC3344] and emphasized below.

   If the extension is added by the Home Agent (extension with subtype
   1) to a Registration Reply or Registration Revocation message, it
   MUST appear before Mobile-Home Authentication Extension [RFC3344].

   If the extension is added by the Foreign Agent (extension with
   subtype 2) to a Registration Reply message, it MUST appear after
   Mobile-Home Authentication Extension [RFC3344] whenever present.
   Also the extension MUST appear before the Mobile-Foreign
   Authentication Extension whenever present.  However, since security
   association between the Mobile Node and Foreign Agent is optional, it
   is possible that the extension is not authenticated in this case.

   There is no confidentiality provided by the extension; the message is
   transferred unencrypted, and if sensitive information is sent for
   display purposes, it may need to be protected by other means.

6.  IANA Considerations

   This specification reserves number 145 for the Message String
   Extension in Section 3 from the space of numbers for skippable
   mobility extensions (i.e., 128-255) defined for Mobile IPv4 [RFC3344]
   at http://www.iana.org/assignments/mobileip-numbers.

   This specification also creates a new subtype space for the type
   number of this extension.  The subtype values 1 and 2 are defined in
   this specification.  The subtype value 1 is reserved for use by the







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   Home Agent and subtype value 2 is reserved for use by the Foreign
   Agent.  Similar to the procedures specified for Mobile IPv4 [RFC3344]
   number spaces, future allocations from this number space require
   expert review [RFC2434].

7.  Acknowledgements

   The authors would like to thank Avi Lior, Curtis Provost, and Henrik
   Levkowetz for their useful comments on an earlier version of this
   document.  Also, Russ Housley, Vidya Narayanan, Blake Ramsdell, Paul
   Hoffman, and Jeff Hutzelman provided justifications to mandate the
   need for only UTF-8 encoding in the message and solicited better
   clarifications in the security considerations section.

8.  Normative References

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

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

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

   [RFC3344]  Perkins, C., Ed., "IP Mobility Support for IPv4", RFC
              3344, August 2002.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.



















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Authors' Addresses

   Venkateshwara Sastry
   Samsung Electronics
   124/C 5th D Cross
   Girinagar I Phase
   Bangalore  560085
   India

   Phone: +91-80-26725942
   EMail: venkat.sastry@gmail.com


   Kent Leung
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   US

   Phone: +1 408-526-5030
   EMail: kleung@cisco.com


   Alpesh Patel
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   US

   Phone: +1 408-853-9580
   EMail: alpesh@cisco.com




















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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

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   contained in BCP 78, and except as set forth therein, the authors
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.







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