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RFC 4064 - Experimental Message, Extensions, and Error Codes for


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Network Working Group                                         A. Patel
Request for Comments: 4064                                    K. Leung
Category: Standards Track                                Cisco Systems
                                                              May 2005

   Experimental Message, Extensions, and Error Codes for Mobile IPv4

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 Internet Society (2005).

Abstract

   Mobile IPv4 message types range from 0 to 255.  This document
   reserves a message type for use by an individual, company, or
   organization for experimental purposes, to evaluate enhancements to
   Mobile IPv4 messages before a formal standards proposal is issued.

Table of Contents

   1.  Introduction .................................................  2
   2.  Terminology ..................................................  3
   3.  Experimental Message .........................................  3
   4.  Experimental Extensions ......................................  4
       4.1.  Non-skippable Mobile IPv4 Experimental Extension .......  5
       4.2.  Non-skippable ICMP Router Discovery Exp. Extension .....  5
       4.3.  Skippable Mobile IPv4 Experimental Extension ...........  6
       4.4.  Skippable ICMP Router Discovery Experimental Extension .  6
   5.  Experimental Error Codes .....................................  7
   6.  Mobility Entity Considerations ...............................  7
   7.  IANA Considerations ..........................................  7
       7.1.  New Message Type .......................................  8
       7.2.  New Extension Values ...................................  8
       7.3.  New Error Codes ........................................  8
   8.  Security Considerations ......................................  8
   9.  Backward Compatibility Considerations ........................  9
   10. Acknowledgements..............................................  9
   11. References ...................................................  9
       11.1. Normative References ...................................  9
       11.2. Informative References .................................  9

1.  Introduction

   Mobile IPv4 message types range from 0 to 255.  This document
   reserves a message type for experimental purposes, to evaluate
   enhancements to Mobile IPv4 messages before a formal standards
   proposal is issued.

   Without experimental message capability, one would have to select a
   type value from the range defined for IANA assignment, which may
   result in collisions.

   Within a message, Mobile IP defines a general extension mechanism
   allowing optional information to be carried by Mobile IP control
   messages.  Extensions are not skippable if defined in the range [0-
   127] and are skippable if defined in the range [128-255].  This
   document reserves extension types in both the skippable and non-
   skippable ranges for experimental use.

   Mobile IPv4 defines error codes for use by the FA [64-127] and HA
   [128-192].  This document reserves an error code in both of these
   ranges for experimental use.

   The definition of experimental numbers in this document is made
   according to the recommendation of Section 2.2 of BCP 82, RFC 3692.

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 [1].

   In addition, this document frequently uses the following terms:

   EXP-MSG-TYPE: A Mobile-IPv4 message number assigned for experimental
   use.  IANA has assigned message number 255 for this.

   EXP-SKIP-EXT-TYPE: A Mobile-IPv4 and ICMP router discovery Agent
   Advertisement extension number assigned for experimental use.  IANA
   has assigned extension number 255 for this.

   EXP-NONSKIP-EXT-TYPE: A Mobile-IPv4 and ICMP router discovery Agent
   Advertisement extension number for experimental use.  IANA has
   assigned extension number 127 for this.

   EXP-HA-ERROR-CODE: A Mobile-IPv4 error code for use by the HA in
   MIPv4 reply messages to indicate an error condition.  IANA has
   assigned error code 192 for this.

   EXP-FA-ERROR-CODE: A Mobile-IPv4 error code for use by FA in reply
   messages to indicate an error condition.  IANA has assigned error
   code 127 for this.

   Mobility Entity: Entities as defined in [2] (home agent, foreign
   agent, and mobile node).

3.  Experimental Message

   As the nature and purpose of an experimental message cannot be known
   in advance, the structure is defined as having an opaque payload.
   Entities implementing the message can interpret the message according
   to their implementation.  Interpreting based on extensions present in
   the message is one suggestion.

   These messages may be used between the mobility entities (Home Agent,
   Foreign Agent, and Mobile Node).  Experimental messages MUST be
   authenticated using any of the authentication mechanisms defined for
   Mobile IP ([2], [5]).

   This message MAY contain extensions defined in Mobile IP, including
   vendor-specific extensions [4].

   IP fields:

      Source Address: Typically the interface address from which
      the message is sent.

      Destination Address: The address of the agent or the Mobile
      Node.

   UDP fields:

      Source Port        Set according to RFC 768 (variable)

      Destination Port   Set to the value 434

   Mobile IP fields shown below follow the UDP header.

   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      |                 Opaque. . .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type       255 (EXP-MSG-TYPE)

   Opaque     Zero or more octets of data, with structure defined only
              by the particular experiment it is used for.

   Once an experimental message has been tested and shown to be useful,
   a permanent number should be obtained through the normal IANA numbers
   assignment procedures.

   A single experimental message type is defined.  This message can
   contain extensions based on which the message can be interpreted.

   Up-to-date values for the message types for Mobile IP control
   messages are specified in the most recent "Assigned Numbers" [3].

4.  Experimental Extensions

   This document reserves Mobile IPv4 extensions in both the skippable
   and non-skippable ranges for experimental purposes.  The long
   extension format (for non-skippable extensions) and short extension
   format (for skippable extensions), as defined by [2], are used for
   Mobile IPv4 experimental extensions.

   Also, ICMP router discovery extension numbers in both the skippable
   and non-skippable ranges are reserved for experimental use.

4.1.  Non-skippable Mobile IPv4 Experimental Extension

   This format is applicable for non-skippable extensions and may carry
   information more than 256 bytes.

   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      |  Sub-Type     |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Opaque. . .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type      127 (EXP-NONSKIP-EXT-TYPE) is the type, which describes an
             experimental extension.

   Sub-Type  A unique number given to each member in the aggregated
             type.

   Length    Indicates the length (in bytes) of the data field within
             this extension.  It does NOT include the Type, Sub-Type,
             and Length fields.

   Opaque    Zero or more octets of data, with structure defined only by
             the particular experiment it is used for.

   As the length field is 16 bits wide, the extension data can exceed
   256 bytes in length.

4.2.  Non-skippable ICMP Router Discovery Exp. Extension

   This format is applicable for non-skippable extensions.

   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     |           Opaque . . .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type     127 (EXP-NONSKIP-EXT-TYPE) is the type, which describes an
            ICMP router discovery experimental extension.

   Length   Indicates the length (in bytes) of the data field within
            this extension.  It does NOT include the Type and Length
            fields.

   Opaque   Zero or more octets of data, with structure defined only by
            the particular experiment it is used for.

   A node that receives a router advertisement with this extension
   should ignore the extension if it does not recognize it.

   A mobility entity that understands this extension but does not
   recognize it should drop (ignore) the router advertisement.

4.3.  Skippable Mobile IPv4 Experimental Extension

   This format is applicable for skippable extensions, which carry
   information less than 256 bytes.

   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    |  Opaque. . .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type     255 (EXP-SKIP-EXT-TYPE) is the type, which describes an
            experimental extension.

   Length   Indicates the length (in bytes) of the data field within
            this extension.  It does NOT include the Type and Length
            fields.

   Sub-Type A unique number given to each member in the aggregated type.

   Opaque   Zero or more octets of data, with structure defined only by
            the particular experiment it is used for.

   As the length field is 8 bits wide, the extension data cannot exceed
   256 bytes in length.

4.4.  Skippable ICMP Router Discovery Experimental Extension

   This format is applicable for skippable ICMP router discovery
   extensions.  This extension should be ignored if an implementation
   does not understand it.

   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     |   Opaque. . .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type     255 (EXP-SKIP-EXT-TYPE) is the type, which describes an
            experimental extension.

   Length   Indicates the length (in bytes) of the data field within
            this extension.  It does NOT include the Type and Length
            fields.

   Opaque   Zero or more octets of data, with structure defined only by
            the particular experiment it is used for.

5.  Experimental Error Codes

   This document reserves the reply error code EXP-FA-ERROR-CODE for use
   by the FA.  This document also reserves the reply error code EXP-HA-
   ERROR-CODE for use by the HA.

   These experimental error codes may be used in registration reply
   messages.

   It is recommended that experimental error codes be used with
   experimental messages and extensions whenever none of the
   standardized error codes are applicable.

6.  Mobility Entity Considerations

   Mobility entities can send and receive experimental messages.
   Implementations that don't understand the message type SHOULD
   silently discard the message.

   Experimental extensions can be carried in experimental messages and
   standards-defined messages.  In the latter case, it is suggested that
   experimental extensions MUST NOT be used in deployed products and
   that usage be restricted to experiments only.

7.  IANA Considerations

   This document defines a control message to be used between mobility
   entities, two new extension formats, and two new error codes.  To
   ensure correct interoperation based on this specification, IANA has
   reserved values in the Mobile IPv4 number space, as defined in [2],
   for one new message type, two new extensions, and two error codes.

7.1.  New Message Type

   A new Mobile IPv4 control message using UDP port 434, type 255 (EXP-
   MSG-TYPE), has been defined by IANA.  This value has been taken from
   the same number space as Mobile IP Registration Request (Type = 1)
   and Mobile IP Registration Reply (Type = 3).

7.2.  New Extension Values

   The following extension types are introduced by this specification:

   Experimental non-skippable extension: The value 127 (EXP-NONSKIP-
   EXT-TYPE) has been assigned from the numbering space for non-
   skippable extensions, which may appear in Mobile IPv4 control
   messages.

   Also, the same number, 127 (EXP-NONSKIP-EXT-TYPE), has been assigned
   from the numbering space for non-skippable extensions, which may
   appear in ICMP router discovery messages.

   Experimental skippable extension: The value 255 (EXP-SKIP-EXT-TYPE)
   has been assigned from the numbering space for skippable extensions,
   which may appear in Mobile IPv4 control messages.

   Also, the same number, 255 (EXP-SKIP-EXT-TYPE), has been assigned
   from the numbering space for skippable extensions, which may appear
   in ICMP router discovery messages.

7.3. New Error Codes

   The value 192 (EXP-HA-ERROR-CODE) has been defined by IANA to be used
   as a code field in messages generated by HA.

   Also, the value 127 (EXP-FA-ERROR-CODE) has been defined by IANA to
   be used as the code field in messages generated by the FA.

8.  Security Considerations

   Like all Mobile IP control messages, the experimental messages MUST
   be authenticated per the requirements specified in [2] or [5].
   Experimental messages without a valid authenticator SHOULD be
   discarded.

9.  Backward Compatibility Considerations

   Mobility entities that don't understand the experimental message MUST
   silently discard it.

   Mobility entities that don't understand the experimental skippable
   extensions MUST ignore them.  Mobility entities that don't understand
   the non-skippable experimental extensions MUST silently discard the
   message containing them.  This behavior is consistent with section
   1.8 of [2].

   Foreign Agents and Home Agents SHOULD include an experimental error
   code in a reply message only if they have a general indication that
   the receiving entity would be able to parse it.  This is indicated if
   the request message was of type EXP-MSG-TYPE or contained at least
   one experimental extension.

10.  Acknowledgements

   The authors would like to acknowledge Henrik Levkowetz for his
   detailed review of the document and suggestion to incorporate
   experimental extensions in this draft.

   The authors would also like to acknowledge Thomas Narten for his
   initial review of the document and reference to [6] for general
   guidelines.

11.  References

11.1.  Normative References

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

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

   [3]  Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an
        On-line Database", RFC 3232, January 2002.

11.2.  Informative References

   [4]  Dommety, G. and K. Leung, "Mobile IP
        Vendor/Organization-Specific Extensions", RFC 3115, April 2001.

   [5]  Perkins, C. and P. Calhoun, "Mobile IPv4 Challenge/Response
        Extensions", RFC 3012, November 2000.

   [6]  Narten, T., "Assigning Experimental and Testing Numbers
        Considered Useful", BCP 82, RFC 3692, January 2004.

Authors' Addresses

   Questions and comments about this document should be directed to the
   Mobile IPv4 working group:

   mip4@ietf.org

   Questions and comments about this document may also be directed to
   the authors:

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

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

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

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

Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   This document is subject to the rights, licenses and restrictions
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