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
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