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.
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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
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.
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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
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].
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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
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.
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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
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.
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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
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.
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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
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.
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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
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.
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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
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.
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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
[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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RFC 4064 Experimental Message, Extensions, and Error Codes May 2005
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Patel & Leung Standards Track [Page 11]
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