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RFC 4917
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
Sastry, et al. Standards Track [Page 1]
RFC 4917 Mobile IPv4 Message String Extension June 2007
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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RFC 4917 Mobile IPv4 Message String Extension June 2007
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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RFC 4917 Mobile IPv4 Message String Extension June 2007
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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RFC 4917 Mobile IPv4 Message String Extension June 2007
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.
Sastry, et al. Standards Track [Page 5]
RFC 4917 Mobile IPv4 Message String Extension June 2007
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
Sastry, et al. Standards Track [Page 6]
RFC 4917 Mobile IPv4 Message String Extension June 2007
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