IETF Mobile IP Working Group Charles E. Perkins
INTERNET DRAFT Nokia Research Center
26 January 2004
Foreign Agent Error Extension for Mobile IPv4
draft-perkins-mip4-faerr-00.txt
Status of This Memo
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Abstract
This document specifies a new extension for use by Foreign Agents
operating Mobile IP for IPv4. The new extension option allows a
foreign agent to supply an error code without disturbing the data
supplied by the Home Agent within the Registration Reply message.
In this way, the mobile node can verify that the Registration
Reply message was generated by the Home Agent even in cases where
the foreign agent is required by protocol to insert new status
information into the Registration Reply message.
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1. Introduction
This document specifies a new non-skippable extension for use
by Foreign Agents operating Mobile IP for IPv4 [2]. The new
extension option allows a foreign agent to supply an error code
without disturbing the data supplied by the Home Agent within the
Registration Reply message. In this way, the mobile node can verify
that the Registration Reply message was generated by the Home Agent
even in cases where the foreign agent is required by protocol to
insert new status information into the Registration Reply message.
2. Terminology
The keywords "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 [1]. Other
terminology is used as already defined in [2].
3. FA Error Extension Format
The format of the FA Error Extension conforms to the Short Extension
format specified for Mobile IPv4 [2]. The FA Error Extension is not
skippable.
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 | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
<To Be Assigned by IANA>
Length
4
Sub-Type
0
Status
A status code used by the foreign agent to supply status
information to the mobile node.
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4. Operation and Use of the FA Error Extension
The FA Error extension is only valid for use within Mobile IPv4
Registration Reply messages. The FA Error Extension is not
skippable. A mobile node that cannot correctly interpret the
contents of the FA Error Extension MUST NOT use the care-of
address provided in the Registration Reply message, until another
Registration Request message has been sent and a successful
Registration Reply message received.
The status codes allowable for use within the FA Error Extension are
as follows:
64 reason unspecified
65 administratively prohibited
66 insufficient resources
68 home agent failed authentication
71 poorly formed Reply
77 invalid care-of address
78 registration timeout
as defined in RFC 3344 [2] for use by the Foreign Agent. Status
codes for use with the FA Error extensions must not be differently
defined for use in the Code field of Registration Reply messages.
When a foreign agent appends a FA Error Extension to the Registration
Reply as received from the Home Agent, it has to update the UDP
Length field in the UDP header [3] to account for the extra 4 bytes
of length.
5. IANA Considerations
This specification reserves one number for the FA Error extension
(see section 3) from the space of numbers for nonskippable mobility
extensions (i.e., 0-127) defined in the specification for Mobile
IPv4 [2].
This specification also creates a new number space of sub-types for
the type number of this extension. Sub-type zero is to be allocated
from this number space for the protocol extension specified in this
document. Future allocations from this number space require IETF
consensus.
6. Security Considerations
The extension in this document improves the security features
of Mobile IPv4 by allowing the mobile node to be assured of the
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authenticity of the information supplied within a Registration
Request. Previously, whenever the foreign agent was required to
provide status information to the mobile node, it could only do so
by destroying the ability of the mobile device to authenticated the
Mobile-Home Authentication Extension data.
References
[1] S. Bradner. Key words for use in RFCs to Indicate Requirement
Levels. Request for Comments (Best Current Practice) 2119,
Internet Engineering Task Force, March 1997.
[2] C. Perkins. IP Mobility Support. Request for Comments (Proposed
Standard) 3344, Internet Engineering Task Force, August 2002.
[3] J. Postel. User Datagram Protocol. Request for Comments
(Standard) 768, Internet Engineering Task Force, August 1980.
Author Address
Questions about this memo can be directed to the author:
Charles E. Perkins
Communications Systems Lab
Nokia Research Center
313 Fairchild Drive
Mountain View, California 94043
USA
Phone: +1-650 625-2986
Fax: +1 650 625-2502
EMail: charles.perkins@.nokia.com
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