IETF Mobile IP Working Group Charles E. Perkins
INTERNET DRAFT Nokia Research Center
20 September 2005
Foreign Agent Error Extension for Mobile IPv4
draft-ietf-mip4-faerr-02.txt
Status of This Memo
This document is a submission by the IETF MIPv4 Working Group Working
Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the mip4@ietf.org mailing list.
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note
that other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document specifies a new extension for use by Foreign Agents
operating Mobile IP for IPv4. Currently, a foreign agent cannot
supply status information without destroying the ability for a mobile
node to verify authentication data supplied by the home agent. The
new extension solves this problem by making a better place for the
foreign agent to provide its status information to the mobile node.
Perkins Expires 20 March 2006 [Page i]
Internet Draft FA Error Extension 20 September 2005
1. Introduction
This document specifies a new non-skippable extension for use
by Foreign Agents operating Mobile IP for IPv4 [4]. 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 [4].
3. FA Error Extension Format
The format of the FA Error Extension conforms to the Short Extension
format specified for Mobile IPv4 [4]. 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
2
Sub-Type
0
Status
A status code used by the foreign agent to supply status
information to the mobile node.
Perkins Expires 20 March 2006 [Page 1]
Internet Draft FA Error Extension 20 September 2005
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.
Status codes allowable for use within the FA Error Extension are
within the range 64-127. The currently specified codes 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 [4] 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 [5] to account for the extra 4 bytes
of length.
This document updates the Mobile IP base specification [4] regarding
the procedures followed by the foreign agent in the case that the
home agent fails authentication. Instead of modifying the "status"
field of the Registration Reply to contain the value 68, now the
foreign agent should append the Foreign Agent Error Extension
containing the status value 68.
5. Mobile Node Considerations
If a mobile node receives a successful Registration Reply (status
code 0 or 1), with a FA Error extension indicating that the foreign
agent is not honoring said Registration Reply, the mobile node SHOULD
then send a deregistration message to the home agent. In this way,
the home agent will not maintain a registration status that is
inconsistent with the status maintained by the foreign agent.
Perkins Expires 20 March 2006 [Page 2]
Internet Draft FA Error Extension 20 September 2005
6. Foreign Agent Considerations
When denying a successful Registration Reply, the Foreign Agent
SHOULD send the a Registration Revocation message [2] to the Home
Agent if a mobility security association exists between them.
For cases when the foreign agent does have the required security
association, this way of informing the home agent does not have the
vulnerability from detrimental actions by malicious foreign agents as
noted in section 8.
7. IANA Considerations
This specification reserves one number for the FA Error extension
(see section 3) from the space of numbers for non-skippable mobility
extensions (i.e., 0-127) defined in the specification for Mobile
IPv4 [4].
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. Similar to the procedures specified for Mobile IP [4]
number spaces, future allocations from this number space require
expert review[3].
The status codes which are allowable in the FA error extension are a
subset of the status codes defined in the specification for Mobile
IPv4 [4]. If, in the future, additional status codes are defined for
Mobile IPv4, the definition for each new status code must indicate
whether or not the new status code is allowable for use in the FA
Error extension.
8. Security Considerations
The extension in this document improves the security features
of Mobile IPv4 by allowing the mobile node to be assured of the
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 verify the Mobile-Home
Authentication Extension data.
In many common cases, the mobile node will not have a security
association with the foreign agent that has sent the extension.
Thus, the mobile node will be unable to ascertain that the foreign
agent sending the extended Registration Reply message is the same
foreign agent that earlier received the associated Registration
Request from the mobile node. Because of this, a malicious foreign
Perkins Expires 20 March 2006 [Page 3]
Internet Draft FA Error Extension 20 September 2005
agent could cause a mobile node to operate as if the registration had
failed, when in fact its home agent and a correctly operating foreign
agent had both accepted the mobile node's Registration Request. In
order to reduce the vulnerability to such maliciously transmitted
Registration Reply messages with the unauthenticated extension, the
mobile node MAY delay processing of such denied Registration Reply
messages for a short while in order to determine whether another
successful Registration Reply might be received from the foreign
agent.
9. Acknowledgements
Thanks to Kent Leung and Henrik Lefkowetz for suggested improvements
to this specification.
References
[1] S. Bradner. Key words for use in RFCs to Indicate Requirement
Levels. RFC 2119, Internet Engineering Task Force, March 1997.
[2] S. Glass and Madhavi Chandra. Registration Revocation in Mobile
IPv4. RFC 3543, Internet Engineering Task Force, August 2003.
[3] T. Narten and H. Alvestrand. Guidelines for Writing an IANA
Considerations Section in RFCs. RFC 2434, Internet Engineering
Task Force, October 1998.
[4] Charles E. Perkins. IP Mobility Support for IPv4. RFC 3344,
Internet Engineering Task Force, August 2002.
[5] J. B. Postel. User Datagram Protocol. RFC 768, Internet
Engineering Task Force, August 1980.
All references are normative.
Perkins Expires 20 March 2006 [Page 4]
Internet Draft FA Error Extension 20 September 2005
Author Address
Questions about this memo can be directed to the author:
Charles E. Perkins
Networking Technology 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
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the
use of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided
on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
Perkins Expires 20 March 2006 [Page 5]
Internet Draft FA Error Extension 20 September 2005
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Perkins Expires 20 March 2006 [Page 6]
