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IETF RFC 3846
Mobile IPv4 Extension for Carrying Network Access Identifiers
Last modified on Thursday, June 24th, 2004
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Network Working Group F. Johansson
Request for Comments: 3846 ipUnplugged
Category: Standards Track T. Johansson
Bytemobile
June 2004
Mobile IPv4 Extension for Carrying Network Access Identifiers
 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 © The Internet Society (2004).
Abstract
When a mobile node moves between two foreign networks, it has to be
re-authenticated. If the home network has both multiple
Authentication Authorization and Accounting (AAA) servers and Home
Agents (HAs) in use, the Home AAA server may not have sufficient
information to process the re-authentication correctly (i.e., to
ensure that the same HA continues to be used). This document defines
a Mobile IP extension that carries identities for the Home AAA and HA
servers in the form of Network Access Identifiers (NAIs). The
extension allows a Home Agent to pass its identity (and that of the
Home AAA server) to the mobile node, which can then pass it on to the
local AAA server when changing its point of attachment. This
extension may also be used in other situations requiring
communication of a NAI between Mobile IP nodes.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements terminology . . . . . . . . . . . . . . . . . . . 2
3. NAI Carrying Extension . . . . . . . . . . . . . . . . . . . . 3
3.1. Processing of the NAI Carrying Extension . . . . . . . . 3
4. HA Identity subtype . . . . . . . . . . . . . . . . . . . . . 4
5. AAAH Identity subtype . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
Jhansson & Johansson Standards Track PAGE 1 
RFC 3846 MIPv4 Extension for AAA NAIs June 2004
9. Normative References . . . . . . . . . . . . . . . . . . . . . 6
10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7
11. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 8
1. Introduction
When building networks one would like to be able to have redundancy.
In order to achieve this, one might place multiple AAA servers in one
domain. When a mobile node registers via a visited network, the
authentication will be handled by one of the AAA servers in the home
domain. At a later point, when the mobile node moves to another
visited domain it again has to be authenticated. However, due to the
redundancy offered by the AAA protocol, it can not be guaranteed that
the authentication will be handled by the same AAAH server as the
previous one, which can result in the new AAAH not knowing to which
HA the session was assigned. This document defines a Mobile IP
extension which can be used to distribute the information needed to
resolve this.
Furthermore, the only information that is normally available about
the home agent in the registration request is the IP address as
defined in RFC 3344 [5]. Unfortunately this may not be enough since
some AAA infrastructures (such as Diameter [6]) use realm based
routing; such a AAA infrastructure needs to know the FQDN identity of
the home agent to be able to correctly handle the assignment of the
home agent. A reverse DNS lookup would only disclose the identity of
the Mobile IP interface for that HA IP address, which may or may not
have a one-to-one correspondence with the home agent FQDN identity.
This is a reason for the HA to also include its own identity in the
registration reply. The MIP v4 extension defined in this document
also has a subtype defined by which this may be done. The HA
identity can then be included by the mobile node in later
registration requests when changing the point of attachment.
2. Requirements 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 BCP 14, RFC 2119 [1].
The Mobile IP related terminology described in RFC 3344 [5] is used
in this document. In addition, the following terms are used:
AAAH
One of several possible AAA Servers in the Home Network
Jhansson & Johansson Standards Track PAGE 2
RFC 3846 MIPv4 Extension for AAA NAIs June 2004
FQDN
Fully Qualified Domain Name.
Identity
The identity of a node is equal to its FQDN.
NAI
Network Access Identifier [2].
3. NAI Carrying Extension
This section defines the NAI Carrying Extension which may be used in
Mobile IP Registration Request and Reply messages, and also in Mobile
IP Agent Advertisements [5]. The extension may be used by any node
that wants to send identity information in the form of a NAI [4].
This document also defines some subtype numbers which identify the
specific type of NAI carried in Sections 4 and 5. It is expected
that other types of NAI will be defined by other documents in the
future.
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 | NAI ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 136 (skippable) [5].
Length 8-bit unsigned integer. Length of the extension, in
octets, excluding the extension Type and the extension Length
fields. This field MUST be set to 1 plus the total length of the
NAI field.
Sub-Type This field describes the particular type NAI which is
carried in the NAI field.
NAI Contains the NAI [2] in a string format.
3.1. Processing of the NAI Carrying Extension
When a mobile node or home agent adds a NAI Carrying Extension to a
registration message, the extension MUST appear prior to any
authentication extensions.
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RFC 3846 MIPv4 Extension for AAA NAIs June 2004
In the event the foreign agent adds a NAI Carrying Extension to a
registration message, the extension MUST appear prior to any
authentication extensions added by the FA.
If an HA has appended a NAI Carrying Extension to a Registration
Reply to an MN, and does not receive the NAI extension in subsequent
Registration Request messages from the MN, the HA can assume that the
MN does not understand this NAI extension. In this case, the HA
SHOULD NOT append this NAI extension to further Registration Reply
messages to the MN.
4. HA Identity subtype
The HA identity uses subtype 1 of the NAI Carrying Extension. It
contains the NAI of the HA in the form hostname@realm. Together the
hostname and realm form the complete FQDN (hostname.realm) of the HA.
A Home Agent using this extension MUST provide it in the first
Registration Reply sent to a Mobile Node which is not currently
registered. The extension only need to be included in subsequent
Registration Replies if the same extension is included in
Registration Requests received from the same Mobile Node.
A mobile node using this extension MUST, if it receives it in a
registration reply message, provide it in every subsequent
registration request when re-authentication is needed. Failure to
re-authenticate, for instance because no AAAH can be reached, will
result in termination of the Mobile-IP session. Upon initiation of a
new session a new HA Identity NAI may be provided to the Mobile node,
and the requirement above will apply to the newly received NAI.
If the mobile node requires a specific home agent and it has the NAI
available it MUST provide this extension in its initial registration
request.
A foreign agent which receives the Home Agent NAI by this extension
in a registration request SHOULD include the Home Agent NAI when
requesting Mobile Node authentication through the AAA infrastructure
if the AAA protocol used can carry the information.
5. AAAH Identity subtype
The AAAH identity uses subtype 2 of the NAI Carrying Extension. It
contains the NAI of the home AAA server in the form hostname@realm.
Together the hostname and realm form the complete FQDN
(hostname.realm) of the home AAA server.
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RFC 3846 MIPv4 Extension for AAA NAIs June 2004
If several AAA servers exist in the Home Network, a Home Agent
providing AAAH selection support according to this document MUST
provide the AAAH identity in the first Registration Reply sent to the
Mobile Node. The extension only needs to be included in subsequent
Registration Replies if the same extension is included in
Registration Requests received from the same Mobile Node.
A mobile node SHOULD save the latest AAAH Identity received in a
registration reply message and SHOULD provide the AAAH Identity in
every registration request sent when re-authenticating, for
efficiency reasons. Failure to reach the indicated AAAH during re-
authentication will result in a new AAAH Identity NAI being returned
(which should then be saved and provided in subsequent registration
requests). Similarly, failure to re-authenticate, for instance
because no AAAH can be reached, will result in termination of the
Mobile-IP session; on initiation of a new session, a new AAAH
Identity NAI may be provided to the Mobile Node for re-use during
later re-registrations.
A foreign agent which receives the AAAH NAI by this extension in a
registration request SHOULD include the AAAH NAI provided when
requesting Mobile Node authentication through the AAA infrastructure
if the AAA protocol used can carry the information.
6. Security Considerations
This specification introduces new Mobile IP extensions that are used
to carry mobility agent and AAA server identities, in the form of
Network Access Identifiers. The Mobile IP messages that carry this
extension MUST be authenticated as described in [4], unless other
authentication methods have been agreed upon. Therefore, this
specification does not lessen the security of Mobile IP messages.
It should be noted that the identities sent in the extensions
specified herein MAY be sent in the clear over the network. However,
the authors do not envision that this information would create
security issues.
7. IANA Considerations
This document defines one new mobile IP extension, and one new Mobile
IP extension sub-type numbering space to be managed by IANA.
Section 3 defines a new Mobile IP extension, the Mobile IP NAI
Carrying Extension. The type number for this extension is 136. This
extension introduces a new sub-type numbering space where the values
Jhansson & Johansson Standards Track PAGE 5
RFC 3846 MIPv4 Extension for AAA NAIs June 2004
1 and 2 have been assigned in this document. Approval of new Mobile
IP NAI Carrying Extension sub-type numbers is subject to Expert
Review, and a specification is required [3].
The content and format for this extension is not specific to AAA
NAIs, so if in the future new NAIs are defined which do not strictly
fall within the category of AAA NAIs, they may nevertheless be
accommodated within the subtype numbering space defined for the NAI
Carrying Extension defined in this document.
The NAI Carrying Extension should be assigned a type value from both
the IANA number space for Mobile IPv4 skippable extensions and from
the IANA number space for Mobile IPv4 advertisement extensions.
Ideally, the numbers assigned from these two numbering spaces should
have the same value.
8. Acknowledgements
Thanks to the original authors of the GNAIE document, Mohamed M
Khalil, Emad Qaddoura, Haseeb Akhtar, and Pat R. Calhoun. The
original document was removed from the MIP WG charter when no use was
seen for the extension. The original ideas have been reused in this
document. Also thanks to Henrik Levkowetz and Kevin Purser for
valuable feedback and help when writing this document.
9. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Aboba, B. and M. Beadles, "The Network Access Identifier", RFC
2486, January 1999.
[3] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[4] Calhoun, P. and C. Perkins, "Mobile IP Network Access Identifier
Extension for IPv4", RFC 2794, March 2000.
[5] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August
2002.
[6] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J. Arkko,
"Diameter Base Protocol", RFC 3588, September 2003.
Jhansson & Johansson Standards Track PAGE 6
RFC 3846 MIPv4 Extension for AAA NAIs June 2004
10. Authors' Addresses
Fredrik Johansson
ipUnplugged AB
Arenavagen 23
Stockholm S-121 28
SWEDEN
Phone: +46 8 725 5916
EMail: fredrik@ipunplugged.com
Tony Johansson
Bytemobile Inc
2029 Stierlin Court
Mountain View, CA 94043
USA
Phone: +1 650 862 0523
EMail: tony.johansson@bytemobile.com
Jhansson & Johansson Standards Track PAGE 7
RFC 3846 MIPv4 Extension for AAA NAIs June 2004
11. Full Copyright Statement
Copyright © The Internet Society (2004). 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.
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 THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Jhansson & Johansson Standards Track PAGE 8
Mobile IPv4 Extension for Carrying Network Access Identifiers
RFC TOTAL SIZE: 16834 bytes
PUBLICATION DATE: Thursday, June 24th, 2004
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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