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IETF RFC 2794
Mobile IP Network Access Identifier Extension for IPv4
Last modified on Friday, April 7th, 2000
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Network Working Group P. Calhoun
Request for Comments: 2794 Sun Microsystems Laboratories
Updates: 2290 C. Perkins
Category: Standards Track Nokia Research Center
March 2000
Mobile IP Network Access Identifier Extension for 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 © The Internet Society (2000). All Rights Reserved.
Abstract
AAA servers are in use within the Internet today to provide
authentication and authorization services for dial-up computers.
Such services are likely to be equally valuable for mobile nodes
using Mobile IP when the nodes are attempting to connect to foreign
domains with AAA servers. AAA servers today identify clients by
using the Network Access Identifier (NAI). Our proposal defines a way
for the mobile node to identify itself, by including the NAI along
with the Mobile IP Registration Request. This memo also updates RFC
2290 which specifies the Mobile-IPv4 Configuration option for IPCP,
by allowing the Mobile Node's Home Address field of this option to be
zero.
Calhoun & Perkins Standards Track PAGE 1 
RFC 2794 Mobile Node NAI March 2000
1. Introduction
AAA servers are in use within the Internet today to provide
authentication and authorization services for dial-up computers.
Such services are likely to be equally valuable for mobile nodes
using Mobile IP when the nodes are attempting to connect to foreign
domains with AAA servers. AAA servers today identify clients by
using the Network Access Identifier (NAI) [1]. This document
specifies the Mobile Node NAI extension to the Mobile IP Registration
Request [7] message from the mobile node.
Since the NAI is typically used to uniquely identify the mobile node,
the mobile node's home address is not always necessary to provide
that function. Thus, it is possible for a mobile node to
authenticate itself, and be authorized for connection to the foreign
domain, without even having a home address. A message containing the
Mobile Node NAI extension MAY set the Home Address field to zero (0)
in the Registration Request, to request that a home address be
assigned.
The "Mobile-IPv4 Configuration" option to IPCP has been specified in
RFC 2290 [8] for proper interaction between a mobile node and a peer,
through which the mobile node connects to the network using PPP.
According to that specification the Mobile Node's Home Address field
of the option MUST not be zero. However, in the context of this memo
which allows a mobile node to be identified by its NAI and to obtain
an address after the PPP phase of connection establishment, the Home
Address field is allowed to be zero while maintaining all other
aspects of RFC 2290. Interpretation of various scenarios from RFC
2290 is given in section 4.
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 [3].
2. Mobile Node NAI Extension
The Mobile Node NAI extension, shown in figure 1, contains the user
name following the format defined in [1]. When it is present in the
Registration Request, the Home Address field MAY be set to zero (0).
The Mobile Node NAI extension MUST appear in the Registration Request
before both the Mobile-Home Authentication extension and Mobile-
Foreign Authentication extension, if present.
Calhoun & Perkins Standards Track PAGE 2
RFC 2794 Mobile Node NAI March 2000
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 | MN-NAI ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The Mobile Node NAI Extension
Type 131 (skippable) [7]
Length The length in bytes of the MN-NAI field
MN-NAI A string in the NAI format defined in [1].
3. Foreign Agent Considerations
If Home Address is zero in the Registration Request, the foreign
agent MUST use the NAI instead in its pending registration request
records, along with the Identification field as usual. If the
foreign agent cannot manage pending registration request records in
this way, it MUST return a Registration Reply with Code indicating
NONZERO_HOMEADDR_REQD (see section 5).
If the mobile node includes the Mobile Node NAI extension in its
Registration Request, then the Registration Reply from the home agent
MUST include the Mobile Node NAI extension. If not, the foreign
agent SHOULD send the Registration Reply to the mobile node, changing
the Code to the value MISSING_NAI (see section 5). The Registration
Reply MUST include a nonzero Home Agent address and mobile node's
Home Address. If not, the foreign agent SHOULD send the Registration
Reply to the mobile node, changing the Code to the value
MISSING_HOME_AGENT or MISSING_HOMEADDR, respectively (see section 5).
4. Interactions with Mobile-IPv4 Configuration Option to IPCP
In the Mobile-IPv4 Configuration Option to IPCP [8], the Mobile
Node's Home Address field may be zero. In this section, we specify
the action to be taken in that case, when the mobile node is using
the Mobile Node NAI extension in the Mobile IP Registration Request.
Whether or not the IP Address Configuration Option contains a nonzero
IP address, the mobile node will subsequently attempt to obtain a
home address from the Mobile IP Registration Reply.
If the IP Address Configuration Option to IPCP has IP address equal
to zero, the PPP peer is expected to allocate and assign a co-located
care-of address to the Mobile Node. If, on the other hand, the IP
Calhoun & Perkins Standards Track PAGE 3
RFC 2794 Mobile Node NAI March 2000
Address Configuration Option to IPCP has a nonzero IP address, the
PPP peer is expected to assign that address to the Mobile Node as its
co-located care-of address.
Finally, if the IP Address Configuration Option is left out of the
IPCP Configure-Request, then no co-located care of address is
assigned during IPCP. The mobile node will acquire a co-located care
of address during a later stage of configuration or will use an FA-
located care-of address.
5. Error Values
Each entry in the following table contains the name and value for the
Code [7] to be returned in a Registration Reply, and the section in
which the error Code is first mentioned in this specification.
Error Name Value Section of Document
---------------------- ----- -------------------
NONZERO_HOMEADDR_REQD 96 3
MISSING_NAI 97 3
MISSING_HOME_AGENT 98 3
MISSING_HOMEADDR 99 3
6. IANA Considerations
The Mobile Node NAI extension defined in Section 2 is a Mobile IP
registration extension as defined in RFC 2002 [7] and extended in RFC
2356 [6]. IANA should assign a value of 131 for this purpose.
The Code values defined in Section 5 are error codes as defined in
RFC 2002 and extended in RFC 2344 [5] and RFC 2356 [6]. They
correspond to error values conventionally associated with rejection
by the foreign agent (i.e., values from the range 64-127). IANA
should record the values as defined in Section 5.
7. Security Considerations
Mobile IP registration messages are authenticated, and the
authentication verified by the recipient. This proposal does not
prohibit the mobile node from sending its NAI in the clear over the
network, but that is not expected to be a security issue.
8. IPv6 Considerations
Supporting NAI-based registrations for Mobile IPv6 [4] is outside the
scope of this document. This section contains some ideas how
Stateless Address Autoconfiguration [9] and DHCPv6 [2] might be
extended to support NAI-based Mobile IPv6 registrations.
Calhoun & Perkins Standards Track PAGE 4
RFC 2794 Mobile Node NAI March 2000
For mobile nodes using IPv6, there are no commonly deployed
mechanisms by which a mobile node may present its credentials, such
as exist today with IPv4. Nevertheless, a mobile node using IPv6
mobility may wish to specify the domain in which their credentials
may be checked, by using a NAI just as this specification proposes
for IPv4. In the case of IPv6, however, there is no foreign agent in
place to manage the connectivity of the mobile node, and thus to
manage the verification of the credentials offered by the mobile
node. To identify the HDAF (see appendix A) that has the expected
relationship with the mobile node, the NAI would have to be forwarded
to a local AAA by the local agent involved with configuring the
care-of address of the mobile node.
This agent can either be a router sending out Router Advertisements
[9], or a DHCPv6 server. In the former case, the router could signal
its ability to handle the NAI by attaching some yet to be defined
option to the Router Advertisement. In the latter case, for managed
links, the mobile node could include a yet to be defined NAI
extension in its DHCP Solicitation message. Such an NAI extension
and appropriate authentication would also be required on the
subsequent DHCP Request sent by the mobile node to the DHCP Server
selected on the basis of received DHCP Advertisements. Once a care-
of address on the foreign network has been obtained, the mobile node
can use regular MIPv6 [4].
9. Acknowledgements
The authors would like to thank Gabriel Montenegro and Vipul Gupta
for their useful discussions. Thanks to Basaravaj Patil and Pete
McCann for text describing actions to be taken when the home address
is zero but the mobile node wishes to use the Mobile-IPv4
Configuration Option to IPCP defined in RFC 2290.
References
[1] Aboba, B. and M. Beadles, "The Network Access Identifier", RFC
2486, January 1999.
[2] Bound, J. and C. Perkins, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", Work in Progress.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Johnson, D. and C. Perkins "Mobility Support in IPv6", Work in
Progress.
Calhoun & Perkins Standards Track PAGE 5
RFC 2794 Mobile Node NAI March 2000
[5] Montenegro, G., "Reverse Tunneling for Mobile IP", RFC 2344, May
1998.
[6] Montenegro, G. and V. Gupta, "Sun's SKIP Firewall Traversal for
Mobile IP", RFC 2356, June 1998.
[7] Perkins, C., "IP Mobility Support", RFC 2002, October 1996.
[8] Solomon, J. and S. Glass, "Mobile-IPv4 Configuration Option for
PPP IPCP", RFC 2290, February 1998.
[9] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
Calhoun & Perkins Standards Track PAGE 6
RFC 2794 Mobile Node NAI March 2000
A. Home Domain Allocation Function (HDAF)
This appendix introduces a new function named the Home Domain
Allocation Function (HDAF) that can dynamically assign a Home Address
to the mobile node.
Figure 2 illustrates the Home HDAF, which receives messages from
foreign agents (e.g., FA) and assigns a Home Address within the Home
Domain. The HDAF does not perform any Mobile IP processing on the
Registration Request, but simply forwards the request to a Home Agent
(HA) within the network that is able to handle the request.
+------+
| |
+---+ HA-1 |
+------+ +------+ +------+ | | |
| | | | | | | +------+
| MN |-------| FA |-------| HDAF +---+ ...
| | | | | | | +------+
+------+ +------+ +------+ | | |
+---+ HA-n |
| |
+------+
Figure 2: Home Domain Allocator Function (HDAF)
Upon receipt of the Registration Request from the mobile node (MN),
FA extracts the NAI and finds the domain name associated with it. FA
then finds the HDAF that handles requests for the mobile node's
domain. The discovery protocol is outside of the scope of this
specification. As an example, however, FA might delegate the duty of
finding a HDAF to a local AAA server. The local AAA server may also
assist FA in the process of verifying the credentials of the mobile
node, using protocols not specified in this document.
Calhoun & Perkins Standards Track PAGE 7
RFC 2794 Mobile Node NAI March 2000
Addresses
The working group can be contacted via the current chairs:
Basavaraj Patil
Nokia Corporation
6000 Connection Drive
M/S M8-540
Irving, TX 75039
USA
Phone: +1 972-894-6709
Fax : +1 972-894-5349
EMail: Basavaraj.Patil@nokia.com
Phil Roberts
Motorola
1501 West Shure Drive
Arlington Heights, IL 60004
USA
Phone: +1 847-632-3148
EMail: QA3445@email.mot.com
Questions about this memo can be directed to:
Charles E. Perkins
Nokia Research Center
313 Fairchild Drive
Mountain View, California 94043
USA
Phone: +1-650 625-2986
Fax: +1 650 625-2502
EMail: charliep@iprg.nokia.com
Pat R. Calhoun
Sun Microsystems Laboratories
15 Network Circle
Menlo Park, California 94025
USA
Phone: +1 650-786-7733
Fax: +1 650-786-6445
EMail: pcalhoun@eng.sun.com
Calhoun & Perkins Standards Track PAGE 8
RFC 2794 Mobile Node NAI March 2000
Full Copyright Statement
Copyright © The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
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The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Calhoun & Perkins Standards Track PAGE 9
Mobile IP Network Access Identifier Extension for IPv4
RFC TOTAL SIZE: 16960 bytes
PUBLICATION DATE: Friday, April 7th, 2000
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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