Network Working Group M. Nakhjiri, Ed.
Request for Comments: 5030 Motorola
Category: Informational K. Chowdhury
Starent Networks
A. Lior
Bridgewater Systems
K. Leung
Cisco Systems
October 2007
Mobile IPv4 RADIUS Requirements
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
This document provides an applicability statement as well as a scope
definition for specifying Remote Authentication Dial-In User Service
(RADIUS) extensions to support Mobile IPv4. The goal is to allow
specification of RADIUS attributes to assist the Mobile IPv4
signaling procedures.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Goals and Non-Goals . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
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1. Introduction
To kick start the Mobile IPv4 [RFC3344] processing of its packets by
Mobile IP agents, a mobile node (MN) needs to be able to acquire a
pair of home and care of addresses (HoA and CoA, respectively), find
a willing agent to act as a Home Agent (HA) for the MN and perform a
registration process with the HA. The registration process consists
of an exchange of a registration request and a registration reply
message between the MN and the HA. The specification in [RFC3344]
allows an MN to start the registration process prior to having
acquired its home address or the address of its HA. Acquiring those
parameters by the MN is typically part of a process referred to as
bootstrapping.
Successful processing of registration request and reply messages,
among other things, depends on successful creation and verification
of a number of authentication extensions developed specifically to
protect the integrity and security of these messages and the entities
processing them, i.e., MN, HA and some times, Foreign Agents (FAs)
[RFC3344]. Creation as well as verification of these extensions
requires existence of trust relationships and shared keys between MN
and each of the mobility agents. However, creation of these trust
relationships, typically referred to as mobility security
associations (MSAs), is considered outside the scope of the base
Mobile IPv4 specification defined in [RFC3344]. Avoiding the
scalability issues arising from creating static security associations
between an MN and all possible mobility agents is desired. Thus,
establishing the associations dynamically, using the pre-existing
relationship between the MN and the AAA server, is preferred.
To allow for utilization of an existing AAA infrastructure in the
bootstrapping of the Mobile IPv4 parameters and security
relationships, the Mobile IPv4 working group has developed Mobile
IPv4 extensions to allow the MN to authenticate to the home AAA
server [RFC4721]. The extensions also allow the MN to request
assistance from the AAA server in creation of mobility security
associations [RFC3957] with the mobility agents, using the pre-
established trust relationship between the MN and its home AAA
server.
While Mobile IPv4 extensions are necessary for implementing a
utilization of the AAA infrastructure for Mobile IPv4 purposes, they
are not sufficient. The interaction between the MN and the mobility
agents (HA and FA) is based on Mobile IP signaling. However, the
signaling beyond the mobility agents to the AAA server is typically
based on AAA protocols. Around the time, when the specification of
the aforementioned Mobile IP extensions was being developed, the AAA
community was in the process of designing a successor to RADIUS.
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RFC 5030 Mobile IPv4 RADIUS Requirements October 2007
Thus, the Mobile IP group developed a set of guidelines and
requirements from the Mobile IP standpoint [RFC2977] specifically for
such a successor (which turned out to be Diameter). These
requirements led to the development of a specification for using
Diameter in Mobile IPv4 bootstrapping [RFC4004]. The requirements
for Mobile IP Authentication, Authorization, and Accounting [RFC2977]
were standardized after the standardization of RADIUS [RFC2865].
Thus, it is obvious that RADIUS does not and cannot meet all the
requirements listed in [RFC2977] without undergoing an extensive
design change. Consequently, within IETF no RADIUS attributes have
been standardized for Mobile IP support thus far. However, in the
absence of IETF standardized RADIUS attributes, different wireless
SDOs have taken the path of developing Vendor Specific Attributes
(VSAs) for providing Mobile IPv4 support. The use of different
vendor specific RADIUS attributes and procedures for the same purpose
of Mobile IPv4 bootstrapping at different SDOs is deemed to cause a
lack interoperability between these wireless standards, potentially
hindering mobility across these wireless networks.
To respond to the described issue, it is desired to standardize a set
of RADIUS attributes within IETF to allow a consistent and
interoperable interaction with RADIUS based AAA infrastructure during
the Mobile IPv4 Registration procedure. The bootstrapping attributes
can include configuration parameters as well as material used for
provisioning security of Mobile IPv4 messaging (authentication) as
defined by [RFC4721] and [RFC3957].
As it stands today, RADIUS cannot meet all the requirements in
[RFC2977]. The purpose of these requirements is to define a set of
goals and non-goals specifically for RADIUS when it comes to
assisting mobile nodes and mobility agents in bootstrapping Mobile
IPv4 operation.
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. Goals and Non-Goals
Since this document serves as a requirement specification for RADIUS
extensions that support Mobile IPv4 interaction with RADIUS
infrastructure, the goals and non-goals refer to only those RADIUS
extensions that are required to support Mobile IPv4.
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RFC 5030 Mobile IPv4 RADIUS Requirements October 2007
3.1. Goals
The scope of the work is to standardize RADIUS attributes and to
define the procedure by which the Mobile IPv4 agents (e.g., Home
agent (HA) and Foreign Agent (FA)) map the Mobile IP registration
message fields into the proposed RADIUS attributes, and vice versa.
o RADIUS servers are REQUIRED to be able to understand and process
the attributes to be defined for Mobile IPv4 support and to
perform verification of authentication extensions specified in
[RFC4721]. RADIUS proxies are expected to be able to forward
messages including the Mobile IPv4 related attributes as they
would with any other RADIUS messages and attributes.
o All RADIUS work MUST be backward compatible with existing RADIUS
RFCs, including RFCs the following: [RFC2865], [RFC2866],
[RFC2867], [RFC2868], [RFC2869], [RFC3576], [RFC3579], and
[RFC3580].
o Mobile IP agents (FA and HA) are REQUIRED to operate as RADIUS
clients (NASes in context of [RFC2865]) when translating RADIUS
signaling into Mobile IP signaling, and vice versa. Details on
the behavior of Mobile IP agents as RADIUS clients are to be
provided by the solution document describing the RADIUS extensions
for Mobile IP support.
3.2. Non-Goals
The scope of this work is to only standardize RADIUS attributes and
to define the procedure by which the Mobile IPv4 agents (e.g., Home
agent (HA) and Foreign Agent (FA)) map the Mobile IP registration
message fields into the proposed RADIUS attributes, and vice versa.
Extension of the functionality of the existing protocol or RADIUS
servers is not intended. More specifically, the following are NON-
GOALS:
o Enhancing RADIUS Security: Creating new security properties for
RADIUS, such as creating key transport capabilities is not the
goal. No new security mechanisms are to be defined for the
transport of RADIUS Access Requests in relation to the support of
Mobile IPv4 bootstrapping. Existing RADIUS authentication
procedures, e.g., Message-Authenticator (80) described in
[RFC2869], are used. The security considerations for using RADIUS
in bootstrapping Mobile IPv4 are described in a later section of
this document.
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o Enhancing RADIUS transport reliability: The transport properties
of RADIUS remain intact. No new reliability mechanisms are
defined in the transport of such Access Requests.
o Extending RADIUS message set: RADIUS extensions for bootstrapping
Mobile IPv4 are not to define new RADIUS messages. The Diameter
Mobile IP application [RFC4004] has defined new command codes to
support Mobile IP signaling, depending on whether Diameter server
is dealing with a Mobile IP HA or an FA. RADIUS currently does
not have any messages that correspond to these Diameter commands.
Instead, RADIUS extensions for Mobile IPv4 bootstrapping need to
provide proposals for new RADIUS attributes that facilitate
Diameter-RADIUS messaging translation without defining any new
RADIUS messaging. At the same time, the RADIUS extensions for
Mobile IPv4 need to re-use Diameter AVPs to the fullest extent
possible.
o RFC 2977 compatibility: Extending RADIUS in a way that fulfills
the full list of requirements in [RFC2977] will not be attempted.
4. Attributes
A specification of the RADIUS extensions for Mobile IPv4 needs to
describe the full set of attributes required for RADIUS-Mobile IP
interaction. While some of the attributes may already be
standardized, others will require standardization and IANA type
assignments.
5. IANA Considerations
This requirement document does not allocate any numbers, so there are
no IANA considerations. On the other hand, future solution documents
for RADIUS support of Mobile IPv4 will likely introduce new RADIUS
attributes. Thus, those documents will need new attribute type
numbers assigned by IANA.
6. Security Considerations
Enhancing security properties of RADIUS are a specific non-goal for
the RADIUS extensions providing support for Mobile IP. Also, as this
is a requirements document and not a solution specification document,
no new security considerations are noted, aside from those that
already exist for RADIUS. As such, the existing RADIUS security
considerations described previously apply, and no additional security
considerations are added here. For instance, the assumption in
RADIUS is that intermediary nodes are trusted, while at the same time
there is a concern on using AAA protocols that use hop-by-hop
security to distribute keys. Use of hop-by-hop security for key
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distribution can be in conflict with some of the requirements stated
in [RFC4962], such as the requirement on binding a key to its context
and the requirement on limitation of the key scope. The former for
instance states that a key MUST be bound to the parties that are
expected to have access to the keying material, while the latter
implies that parties that do not require access to a key to perform
their role MUST not have access to the key. Both of these
requirements rule against trusting intermediary nodes and proxies
with distribution of keys. Due to lack of end-to-end security
mechanisms for RADIUS, imposing a MUST requirement for not trusting
proxies is not possible. The RADIUS Extension working group is in
the process of specifying procedures for wrapping key materials
within RADIUS attributes. For the time being, support of Mobile IP
within RADIUS may need to be based on trust of intermediaries,
despite the security considerations described.
When it comes to protecting attributes in the Access Request,
[RFC2868], Section 3.5 provides a mechanism for encrypting RADIUS
attributes, such as passwords. There is also work under progress for
specifying wrapping of sensitive attributes, such as key material
within RADIUS Access Accept messages. This work is currently
considered part of RADIUS crypto-agility extensions and when
completed can be used in the process of distributing sensitive
attributes, such as keying material from RADIUS servers.
It is also possible to protect RADIUS transactions using IPsec (e.g.,
as in RFC3579).
7. Acknowledgements
The authors would like to thank Alan DeKok for review and feedback,
and Pete McCann and Jari Arkko for diligent shepherding of this
document.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
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[RFC2867] Zorn, G., Aboba, B., and D. Mitton, "RADIUS Accounting
Modifications for Tunnel Protocol Support", RFC 2867,
June 2000.
[RFC2977] Glass, S., Hiller, T., Jacobs, S., and C. Perkins, "Mobile
IP Authentication, Authorization, and Accounting
Requirements", RFC 2977, October 2000.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[RFC3957] Perkins, C. and P. Calhoun, "Authentication,
Authorization, and Accounting (AAA) Registration Keys for
Mobile IPv4", RFC 3957, March 2005.
[RFC4004] Calhoun, P., Johansson, T., Perkins, C., Hiller, T., and
P. McCann, "Diameter Mobile IPv4 Application", RFC 4004,
August 2005.
[RFC4721] Perkins, C., Calhoun, P., and J. Bharatia, "Mobile IPv4
Challenge/Response Extensions (Revised)", RFC 4721,
January 2007.
[RFC4962] Housley, R. and B. Aboba, "Guidance for Authentication,
Authorization, and Accounting (AAA) Key Management",
BCP 132, RFC 4962, July 2007.
8.2. Informative References
[RFC2868] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege,
M., and I. Goyret, "RADIUS Attributes for Tunnel Protocol
Support", RFC 2868, June 2000.
[RFC2869] Rigney, C., Willats, W., and P. Calhoun, "RADIUS
Extensions", RFC 2869, June 2000.
[RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 3576,
July 2003.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.
[RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,
"IEEE 802.1X Remote Authentication Dial In User Service
(RADIUS) Usage Guidelines", RFC 3580, September 2003.
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Authors' Addresses
Madjid Nakhjiri (editor)
Motorola
EMail: madjid.nakhjiri@motorola.com
Kuntal Chowdhury
Starent Networks
EMail: kchowdhury@starentnetworks.com
Avi Lior
Bridgewater Systems
EMail: avi@bridgewatersystems.com
Kent Leung
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
US
EMail: kleung@cisco.com
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RFC 5030 Mobile IPv4 RADIUS Requirements October 2007
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Nakhjiri, et al. Informational [Page 9]
