Mobile IPv4 RADIUS Requirements
RFC 5030

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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   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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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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