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Versions: 00 01 02 03 04 05 06                                          
Internet-Draft                                   Yoshihiro Ohba (Editor)
Expires: October, 2003                                         Subir Das
                                                         Basavaraj Patil
                                                          Hesham Soliman
                                                             Alper Yegin


                                                           April 8, 2003


             Problem Statement and Usage Scenarios for PANA

                <draft-ietf-pana-usage-scenarios-05.txt>


Status of This Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.

   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 addresses a set of problems which a network layer
   protocol called PANA (Protocol for carrying Authentication for
   Network Access) is trying to solve in the area of network access
   authentication and describes several usage scenarios where PANA is
   applicable.  It also helps to facilitate the discussion for PANA
   requirements and security threat analysis that are used as basis of
   actual PANA protocol design.














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Table of Contents

   1         Introduction ............................................ 2
   2.        Acronyms ................................................ 2
   3.        Problem Statement ....................................... 3
   4.        Usage Scenarios ......................................... 5
   4.1.      PANA with Physical Layer Security ....................... 5
   4.2.      PANA with Link-Layer Security ........................... 5
   4.3.      PANA in the Absence of Any Lower-Layer Security ......... 6
   4.4.      Mobile IP ............................................... 7
   4.5.      Personal Area Networks .................................. 7
   4.6.      Limited Free Access ..................................... 8
   5.        Security Considerations ................................. 9
   6.        Acknowledgments ......................................... 9
   7.        References .............................................. 9
   7.1.      Normative References .................................... 9
   7.2.      Informative References ................................. 10
   8.        Authors' Information ................................... 10
   9.        Intellectual Property Notices .......................... 10
   10.       Copyright Notice ....................................... 11


1  Introduction

   Networks in most cases require some form of authentication in order
   to prevent unauthorized access.  Only authenticated and authorized
   clients should be able to attach to an access network for sending and
   receiving IP packets.

   There are various mechanisms to provide this required functionality.
   In its simplest form, unintended clients can be physically kept away
   from the access networks.  But there exist some scenarios where a
   solution based on physical security might not be practical.  Public
   access networks and wireless networks are such examples.  In the
   absence of physical security (and sometimes in addition to it) a
   higher layer access authentication mechanism is needed.  Link-layer
   based authentication mechanisms are used whenever they can serve the
   needs of a particular deployment.  However, not all link-layers
   support multiple authentication methods or allow independent
   authentications for the link access and Internet service providers.
   A higher layer authentication mechanism is needed whenever such
   additional requirements are not met by the underlying link-layers.
   Generally a network or higher layer mechanism can be used instead of
   or in addition to available link-layer and physical security.
   Currently there is not a standard protocol to perform network access
   authentication above the link-layer.  Instead, a number of ad-hoc and
   inadequate solutions are being used.  PANA will be developed to fill
   this gap by defining a network-layer access authentication protocol.

   This I-D discusses the need for a standard network access
   authentication protocol and covers various usage scenarios where such
   a protocol is applicable.


2.  Acronyms

   AAA: Authentication, Authorization and Accounting



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   DSL: Digital Subscriber Line

   EAP: Extensible Authentication Protocol

   GPRS: General Packet Radio Service

   HDLC: High-level Data Link Control

   IKE: Internet Key Exchange

   ISP: Internet Service Provider

   MSC: Mobile Switching Center

   MN: Mobile Node

   MT: Mobile Termination

   NAI: Network Access Identifier

   NAP: Network Access Provider

   PPP: Point-to-Point Protocol

   PPPoE: PPP over Ethernet

   TE: Terminal Equipment

   UE: User Equipment

   VLR: Visiting Location Register


3.  Problem Statement

   Access networks usually require clients to go through an
   authentication and authorization process.  Network access
   authentication of clients necessitates a protocol between the client
   and the network to execute one or more authentication methods (e.g.,
   CHAP, TLS, SIM, etc.).  In the light of proliferation of various
   access technologies (e.g., GPRS, IEEE 802.11, DSL, etc.), it is
   important that the authentication methods are not tied to the
   underlying link-layer.  An authentication protocol must be able to
   carry various authentication methods regardless of the underlying
   access technologies.

   Some deployment scenarios require a separation between a network
   access provider (NAP) and an Internet service provider (ISP), where
   the NAP provides physical and link-layer connectivity to an access
   network it manages, and the ISP provides Internet connectivity for
   the NAP.  An important aspect of network access is the ability to
   enable dynamic ISP selection during the initial connection process.
   This is usually achieved by either using link-layer specific
   selectors during link establishment or presenting a client identifier
   which carries ISP domain information during the authentication
   process.  An example of such client identifier would be the
   NAI[RFC2486] (e.g., john@anyisp.com.)  The authentication agent in



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   the access network would consult the backend authentication servers
   in the given domain, and the respective ISP service will be used once
   the client access is authorized.  This is also essential in providing
   roaming service to clients.  A single authentication between the
   client and the ISP is generally sufficient for both NAP and ISP
   access by relying on the pre-established trust relation between the
   NAP and the ISP.  Nevertheless, there are some scenarios where NAPs
   and ISPs require their independent authentication with the client.
   If the NAP authentication is performed using a link-layer mechanism,
   ISP authentication can be left to a network-layer mechanism.  An
   example of a multi-layer authentication can be seen in cdma2000
   networks as described in section 4.2.

   The Extensible Authentication Protocol (EAP) [RFC2284bis] offers a
   natural way to encapsulate many different authentication methods.
   Among all the link-layers, only IEEE 802 defines how to carry EAP on
   the link-layer [802.1X].  Any other link-layer has to resort to using
   PPP/PPPoE [RFC1661,RFC2516] as a link-layer agnostic way of carrying
   EAP. The ungainly insertion of this extra layer incurs additional
   round-trips at connection time, generates overhead of PPP processing
   even for subsequent data packets, and forces the network topology
   into a point-to-point model. EAP could achieve greater applicability
   if it could be carried directly over IP. That way, the resulting IP
   packets could be carried over any link technology without incurring
   additional cost or limitation on the architectures.

   In general terms, PANA will be defined as a network-layer transport
   for EAP.  PANA can be used over any link-layer.  The primary purpose
   of PANA is to authenticate a client to a server for the purpose of
   network access.  Initial client authentication needs to be bound to
   subsequent traffic to prevent spoofing of data packets and resulting
   service theft.  Therefore, this authentication might be required to
   generate cryptographic keying material unless presence of a secure
   physical or link-layer channel is assured prior to it.  The task of
   generating and distributing such keying material can be accomplished
   by various authentication methods carried by EAP.  Once the keying
   material is present, it can be used with link-layer ciphers or IPsec
   for providing subsequent per-packet authentication.  It should be
   noted that the keying material produced by the authentication methods
   is generally not readily usable by IPsec.  A key exchange protocol
   like IKE [RFC2409] might be used to create the required IPsec
   security associations.  The mechanisms that are used to turn keying
   material produced by the initial authentication method into link-
   layer or network-layer ciphers are outside the scope of PANA
   protocol.

   Until a standard solution like PANA is developed, architectures that
   use neither IEEE 802 nor PPP as link-layers are forced to design
   their own ad-hoc mechanisms to the problem.  One such mechanism is
   the application-layer authentication method implemented by http
   redirects and web-based login.  In addition to being a non-standard
   solution, this provides an incomplete network access authentication
   with well-known vulnerabilities, and therefore is regarded as a stop-
   gap mechanism.

   Another method designed to provide network access authentication is
   based on overloading an existing network-layer protocol.  The Mobile



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   IPv4 [RFC3344] protocol has a built-in authentication mechanism.
   Regardless of whether mobile nodes need to use a foreign agent in an
   access network, registration via a foreign agent can be required by
   using an appropriate flag in the agent advertisements.  This forces
   the nodes to register with a foreign agent, and therefore utilizes
   Mobile IPv4 for network access authentication.  Such a solution has
   very limited applicability as a link-layer agnostic method since it
   relies on the deployment of the Mobile IPv4 protocol.


4.  Usage Scenarios

   In this section, the first three subsections describe generic PANA
   usage scenarios categorized in terms of lower-layer security.  The
   remaining subsections describe specific scenarios for Mobile IP,
   personal area networks, and limited free access.


4.1.  PANA with Physical Layer Security

   Even in networks where a certain degree of security is provided at
   the physical layer, authenticating the client may still be essential
   if the physical layer does not provide identification information on
   the client.  However, per-packet authentication and encryption may
   not be necessary.  DSL networks that are implemented on top of point-
   to-point phone lines are such an example.  In this type of networks,
   PANA can be used for client authentication and a hook to an
   appropriate access control.

   In DSL networks, there are a number of deployment scenarios with
   regard to client configuration and client authentication.  In DSL
   networks where PPP or PPPoE is used for both configuration and
   authentication, PANA may not be required.  On the other hand, there
   are some DSL networks that use some configuration method other than
   PPP or PPPoE, i.e., DHCP or static configuration.  Those networks use
   either an ad-hoc network access authentication method such as http-
   redirect with web-based login or no authentication method at all.  A
   standard, link-layer agnostic network access authentication would be
   an improvement for this type of network.  In addition, the variation
   in DSL deployment scenarios, particularly the variation in physical
   topology between DSL modem and ISP edge router, makes it difficult to
   define a single authentication scheme which operates at the link-
   layer and works with any physical topology.  It is highly possible
   that a link-layer agnostic, single network access authentication
   solution will be demanded for future DSL deployments as long as the
   variation is supposed to exist.


4.2.  PANA with Link-Layer Security

   Certain cellular link-layers such as GSM and cdma2000 provide their
   own authentication mechanisms as well as ciphering of data sent over
   the air interface.  This technology specific authentication enables
   authorization for link access by the NAP, and can provide per-packet
   authentication, integrity and replay protection at the link-layer.
   However, it does not necessarily provide authorization at the
   network-layer which can only be done by authenticating the client to



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   an ISP.  So, this necessitates another layer of authentication.  It
   should be noted that this second authentication takes place over a
   secure channel.

   cdma2000 is a good example of such an architecture where multi-
   layered authentication for network access takes place.  cdma2000
   networks require the user/device to authenticate with the MSC/VLR
   before providing access to the packet data network.  The technology
   specific access authentication which uses the CAVE (cellular
   authentication and voice encryption) algorithm also provides cipher
   keys to the mobile and the base station for securing the link layer
   for all subsequent voice and data carried on the air interface.  In
   the Simple IP mode of cdma2000 service, the ISP authentication is
   provided by using CHAP within PPP.  In the Mobile IP mode of
   cdma2000, the Mobile IPv4 protocol supports a challenge/response
   style authentication.

   As this architecture evolves, PANA could be supported as a single
   unifying network-layer authentication mechanism.  This would replace
   both CHAP, which would allow for potential evolution of the link-
   layer away from PPP, and the challenge/response style authentication
   in Mobile IPv4, which is important because Mobile IPv6 does not
   support the foreign agent concept.


4.3.  PANA in the Absence of Any Lower-Layer Security

   There are scenarios where neither physical nor link-layer access
   control is available on the network.  One possible cause of this
   scenario is due to the lack of adequate client authentication
   capabilities (i.e., authentication methods) on the link-layer
   technology being used even when the link-layer has sufficient cipher
   suite support.  It is desirable to support various authentication
   methods without being limited to the ones that are specific to the
   underlying technology.  Another cause of missing lower-layer
   authentication is due to the difficulty of deployment.  For example,
   physical security is not practical for public access wireless
   networks.

   In the absence of such lower-layer security and authentication
   mechanism not only providers are unable to control the unauthorized
   use of their networks but also users feel insecure while exchanging
   sensitive information.  In order to support authentication
   functionality in such systems, many providers today use a higher-
   layer authentication scheme, such as http-redirect commonly known as
   web-based login.  In this method, once the link is established,
   users' traffic are re-directed to a web server which in turn
   generates a web-based login forcing users to provide the
   authentication information.  While this method solves the problem
   partially by allowing only authorized users to access the network, it
   however does not enable the lower-layer security such as, per-packet
   authentication and encryption, etc.  Moreover, it is a non-standard
   ad hoc solution that provides only limited authentication method
   support.

   In such scenarios, a standard mechanism is necessary which can
   provide network access authentication irrespective of whether the



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   underlying layers are secured or not.  A solution like PANA at the
   network layer may be adequate if it can specify appropriate
   authentication methods that can derive and distribute keys for
   authentication, integrity and confidentiality of data traffic either
   at the link or at the network layer.  For example, if link-layer does
   not support the desired authentication method but supports ciphering,
   PANA can be used to bootstrap the latter.  On the other hand, if
   link-layer neither supports the desired authentication method nor
   ciphering, PANA can be used to bootstrap higher layer security
   protocols, such as, IKE and IPsec.  Thus successful PANA
   authentication can result to a secured network environment although
   the underlying layers were not secured at the beginning.  Also
   assuming PANA will provide support to various authentication schemes,
   providers will have advantage using a single framework across
   multiple environments.


4.4.  Mobile IP

   Mobile IPv4 defines its own authentication extensions to authenticate
   and authorize mobile nodes at the foreign agents and home agents.
   One of the possible modes of Mobile IPv4 is used when the mobile node
   uses a co-located care-of address and doesn't rely on any mobility
   management functionality of the foreign agent on the access network.
   In this case, mobile node can send its registration request directly
   to the home agent.  Even in the co-located care-of address case, the
   protocol has a way to require mobile nodes to register with a foreign
   agent by setting Registration-Required bit in the agent
   advertisements.  This forces mobile nodes to send their registration
   requests via the foreign agent, even though they do not have to
   interact with that agent otherwise.

   This type of Mobile IP registrations are used for performing network
   access authentication.  This method can only be used in IPv4 networks
   where every client implements mobile node functionality.  Even for
   IPv4 clients, a better approach would be to replace this protocol-
   specific authentication method by a common authentication protocol
   such as PANA.  PANA can be used with any client regardless of Mobile
   IPv4 support and it can support various authentication methods.  PANA
   can also be used with IPv6-only clients or dual-stack clients.  The
   Mobile IPv6 [MIPv6] protocol doesn't define a foreign agent in the
   access networks and provide any protocol support for access
   authentication.

   Network access authentication can be handled by PANA regardless of IP
   version of the clients and independently of whether they support or
   use Mobile IP.


4.5.  Personal Area Networks

   A personal area network (PAN) is the interconnection of devices
   within the range of an individual person.  For example connecting a
   cellular phone, PDA, and laptop together via short range wired or
   wireless links would form a PAN.

   Devices in a PAN can directly communicate with each other, and access



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   the Internet if any one of them is specifically designated as a
   mobile router for providing gateway functionality.  Just like any
   access network, a PAN also requires authentication and authorization
   prior to granting access to its clients.  A mobile router can
   terminate the link-layer from different PAN nodes, and therefore it
   acts as the first-hop router for them.  Additionally, it can also
   perform access control as an authentication agent.  Different nodes
   might be using different link-layer technologies to connect to a
   mobile router.  Therefore, it is desirable to use authentication
   methods independent of the underlying link and rely on a link-layer
   agnostic authentication protocol like PANA to carry authentication
   information.

   Another characteristic of PANs is its small scale.  Only a handful of
   nodes are expected to be part of a given PAN without a need to
   support roaming in the PAN; therefore the authentication process does
   not necessarily require a managed backend AAA infrastructure for
   credential verification.  Locally stored information can be used in
   this kind of PANA deployment without relying on a AAA backend.

   The 3GPP architecture allows separation of MT (mobile termination,
   such as cellular phone) and TE (terminal equipment, such as laptop)
   [RFC3314].  TE can be connected to the Internet via MT by
   establishing a PPP connection.  One or more TEs can be connected to a
   MT to form a PAN.  The current architecture does not allow direct
   communication between the TEs (if more than one are connected to the
   MT) without having to go through the cellular interface of the MT.
   This architecture will benefit from using shared links (e.g.,
   Ethernet) between the TE and MT.  Shared links would allow TEs to
   communicate directly to each other without having to send data
   through the power-limited MT or over the expensive air interface.
   PANA can be used for authenticating PAN nodes when shared links are
   used between the TEs and MT.


4.6.  Limited Free Access

   Certain networks might allow clients to access a limited topology
   without any explicit authentication and authorization.  However, the
   policy may be such that an access beyond this topology requires
   authentication and authorization.  For example, in an airport
   network, information such as, flight arrival and departure gate
   numbers, airport shops and restaurants, etc., is offered as free
   services by the airlines or airport authorities for their passengers.
   In order to access such information, users can simply plug in their
   devices into the network without performing any authentication.  In
   fact, the network will only offer link-layer connectivity and limited
   network layer access to users.  On the other hand, access to further
   services or sites using such local networks requires authentication
   and authorization.  If users want such services, the access network
   can detect that attempt and initiate authentication.  This also
   allows the network to initiate the authentication whenever
   appropriate.  Once users perform the authentication it will be
   allowed to go beyond the free access zone.  PANA can be an enabler to
   such limited free access scenarios and can offer a flexible access
   control framework for public access networks.




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5.  Security Considerations

   This Internet-Draft identifies the need for a standard network-layer
   authentication protocol and illustrates a number of possible usage
   scenarios.  The actual protocol design is not specified in this
   draft, neither are the security considerations around it.  The
   scenarios described in this document are used as input to a separate
   security threats analysis document [SECTHREAT].  Eventually, the
   requirements are derived from both the scenarios described in this
   document and also the threats analyzed in the latter document.  These
   requirements are being collected in the [PANAREQ] Internet-Draft.
   The readers are urged to read these two documents for security
   considerations around designing PANA.


6.  Acknowledgments

   The authors would like to thank Bernard Aboba, James Carlson, Jacques
   Caron, Francis Dupont, Paal Engelstad, Henry Haverinen, Prakash
   Jayaraman, James Kempf, Pete McCann, Thomas Narten, Erik Nordmark,
   Mohan Parthasarathy, Reinaldo Penno, Phil Roberts, David Spence,
   Barani Subbiah, Hannes Tschofenig, George Tsirtsis, John Vollbrecht,
   Cliff Wang and the rest of the PANA Working Group for the ideas and
   support they have given to this document.


7.  References

7.1.  Normative References

   [MIPv6] D. Johnson, et al., "Mobility Support in IPv6", (draft-ietf-
       mobileip-ipv6-21.txt).

   [PANAREQ] R. Penno, et al., "Protocol for Carrying Authentication for
       Network Access (PANA) Requirements and Terminology" (draft-ietf-
       pana-requirements-05.txt).

   [RFC1661] W. Simpson, "The Point-to-Point Protocol (PPP)", RFC 1661
       (STD 51), July 1994.

   [RFC2284bis] L. Blunk, et al., "Extensible Authentication Protocol
       (EAP)" (draft-ietf-eap-rfc2284bis-01.txt).

   [RFC2409] D. Harkins and D. Carrel, "The Internet Key Exchange
       (IKE)", RFC 2409, November 1998.

   [RFC2486] B. Aboba, et al., "The Network Access Identifier", RFC
       2486, January 1999.

   [RFC2516] L. Mamakos, et al., "A Method for Transmitting PPP Over
       Ethernet (PPPoE)", RFC 2516, February 1999.

   [RFC3314] M. Wasserman et al., "Recommendations for IPv6 in Third
       Generation Partnership Project (3GPP) Standards", RFC 3314,
       September 2002.

   [RFC3344] C. Perkins, "IP Mobility Support for IPv4", RFC 3344,



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       August 2002.

   [SECTHREAT] M. Parthasarathy, "PANA Threat Analysis and security
       requirements" (draft-ietf-pana-threats-02.txt).

7.2.  Informative References

   [802.1X] IEEE Standard for Local and Metropolitan Area Networks,
       "Port-Based Network Access Control", IEEE Std 802.1X-2001.


8.  Authors' Information

   Yoshihiro Ohba
   Toshiba America Information Systems, Inc.
   9740 Irvine Blvd.
   Irvine, CA 92618-1697
   USA
   Phone: +1 949 583 3273
   Email: yohba@tari.toshiba.com

   Subir Das
   MCC 1D210R, Telcordia Technologies
   445 South Street, Morristown, NJ 07960
   Phone: +1 973 829 4959
   email: subir@research.telcordia.com

   Basavaraj Patil
   Nokia
   6000 Connection Dr.
   Irving, TX. 75039
   USA
   Phone:  +1 972-894-6709
   Email:  Basavaraj.Patil@nokia.com

   Hesham Soliman
   Ericsson Radio Systems AB
   Torshamnsgatan 29,
   Kista, Stockholm 16480
   Sweden
   Phone:  +46 8 4046619
   Fax:    +46 8 4047020
   Email: Hesham.Soliman@era.ericsson.se

   Alper E. Yegin
   DoCoMo USA Labs
   181 Metro Drive, Suite 300
   San Jose, CA, 95110
   USA
   Phone: +1 408 451 4743
   Email: alper@docomolabs-usa.com


9.  Intellectual Property Notices

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to



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   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; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication 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 implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.


10.  Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
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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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