Internet-Draft Yoshihiro Ohba (Editor)
Expires: October, 2003 TAIS
Subir Das
Telcordia Technologies
Basavaraj Patil
Nokia
Hesham Soliman
Ericsson
Alper Yegin
DoCoMo USA Labs
April 28, 2003
Problem Statement and Usage Scenarios for PANA
<draft-ietf-pana-usage-scenarios-06.txt>
Status of This Memo
This document is an Internet-Draft and is in full conformance with
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Abstract
Network access authentication is a function that is typically
required in most scenarios. This is accomplished in most networks
via protocols such as PPP, PPPoE, IEEE 802.1X and others. The PANA
(Protocol for carrying Authentication for Network Access) WG is
considering the network access authentication function being
performed at or above the IP layer. This document captures the
various usage scenarios/applicability of a protocol that is used for
network access authentication that is at layer-3 or above and
additionally identifies the problem being addressed by the WG.
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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 .................................. 8
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 .......................... 11
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 are able to attach to an access network for sending and
receiving IP packets.
There are various mechanisms currently used by networks to prevent
unauthorized access. In its simplest form, unintended clients can be
physically isolated 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 model. 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 to overcome
the problem. PANA will be developed to fill this gap by defining a
network-layer access authentication protocol.
This document discusses the need for a standard network access
authentication protocol and covers various usage scenarios where such
a protocol is applicable.
2. Acronyms
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AAA: Authentication, Authorization and Accounting
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 for network access. Network
access authentication of clients necessitates a protocol between the
client and the network to execute one or more authentication methods
(e.g., PAP, CHAP, TLS, SIM, etc.). With the increasing number of the
various types of networks being deployed (e.g., GPRS, IEEE 802.11,
DSL, etc.), it is important that the authentication methods are not
tied to the underlying link-layer (technology specific). An
authentication protocol must be able to support various
authentication methods regardless of the underlying access
technology.
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 by presenting a client
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identifier which carries the ISP domain information during the
authentication process. An example of such a client identifier would
be the NAI[RFC2486] (e.g., john@anyisp.com.) The authentication
agent in 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 independent authentication by 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 the various types of link-layers, only IEEE 802 defines how to
carry EAP on the link-layer [802.1X]. Other link-layers 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 may be required to
generate cryptographic keying material unless presence of a secure
physical or link-layer channel is assured a priori. The task of
generating and distributing such keying material can be accomplished
by various EAP methods. 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]
may 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 address the problem of authentication
for network access. 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.
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Another method designed to provide network access authentication is
based on overloading an existing network-layer protocol. The Mobile
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 the identity of 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 such networks, PANA can be
used for client authentication and be the basis for an appropriate
access control mechanism.
In DSL networks, there are a number of deployment models with respect
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. Such 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 deployments. In addition, the
variations in DSL deployment scenarios, particularly the variation in
physical topology between the DSL modem and the ISPs 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 possible that a link-layer agnostic, single network access
authentication solution may be required in the future for DSL
deployments as long as the variations in deployment topologies are
expected to continue.
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 radio link. This technology specific authentication enables
authorization for link access by the NAP, and can provide per-packet
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authentication, integrity and replay protection at the link-layer.
In the case where such access networks are used for accessing the
Internet via some ISP, it does not provide authorization at the
network-layer which can only be done by authenticating the client to
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 radio link. In the
Simple IP mode of operation in 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. For a high level overview
of the cdma2000 architecture refer to [RFC3141].
As the packet data network architecture in cdma2000 evolves, PANA
could be supported as a single unifying network-layer authentication
mechanism. This would result in the replacement of CHAP
authentication via PPP with the added benefit of considering the use
of running IP directly over a simplified framing protocol instead of
PPP. In the case of Mobile IP mode of operation the need for the
challenge response scheme could be deprecated as well as enabling the
smooth migration to Mobile IPv6 deployment, the reason being the
decoupling of IP mobility from access authentication.
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 for the lack of 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 are service providers unable to control the
unauthorized use of their networks but also end-users feel insecure
about using such networks at all. 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 is 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
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allowing only authorized users to access the network, it however does
not enable the lower-layer security such as, per-packet
authentication and encryption over the radio link. Moreover, it is a
non-standard ad hoc solution that provides support for only a limited
set of authentication methods.
In such scenarios, a standard mechanism is necessary which can
provide network access authentication irrespective of whether the
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 a successful PANA
authentication can result in a secured network environment although
the underlying layers were not secured to begin with. Also assuming
PANA will provide support to various authentication schemes,
providers will have the 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. In
the co-located care-of-address mode, the mobile node itself is the
tunnel end-point for packets tunneled from the home agent to the
mobile. In this mode of operation the mobile does not rely on the
existence of a foreign agent in the visited network. In this case, a
mobile node can send its registration request directly to the home
agent. However 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 the 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. The intent of forcing the mobile
to register via the foreign agent is primarily driven by the access
networks requirement to authenticate mobile nodes before allowing
access.
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. PANA can provide the access network authentication
in the case of Mobile IPv6.
Network access authentication can be handled by PANA regardless of
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the 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
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 any 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
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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.
5. Security considerations
This document 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
document, 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] document.
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-02.txt).
[RFC2409] D. Harkins and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
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[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,
August 2002.
[SECTHREAT] M. Parthasarathy, "PANA Threat Analysis and security
requirements" (draft-ietf-pana-threats-eval-03.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.
[RFC3141] T. Hiller et al., "CDMA2000 Wireless Data Requirements for
AAA", RFC 3141, June 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
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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
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
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
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Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
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English.
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
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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