Internet-Draft Yoshihiro Ohba (Editor) Expires: August, 2003 Subir Das Basavaraj Patil Hesham Soliman Alper Yegin February 20, 2003 Problem Statement and Usage Scenarios for PANA 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. Expires August, 2003 [Page 1] Internet-Draft PANA Usage Scenarios February 20, 2003 Table of Contents 1 Introduction ............................................ 2 2. Problem Statement ....................................... 2 3. Usage Scenarios ......................................... 4 3.1. PANA with Physical Layer Security ....................... 4 3.2. PANA with Link-Layer Security ........................... 5 3.3. PANA in the Absence of Any Lower-Layer Security ......... 6 3.4. Mobile IP ............................................... 6 3.5. Personal Area Networks .................................. 7 3.6. Limited Free Access ..................................... 8 4. Acronyms ................................................ 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 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. Ability to support multiple authentication methods or to perform both network access provider and Internet service provider authentication are not available to all link-layers. An even higher layer authentication mechanisms are 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 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. Problem Statement Expires August, 2003 [Page 2] Internet-Draft PANA Usage Scenarios February 20, 2003 Access networks usually require clients to go through an authentication and authorization process unless physical security is used as a substitute. 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. Authentication protocol must be able to carry various authentication methods regardless of the underlying access technologies. An important aspect of network access is the ability to enable dynamic service provider selection. Regardless of their network access provider (NAP), clients should be able to select an Internet access provider (ISP) of their choice. This is usually achieved by clients presenting an identifier which carries domain information during the authentication process unless some other link-layer specific selectors are used during link establishment. An example of such 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 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 3.2. A network-layer authentication mechanism that will support various authentication methods can be developed by using a protocol that carries EAP [RFC2284bis]. EAP acts as an encapsulation of arbitrary authentication methods, but it still requires a transport between the client and the access network. 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. Inserting this additional layer(s) between the link-layer and network-layer to achieve this goal is an inadequate method. Using PPP just for client authentication incurs extra round-trips, generates overhead of PPP processing for data packets, and forces the network topology into a point-to-point model. In general terms, PANA will be defined as a network-layer transport for EAP. It is believed that EAP is a key protocol in supporting various authentication methods for network access, and its applicability should not be limited to access networks that are using IEEE 802 and PPP links. PANA can be used over any link-layer that does not support EAP encapsulation. PPP might be perceived as a link-layer agnostic transport for EAP, but using PPP solely for authentication purpose incurs unnecessary cost and imposes additional limitations. Expires August, 2003 [Page 3] Internet-Draft PANA Usage Scenarios February 20, 2003 The primary purpose of PANA is to authenticate a client to a server for the network access purpose. Initial client authentication needs to be bound to subsequent traffic to prevent spoofing and hijacking of data packets. 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. PANA is only responsible for carrying EAP and it should not have to deal with the keying material. 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. 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 regarded as a stop-gap mechanism. Another method designed to provide network access authentication is based on overloading an existing network-layer protocol. 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 protocol for network access authentication. Such a solution has very limited applicability as a link-layer agnostic method since it relies on the deployment of Mobile IPv4 protocol. 3. Usage Scenarios The first three subsections describe PANA usage scenarios categorized in terms of lower-layer security. Other subsections describe scenarios that are not categorized in terms of lower-layer security. 3.1. PANA with Physical Layer Security In the networks where a certain degree of security is provided at physical layer, authenticating the client is still essential since physical layer does not provide information on the client, but per- packet authentication and encryption may not necessarily be provided at higher layers. 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. Expires August, 2003 [Page 4] Internet-Draft PANA Usage Scenarios February 20, 2003 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 (and IP encapsulation), the providers may not require to migrate to use PANA. 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 is needed for this type of DSL networks and PANA can be used to fill the demand. 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 lower-layer and works with any physical topology. It is highly possible that an link-layer agnostic, single network access authentication solution will be demanded for future DSL deployments as long as the variation is supposed to exist. 3.2. PANA with Link-Layer Security Certain link-layers in radio networks such as GSM and cdma2000 provide their own authentication mechanisms as well as ciphering of data sent over the physical air interface. This air- interface/technology specific authentication enables authorization for accessing the link by the NAP, and provides per-packet authentication, integrity and replay protection on the link-layer. But it does not necessarily provide authorization at the network- layer which can be done by authenticating the client to an ISP. So this still 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) algorithms 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 services, the ISP authentication is provided by using PPP in the stack. Currently there are proposals to remove PPP from the architecture and adopt a simple framing scheme such as HDLC or variants. One of the functionalities of PPP that needs to be taken over by another protocol or mechanism is the authentication capability. In such a scenario, network access authentication may be done using PANA protocol. Where a multi-layer authentication for network access is needed, and access technology specific authentication is already provided by another protocol, PANA can be used as the network-layer authentication protocol. In this case PANA will be running over a cryptographically secured channel. Expires August, 2003 [Page 5] Internet-Draft PANA Usage Scenarios February 20, 2003 3.3. 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 the lack of adequate authentication capabilities on the link-layer technology being used. Link-layer technologies generally provide sufficient cipher suite support but inadequate authentication method support. It is desirable to support arbitrary 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. Assuring physical security or enabling link-layer security might not be practical for various reasons. 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 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. 3.4. 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 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 Expires August, 2003 [Page 6] Internet-Draft PANA Usage Scenarios February 20, 2003 agent by setting Registration-Required bit in the agent advertisements. This forces mobile nodes to send their registration requests via 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 clients, or dual-stack clients. 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 independent of whether they support or use Mobile IP. 3.5. 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 wireless 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; 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., Expires August, 2003 [Page 7] Internet-Draft PANA Usage Scenarios February 20, 2003 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. 3.6. 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., are 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 hot-spot networks. 4. Acronyms 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 Expires August, 2003 [Page 8] Internet-Draft PANA Usage Scenarios February 20, 2003 PPPoE: PPP over Ethernet TE: Terminal Equipment UE: User Equipment VLR: Visiting Location Register 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, Thomas Narten, Erik Nordmark, 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-ipv6-20.txt). [PANAREQ] R. Penno, et al., "Protocol for Carrying Authentication for Network Access (PANA) Requirements and Terminology" (draft-ietf- pana-requirements-04.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. Expires August, 2003 [Page 9] Internet-Draft PANA Usage Scenarios February 20, 2003 [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-01.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 Research, Inc. P.O. Box 136 Convent Station, NJ 07961-0136 USA Phone: +1 973 829 5174 Fax: +1 973 829 5601 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 Expires August, 2003 [Page 10] Internet-Draft PANA Usage Scenarios February 20, 2003 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. 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