INTERNET DRAFT Pat R. Calhoun Category: Standards Track Sun Microsystems, Inc. Title: draft-calhoun-diameter-framework-00.txt Glen Zorn Date: May 1998 Microsoft Corporation Ping Pan IBM T. J. Watson Research Center DIAMETER Framework Document <draft-calhoun-diameter-framework-00.txt> Status of this Memo This document is an Internet-Draft. Internet-Drafts are working docu- ments of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute work- ing documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months. Internet-Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet- Drafts as reference material or to cite them other than as a ``work- ing draft'' or ``work in progress.'' To view the entire list of current Internet-Drafts, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Abstract As the number of new internet services has increased in the past cou- ple of years, routers and network access servers (NAS) have had to undergo re-engineering to support them. These new services could often benefit from an Authentication, Authorization and Accounting (AAA) protocol to facilitate off-loading policy information to an external server. The DIAMETER protocol defines a policy protocol used by clients to perform Policy, AAA and Resource Control. This allows a single server to handle policies for many services. Calhoun et al. expires November 1998 [Page 1]
INTERNET DRAFT May 1998 Table of Contents 1.0 Introduction 1.1 Terminology 1.2 Specification Language 2.0 DIAMETER Architecture 2.1 DIAMETER Base Protocol 2.1.1 DIAMETER Security 2.2 Resource Management Extension 2.3 Accounting Extension 2.5 QOS Extension 2.6 Mobile IP Extension 3.0 Why not LDAP? 4.0 References 5.0 Acknowledgements 6.0 Author's Address Appendix A. "Drinks" Policy Extension 1.0 Introduction As the number of new internet services has increased in the past cou- ple of years, routers and network access servers (NAS) have had to undergo re-engineering to support them. These new services could often benefit from an Authentication, Authorization and Accounting (AAA) protocol to facilitate off-loading policy information to an external server. An example of such a service is dial-up PPP Internet access. Large ISPs cannot bear the administrative burden to configure all of their users on each NAS everytime a new device is deployed. In this case RADIUS [1] has been used successfully by many such ISPs. New services such as Voice over IP, Fax over IP [6], Mobile IP [7] and RAP [5] also require similar services in order to be able to authenticate, retrieve authorization information, and generate accounting records for billing purposes. The current trend is for each working groups to define its own policy protocol for a specific service, each with their own nuances. This requires requires customers to deploy several policy servers, which increases the cost of administration and complicates deployment. DIAMETER offers a common solution by defining a base protocol that defines the header formats, security extensions and requirements as well as a small number of mandatory commands and AVPs. A new service Calhoun et al. expires November 1998 [Page 2]
INTERNET DRAFT May 1998 can extend DIAMETER by extending the base protocol to support new functionality. 1.1 Terminology AAA Authentication, Authorization and Accounting. AVP The DIAMETER protocol consists of a header followed by objects. Each object is encapsulated in a header known as an Attribute- Value-Pair. Commands The DIAMETER Protocol is a request/response protocol. Each DIAME- TER message includes a Command AVP that is used to identify the type of request or response. Integrity Check Vector (ICV) An Integrity Check Vector is an unforgeable or secure hash of the packet with a shared secret. 1.2 Specification Language In this document, several words are used to signify the requirements of the specification [8]. These words are often capitalized. MUST This word, or the adjective "required", means that the definition is an absolute requirement of the specification. MUST NOT This phrase means that the definition is an absolute prohibition of the specification. SHOULD This word, or the adjective "recommended", means that, in some circumstances, valid reasons may exist to ignore this item, but the full implications must be understood and carefully weighed before choosing a different course. Unexpected results may result otherwise. Calhoun et al. expires November 1998 [Page 3]
INTERNET DRAFT May 1998 MAY This word, or the adjective "optional", means that this item is one of an allowed set of alternatives. An implementation which does not include this option MUST be prepared to interoperate with another implementation which does include the option. Calhoun et al. expires November 1998 [Page 4]
INTERNET DRAFT May 1998 2.0 DIAMETER Architecture The Base DIAMETER Architecture consists of three modules, which defines a small set of primitives that MUST be implemented by all DIAMETER entities. Many applications require that the policy server maintain session state information. The Resource Management extension provides this capability between client and a server as well as between two servers. Most services using DIAMETER require accounting. The current IETF's standard protocol for accounting is SNMP, but experience indicates that SNMP often is not the correct protocol for service accounting. Many applications and services use RADIUS Accounting [4] as their accounting protocol, however RADIUS accounting is not a standard pro- tocol and is informational only. A standard accounting protocol is required. The following diagram provides a representation of the DIAMETER Architecture. As an example, a fictional Policy Extension has been added to the architecture. This fictional service is described here in order to to illustrate how a service could make use of DIAMETER. +------------+ | Policy | | | | Extension | +------------+ +------------+ / \ +------------+ | Resource | | | Accounting | | | | | | | Management | | | Extension | +------------+ | +------------+ / \ | / \ | | | \ / \ / \ / +--------------------------------------------------+ | | | DIAMETER Base Protocol | | | +--------------------------------------------------+ Figure 1: DIAMETER Protocol Architecture Design direction for more extensions will be taken from the user (ISP and network operations) community. Calhoun et al. expires November 1998 [Page 5]
INTERNET DRAFT May 1998 2.1 DIAMETER Base Protocol The Base Protocol defines a set of primitives and the security model used between DIAMETER peers. The following goals motivate the defini- tion of the base protocol: - Base protocol MUST be lightweight and simple to implement. - Allow unsolicited messages from the Policy Server to the client. - Feature discovery. - Version negotiation. - unsupported extension notification instead of silent discard. - Efficient encoding of Attributes. - The AVP address space MUST be large (i.e. 32 bits) - The protocol MUST ensure that 32 bit alignment is observed. - Support for vendor specific AVPs and Commands. - The protocol MUST support both TCP and UDP. - client to server as well as server to server communication (as in figure 2) is needed. - Authentication and privacy for policy messages. - Communication with a DIAMETER entity through an intermediate DIAMETER entity. Feature Discovery is intended to dramatically reduce the administra- tive overhead associated with Policy Server configuration. A DIAMETER client can use the a DIAMETER service-type request over SLP [2] to locate Policy Servers within the network, and then a set of DIAMETER messages to retrieve the supported extensions. DIAMETER version negotiation will also reduce the administrative overhead in policy server configuration. DIAMETER entities SHOULD agree to use the higher DIAMETER protocol version number that they commonly support. UDP is preferable for policy applications that require "fine tuned" retransmission strategies. For applications that require support for larger messages and are not as concerned with the retransmission Calhoun et al. expires November 1998 [Page 6]
INTERNET DRAFT May 1998 policy, TCP can be used. Each individual extension may specify the underlying transport requirements. As mentioned above, DIAMETER supports server to server communication (see figure 2). Servers can either belong to the same administrative domain, or they may belong to different domains. This is commonly called "proxying" DIAMETER requests, where a proxy server is used in order to reach the end policy server. This functionality is described in [3] and has many different applications besides Internet dial-up access. +--------+ +--------+ | proxy | | policy | | policy |<--------------->| | | server | server-server | server | +--------+ communication +--------+ / /|\ / | client-server / | communication |/_ \|/ +--------+ +--------+ | router | | router | +--------+ +--------+ Figure 2: Client through a Proxy Server 2.1.1 DIAMETER Security The protocol presents three different security methods. The first and most obvious method requires no security and can be used with IPSEC. The second method is to make use of shared secrets between two enti- ties. In this case the protocol could include an HMAC-MD5-96 [8] Integrity Check Vector (ICV) within an AVP to provide integrity of the message. Figure 3 depicts an example of Hop-by-Hop security where Policy Server 1 (PS1) and Proxy Server 2 (PS2) share a secret as well as PS2 and Policy Server 3 (PS3). In this example PS1 sends a message to PS3 through PS2 with an ICV that is computed using the secret it shares with PS2. Upon receipt of the message, PS2 validates the ICV, removes it and adds an ICV that is computed using the secret it shares with PS3. This is commonly called Hop-by-Hop security since it does not provide message integrity between PS1 and PS3. The third method, called End-to-End security, allows a DIAMETER entity to communicate with a Server through a set of intermediate Proxies (see figure 3). In this case the initiator MUST sign the Calhoun et al. expires November 1998 [Page 7]
INTERNET DRAFT May 1998 message using public key cryptography since it is the only way for the end server to ensure that a proxy has not modified the original message. +----------+ +----------+ | policy |<--------------->| proxy | | server 1 | server-server | server 2 | +----------+ communication +----------+ /|\ | server-server | communication \|/ +----------+ | policy | | server 3 | +----------+ Figure 3: Proxy Server Communication If certificates are not statically configured or retrieved through some other means (i.e. Certificate Authority), it requires that both the client and the server exchange certificates as part of the DIAME- TER bootstrap protocol. For both the second and the third method the base protocol MUST pro- vide replay protection. 2.2 Resource Management Extension The Resource Management Extension enables Servers to maintain session state information. Many applications require the policy server to make decisions not only based on a static policy, but also based on network events. The Resource Management Extension allows a client and server to exchange state information as well as two Servers. Some servers may also use a distributed back-end database to share state information. The Resource Management extension does not provide a message to create a session. This is handled through an extension's authoriza- tion response message. An example would be when the server authorizes the allocation of bandwidth through a successful response message. A response message would then create state information within the client and the server that can be handled through the resource management extensions at a later time, using the session identifier assigned to the session. Calhoun et al. expires November 1998 [Page 8]
INTERNET DRAFT May 1998 The following abilities supported by the Resource Management exten- sion: - Associating resources with clients. - Identifying when a session is terminated. - Session termination by servers. - State update/refresh from the client or other servers. In order for the server to maintain accurate state information, it MUST be notified when a session is terminated. State update and refresh is very important in the case where the server has lost state information (i.e. reboot). The server MUST be able to request information about a specific session as well as a generic request to retrieve all state information. For services that require fault tolerance, servers SHOULD share state information. The server must be able to request that a client terminate a session. This is required in services where policy can pre-empt a low priority session. Because multiple servers need to share state information, the server MUST generate resource tokens. These resource tokens are returned by the server at authorization time by the appropriate extension. The resource token is sent by the client to the server when it receives a request for a state update, and must contain enough information for the server to rebuild session state information. Furthermore since state information is shared amongst servers it is required that each session have a universally unique session identif- ier associated with it that is assigned by the client. 2.3 Accounting Extension The Accounting Extension defines the messages used for service accounting. The accounting extension MUST provide the following func- tionality (a separate effort is in place to define the exact require- ments of the accounting extension): - Negotiable transfer mechanism. - Provide general purpose AVPs. - Flexible to allows new extensions to use the accounting Calhoun et al. expires November 1998 [Page 9]
INTERNET DRAFT May 1998 extension. - Scalable to allows millions to users and thousands of sites. - Secure accounting data transfer. The accounting extension must be able to transfer accounting records in an event-driven or batch manner. The selected transfer mechanism must be negotiable, and it must be possible to initiate batch transfer from either peer. The extension MUST Support accounting finite and infinite sessions as well indivisible events. Other detailed requirements call for sup- porting service name/id, amount and length of attributes. It must also be flexible to work in many applications areas. This requires extensibility, application defined level of security, minimal storage and code size requirements, and the ability to work in both real-time and non-real time situations. The accounting protocol must be scalable to the size of global shared-use networks with millions of users and thousands of sites and accounting systems.Transmission, header, and security overhead MUST be amortized over several accounting records. Only a per-entity state needs to be held by the accounting systems (as opposed to a per- session state). The accounting protocol must be secure. End-to-end and hop-by-hop integrity and confidentiality, data-based access control are all needed. Standard Internet security protocols are to be used where possible. 3.0 Why not LDAP? Many people have asked whether LDAP would provide the functionality required. A Server MAY wish to access policies using LDAP, but the use of LDAP between the client and the server is not possible. The use of LDAP in this case would require that all routers have write access to the directory. Most customers would not accept this requirements and it is not efficient. In the case of roaming, customers would have to open up their direc- tory so outside routers have writeable access. Moreover, having 1000's of routers constantly write to the directory would cause some Calhoun et al. expires November 1998 [Page 10]
INTERNET DRAFT May 1998 additional problems to the Directory Service. Finally, LDAP does not provide server initiated messages which is a requirement for an AAA protocol. 4.0 References [1] Rigney, et alia, "RADIUS", RFC-2138, Livingston, April 1997 [2] Veizades, Guttman, Perkins, Kaplan, "Service Location Protocol", RFC-2165, June 1997. [3] Aboba, Zorn, "Roaming Requirements", draft-ietf-roamops- roamreq-08.txt, March 1998. [4] Rigney, "RADIUS Accounting", RFC-2139, April 1997. [5] Yavatkar, Pendarakis, Guerin, "A Framework for Policy-based Admission Control", draft-ietf-rap-framework-00.txt, November 1997. [6] Masinter, "Terminology and Goals for Internet Fax", draft-ietf-fax-goals-02.txt, March 1998. [7] C. Perkins, Editor. IP Mobility Support. RFC 2002, October 1996. [8] Krawczyk, Bellare, Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, January 1997. [9] Bradner, "Key words for use in RFCs to Indicate Requirements Levels", BCP 14, RFC 2119, March 1997. 5.0 Acknowledgements The Authors would like to thanks Bernard Aboba and Jari Arkko for their Accounting Requirements contribution. Calhoun et al. expires November 1998 [Page 11]
INTERNET DRAFT May 1998 6.0 Author's Address Questions about this memo can be directed to: Pat R. Calhoun Technology Development Sun Microsystems, Inc. 15 Network Circle Menlo Park, California, 94025 USA Phone: 1-650-786-7733 Fax: 1-650-786-6445 E-mail: pcalhoun@eng.sun.com Glen Zorn Microsoft Corporation One Microsoft Way Redmond, WA 98052 USA Phone: 1-425-703-1559 E-Mail: glennz@microsoft.com Ping Pan IBM T. J. Watson Research Center 30 Saw Mill River Road, Hawthorne, NY 10532 Phone: 1-914-784-6579 Fax: 1-914-784-6205 E-mail: pan@watson.ibm.com Calhoun et al. expires November 1998 [Page 12]
INTERNET DRAFT May 1998 Appendix A. "Drinks" Policy Extension This section is provided as an example only and is intended to pro- vide the reader with a better understanding of how DIAMETER could be used by services. This protocol will provide authentication, authorization and account- ing services for bar customers. Each user will be provided with a smart card that contains the user's identity and private key. When a user enters a bar he may use the automated facility by insert- ing his card into a card slot and wait for the appropriate retina scan to be performed. The user also selects a drink, and may simply hit the "favorite drink" button on the machine. The DIAMETER Client then issues the authentication request to the Server which authenticates the user. The message MUST contain a unique session identifier that will be used while the user is present in the bar. The authentication phase consists of a check that the key and retina scan matches the user's identity and that the user is of age (this is a local decision since each state has different minimum age requirements). If the user is successfully authenticated the server adds authoriza- tion information. Authorization information MAY include the user's favorite drinks, whether the user's martini should be shaken or stirred, any known allergic reactions to peanuts or other assorted snacks, etc. Upon receipt of the response, the DIAMETER client dispenses the drink to the customer and generates and accounting request to the DIAMETER accounting server (which MAY be different from the authentication and authorization server). Since the Policy server adapts itself according to the user's drink- ing habits, it knows how often to send a message to the DIAMETER Client to offer another drink to the customer. Since the policy server also knows about the user's favorite drinks, it may even "sug- gest" a list of drinks to the user periodically. This is achieved using the Resource Management extensions defined earlier. When the user wishes to order a new drink, the same mechanism occurs as defined above, but the Session Identifier is constant. When the user leaves the bar, the DIAMETER Client sends a message to the server stating that it is terminating a session (based on the Session ioni Calhoun et al. expires November 1998 [Page 13]