AAA Working Group Pat R. Calhoun Internet-Draft Sun Microsystems, Inc. Category: Informational Glen Zorn <draft-calhoun-diameter-framework-09.txt> Cisco Systems, Inc. Ping Pan Bell Labs Haseeb Akhtar Nortel Networks February 2001 Diameter Framework Document Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. This document is an individual contribution for consideration by the AAA Working Group of the Internet Engineering Task Force. Comments should be submitted to the diameter@diameter.org mailing list. Distribution of this memo is unlimited. Copyright (C) The Internet Society 1999. All Rights Reserved. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 1]
Internet-Draft February 2001 Abstract Current Internet Service Providers (ISPs) scale their networks by using the RADIUS protocol, which provides user Authentication, Authorization and Accounting (AAA) of Dial-up PPP clients. The recent work done in the Roaming Operations (ROAMOPS) Working Group was to investigate whether RADIUS could be used in a roaming network, and concluded that RADIUS was ill-suited for inter-domain purposes. The IETF has formed a new NAS Requirements Working Group, and part of their charter is to document the next generation NAS' AAA requirements. Recently, the Mobile-IP Working Group also documented their own AAA requirements that would help Mobile IP scale for Inter-Domain mobility. The Diameter protocol is a follow-on to the RADIUS protocol. Diameter addresses the known RADIUS deficiencies, and is intended for use with the NASREQ, ROAMOPS and Mobile IP application space. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 2]
Internet-Draft February 2001 Table of Contents 1.0 Introduction 1.1 Requirements language 1.2 Terminology 2.0 Problems to be addressed 2.1 Strict limitation of attribute data 2.2 Strict limitation on concurrent pending messages 2.3 Inability to control flow to servers 2.4 No retransmission procedure 2.5 End to end message acknowledgment 2.6 Heavy processing cost 2.7 Silent discarding of packets 2.8 Inefficient Server Fail-Over 2.9 Inefficient use of RADIUS servers in proxy environments 2.10 No unsolicited messages 2.11 Replay Attacks 2.12 Hop-by-Hop security 2.13 No support for vendor-specific commands 2.14 No alignment requirements 2.15 Mandatory Shared Secret 3.0 Diameter Architecture 3.1 Diameter Base Protocol 3.1.1 Proxy Support 3.1.2 Broker Support 3.2 Strong Security Extension 3.3 Mobile-IP Extension 3.4 NASREQ Extension 3.5 Accounting Extension 3.6 Resource Management 3.7 Diameter Command Naming Conventions 3.7.1 Request/Answer 3.7.2 Query/Response 3.7.3 Indication 4.0 Why not LDAP? 5.0 References 6.0 Acknowledgements 7.0 Author's Addresses 8.0 Full Copyright Statement Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 3]
Internet-Draft February 2001 1.0 Introduction Historically, the RADIUS protocol has been used to provide AAA services for dial-up PPP [17] and terminal server access. Over time, routers and network access servers (NAS) have increased in complexity and density, making the RADIUS protocol increasingly unsuitable for use in such networks. The Roaming Operations Working Group (ROAMOPS) has published a set of specifications [19, 20, 21] that define how a PPP user can gain access to the Internet without having to dial into his/her home service provider's modem pool. This is achieved by allowing service providers to cross-authenticate their users. Effectively, a user can dial into any service provider's point of presence (POP) that has a roaming agreement with his/her home Internet service provider (ISP), the benefit being that the user does not have to incur a long distance charge while traveling, which can sometimes be quite expensive. Given the number of ISPs today, ROAMOPS realized that requiring each ISP to set up roaming agreements with all other ISPs did not scale. Therefore, the working group defined a "broker", which acts as an intermediate server, whose sole purpose is to set up these roaming agreements. A collection of ISPs and a broker is called a "roaming consortium". There are many such brokers in existence today; many also provide settlement services for member ISPs. The Mobile-IP Working Group has recently changed its focus to inter administrative domain mobility, which is a requirement for cellular carriers wishing to deploy IETF-based mobility protocols. The current cellular carriers requirements [22, 23] are very similar to the ROAMOPS model, with the exception that the access protocol is Mobile-IP [2] instead of PPP. The Diameter protocol was not designed from the ground up. Instead, the basic RADIUS model was retained while fixing the flaws in the RADIUS protocol itself. Diameter does not share a common protocol data unit (PDU) with RADIUS, but does borrow sufficiently from the protocol to ease migration. The basic concept behind Diameter is to provide a base protocol that can be extended in order to provide AAA services to new access technologies. Currently, the protocol only concerns itself with Internet access, both in the traditional PPP sense as well as taking into account the ROAMOPS model, and Mobile-IP. Although Diameter could be used to solve a wider set of AAA problems, we are currently limiting the scope of the protocol in order to Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 4]
Internet-Draft February 2001 ensure that the effort remains focussed on satisfying the requirements of network access. Note that a truly generic AAA protocol used by many applications might provide functionality not provided by Diameter. Therefore, it is imperative that the designers of new applications understand their requirements before using Diameter. 1.1 Requirements language In this document, the key words "MAY", "MUST", "MUST NOT", "optional", "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [9]. 1.2 Terminology Accounting The act of collecting information on resource usage for the purpose of trend analysis, auditing, billing, or cost allocation. Authentication The act of verifying the identity of an entity (subject). Authorization The act of determining whether a requesting entity (subject) will be allowed access to a resource (object). AVP The Diameter protocol consists of a header followed by one or more Attribute-Value-Pair (AVP). The AVP includes a header and is used to encapsulation authentication, authorization or accounting information. Broker A broker is a business term commonly used in AAA infrastructures. A broker is either a proxy or redirect server, and MAY be operated by roaming consortiums. Diameter Client A Diameter Client is a device at the edge of the network that performs access control. An example of a Diameter client is a Network Access Server (NAS) or a Foreign Agent (FA). Diameter Server A Diameter server is a device that is not acting as a NAS or FA. Servers can be proxy, redirect, or home servers Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 5]
Internet-Draft February 2001 Downstream Server Diameter Proxy servers identify a downstream server as one that is providing routing services towards the home server for a particular message. Home Domain A Home Domain is the administrative domain with whom the user maintains an account relationship. Home Server A Diameter Home Server is one that authenticates and/or authorizes access for users of a particular realm. The same server MAY also act as a proxy or redirect server for other realms, in which case it is not acting as a Home Server for these realms. Integrity Check Value (ICV) An Integrity Check Value is an unforgeable or secure hash of the message with a shared secret. Interim accounting An interim accounting message provides a snapshot of usage during a user's session. It is typically implemented in order to provide for partial accounting of a user's session in the event of a device reboot or other network problem that prevents the reception of a session summary message or session record. Local Domain A local domain is the administrative domain providing services to a user. An administrative domain MAY act as a local domain for certain users, while being a home domain for others. Network Access Identifier The Network Access Identifier, or NAI [3], is used in the Diameter protocol to extract a user's identity and realm. The identity is used to identify the user during authentication and/or authorization, while the realm is used for message routing purposes. Proxy Server A proxy server úses the realm portion of the NAI to route Diameter messages. Proxy servers are typically used to minimize the number of security relationships that are required between Diameter servers. Realm The string in the NAI that immediately follows the '@' character. NAI realm names are required to be unique, and are piggybacked on the administration of the DNS namespace. Diameter makes use of the Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 6]
Internet-Draft February 2001 realm, also loosely referred to as domain, to determine whether messages can be satisfied locally, or whether they must be proxied. Real-time Accounting Real-time accounting involves the processing of information on resource usage within a defined time window. Time constraints are typically imposed in order to limit financial risk. Redirect Server A Diameter redirect server provides realm to address translation, by returning information necessary for Diameter peers to communicate directly. Redirect servers are different from proxies since they do not participate in the routing of messages between end Diameter nodes. Roaming Relationships Roaming relationships include relationships between companies and ISPs, relationships among peer ISPs within a roaming association, and relationships between an ISP and a roaming consortia. Together, the set of relationships forming a path between a local ISP's authentication proxy and the home authentication server is known as the roaming relationship path. Session The Diameter protocol is session based. When an authorization request is initially transmitted, it includes a session identifier that is used for the duration of the session. The Session- Identifier AVP contains the identifier and must be globally unique. Session record A session record represents a summary of the resource consumption of a user over the entire session. Accounting gateways creating the session record may do so by processing interim accounting events or accounting events from several devices serving the same user. Upstream Server Diameter Proxy servers identify an upstream server as one that is providing routing services towards the Diameter client. 2.0 Problems to be addressed The RADIUS protocol was designed in the early 1990's as an attempt to solve a scaling problem associated with dial-in and telnet servers. Over time the networks became more complex (e.g. roaming networks) Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 7]
Internet-Draft February 2001 and the Network Access Servers (NAS) increased in complexity and density. These changes combined with a massive deployment of the protocol uncovered some fundamental issues with the protocol that needed to be fixed. The Diameter protocol was designed as a next generation RADIUS protocol, designed with roaming and high density NASes in mind. This section will describe the documented, and undocumented, RADIUS problems known today. Further sections will describe how the Diameter protocol addresses each one of these problems. 2.1 Strict limitation of attribute data One of problems that RADIUS suffers from is its inherent limitation on the length of attribute data. This limitation is imposed by the fact that the protocol's attribute header only reserves one byte for the length field. The RADIUS protocol does specify that larger data can be spanned across multiple attributes, however doing so introduces a new set of problems. The RADIUS protocol also allows multiple attributes of the same type to be included within a message. Therefore, it is difficult for a RADIUS server, or client, to determine whether multiple identical attributes are in fact multiple independent attributes, or a single fragmented attribute. 2.2 Strict limitation on concurrent pending messages The RADIUS protocol states that the identifier field, found within the header, is used to identify retransmissions. This one byte field imposes a strict limitation on the number of requests that can be pending at any given time to 255. In the early 1990's, this number was sufficient, but the increased density of most NASes today make the protocol nearly unusable. Later versions of the protocol specification attempts to solve this problem by making use of multiple UDP ports, and making use of as many ports as necessary to ensure that no more than 255 simultaneous requests are pending. The RADIUS protocol also requires that retransmitted request, which include changes to the packet, include a new value in the Identifier field. Note that most retransmissions do include updated information, and therefore typically require a new Identifier field. This further reduces the number of sessions that can be supported by the Identifier field. 2.3 Inability to control flow to servers Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 8]
Internet-Draft February 2001 Given the rather bursty nature of the RADIUS protocol, current servers have no way of properly managing their receive buffers. This is in part due to the fact that RADIUS operates over UDP, and does not include any windowing support. This has been known to cause large bursts of requests to be directed to a server, which can burden a server's ability to respond in a timely manner. This problem is most prevalent in cases where a server becomes unavailable and all requests must be sent to an alternate server, or when an ingress port on the NAS becomes available (e.g. T3 port on NAS). 2.4 No retransmission procedure Given that the RADIUS protocol requires that the Identifier field be changed in retransmissions that have updated information, RADIUS server developers have had to design clever tricks to identify retransmissions. One common method is to cache all packets received in a time window (e.g. 60 seconds). When such servers receive a packet, it compares the contents of certain attributes, which are know to be static across retransmissions, with corresponding attributes in all packets in the cache. When a match is found, a retransmission has been detected. This burden placed on RADIUS servers add additional latency, which may cause NAS retransmissions (see Section 2.5). 2.5 End to end message acknowledgment The RADIUS protocol requires that a NAS retransmit a request until a successful or failed response is received, and does not permit a RADIUS server to retransmit a response. Since RADIUS servers typically have to perform a database lookup to authenticate the user, such operations MAY be lengthy, and cause the NAS to assume that the request was never received, and retransmit (causing further congestion). In cases when proxy servers are used, retransmissions are even more likely since each proxy must identify retransmissions, validate the request, optionally impose some local policy decision, and forward to the downstream server. 2.6 Limited server failure detection The RADIUS protocol, operating over UDP, does not provide a clear method for a NAS to detect whether the lack of a response for a given request is the result of congestion, or server failure. In networks that do not employ proxies, this is not an issue. However, in Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 9]
Internet-Draft February 2001 networks that do make use of proxies, the lack of a response MAY not be a local problem, but a problem with a downstream or home server. The NAS does not have a mechanism to identify that the local server is still available, and MUST retransmit all pending requests to an alternate server, including those destined for different downstream or home servers. This places a burden not only on the offending home server, but also on the NAS, proxies and all other home servers that will receive retransmissions. 2.7 Silent discarding of packets The RADIUS protocol states that messages that do not contain the expected information, or messages that have errors are silently discarded. Silently discarding messages causes the NAS to assume that the local RADIUS server is no longer reachable, and causes it to retransmit all pending requests to alternate servers (see Section 2.6). Such messages will be retransmitted to alternate servers, and again silently discarded, and so on. This will occur until the NAS abandons the request. 2.8 Inefficient Server Fail-Over Most NAS implementations support a number of RADIUS servers, consisting of a primary server with a set of alternate servers. When the NAS detects that the primary can no longer be used, all pending messages are transmitted to an alternate server. When the alternate is not available, the next alternate server in the list is used. Given that the RADIUS server operates over UDP, and has no watchdog mechanism, the NAS has no way to know in advance whether an alternate server is reachable. Therefore, if two or more consecutive servers in the server list are unavailable, denial of service to users can be very lengthy. 2.9 Inefficient use of RADIUS servers in proxy environments As previously mentioned, NASes have no method of knowing whether the lack of a response is due to a failure on the local, downstream proxies, or the home server. Further, servers do not retransmit RADIUS requests on behalf of the NAS. Therefore, should a primary home server become unavailable, the local server does not retransmit to an alternate server in the home network, but rather waits for the NAS to timeout and retransmit to the local alternate server, requiring parallel links between servers (see figure 1). Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 10]
Internet-Draft February 2001 Local ISP Home ISP +--------+ +--------+ | Primary| | Primary| +-------+ | Proxy |----------->| Home | | |----------->| Server | | Server | |Network| +--------+ +--------+ |Access | |Server | +--------+ +--------+ | |----------->| 2 nd | | 2 nd | +-------+ | Proxy |----------->| Home | | Server | | Server | +--------+ +--------+ Figure 1: RADIUS Proxy Network Take an example where an ISP issues two authentication requests, one for abc.net and another for xyz.com. Let's also assume that abc.net's primary server is down, while xyz's 2nd server is down. Should such a problem occur, all requests for abc.net would cause the NAS to switch to the local ISP's 2nd server, while all requests to xyz.net would cause the NAS to switch back to the local ISP's primary server. 2.10 No unsolicited messages The RADIUS protocol does not allow a server to send unsolicited messages to the NAS. As network services became more complex, this limitation has forced manufacturers to deviate from the RADIUS protocol, causing interoperability problems. Server initiated messages are typically used for accounting purposes and to request that a NAS terminate a specific user session. 2.11 Replay Attacks Although RADIUS messages contain hop-by-hop authentication, the protocol does not include any replay attack prevention. This means that a malfunctioning server, or malicious user, can replay an old packet without detection. For servers that maintain state information, such as those that limit the number of concurrent sessions for a given user, a denial of service is very simple by replaying old RADIUS messages. For other servers, this problem is limited to duplicate accounting messages. 2.12 Hop-by-Hop security The RADIUS protocol uses hop-by-hop security, which means that every Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 11]
Internet-Draft February 2001 hop in a RADIUS proxy network adds authentication data that is used by the next peer in the chain. RADIUS has no facility for securing the message between the NAS and the home server, eliminating the ability for proxy servers to modify critical components in messages. This has caused opportunities for fraud in RADIUS networks, since intermediate nodes can easily modify information (e.g. accounting information), and such events are difficult to traceable. 2.13 No support for vendor-specific commands Although the RADIUS protocol does support vendor-specific attributes, it does not allow for vendor-specific commands. This has forced vendors to abuse the address space, creating interoperability problems in mixed vendor environments. 2.14 No alignment requirements Unlike most newer IETF protocols, the RADIUS protocol does not impose any alignment requirements, which adds an unnecessary burden on most processors. All fields within the header and attributes must be treated as byte aligned characters. 2.15 Mandatory Shared Secret The RADIUS protocol requires that a shared secret exists between two peers. Therefore, even if IP Security was deployed to secure to communication, the shared secret would still be required. 3.0 Diameter Architecture The Diameter architecture consists of a base protocol and a set of protocol extensions (such as strong security, NASREQ, Mobile-IP and accounting). Functionality common to all supported services is implemented in the base protocol, while application-specific functionality may be provided through the extension mechanism. The base protocol [18] must be supported for all Diameter applications, and defines the basic PDU format, a few primitives and the basic security services offered by the protocol. Unlike RADIUS, the Diameter protocol operates over SCTP [24], which provides reliability and an well defined retransmission and timeout mechanism. Additionally, Diameter defines a fail-over strategy, which is lacking in the RADIUS protocol. SCTP provides a windowing scheme, which allows the AAA servers to limit the flow of incoming packets. This Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 12]
Internet-Draft February 2001 can then be used by the AAA clients to distribute the traffic load across multiple servers. The transport layer's retransmission and timeout timers allow clients and servers to detect the reachability state of peers, allowing for quick transition to back-up servers. As previously discussed, the ROAMOPS model introduces the proxy, or broker, which acts as an intermediate server forwarding requests to user's home ISPs. ROAMOPS also described a set of attacks that one could mount if such a network was built using the RADIUS protocol [21]. In order to provide secure broker services, security between the NAS and the home server is required at the application layer, preventing such servers from modifying contents of RADIUS messages. The Diameter Strong Security Extension defines a set of extensions to the base protocol that provide authentication, confidentiality and non-repudiation at the Attribute-Value-Pair (AVP) level. With these extensions, it is possible to secure portions of a Diameter message, while other parts of the message are not secured. Secured objects are called protected AVPs; non-secured objects are called unprotected AVPs. Using Diameter, proxies can add, delete or modify unprotected AVPs in a message. The RADIUS protocol provides dial-up PPP AAA services by providing three commands and many Attributes. Attributes in RADIUS are analogous to AVPs in Diameter. In order to ease migration from RADIUS to Diameter, the first 256 AVPs in the Diameter AVP space are reserved for RADIUS compatibility. This allows both protocols to share a common dictionary and policy rules for PPP user profiles. The RADIUS protocol has support for the Extensible Authentication Protocol (EAP) [10], but RADIUS' lack of support for large attributes and its inherent unreliability has made the integration of the protocols very difficult. The Diameter NASREQ Extension defines a set of authentication/authorization commands, which can be used for CHAP, PAP and EAP. Diameter's support for larger AVPs and the SCTP transport properties have made the use of EAP much more palatable, allowing for end-to-end user authentication, which reduces many of authentication replay attacks known to exist with CHAP and PAP. Unlike PPP, Mobile-IP hosts do not have a long-lived "nailed-up" connection to a PPP server, but rather get service from routers that provide service in a particular cell. In the Mobile-IP world, the router is known as a Foreign Agent, while the moving hosts are known as Mobile Nodes. The mobile node's home network has a host that forwards all messages destined to the mobile node through the Foreign Agent. This router is commonly referred to as the Home Agent. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 13]
Internet-Draft February 2001 Mobile-IP [7] allows the mobile nodes to move from one cell (subnet) to another while retaining the same IP address, minimizing the impact to applications. Although the Mobile-IP protocol could be deployed in a small network with any AAA services, a larger network suffers from many scaling issues such as: - Static mobile node home address - Static mobile node home agent - Requirement to pre-configure mobile node profile on home agents - No inter-domain mobility Both PPP and Mobile-IP require that usage data be collected for uses such as capacity planning and for accounting purposes. The current standard protocol for accounting is SNMP [12], but experience indicates that SNMP often is not the correct protocol for service accounting. Today many applications and services use RADIUS accounting [4] as their accounting protocol, however the RADIUS accounting protocol is not an IETF standard; in addition, it suffers from similar scaling and security problems. The Diameter accounting extension [11] is designed to allow accounting information to be sent across administrative domains (optionally through brokers), and has been derived from an accounting requirements document [6, 8]. +-----------+ | Mobile-IP | | | | Extension | +-----------+ +-----------+ ^ +------------+ | NASREQ | | | Accounting | | | | | | | Extension | | | Extension | +-----------+ | +------------+ ^ | ^ | | | v v v +----------------------------------+---------------------+ | | | | Diameter Base Protocol | Strong Security | | | | +----------------------------------+---------------------+ Figure 2: Diameter Protocol Architecture 3.1 Diameter Base Protocol The Base Protocol defines the Diameter message format, a set of primitives and how the messages are transmitted in a secure fashion. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 14]
Internet-Draft February 2001 The Base Protocol assumes a peer-to-peer communication model, as opposed to a client-server model. The following goals motivated the design of the base protocol: - lightweight and simple to implement protocol - Large AVP space - Efficient encoding of attributes, similar to RADIUS - Support for vendor specific AVPs and Commands - Support for large number of simultaneous pending requests - Reliability provided by underlying SCTP - Well-defined fail-over scheme - Ability to quickly detect unreachable peers - No silent message discards - Support of unsolicited messages to "clients" - integrity and confidentiality at the AVP level - Hop-by-Hop security - One session per authentication/authorization flow - Provide redirect (referal) services, to allow bypassing of broker The Diameter base protocol is intended to simply provide a secure transport for the messages defined in the various application- specific extensions. It is therefore imperative that the base be lightweight and simple to implement. In the Diameter protocol, data objects are encapsulated within the Attribute Value Pair (AVP). An AVP consists of three parts: the Identifier, Length and Data. A unique AVP Identifier is assigned to all data objects in order to be able to distinguish the data contained. The AVP Identifier namespace must be sufficiently large to ensure that future protocol extensibility is not limited by the size of the namespace, as in the RADIUS protocol. Furthermore, vendors wishing to add "proprietary" extensions must be allowed to do so by using a vendor-specific namespace, managed by IANA. For many years the question as to whether RADIUS should operate over UDP or TCP has led to heated discussion. It must be determined whether the benefits that UDP provides are worth the implementation complexities. Over time, it has become clear that these benefits are well worth the cost. The issue with TCP is that an AAA protocol requires a quick retransmission and fail-over scheme, which TCP cannot provide. The Diameter protocol must be able to operate over a transport that has an aggressive retransmission strategy in order to efficiently switch to an alternate host when the peer in question is no longer reachable. Contrary to RADIUS, the Diameter protocol requires that each node in a proxy chain acknowledge a request, or response, at the "transport" Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 15]
Internet-Draft February 2001 layer. Since Diameter operates over SCTP, which provides a reliable transport, each node in a proxy chain is responsible for retransmission of unacknowledged messages. The SCTP transport provides retransmission detection, which greatly simplifies server implementations, and consequently allows a given server to support a much larger number of transactions per second. SCTP also provides windowing, which allows the flow of packets to a specific server to be controlled. Clever implementations can then decide to send the packets to an alternate server that can handle the load. With the exception of a few security related errors, the Diameter protocol requires that all messages be acknowledged, either with a successful response or one that contains an error code. Where the RADIUS protocol is client-server, the Diameter protocol is peer to peer, allowing unsolicited messages to be sent to NASes. There are many benefits to peer-to-peer AAA protocols. One example is the on-demand retrieval of accounting data; another, server-initiated session termination. The Base Diameter protocol provides for hop-by-hop security, similar to the scheme employed by RADIUS today. However, the Diameter protocol also provides for replay protection through a timestamp mechanism. This security scheme requires a long lived security association to be established by peers, or can make use of keying material negotiated out of band. The Base Protocol also allows the built-in security measure to be turned off, (i.e., in cases where IPSec is in use). The Diameter protocol is a session-oriented protocol, meaning that for each user being authenticated, there exists a session between the initiator of the authentication/authorization request and the home Diameter server. Sessions are identified through a session identifier, which is globally unique at any given time. All subsequent Diameter transactions (e.g. accounting) must include the session identifier to reference the session. A Session termination message exists in order to end a Diameter session, and all sessions have a timeout value in order to ensure that they can be cleaned up properly. Since today's processors work more efficiently when objects are aligned on a 32-bit boundary, the Diameter protocol requires 32-bit alignment of all headers and the data. This has recently become a common requirement for many new protocols at the IETF. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 16]
Internet-Draft February 2001 3.1.1 Proxy Support The Diameter protocol was designed from the beginning to support roaming networks. This means that every node in the network is responsible for it's own retransmissions, and the protocol does allow each node to know a priori the reachability state of each peer. This allows for a resilient network, and efficient retransmission scheme. Figure 3 depicts a network where each Diameter server can communicate with all other servers. Figure 3 depicts an example of a Diameter network that includes two proxy servers in the local network for resilience. Once a message has been sent from the NAS to one of its local proxy servers, they are responsible for any retransmissions of the message to one of the home servers. Since the underlying transport provides quick peer failure detection, upon such notification, the local proxies can quickly transmit the message to the alternate peer in the home network. Figure 3 depicts an example of a proxy network that includes alternate servers for resilience. Each node in the proxy chain is responsible for its own retransmissions and fail-over detection. This provides the following benefits: - The number of Diameter nodes in the network is greatly reduced - The latency involved in switch-over to an alternate peer is greatly reduced - Reliability is increased local ISP Home ISP +--------+ +--------+ | Primary| | Primary| +-------+ | Proxy |------------>| Home | | |----------->| Server |<-----+----->| Server | |Network| +--------+ | +--------+ |Access | | |Server | +--------+ | +--------+ | |----------->| 2 nd |<-----+----->| 2 nd | +-------+ | Proxy |------------>| Home | | Server | | Server | +--------+ +--------+ Figure 3: Diameter Proxy Network 3.1.2 Redirect Support A redirect server is one that provides simple Diameter message "routing" functions. Redirect servers are generally deployed in order Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 17]
Internet-Draft February 2001 to reduce the configuration information that would otherwise be necessary on all servers owned members of a roaming consortium. Redirect servers allow Diameter entities to communicate directly by providing NAI realm to home server translation services. When a request is received by a redirect server, a redirect response is returned to the initiator of the request with the information necessary to communicate directly with servers in the home domain. A broker, owned by a roaming consortium, MAY also provide Certificate Authority services, by issuing certificates to all Diameter servers within the consortium (or alternatively sign existing certificates). This eliminates the need for long lived shared secrets between Diameter servers, and enables protocols such as IP Security to be used. In the event that non repudiation is required, public key cryptography can be used to sign usage information in accounting messages. If deemed necessary, a redirect server MAY include the home server's certificates in the redirect response to the requesting Diameter server. +------------------+ +---------+ | Redirect | | CRL DB/ | | Server | | OCSP | +------------------+ +---------+ ^ Request | Response with | Result Code = | Redirect v +----------+ +----------+ | Local | | Home | | Diameter |<------------>| Diameter | | Server | | Server | +----------+ Direct +----------+ Communication Figure 4: Diameter Broker Returning Redirect Indication It is important to note that redirect servers MAY forbid direct communication of accounting messages. This may be required in cases where the server needs such information to provide such services as auditing and settlement services. Such servers MAY also required that both parties sign accounting messages in a serial fashion, as specified in [26]. 3.2 Strong Security Extension Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 18]
Internet-Draft February 2001 The Diameter base protocol allows Diameter servers to communicate securely, using hop-by-hop authentication. Hop-by-hop authentication means that the requesting server has secure communication with a proxy or redirect server, and the proxy has secure communicate with the home server. The Strong Security extension [26] provides strong authentication of selective AVPs, which MAY be used for repudiation purposes. This extension also allows for secure communication through intermediate Diameter proxies. The extension achieves this functionality by allowing the Cryptographic Message Syntax (CMS) S/MIME object to be encapsulated within a Diameter AVP. The CMS object MAY be used for authentication, confidentiality and to carry certificates and certificate revocation lists (CRLs). The extension also provides for multi-party signatures, which is useful in environments where two or more parties must sign information, such as an accounting record. Diameter clients (e.g. NAS, FA) aren't required to implement strong security. It is possible for the local Proxy server to provide this functionality, and MAY require that strong security only be used when messages traverse administrative domain boundaries. The strong security extension MUST only be used in networks that include a Public Key Infrastructure (PKI). 3.3 Mobile-IP Extension The Mobile-IP protocol is used to manage mobility of an IP host across IP subnets [7]. Recent activity within the Mobile-IP Working Group has defined the interaction between Mobile-IP and AAA in order to provide: - Better scaling of security associations - Mobility across administrative domain boundaries - Dynamic home agent assignment The Mobile IP protocol [7] works well when all mobile nodes belong to the same administrative domain. Some of the current work within the Mobile IP Working Group is to allow Mobile IP to scale across administrative domains. This work requires modifications to the existing Mobile IP trust model. Figure 5 depicts the Diameter trust model for Mobile-IP. In this model each network contains mobile nodes (MN) and a Diameter server. Each mobility device shares a security association (SA) with the Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 19]
Internet-Draft February 2001 Diameter server within its own home network. This means that none of the mobility devices initially share a security association. The Diameter servers in both administrative domains can either share a direct security association, or can have a security association with an intermediate proxy. Proxy AAA +--------+ | | |Diameter| +------->| |<------+ | +--------+ | Local | SA SA | Home AAA v v AAA +--------+ +--------+ | | SA4 | | |Diameter|=======================|Diameter| | |(when no proxy is used)| | +--------+ +--------+ ^ ^ ^ | | | SA1 | SA2 | | SA3 | | | v v v +--------+ +--------+ +--------+ | | | | | | | FA | | MN | | HA | | | | | | | +--------+ +--------+ +--------+ Figure 5 - Mobile-IP AAA Trust Model Figure 6 provides an example of a Mobile-IP network that includes Diameter. In the integrated Mobile-IP/Diameter Network, it is assumed that each mobility agent shares a security association between itself and its local Diameter server. Further, the Home and Local Diameter servers both share a security association with the broker's Diameter server. Lastly, it is assumed that each mobile node shares a trust relationship with its home Diameter Server. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 20]
Internet-Draft February 2001 Local Access Broker Home IP Provider Network Network Network +--------+ +--------+ +--------+ | | | | | | |Diameter|<---->|Diameter|<---->|Diameter| | | | | | | +--------+ +--------+ +--------+ ^ ^ | | AAA | | AAA | | v v +---------+ +---------+ | | | | | FA | | HA | | | | | +---------+ +---------+ ^ | Home Network | -Private Network Mobile | -Home Provider IP | -Home ISP v +--------+ | Mobile | | Node | +--------+ Figure 6 - General Wireless IP Architecture for Mobile-IP AAA In this example, a Mobile Node appears within a local network and issues a registration to the Foreign Agent. Since the Foreign Agent does not share any security association with the Home Agent, it sends a Diameter request to its local Diameter server, which includes the authentication information and the Mobile-IP registration request. The Mobile Node cannot communicate directly with the home Diameter Server for two reasons: - It does not have access to the network. The registration request is sent by the Mobile Node to request access to the network. - The Mobile Node may not have an IP address, and may be requesting that one be assigned to it by its home provider. The Local Diameter Server will determine whether the request can be satisfied locally through the use of the Network Access Identifier [3] provided by the Mobile Node. The NAI has the form of user@realm and the Diameter Server uses the realm portion of the NAI to identify the Mobile Node's home Diameter Server. If the Local Diameter Server Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 21]
Internet-Draft February 2001 does not share any security association with the Mobile Node's home Diameter Server, it may forward the request to a proxy or redirect server. If the server has a relationship with the home network, it can forward the request (or redirect), otherwise a failure indication is sent back to the Local Diameter Server. When the home Diameter Server receives the Diameter Request, it authenticates the user and begins the authorization phase. The authorization phase includes the generation of: - Dynamic session keys to be distributed among all mobility agents - Optional dynamic assignment of a home agent - Optional dynamic assignment of a home address (note this could be done by the home agent). - Optional assignment of QOS parameters for the mobile node [22] Once authorization is complete, the home Diameter Server issues an unsolicited Diameter request to the Home Agent, which includes the information in the original Diameter request as well as the authorization information generated by the home Diameter server. The Home Agent retrieves the Registration Request from the Diameter request and processes it, then generates a Registration Reply that is sent back to the home Diameter server in a Diameter response. The message is sent to the Local Server, through the proxy if one was used, and finally to the Foreign Agent. The Diameter servers maintain session state information based on the authorization information. If a Mobile Node moves to another Foreign Agent within the local administrative domain, a request to the local Diameter server can be done in order to immediately return the keys that were issued to the previous Foreign Agent. This eliminates an additional round trip through the internet when micro mobility is involved, and enables smooth hand-off. In order for the Diameter server to be able to provide the keying information to the new Foreign Agent, they must have a pre-existing security association. Note that smooth hand-off is really a mobility function, and it is not clear that Diameter should be involved. However, this example is provided for completeness. If the Mobile Node enters a service area owned by a new service provider, the authentication and authorization request will have to be sent back to the home Diameter server, which will create new keying information. 3.3.1. Minimized Internet Traversal Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 22]
Internet-Draft February 2001 Although it would have been possible for the Diameter interactions to be performed for basic authentication and authorization, and the Registration flow to be sent directly to the Home Agent from the Foreign Agent, one of the key Mobile-IP Diameter requirements is to minimize Internet traversals. Including the Registration Request and Replies in the Diameter messages allows for a single traversal to authenticate the user, perform authorization and process the Registration Request. This streamlined approach is required in order to minimize the latency involved in getting wireless (cellular) devices access to the network. New registrations should not increase the connect time more than what the current cellular networks provide. 3.3.2. Key Distribution In order to allow the scaling of wireless data access across administrative domains, it is necessary to minimize the security associations required. This means that each Foreign Agent does not share a security association with each Home Agent on the Internet. The Mobility Agents share a security association with their local Diameter server, which in turn shares a security association with other Diameter servers. Again, the use of proxies (as defined by ROAMOPS) allows such services to scale by allowing the number of relationships established by the providers to be reduced. After a Mobile Node is authenticated, the authorization phase includes the generation of Sessions Keys. Specifically, three keys are generated: - K1 Key to be shared between the Mobile Node and the Home Agent - K2 Key to be shared between the Mobile Node and the Foreign Agent - K3 Key to be shared between the Foreign Agent and the Home Agent Each key is encrypted in two separate methods. K1 is encrypted using SA3 (for the Home Agent), and using SA2 (for the Mobile Node). K2 is encrypted using SA4 (for the Foreign Agent) and using SA2 (for the Mobile Node). Lastly, K3 is encrypted using SA4 (for the Foreign Agent), and using SA3 (for the Home Agent). When the Foreign Diameter Server receives the keys, they are decrypted and re-encrypted using SA1. All of the Security Associations (SAx) are shown in figure 5. The keys destined for the foreign and home agent are propagated to the mobility nodes via the Diameter protocol, while the keys destined for the Mobile Node are sent via the Mobile-IP protocol. Figure 7 depicts the new security associations used for Mobile-IP message integrity using the keys derived by the Diameter server. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 23]
Internet-Draft February 2001 +--------+ +--------+ | | K3 | | | FA |<-------------------->| HA | | | | | +--------+ +--------+ ^ ^ | K2 K1 | | +--------+ | | | | | +------>| MN |<------+ | | +--------+ Figure 7 - Security Association after Key Distribution Once the session keys have been established and propagated, the mobility devices can exchange registration information directly without the need of the Diameter infrastructure. However the session keys have a lifetime, after which the Diameter infrastructure must be used in order to acquire new session keys. 3.4 NASREQ Extension The NASREQ extension provides authentication and authorization for dial-in PPP users, terminal server access and tunneling applications, such as L2TP. The extension makes use of the attributes defined in the RADIUS protocol to carry the data objects. This was intended to ease migration of existing RADIUS servers to Diameter since they could share a single dictionary and user profile. Furthermore, this would reduce the amount of processing required for an inter-working system that acts as a RADIUS/Diameter bridge. Diameter has native EAP support that solves known problems in the RADIUS protocol. Furthermore, Diameter takes end-to-end authentication one step further by providing for end-to-end authentication via PPP's CHAP. This allows for a more secure authentication infrastructure without having to replace or modify the installed base of clients. If end-to-end CHAP is used in bridged Diameter/RADIUS environments, the bridge host is responsible for generating the challenge to the user. The remaining authentication and authorization logic found in RADIUS implementations can then be re-used. The basic changes are the message formats and the transmission mechanism as defined in the Diameter base protocol. This section does not detail RADIUS authentication and authorization. The interested reader should refer Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 24]
Internet-Draft February 2001 to [1]. 3.5 Accounting Extension The Accounting extension provides usage collection to both the Mobile-IP and the NASREQ extensions. The accounting requirements specifications [6, 8] define that an accounting protocol must provide the following functionality: - Negotiable transfer mechanism. - Provide general purpose AVPs. - Flexible to allows new extensions to use the accounting extension. - Scalable to allows millions to users and thousands of sites. - Secure accounting data transfer. Like the RADIUS protocol, Diameter includes accounting usage information in AVPs. The Accounting extension defines a set of accounting AVPs that are used for all services, while each extension defines their own service specific accounting AVPs. The Diameter Accounting Extension allows accounting information to be sent in real-time. Real-time accounting transfers are useful in environments where timely arrival of the information is required, such as when debit cards are used. The Diameter protocol is session oriented, and each session typically has a finite lifetime. Prior to the timeout of a session, a user typically needs to be re-authentication and/or re-authorized in order to extend the life of the session. In the Mobile-IP world, this equates to the mobility registration lifetime, while in PPP this means that the PPP authentication must be re-opened. When a re- authentication and/or re-authorization occurs, a new token is generated, which is used in the corresponding accounting message. The Diameter Accounting extension combined with the Strong Security [26] extension (see section 3.2), provides strong authentication of accounting data, which MAY be used for repudiation purposes. The strong security extension also allows multiple parties to sign the accounting information, which is beneficial in environments that include a referral broker. The foreign and home servers can both sequentially sign the accounting record, and submit the result to the broker. The broker can then use the signatures to ensure that both parties agreed to the contents of the accounting record. 3.6 Resource Management Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 25]
Internet-Draft February 2001 Many network access services requiring AAA support have a requirement for servers that maintain session state information. An example of such a requirement is in the dial-up PPP world. With the introduction of flat-rate internet access, there has been a surge in fraud where a user provides his username/password pair to other people. The end result is that a single username (account) can have simultaneous concurrent sessions. Internet Service Providers have had to implement proprietary extensions to RADIUS, in order to attempt to identify when such fraud occurs. Unfortunately, since RADIUS does not provide the necessary functionality required to maintain state information, these solutions have been largely unreliable. The Diameter Base Protocol [18], the Accounting extension [11], the Mobile IP [13] and NASREQ [23] extensions provide some of the functionality that is required for servers to maintain state information, such as: - Reliable Transport - Indication of the termination of a session - A Reboot message - Interim Accounting - Accounting On/Off message - Ability to re-authorize an existing session Although the above features do allow nodes to maintain state information, it MAY be necessary for Diameter nodes to request a snapshot of active sessions from a peer. This may be used when state information is lost, which could occur after a device failure, or this may be done periodically in order to ensure that the state is current. The Diameter Resource Management extension [5] provides the messages that are required for a node to request a snapshot of active sessions from a peer. State information is exchange via the Resource-Token AVP, which is used to encapsulate a set of AVPs that describe the session and resources used. There is one Resource-Token AVP for each active session. 3.7 Diameter Command Naming Conventions The following conventions are proposed for the naming of Diameter messages. Diameter commands typically start with an object name, and end with one of the following verbs: Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 26]
Internet-Draft February 2001 3.7.1 Request/Answer Request is used when the command is asking the peer to do something for it, for example, authorize a user, or terminate a session. The Answer MUST contain either a positive or negative result code, telling the requester whether or not the request successfully occurred. Other information can also be returned in the Answer. For example, AA-Request asks the peer device to authorize and/or authenticate a user in order to set up a session. The request may fail, thus the answer may be positive or negative. 3.7.2 Query/Response Query is used when the command is asking for information that it expects the peer to have. An example would be querying for current configuration information, or querying for information on resources or sessions in use. The Response usually contains a positive result code and the information, or a negative result code with the reason for not answering the query. For example, Resource-Query requests the peer device to return specific information about one or more resources. The answer is returned in a Resource-Response. 3.7.3 Indication Indication is used when the command is giving information on something that is about to or has already occurred. The peer receiving the message does not respond to the message, but a transport level acknowledgement must be done in order to ensure that the message was reliably delivered. 4.0 Why not LDAP? One common question is 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 read/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 Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 27]
Internet-Draft February 2001 directory so outside routers have writable access. The security implications set aside, having 1000's of routers constantly read/write to the directory would cause some additional problems to the Directory Service. Finally, LDAP does not provide server initiated messages which is a requirement for an AAA protocol. 5.0 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, Beadles, "The Network Access Identifier", RFC 2486, Janu- ary 1999. [4] Rigney, "RADIUS Accounting", RFC-2139, April 1997. [5] P. Calhoun, "Diameter Resource Management", draft-calhoun- diameter-res-mgmt-07.txt, IETF Work in Progress, January 2001. [6] B. Aboba, J. Arkko, D. Harrington. "Introduction to Accounting Management", draft-ietf-aaa-acct-05.txt, IETF work in progress, June 2000. [7] C. Perkins, Editor. IP Mobility Support. RFC 2002, October 1996. [8] S. Kent, R. Atkinson, "Security Architecture for the Internet Protocol", RFC 1825, November 1998. [9] Bradner, "Key words for use in RFCs to Indicate Requirements Levels", BCP 14, RFC 2119, March 1997. [10] L. Blunk, J. Vollbrecht, "Extensible Authentication Protocol (EAP)", RFC 2284, March 1998. [11] J. Arkko, P. Calhoun, P. Patel, G. Zorn, "Diameter Accounting Extension", draft-calhoun-diameter-accounting-09.txt, IETF work in progress, January 2001. [12] J. Case, D. Harrington, R. Presuhn, B. Wijnen, "Message Process- ing and Dispatching for the Simple Network Management Proto- col:", RFC 2572, April 1999. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 28]
Internet-Draft February 2001 [13] P. Calhoun, C. Perkins, "Diameter Mobile IP Extensions", draft- calhoun-diameter-mobileip-12.txt, IETF work in progress, January 2001. [14] M. Baum, H. Perritt, "Electronic Contracting, Publishing and EDI Law", Prentice-Hall, ISBN 0-471-53135-9. [15] P. Calhoun, C. Perkins "Mobile IP Foreign Agent Challenge/Response Extension", RFC 3012, November 2000. [16] D. Harkins, D. Carrell, "The Internet Key Exchange (IKE)" RFC 1409, November 1998. [17] W. Simpson, "The Point-to-Point Protocol (PPP)", RFC 1661, STD 51, July 1994. [18] P. Calhoun, A. Rubens, H. Akhtar, E. Guttman, "Diameter Base Protocol", draft-calhoun-diameter-18.txt, IETF work in progress, January 2001. [19] B. Aboba, G. Zorn, "Criteria for Evaluating Roaming Protocols", RFC 2477, January 1999. [20] B. Aboba, J. Lu, J. Alsop, J. Ding, W. Wang, "Review of Roaming Implementations", RFC 2194, September 1997. [21] B. Aboba, J. Vollbrecht, "Proxy Chaining and Policy Implementa- tion in Roaming", RFC 2607, June 1999. [22] T. Hiller and al, "CDMA2000 Wireless Data Requirements for AAA", draft-hiller-cdma2000-aaa-02.txt, IETF work in progress, Sep- tember 2000. [23] P. Calhoun, W. Bulley, A. Rubens, J. Haag, "Diameter NASREQ Extension", draft-calhoun-diameter-nasreq-06.txt, IETF work in progress, January 2001. [24] R. Stewart et al., "Simple Control Transmission Protocol", RFC 2960, October 2000. [25] Myers, Ankney, Malpani, Galperin, Adams, "X.509 Internet Public Key Infrastructure Online Certificate Status Protocol (OCSP)", RFC 2560, June 1999. [26] P. Calhoun, W. Bulley, S. Farrell, "Diameter Strong Security Extension", draft-calhoun-diameter-strong-crypto-06.txt, IETF work in progress, January 2001. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 29]
Internet-Draft February 2001 6.0 Acknowledgements The Authors would like to thanks Bernard Aboba and Jari Arkko for their Accounting Requirements contribution. Thanks also goes to Erik Guttman for some very useful comments in helping make this draft more readable. The Mobile-IP Extension section was text originally writ- ten by Pat Calhoun for another Internet-Draft, which was subsequently cleaned up by Dave Spence. The authors would like to thank Nenad Trifunovic, Tony Johansson and Pankaj Patel for their participation in the Document Reading Party. A final thanks to Stephen Farrell for his security review. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 30]
Internet-Draft February 2001 7.0 Author's Addresses Questions about this memo can be directed to: Pat R. Calhoun Sun Laboratories, Network and Security 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 Cisco Systems, Inc. 500 108th Avenue N.E., Suite 500 Bellevue, WA 98004 USA Phone: +1 425 438 8218 E-Mail: gwz@cisco.com Ping Pan Bell Laboratories Lucent Technologies 101 Crawfords Corner Road Holmdel, NJ 07733 USA Phone: +1 732-332-6744 E-mail: pingpan@dnrc.bell-labs.com Haseeb Akhtar Wireless Technology Labs Nortel Networks 2221 Lakeside Blvd. Richardson, TX 75082-4399 USA Phone: +1 972-684-8850 E-Mail: haseeb@nortelnetworks.com Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 31]
Internet-Draft February 2001 8.0 Full Copyright Statement Copyright (C) The Internet Society (2001). 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 docu- ment itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of develop- ing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The lim- ited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DIS- CLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 9.0 Expiration Date This memo is filed as <draft-calhoun-diameter-framework-09.txt> and expires in July 2001. Calhoun, Zorn, Pan, Akhtar expires July 2001 [Page 32]