AAA Working Group Pat R. Calhoun Internet-Draft Sun Microsystems, Inc. Category: Standards Track Haseeb Akhtar <draft-ietf-aaa-diameter-06.txt> Nortel Networks Jari Arkko Oy LM Ericsson Ab Erik Guttman Sun Microsystems, Inc. Allan C. Rubens Tut Systems, Inc. Glen Zorn Cisco Systems, Inc. June 2001 Diameter Base Protocol 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. Distribution of this memo is unlimited. Copyright (C) The Internet Society 2001. All Rights Reserved. Calhoun et al. expires December 2001 [Page 1]
Internet-Draft June 2001 Abstract The Diameter base protocol is intended to provide a AAA framework for Mobile-IP, NASREQ and ROAMOPS. This draft specifies the message format, transport, error reporting and security services to be used by all Diameter applications and MUST be supported by all Diameter implementations. Table of Contents 1.0 Introduction 1.1 Diameter Protocol 1.2 Requirements language 1.3 Terminology 2.0 Protocol Overview 2.1 Transport 2.1.1 SCTP Guidelines 2.2 Securing Diameter Messages 2.3 Diameter Protocol Extensibility 2.3.1 Defining new AVP Values 2.3.2 Creating new AVPs 2.3.3 Creating a new Diameter Applications 2.3.4 Application authentication procedures 2.4 Diameter Applications 2.5 Role of Diameter Agents 2.5.1 Relay Agents 2.5.2 Proxy Agents 2.5.3 Redirector Agents 2.5.4 Translation Agents 2.6 Diameter Server Discovery 3.0 Diameter Header 3.1 Command Code Definitions 3.2 Command Code ABNF specification 3.3 Diameter Command Naming Conventions 4.0 Diameter AVPs 4.1 AVP Header 4.2 Optional Header Elements 4.3 AVP Data Formats 4.4 Derived AVP Data Formats 4.5 Grouped AVP Values 4.5.1 Example AVP with a Grouped Data type 4.6 Diameter Base Protocol AVPs 5.0 Diameter message processing 5.1 Diameter request routing overview 5.1.1 Originating a Request 5.1.2 Sending a Request 5.1.3 Processing Local Requests Calhoun et al. expires December 2001 [Page 2]
Internet-Draft June 2001 5.1.4 Request Forwarding 5.1.5 Peer Table 5.1.6 Request Routing 5.1.7 Realm-Based Routing Table 5.1.8 Redirecting requests 5.1.9 Relaying and Proxying Requests 5.2 Diameter Answer Processing 5.2.1 Processing received Answers 5.2.2 Relaying and Proxying Answers 5.3 Hiding Network Topology 5.4 Origin-Host AVP 5.5 Origin-Realm AVP 5.6 Destination-Host AVP 5.7 Destination-Realm AVP 5.8 Routing AVPs 5.8.1 Route-Record AVP 5.8.2 Proxy-Info AVP 5.8.3 Proxy-Host AVP 5.8.4 Proxy-State AVP 5.9 Redirect-Host AVP 5.10 Redirect-Host-Usage AVP 5.11 Redirect-Max-Cache-Time AVP 6.0 Capabilities Negotiation 6.1 Application Identifiers 6.2 Capabilities-Exchange-Request 6.3 Capabilities-Exchange-Answer 6.4 Vendor-Id AVP 6.5 Firmware-Revision AVP 6.6 Auth-Application-Id AVP 6.7 Host-IP-Address AVP 6.8 Supported-Vendor-Id AVP 6.9 Product-Name AVP 6.10 Acct-Application-Id AVP 6.11 Vendor-Specific-Application-Id AVP 7.0 Transport Failure Detection 7.1 Device-Watchdog-Request 7.2 Device-Watchdog-Answer 7.3 Failover/Failback Procedures 8.0 Peer State Machine 8.1 Incoming connections 8.2 Events 8.3 Actions 8.4 The Election Process 9.0 Error Handling 9.1 Result-Code AVP 9.1.1 Informational 9.1.2 Success 9.1.3 Protocol Errors Calhoun et al. expires December 2001 [Page 3]
Internet-Draft June 2001 9.1.4 Transient Failures 9.1.5 Permanent Failures 9.2 Message-Reject-Answer 9.3 Error-Message AVP 9.4 Error-Reporting-Host AVP 9.5 Failed-AVP AVP 10.0 Diameter User Sessions 10.1 Authorization Session State Machine 10.2 Accounting Session State Machine 10.3 Server-Initiated Re-Auth 10.3.1 Re-Auth-Request 10.3.2 Re-Auth-Answer 10.4 Session Termination 10.4.1 Session-Termination-Request 10.4.2 Session-Termination-Answer 10.5 Aborting a Session 10.5.1 Abort-Session-Request 10.5.2 Abort-Session-Answer 10.6 Inferring Session Termination from Origin-State-Id 10.7 Session-Id AVP 10.8 Authorization-Lifetime AVP 10.9 Session-Timeout AVP 10.10 User-Name AVP 10.11 Termination-Cause AVP 10.12 Origin-State-Id AVP 10.13 Session-Binding AVP 10.14 Session-Server-Failover AVP 10.15 Multi-Round-Time-Out AVP 10.16 Class AVP 11.0 Accounting 11.1 Server Directed Model 11.2 Protocol Messages 11.3 Application document requirements 11.4 Fault Resilience 11.5 Accounting Records 11.6 Correlation of Accounting Records 12.0 Accounting Command-Codes 12.1 Accounting-Request 12.2 Accounting-Answer 13.0 Accounting AVPs 13.1 Accounting-Record-Type AVP 13.2 Accounting-Interim-Interval AVP 13.3 Accounting-Record-Number AVP 13.4 Accounting-Session-Id AVP 13.5 Accounting-Multi-Session-Id AVP 14.0 AVP Occurrence Table 14.1 Base Protocol Command AVP Table 14.2 Accounting AVP Table Calhoun et al. expires December 2001 [Page 4]
Internet-Draft June 2001 15.0 IANA Considerations 15.1 AVP Header 15.1.1 AVP Code 15.1.2 AVP Flags 15.2 Diameter Header 15.2.1 Command Codes 15.2.2 Message Flags 15.3 Application Identifier Values 15.4 Result-Code AVP Values 15.5 Accounting-Record-Type AVP Values 15.6 Termination-Cause AVP Values 15.7 Redirect-Host-Usage AVP Values 15.8 Session-Server-Failover AVP Values 15.9 Session-Binding AVP Values 15.10 Diameter TCP/SCTP Port Numbers 16.0 Diameter protocol related configurable parameters 17.0 Security Considerations 18.0 References 19.0 Acknowledgements 20.0 Authors' Addresses 21.0 Full Copyright Statement 22.0 Expiration Date Appendix A. Diameter Service Template Calhoun et al. expires December 2001 [Page 5]
Internet-Draft June 2001 1.0 Introduction Historically, the RADIUS protocol has been used to provide AAA services for dial-up PPP [42] 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 [20, 43, 44] 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 [45] 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 et al. expires December 2001 [Page 6]
Internet-Draft June 2001 ensure that the effort remains focused 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 Diameter Protocol The Diameter protocol allows peers to exchange a variety of messages. The base protocol provides the following facilities: - Delivery of AVPs (attribute value pairs) - Capabilities negotiation, as required in [20] - Error notification - Extensibility, through addition of new commands and AVPs, as required in [21] All data delivered by the protocol is in the form of an AVP. Some of these AVP values are used by the Diameter protocol itself, while others deliver data associated with particular applications which employ Diameter. AVPs may be added arbitrarily to Diameter messages, so long as the required AVPs are included and AVPs which are explicitly excluded are not included. AVPs are used by base Diameter protocol to support the following required features: - Transporting of user authentication information, for the purposes of enabling the Diameter server to authenticate the user. - Transporting of service specific authorization information, between client and servers, allowing the peers to decide whether a user's access request should be granted. - Exchanging resource usage information, which MAY be used for accounting purposes, capacity planning, etc. - Relaying, proxying and re-directing of Diameter messages through a server hierarchy. The Diameter base protocol provides the minimum requirements needed for an AAA transport protocol, as required by NASREQ [21], Mobile IP [22, 23], and ROAMOPS [20]. The base protocol is not intended to be used by itself, and must be used with a Diameter application, such as Mobile IP [10]. The Diameter protocol was heavily inspired and builds upon the tradition of the RADIUS [1] protocol. See section 2.4. for more information on Diameter applications. Any node can initiate a request. In that sense, Diameter is a peer to peer protocol. In this document, a Diameter client is the device that normally initiates a request for authentication and/or authorization Calhoun et al. expires December 2001 [Page 7]
Internet-Draft June 2001 of a user. A Diameter server is the device that either forwards the request to another Diameter server (known as a proxy), or one that performs the actual authentication and/or authorization of the user based on some profile. Given that the server MAY send unsolicited messages to clients, it is possible for the server to initiate such messages. An example of an unsolicited message would be for a request that the client issue an accounting update. 1.2 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 [13]. 1.3 Terminology Accounting The act of collecting information on resource usage for the purpose of trend analysis, auditing, billing, or cost allocation. Accounting 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 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 relay, proxy or redirect server, and MAY be operated by roaming consortiums. Diameter Agent Calhoun et al. expires December 2001 [Page 8]
Internet-Draft June 2001 A Diameter Agent is a host that is providing either server, relay, proxy or redirector services. 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 Node A Diameter node is a host that implements the Diameter protocol, and acts either as a Client, or as a Proxy, Redirector, Server or Translation agent. Diameter Server A Diameter Server is one that handles authentication, authorization and accounting requests for a particular realm. By its very nature, a Diameter Server MUST support Diameter applications in addition to the base protocol. Downstream Server Diameter Proxy servers identify a downstream server as one that is providing routing services towards the Diameter client. Home Domain A Home Domain is the administrative domain with whom the user maintains an account relationship. Home Server See Diameter Server. 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. Calhoun et al. expires December 2001 [Page 9]
Internet-Draft June 2001 Proxy In addition to forwarding requests and responses, proxies enforce policies relating to resource usage and provisioning. This is typically accomplished by tracking the state of NAS devices. While proxies typically do not respond to client Requests prior to receiving a Response from the server, they may originate Reject messages in cases where policies are violated. As a result, proxies need to understand the semantics of the messages passing through them, and may not support all Diameter applications. 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 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. Relay Relays forward requests and responses based on routing-related AVPs and domain forwarding table entries. Since relays do not enforce policies, they do not examine or alter non-routing AVPs. As a result, relays never originate messages, do not need to understand the semantics of messages or non-routing AVPs, and are capable of handling any Diameter applications or message type. Since relays make decisions based on information in routing AVPs and domain forwarding tables they do not keep state on NAS resource usage or conversations in progress. Redirector Rather than forwarding requests and responses between clients and servers, Re-directs refer clients to servers and allow them to communicate directly. Since Re-directs do not sit in the forwarding path, they do not alter any AVPs transitting between client and server. Re-direct proxies do not originate messages and are capable of handling any message type, although they may be configured only to re-direct messages of certain types, while acting as Routing or Policy proxies for other types. As with Routing proxies, re-directs do not keep state with respect to conversations or NAS resources. Roaming Relationships Calhoun et al. expires December 2001 [Page 10]
Internet-Draft June 2001 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. devices serving the same user. Upstream Server Diameter Proxy servers identify an upstream server as one that is providing routing services towards the home server for a particular message. 2.0 Protocol Overview The base Diameter protocol is never used on its own. It is always extended for a particular application. Three Diameter applications are defined by companion documents: NASREQ [7], Mobile IP [10], CMS Security [11]. These options are introduced in this document but specified elsewhere. Additional Diameter applications MAY be defined in the future (see Section 15.3). Diameter Clients MUST support the base protocol, which includes accounting. In addition, they MUST fully support each Diameter application which is needed to implement the client's service, e.g. NASREQ and/or Mobile IP. A Diameter Client which does not support both NASREQ and Mobile IP, MUST be referred to as "Diameter X Client" where X is the application which it supports, and not a "Diameter Client." Diameter Servers must support the base protocol, which includes accounting. In addition, they MUST fully support each Diameter application which is needed to implement the intended service, e.g. NASREQ and/or Mobile IP. A Diameter Server which does not support both NASREQ and Mobile IP, MUST be referred to as "Diameter X Server" where X is the application which it supports, and not a "Diameter Server." Diameter Relays and Redirectors are, by definition, protocol transparent, and MUST transparently support the Diameter base protocol, which includes accounting, and all Diameter applications. Calhoun et al. expires December 2001 [Page 11]
Internet-Draft June 2001 Diameter Proxies MUST suppport the base protocol, which includes accounting. in addition, they MUST fully support each Diameter application which is needed to implement proxied services, e.g. NASREQ and/or Mobile IP. A Diameter Proxy which does not support also both NASREQ and Mobile IP, MUST be referred to as "Diameter X Proxy" where X is the application which it supports, and not a "Diameter Proxy." The CMS Diameter security application [11] contains two features: 1. A set of messages that allows a Diameter node to establish a security association, which is used to secure AVPs within a Diameter message, even though the message may traverse intermediate Diameter agents. A set of AVPs are also defined to sign and encrypt AVPs, as well as to transport certificates. This feature MUST be supported by Diameter server and proxy agents, SHOULD be supported by Diameter clients, and MAY be supported by relay and redirector agents. 2. A set of messages, known as PDSR and PDSA, allows a Diameter client to request that an agent establish a Diameter security association with a server in a specific realm. This feature MUST be supported by Diameter clients and Proxy agents, and MAY be supported by Diameter servers, relay and redirector agents. The base Diameter protocol concerns itself with capabilities negotiation, and how messages are sent and how peers may eventually be abandoned. The base protocol also defines certain rules which apply to all exchanges of messages between Diameter peers. Communication between Diameter peers begins with one peer sending a message to another Diameter peer. The set of AVPs included in the message is determined by a particular Diameter application. One AVP that is included to reference a user's session is the Session-Id. The initial request for authentication and/or authorization of a user would include the Session-Id. The Session-Id is then used in all subsequent messages to identify the user's session (see section 10.0 for more information). The communicating party may accept the request, or reject it by returning an answer message with Result-Code AVP set to indicate an error occurred. The specific behavior of the diameter server or client receiving a request depends on the Diameter application employed. Session state (associated with a Session-Id) MUST be freed upon receipt of the Session-Termination-Request, Session-Termination- Answer, expiration of authorized service time in the Session-Timeout AVP, and according to rules established in a particular Diameter application. Calhoun et al. expires December 2001 [Page 12]
Internet-Draft June 2001 The Diameter base protocol provides the Authorization-Lifetime AVP, which MAY be used by applications to specify the duration of a specific authorized session. 2.1 Transport The base Diameter protocol is run on port TBD of both TCP [27] and SCTP [26] transport protocols (for interoperability test purposes port 1812 will be used until IANA assigns a port to the protocol). When used with TLS [38], The Diameter protocol is run on port TBD of both TCP and SCTP. Diameter clients MUST support either TCP or SCTP, while agents and servers MUST support both. Future versions of this specification MAY mandate that clients support SCTP. A Diameter node MAY initiate connections from any source port, but MUST be prepared to receive connections on port TBD. Note that the source and destination addresses used in request and replies MAY any of a peer's valid IP addresses. A given Diameter process SHOULD use the same port number to send all messages to aid in identifying which process sent a given message. More than one Diameter process MAY exist within a single host, so the sender's port number is needed to discriminate them. When no transport connection exists with a peer, an attempt to connect SHOULD be periodically attempted. This behavior is handled via the Tc timer, whose recommended value is 30 seconds. When connecting to a peer, and either zero or more transports are specified, SCTP SHOULD be tried first, followed by TCP. See section 2.6 for more information on peer discovery. Diameter implementations SHOULD be able to interpret ICMP protocol and port unreachable messages as explicit indications that the server is not reachable, in addition to interpreting ECONNREFUSED (a reset from the transport) and timed-out connection attempts. 2.1.1 SCTP Guidelines The following are guidelines for Diameter implementations that support SCTP: 1. For interoperability: All Diameter nodes MUST be prepared to receive Diameter messages on any SCTP stream in the Calhoun et al. expires December 2001 [Page 13]
Internet-Draft June 2001 association. 2. To prevent blocking: All Diameter nodes SHOULD utilize all SCTP streams available to the association to prevent head-of-the- line blocking. 2.2 Securing Diameter Messages Diameter clients, such as Network Access Servers (NASes) and Foreign Agents MUST support IP Security [37], and MAY support TLS [38]. Diameter servers MUST support TLS, but the administrator MAY opt to configure IPSec instead of using TLS. Operating the Diameter protocol without any security mechanism is not recommended. 2.3 Diameter Protocol Extensibility There are various ways the Diameter protocol can be extended. This section is intended to assist protocol designers in selecting the best method of using the Diameter protocol. 2.3.1 Defining new AVP Values Defining a new AVP value is the best approach when a new application needs to make use of an existing Diameter application, but requires that an existing AVP communicate different service-specific information (e.g. NAS-Port-Type set to avian carriers). When an existing AVP can be used to communicate the new information, this approach is preferred over creating new AVPs. In order to allocate a new AVP value, a request MUST be sent to IANA, with a detailed explanation of the value. Furthermore, if the command code on which the AVP value is to be used would require a different set of mandatory AVPs be present, the list of AVPs must accompany the request. 2.3.2 Creating new AVPs New AVPs may be created when a new application requiring Diameter support can make use of an existing Diameter application, but requires new AVPs to communicate service-specific information. Prior to defining the AVP, the AVP type MUST be one of the types listed in section 4.3. In the event that a logical grouping of AVPs is necessary, and multiple "groups" are possible in a given command, Calhoun et al. expires December 2001 [Page 14]
Internet-Draft June 2001 it is highly recommended that a Grouped AVP be used (see Section 4.5). In order to create a new AVP, a request MUST be sent to IANA, with a detailed explanation of the AVP, its type and possible values. Furthermore, the request MUST include the commands that would make use of the AVP. Note that new AVPS to be used with an existing application MUST NOT be defined to have the 'M'andatory bit set. 2.3.3 Creating new Diameter Applications Should a new application require Diameter support, but it cannot fit within an existing application without requiring major changes to the specification, it may be desirable to create a new Diameter application. Major changes to an application include: - Requiring a whole different set of mandatory AVPs to a command - Requiring a command that has a different number of round trips to satisfy a request (e.g. application foo has a command that requires one round trip, but new application bar has a command that requires two round trips to complete). - The method used to authenticate the user is drastically different from any existing application, and the authentication information cannot be carried within the AVPs defined in the application. Note that the creation of a new application should be viewed as a last resort. New Diameter applications MUST define at least one Command Code, the expected AVPs in an ABNF [31] grammar (see section 3.2), and MAY also define new AVPs. If the Diameter application has any accounting requirements, it MUST also specify the AVPs that are to be present in the Diameter Accounting messages (see section 11.3). When possible, a new Diameter application SHOULD attempt to re-use any existing Diameter AVP, in order to reduce the possibility of having multiple AVPs that carry similar information. Every Diameter application specification MUST have an IANA assigned Application Identifier (see section 2.4). 2.3.4 Application authentication procedures When possible, applications SHOULD be designed such that new Calhoun et al. expires December 2001 [Page 15]
Internet-Draft June 2001 authentication methods MAY be added without requiring changes to the application. This MAY require that new AVP values be assigned to represent the new authentication transform, or any other scheme that produces similar results. When possible, authentication frameworks, such as Extensible Authentication Protocol [25], SHOULD be used. 2.4 Diameter Application Compliance Application Identifiers are advertised during the capabilities exchange phase (see section 6.0). For a given application, there are two different ways of advertising support. First, advertising support of the application via the Auth-Application-Id implies that the sender supports all authentication and authorization command codes, and the AVPs specified in the associated ABNFs, described in the specification. Second, advertising support of the application via the Acct-Application-Id implies that the sender supports the Accounting command codes defined in this specification, as well as the accounting AVPs defined in the application's specification. An implementation MAY add arbitrary AVPs to any command defined in an application, including vendor-specific AVPs. However, implementations that add such AVPs with the Mandatory 'M' bit set are not compliant, and are at fault if the peer rejects the request. If the sender of such a message wishes to provide service, it MUST resend the message with the offending AVPs removed. 2.5 Role of Diameter Agents In addition to client and servers, the Diameter protocol introduces relays, redirectors, proxies and translation gateways, each of which is defined in Section 1.3. These Diameter agents are useful for several reasons: - They can distribute administration of systems to a configurable grouping, including the maintenance of security associations. - They can be used for concentration of requests from an number of co-located or distributed NAS equipment sets to a set of like user groups. - They can do value-added processing to the requests or responses. - They can be used for load balancing. - A complex network will have multiple authentication sources, they can sort requests and forward towards the correct target. The Diameter protocol requires that agents maintain transaction state, which is used for failover purposes. Transaction state implies that upon forwarding a request, it's Hop-by-Hop identifier is saved, the field is replaced with a locally unique identifier, which is Calhoun et al. expires December 2001 [Page 16]
Internet-Draft June 2001 restored to its original value when the corresponding answer is received. The request's state is released upon receipt of the answer. A stateless agent is one that only maintains transaction state. The Proxy-Info AVP allows stateless agents to add local state to a Diameter request, with the guarantee that the same state will be present in the answer. However, the protocol's failover procedures require that agents maintain a copy of pending requests. A stateful agent is one that maintains session state information, by keeping track of all authorized active sessions. Each authorized session is bound to a particular service, and its state is considered active either until it is notified otherwise, or by expiration. Each authorized session has a expiration, which is communicated by Diameter servers via the Authorized-Lifetime AVP. Maintaining session state MAY be useful in certain applications, such as: - Protocol translation (e.g. RADIUS <-> Diameter) - Limiting resources authorized to a particular user - Per user or transaction auditing A Diameter agent MAY act in a stateful manner for some requests, while be stateless for others. A Diameter implementation MAY act as one type of agent for some requests, and as another type of agent for others. 2.5.1 Relay Agents Relay Agents are Diameter agents that accept requests and route messages to other Diameter agents based on information found in the messages (e.g. Destination-Realm). This routing decision is performed using a list of supported domains, and known peers. This is known as the Diameter Routing Table, as is defined further in section 5.1.7. Relays MAY be used to aggregate requests from multiple Network Access Servers (NASes) within a common geographical area (POP). The use of Relays is advantageous since it eliminates the need for NASes to be configured with the necessary security information they would otherwise require to communicate with Diameter servers in other realms. Likewise, this reduces the configuration load on Diameter servers that would otherwise be necessary when NASes are added, changed or deleted. Relays modify Diameter messages by inserting, and removing, routing information, but do not modify any other portion of a message. Further, Relays inherent simplicity implies that they are stateless, Calhoun et al. expires December 2001 [Page 17]
Internet-Draft June 2001 and therefore SHOULD NOT maintain session state, but MUST maintain transaction state. +------+ ---------> +------+ ---------> +------+ | | 1. Request | | 2. Request | | | NAS | | DRL | | HMS | | | 4. Answer | | 3. Answer | | +------+ <--------- +------+ <--------- +------+ mno.net mno.net abc.com Figure 1: Relaying of Diameter messages The example provided in Figure 1 depicts a request issued from NAS, which is an access device, for the user bob@abc.com. Prior to issuing the request, NAS performs a Diameter route lookup, using "abc.com" as the key, and determines that the message is to be relayed to DRL, which is a Diameter Relay. DRL performs the same route lookup as NAS, and relays the message to HMS, which is abc.com's Home Diameter Server. HMS identifies that the request can be locally supported (via the realm), processes the authentication and/or authorization request, and replies with an answer, which is routed back to NAS using Diameter routing AVPs. Since Relays do not perform any application level processing, they provide relaying services for all Diameter applications, and therefore MUST advertise the Relay Application Identifier. 2.5.2 Proxy Agents Similarly to Relays, Proxy agents route Diameter messages using the Diameter Routing Table. However, they differ since they modify messages to implement policy enforcement. This requires that proxies maintain the state of their downstream peers (e.g. access devices) to enforce resource usage, provide admission control, and provisioning. It is important to note that although proxies MAY provide a value-add function for NASes, they do not allow access devices to use the Diameter CMS Security application, since modifying messages breaks authentication. Proxies MAY be used in call control centers or access ISPs that provide outsourced connections, they can monitor the number and types of ports in use, and make allocation and admission decisions according to their configuration. Proxies that wish to limit resources MUST be stateful, and all Proxies MUST maintain transaction state. Calhoun et al. expires December 2001 [Page 18]
Internet-Draft June 2001 Proxy agents MUST NOT allow CMS security to be established between two peers if it expects to modify ANY non-routing AVP in messages exchanged between the peers. See [11] for more information. Since enforcing policies requires an understanding of the service being provided, Proxies MUST only advertise the Diameter applications they support. 2.5.3 Redirector Agents Redirector agents provide Realm to Server address resolution, and use the Diameter routing table to determine where a given request should be forwarded. When a request is received by a Diameter redirector, a special answer is created, which includes the identity of the Diameter server(s) the originator of the request should contact directly. Redirectors are useful in scenarios where the Diameter routing configuration needs to be centralized. An example is a redirector that provides services to all members of a consortium, but does not wish to be burdened with relaying all messages between domains. This scenario is advantageous since it does not require that the consortium provide routing updates to its members when changes are made to a member's infrastructure. Since redirectors do not relay messages, and only return an answer with the information necessary for Diameter agents to communicate directly, they do not modify messages. Since redirectors do not receive answer messages, they cannot maintain session state. Further, since redirectors never relay requests, they are not required to maintain transaction state. The example provided in Figure 2 depicts a request issued from the access device, NAS, for the user bob@abc.com. The message is forwarded by the NAS to its relay, DRL, which does not have a routing entry in its Diameter Routing Table for abc.com. DRL has a default route configured to DRD, which is a redirector that returns a redirect notification to DLR, as well as HMS' contact information. Upon receipt of the redirect notification, DRL establishes a transport connection with HMS, if one doesn't already exist, and forwards the request to it. Calhoun et al. expires December 2001 [Page 19]
Internet-Draft June 2001 +------+ | | | DRD | | | +------+ ^ | 2. Request | | 3. Redirection | | Notification | v +------+ ---------> +------+ ---------> +------+ | | 1. Request | | 4. Request | | | NAS | | DRL | | HMS | | | 6. Answer | | 5. Answer | | +------+ <--------- +------+ <--------- +------+ mno.net mno.net abc.com Figure 2: Redirecting a Diameter Message Since Redirectors do not perform any application level processing, they provide relaying services for all Diameter applications, and therefore MUST advertise the Relay Application Identifier. 2.5.4 Translation Agents A Translation Agent is a device that provides translation between two protocols (e.g. RADIUS<->Diameter, TACACS+<->Diameter). Translation agents are likely to be used as aggregation servers to communicate with a Diameter infrastructure, while allowing for the embedded systems to be migrated at a slower pace. Given that the Diameter protocol introduces the concept of long-lived authorized sessions, translation agents MUST be stateful and MUST maintain transaction state. Translation of messages can only occur if the agent recognizes the application of a particular request, and therefore MUST only advertise their locally supported applications. +------+ ---------> +------+ ---------> +------+ | | RADIUS Request | | Diameter Request | | | NAS | | TLA | | HMS | | | RADIUS Answer | | Diameter Answer | | +------+ <--------- +------+ <--------- +------+ mno.net mno.net abc.com Figure 3: Translation of RADIUS to Diameter 2.6 Diameter Agent Discovery Calhoun et al. expires December 2001 [Page 20]
Internet-Draft June 2001 Allowing for dynamic Diameter agent discovery will make it possible for simpler and more robust deployment of AAA services. In order to promote interoperable implementations of Diameter agent discovery, the following mechanisms are described. These are based on existing IETF standards. There are two cases where Diameter agent discovery may be performed. The first is when a Diameter client needs to discover a first-hop Diameter agent. The second case is when a Diameter agent needs to discover another agent - for further handling of a Diameter operation. In both cases, the following 'search order' is recommended: 1. The Diameter implementation consults its list of static (manual) configured Diameter agent locations. These will be used if they exist and respond. 2. The Diameter implementation uses SLPv2 [28] to discover Diameter services. The Diameter service template [32] is included in Appendix A. It is recommended that SLPv2 security be deployed (this requires distributing keys to SLPv2 agents.) This is discussed further in Appendix A. SLPv2 will allow Diameter implementations to discover the location of Diameter agents in the local site, as well as their characteristics. Diameter agents with specific capabilities (say support for the Mobile IP application) can be requested, and only those will be discovered. 3. The Diameter implementation uses DNS to request the SRV RR [33] for the '_diameter._sctp' and/or '_diameter._tcp' server in a particular domain. The Diameter implementation has to know in advance which domain to look for a Diameter agent in. This could be deduced, for example, from the 'realm' in a NAI that a Diameter implementation needed to perform a Diameter operation on. 3.1 If the destination address is a numeric IP address, the requestor contacts the peer at the given address and the port number specified in the SRV record or, if not specified, the default port (TBD). 3.2 The results of the query or queries are merged and ordered based on priority. Then, the searching technique outlined in [46] is used to select servers in order. The requestor attempts to contact each peer in the order listed, at the port number specified in the SRV record. If none of the servers can be contacted, the requestor gives up. If there Calhoun et al. expires December 2001 [Page 21]
Internet-Draft June 2001 are no SRV records, DNS address records are used, as described below. 3.3 If there are no SRV records, the requestor queries the DNS server for address records for the destination address '_diameter._sctp'.domain or '_diameter._tcp'.domain. Address records include A RR's, AAAA RR's, A6 RR's or other similar records, chosen according to the requestor's network protocol capabilities. If the DNS server returns no address records, the requestor gives up. If there are address records, the same rules as in step 3.2 apply. Requestors MUST NOT cache query results except according to the rules in [47]. Diameter allows AAA peers to protect the integrity and privacy of communication as well as to perform end-point authentication. Still, it is prudent to employ DNS Security as a precaution when using DNS SRV RRs to look up the location of a Diameter agent. [34, 35, 36] 3.0 Diameter Header A summary of the Diameter header format is shown below. The fields are transmitted in network byte order. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ver | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R P r r r r r r| Command-Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Hop-by-Hop Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | End-to-End Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVPs ... +-+-+-+-+-+-+-+-+-+-+-+-+- Version This Version field MUST be set to 1 to indicate Diameter Version 1. Calhoun et al. expires December 2001 [Page 22]
Internet-Draft June 2001 Message Length The Message Length field is two octets and indicates the length of the Diameter message including the header fields. Command Flags The Command Flags field is eight bits. The following bits are assigned: R(equest) - If set, the message is a request. If cleared, the message is an answer. P(roxiable) - If set, the message MAY be proxied. If cleared, the message MUST be locally processed. r(eserved) - this flag bit is reserved for future use, and MUST be set to zero. Command-Code The Command-Code field is three octets, and is used in order to communicate the command associated with the message. The 24-bit address space is managed by IANA (see section 15.2). Vendor-ID In the event that the Command-Code field contains a vendor specific command, the four octet Vendor-ID field contains the IANA assigned "SMI Network Management Private Enterprise Codes" [2] value. If the Command-Code field contains an IETF standard Command, the Vendor-ID field MUST be set to zero (0). Any vendor wishing to implement a vendor-specific Diameter command MUST use their own Vendor-ID along with their privately managed Command- Code address space, guaranteeing that they will not collide with any other vendor's vendor-specific command, nor with future IETF applications. Hop-by-Hop Identifier The Hop-by-Hop Identifier field is four octets, and aids in matching requests and replies. The sender MUST ensure that the Hop-by-Hop identifier in a request is locally unique (to the sender) at any given time, and MAY attempt to ensure that the number is unique across reboots. The sender of an Answer message MUST ensure that the Hop-by-Hop Identifier field contains the same value that was found in the corresponding request. The Hop-by-Hop identifier is normally a monotonically increasing number, whose start value was randomly generated. An answer message that is received with an unknown Hop-by-Hop Identifier MUST be discarded. End-to-End Identifier Unlike the Hop-by-Hop Identifier, the End-to-End Identifier is used to detect duplicate messages, and relay agents MUST NOT Calhoun et al. expires December 2001 [Page 23]
Internet-Draft June 2001 modify this field. The sender of a request or answer message MUST insert a locally unique value in this field. The combination of the Origin-Host AVP and this field is used to detect duplicates. An Answer message which is received with a previously seen End- to-End Identifier, and is to be locally consumed (see Section 5.2) SHOULD be silently discarded. AVPs AVPs are a method of encapsulating information relevant to the Diameter message. See section 4. for more information on AVPs. 3.1 Command Codes Each command Request/Answer pair is assigned a command code, and the sub-type (e.g. request or answer) is identified via the 'R' bit in the Command Flags field of the Diameter header. Every Diameter message MUST contain a command code in its header's Command-Code field, which is used to determine the action that is to be taken for a particular message. The following Command Codes are defined in the Diameter base protocol: Command-Name Abbrev. Code Reference -------------------------------------------------------- Abort-Session-Request ASR 274 10.5.1 Abort-Session-Answer ASA 274 10.5.2 Accounting-Request ACR 271 12.1 Accounting-Answer ACA 271 12.2 Capabilities-Exchange- CER 257 6.2 Request Capabilities-Exchange- CEA 257 6.3 Answer Device-Watchdog-Request DWR 280 7.1 Device-Watchdog-Answer DWA 280 7.2 Message-Reject-Answer MRA 282 9.2 Re-Auth-Request RAR 258 10.3.1 Re-Auth-Answer RAA 258 10.3.2 Session-Termination- STR 275 10.4.1 Request Session-Termination- STA 275 10.4.2 Answer 3.2 Command Code ABNF specification Every Command Code defined MUST include a corresponding ABNF specification, which is used to define the AVPs that MUST or MAY be Calhoun et al. expires December 2001 [Page 24]
Internet-Draft June 2001 present. The following format is used in the definition: command-def = command-name "::=" diameter-message diameter-name = ALPHA *(ALPHA / DIGIT / "-") command-name = diameter-name ; The command-name has to be Command name, ; defined in the base or extended Diameter ; specifications. diameter-message = header [ *fixed] [ *required] [ *optional] [ *fixed] header = "<Diameter-Header:" command-id [r-bit] [p-bit] ">" command-id = 1*DIGIT ; The Command Code assigned to the command r-bit = ", REQ" ; If present, the 'R' bit in the Command ; Flags is set, indicating that the message ; is a request, as opposed to an answer. p-bit = ", PXY" ; If present, the 'P' bit in the Command ; Flags is set, indication that the message ; is proxiable. fixed = [qual] "<" avp-spec ">" ; Defines the fixed position of an AVP required = [qual] "{" avp-spec "}" ; The AVP MUST be present optional = [qual] "[" avp-name "]" ; The avp-name in the 'optional' rule cannot ; evaluate to any AVP Name which is included ; in a fixed or required rule. qual = [min] "*" [max] ; See ABNF conventions, RFC 2234 section 6.6. ; The absence of any qualifiers implies that ; one and only one such AVP MUST be present. ; ; NOTE: "[" and "]" have a different meaning ; than in ABNF (see the optional rule, above). ; These braces cannot be used to express Calhoun et al. expires December 2001 [Page 25]
Internet-Draft June 2001 ; optional fixed rules (such as an optional ; ICV at the end.) To do this, the convention ; is '0*1fixed'. min = 1*DIGIT ; The minimum number of times the element may ; be present. The default value is zero. max = 1*DIGIT ; The maximum number of times the element may ; be present. The default value is infinity. avp-spec = diameter-name ; The avp-spec has to be an AVP Name, defined ; in the base or extended Diameter ; specifications. avp-name = avp-spec | "AVP" ; The string "AVP" stands for *any* arbitrary ; AVP Name, which does not conflict with the ; required or fixed position AVPs defined in ; the command code definition. The following is a definition of a fictitious command code: Example-Request ::= < Diameter-Header: 9999999, REQ, PXY > { User-Name } * { Origin-Host } * [ AVP ] 3.3 Diameter Command Naming Conventions The following conventions are required for the naming of Diameter messages. Diameter commands typically start with an object name, and end with either the Request or Answer verb. The Request/Answer message pair is used when a Diameter node requests that some action be performed by a peer (e.g. authorize a user, terminate a session). The corresponding answer MUST contain either a positive or negative result code, informing the requester whether the request was successful or not. Other information MAY also be returned in the Answer message. Request and Answer messages share the same command code, and the R(equest) bit in the Diameter header is used to identify whether a message is the request or answer. Calhoun et al. expires December 2001 [Page 26]
Internet-Draft June 2001 4.0 Diameter AVPs Diameter AVPs carry specific authentication, accounting and authorization information, security information as well as configuration details for the request and reply. Some AVPs MAY be listed more than once. The effect of such an AVP is specific, and is specified in each case by the AVP description. Each AVP of type OctetString MUST be padded to align on a 32 bit boundary, while other AVP types align naturally. NULL bytes are added to the end of the AVP Data field till a word boundary is reached. The length of the padding is not reflected in the AVP Length field. 4.1 AVP Header The fields in the AVP header MUST be sent in network byte order. The format of the header is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVP Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V M P r r r r r| AVP Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-ID (opt) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data ... +-+-+-+-+-+-+-+-+ AVP Code The AVP Code, combined with the Vendor-Id field, identifies the attribute uniquely. The first 256 AVP numbers are reserved for backward compatibility with RADIUS and are to be interpreted as per NASREQ [7]. AVP numbers 256 and above are used for Diameter, which are allocated by IANA (see section 15.1). AVP Flags The AVP Flags field informs the receiver how each attribute must be handled. The 'r' (reserved) bits are unused and SHOULD be set to 0. Note that subsequent Diameter applications MAY define additional bits within the AVP Header, and an unrecognized bit SHOULD be considered an error. The 'P' bit is defined in [11]. The 'M' Bit, known as the Mandatory bit, indicates whether support of the AVP is required. If an unrecognized AVP with the 'M' bit Calhoun et al. expires December 2001 [Page 27]
Internet-Draft June 2001 set is received by a Diameter node, the message MUST be rejected. Diameter Relay and Redirector agents MUST NOT reject messages with unrecognized AVPs. A Diameter node that sets the 'M' bit in an AVP that is not defined in a given message's ABNF is at fault if the message is rejected. In order to provide service to the user, the node at fault MUST re-issue a request either without the AVP, or without setting its 'M' bit. A Diameter node that rejects a message due to an unrecognized AVP with the 'M' bit set, and the AVP in question is defined in the message's ABNF is at fault. In most cases the initiator of the failing request will not provide service to the user. AVPs with the 'M' bit cleared are informational only and a receiver that receives a message with such an AVP that is not supported MAY simply ignore the AVP. The 'V' bit, known as the Vendor-Specific bit, indicates whether the optional Vendor-ID field is present in the AVP header. When set the AVP Code belongs to the specific vendor code address space. Unless otherwise noted, AVPs will have the following default AVP Flags field settings: The 'M' bit MUST be set. The 'V' bit MUST NOT be set. AVP Length The AVP Length field is three octets, and indicates the length of this AVP including the AVP Code, AVP Length, AVP Flags, Reserved, the Vendor-ID field (if present) and the AVP data. If a message is received with an invalid attribute length, the message SHOULD be rejected. 4.2 Optional Header Elements The AVP Header contains one optional field. This field is only present if the respective bit-flag is enabled. Vendor-ID The Vendor-ID field is present if the 'V' bit is set in the AVP Flags field. The optional four octet Vendor-ID field contains the IANA assigned "SMI Network Management Private Enterprise Codes" [2] value, encoded in network byte order. Any vendor wishing to implement a vendor-specific Diameter AVP MUST use their own Vendor-ID along with their privately managed AVP address space, Calhoun et al. expires December 2001 [Page 28]
Internet-Draft June 2001 guaranteeing that they will not collide with any other vendor's vendor-specific AVP, nor with future IETF applications. A vendor ID value of zero (0) corresponds to the IETF adopted AVP values, as managed by the IANA. Since the absence of the vendor ID field implies that the AVP in question is not vendor specific, implementations SHOULD not use the zero (0) vendor ID. 4.3 AVP Base Data Format The Data field is zero or more octets and contains information specific to the Attribute. The format and length of the Data field is determined by the AVP Code and AVP Length fields. The format of the Data field MUST be one of the following base data types or a data type derived from the base data types. In the event that a new AVP Base Data Format is needed, a new version of this RFC must be created. OctetString The data contains arbitrary data of variable length. Unless otherwise noted, the AVP Length field MUST be set to at least 8 (12 if the 'V' bit is enabled). AVP Values of this type that do not align on a 32-bit boundary MUST have the necessary padding. Integer32 32 bit signed value, in network byte order. The AVP Length field MUST be set to 12 (16 if the 'V' bit is enabled). Integer64 64 bit signed value, in network byte order. The AVP Length field MUST be set to 16 (20 if the 'V' bit is enabled). Unsigned32 32 bit unsigned value, in network byte order. The AVP Length field MUST be set to 12 (16 if the 'V' bit is enabled). Unsigned64 64 bit unsigned value, in network byte order. The AVP Length field MUST be set to 16 (20 if the 'V' bit is enabled). Float32 This represents floating point values of single precision as described by [30]. The 32 bit value is transmitted in network byte order. The AVP Length field MUST be set to 12 (16 if the Float64 Calhoun et al. expires December 2001 [Page 29]
Internet-Draft June 2001 This represents floating point values of double precision as described by [30]. The 64 bit value is transmitted in network byte order. The AVP Length field MUST be set to 16 (20 if the Float128 This represents floating point values of quadruple precision as described by [30]. The 128 bit value is transmitted in network byte order. The AVP Length field MUST be set to 24 (28 if the Grouped The Data field is specified as a sequence of AVPs. Each of these AVPs follows - in the order in which they are specified - including their headers and padding. The AVP Length field is set to 8 (12 if the 'V' bit is enabled) plus the total length of all included AVPs, including their headers and padding. 4.4 Derived AVP Data Formats In addition to the AVP Base Data Formats, applications may define data formats derived from the AVP Base Data Formats. New AVP Derived Data Formats MUST be registered with IANA. An application that uses AVP Derived Data Formats other than those defined in the base protocol MUST have a section "AVP Derived Data Formats" that includes each of these formats. In that section, each format is either defined or listed with a reference to the RFC that defines this format. If the AVP Derived Data Format is defined, it SHOULD use a format similar to the format definitions below. The below AVP Derived DATA Formats are commonly used by applications. IPAddress The IPAddress format is derived from the OctetString AVP Base Format. It represents 32 bit (IPv4) [17] or 128 bit (IPv6) [16] address, most significant octet first. The format of the address (IPv4 or IPv6) is determined by the length. If the attribute value is an IPv4 address, the AVP Length field MUST be 12 (16 if 'V' bit is enabled), otherwise the AVP Length field MUST be set to 24 (28 if the 'V' bit is enabled) for IPv6 addresses. Time The Time format is derived from the Unsigned32 AVP Base Format. This is 32 bit unsigned value containing the four most significant octets returned from NTP [18], in network byte order. Calhoun et al. expires December 2001 [Page 30]
Internet-Draft June 2001 This represent the number of seconds since 0h on 1 January 1900 with respect to the Coordinated Universal Time (UTC). On 6h 28m 16s UTC, 7 February 2036 the time value will overflow. NTP [18] describes a procedure to extend the time to 2104. UTF8String The UTF8String format is derived from the OctetString AVP Base Format. This is a human readable string represented using the ISO/IEC IS 10646-1 character set, encoded as an OctetString using the UTF-8 [29] transformation format described in RFC 2279. Since additional code points are added by amendments to the 10646 standard from time to time, implementations MUST be prepared to encounter any code point from 0x00000001 to 0x7fffffff. Byte sequences that do not correspond to the valid UTF-8 encoding of a code point or are outside this range are prohibited. Note that since a code point of 0x00000000 is prohibited, no octet will contain a value of 0x00. The use of control codes SHOULD be avoided. When it is necessary to represent a newline, the control code sequence CR LF SHOULD be used. The use of leading or trailing white space SHOULD be avoided. For code points not directly supported by user interface hardware or software, an alternative means of entry and display, such as hexadecimal, MAY be provided. For information encoded in 7-bit US-ASCII, the UTF-8 encoding is identical to the US-ASCII encoding. UTF-8 may require multiple bytes to represent a single character / code point; thus the length of a UTF8String in octets may be different from the number of characters encoded. Note that the size of an UTF8String is measured in octets, not characters. The UTF8String MUST not contain any octets with a value of zero. DiameterIdentity The DiameterIdentity format is derived from the OctetString AVP Base Format. It uses the UTF-8 encoding and has the same Calhoun et al. expires December 2001 [Page 31]
Internet-Draft June 2001 requirements as the UTF8String. In addition, it must follow the Uniform Resource Identifiers (URI) syntax [29] rules specified below: Diameter-Identity = [scheme-name] fqdn [ port ] [ transport ] scheme-name = "aaa://" aaa-protocol "/" ; If absent, the default BASE for relative URI references ; is aaa://diameter/ aaa-protocol = ( "diameter" | "radius" | "tacacs+" ) fqdn = Fully Qualified Host Name port = ":" 1*DIGIT ; One of the ports used to listen for incoming connections. ; If absent, the default Diameter port (TBD) is assumed. transport = ";transport=" ( "tcp" | "sctp" | "udp") ; One of the transports used to listen for incoming ; connections. If absent, the default SCTP [26] protocol is ; assumed. UDP MUST NOT be used when the aaa-protocol field ; is set to diameter. The following are examples of valid Diameter host identities: host.abc.com;transport=tcp host.abc.com:6666;transport=tcp aaa://diameter/host.abc.com aaa://diameter/host.abc.com:6666 aaa://diameter/host.abc.com:6666;transport=tcp aaa://radius/host.abc.com:1813;transport=udp The first two forms are relative URI references, against the default base of aaa://diameter/. Since multiple Diameter processes on a single host cannot listen for incoming connections on the same port on a given protocol, the DiameterIdentity is guaranteed to be unique per host. A Diameter node MAY advertise different identities on each connection, via the CER and CEA's Origin-Host AVP, but the same identity MUST be used throughout the duration of a connection. When comparing AVPs of this format, it is necessary to add any absent fields with the default values prior to the comparison. Calhoun et al. expires December 2001 [Page 32]
Internet-Draft June 2001 For example, diameter-host.abc.com would be expanded to aaa://diameter/diameter-host.abc.com:TBD;protocol=sctp. Enumerated Enumerated is derived from the Integer32 AVP Base Format. This contains a list of valid values and their interpretation and is described in the Diameter application introducing the AVP. 4.5 Grouped AVP Values The Diameter protocol allows AVP values of type 'Grouped.' This implies that the Data field is actually a sequence of AVPs. It is possible to include an AVP with a Grouped type within a Grouped type, that is, to nest them. AVPs within an AVP of type Grouped have the same padding requirements as non-Grouped AVPs, as defined in section 4.0. The AVP Code numbering space of all AVPs included in a Grouped AVP is the same as for non-grouped AVPs. Further, if any of the AVPs encapsulated within a Grouped AVP has the 'M' (mandatory) bit set, the Grouped AVP itself MUST also include the 'M' bit set. All AVPs included in a Grouped AVP Every Grouped AVP defined MUST include a corresponding grammar, using ABNF [31] (with modifications), as defined below. avp-def = name "::=" avp name-fmt = ALPHA *(ALPHA / DIGIT / "-") name = name-fmt ; The name has to be the name of an AVP, ; defined in the base or extended Diameter ; specifications. avp = header [ *fixed] [ *required] [ *optional] [ *fixed] header = "<AVP-Header:" avpcode ">" avpcode = 1*DIGIT ; The AVP Code assigned to the Grouped AVP fixed = [qual] "<" avp-spec ">" required = [qual] "{" avp-spec "}" Calhoun et al. expires December 2001 [Page 33]
Internet-Draft June 2001 optional = [qual] "[" avp-name "]" ; The avp-name in the 'optional' rule cannot ; evaluate to any AVP Name which is included ; in a fixed or required rule. qual = [min] "*" [max] ; See ABNF conventions, RFC 2234 section 6.6. ; The absence of any qualifiers implies that ; one and only one such AVP MUST be present. ; ; NOTE: "[" and "]" have a different meaning ; than in ABNF (see the optional rule, above). ; These braces cannot be used to express ; optional fixed rules (such as an optional ; ICV at the end.) To do this, the convention ; is '0*1fixed'. min = 1*DIGIT ; The minimum number of times the element may ; be present. max = 1*DIGIT ; The maximum number of times the element may ; be present. avp-spec = name-fmt ; The avp-spec has to be an AVP Name, defined ; in the base or extended Diameter ; specifications. avp-name = avp-spec | "AVP" ; The string "AVP" stands for *any* arbitrary ; AVP Name, which does not conflict with the ; required or fixed position AVPs defined in ; the command code definition. 4.5.1 Example AVP with a Grouped Data type The Example AVP (AVP Code 999999) is of type Grouped and is used to clarify how Grouped AVP values work. The Grouped Data field has the following ABNF grammar: Example-AVP ::= < AVP Header: 999999 > { Origin-Host } 1*{ Session-Id } *[ AVP ] Calhoun et al. expires December 2001 [Page 34]
Internet-Draft June 2001 An Example AVP with Grouped Data follows. The Origin-Host AVP is required. In this case: Origin-Host = "example.com". One or more Session-Ids must follow. Here there are two: Session-Id = "grump.example.com:33041;23432;893;0AF3B81" Session-Id = "grump.example.com:33054;23561;2358;0AF3B82" optional AVPs included are Recovery-Policy = <binary> 2163bc1d0ad82371f6bc09484133c3f09ad74a0dd5346d54195a7cf0b35 2cabc881839a4fdcfbc1769e2677a4c1fb499284c5f70b48f58503a45c5 c2d6943f82d5930f2b7c1da640f476f0e9c9572a50db8ea6e51e1c2c7bd f8bb43dc995144b8dbe297ac739493946803e1cee3e15d9b765008a1b2a cf4ac777c80041d72c01e691cf751dbf86e85f509f3988e5875dc905119 26841f00f0e29a6d1ddc1a842289d440268681e052b30fb638045f7779c 1d873c784f054f688f5001559ecff64865ef975f3e60d2fd7966b8c7f92 Futuristic-Acct-Record = <binary> fe19da5802acd98b07a5b86cb4d5d03f0314ab9ef1ad0b67111ff3b90a0 57fe29620bf3585fd2dd9fcc38ce62f6cc208c6163c008f4258d1bc88b8 17694a74ccad3ec69269461b14b2e7a4c111fb239e33714da207983f58c 41d018d56fe938f3cbf089aac12a912a2f0d1923a9390e5f789cb2e5067 d3427475e49968f841 The data for the optional AVPs is represented in hex since the format of these AVPs is neither known at the time of definition of the Example-AVP group, nor (likely) at the time when the example instance of this AVP is interpreted - except by Diameter implementations which support the same set of AVPs. The encoding example illustrates how padding is used, how length fields are calculated and how AVPs do not have to begin on 8 byte boundaries. Also note that AVPs may be present in the Grouped AVP value which the receiver cannot interpret (here, the Recover-Policy and Futuristic-Acct-Record AVPs). This AVP would be encoded as follows: Calhoun et al. expires December 2001 [Page 35]
Internet-Draft June 2001 0 1 2 3 4 5 6 7 +-------+-------+-------+-------+-------+-------+-------+-------+ 0 | Example AVP Header (AVP Code = 999999), Length = 468 | +-------+-------+-------+-------+-------+-------+-------+-------+ 8 | Origin-Host AVP Header (AVP Code = 264), Length = 19 | +-------+-------+-------+-------+-------+-------+-------+-------+ 16 | 'e' | 'x' | 'a' | 'm' | 'p' | 'l' | 'e' | '.' | +-------+-------+-------+-------+-------+-------+-------+-------+ 24 | 'c' | 'o' | 'm' |Padding| Session-Id AVP Header | +-------+-------+-------+-------+-------+-------+-------+-------+ 32 | (AVP Code = 263), Length = 50 | 'g' | 'r' | 'u' | 'm' | +-------+-------+-------+-------+-------+-------+-------+-------+ . . . +-------+-------+-------+-------+-------+-------+-------+-------+ 64 | 'A' | 'F' | '3' | 'B' | '8' | '1' |Padding|Padding| +-------+-------+-------+-------+-------+-------+-------+-------+ 68 | Session-Id AVP Header (AVP Code = 263), Length = 51 | +-------+-------+-------+-------+-------+-------+-------+-------+ 72 | 'g' | 'r' | 'u' | 'm' | 'p' | '.' | 'e' | 'x' | +-------+-------+-------+-------+-------+-------+-------+-------+ . . . +-------+-------+-------+-------+-------+-------+-------+-------+ 104 | '0' | 'A' | 'F' | '3' | 'B' | '8' | '2' |Padding| +-------+-------+-------+-------+-------+-------+-------+-------+ 112 | Recovery-Policy Header (AVP Code = 8341), Length = 223 | +-------+-------+-------+-------+-------+-------+-------+-------+ 120 | 0x21 | 0x63 | 0xbc | 0x1d | 0x0a | 0xd8 | 0x23 | 0x71 | +-------+-------+-------+-------+-------+-------+-------+-------+ . . . +-------+-------+-------+-------+-------+-------+-------+-------+ 320 | 0x2f | 0xd7 | 0x96 | 0x6b | 0x8c | 0x7f | 0x92 |Padding| +-------+-------+-------+-------+-------+-------+-------+-------+ 328 | Futuristic-Acct-Record Header (AVP Code = 15930), Length = 137| +-------+-------+-------+-------+-------+-------+-------+-------+ 336 | 0xfe | 0x19 | 0xda | 0x58 | 0x02 | 0xac | 0xd9 | 0x8b | +-------+-------+-------+-------+-------+-------+-------+-------+ . . . +-------+-------+-------+-------+-------+-------+-------+-------+ 464 | 0x41 |Padding|Padding|Padding| +-------+-------+-------+-------+ 4.6 Diameter Base Protocol AVPs The following table describes the Diameter AVPs defined in the base protocol, their AVP Code values, types, possible flag values and whether the AVP MAY be encrypted. Calhoun et al. expires December 2001 [Page 36]
Internet-Draft June 2001 +---------------------+ | AVP Flag rules | |----+-----+----+-----|----+ AVP Section | | |SHLD| MUST|MAY | Attribute Name Code Defined Data Type |MUST| MAY | NOT| NOT|Encr| -----------------------------------------|----+-----+----+-----|----| Accounting- 482 13.2 Unsigned32 | M | P | | V | Y | Interim-Interval | | | | | | Accounting- 50 13.5 OctetString| M | P | | V | Y | Multi-Session-Id | | | | | | Accounting- 485 13.3 Unsigned32 | M | P | | V | Y | Record-Number | | | | | | Accounting- 480 13.1 Unsigned32 | M | P | | V | Y | Record-Type | | | | | | Accounting- 44 13.4 OctetString| M | P | | V | Y | Session-Id | | | | | | Acct- 259 6.10 Integer32 | M | | | V | N | Application-Id | | | | | | Auth- 258 6.6 Integer32 | M | | | V | N | Application-Id | | | | | | Authorization- 291 10.8 Unsigned32 | M | | | V | N | Lifetime | | | | | | Class 25 10.16 OctetString| M | P | | V | Y | Destination-Host 293 5.6 OctetString| M | | | V | N | Destination- 283 5.7 OctetString| M | | | V | N | Realm | | | | | | Error-Message 281 9.3 OctetString| | | | V | N | Error-Reporting- 294 9.4 OctetString| | | | V | N | Host | | | | | | Failed-AVP 279 9.5 OctetString| M | | | V | Y | Firmware- 267 6.5 Unsigned32 | | | | V,M | N | Revision | | | | | | Host-IP-Address 257 6.7 IPAddress | M | | | V | N | Multi-Round- 272 10.15 Unsigned32 | M | | | V | Y | Time-Out | | | | | | Origin-Host 264 5.4 OctetString| M | | | V | N | Origin-Realm 296 5.5 OctetString| M | | | V | N | Product-Name 269 6.9 OctetString| | | | V | N | Proxy-Host 280 5.8.3 IPAddress | M | | | V | N | Proxy-Info 284 5.8.2 Grouped | M | | | V | N | Proxy-State 33 5.8.4 OctetString| M | | | V | N | Redirect-Host 292 5.9 OctetString| M | | | V | Y | Redirect-Host- 261 5.10 Enumerated | M | | | V | N | Usage | | | | | | Redirect-Max- 262 5.11 Unsigned32 | M | | | V | N | Cache-Time | | | | | | Result-Code 268 9.1 Unsigned32 | M | | | V | N | -----------------------------------------|----+-----+----+-----|----| Calhoun et al. expires December 2001 [Page 37]
Internet-Draft June 2001 +---------------------+ | AVP Flag rules | |----+-----+----+-----|----+ AVP Section | | |SHLD| MUST|MAY | Attribute Name Code Defined Data Type |MUST| MAY | NOT| NOT|Encr| -----------------------------------------|----+-----+----+-----|----| Route-Record 282 5.8.1 OctetString| M | | | V | N | Session-Id 263 10.7 OctetString| M | | | V | Y | Session-Timeout 27 10.9 Unsigned32 | M | | | V | N | Origin-State-Id 278 10.12 Unsigned32 | M | | | V | N | Session-Binding 270 10.13 Unsigned32 | M | | | V | Y | Session-Server- 271 10.14 Enumerated | M | | | V | Y | Failover | | | | | | Supported- 265 6.8 Unsigned32 | M | | | V | N | Vendor-Id | | | | | | Termination- 295 10.11 Enumerated | M | | | V | N | Cause | | | | | | User-Name 1 10.10 OctetString| M | | | V | Y | Vendor-Id 266 6.4 Unsigned32 | M | | | V,M | N | Vendor-Specific- 260 6.11 Grouped | M | | | V,M | N | Application-Id | | | | | | -----------------------------------------|----+-----+----+-----|----| 5.0 Diameter message processing This section describes how Diameter requests and answers are created and processed. 5.1 Diameter request routing overview A request is sent towards its final destination using a combination of the Destination-Realm and Destination-Host AVPs, in one of these three combinations: - a request that is not proxiable (such as CER) MUST NOT contain either Destination-Realm or Destination-Host AVPs. - a request that needs to be sent to a home server serving a specific realm, but not to a specific server (such as the first request of a series of round-trips), MUST contain a Destination-Realm AVP, but MUST NOT contain a Destination-Host AVP. - a request that needs to be sent to a specific home server among those serving a given realm, MUST contain both the Destination- Realm and Destination-Host AVPs. The Destination-Host AVP is used as described above when the destination of the request is fixed, which includes: Calhoun et al. expires December 2001 [Page 38]
Internet-Draft June 2001 - Authentication requests that span multiple round trips - A Diameter message that uses a security mechanism that makes use of a pre-established session key shared between the source and the final destination of the message. - Server initiated messages that MUST be received by a specific Diameter client (e.g. access device), such as the Abort- Session-Request message, which is used to request that a particular user's session be terminated. Note that an agent can forward a request to a host described in the Destination-Host AVP only if the host in question is included in its peer table (see sections 5.1.4 and 5.1.5). Otherwise, the request is routed based on the Destination-Realm only (see sections 5.1.6 and 5.1.7). The Destination-Realm AVP MUST be present if the message is routable. A message that MUST NOT be relayed, proxied or redirected MUST NOT include the Destination-Realm in its ABNF. The value of the Destination-Realm AVP MAY be extracted from the User-Name AVP, or other application-specific methods. When a message is received, the message is processed in the following order: 1. If the message is destined for the local host, the procedures listed in section 5.1.1 are followed. 2. If the message is intended for a Diameter peer with whom the local host is able to directly communicate with, the procedures listed in section 5.1.2 are followed. This is known as Message Forwarding. 3. The procedures listed in section 5.1.4 are followed, which is known as Message Routing. 4. If none of the above are successful, an answer is returned with the Result-Code set to DIAMETER_UNABLE_TO_DELIVER. Note the processing rules contained in this section are intended to be used as general guidelines to Diameter developers. Certain implementations MAY use different methods than the ones described here, and still be in compliance with the protocol specification. 5.1.1 Originating a Request When creating a request, in addition to any other procedures described in the application definition for that specific request, the following procedures MUST be followed: - the Command-Code should be set to the appropriate value - the 'R' bit should be set - the End-to-End Identifier should be set to a locally unique Calhoun et al. expires December 2001 [Page 39]
Internet-Draft June 2001 value - the Origin-Host and Origin-Realm AVPs MUST be set to the appropriate values, used to identify the source of the message - the Destination-Host and Destination-Realm AVPs MUST be set to the appropriate values as described in section 5.1. 5.1.2 Sending a Request When sending a request, either originated locally, or as the result of a forwarding or routing operation, the following procedures MUST be followed: - the Hop-by-Hop Identifier should be set to a locally unique value - the message should be saved in the list of pending requests Other actions to perform on the message based on the particular role the agent is playing are described in the following sections. 5.1.3 Processing Local Requests A request is known to be for local comsumption when one of the following conditions occur: - The Destination-Host AVP contains the local host's identity, - The Destination-Host AVP is not present, the Destination-Realm AVP contains a realm the server is configured to process locally, and the Diameter application is locally supported, or - The Destination-Realm AVP is not present. When a request is locally processed, the rules in section 5.2 should be used to generate the corresponding answer. 5.1.4 Request Forwarding Request forwarding is done using the Diameter Peer Table. The Diameter peer table contains all of the peers that the local node is able to directly communicate with. When a request is received, and the host encoded in the Destination- Host AVP is one that is present in the peer table, the message SHOULD be forwarded to the peer. 5.1.5 Peer Table The Diameter Peer Table is used in message forwarding, and referenced Calhoun et al. expires December 2001 [Page 40]
Internet-Draft June 2001 by the Domain Routing Table. A Peer Table entry contains the following fields: - Host identity, following the conventions described for the DiameterIdentity derived AVP data format in section 4.4. This MAY be resolved locally, or dynamically updated via the Origin- Host AVP of the CER or CEA messages. - TLS Enabled. Specifies whether TLS is to be used when communicating with the peer. - Additional security information, when needed (e.g. keys, certificates) 5.1.6 Request Routing Diameter request message routing is done via realms. A Diameter message that is proxyable MUST include the target realm in the Destination-Realm AVP. The realm MAY be retrieved from the User-Name AVP, which is in the form of a Network Access Identifier (NAI). The realm portion of the NAI is inserted in the Destination-Realm AVP. Diameter agents MAY have a list of locally supported realms, and MAY have a list of externally supported realms. When a request is received that includes a realm that is not locally supported, the message is routed to the peer configured in the Domain Routing Table table (see section 5.1.7). 5.1.7 Realm-Based Routing Table All Realm-Based routing lookups are performed against what is commonly known as the Domain Routing Table (see section 16.0). A Domain Routing Table Entry contains the following fields: - Realm Name. This is the field that is typically used as a primary key in the routing table lookups. Note that some implementations perform their lookups based on longest-match- from-the-right on the realm rather than requiring an exact match. - Application Identifier. It is possible for a routing entry to have a different destination based on the Acct-Application-Id (for accounting messages) or Auth-Application-Id (for non- accounting messages) of the message. This field is typically used as a secondary key field in routing table lookups. - Local Action. The Local Action field is used to identify how a message should be treated. The following actions are supported: 1. LOCAL - Diameter messages that resolve to a routing entry with the Local Action set to Local can be satisfied locally, and do not need to be routed to another server. 2. RELAY - All Diameter messages that fall within this Calhoun et al. expires December 2001 [Page 41]
Internet-Draft June 2001 category MUST be routed to a next hop server, without modifying any non-routing AVPs. See section 5.1.9 for relaying guidelines 3. PROXY - All Diameter messages that fall within this category MUST be routed to a next hop server. The local server MAY apply its local policies to the message by including new AVPs to the message prior to routing. See section 5.1.9 for relaying guidelines. 4. REDIRECT - Diameter messages that fall within this category MUST have the identity of the home Diameter server(s) appended, and returned to the sender of the message. See section 5.1.8 for redirect guidelines. - Server Identifier - One or more servers the message is to be routed to. These servers MUST also be present in the Peer table. When the Local Action is set to RELAY or PROXY, this field contains the identity of the server(s) the message must be routed to. When the Local Action field is set to REDIRECT, this field contains the identity of one or more servers the message should be redirected to. It is important to note that Diameter agents MUST support at least one of the LOCAL, RELAY, PROXY or REDIRECT modes of operation. Agents do not need to support all modes of operation in order to conform with the protocol specification, but MUST follow the protocol compliance guidelines in section 2.0. Relay agents MUST NOT reorder AVPs, and proxies SHOULD NOT reorder AVPs. The routing table MAY include a default entry which MUST be used for any requests not matching any of the other entries. The routing table MAY consist of only such an entry. When a request is routed, the target server MUST have advertised the Application Identifier (see section 6.1) for the given message, or have advertised itself as a relay or proxy agent. 5.1.8 Redirecting requests When a redirector agent receives a request whose routing entry is set to REDIRECT, it MUST answer the request with Message-Reject-Answer, while maintaining the Hop-by-Hop Identifier in the header, and include the Result-Code AVP to DIAMETER_REDIRECT_INDICATION. Each of the servers associated with the routing entry are added in separate Redirect-Host AVP. Calhoun et al. expires December 2001 [Page 42]
Internet-Draft June 2001 +------------------+ | Diameter | | Redirector Agent | +------------------+ ^ | 1. Request | | 2. MRA + joe@xyz.com | | Result-Code = DIAMETER_REDIRECT_INDICATION + | | Redirect-Host AVP(s) | v +---------+ 3. Request +----------+ | abc.net |------------->| xyz.net | | Relay | | Diameter | | Agent |<-------------| Server | +---------+ 4. Answer +----------+ Figure 7: Diameter Redirect Server Redirector agents MAY also include the certificate of the servers in the Redirect-Host AVP(s). These certificates are encapsulated in a CMS-Cert AVP [11]. The receiver of the MRA message with the Result-Code AVP set to DIAMETER_REDIRECT_INDICATION uses the hop-by-hop field in the Diameter header to identify the request in the pending message queue (see Section 7.3) that is to be redirected. If no transport connection exists with the new agent, one is created, and the request is sent directly to it. 5.1.9 Relaying and Proxying Requests A relay or proxy agent MUST check for forwarding loops before forwarding requests. A loop is detected if the server finds its own address in a Route-Record AVP. When such an event occurs, the agent MUST answer with the Result-Code AVP set to DIAMETER_LOOP_DETECTED. A relay or proxy agent MUST append a Route-Record AVP that includes its identity to all requests forwarded. The last Route-Record AVP in all requests received MUST be validated, by ensuring that the host encoded in the AVP is the same as the peer the message was received from. The Hop-by-Hop identifier in the request is saved, and replaced with a locally unique value. The source of the request is also saved, which includes the IP address, port and protocol. Relay and Proxy agents MAY include the Proxy-Info AVP in requests if it requires access any local state information when the corresponding response is received. Alternatively, it MAY simply use local storage Calhoun et al. expires December 2001 [Page 43]
Internet-Draft June 2001 to store state information. The message is then forwarded to the next hop, as identified in the Domain Routing Table. Figure 6 provides an example of message routing using the procedures listed in these sections. (Origin-Host=nas.mno.net) (Origin-Host=nas.mno.net) (Origin-Realm=mno.net) (Origin-Realm=mno.net) (Destination-Realm=abc.com) (Destination-Realm=abc.com) (Route-Record=drl.mno.net) +------+ ------> +------+ ------> +------+ | | (Request) | | (Request) | | | NAS +-------------------+ DRL +-------------------+ HMS | | | | | | | +------+ <------ +------+ <------ +------+ mno.net (Answer) mno.net (Answer) abc.com (Origin-Host=hms.abc.com) (Origin-Host=hms.abc.com) (Origin-Realm=abc.com) (Origin-Realm=abc.com) Figure 6: Routing of Diameter messages 5.2 Diameter Answer Processing When an request is locally processed, the following procedures MUST be applied to create the associated answer, in addition to any additional procedures that MAY be discussed in the Diameter application defining the command: - The same Hop-by-Hop identifier in the request is used in the answer. - The local host's identity is encoded in the Origin-Host AVP. - The Destination-Host and Destination-Realm AVPs MUST NOT be present in the answer message. - The Result-Code AVP is added with its value indicating success or failure. - If the Session-Id is present in the request, it MUST be included in the answer. - Any Proxy-Info AVPs in the request MUST be added to the answer message, in the same order they were present in the request. 5.2.1 Processing received Answers A Diameter client or proxy MUST match the Hop-by-Hop Identifier in an answer received against the list of pending requests. The corresponding message should be removed from the list of pending Calhoun et al. expires December 2001 [Page 44]
Internet-Draft June 2001 requests. It SHOULD ignore answers received that do not match a known Hop-by-Hop Identifier. 5.2.2 Relaying and Proxying Answers If the answer is for a request which was proxied or relayed, the agent MUST restore the original value of the Diameter header's Hop- by-Hop Identifier field. If the last Proxy-Info AVP in the message is targeted to the local Diameter server, the AVP MUST be removed before the answer is forwarded. If a relay or proxy agent receives an answer with a Result-Code AVP indicating a failure, it MUST NOT modify the contents of the AVP. Any additional local errors detected SHOULD be logged, but not reflected in the Result-Code AVP. If the agent receives an answer message with a Result-Code AVP indicating success, and it wishes to modify the AVP to indicate an error, it MUST issue an STR on behalf of the access device. The agent MUST then send the answer to the host which it received the original request from. 5.3 Hiding Network Topology A Relay or Proxy agent routing messages outside of their administrative domain MAY need to hide the internal Diameter topology. This is done by removing all Route-Record AVPs in a request. 5.4 Origin-Host AVP The Origin-Host AVP (AVP Code 264) is of type DiameterIdentity, and MUST be present in all Diameter messages. This AVP identifies the endpoint which originated the Diameter message, i.e. the access device, home server, or broker. Relay agents MUST NOT modify this AVP. The value of the Origin-Host AVP is guaranteed to be unique within a single host. Note that the Origin-Host AVP may resolve to more than one address as the Diameter peer may support more than one address. Calhoun et al. expires December 2001 [Page 45]
Internet-Draft June 2001 This AVP SHOULD be placed as close to the Diameter header as possible. 5.5 Origin-Realm AVP The Origin-Realm AVP (AVP Code 296) is of type UTF8String. This AVP contains the Realm of the originator of any Diameter message and MUST be present in all messages This AVP SHOULD be placed as close to the Diameter header as possible. 5.6 Destination-Host AVP The Destination-Host AVP (AVP Code 293) is of type DiameterIdentity. This AVP MUST be present in all unsolicited agent initiated messages, MAY be present in request messages, and MUST NOT be present in Answer messages. The absence of the Destination-Host AVP will cause a message to be sent to any Diameter server supporting the application within the realm specified in Destination-Realm AVP. This AVP SHOULD be placed as close to the Diameter header as possible. 5.7 Destination-Realm AVP The Destination-Realm AVP (AVP Code 283) is of type UTF8String, and contains the realm the message is to be routed to. The Destination- Realm AVP MUST NOT be present in Answer messages. Diameter Clients insert the realm portion of the User-Name AVP. Diameter servers initiating a request message use the value of the Origin-Realm AVP from a previous message received from the intended target host (unless it is known a priori). When present, the Destination-Realm AVP is used to perform message routing decisions. Request messages whose ABNF does not list the Destination-Realm AVP as a mandatory AVP are inherently non-routable messages. This AVP SHOULD be placed as close to the Diameter header as possible. 5.8 Routing AVPs Calhoun et al. expires December 2001 [Page 46]
Internet-Draft June 2001 The AVPs defined in this section are Diameter AVPs used for routing purposes. These AVPs change as Diameter messages are processed by agents, and therefore MUST NOT be protected using the Diameter CMS Security application [11]. 5.8.1 Route-Record AVP The Route-Record AVP (AVP Code 282) is of type DiameterIdentity. The identity added in this AVP MUST be the same as the one sent in the Origin-Host of the Capabilities-Exchange-Request message. 5.8.2 Proxy-Info AVP The Proxy-Info AVP (AVP Code 284) is of type Grouped. The Grouped Data field has the following ABNF grammar: Proxy-Info ::= < AVP Header: 284 > { Proxy-Host } { Proxy-State } * [ AVP ] 5.8.3 Proxy-Host AVP The Proxy-Host AVP (AVP Code 280) is of type DiameterIdentity. This AVP contains the identity of the host that added the Proxy-Info AVP. 5.8.4 Proxy-State AVP The Proxy-State AVP (AVP Code 33) is of type OctetString, and contains state local information, and MUST be treated as opaque data. 5.9 Redirect-Host AVP The Redirect-Host AVP (AVP Code 292) is of type DiameterIdentity. This AVP MUST be present in Message-Reject-Answer messages that include the Result-Code AVP set to DIAMETER_REDIRECT_INDICATION. Upon receiving the above, the receiving Diameter node SHOULD forward the request directly to the host identified in this AVP. The server contained in the Redirect-Host SHOULD be used for all messages pertaining to this session. Calhoun et al. expires December 2001 [Page 47]
Internet-Draft June 2001 5.10 Redirect-Host-Usage AVP The Redirect-Host-Usage AVP (AVP Code 261) is of type Enumerated. This AVP MAY be present in Message-Reject-Answer messages that include the Result-Code AVP set to DIAMETER_REDIRECT_INDICATION. When present, this AVP dictates how the routing entry resulting from the MRA is to be used. The following values are supported: DONT_CACHE 0 The host specified in the Redirect-Host AVP should not be cached. This is the default value. ALL_SESSION 1 All messages within the same session, as defined by the same value of the Session-ID AVP MAY be sent to the host specified in the Redirect-Host AVP. ALL_REALM 2 All messages destined for the realm requested MAY be sent to the host specified in the Redirect-Host AVP. REALM_AND_APPLICATION 3 All messages for the application requested to the realm specified MAY be sent to the host specified in the Redirect- Host AVP. ALL_APPLICATION 4 All messages for the application requested MAY be sent to the host specified in the Redirect-Host AVP. ALL_HOST 5 All messages that would be sent to the host that generated the MRA MAY be sent to the host specified in the Redirect-Host AVP. 5.11 Redirect-Max-Cache-Time AVP The Redirect-Max-Cache-Time AVP (AVP Code 262) is of type Unsigned32. This AVP MUST be present in Message-Reject-Answer messages that include the Result-Code AVP set to DIAMETER_REDIRECT_INDICATION, and the Redirect-Host-Usage AVP set to a non-zero value. This AVP contains the maximum number of seconds the peer and route table entries, created as a result of the Redirect-Host, will be cached. Note that once a host created due to a redirect indication is no longer reachable, any associated peer and routing table entries MUST be deleted. Calhoun et al. expires December 2001 [Page 48]
Internet-Draft June 2001 6.0 Capabilities Exchange When two Diameter peers establish a transport connection, they MUST exchange the Capabilities Exchange messages, as specified in the peer state machine (see section 8.0). This message allows the discovery of a peer's identity and its capabilities (protocol version number, supported Diameter applications, etc.) The receiver only issues commands to its peers that have advertised support for the Diameter application that defines the command. A Diameter node MUST cache the supported applications in order to ensure that unrecognized commands and/or AVPs are not unnecessarily sent to a peer. A receiver of a Capabilities-Exchange-Req (CER) message which does not have any applications in common with the sender MUST return a Capabilities-Exchange-Answer (CEA) with the Result-Code AVP set to DIAMETER_NO_COMMON_APPLICATION, and SHOULD disconnect the transport layer connection. Note that receiving a CER or CEA from a peer advertising itself as a Relay (see section 6.1) MUST be interpreted as having common applications with the peer. The CER and CEA messages MUST NOT be proxied, or redirected. Since the CER/CEA messages cannot be proxied, it is still possible that an upstream proxy receives a message for which it has no available peers to handle the application that corresponds to the Command-Code. In such instances, the Message-Reject-Answer message is used (see Section 9.2.1) to inform the downstream to take action (e.g. re-routing request to an alternate peer). With the exception of the Capabilities-Exchange-Request message, a message of type Request that includes the Auth-Application-Id or Acct-Application-Id AVPs, or a message with an application-specific command code, MAY only be forwarded to a host that has explicitly advertised support for the application (or has advertised the Relay Application Identifier). 6.1 Application Identifiers Each Diameter application MUST have an IANA assigned Application Identifier (see section 15.3). The base protocol does not require an application Identifier since its support is mandatory. Application Identifiers are communicated via two separate AVPs; Auth-Application-Id and Acct-Application-Id. The Auth-Application-Id AVP is used to communicate support for the authentication and Calhoun et al. expires December 2001 [Page 49]
Internet-Draft June 2001 authorization portion of an application. The Acct-Application-Id AVP, on the other hand, communicates support for the accounting portion of an application. This separation of AVPs allows a server to communicate that it is willing to accept only accounting messages for a given application. The following Application Identifier values are defined: NASREQ 1 [7] End-to-End Security 2 [11] Mobile-IP 4 [10] Relay 0xffffffff Relay and redirect agents MUST advertise the Relay application identifier, while all other Diameter nodes MUST advertise locally supported applications. The receiver of a Capabilities Exchange message advertising Relay service MUST assume that the sender supports all current and future applications. Diameter relay and proxy agents are responsible for finding an upstream server that supports the application of a particular message. If none can be found, a MRA message is returned with the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER. 6.2 Capabilities-Exchange-Request The Capabilities-Exchange-Request (CER), indicated by the Command- Code set to 257 and the Command Flags' 'R' bit set, is sent to inform a peer that a reboot has occurred. When Diameter is run over SCTP [26], which allows for connections to span multiple interfaces, hence multiple IP addresses, the Capabilities-Exchange-Request message MUST contain one Host-IP- Address AVP for each potential IP address that MAY be locally used when transmitting Diameter messages. Message Format Calhoun et al. expires December 2001 [Page 50]
Internet-Draft June 2001 <Capabilities-Exchange-Req> ::= < Diameter Header: 257, REQ > { Origin-Host } { Origin-Realm } 1* { Host-IP-Address } { Vendor-Id } { Product-Name } [ Origin-State-Id ] * [ Supported-Vendor-Id ] * [ Auth-Application-Id ] * [ Acct-Application-Id ] [ Destination-Host ] [ Firmware-Revision ] * [ AVP ] 6.3 Capabilities-Exchange-Answer The Capabilities-Exchange-Request (CEA), indicated by the Command- Code set to 257 and the Command Flags' 'R' bit cleared, is sent in response to a CER message. When Diameter is run over SCTP [26], which allows for connections to span multiple interfaces, hence multiple IP addresses, the Capabilities-Exchange-Answer message MUST contain one Host-IP-Address AVP for each potential IP address that MAY be locally used when transmitting Diameter messages. Message Format <Capabilities-Exchange-Answer> ::= < Diameter Header: 257 > { Result-Code } { Origin-Host } { Origin-Realm } 1* { Host-IP-Address } { Vendor-Id } { Product-Name } [ Origin-State-Id ] * [ Supported-Vendor-Id ] * [ Auth-Application-Id ] * [ Acct-Application-Id ] [ Destination-Host ] [ Firmware-Revision ] * [ AVP ] 6.4 Vendor-Id AVP The Vendor-Id AVP (AVP Code 266) is of type Unsigned32 and contains Calhoun et al. expires December 2001 [Page 51]
Internet-Draft June 2001 the IANA "SMI Network Management Private Enterprise Codes" [2] value assigned to the vendor of the Diameter device. In combination with the Supported-Vendor-Id AVP (section 6.8), this MAY be used in order to know which vendor specific attributes may be sent to the peer. It is also envisioned that the combination of the Vendor-Id, Product-Name (section 6.9) and the Firmware-Revision (section 6.5) AVPs MAY provide very useful debugging information. A Vendor-Id value of zero in the CER or CEA messages is reserved and indicates that the Diameter peer is in the experimental or concept stage and that an IANA Private Enterprise Number has yet to be obtained by the implementor. 6.5 Firmware-Revision AVP The Firmware-Revision AVP (AVP Code 267) is of type Unsigned32 and is used to inform a Diameter peer of the firmware revision of the issuing device. For devices that do not have a firmware revision (general purpose computers running Diameter software modules, for instance), the revision of the Diameter software module may be reported instead. 6.6 Auth-Application-Id AVP The Auth-Application-Id AVP (AVP Code 258) is of type Unsigned32 and is used in order to advertise support of the Authentication and Authorization portion of an application (see Section 6.1). The Auth- Application-Id MUST also be present in all Authentication and/or Authorization messages that are defined in a separate Diameter specification and have an Application ID assigned. This AVP SHOULD be placed as close to the Diameter header as possible. 6.7 Host-IP-Address AVP The Host-IP-Address AVP (AVP Code 257) is of type IPAddress and is used to inform a Diameter peer of the sender's IP address. All source addresses that a Diameter node expects to use with SCTP [26] MUST be advertised in the CER and CEA messages by including a Host- IP-Address AVP for each address. This AVP MUST ONLY be used in the CER and CEA messages. Calhoun et al. expires December 2001 [Page 52]
Internet-Draft June 2001 6.8 Supported-Vendor-Id AVP The Supported-Vendor-Id AVP (AVP Code 265) is of type Unsigned32 and contains the IANA "SMI Network Management Private Enterprise Codes" [2] value assigned to a vendor other than the device vendor. This is used in the CER and CEA messages in order to inform the peer that the sender supports a subset of the vendor-specific commands and/or AVPs defined by the vendor identified in this AVP. 6.9 Product-Name AVP The Product-Name AVP (AVP Code 269) is of type UTF8String, and contains the vendor assigned name for the product. The Product-Name AVP SHOULD remain constant across firmware revisions for the same product. 6.10 Acct-Application-Id AVP The Acct-application-Id AVP (AVP Code 259) is of type Unsigned32 and is used in order to advertise support of the Accounting portion of an application (see Section 6.1). The Acct-Application-Id MUST also be present in all Accounting messages that are defined in a separate Diameter specification and have an Application ID assigned. This AVP SHOULD be placed as close to the Diameter header as possible. 6.11 Vendor-Specific-Application-Id AVP The Vendor-Specific-Application-Id AVP (AVP Code 260) is of type Grouped and is used to advertise support of a vendor-specific Diameter Application. Either the Auth-Application-Id or the Acct- Application-Id AVP MAY be present. Both AVPs MAY be present if they both contain the same value. This AVP MUST also be present in all vendor-specific commands defined in the vendor-specific application. This AVP SHOULD be placed as close to the Diameter header as possible. AVP Format Calhoun et al. expires December 2001 [Page 53]
Internet-Draft June 2001 <Vendor-Specific-Application-Id> ::= < AVP Header: 260 > 1* [ Vendor-Id ] 0*1{ Auth-Application-Id } 0*1{ Acct-Application-Id } 7.0 Transport Failure Detection Given the nature of the Diameter protocol, it is recommended that transport failures be detected as soon as possible. Detecting such failures will minimize the occurrence of messages sent to unavailable servers, resulting in unnecessary delays, and will provide better failover performance. The Device-Watchdog-Request and Device- Watchdog-Answer messages, defined in this section, are used to pro- actively detect transport failures. The watchdog behavior is controlled by the Tw timer, which ranges between 30 and 60 seconds. In order to avoid synchronization behaviors that can occur with fixed timers among distributed systems, each time the watchdog interval is calculated with a jitter by using the Tw value (which defaults to 30 seconds) and randomly adding or subtracting a random value drawn between 0.5 and 2 seconds. Alternative calculations to create jitter MAY be used. These MUST be pseudo-random and not cyclic. When a response is received, Tw is reset. Receiving a watchdog from a peer constitutes activity, and Tw should be reset. On sending a message, if the queue is empty, then Tw is reset. If the watchdog timer expires and the queue is empty, then a watchdog packet is sent. 7.1 Device-Watchdog-Request The Device-Watchdog-Request (DWR), indicated by the Command-Code set to 280 and the Command Flags' 'R' bit set, is sent to a peer when no traffic has been exchanged between two peers as defined in Section 7.0, and no requests are pending with the peer. Message Format <Device-Watchdog-Request> ::= < Diameter Header: 280, REQ > { Origin-Host } { Origin-Realm } { Destination-Host } 7.2 Device-Watchdog-Answer Calhoun et al. expires December 2001 [Page 54]
Internet-Draft June 2001 The Device-Watchdog-Answer (DWA), indicated by the Command-Code set to 280 and the Command Flags' 'R' bit cleared, is sent as a response to the Device-Watchdog-Request message. Message Format <Device-Watchdog-Answer> ::= < Diameter Header: 280 > { Result-Code } { Origin-Host } { Origin-Realm } { Destination-Host } 7.3 Failover/Failback Procedures In the event that a transport failure is detected with a peer, it is necessary for all pending request messages to be forwarded to an alternate agent, if possible. This is commonly referred to as failover. In order for a Diameter node to perform failover procedures, it is necessary for the node to maintain a pending message queue for a given peer. When an answer message is received, the corresponding request is removed from the queue. The Hop-by-Hop Identifier field MAY be used to match the answer with the queued request. When a transport failure is detected, all messages in the queue are sent to an alternate agent, if possible. An example of a case where it is not possible for forward the message to an alternate server is when the message has a fixed destination, and the unavailable peer is the message's final destination (see Destination-Host AVP). Such an error requires that the agent return an MRA with the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER. It is important to note that multiple identical request or answer MAY be received as a result of a failover. The End-to-End Identifier field in the Diameter header along with the Origin-Host AVP MUST be used to identify duplicate messages. As described in section 2.1, a connection request should be periodically attempted with the failed peer in order to re-establish the transport connection. Once a connection has been successfully established, messages can once again be forwarded to the peer. This is commonly referred to as failback. 8.0 Peer State Machine Calhoun et al. expires December 2001 [Page 55]
Internet-Draft June 2001 This section contains a finite state machine, that MUST be observed by all Diameter implementations. Each Diameter node MUST follow the state machine described below when communicating with each peer. Multiple actions are separated by commas, and may continue on succeeding lines as space requires. Similarly, state and next state may also span multiple lines as space requires. There may be at most one transport connection between any two peers over which Diameter messages may be passed. This state machine is intended to handle both the simple case, in which one peer initiates a connection to the other, and the complex case, in which each peer simultaneously initiates a connection to the other. In the complex case, an election occurs to determine which transport connection will survive. It is important to note that the port on which a connection is initiated MUST NOT be the port Diameter listens for incoming connections. I- is used to represent the initiator (connecting) connection, while the R- is used to represent the responder (listening) connection. The lack of a prefix indicates that the event or action is the same regardless of the connection on which the event occurred. The stable states that a state machine may be in are Closed, I-Open and R-Open; all other states are intermediate. Note that I-Open and R-Open are equivalent except for whether the initiator or responder transport connection is used for communication. A CER message is always sent on the initiating connection immediately after the connection request is successfully completed. In the case of an election, one of the two connections will shut down. The responder connection will survive if the Origin-Host of the local Diameter entity is higher than that of the peer; the initiator connection will survive if the peer's Origin-Host is higher. All subsequent messages are sent on the surviving connection. Note that the results of an election on one peer are guaranteed to be the inverse of the results on the other. The state machine constrains only the behavior of a Diameter implementation as seen by Diameter peers through events on the wire. Any implementation that produces equivalent results is considered compliant. state event action next state ----------------------------------------------------------------- Closed Start I-Snd-Conn-Req Wait-Conn-Ack R-Conn-CER R-Accept, R-Open Process_CER, Calhoun et al. expires December 2001 [Page 56]
Internet-Draft June 2001 R-Snd-CEA Wait-Conn-Ack I-Rcv-Conn-Ack I-Snd-CER Wait-I-CEA I-Rcv-Conn-Nack Cleanup Closed R-Conn-CER R-Accept, Wait-Conn-Ack/ Process-CER Elect Timeout Error Closed Wait-I-CEA I-Rcv-CEA Process-CEA I-Open R-Conn-CER R-Accept, Wait-Returns Process_CER, Elect I-Peer-Disc I-Disc Closed I-Rcv-Non-CEA Error Closed Timeout Error Closed Wait-Conn-Ack/ I-Rcv-Conn-Ack I-Snd-CER,Elect Wait-Returns Elect I-Rcv-Conn-Nack R-Snd-CEA R-Open R-Peer-Disc R-Disc Wait-Conn-Ack R-Conn-CER R-Reject Wait-Conn-Ack/ Elect Timeout Error Closed Wait-Returns Win-Election I-Disc,R-Snd-CEA R-Open I-Peer-Disc I-Disc,R-Snd-CEA R-Open I-Rcv-CEA R-Disc I-Open R-Peer-Disc R-Disc Wait-I-CEA R-Conn-CER R-Reject Wait-Returns Timeout Error Closed R-Open Send-Message R-Snd-Message R-Open R-Rcv-Message Process R-Open WatchDog-Timer R-Snd-DWR R-Open R-Rcv-DWR Process-DWR, R-Open R-Snd-DWA R-Rcv-DWA Process-DWA R-Open R-Conn-CER R-Reject R-Open Stop R-Disc Closed R-Peer-Disc R-Disc Closed R-Rcv-CER Error Closed R-Rcv-CEA Error Closed I-Open Send-Message I-Snd-Message I-Open I-Rcv-Message Process I-Open WatchDog-Timer I-Snd-DWR I-Open I-Rcv-DWR Process-DWR, I-Open I-Snd-DWA I-Rcv-DWA Process-DWA I-Open Calhoun et al. expires December 2001 [Page 57]
Internet-Draft June 2001 R-Conn-CER R-Reject I-Open Stop I-Disc Closed I-Peer-Disc I-Disc Closed I-Rcv-CER Error Closed I-Rcv-CEA Error Closed 8.1 Incoming connections When a connection request is received from a Diameter peer, it is not, in the general case, possible to know the identity of that peer until a CER is received from it. This is because the identity of a Diameter peer is determined by host and port; and the source port of an incoming connection is arbitrary. Upon receipt of CER, the identity of the connecting peer can be uniquely determined from Origin-Host. For this reason, a Diameter peer must employ logic separate from the state machine to receive connection requests, accept them, and await CER. Once CER arrives on a new connection, the Origin-Host which identifies the peer is used to locate the state machine associated with that peer, and the new connection and CER are passed to the state machine as an R-Conn-CER event. The logic that handles incoming connections SHOULD close and discard the connection if any message other than CER arrives, or if an implementation-defined timeout occurs prior to receipt of CER. Because handling of incoming connections up to and including receipt of CER requires logic separate from that of any individual state machine associated with a particular peer, it is described separately in this section rather than in the state machine below. 8.2 Events Transitions and actions in the automaton are caused by events. In this section we will ignore the -I and -R prefix, since the actual event would be identical, but would occur on one of two possible connections. Start The Diameter application has signaled that a connection should be initiated with the peer. R-Conn-CER A new incoming connection and associated CER has arrived. Rcv-Conn-Ack A positive acknowledgement was received to a Calhoun et al. expires December 2001 [Page 58]
Internet-Draft June 2001 locally initiated transport connection. Rcv-Conn-Nack A negative acknowledgement was received to a locally initiated transport connection. Timeout An application-defined timer has expired while waiting for some event. Rcv-CER A CER message from the peer was received. Rcv-CEA A CEA message from the peer was received. Rcv-Non-CEA A message other than CEA from the peer was received. Peer-Disc A disconnection indication from the peer was received. Win-Election An election was held, and the local node was the winner. Send-Message A message is to be sent. Rcv-Message A message other than CER, CEA, DWR, or DWA was received. WatchDog-Timer The Watchdog timer expired, indicating that a DWR message is to be sent to the peer. Rcv-DWR A DWR message was received. Rcv-DWA A DWA message was received. Stop The Diameter application has signaled that a connection should be terminated (e.g., on system shutdown). 8.3 Actions Actions in the automaton are caused by events and typically indicate the transmission of packets and/or an action to be taken on the connection. In this section we will ignore the I- and R- prefix, since the actual action would be identical, but would occur on one of two possible connections. Snd-Conn-Req A transport connection is initiated with the peer. Calhoun et al. expires December 2001 [Page 59]
Internet-Draft June 2001 Accept The incoming connection associated with the R- Conn-CER is accepted as the responder connection. Reject The incoming connection associated with the R- Conn-CER is disconnected. Process-CER The CER associated with the R-Conn-CER is processed. Snd-Conn-Ack an acknowledgement is sent in response to a connect request, confirming that the transport layer connection is open. Snd-CER A CER message is sent to the peer. Snd-CEA A CEA message is sent to the peer. Cleanup If necessary, the connection is shutdown, and any local resources are freed. Error The transport layer connection is disconnected, either politely or abortively, in response to an error condition. Local resources are freed. Process-CEA A received CEA is processed. Disc The transport layer connection is disconnected, and local resources are freed. Elect An election occurs (see Section 8.4 for more information). Snd-Message A message is sent. Snd-DWR A DWR message is sent. Snd-DWA A DWA message is sent. Process-DWR The DWR message is serviced. Process-DWA The DWA message is serviced. Process A message is serviced. 8.4 The Election Process The election is performed on the responder. The responder compares Calhoun et al. expires December 2001 [Page 60]
Internet-Draft June 2001 the Origin-Host received in the CER sent by its peer with its own Origin-Host. If the local Diameter entity's Origin-Host is higher than the peer's, a Win-Election event is issued locally. The comparison proceeds by considering the shorter OctetString to be null-padded to the length of the longer, then performing an octet by octet unsigned comparison with the first octet being most significant. Hanging octets are assumed to have value 0x80, but dimpled octets are ignored. 9.0 Error Handling There are two different types of errors in Diameter; protocol and applications. A protocol error is one that occurs at the base protocol level, and MAY require per hop attention (e.g. message routing error). Application errors, on the other hand, are generally occur due to a problem with a function specified in a Diameter application (e.g. user authentication, Missing AVP). Result-Code AVP values that are used to report protocol errors MUST be used in the Message-Reject-Answer command. Unlike most Diameter commands, the Message-Reject-Answer does not have a corresponding request. When a request message is received that causes a protocol error, the command code is changed to Message-Reject-Answer, and the Result-Code AVP is set to the appropriate protocol error value. As the answer is sent back towards the originator of the request, each proxy or relay agent MAY take action on the message. 1. Request +---------+ Link Broken +-------------------------->|Diameter |----///----+ | +---------------------| | v +------+--+ | 2. MRA | Relay 2 | +--------+ |Diameter |<-+ (Unable to Forward) +---------+ |Diameter| | | | Home | | Relay 1 |--+ +---------+ | Server | +---------+ | 3. Request |Diameter | +--------+ +-------------------->| | ^ | Relay 3 |-----------+ +---------+ Figure 4 - Example of Protocol Error causing MRA message Figure 4 provides an example of a message forwarded upstream by a Diameter relay. When the message is received by Relay 2, and it detects that it cannot forward the request to the home server, an MRA message is returned with the Result-Code AVP set to Calhoun et al. expires December 2001 [Page 61]
Internet-Draft June 2001 DIAMETER_UNABLE_TO_DELIVER. Given that this error falls within the protocol error category, Relay 1 would take special action, and given the error, attempt to route the message through its alternate Relay 3. +---------+ 1. Request +---------+ 2. Request +---------+ | Access |------------>|Diameter |------------>|Diameter | | | | | | Home | | Device |<------------| Relay |<------------| Server | +---------+ 4. Answer +---------+ 3. Answer +---------+ (Missing AVP) (Missing AVP) Figure 5 - Example of Application Error Answer message Figure 5 provides an example of a Diameter message that caused an application error. When application errors occur, the Diameter entity reporting the error clears the 'R' bit in the Command Flags, and adds the Result-Code AVP with the proper value. Application errors do not require any proxy or relay agent involvement, and therefore the message would be forwarded back to the originator of the request. There are certain Result-Code AVP application errors that require additional AVPs to be present in the answer. In these cases, the Diameter node that sets the Result-Code AVP to indicate the error MUST add the AVPs. Examples are: - An unrecognized AVP is received with the 'M' bit (Mandatory bit) set, causes an answer to be sent with the Result-Code AVP set to DIAMETER_AVP_UNSUPPORTED, and the Failed-AVP AVP containing the offending AVP. - An AVP that is received with an unrecognized value causes an answer to be returned with the Result-Code AVP set to DIAMETER_INVALID_AVP_VALUE, with the Failed-AVP AVP containing the AVP causing the error. - A command is received with an AVP that is ommitted, yet is mandatory according to the command's ABNF. The receiver issues an answer with the Result-Code set to DIAMETER_MISSING_AVP, and creates an AVP with the AVP Code and other fields set to the missing AVP's. The created AVP is then added to the Failed-AVP AVP. The Result-Code AVP contains additional errors conditions, and defines the expected behavior of each. 9.1 Result-Code AVP The Result-Code AVP (AVP Code 268) is of type Unsigned32 and indicates whether a particular request was completed successfully or Calhoun et al. expires December 2001 [Page 62]
Internet-Draft June 2001 whether an error occurred. All Diameter answer messages MUST include one Result-Code AVP. A non-successful Result-Code AVP (one containing a non 2xxx value) MUST include the Error-Reporting-Host AVP if the host setting the Result-Code AVP is different from the identity encoded in the Origin-Host AVP. The Result-Code data field contains an IANA-managed 32-bit address space representing errors (see section 15.4). Diameter provides the following classes of errors, all identified by the thousands digit: - 1xxx (Informational) - 2xxx (Success) - 3xxx (Protocol Errors) - 4xxx (Transient Failures) - 5xxx (Permanent Failure) A non-recognize class (one whose first digit is not defined in this section) MUST be handled as a permanent failure. 9.1.1 Informational Errors that fall within this category are used to inform the requester that a request could not be satisfied, and additional action is required on its part before access is granted. DIAMETER_MULTI_ROUND_AUTH 1001 This informational error is returned by a Diameter server to inform the access device that the authentication mechanism being used required multiple round trip, and a subsequent request needs to be issued in order for access to be granted. 9.1.2 Success Errors that fall within the Success category are used to inform a peer that a request has been successfully completed. DIAMETER_SUCCESS 2001 The Request was successfully completed. DIAMETER_LIMITED_SUCCESS 2002 When returned, the request was successfully completed, but additional processing is required by the application in order to provide service to the user. 9.1.3 Protocol Errors Calhoun et al. expires December 2001 [Page 63]
Internet-Draft June 2001 Errors that fall within the Protocol Error category SHOULD be treated on a per-hop basis, and Diameter proxies MAY attempt to correct the error, if it is possible. Note that these errors MUST only be used in the Message-Rejected-Answer message, therefore a Diameter entity that wishes to return an error in this category MUST change the command code to Message-Rejected-Answer message. DIAMETER_INVALID_ROUTE_RECORD 3001 The last Route-Record AVP in the message is not set to the identity of the sender of the message. See Section 11.0 for more information. DIAMETER_COMMAND_UNSUPPORTED 3002 The Request contained a Command-Code that the receiver did not recognize or support. DIAMETER_UNABLE_TO_DELIVER 3003 The realm requested is recognized, but no host within the realm was available to process the request. This event occurs if no Diameter server supporting the requested application is reachable within the intended realm. DIAMETER_REALM_NOT_SERVED 3004 The intended realm of the request is not recognized. DIAMETER_TOO_BUSY 3005 When returned, a Diameter node SHOULD attempt to send the message to an alternate peer. DIAMETER_INVALID_CMS_DATA 3006 The Request did not contain a valid CMS-Data [11] AVP. DIAMETER_LOOP_DETECTED 3007 An agent detected a loop while trying to get the message to the Home Diameter server. The message MAY be sent to an alternate peer, if one is available, but the peer reporting the error has identified a configuration problem. DIAMETER_END_2_END_SECURITY 3008 A proxy has detected that end-to-end security has been applied to portions of the Diameter message, and the proxy does not allow this security mode since it needs to alter the message by applying some local policies. DIAMETER_REDIRECT_INDICATION 3009 A redirector has determined that the request could not be satisfied locally and the initiator of the request should direct the request directly to the server, whose contact Calhoun et al. expires December 2001 [Page 64]
Internet-Draft June 2001 information has been added to the response. When set, the Redirect-Host AVP MUST be present. 9.1.4 Transient Failures Errors that fall within the transient failures category are used to inform a peer that the request could not be satisfied at the time it was received, but MAY be able to satisfy the request in the future. DIAMETER_AUTHENTICATION_REJECTED 4001 The authentication process for the user failed, most likely due to an invalid password used by the user. Further attempts MUST only be tried after prompting the user for a new password. DIAMETER_OUT_OF_SPACE 4002 A Diameter node received the accounting request but was unable to commit it to stable storage due to a temporary lack of space. 9.1.5 Permanent Failures Errors that fall within the permanent failures category are used to inform the peer that the request failed, and should not be attempted again. DIAMETER_USER_UNKNOWN 5001 A request was received for a user that is unknown, therefore authentication and/or authorization failed. DIAMETER_AVP_UNSUPPORTED 5002 The peer received a message that contained an AVP that is not recognized or supported and was marked with the Mandatory bit. A Diameter message with this error MUST contain one or more Failed-AVP AVP containing the AVPs that caused the failure. DIAMETER_UNKNOWN_SESSION_ID 5003 The request contained an unknown Session-Id. DIAMETER_AUTHORIZATION_REJECTED 5004 A request was received for which the user could not be authorized. This error could occur if the service requested is not permitted to the user. DIAMETER_INVALID_AVP_VALUE 5005 The request contained an AVP with an invalid value in its data portion. A Diameter message indicating this error MUST include Calhoun et al. expires December 2001 [Page 65]
Internet-Draft June 2001 the offending AVPs within a Failed-AVP AVP. DIAMETER_MISSING_AVP 5006 The request did not contain an AVP that is required by the Command Code definition. If this value is sent in the Result- Code AVP, a Failed-AVP AVP SHOULD be included in the message. The Failed-AVP AVP MUST contain an example of the missing AVP complete with the Vendor-Id if applicable. The value field of the missing AVP should be of correct minimum length and contain zeroes. DIAMETER_RESOURCES_EXCEEDED 5007 A request was received that cannot be authorized because the user has already expended allowed resources. An example of this error condition is a user that is restricted to one dial-up PPP port, attempts to establish a second PPP connection. DIAMETER_CONTRADICTING_AVPS 5008 The Home Diameter server has detected AVPs in the request that contradicted each other, and is not willing to provide service to the user. One or more Failed-AVP AVPs MUST be present, containing the AVPs that contradicted each other. DIAMETER_AVP_NOT_ALLOWED 5009 A message was received with an AVP that MUST NOT be present. The Failed-AVP AVP MUST be included and contain a copy of the offending AVP. DIAMETER_AVP_OCCURS_TOO_MANY_TIMES 5010 A message was received that included an AVP that appeared more often than permitted in the message definition. The Failed-AVP AVP MUST be included and contain a copy of the first instance of the offending AVP that exceeded the maximum number of occurrences DIAMETER_UNSUPPORTED_TRANSFORM 5011 A message was received that included an CMS-Data AVP [11] that made use of an unsupported transform. DIAMETER_NO_COMMON_APPLICATION 5012 This error is returned when a CEA message is received, and there are no common applications supported between the peer. DIAMETER_UNSUPPORTED_VERSION 5013 This error is returned when a CEA message is received, and the Diameter message is unsupported. DIAMETER_UNABLE_TO_COMPLY 5014 Calhoun et al. expires December 2001 [Page 66]
Internet-Draft June 2001 This error is returned when a request is rejected for unspecified reasons. DIAMETER_INVALID_BIT_IN_HEADER 5015 This error is returned when an unrecognized bit in the Diameter header is set to one (1). DIAMETER_INVALID_AVP_LENGTH 5016 The request contained an AVP with an invalid length. A Diameter message indicating this error MUST include the offending AVPs within a Failed-AVP AVP. DIAMETER_INVALID_MESSAGE_LENGTH 5017 This error is returned when a request is received with an invalid message length. 9.2 Message-Reject-Answer The Message-Reject-Answer (MRA), indicated by the Command-Code set to 282, and the Command Flags' 'R' bit cleared, is sent in response to a request that has caused a protocol error. Although the command code is different from the one found in the request, the same procedures used in issuing an answer message is followed. The Result-Code AVP MUST be present, and include a value in the "Protocol Error" category. Proxies receiving an MRA message MAY attempt to rectify the error reported, if possible. In the event that no proxy is able to correct the problem, the MRA will be returned to the originator of the request message. Message Format <Message-Reject-Answer> ::= < Diameter Header: 282 > < Session-Id > { Origin-Host } { Origin-Realm } { Result-Code } { Destination-Host } [ Origin-State-Id ] [ Error-Reporting-Host ] * [ AVP ] 9.3 Error-Message AVP Calhoun et al. expires December 2001 [Page 67]
Internet-Draft June 2001 The Error-Message AVP (AVP Code 281) is of type UTF8String. It MAY accompany a Result-Code AVP as a human readable error message. The Error-Message AVP is not intended to be useful in real-time, and SHOULD NOT be expected to be parsed by network entities. 9.4 Error-Reporting-Host AVP The Error-Reporting-Host AVP (AVP Code 294) is of type DiameterIdentity. This AVP contains the identity of the Diameter host that sent the Result-Code AVP to a value other than 2001 (Success), only if the host setting the Result-Code is different from the one encoded in the Origin-Host AVP. This AVP is intended to be used for troubleshooting purposes, and MUST be set when the Result- Code AVP indicates a failure. 9.5 Failed-AVP AVP The Failed-AVP AVP (AVP Code 279) is of type Grouped and provides debugging information in cases where a request is rejected or not fully processed due to erroneous information in a specific AVP. The value of the Result-Code AVP will provide information on the reason for the Failed-AVP AVP. The possible reasons for this AVP are the presence of an improperly constructed AVP, an unsupported or unrecognized AVP, an invalid AVP value, the omission of a required AVP, the presence of an explicitly excluded AVP (see table 12.0), or the presence of two or more occurrences of an AVP which table 14.1 restricts to 0, 1, or 0-1 occurrences. A Diameter message MAY contain one Failed-AVP AVP, containing the entire AVP that could not be processed successfully. If the failure reason is omission of a required AVP, an AVP with the missing AVP code, the missing vendor id, and a zero filled payload of the minimum required length for the ommitted AVP will be added. AVP Format <Failed-AVP> ::= < AVP Header: 279 > 1* {AVP} 10.0 Diameter User Sessions Diameter can provide two different type of services to applications. The first involves authentication and authorization, and can Calhoun et al. expires December 2001 [Page 68]
Internet-Draft June 2001 optionally make use of accounting. The second only makes use of accounting. When a service makes use of the authentication and/or authorization portion of an application, and a user requests access to the network, the Diameter client issues an auth request to its local server. The auth request is defined in a service specific Diameter application (e.g. NASREQ). The request contains a Session-Id AVP, which is used in subsequent messages (e.g. subsequent authorization, accounting, etc) relating to the user's session. The Session-Id AVP is a means for the client and servers to correlate a Diameter message with a user session. When a Diameter server authorizes a user to use network resources, it SHOULD add the Authorization-Lifetime AVP to the answer message. The Authorization-Lifetime AVP defines the maximum amount of time a user MAY make use of the resources before another authorization request is to be transmitted to the server. If the server does not receive another authorization request before the timeout occurs, it SHOULD release any state information related to the user's session. Note that the Authorization-Lifetime AVP implies how long the Diameter server is willing to pay for the services rendered, therefore a Diameter client SHOULD NOT expect payment for services rendered past the session expiration time. An access device MAY include an Authorization-Lifetime AVP with a value of zero to inform the Diameter server that the authorization requested will only occur once, and no further auth messages are to be sent with this particular session identifier. The Diameter server MAY accept the hint from the access device, or it MAY override the Authorization-Lifetime in the answer message with a non-zero value. By accepting an Authorization-Lifetime with a zero value, the Diameter server agrees that it will not receive a indication of session termination once service to the user is terminated, and therefore cannot maintain state for the session. Note that a zero Authorization-Lifetime MUST NOT be used in subsequent re- authorization messages. The base protocol does not include any authorization request messages, since these are largely application-specific and are defined in a Diameter application document. However, the base protocol does define a set of messages that are used to terminate user sessions. These are used to allow servers that maintain state information to free resources. When a service only makes use of the Accounting portion of the Diameter protocol, even in combination with an application, the Session-Id is still used to identify user sessions. However, the Calhoun et al. expires December 2001 [Page 69]
Internet-Draft June 2001 session termination messages are not used, since a session is signaled as being terminated by issuing an accounting stop message. 10.1 Authorization Session State Machine This section contains a finite state machine, representing the life cycle of Diameter sessions, and MUST be observed by all Diameter implementations that makes use of the authentication and/or authorization portion of a Diameter application. The term Service- Specific below refers to a message defined in a Diameter application (e.g. Mobile IP, NASREQ). The following table contains the authorization session state machine. State Event Action New State ------------------------------------------------------------- Idle Client or Device Requests send Pending access service specific auth req Idle Service-Specific authorization send serv. Open request received, and specific successfully processed answer Pending Successful Service-Specific Grant Open Authorization answer Access received with non-zero Authorization-Lifetime Pending Successful Service-Specific Grant Active Authorization answer Access received with zero Authorization-Lifetime Pending Successful Service-Specific Sent STR Discon authorization answer received but service not provided Pending Error processing successful Sent STR Discon Service-Specific authorization answer Open Authorization-Lifetime about send Open to expire on access device service specific auth req Calhoun et al. expires December 2001 [Page 70]
Internet-Draft June 2001 Open Successful Service-Specific Extend Open Authorization answer Access received Open Accounting message sent or process Open received Open Failed Service-Specific Discon. Closed Authorization answer user/device received. Open Session-Timeout Expires on send STR Discon Access Device Open SKR Received send SKA, Discon STR Open Session-Timeout or Cleanup Discon Authorization-Lifetime expires on home AAA server Open SKA Received Cleanup Closed Discon SKR Received ignore Discon Discon STR Received Send STA Closed Discon STA Received Discon. Closed user/device Active Service to user is terminated Cleanup Closed Closed Transition to state Cleanup When the Cleanup action is invoked, the Diameter node MAY attempt to release all resources for the particular session. Any event not listed above MUST be considered as an error condition, and an answer, if applicable, MUST be returned to the originator of the message. 10.2 Accounting Session State Machine For applications that only require accounting services, the following state machine MUST be supported. Calhoun et al. expires December 2001 [Page 71]
Internet-Draft June 2001 State Event Action New State ------------------------------------------------------------- Idle Client or device requests send Pending access accounting start req. Idle Accounting start request send Open received, and successfully accounting processed. start answer Pending Successful accounting grant Open start answer received access Open Receive Interim Record send Open accounting answer Open User service terminated send Discon accounting stop req. Open Accounting stop request send Closed received, and successfully accounting processed stop answer Discon Successful accounting discon. Closed stop answer received user/device 10.3 Server-Initiated Re-Auth A Diameter server may initiate a re-authentication and/or re- authorization service for a particular session by issuing a Re-Auth- Request (RAR). For example, for pre-paid services, the Diameter server that originally authorized a session may need some confirmation that the user is still using the services. An access device that receives a RAR message with Session-Id equal to a currently active session MUST initiate a re-auth towards the user, if the service supports this particular feature. Each Diameter application MUST state whether service-initiated re-auth is supported, since some applications do not allow for access devices to prompt the user for re-auth. Calhoun et al. expires December 2001 [Page 72]
Internet-Draft June 2001 10.3.1 Re-Auth-Request The Re-Auth-Request (RAR), indicated by the Command-Code set to 258 and the message flags' 'R' bit set, may be sent by any server to the access device that is providing session service, to request that the user be re-authenticated and/or re-authorized. Message Format <Re-Auth-Request> ::= < Diameter Header: 258, REQ, PXY > < Session-Id > { Origin-Host } { Origin-Realm } { Destination-Realm } { Destination-Host } [ Origin-State-Id ] * [ AVP ] * [ Proxy-Info ] * [ Route-Record ] 10.3.2 Re-Auth-Answer The Re-Auth-Answer (RAA), indicated by the Command-Code set to 258 and the message flags' 'R' bit clear, is sent in response to the RAR. The Result-Code AVP MUST be present, and indicates the disposition of the request. A successful RAA message MUST be followed by an application-specific authentication and/or authorization message. Message Format <Re-Auth-Answer> ::= < Diameter Header: 258, PXY > < Session-Id > { Result-Code } { Origin-Host } { Origin-Realm } { Destination-Host } [ Origin-State-Id ] * [ AVP ] * [ Proxy-Info ] * [ Route-Record ] 10.4 Session Termination It is necessary for a Diameter server that authorized a session to be Calhoun et al. expires December 2001 [Page 73]
Internet-Draft June 2001 notified when that session is no longer active, both for tracking purposes as well as to allow stateful agents to release any resources that they may have provided for the user's session. When a user session that required Diameter authorization terminates, the access device that provided the service MUST issue a Session- Termination- Request (STR) message to the Diameter server that authorized the service, to notify it that the session is no longer active. An STR MUST be issued when a user session terminates for any reason, including user logoff, expiration of Session-Timeout, administrative action, termination upon receipt of an Abort-Session- Request (see below), orderly shutdown of the access device, etc. The access device also MUST issue an STR for a session that was authorized but never actually started. This could occur, for example, due to a sudden resource shortage in the access device, or because the access device is unwilling to provide the type of service requested in the authorization, or because the access device does not support a mandatory AVP returned in the authorization, etc. It is also possible that a session that was authorized is never actually started due to action of a proxy. For example, a proxy may modify an authorization answer, converting the result from success to failure, prior to forwarding the message to the access device. A proxy that causes an authorized session not to be started MUST issue an STR to the Diameter server that authorized the session, since the access device has no way of knowing that the session had been authorized. A Diameter server that receives an STR message MUST clean up resources (e.g., session state) associated with the Session-Id specified in the STR, and return a Session-Termination-Answer. A Diameter server also MUST clean up resources when the Session- Timeout expires, or when the Authorization-Lifetime expires without re-authorization, regardless of whether an STR for that session is received. The access device is not expected to provide service beyond the expiration of these timers; thus, expiration of either of these timers implies that the access device may have unexpectedly shut down. 10.4.1 Session-Termination-Request The Session-Termination-Request (STR), indicated by the Command-Code set to 275 and the Command Flags' 'R' bit set, is sent by the access device to inform the Diameter Server that an authenticated and/or authorized session is being terminated. Calhoun et al. expires December 2001 [Page 74]
Internet-Draft June 2001 Message Format <Session-Termination-Req> ::= < Diameter Header: 275, REQ, PXY > < Session-Id > { Origin-Host } { Origin-Realm } { Destination-Realm } { Destination-Host } { User-Name } { Termination-Cause } [ Origin-State-Id ] * [ AVP ] * [ Proxy-Info ] * [ Route-Record ] 10.4.2 Session-Termination-Answer The Session-Termination-Answer (STA), indicated by the Command- Code set to 275 and the message flags' 'R' bit clear, is sent by the Diameter Server to acknowledge the notification that the session has been terminated. The Result-Code AVP MUST be present, and MAY contain an indication that an error occurred while servicing the STR. Upon sending or receipt of the STA, the Diameter Server MUST release all resources for the session indicated by the Session-Id AVP. Any intermediate server in the Proxy-Chain MAY also release any resources, if necessary. Message Format <Session-Termination-Answer> ::= < Diameter Header: 275, PXY > < Session-Id > { Result-Code } { Origin-Host } { Origin-Realm } { Destination-Host } { User-Name } [ Origin-State-Id ] * [ AVP ] * [ Proxy-Info ] * [ Route-Record ] 10.5 Aborting a Session A Diameter server may request that the access device stop providing service for a particular session by issuing an Abort-Session-Request Calhoun et al. expires December 2001 [Page 75]
Internet-Draft June 2001 (ASR). For example, the Diameter server that originally authorized the session may be required to cause that session to be stopped for credit or other reasons that were not anticipated when the session was first authorized. Or, an operator may maintain a management server for the purpose of issuing ASRs to administratively remove users from the network. An access device that receives an ASR with Session-ID equal to a currently active session MAY stop the session. Whether the access device stops the session or not is implementation- and/or configuration- dependent. For example, an access device may honor ASRs from certain agents only. In any case, the access device MUST respond with an Abort-Session-Answer, including a Result-Code AVP to indicate what action it took. Note that if the access device does stop the session upon receipt of an ASR, it issues an STR to the authorizing server (which may or may not be the agent issuing the ASR) just as it would if the session were terminated for any other reason. 10.5.1 Abort-Session-Request The Abort-Session-Request (ASR), indicated by the Command-Code set to 274 and the message flags' 'R' bit set, may be sent by any server to the access device that is providing session service, to request that the session identified by the Session-Id be stopped. Message Format <Abort-Session-Request> ::= < Diameter Header: 274, REQ, PXY > < Session-Id > { Origin-Host } { Origin-Realm } { Destination-Realm } { Destination-Host } [ Origin-State-Id ] * [ AVP ] * [ Proxy-Info ] * [ Route-Record ] 10.5.2 Abort-Session-Answer The Abort-Session-Answer (ASA), indicated by the Command-Code set to 274 and the message flags' 'R' bit clear, is sent in response to the Calhoun et al. expires December 2001 [Page 76]
Internet-Draft June 2001 ASR. The Result-Code AVP MUST be present, and indicates the disposition of the request. If the session identified by Session-Id in the ASR was successfully terminated, Result-Code is set to DIAMETER_SUCCESS. If the session is not currently active, Result-Code is set to DIAMETER_UNKNOWN_SESSION_ID. If the access device does not stop the session for any other reason, Result-Code is set to DIAMETER_UNABLE_TO_COMPLY. Message Format <Abort-Session-Answer> ::= < Diameter Header: 274, PXY > < Session-Id > { Result-Code } { Origin-Host } { Origin-Realm } { Destination-Host } [ Origin-State-Id ] * [ AVP ] * [ Proxy-Info ] * [ Route-Record ] 10.6 Inferring Session Termination from Origin-State-Id Origin-State-Id is used to allow rapid detection of terminated sessions for which no STR would have been issued, due to unanticipated shutdown of an access device. By including Origin-State-Id in CER/CAA messages, an access device allows a next-hop server to determine immediately upon connection whether the device has lost its sessions since the last connection. By including Origin-State-Id in request messages, an access device also allows a server with which it communicates via proxy to make such a determination. However, a server that is not directly connected with the access device will not discover that the access device has been restarted unless and until it receives a new request from the access device. Thus, use of this mechanism across proxies is opportunistic rather than reliable, but useful nonetheless. When a Diameter server receives a Origin-State-Id that is greater than the Origin-State-Id previously received from the same issuer, it may assume that the issuer has lost state since the previous message and that all sessions that were active under the lower Origin-State- Id have been terminated. The Diameter server MAY clean up all session state associated with such lost sessions, and MAY also issues STRs Calhoun et al. expires December 2001 [Page 77]
Internet-Draft June 2001 for all such lost sessions that were authorized on upstream servers, to allow session state to be cleaned up globally. 10.7 Session-Id AVP The Session-Id AVP (AVP Code 263) is of type UTF8String and is used to identify a specific session (see section 10.0). All messages pertaining to a specific session MUST include only one Session-Id AVP and the same value MUST be used throughout the life of a session. When present, the Session-Id SHOULD appear immediately following the Diameter Header (see section 3.0). The Session-Id MUST be globally and eternally unique, as it is meant to uniquely identify a user session without reference to any other information, and may be needed to correlate historical authentication information with accounting information. The Session-Id includes a mandatory portion and an implementation-defined portion; a recommended format for the implementation-defined portion is outlined below. The Session-Id MUST begin with the sender's identity encoded in the DiameterIdentity type (see section 4.4). The remainder of the Session-Id MAY be any sequence that the client can guarantee to be eternally unique; however, the following format is recommended, (square brackets [] indicate an optional element): <diameterIdentity>;<high 32 bits>;<low 32 bits>[;<optional value>] <high 32 bits> and <low 32 bits> are decimal representations of the high and low 32 bits of a monotonically increasing 64-bit value. The 64-bit value is rendered in two part to simplify formatting by 32-bit processors. At startup, the high 32 bits of the 64-bit value MAY be initialized to the time, and the low 32 bits MAY be initialized to 0. This will for practical purposes eliminate the possibility of overlapping Session-Ids after a reboot, assuming the reboot process takes longer than a second. Alternatively, an implementation MAY keep track of the increasing value in non-volatile memory. <optional value> is implementation specific but may include a modem's device Id, a layer 2 address, timestamp, etc. Example, in which the standard port is used and there is no optional value: aaa://diameter/accesspoint7.acme.com;1876543210;523 or accesspoint7.acme.com;1876543210;523 Calhoun et al. expires December 2001 [Page 78]
Internet-Draft June 2001 Example, in which a non-standard port is used and there is an optional value: accesspoint7.acme.com:831;1876543210;523;mobile@200.1.1.88 The session Id is created by the Diameter device initiating the session, which in most cases is done by the client. Note that a Session-Id MAY be used for both the authorization and accounting commands of a given application. 10.8 Authorization-Lifetime AVP The Authorization-Lifetime AVP (AVP Code 291) is of type Unsigned32 and contains the maximum number of seconds of service to be provided to the user before the user is to be re-authenticated and/or re- authorized. Great care should be taken when the Authorization- Lifetime value is determined, since a low, non-zero, value could create significant Diameter traffic, which could congest both the network and the agents. If both this AVP and the Session-Timeout AVP are present in a message, the value of the latter MUST NOT be smaller than the Authorization-Lifetime AVP. This AVP MAY be provided by the client as a hint of the maximum duration that it is willing to accept. However, the server DOES NOT have to observe the hint, and MAY return a value that is smaller than the hint. A value of zero means that no re-authorization is required, and no session termination message will be sent to the Diameter server. 10.9 Session-Timeout AVP The Session-Timeout AVP (AVP Code 27) [1] is of type Unsigned32 and contains the maximum number of seconds of service to be provided to the user before termination of the session. A session terminated due to the Session-Timeout expiration MUST NOT generate a re- authentication and/or re-authorization. A value of zero, or the absence of this AVP, means that this session has an unlimited number of seconds before termination. This AVP MAY be provided by the client as a hint of the maximum duration that it is willing to accept. However, the server DOES NOT have to observe the hint, and MAY return a value that is smaller than the hint. Calhoun et al. expires December 2001 [Page 79]
Internet-Draft June 2001 10.10 User-Name AVP The User-Name AVP (AVP Code 1) [1] is of type UTF8String, which contains the User-Name, in a format consistent with the NAI specification [8]. 10.11 Termination-Cause AVP The Termination-Cause AVP (AVP Code 295) is of type Enumerated, and is used to indicate the reason why a session was terminated on the access device. The following values are defined: DIAMETER_LOGOUT 1 The user initiated a disconnect DIAMETER_SERVICE_NOT_PROVIDED 2 This value is used when the user disconnected prior to the receipt of the authorization answer message. DIAMETER_BAD_ANSWER 3 This value indicates that the authorization answer received by the access device was not processed successfully. DIAMETER_ADMINISTRATIVE 4 The user was not granted access, or was disconnected, due to administrative reasons, such as the receipt of a Session-Kill- Request message. DIAMETER_LINK_BROKEN 5 The communication to the user was abruptly disconnected. 10.12 Origin-State-Id AVP The Origin-State-Id AVP (AVP Code 278), of type Unsigned32, is a monotonically increasing value that is advanced whenever a Diameter entity restarts with loss of previous state, for example upon reboot. Origin-State-Id MAY be included in any Diameter message, including CER. A Diameter entity issuing this AVP MUST create a higher value for this AVP each time its state is reset. A Diameter entity MAY set Origin-State-Id to the time of startup, or it MAY use an incrementing counter retained in non-volatile memory across restarts. The Origin-State-Id, if present, MUST reflect the state of the entity indicated by Origin-Host. If a proxy modifies Origin-Host, it MUST Calhoun et al. expires December 2001 [Page 80]
Internet-Draft June 2001 either remove Origin-State-Id or modify it appropriately as well. Typically, Origin-State-Id is used by an access device that always starts up with no active sessions; that is, any session active prior to restart will have been been lost. By including Origin-State-Id in a message, it allows other Diameter entities to infer that sessions associated with a lower Origin-State-Id are no longer active. If an access device does not intend for such inferences to be made, it MUST either not include Origin-State-Id in any message, or set its value to 0. 10.13 Session-Binding AVP The Session-Binding AVP (AVP Code 270) is of type Unsigned32, and MAY be present in application-specific authorization answer messages. If present, this AVP MAY inform the Diameter client that all future application-specific re-auth messages for this session MUST be sent to the same authorization server. This AVP MAY also specify that a Session-Termination-Request message for this session MUST be sent to the same authorizing server. This field is a bit mask, and the following bits have been defined: RE_AUTH 1 When set, future re-auth messages for this session MUST NOT include the Destination-Host AVP. When cleared, the default value, the Destination-Host AVP MUST be present in all re-auth messages for this session. STR 2 When set, the STR message for this session MUST NOT include the Destination-Host AVP. When cleared, the default value, the Destination-Host AVP MUST be present in the STR message for this session. ACCOUNTING 4 When set, all accounting messages for this session MUST NOT include the Destination-Host AVP. When cleared, the default value, the Destination-Host AVP MUST be present in all accounting messages for this session. 10.14 Session-Server-Failover AVP The Session-Server-Failover AVP (AVP Code 271) is of type Enumerated, and MAY be present in application-specific authorization answer Calhoun et al. expires December 2001 [Page 81]
Internet-Draft June 2001 messages that either do not include the Session-Binding AVP or include the Session-Binding AVP with any of the bits set to a zero value. If present, this AVP MAY inform the Diameter client that if a re-auth or STR message fails due to a delivery problem, the Diameter client SHOULD issue a subsequent message without the Destination-Host AVP. When absent, the default value is REFUSE_SERVICE. The following values are supported: REFUSE_SERVICE 0 If either the re-auth or the STR message delivery fails, terminate service with the user, and do not attempt any subsequent attempts. TRY_AGAIN 1 If either the re-auth or the STR message delivery fails, resend the failed message without the Destination-Host AVP present. ALLOW_SERVICE 2 If re-auth message delivery fails, assume that re-authorization succeeded. If STR message delivery fails, terminate the session. TRY_AGAIN_ALLOW_SERVICE 3 If either the re-auth or the STR message delivery fails, resend the failed message without the Destination-Host AVP present. If the second delivery fails for re-auth, assume re- authorization succeeded. If the second delivery fails for STR, terminate the session. 10.15 Multi-Round-Time-Out AVP The Multi-Round-Time-Out AVP (AVP Code 272) is of type Unsigned32, and SHOULD be present in application-specific authorization answer messages whose Result-Code AVP is set to DIAMETER_MULTI_ROUND_AUTH. This AVP contains the maximum number of seconds that the access device MUST provide the user in responding to an authentication request. 10.16 Class AVP The Class AVP (AVP Code 25) is of type OctetString and is used to by Diameter servers to return state information to the access device. When one or more Class AVPs are present in application-specific authorization answer messages, they MUST be present in subsequent re-authorization, session termination and accounting messages. Class Calhoun et al. expires December 2001 [Page 82]
Internet-Draft June 2001 AVPs found in a re-authorization answer message override the ones found in any previous authorization answer message. Diameter server implementations SHOULD NOT return Class AVPs that require more than 4096 bytes of storage on the Diameter client. A Diameter client that receives Class AVPs whose size exceeds local available storage MUST terminate the session. 11.0 Accounting This accounting protocol is based on a server directed model with capabilities for real-time delivery of accounting information. Several fault resilience methods [40] have been built in to the protocol in order minimize loss of accounting data in various fault situations and under different assumptions about the capabilities of the used devices. 11.1 Server Directed Model The server directed model means that the device generating the accounting data gets information from either the authorization server (if contacted) or the accounting server regarding the way accounting data shall be forwarded. This information includes accounting record timeliness requirements. As discussed in [40], real-time transfer of accounting records is a requirement, such as the need to perform credit limit checks and fraud detection. Note that batch accounting is not a requirement, and is therefore not supported by Diameter. Should Batched Accounting be required in the future, a new Diameter application will need to be created, or it could be handled using another protocol. The authorization server (chain) directs the selection of proper transfer strategy, based on its knowledge of the user and relationships of roaming partnerships. The server (or agents) uses the Accounting-Interim-Interval AVP to control the operation of the Diameter peer operating as a client. The Accounting-Interim-Interval AVP, when present, instructs the Diameter node acting as a client to produce accounting records continuously even during a session. The Diameter accounting server MAY override the interim interval by including an Accounting-Interim-Interval AVP in the Accounting-Answer message. When the AVP is present, the latest value received SHOULD be used in the generation of interim accounting messages. 11.2 Protocol Messages Calhoun et al. expires December 2001 [Page 83]
Internet-Draft June 2001 A Diameter node that receives a successful authentication and/or authorization messages from the Home AAA Server, MUST collect accounting information for the session. The Accounting-Request message is used to transmit the accounting information to the Home AAA server, which MUST reply with the Accounting-Answer message to confirm reception. The Accounting-Answer message includes the Result-Code AVP, which MAY indicate that an error was present in the accounting message. A rejected Accounting-Request message SHOULD cause the user's session to be terminated. Each Diameter Accounting protocol message MAY be compressed using IPComp [41] in order to reduce the used network bandwidth, which MAY use IKE [15] to negotiate the compression parameters. 11.3 Application document requirements Each Diameter application (e.g. NASREQ, MobileIP), MUST define their Service-Specific AVPs that MUST be present in the Accounting-Request message in a section entitled "Accounting AVPs". The application MUST assume that the AVPs described in this document will be present in all Accounting messages, so only their respective service-specific AVPs need to be defined in this section. 11.4 Fault Resilience Diameter Base protocol mechanisms are used to overcome small message loss and network faults of temporary nature. Diameter peers acting as clients MUST implement the use of failover to guard against server failures and certain network failures. Diameter peers acting as agents or related off-line processing systems MUST detect duplicate accounting records caused by the sending of same record to several servers and duplication of messages in transit. This detection MUST be based on the inspection of the Session-Id and Accounting-Record-Number AVP pairs. Diameter clients MAY have non-volatile memory for the safe storage of accounting records over reboots or extended network failures, network partitions, and server failures. If such memory is available the client SHOULD store new accounting records there as soon as the records are created and until a positive acknowledgement of their reception from the Diameter Server has been received. Upon a reboot, the client MUST starting sending the records in the non-volatile memory to the accounting server with appropriate modifications in termination cause, session length, and other relevant information in the records. Calhoun et al. expires December 2001 [Page 84]
Internet-Draft June 2001 A further application of this protocol may include AVPs to control how many accounting records may at most be stored in the Diameter client without committing them to the non-volatile memory or transferring them to the Diameter server. The client SHOULD NOT remove the accounting data from any of its memory areas before the correct Accounting-Answer has been received. The client MAY remove oldest, undelivered or yet unacknowledged accounting data if it runs out of resources such as memory. It is an implementation dependent matter for the client to accept new sessions under this condition. 11.5 Accounting Records In all accounting records the Session-Id and User-Name AVPs MUST be present. If end-to-end authentication is required, as described in [11], the CMS-Data AVP may be used to authenticate the Accounting Data and Service Specific AVPs. It is not typically necessary, nor recommended, that the end-to-end authentication cover any additional AVPs since the Data and Service Specific AVP, and associated CMS- Data, MAY need to be submitted to a third party. Different types of accounting records are sent depending on the actual type of accounted service and the authorization server's directions for interim accounting. If the accounted service is a one-time event, meaning that the start and stop of the event are simultaneous, then the Accounting-Record-Type AVP MUST be present and set to the value EVENT_RECORD. If the accounted service is of a measurable length, then the AVP MUST use the values START_RECORD, STOP_RECORD, and possibly, INTERIM_RECORD. If the authorization server has directed interim accounting to be enabled for the session, but no interim interval was specified, two accounting records MUST be generated for each service of type session. When the initial Accounting-Request is sent for a given session is sent, the Accounting-Record-Type AVP MUST be set to the value START_RECORD. When the last Accounting-Request is sent, the value MUST be STOP_RECORD. If a specified interim interval exists, the Diameter client MUST produce additional records between the START_RECORD and STOP_RECORD, marked INTERIM_RECORD. The production of these records is directed both by Accounting-Interim-Interval as well as any re-authentication or re-authorization of the session. The Diameter client MUST overwrite any previous interim accounting records that are locally stored for delivery, if a new record is being generated for the same session. This ensures that only one pending interim record can exist Calhoun et al. expires December 2001 [Page 85]
Internet-Draft June 2001 on an access device for any given session. A particular value of Accounting-Session-Id MUST appear only in one sequence of accounting records from a DIAMETER client, except for the purposes of retransmission. The one sequence that is sent MUST be either one record with Accounting-Record-Type AVP set to the value EVENT_RECORD, or several records starting with one having the value START_RECORD, followed by zero or more INTERIM_RECORD, and a single STOP_RECORD. A particular Diameter application specification MUST define the type of sequences that MUST be used. 11.6 Correlation of Accounting Records The Diameter protocol's Session-Id AVP, which is globally unique (see section 10.7), is used during the authorization phase to identify a particular session. Services that do not require any authorization still use the Session-Id AVP to identify sessions. However, there are certain applications that require multiple accounting sub-sessions. Such applications would send messages with a constant Session-Id AVP, but a different Accounting-Session-Id AVP. In these cases, correlation is performed using the Session-Id. Furthermore, there are certain applications where a user receives service from different access devices (e.g. Mobile IP), each with their own unique Session-Id. In such cases, the Accounting-Multi- Session-Id AVP is used for correlation. During authorization, a server that determines that a request is for an existing session, SHOULD include the Accounting-Multi-Session-Id AVP, which the access device MUST include in all subsequent accounting messages. The Accounting-Multi-Session-Id AVP MAY include the value of the original Session-Id. It's contents are implementation specific, but MUST be globally unique across other Accounting-Multi-Session-Id, and MUST NOT change during the life of a session. A Diameter application document MUST define the exact concept of a session that is being accounted, and MAY define the concept of a multi-session. For instance, the NASREQ DIAMETER application treats a single PPP connection to a Network Access Server as one session, and a set of Multilink PPP sessions as one multi-session. 12.0 Accounting Command-Codes This section defines new Command-Code values that MUST be supported by all Diameter implementations that provide Accounting services. Calhoun et al. expires December 2001 [Page 86]
Internet-Draft June 2001 12.1 Accounting-Request The Accounting-Request command, indicated by the Command-Code field set to 271 and the Command Flags' 'R' bit set, is sent by a Diameter node, acting as a client, in order to exchange accounting information with a peer. When the Accounting-Request is being submitted to a third party (e.g. settlement service), and includes the CMS-Data AVP [11], the CMS-Data AVP MUST be signed by both the local and home Diameter server using the countersignature procedures described in [11]. The AVP listed below SHOULD include service specific accounting AVPs, as described in section 11.3. Message Format <Accounting-Request> ::= < Diameter Header: 271, REQ, PXY > < Session-Id > { Acct-Application-Id } { User-Name } { Origin-Host } { Origin-Realm } { Destination-Realm } { Accounting-Record-Type } { Accounting-Record-Number } { Accounting-Session-Id } [ Accounting-Interim-Interval ] [ Origin-State-Id ] * [ AVP ] * [ Proxy-Info ] * [ Route-Record ] 12.2 Accounting-Answer The Accounting-Answer command, indicated by the Command-Code field set to 271 and the Command Flags' 'R' bit cleared, is used to acknowledge an Accounting-Request command. The Accounting-Answer command contains the same Session-Id and MAY contains the same Accounting Description and Usage AVPs that were sent in the Accounting-Request command. If the CMS-Data AVP was present in the Accounting-Request, the corresponding ACA message MUST include the CMS-Data AVP signed by the responder to provide strong AVP authentication, which MAY be used for the purposes of repudiation. Only the target Diameter Server, known as the home Diameter Server, SHOULD respond with the Accounting-Answer command. Calhoun et al. expires December 2001 [Page 87]
Internet-Draft June 2001 The AVP listed below SHOULD include service specific accounting AVPs, as described in section 11.3. Message Format <Accounting-Answer> ::= < Diameter Header: 271, PXY > < Session-Id > { Acct-Application-Id } { User-Name } { Result-Code } { Origin-Host } { Origin-Realm } { Destination-Host } { Accounting-Record-Type } { Accounting-Record-Number } { Accounting-Session-Id } [ Error-Reporting-Host ] [ Accounting-Interim-Interval ] [ Origin-State-Id ] * [ AVP ] * [ Proxy-Info ] * [ Route-Record ] 13.0 Accounting AVPs This section contains AVPs that describe accounting usage information related to a specific session. 13.1 Accounting-Record-Type AVP The Accounting-Record-Type AVP (AVP Code 480) is of type Enumerated and contains the type of accounting record being sent. The following values are currently defined for the Accounting-Record-Type AVP: EVENT_RECORD 1 An Accounting Event Record is used to indicate that a one-time event has occurred (meaning that the start and end of the event are simultaneous). This record contains all information relevant to the service, and is the only record of the service. START_RECORD 2 An Accounting Start, Interim, and Stop Records are used to indicate that a service of a measurable length has been given. An Accounting Start Record is used to initiate an accounting session, and contains accounting information that is relevant to the initiation of the session. Calhoun et al. expires December 2001 [Page 88]
Internet-Draft June 2001 INTERIM_RECORD 3 An Interim Accounting Record contains cumulative accounting information for an existing accounting session. Interim Accounting Records SHOULD be sent every time a re- authentication or re-authorization occurs. Further, additional interim record triggers MAY be defined by application-specific Diameter applications. The selection of whether to use INTERIM_RECORD records is directed by the Accounting-Interim- Interval AVP. STOP_RECORD 4 An Accounting Stop Record is sent to terminate an accounting session and contains cumulative accounting information relevant to the existing session. 13.2 Accounting-Interim-Interval AVP The Accounting-Interim-Interval AVP (AVP Code 482) is of type Unsigned32 and is sent from the Diameter home authorization server to the Diameter client. The client uses information in this AVP to decide how and when to produce accounting records. With different values in this AVP, service sessions can result in one, two, or two+N accounting records, based on the needs of the home-organization. The following accounting record production behavior is directed by the inclusion of this AVP: 1. The omission of the Accounting-Interim-Interval AVP or its inclusion with Value field set to 0 means that EVENT_RECORD, START_RECORD, and STOP_RECORD are produced, as appropriate for the service. 2. The inclusion of the AVP with Value field set to a non-zero value means that INTERIM_RECORD records MUST be produced between the START_RECORD and STOP_RECORD records. The Value field of this AVP is the nominal interval between these records in seconds. The Diameter node that originates the accounting information, known as the client, MUST produce the first INTERIM_RECORD record roughly at the time when this nominal interval has elapsed from the START_RECORD, the next one again as the interval has elapsed once more, and so on until the session ends and a STOP_RECORD record is produced. The client MUST ensure that the interim record production times are randomized so that large accounting message storms are not created either among records or around a common service start time. Calhoun et al. expires December 2001 [Page 89]
Internet-Draft June 2001 13.3 Accounting-Record-Number AVP The Accounting-Record-Number AVP (AVP Code 485) is of type Unsigned32 and identifies this record within one session. As Session-Id AVPs are globally unique, the combination of Session-Id and Accounting- Record-Number AVPs is also globally unique, and can be used in matching accounting records with confirmations. An easy way to produce unique numbers is to set the value to 0 for records of type EVENT_RECORD and START_RECORD, and set the value to 1 for the first INTERIM_RECORD, 2 for the second, and so on until the value for STOP_RECORD is one more than for the last INTERIM_RECORD. 13.4 Accounting-Session-Id AVP The Accounting-Session-Id AVP (AVP Code 44) is of type UTF8String, following the format specified in section 10.7. The Accounting- Session-Id is not used by the Diameter protocol, since the Session-Id defined in [1] is used for both authentication/authorization and accounting purposes. However, a RADIUS/Diameter gateway MAY need to include the Accounting-Session-Id in Diameter accounting messages. 13.5 Accounting-Multi-Session-Id AVP The Accounting-Multi-Session-Id AVP (AVP Code 50) is of type UTF8String, following the format specified in section 10.7. The Accounting-Multi-Session-Id AVP is used to link together multiple related accounting sessions, where each session would have a unique Accounting-Session-Id, but the same Acounting-Multi-Session-Id AVP. This AVP MAY be returned by the Diameter server in an authorization answer, and MUST be used in all accounting messages for the given session. 14.0 AVP Occurrence Table The following tables presents the AVPs defined in this document, and specifies in which Diameter messages they MAY, or MAY NOT be present. Note that AVPs that can only be present within a Grouped AVP are not represented in this table. The table uses the following symbols: 0 The AVP MUST NOT be present in the message. 0+ Zero or more instances of the AVP MAY be present in the message. 0-1 Zero or one instance of the AVP MAY be present in the message. It is considered an error if there are more than Calhoun et al. expires December 2001 [Page 90]
Internet-Draft June 2001 once instance of the AVP. 1 One instance of the AVP MUST be present in the message. 1+ At least one instance of the AVP MUST be present in the message. 14.1 Base Protocol Command AVP Table The table in this section is limited to the non-accounting Command Codes defined in this specification. +-----------------------------------+ | Command-Code | |---+---+---+---+---+---+---+---+---+ Attribute Name |CER|CEA|MRA|DWR|DWA|ASR|ASA|STR|STA| ------------------------------|---+---+---+---+---+---+---+---+---| Acct-Application-Id |0+ |0+ |0 |0 |0 |0 |0 |0 |0 | Auth-Application-Id |0+ |0+ |0 |0 |0 |0 |0 |0 |0 | Authorization-Lifetime |0 |0 |0 |0 |0 |0 |0 |0 |0 | Class |0 |0 |0 |0+ |0 |0 |0 |0+ |0+ | Destination-Host |0-1|0 |0 |0-1|0 |1 |0 |0-1|0 | Destination-Realm |0 |0 |0 |0 |0 |1 |0 |1 |0 | Error-Message |0 |0 |0 |0 |0 |0 |0-1|0 |0 | Error-Reporting-Host |0 |0 |0 |0 |0 |0 |0-1|0 |0 | Failed-AVP |0 |0+ |0+ |0 |0+ |0 |0+ |0 |0+ | Firmware-Revision |0-1|0-1|0 |0 |0 |0 |0 |0 |0 | Host-IP-Address |1+ |1+ |0 |0 |0 |0 |0 |0 |0 | Multi-Round-Time-Out |0 |0 |0 |0 |0 |0 |0 |0 |0 | Origin-Host |1 |1 |1 |1 |1 |1 |1 |1 |1 | Origin-Realm |1 |1 |1 |1 |1 |1 |1 |1 |1 | Product-Name |1 |1 |0 |0 |0 |0 |0 |0 |0 | Proxy-Info |0 |0 |0 |0 |0 |0+ |0+ |0+ |0+ | Redirect-Host |0 |0 |0+ |0 |0 |0 |0 |0 |0 | Redirect-Host-Usage |0 |0 |0+ |0 |0 |0 |0 |0 |0 | Redirect-Max-Cache-Time |0 |0 |0+ |0 |0 |0 |0 |0 |0 | Result-Code |0 |1 |1 |0 |1 |0 |0 |0 |1 | Route-Record |0 |0 |0 |0 |0 |0+ |0+ |0+ |0+ | Session-Binding |0 |0 |0 |0 |0 |0 |0 |0 |0 | Session-Id |0 |0 |1 |0 |0 |1 |1 |1 |1 | Session-Server-Failover |0 |0 |0 |0 |0 |0 |0 |0 |0 | Session-Timeout |0 |0 |0 |0 |0 |0 |0 |0 |0 | Origin-State-Id |0-1|0-1|0-1|0-1|0-1|0-1|0-1|0-1|0-1| Supported-Vendor-Id |0+ |0 |0 |0 |0 |0 |0 |0 |0 | Termination-Cause |0 |0 |0 |0 |0 |0 |0 |1 |0 | User-Name |0 |0 |0 |0 |0 |1 |1 |1 |1 | Vendor-Id |1 |1 |0 |0 |0 |0 |0 |0 |0 | Vendor-Specific-Application-Id|0+ |0+ |0 |0 |0 |0 |0 |0 |0 | ------------------------------|---+---+---+---+---+---+---+---+---| Calhoun et al. expires December 2001 [Page 91]
Internet-Draft June 2001 14.2 Accounting AVP Table The table in this section is used to represent which AVPs defined in this document are to be present in the Accounting messages. +-----------+ | Command | | Code | |-----+-----+ Attribute Name | ACR | ACA | ------------------------------|-----+-----+ Accounting-Interim-Interval | 0-1 | 0-1 | Accounting-Multi-Session-Id | 0-1 | 0-1 | Accounting-Record-Number | 1 | 1 | Accounting-Record-Type | 1 | 1 | Accounting-Session-Id | 1 | 1 | Acct-Application-Id | 1 | 1 | Class | 0+ | 0+ | Destination-Host | 0-1 | 0 | Destination-Realm | 1 | 0 | Error-Reporting-Host | 0 | 0+ | Max-Time-Wait | 0+ | 0 | Origin-Host | 1 | 1 | Origin-Realm | 1 | 1 | Proxy-Info | 0+ | 0+ | Route-Record | 0+ | 0+ | Result-Code | 0 | 1 | Session-Id | 1 | 1 | ------------------------------|-----+-----+ 15.0 IANA Considerations This document defines a number of assigned numbers to be maintained by the IANA. This section explains the criteria to be used by the IANA to assign additional numbers in each of these lists. The following subsections describe the assignment policy for the namespaces defined elsewhere in this document. 15.1 AVP As defined in section 4.0, the AVP header contains two fields that requires IANA namespace management; the AVP Code and Flags field. 15.1.1 AVP Code the AVP Code namespace is used to identify attributes. When the Calhoun et al. expires December 2001 [Page 92]
Internet-Draft June 2001 Vendor ID value is set to zero (0), IANA will maintain a registry of assigned AVP codes, and in some cases also their values. AVP Codes 0-254 are managed separately as RADIUS Attribute Types [46], while the remaining namespace is available for assignment via Specification Required [12]. Vendor-Specific AVP Codes, where the Vendor-Id field in the AVP header is set to a non-zero value, is for Private Use. This document defines the AVP Codes 257-272, 278-284, 291-297, 480, 482 and 485-486. See section 4.6 for the assignment of the namespace in this specification. 15.1.2 AVP Flags There are 8 bits in the AVP Flags field of the AVP header, defined in section 4.0. This document assigns bit 8 ('V'endor Specific), bit 7 ('M'andatory) and bit 6 ('P'rotected). The remaining bits should only be assigned via a Standards Action [12]. 15.2 Diameter Header As defined in section 3.0, the Diameter header contains two fields that require IANA namespace management; Command Code and Command Flags. 15.2.1 Command Codes The Command Code namespace is used to identify Diameter commands. The values 0-255 are reserved for RADIUS backward compatibility, and are defined as "RADIUS Packet Type Codes" in [46]. The remaining values are available via Standards Action [12]. Vendor-Specific Command Codes, where the Vendor-Id field in the Diameter header is set to a non-zero value, is for Private Use. This document defines the Command Codes 257, 258, 271, 274-275, 280 and 282. See section 3.1 for the assignment of the namespace in this specification. 15.2.2 Command Flags There are eight bits in the Command Flags field of the Diameter header. This document assigns bit 8 ('R'equest) and bit 7 ('P'roxy). Calhoun et al. expires December 2001 [Page 93]
Internet-Draft June 2001 Bits 1 through 6 MUST only be assigned via a Standards Action [12]. 15.3 Application Identifiers As defined in section 6.1, the Application Identifier is used to identify a specific Diameter Application. All values, other than zero (0) are available for assignment via Standards Action [12]. Vendor-Specific Application Identifiers, encoded in the Vendor- Specific-Application-Id Grouped AVP, with the Vendor-Id AVP set to the vendor's enterprise number, is for Private Use. Note that the Diameter protocol is not intended to be extended for any purpose. Any applications defined MUST ensure that they fit within the existing framework, and that no changes to the base protocol are required. 15.4 Result-Code AVP Values As defined in Section 9.1, the Result-Code AVP (AVP Code 268) defines the values 1001, 2001-2002, 3001-3009, 4001-4003 and 5001-5017. All remaining values are available for assignment via IETF Consensus [12]. 15.5 Accounting-Record-Type AVP Values As defined in Section 13.1, the Accounting-Record-Type AVP (AVP Code 480) defines the values 1-4. All remaining values are available for assignment via IETF Consensus [12]. 15.6 Termination-Cause AVP Values As defined in Section 10.10, the Termination-Cause AVP (AVP Code 295) defines the values 1-5. All remaining values are available for assignment via IETF Consensus [12]. 15.7 Redirect-Host-Usage AVP Values As defined in Section 5.10, the Redirect-Host-Usage AVP (AVP Code 261) defines the values 0-5. All remaining values are available for assignment via IETF Consensus [12]. Calhoun et al. expires December 2001 [Page 94]
Internet-Draft June 2001 15.8 Session-Server-Failover AVP Values As defined in Section 10.14, the Session-Server-Failover AVP (AVP Code 271) defines the values 0-3. All remaining values are available for assignment via IETF Consensus [12]. 15.9 Session-Binding AVP Values As defined in Section 10.13, the Session-Server-Failover AVP (AVP Code 270) defines the bits 1-4. All remaining bits are available for assignment via IETF Consensus [12]. 15.10 Diameter TCP/SCTP Port Numbers An IANA request has been placed for TCP and SCTP port numbers. The IANA has informed the authors that "TBD" should be used in section 2.1 this document, and will be updated by the RFC editor during the RFC publication process. IANA should also replace "TBD" in section 4.4 with the port number assigned in section 2.1 16.0 Diameter protocol related configurable parameters This section contains the configurable parameters that are found throughout this document: Diameter Peer A Diameter entity MAY communicate with peers that are statically configured. A statically configured Diameter peer would require that either the IP address or the fully qualified domain name (FQDN) be supplied, which would then be used to resolve through DNS. Realm Routing Table A Diameter Proxy server routes messages based on the realm portion of a Network Access Identifier (NAI). The server MUST have a table of Realms Names, and the address of the peer to which the message must be forwarded to. The routing table MAY also include a "default route", which is typically used for all messages that cannot be locally processed. Tc timer The Tc timer controls the frequency that transport connection attempts are done to a peer with whom no active transport Calhoun et al. expires December 2001 [Page 95]
Internet-Draft June 2001 connection exists. The recommended value is 30 seconds. Tw timer The Tw timer controls the frequency the watchdog messages are to be sent to inactive peers. The recommended value is 30 seconds. 17.0 Security Considerations The Diameter base protocol assumes that messages are secured by using either IP Security, or TLS. This security model is acceptable in environments where there are no untrusted third party relay, proxy, or redirect servers. When third party brokers or redirect servers are used, strong application level security SHOULD be required, such as non- repudiation. When the communicating peers do require this level of security either for legal or business purposes, the Diameter application defined in [11] MAY be used. This security model provides AVP-level authentication, and the encryption mechanism is designed such that only the target host has the keying information required to decrypt the information. 18.0 References [1] C. Rigney, A. Rubens, W. Simpson, S. Willens, "Remote Authenti- cation Dial In User Service (RADIUS)", RFC 2865, June 2000. [2] Reynolds, Postel, "Assigned Numbers", RFC 1700, October 1994. [3] Postel, "User Datagram Protocol", RFC 768, August 1980. [4] Rivest, "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [5] Kaufman, Perlman, Speciner, "Network Security: Private Communi- cations in a Public World", Prentice Hall, March 1995, ISBN 0- 13-061466-1. [6] Krawczyk, Bellare, Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, January 1997. [7] P. Calhoun, W. Bulley, A. Rubens, J. Haag, "Diameter NASREQ Application", draft-ietf-aaa-diameter-nasreq-05.txt, IETF work in progress, June 2001. Calhoun et al. expires December 2001 [Page 96]
Internet-Draft June 2001 [8] Aboba, Beadles "The Network Access Identifier." RFC 2486. Janu- ary 1999. [10] P. Calhoun, C. Perkins, "Diameter Mobile IP Application", draft-ietf-aaa-diameter-mobileip-05.txt, IETF work in progress, June 2001. [11] P. Calhoun, W. Bulley, S. Farrell, "Diameter CMS Security appli- cation", draft-ietf-aaa-diameter-cms-sec-00.txt (work in pro- gress), June 2001. [12] Narten, Alvestrand,"Guidelines for Writing an IANA Considera- tions Section in RFCs", BCP 26, RFC 2434, October 1998 [13] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [14] Myers, Ankney, Malpani, Galperin, Adams, "X.509 Internet Public Key Infrastructure Online Certificate Status Protocol (OCSP)", RFC 2560, June 1999. [15] D. Harkins, D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, November 1998. [16] Hinden, Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [17] ISI, "Internet Protocol", RFC 791, September 1981. [18] Mills, "Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI, RFC 2030, October 1996. [19] Housley, Ford, Polk, Solo, "Internet X.509 Public Key Infras- tructure Certificate and CRL Profile", RFC 2459, January 1999. [20] B. Aboba, G. Zorn, "Criteria for Evaluating Roaming Protocols", RFC 2477, January 1999. [21] M. Beadles, D. Mitton, "Criteria for Evaluating Network Access Server Protocols", draft-ietf-nasreq-criteria-05.txt, IETF work in progress, June 2000. [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] S. Glass, S. Jacobs, C. Perkins, "Mobile IP Authentication, Authorization, and Accounting Requirements". RFC 2977. October Calhoun et al. expires December 2001 [Page 97]
Internet-Draft June 2001 2000. [24] F. Yergeau, "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [25] L. J. Blunk, J. R. Vollbrecht, "PPP Extensible Authentication Protocol (EAP)." RFC 2284, March 1998. [26] R. Stewart et al., "Stream Control Transmission Protocol". RFC 2960. October 2000. [27] Postel, J. "Transmission Control Protocol", RFC 793, January 1981. [28] E. Guttman, C. Perkins, J. Veizades, M. Day. "Service Location Protocol, Version 2", RFC 2165, June 1999. [29] T. Berners-Lee, R. Fielding, U.C. Irvine, L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax". RFC 2396, August 1998. [30] Institute of Electrical and Electronics Engineers, "IEEE Stan- dard for Binary Floating-Point Arithmetic", ANSI/IEEE Standard 754-1985, August 1985. [31] D. Crocker, P. Overell, "Augmented BNF for Syntax Specifica- tions: ABNF", RFC 2234, November 1997. [32] E. Guttman, C. Perkins, J. Kempf, "Service Templates and Ser- vice: Schemes", RFC 2609, June 1999. [33] A. Gulbrandsen, P. Vixie, L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. [34] D. Eastlake, "Domain Name System Security Extensions", RFC 2535, March 1999. [35] D. Eastlake, "DNS Security Operational Considerations", RFC 2541, March 1999. [36] D. Eastlake, "DNS Request and Transaction Signatures ( SIG(0)s )", RFC 2931, September 2000. [37] S. Kent, R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [38] T. Dierks, C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. Calhoun et al. expires December 2001 [Page 98]
Internet-Draft June 2001 [39] "The Communications of the ACM" Vol.33, No.6 (June 1990), pp. 677-680. [40] B. Aboba, J. Arkko, D. Harrington. "Introduction to Accounting Management", RFC 2975, October 2000. [41] A. Shacham, R. Monsour, R. Pereira, M. Thomas, "IP Payload Compression Protocol (IPComp)", RFC 2393, December 1998. [42] W. Simpson, "The Point-to-Point Protocol (PPP)", RFC 1661, STD 51, July 1994. [43] B. Aboba, J. Lu, J. Alsop, J. Ding, W. Wang, "Review of Roaming Implementations", RFC 2194, September 1997. [44] B. Aboba, J. Vollbrecht, "Proxy Chaining and Policy Implementa- tion in Roaming", RFC 2607, June 1999. [45] C. Perkins, Editor. IP Mobility Support. RFC 2002, October 1996. [46] IANA, "RADIUS Types", http://www.isi.edu/in- notes/iana/assignments/radius-types [47] A. Gulbrandsen, P. Vixie, and L. Esibov, "A DNS RR for specify- ing the location of services (DNS SRV)," RFC 2782, February 2000. [48] P. V. Mockapetris, "Domain names - implementation and specifica- tion," RFC 1035, November 1987. 19.0 Acknowledgements The authors would like to thank Nenad Trifunovic, Tony Johansson and Pankaj Patel for their participation in the pre-IETF Document Reading Party. Allison Mankin's, Jonathan Wood and Bernard Aboba's assistance was invaluable in working out transport issues, and similarly with Steven Bellovin's help in the security area. Paul Funk and David Mitton were instrumental in getting the Peer State Machine correct, and our deep thanks go to them for their time. Text in this document was also provided by Paul Funk, Mark Eklund, Mark Jones and Dave Spence. Jacques Caron provided many great com- ments as a result of a throrough review of the spec. The authors would also like to acknowledge the following people for Calhoun et al. expires December 2001 [Page 99]
Internet-Draft June 2001 their contribution in the development of the Diameter protocol: William Bulley, David Frascone, Daniel C. Fox, Lol Grant, Ignacio Goyret, Nancy Greene, Peter Heitman, Fredrik Johansson, Mark Jones, Martin Julien, Paul Krumviede, Fergal Ladley, Ryan Moats, Victor Mus- lin, Kenneth Peirce, Stephen Farrell, Sumit Vakil, John R. Vollbrecht and Jeff Weisberg 20.0 Authors' Addresses Questions about this memo can be directed to: Pat R. Calhoun Network and Security Research Center, Sun Laboratories 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 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 Jari Arkko Oy LM Ericsson Ab 02420 Jorvas Finland Phone: +358 40 5079256 E-Mail: Jari.Arkko@ericsson.com Calhoun et al. expires December 2001 [Page 100]
Internet-Draft June 2001 Erik Guttman Solaris Advanced Development Sun Microsystems, Inc. Eichhoelzelstr. 7 74915 Waibstadt Germany Phone: +49-7263-911-701 E-mail: erik.guttman@germany.sun.com Allan C. Rubens Tut Systems, Inc. 220 E. Huron, Suite 260 Ann Arbor, MI 48104 USA Phone: +1 734-995-1697 E-Mail: arubens@tutsys.com Glen Zorn Cisco Systems, Inc. 500 108th Avenue N.E., Suite 500 Bellevue, WA 98004 USA Phone: +1 425 438 8218 21.0 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 Calhoun et al. expires December 2001 [Page 101]
Internet-Draft June 2001 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. 22.0 Expiration Date This memo is filed as <draft-ietf-aaa-diameter-06.txt> and expires in December 2001. Calhoun et al. expires December 2001 [Page 102]
Internet-Draft June 2001 Appendix A. Diameter Service Template The following service template describes the attributes used by Diam- eter servers to advertise themselves. This simplifies the process of selecting an appropriate server to communicate with. A Diameter client can request specific Diameter servers based on characteristics of the Diameter service desired (for example, an AAA server to use for accounting.) Name of submitter: "Erik Guttman" <Erik.Guttman@sun.com> Language of service template: en Security Considerations: Diameter clients and servers use various cryptographic mechanisms to protect communication integrity, confidentiality as well as perform end-point authentication. It would thus be difficult if not impossible for an attacker to advertise itself using SLPv2 and pose as a legitimate Diameter peer without proper preconfigured secrets or cryptographic keys. Still, as Diameter services are vital for network operation it is important to use SLPv2 authenti- cation to prevent an attacker from modifying or eliminating ser- vice advertisements for legitimate Diameter servers. Template text: -------------------------template begins here----------------------- template-type=service:diameter template-version=0.0 template-description= The Diameter protocol is defined by draft-ietf-aaa-diameter-04.txt template-url-syntax= url-path= ; The diameter URL format is described in section 4.4. ; Example: 'diameter://aaa.example.com:1812;transport=tcp Calhoun et al. expires December 2001 [Page 103]
Internet-Draft June 2001 supported-auth-applications= string L M # This attribute lists the Diameter applications supported by the # AAA implementation. The applicationss currently defined are: # Application Name Defined by # ---------------- ----------------------------------- # NASREQ draft-ietf-aaa-diameter-nasreq-04.txt # MobileIP draft-ietf-aaa-diameter-mobileip-04.txt # CMS Security draft-ietf-aaa-diameter-cms-sec-00.txt # # Notes: # . Diameter implementations support one or more applications. # . Additional applications may be defined in the future. # An updated service template will be created at that time. # NASREQ,MobileIP,CMS Security supported-acct-applications= string L M # This attribute lists the Diameter applications supported by the # AAA implementation. The applicationss currently defined are: # Application Name Defined by # ---------------- ----------------------------------- # NASREQ draft-ietf-aaa-diameter-nasreq-04.txt # MobileIP draft-ietf-aaa-diameter-mobileip-04.txt # CMS Security draft-ietf-aaa-diameter-cms-sec-00.txt # # Notes: # . Diameter implementations support one or more applications. # . Additional applications may be defined in the future. # An updated service template will be created at that time. # NASREQ,MobileIP,CMS Security supported-transports= string L M SCTP # This attribute lists the supported transports that the Diameter # implementation accepts. Note that a compliant Diameter # implementation MUST support SCTP, though it MAY support other # transports, too. SCTP,TCP -------------------------template ends here----------------------- Calhoun et al. expires December 2001 [Page 104]
