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| author | Anders Svensson <[email protected]> | 2013-02-19 15:50:41 +0100 |
|---|---|---|
| committer | Anders Svensson <[email protected]> | 2013-02-22 18:07:48 +0100 |
| commit | acb318e1d702d6ea9ca79257abd09473c091fc9f (patch) | |
| tree | 9cdd672edad12186b273a9a6eadcad388458d906 /lib/diameter/doc/src/diameter_soc_rfc6733.xml | |
| parent | 2a6751d20f02e027e956faac6bf4a5c3cccb60e7 (diff) | |
| download | otp-acb318e1d702d6ea9ca79257abd09473c091fc9f.tar.gz otp-acb318e1d702d6ea9ca79257abd09473c091fc9f.tar.bz2 otp-acb318e1d702d6ea9ca79257abd09473c091fc9f.zip | |
Add RFC 6733 commentary to SoC chapter
The commentary is not yet complete. It currently stops at chapter 4 of
the RFC.
Diffstat (limited to 'lib/diameter/doc/src/diameter_soc_rfc6733.xml')
| -rw-r--r-- | lib/diameter/doc/src/diameter_soc_rfc6733.xml | 8692 |
1 files changed, 8692 insertions, 0 deletions
diff --git a/lib/diameter/doc/src/diameter_soc_rfc6733.xml b/lib/diameter/doc/src/diameter_soc_rfc6733.xml new file mode 100644 index 0000000000..8d85569650 --- /dev/null +++ b/lib/diameter/doc/src/diameter_soc_rfc6733.xml @@ -0,0 +1,8692 @@ +<?xml version="1.0" encoding="latin1" ?> + +<!-- + +<copyright> +<year>2013</year> +<holder>Ericsson AB. All Rights Reserved.</holder> +</copyright> + +<legalnotice> +The contents of this file are subject to the Erlang Public License, +Version 1.1, (the "License"); you may not use this file except in +compliance with the License. You should have received a copy of the +Erlang Public License along with this software. If not, it can be +retrieved online at http://www.erlang.org/. + +Software distributed under the License is distributed on an "AS IS" +basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See +the License for the specific language governing rights and limitations +under the License. + +</legalnotice> + +--> + +<!DOCTYPE section SYSTEM "chapter.dtd" [ + <!ENTITY gen_sctp '<seealso marker="kernel:gen_sctp">gen_sctp(3)</seealso>'> + <!ENTITY gen_tcp '<seealso marker="kernel:gen_tcp">gen_tcp(3)</seealso>'> + <!ENTITY service '<seealso marker="diameter#start_service-2">service</seealso>'> + <!ENTITY capabilities '<seealso marker="diameter#capability">capabilities</seealso>'> + <!ENTITY events '<seealso marker="diameter#service_event">events</seealso>'> + <!ENTITY nada '<p>No comment.</p>'> + <!ENTITY % also SYSTEM "seealso.ent" > + %also; +]> + +<section> +<title>Commentary</title> + +<p> +A more detailed commentary on &the_rfc; follows. +Its purpose is to (hopefully) clarify not only what is supported but +how, given that semantics and features discussed in the RFC are not +solely the responsibility of the diameter application: +in many cases much depends on the configuration a user passes to +diameter, the implementation of &man_app; callback modules in +particular.</p> + +<p> +Comments apply to all text following the preceding comment. +Be sure to distinguish between capitalized <em>Diameter</em>, the +protocol defined by the RFC, and lowercase <em>diameter</em>, the +Erlang application to which the commentary applies.</p> + +<warning> +<p> +The commentary is not yet complete. +Comments currently stop at chapter 4.</p> +</warning> + +<pre> +Fajardo, et al. Standards Track [Page 6] + +RFC 6733 Diameter Base Protocol October 2012 + + +1. Introduction + + Authentication, Authorization, and Accounting (AAA) protocols such as + TACACS [RFC1492] and RADIUS [RFC2865] were initially deployed to + provide dial-up PPP [RFC1661] and terminal server access. Over time, + AAA support was needed on many new access technologies, the scale and + complexity of AAA networks grew, and AAA was also used on new + applications (such as voice over IP). This led to new demands on AAA + protocols. +</pre> + +<p> +Note that diameter implements the Diameter protocol as defined in +&the_rfc;. +It also supported the previous version of the protocol, as defined in +RFC 3588, when there are differences. +(Which will be noted below.) +It does not support RADIUS.</p> + +<pre> + + Network access requirements for AAA protocols are summarized in + Aboba, et al. [RFC2989]. These include: + + Failover + + [RFC2865] does not define failover mechanisms and, as a result, + failover behavior differs between implementations. In order to + provide well-defined failover behavior, Diameter supports + application-layer acknowledgements and defines failover algorithms + and the associated state machine. +</pre> + +&nada; + +<pre> + + Transmission-level security + + RADIUS [RFC2865] defines an application-layer authentication and + integrity scheme that is required only for use with response + packets. While [RFC2869] defines an additional authentication and + integrity mechanism, use is only required during Extensible + Authentication Protocol (EAP) [RFC3748] sessions. While attribute + hiding is supported, [RFC2865] does not provide support for per- + packet confidentiality. In accounting, [RFC2866] assumes that + replay protection is provided by the backend billing server rather + than within the protocol itself. + + While [RFC3162] defines the use of IPsec with RADIUS, support for + IPsec is not required. In order to provide universal support for + transmission-level security, and enable both intra- and inter- + domain AAA deployments, Diameter provides support for TLS/TCP and + DTLS/SCTP. Security is discussed in Section 13. +</pre> + +<p> +Whether or not IPsec is used is transparent to diameter.</p> + +<p> +The transport protocol used on a given peer connection is also +transparent to diameter in that transport to diameter is simply a +module that implements the transport protocol documented in +&man_transport;. +A diameter user configures this module as the &mod_transport_opt; +<c>transport_module</c>.</p> + +<p> +While a user can implement their own transport modules, diameter +includes implementations for TCP and SCTP: +&man_tcp; based on &gen_tcp; and &man_sctp; based on &gen_sctp;. +The former supports TLS but the latter does not currently support +DTLS.</p> + +<pre> + + Reliable transport + + RADIUS runs over UDP, and does not define retransmission behavior; + as a result, reliability varies between implementations. As + described in [RFC2975], this is a major issue in accounting, where + packet loss may translate directly into revenue loss. In order to + + + + + + +Fajardo, et al. Standards Track [Page 7] + +RFC 6733 Diameter Base Protocol October 2012 + + + provide well-defined transport behavior, Diameter runs over + reliable transport mechanisms (TCP, Stream Control Transmission + Protocol (SCTP)) as defined in [RFC3539]. + + Agent support + + RADIUS does not provide for explicit support for agents, including + proxies, redirects, and relays. Since the expected behavior is + not defined, it varies between implementations. Diameter defines + agent behavior explicitly; this is described in Section 2.8. +</pre> + +&nada; + +<pre> + + Server-initiated messages + + While server-initiated messages are defined in RADIUS [RFC5176], + support is optional. This makes it difficult to implement + features such as unsolicited disconnect or re-authentication/ + re-authorization on demand across a heterogeneous deployment. To + address this issue, support for server-initiated messages is + mandatory in Diameter. +</pre> + +<p> +A diameter user can both send and receive messages.</p> + +<pre> + + Transition support + + While Diameter does not share a common protocol data unit (PDU) + with RADIUS, considerable effort has been expended in enabling + backward compatibility with RADIUS so that the two protocols may + be deployed in the same network. Initially, it is expected that + Diameter will be deployed within new network devices, as well as + within gateways enabling communication between legacy RADIUS + devices and Diameter agents. This capability enables Diameter + support to be added to legacy networks, by addition of a gateway + or server speaking both RADIUS and Diameter. +</pre> + +<p> +RADIUS Attributes can be redefined as Diameter AVP's using diameter's +&man_dict; interface but diameter provides no such definitions.</p> + +<pre> + + In addition to addressing the above requirements, Diameter also + provides support for the following: + + Capability negotiation + + RADIUS does not support error messages, capability negotiation, or + a mandatory/non-mandatory flag for attributes. Since RADIUS + clients and servers are not aware of each other's capabilities, + they may not be able to successfully negotiate a mutually + acceptable service or, in some cases, even be aware of what + service has been implemented. Diameter includes support for error + handling (Section 7), capability negotiation (Section 5.3), and + mandatory/non-mandatory Attribute-Value Pairs (AVPs) + (Section 4.1). + + + + + +Fajardo, et al. Standards Track [Page 8] + +RFC 6733 Diameter Base Protocol October 2012 + + + Peer discovery and configuration + + RADIUS implementations typically require that the name or address + of servers or clients be manually configured, along with the + corresponding shared secrets. This results in a large + administrative burden and creates the temptation to reuse the + RADIUS shared secret, which can result in major security + vulnerabilities if the Request Authenticator is not globally and + temporally unique as required in [RFC2865]. Through DNS, Diameter + enables dynamic discovery of peers (see Section 5.2). Derivation + of dynamic session keys is enabled via transmission-level + security. + + Over time, the capabilities of Network Access Server (NAS) devices + have increased substantially. As a result, while Diameter is a + considerably more sophisticated protocol than RADIUS, it remains + feasible to implement it within embedded devices. +</pre> + +&nada; + +<pre> + +1.1. Diameter Protocol + + The Diameter base protocol provides the following facilities: + + o Ability to exchange messages and deliver AVPs +</pre> + +<p> +There are two interfaces directly involved in message exchange when +using diameter: the function &mod_call; for sending outgoing requests, +and the application callback interface, documented in &man_app; for +receiving incoming request and answers.</p> + +<pre> + + o Capabilities negotiation +</pre> + +<p> +Capabilities negotiation is the responsibility of diameter: +a user configures a diameter service and/or transport with +&capabilities; to provide AVP values for CER and CEA messages but it +is diameter itself that sends these messages. +A user receives notification of a successful capabilities exchange by +way of &app_peer_up; callbacks.</p> + +<pre> + + o Error notification +</pre> + +<p> +A user can subscribe to &events;, using &mod_subscribe;, in order to +receive notification of various failures. +Errors in Diameter messaging are communicated via the application +callbacks &app_handle_request;, &app_handle_answer; and +&app_handle_error;.</p> + + +<pre> + + o Extensibility, required in [RFC2989], through addition of new + applications, commands, and AVPs +</pre> + +<p> +Support for applications, commands and AVP's is extensible using +diameter's dictionary interface, as documented in &man_dict;. +Dictionaries are compiled to Erlang encode/decode modules using +&man_compile; or &man_make;.</p> + +<pre> + + o Basic services necessary for applications, such as the handling of + user sessions or accounting +</pre> + +<p> +Compiled dictionaries are provided for the RFC 3588 and RFC 6733 +Diameter applications: common, base accounting and relay. +Dictionaries for a number of standardized +applications are provided in uncompiled form below the <c>examples</c> +subdirectory of the diameter application directory.</p> + +<pre> + + All data delivered by the protocol is in the form of AVPs. Some of + these AVP values are used by the Diameter protocol itself, while + others deliver data associated with particular applications that + employ Diameter. AVPs may be arbitrarily added to Diameter messages, + the only restriction being that the Command Code Format (CCF) + specification (Section 3.2) be satisfied. AVPs are used by the base + Diameter protocol to support the following required features: + + o Transporting of user authentication information, for the purposes + of enabling the Diameter server to authenticate the user + + o Transporting of service-specific authorization information, + between client and servers, allowing the peers to decide whether a + user's access request should be granted + + + +Fajardo, et al. Standards Track [Page 9] + +RFC 6733 Diameter Base Protocol October 2012 + + + o Exchanging resource usage information, which may be used for + accounting purposes, capacity planning, etc. + + o Routing, relaying, proxying, and redirecting of Diameter messages + through a server hierarchy + + The Diameter base protocol satisfies the minimum requirements for a + AAA protocol, as specified by [RFC2989]. The base protocol may be + used by itself for accounting purposes only, or it may be used with a + Diameter application, such as Mobile IPv4 [RFC4004], or network + access [RFC4005]. It is also possible for the base protocol to be + extended for use in new applications, via the addition of new + commands or AVPs. The initial focus of Diameter was network access + and accounting applications. 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. + See Section 1.3.4 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 a device at + the edge of the network that performs access control, such as a + Network Access Server (NAS) or a Foreign Agent (FA). A Diameter + client generates Diameter messages to request authentication, + authorization, and accounting services for the user. A Diameter + agent is a node that does not provide local user authentication or + authorization services; agents include proxies, redirects, and relay + agents. A Diameter server performs authentication and/or + authorization of the user. A Diameter node may act as an agent for + certain requests while acting as a server for others. + + The Diameter protocol also supports server-initiated messages, such + as a request to abort service to a particular user. +</pre> + +&nada; + +<pre> + +1.1.1. Description of the Document Set + + The Diameter specification consists of an updated version of the base + protocol specification (this document) and the Transport Profile + [RFC3539]. This document obsoletes both RFC 3588 and RFC 5719. A + summary of the base protocol updates included in this document can be + found in Section 1.1.3. + + This document defines the base protocol specification for AAA, which + includes support for accounting. There are also a myriad of + applications documents describing applications that use this base + specification for Authentication, Authorization, and Accounting. + These application documents specify how to use the Diameter protocol + within the context of their application. + + + +Fajardo, et al. Standards Track [Page 10] + +RFC 6733 Diameter Base Protocol October 2012 + + + The Transport Profile document [RFC3539] discusses transport layer + issues that arise with AAA protocols and recommendations on how to + overcome these issues. This document also defines the Diameter + failover algorithm and state machine. + + "Clarifications on the Routing of Diameter Request Based on the + Username and the Realm" [RFC5729] defines specific behavior on how to + route requests based on the content of the User-Name AVP (Attribute + Value Pair). + +1.1.2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [RFC2119]. +</pre> + +&nada; + +<pre> + +1.1.3. Changes from RFC 3588 + + This document obsoletes RFC 3588 but is fully backward compatible + with that document. The changes introduced in this document focus on + fixing issues that have surfaced during the implementation of + Diameter (RFC 3588). An overview of some the major changes are given + below. +</pre> + +<p> +RFC 6733 is not fully backwards compatible with RFC 3588. +(For example, in what values of Result-Code values are permissible with +the E-bit.) +The implications of incompatibilities for diameter are noted where +appropriate.</p> + +<pre> + + o Deprecated the use of the Inband-Security AVP for negotiating + Transport Layer Security (TLS) [RFC5246]. It has been generally + considered that bootstrapping of TLS via Inband-Security AVP + creates certain security risks because it does not completely + protect the information carried in the CER/CEA (Capabilities- + Exchange-Request/Capabilities-Exchange-Answer). This version of + Diameter adopts the common approach of defining a well-known + secured port that peers should use when communicating via TLS/TCP + and DTLS/SCTP. This new approach augments the existing in-band + security negotiation, but it does not completely replace it. The + old method is kept for backward compatibility reasons. +</pre> + +<p> +&man_tcp; supports both methods of negotiating TLS: +bootstrapping via Inband-Security and directly following connection +establishment.</p> + +<pre> + + o Deprecated the exchange of CER/CEA messages in the open state. + This feature was implied in the peer state machine table of RFC + 3588, but it was not clearly defined anywhere else in that + document. As work on this document progressed, it became clear + that the multiplicity of meaning and use of Application-Id AVPs in + the CER/CEA messages (and the messages themselves) is seen as an + abuse of the Diameter extensibility rules and thus required + simplification. Capabilities exchange in the open state has been + re-introduced in a separate specification [RFC6737], which clearly + defines new commands for this feature. +</pre> + +<p> +Capabilities exchange in the open state is not supported: an incoming +CER in the open state will cause diameter to ask the relevant +transport process to terminate, which implies the loss of the peer +connection in the case of &man_tcp; and &man_sctp;.</p> + +<p> +Capabilities update, as defined by RFC 6737, is not yet supported. +Support will require diameter to handle CUR/CUA in the same way that +it handles CER/CEA.</p> + +<pre> + + + + + +Fajardo, et al. Standards Track [Page 11] + +RFC 6733 Diameter Base Protocol October 2012 + + + o Simplified security requirements. The use of a secured transport + for exchanging Diameter messages remains mandatory. However, TLS/ + TCP and DTLS/SCTP have become the primary methods of securing + Diameter with IPsec as a secondary alternative. See Section 13 + for details. The support for the End-to-End security framework + (E2E-Sequence AVP and 'P'-bit in the AVP header) has also been + deprecated. +</pre> + +<p> +The End-to-End security framework is not supported since it's use is +largely unspecified: diameter will set the P-bit in outgoing AVP's as +directed by the relevant dictionary and/or &app_prepare_request; or +&app_handle_request; callbacks, but whether or not the P-bit is set on +incoming AVP's has no consequence.</p> + +<p> +As noted above, DTLS is not currently supported and whether or not +IPsec is used is transparent to diameter.</p> + +<pre> + + o Changed Diameter extensibility. This includes fixes to the + Diameter extensibility description (Section 1.3 and others) to + better aid Diameter application designers; in addition, the new + specification relaxes the policy with respect to the allocation of + Command Codes for vendor-specific uses. + + o Clarified Application Id usage. Clarify the proper use of + Application Id information, which can be found in multiple places + within a Diameter message. This includes correlating Application + Ids found in the message headers and AVPs. These changes also + clearly specify the proper Application Id value to use for + specific base protocol messages (ASR/ASA, STR/STA) as well as + clarify the content and use of Vendor-Specific-Application-Id. + + o Clarified routing fixes. This document more clearly specifies + what information (AVPs and Application Ids) can be used for making + general routing decisions. A rule for the prioritization of + redirect routing criteria when multiple route entries are found + via redirects has also been added (see Section 6.13). + + o Simplified Diameter peer discovery. The Diameter discovery + process now supports only widely used discovery schemes; the rest + have been deprecated (see Section 5.2 for details). +</pre> + +<p> +Peer discover is not currently supported: peers to which a node should +connect must be configured. +Connection requests are accepted from arbitrary peers but a +&mod_transport_opt; <c>capabilities_cb</c> can be used to reject a +peer based on an incoming CER or CEA.</p> + +<pre> + + There are many other miscellaneous fixes that have been introduced in + this document that may not be considered significant, but they have + value nonetheless. Examples are removal of obsolete types, fixes to + the state machine, clarification of the election process, message + validation, fixes to Failed-AVP and Result-Code AVP values, etc. All + of the errata filed against RFC 3588 prior to the publication of this + document have been addressed. A comprehensive list of changes is not + shown here for practical reasons. + +1.2. Terminology + + AAA + + Authentication, Authorization, and Accounting. + + + + + +Fajardo, et al. Standards Track [Page 12] + +RFC 6733 Diameter Base Protocol October 2012 + + + ABNF + + Augmented Backus-Naur Form [RFC5234]. A metalanguage with its own + formal syntax and rules. It is based on the Backus-Naur Form and + is used to define message exchanges in a bi-directional + communications protocol. + + Accounting + + The act of collecting information on resource usage for the + purpose of capacity planning, auditing, billing, or cost + allocation. + + Accounting Record + + An accounting record represents a summary of the resource + consumption of a user over the entire session. Accounting servers + creating the accounting record may do so by processing interim + accounting events or accounting events from several devices + serving the same user. + + 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). + + Attribute-Value Pair (AVP) + + The Diameter protocol consists of a header followed by one or more + Attribute-Value-Pairs (AVPs). An AVP includes a header and is + used to encapsulate protocol-specific data (e.g., routing + information) as well as authentication, authorization, or + accounting information. +</pre> + +&nada; + +<pre> + + Command Code Format (CCF) + + A modified form of ABNF used to define Diameter commands (see + Section 3.2). +</pre> + +<p> +The <c>@messages</c> section of the &man_dict; format has the CCF as +content.</p> + +<pre> + + Diameter Agent + + A Diameter Agent is a Diameter node that provides relay, proxy, + redirect, or translation services. + + + + +Fajardo, et al. Standards Track [Page 13] + +RFC 6733 Diameter Base Protocol October 2012 + + + Diameter Client + + A Diameter client is a Diameter node that supports Diameter client + applications as well as the base protocol. Diameter clients are + often implemented in devices situated at the edge of a network and + provide access control services for that network. Typical + examples of Diameter clients include the Network Access Server + (NAS) and the Mobile IP Foreign Agent (FA). + + Diameter Node + + A Diameter node is a host process that implements the Diameter + protocol and acts as either a client, an agent, or a server. + + Diameter Peer + + Two Diameter nodes sharing a direct TCP or SCTP transport + connection are called Diameter peers. + + Diameter Server + + A Diameter server is a Diameter node that handles authentication, + authorization, and accounting requests for a particular realm. By + its very nature, a Diameter server must support Diameter server + applications in addition to the base protocol. +</pre> + +<p> +A Diameter Node is implemented by configuring a service +using &mod_start_service; and one or more transports using +&mod_add_transport;. +The service typically represents a Diameter Node but since +capabilities can be configured on individual transports it's more +accurate to say that the node is a collection of transports +advertising the same Origin-Host.</p> + +<p> +The role of a node (agent, client or server) is not something that's +configured explicitly. +Transports are either connecting or listening, depending on whether +diameter should establish a peer connection and send CER or accept +connections and receive CER, but the role a node implements depends +largely on dictionary configuration and &man_app; callback +implementation.</p> + +<pre> + + Downstream + + Downstream is used to identify the direction of a particular + Diameter message from the home server towards the Diameter client. + + Home Realm + + A Home Realm is the administrative domain with which the user + maintains an account relationship. + + Home Server + + A Diameter server that serves the Home Realm. + + Interim Accounting + + An interim accounting message provides a snapshot of usage during + a user's session. Typically, it is implemented in order to + provide for partial accounting of a user's session in case a + device reboot or other network problem prevents the delivery of a + session summary message or session record. + + + + +Fajardo, et al. Standards Track [Page 14] + +RFC 6733 Diameter Base Protocol October 2012 + + + Local Realm + + A local realm is the administrative domain providing services to a + user. An administrative domain may act as a local realm for + certain users while being a home realm for others. + + Multi-session + + A multi-session represents a logical linking of several sessions. + Multi-sessions are tracked by using the Acct-Multi-Session-Id. An + example of a multi-session would be a Multi-link PPP bundle. Each + leg of the bundle would be a session while the entire bundle would + be a multi-session. + + Network Access Identifier + + The Network Access Identifier, or NAI [RFC4282], is used in the + Diameter protocol to extract a user's identity and realm. The + identity is used to identify the user during authentication and/or + authorization while the realm is used for message routing + purposes. + + Proxy Agent or Proxy + + In addition to forwarding requests and responses, proxies make + policy decisions relating to resource usage and provisioning. + Typically, this is accomplished by tracking the state of NAS + devices. While proxies usually 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 they 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 + routed or redirected. In RADIUS, realm names are not necessarily + piggybacked on the DNS namespace but may be independent of it. + + + + + + + + +Fajardo, et al. Standards Track [Page 15] + +RFC 6733 Diameter Base Protocol October 2012 + + + Real-Time Accounting + + Real-time accounting involves the processing of information on + resource usage within a defined time window. Typically, time + constraints are imposed in order to limit financial risk. The + Diameter Credit-Control Application [RFC4006] is an example of an + application that defines real-time accounting functionality. + + Relay Agent or Relay + + Relays forward requests and responses based on routing-related + AVPs and routing table entries. Since relays do not make policy + decisions, 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 application or message type. Since relays + make decisions based on information in routing AVPs and realm + forwarding tables, they do not keep state on NAS resource usage or + sessions in progress. + + Redirect Agent + + Rather than forwarding requests and responses between clients and + servers, redirect agents refer clients to servers and allow them + to communicate directly. Since redirect agents do not sit in the + forwarding path, they do not alter any AVPs transiting between + client and server. Redirect agents do not originate messages and + are capable of handling any message type, although they may be + configured only to redirect messages of certain types, while + acting as relay or proxy agents for other types. As with relay + agents, redirect agents do not keep state with respect to sessions + or NAS resources. +</pre> + +&nada; + +<pre> + + Session + + A session is a related progression of events devoted to a + particular activity. Diameter application documents provide + guidelines as to when a session begins and ends. All Diameter + packets with the same Session-Id are considered to be part of the + same session. +</pre> + +<p> +Sessions are not something that diameter is aware of. +The function &mod_session_id; can be used to construct appropriate +values for Session-Id AVP's but logic connecting events in the same +session is the responsibility of the diameter user.</p> + +<pre> + + Stateful Agent + + 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 + until expiration. + + + +Fajardo, et al. Standards Track [Page 16] + +RFC 6733 Diameter Base Protocol October 2012 + + + Sub-session + + A sub-session represents a distinct service (e.g., QoS or data + characteristics) provided to a given session. These services may + happen concurrently (e.g., simultaneous voice and data transfer + during the same session) or serially. These changes in sessions + are tracked with the Accounting-Sub-Session-Id. + + Transaction State + + The Diameter protocol requires that agents maintain transaction + state, which is used for failover purposes. Transaction state + implies that upon forwarding a request, the Hop-by-Hop Identifier + is saved; the field is replaced with a locally unique identifier, + which is 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. + + Translation Agent + + A translation agent (TLA in Figure 4) is a stateful Diameter node + that performs protocol translation between Diameter and another + AAA protocol, such as RADIUS. + + Upstream + + Upstream is used to identify the direction of a particular + Diameter message from the Diameter client towards the home server. + + User + + The entity or device requesting or using some resource, in support + of which a Diameter client has generated a request. +</pre> + +&nada; + +<pre> + +1.3. Approach to Extensibility + + The Diameter protocol is designed to be extensible, using several + mechanisms, including: + + o Defining new AVP values + + o Creating new AVPs + + o Creating new commands + + o Creating new applications + + + + +Fajardo, et al. Standards Track [Page 17] + +RFC 6733 Diameter Base Protocol October 2012 + + + From the point of view of extensibility, Diameter authentication, + authorization, and accounting applications are treated in the same + way. +</pre> + +<p> +Extensibility in diameter is by way of the dictionary interface +documented in &man_dict;: a diameter user creates applications, +commands and AVP's by implementing a new dictionary, +compiling the dictionary to a codec module using &man_compile; or +&man_make;, and configuring the resulting dictionary module on a +service. +The dictionary modules provided with diameter are all implemented in +this manner.</p> + +<pre> + Note: Protocol designers should try to reuse existing functionality, + namely AVP values, AVPs, commands, and Diameter applications. Reuse + simplifies standardization and implementation. To avoid potential + interoperability issues, it is important to ensure that the semantics + of the reused features are well understood. Given that Diameter can + also carry RADIUS attributes as Diameter AVPs, such reuse + considerations also apply to existing RADIUS attributes that may be + useful in a Diameter application. +</pre> + +<p> +Reuse in dictionary files is achieved by way of the <c>@inherits</c> +section. +AVP's are inherited, commands are not.</p> + +<pre> + +1.3.1. Defining New AVP Values + + In order to allocate a new AVP value for AVPs defined in the Diameter + base protocol, the IETF needs to approve a new RFC that describes the + AVP value. IANA considerations for these AVP values are discussed in + Section 11.3. + + The allocation of AVP values for other AVPs is guided by the IANA + considerations of the document that defines those AVPs. Typically, + allocation of new values for an AVP defined in an RFC would require + IETF Review [RFC5226], whereas values for vendor-specific AVPs can be + allocated by the vendor. + +1.3.2. Creating New AVPs + + A new AVP being defined MUST use one of the data types listed in + Sections 4.2 or 4.3. If an appropriate derived data type is already + defined, it SHOULD be used instead of a base data type to encourage + reusability and good design practice. + + In the event that a logical grouping of AVPs is necessary, and + multiple "groups" are possible in a given command, it is recommended + that a Grouped AVP be used (see Section 4.4). + + The creation of new AVPs can happen in various ways. The recommended + approach is to define a new general-purpose AVP in a Standards Track + RFC approved by the IETF. However, as described in Section 11.1.1, + there are other mechanisms. +</pre> + +<p> +Creating new AVP's is an issue for the dictionary designer, not +diameter.</p> + +<pre> + +1.3.3. Creating New Commands + + A new Command Code MUST be allocated when required AVPs (those + indicated as {AVP} in the CCF definition) are added to, deleted from, + or redefined in (for example, by changing a required AVP into an + optional one) an existing command. + + + +Fajardo, et al. Standards Track [Page 18] + +RFC 6733 Diameter Base Protocol October 2012 + + + Furthermore, if the transport characteristics of a command are + changed (for example, with respect to the number of round trips + required), a new Command Code MUST be registered. + + A change to the CCF of a command, such as described above, MUST + result in the definition of a new Command Code. This subsequently + leads to the need to define a new Diameter application for any + application that will use that new command. + + The IANA considerations for Command Codes are discussed in + Section 3.1. +</pre> + +<p> +Creating new commands is an issue for the dictionary designer, not +diameter.</p> + +<pre> + +1.3.4. Creating New Diameter Applications + + Every Diameter application specification MUST have an IANA-assigned + Application Id (see Section 2.4). The managed Application ID space + is flat, and there is no relationship between different Diameter + applications with respect to their Application Ids. As such, there + is no versioning support provided by these Application Ids + themselves; every Diameter application is a standalone application. + If the application has a relationship with other Diameter + applications, such a relationship is not known to Diameter. +</pre> + +<p> +Creating new applications is an issue for the dictionary designer, +not diameter.</p> + +<p> +An application's Application Id is specified in the <c>@id</c> section +of a dictionary file.</p> + +<pre> + + Before describing the rules for creating new Diameter applications, + it is important to discuss the semantics of the AVP occurrences as + stated in the CCF and the M-bit flag (Section 4.1) for an AVP. There + is no relationship imposed between the two; they are set + independently. + + o The CCF indicates what AVPs are placed into a Diameter command by + the sender of that command. Often, since there are multiple modes + of protocol interactions, many of the AVPs are indicated as + optional. + + o The M-bit allows the sender to indicate to the receiver whether or + not understanding the semantics of an AVP and its content is + mandatory. If the M-bit is set by the sender and the receiver + does not understand the AVP or the values carried within that AVP, + then a failure is generated (see Section 7). +</pre> + +<p> +The M-bit is set on outgoing AVP's as directed by the relevant +dictionary. +For incoming AVP's, an M-bit set on an AVP that isn't +explicitly included in the definition of the command in question is +interpreted as a 5001 error, DIAMETER_AVP_UNSUPPORTED, the +consequences of which depend on the value of the &mod_application_opt; +<c>answer_errors</c> or <c>request_errors</c>.</p> + +<pre> + + It is the decision of the protocol designer when to develop a new + Diameter application rather than extending Diameter in other ways. + However, a new Diameter application MUST be created when one or more + of the following criteria are met: + + + + + + + +Fajardo, et al. Standards Track [Page 19] + +RFC 6733 Diameter Base Protocol October 2012 + + + M-bit Setting + + An AVP with the M-bit in the MUST column of the AVP flag table is + added to an existing Command/Application. An AVP with the M-bit + in the MAY column of the AVP flag table is added to an existing + Command/Application. + + Note: The M-bit setting for a given AVP is relevant to an + Application and each command within that application that includes + the AVP. That is, if an AVP appears in two commands for + application Foo and the M-bit settings are different in each + command, then there should be two AVP flag tables describing when + to set the M-bit. + + Commands + + A new command is used within the existing application because + either an additional command is added, an existing command has + been modified so that a new Command Code had to be registered, or + a command has been deleted. + + AVP Flag bits + + If an existing application changes the meaning/semantics of its + AVP Flags or adds new flag bits, then a new Diameter application + MUST be created. + + If the CCF definition of a command allows it, an implementation may + add arbitrary optional AVPs with the M-bit cleared (including vendor- + specific AVPs) to that command without needing to define a new + application. Please refer to Section 11.1.1 for details. +</pre> + +&nada; + +<pre> + +2. Protocol Overview + + The base Diameter protocol concerns itself with establishing + connections to peers, capabilities negotiation, how messages are sent + and routed through peers, and how the connections are eventually torn + down. The base protocol also defines certain rules that apply to all + message exchanges between Diameter nodes. + + 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 AVP. The Session-Id is then used in all + subsequent messages to identify the user's session (see Section 8 for + + + +Fajardo, et al. Standards Track [Page 20] + +RFC 6733 Diameter Base Protocol October 2012 + + + more information). The communicating party may accept the request or + reject it by returning an answer message with the Result-Code AVP set + to indicate that 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. +</pre> + +<p> +Like Session-Id, session state is maintained by the diameter user: +diameter has no session state of its own and does not interpret +STR/STA in any way.</p> + +<pre> + + The base Diameter protocol may be used by itself for accounting + applications. For authentication and authorization, it is always + extended for a particular application. + + Diameter clients MUST support the base protocol, which includes + accounting. In addition, they MUST fully support each Diameter + application that is needed to implement the client's service, e.g., + Network Access Server Requirements (NASREQ) [RFC2881] and/or Mobile + IPv4. A Diameter client MUST be referred to as "Diameter X Client" + where X is the application that 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 that is needed to implement the intended service, e.g., + NASREQ and/or Mobile IPv4. A Diameter server MUST be referred to as + "Diameter X Server" where X is the application that it supports, and + not a "Diameter Server". + + Diameter relays and redirect agents are transparent to the Diameter + applications, but they MUST support the Diameter base protocol, which + includes accounting, and all Diameter applications. + + Diameter proxies MUST support the base protocol, which includes + accounting. In addition, they MUST fully support each Diameter + application that is needed to implement proxied services, e.g., + NASREQ and/or Mobile IPv4. A Diameter proxy MUST be referred to as + "Diameter X Proxy" where X is the application which it supports, and + not a "Diameter Proxy". + +</pre> + +&nada; + +<pre> + + + + + + + + + +Fajardo, et al. Standards Track [Page 21] + +RFC 6733 Diameter Base Protocol October 2012 + + +2.1. Transport + + The Diameter Transport profile is defined in [RFC3539]. + + The base Diameter protocol is run on port 3868 for both TCP [RFC0793] + and SCTP [RFC4960]. For TLS [RFC5246] and Datagram Transport Layer + Security (DTLS) [RFC6347], a Diameter node that initiates a + connection prior to any message exchanges MUST run on port 5658. It + is assumed that TLS is run on top of TCP when it is used, and DTLS is + run on top of SCTP when it is used. +</pre> + +<p> +Which port a transport connects to or listens on is a matter of +configuration. +Both &man_tcp; and &man_sctp; will default to 3868 if no other value +is specified.</p> + +<pre> + + If the Diameter peer does not support receiving TLS/TCP and DTLS/SCTP + connections on port 5658 (i.e., the peer complies only with RFC + 3588), then the initiator MAY revert to using TCP or SCTP on port + 3868. Note that this scheme is kept only for the purpose of backward + compatibility and that there are inherent security vulnerabilities + when the initial CER/CEA messages are sent unprotected (see + Section 5.6). + + Diameter clients MUST support either TCP or SCTP; agents and servers + SHOULD support both. + + A Diameter node MAY initiate connections from a source port other + than the one that it declares it accepts incoming connections on, and + it MUST always be prepared to receive connections on port 3868 for + TCP or SCTP and port 5658 for TLS/TCP and DTLS/SCTP connections. + When DNS-based peer discovery (Section 5.2) is used, the port numbers + received from SRV records take precedence over the default ports + (3868 and 5658). + + A given Diameter instance of the peer state machine MUST NOT use more + than one transport connection to communicate with a given peer, + unless multiple instances exist on the peer, in which, case a + separate connection per process is allowed. +</pre> + +<p> +The &mod_service_opt; <c>restrict_connection</c> controls to what +extent a diameter service allows multiple connections to the same +peer. +(As identified by the value of Origin-Host received from it +during capabilities exchange.)</p> + +<pre> + + When no transport connection exists with a peer, an attempt to + connect SHOULD be made periodically. This behavior is handled via + the Tc timer (see Section 12 for details), whose recommended value is + 30 seconds. There are certain exceptions to this rule, such as when + a peer has terminated the transport connection stating that it does + not wish to communicate. + +</pre> + +<p> +The frequency of reconnection attempts is configured with the +&mod_transport_opt; <c>reconnect_timer</c> and +<c>watchdog_timer</c>.</p> + +<pre> + + When connecting to a peer and either zero or more transports are + specified, TLS SHOULD be tried first, followed by DTLS, then by TCP, + and finally by SCTP. See Section 5.2 for more information on peer + discovery. +</pre> + +<p> +The order in which different transports are attempted depends on the +order of &mod_transport_opt; <c>transport_module</c> and +<c>transport_config</c> tuples in transport configuration.</p> + +<pre> + + + +Fajardo, et al. Standards Track [Page 22] + +RFC 6733 Diameter Base Protocol October 2012 + + + Diameter implementations SHOULD be able to interpret ICMP protocol + port unreachable messages as explicit indications that the server is + not reachable, subject to security policy on trusting such messages. + Further guidance regarding the treatment of ICMP errors can be found + in [RFC5927] and [RFC5461]. Diameter implementations SHOULD also be + able to interpret a reset from the transport and timed-out connection + attempts. If Diameter receives data from the lower layer that cannot + be parsed or identified as a Diameter error made by the peer, the + stream is compromised and cannot be recovered. The transport + connection MUST be closed using a RESET call (send a TCP RST bit) or + an SCTP ABORT message (graceful closure is compromised). +</pre> + +<p> +ICMP messages and other transport-level errors aren't directly +visible to diameter but transport implementations like &man_tcp; and +&man_sctp; propagate these as terminating transport processes.</p> + +<pre> + +2.1.1. SCTP Guidelines + + Diameter messages SHOULD be mapped into SCTP streams in a way that + avoids head-of-the-line (HOL) blocking. Among different ways of + performing the mapping that fulfill this requirement it is + RECOMMENDED that a Diameter node send every Diameter message (request + or response) over stream zero with the unordered flag set. However, + Diameter nodes MAY select and implement other design alternatives for + avoiding HOL blocking such as using multiple streams with the + unordered flag cleared (as originally instructed in RFC 3588). On + the receiving side, a Diameter entity MUST be ready to receive + Diameter messages over any stream, and it is free to return responses + over a different stream. This way, both sides manage the available + streams in the sending direction, independently of the streams chosen + by the other side to send a particular Diameter message. These + messages can be out-of-order and belong to different Diameter + sessions. +</pre> + +<p> +&man_sctp; allows the sender to specify a stream number explicitly. +The stream on which an incoming message is received it passed to +&app_handle_request; and &app_handle_answer; callbacks as +<c>transport_data</c> in a <c>#diameter_packet{}</c>.</p> + +<p> +Ordered or unordered delivery can be configured per transport.</p> + +<pre> + + Out-of-order delivery has special concerns during a connection + establishment and termination. When a connection is established, the + responder side sends a CEA message and moves to R-Open state as + specified in Section 5.6. If an application message is sent shortly + after the CEA and delivered out-of-order, the initiator side, still + in Wait-I-CEA state, will discard the application message and close + the connection. In order to avoid this race condition, the receiver + side SHOULD NOT use out-of-order delivery methods until the first + message has been received from the initiator, proving that it has + moved to I-Open state. To trigger such a message, the receiver side + could send a DWR immediately after sending a CEA. Upon reception of + the corresponding DWA, the receiver side should start using out-of- + order delivery methods to counter the HOL blocking. +</pre> + +<p> +&man_sctp; does not currently allow the user to switch between ordered +and unordered delivery, or to specify the manner of sending per +message: one or the other must be configured, the defaults being +ordered.</p> + +<pre> + + Another race condition may occur when DPR and DPA messages are used. + Both DPR and DPA are small in size; thus, they may be delivered to + the peer faster than application messages when an out-of-order + delivery mechanism is used. Therefore, it is possible that a DPR/DPA + + + +Fajardo, et al. Standards Track [Page 23] + +RFC 6733 Diameter Base Protocol October 2012 + + + exchange completes while application messages are still in transit, + resulting in a loss of these messages. An implementation could + mitigate this race condition, for example, using timers, and wait for + a short period of time for pending application level messages to + arrive before proceeding to disconnect the transport connection. + Eventually, lost messages are handled by the retransmission mechanism + described in Section 5.5.4. + + A Diameter agent SHOULD use dedicated payload protocol identifiers + (PPIDs) for clear text and encrypted SCTP DATA chunks instead of only + using the unspecified payload protocol identifier (value 0). For + this purpose, two PPID values are allocated: the PPID value 46 is for + Diameter messages in clear text SCTP DATA chunks, and the PPID value + 47 is for Diameter messages in protected DTLS/SCTP DATA chunks. +</pre> + +&nada; + +<pre> + +2.2. Securing Diameter Messages + + Connections between Diameter peers SHOULD be protected by TLS/TCP and + DTLS/SCTP. All Diameter base protocol implementations MUST support + the use of TLS/TCP and DTLS/SCTP. If desired, alternative security + mechanisms that are independent of Diameter, such as IPsec [RFC4301], + can be deployed to secure connections between peers. The Diameter + protocol MUST NOT be used without one of TLS, DTLS, or IPsec. +</pre> + +<p> +As noted above, DTLS is not currently supported and IPsec usage is +transparent to diameter. +Security is not enforced by diameter.</p> + +<pre> + +2.3. Diameter Application Compliance + + Application Ids are advertised during the capabilities exchange phase + (see Section 5.3). Advertising support of an application implies + that the sender supports the functionality specified in the + respective Diameter application specification. + + Implementations MAY add arbitrary optional AVPs with the M-bit + cleared (including vendor-specific AVPs) to a command defined in an + application, but only if the command's CCF syntax specification + allows for it. Please refer to Section 11.1.1 for details. +</pre> + +&nada; + +<pre> + +2.4. Application Identifiers + + Each Diameter application MUST have an IANA-assigned Application ID. + The base protocol does not require an Application Id since its + support is mandatory. During the capabilities exchange, Diameter + nodes inform their peers of locally supported applications. + Furthermore, all Diameter messages contain an Application Id, which + is used in the message forwarding process. + + + + + + + +Fajardo, et al. Standards Track [Page 24] + +RFC 6733 Diameter Base Protocol October 2012 + + + The following Application Id values are defined: + + Diameter common message 0 + Diameter base accounting 3 + Relay 0xffffffff +</pre> + +<p> +These applications are implemented in the dictionary modules +<c>diameter_gen_base_rfc6733</c>, <c>diameter_gen_acct_rfc6733</c> and +<c>diameter_relay</c> respectively. +There are also RFC 3588 versions or the common and accounting +dictionaries: <c>diameter_gen_base_rfc3588</c> and +<c>diameter_base_accounting</c>. +(The inconsistent naming is historical.) +Dictionary modules are configured using the &mod_application_opt; +<c>dictionary</c>.</p> + +<pre> + Relay and redirect agents MUST advertise the Relay Application ID, + 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, an error message is returned with the + Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER. +</pre> + +&nada; + +<pre> + +2.5. Connections vs. Sessions + + This section attempts to provide the reader with an understanding of + the difference between "connection" and "session", which are terms + used extensively throughout this document. + + A connection refers to a transport-level connection between two peers + that is used to send and receive Diameter messages. A session is a + logical concept at the application layer that exists between the + Diameter client and the Diameter server; it is identified via the + Session-Id AVP. + + +--------+ +-------+ +--------+ + | Client | | Relay | | Server | + +--------+ +-------+ +--------+ + <----------> <----------> + peer connection A peer connection B + + <-----------------------------> + User session x + + Figure 1: Diameter Connections and Sessions + + In the example provided in Figure 1, peer connection A is established + between the client and the relay. Peer connection B is established + between the relay and the server. User session X spans from the + client via the relay to the server. Each "user" of a service causes + an auth request to be sent, with a unique session identifier. Once + accepted by the server, both the client and the server are aware of + the session. + + + + +Fajardo, et al. Standards Track [Page 25] + +RFC 6733 Diameter Base Protocol October 2012 + + + It is important to note that there is no relationship between a + connection and a session, and that Diameter messages for multiple + sessions are all multiplexed through a single connection. Also, note + that Diameter messages pertaining to the session, both application- + specific and those that are defined in this document such as ASR/ASA, + RAR/RAA, and STR/STA, MUST carry the Application Id of the + application. Diameter messages pertaining to peer connection + establishment and maintenance such as CER/CEA, DWR/DWA, and DPR/DPA + MUST carry an Application Id of zero (0). +</pre> + +<p> +As noted above, diameter is not involved in session management. +This is the responsibility of the diameter user.</p> + +<pre> + +2.6. Peer Table + + The Diameter peer table is used in message forwarding and is + referenced by the 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 4.3.1, this field contains the + contents of the Origin-Host (Section 6.3) AVP found in the CER or + CEA message. + + StatusT + + This is the state of the peer entry, and it MUST match one of the + values listed in Section 5.6. + + Static or Dynamic + + Specifies whether a peer entry was statically configured or + dynamically discovered. + + Expiration Time + + Specifies the time at which dynamically discovered peer table + entries are to be either refreshed or expired. If public key + certificates are used for Diameter security (e.g., with TLS), this + value MUST NOT be greater than the expiry times in the relevant + certificates. + + TLS/TCP and DTLS/SCTP Enabled + + Specifies whether TLS/TCP and DTLS/SCTP is to be used when + communicating with the peer. + + Additional security information, when needed (e.g., keys, + certificates). +</pre> + +<p> +The Peer Table is not directly accessible to the diameter user. +Information about connected peers can be retrieved using +&mod_service_info;.</p> + +<pre> + + + +Fajardo, et al. Standards Track [Page 26] + +RFC 6733 Diameter Base Protocol October 2012 + + +2.7. Routing Table + + All Realm-Based routing lookups are performed against what is + commonly known as the routing table (see Section 12). Each routing + table entry contains the following fields: + + Realm Name + + This is the field that MUST be 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 + + An application is identified by an Application Id. A route entry + can have a different destination based on the Application Id in + the message header. This field MUST be 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 can be satisfied locally and do + not need to be routed to another Diameter entity. + + 2. RELAY - All Diameter messages that fall within this category + MUST be routed to a next-hop Diameter entity that is indicated + by the identifier described below. Routing is done without + modifying any non-routing AVPs. See Section 6.1.9 for + relaying guidelines. + + 3. PROXY - All Diameter messages that fall within this category + MUST be routed to a next Diameter entity that is indicated by + the identifier described below. The local server MAY apply + its local policies to the message by including new AVPs to the + message prior to routing. See Section 6.1.9 for proxying + 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 6.1.8 for redirection guidelines. + + + + + + +Fajardo, et al. Standards Track [Page 27] + +RFC 6733 Diameter Base Protocol October 2012 + + + Server Identifier + + The identity of one or more servers to which the message is to be + routed. This identity MUST also be present in the Host Identity + field of the peer table (Section 2.6). When the Local Action is + set to RELAY or PROXY, this field contains the identity of the + server(s) to which the message MUST be routed. When the Local + Action field is set to REDIRECT, this field contains the identity + of one or more servers to which the message MUST be redirected. + + Static or Dynamic + + Specifies whether a route entry was statically configured or + dynamically discovered. + + Expiration Time + + Specifies the time at which a dynamically discovered route table + entry expires. If public key certificates are used for Diameter + security (e.g., with TLS), this value MUST NOT be greater than the + expiry time in the relevant certificates. + + 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 they MUST follow the + protocol compliance guidelines in Section 2. Relay agents and + proxies MUST NOT reorder AVPs. + + The routing table MAY include a default entry that 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 Id (see Section 2.4) for the given message or have + advertised itself as a relay or proxy agent. Otherwise, an error is + returned with the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER. +</pre> + +<p> +Routing does not need specific support in diameter: a user can +maintain their own routing table if desired and implement any desired +routing in &man_app; callbacks. +However, it may be convenient to add more specific routing support to +diameter in the future.</p> + +<pre> + +2.8. Role of Diameter Agents + + In addition to clients and servers, the Diameter protocol introduces + relay, proxy, redirect, and translation agents, each of which is + defined in Section 1.2. Diameter agents are useful for several + reasons: +</pre> + +<p> +An noted above, the role a node plays is largely a question of +configuration and &man_app; callback implementation.</p> + +<pre> + + o They can distribute administration of systems to a configurable + grouping, including the maintenance of security associations. + + + + +Fajardo, et al. Standards Track [Page 28] + +RFC 6733 Diameter Base Protocol October 2012 + + + o They can be used for concentration of requests from a number of + co-located or distributed NAS equipment sets to a set of like user + groups. + + o They can do value-added processing to the requests or responses. + + o They can be used for load balancing. + + o 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, its Hop-by-Hop Identifier is + saved; the field is replaced with a locally unique identifier, which + is 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 until either the agent is notified otherwise or the session + expires. Each authorized session has an expiration, which is + communicated by Diameter servers via the Session-Timeout AVP. + + Maintaining session state may be useful in certain applications, such + as: + + o Protocol translation (e.g., RADIUS <-> Diameter) + + o Limiting resources authorized to a particular user + + o Per-user or per-transaction auditing + + A Diameter agent MAY act in a stateful manner for some requests and + 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. +</pre> + +&nada; + +<pre> + + + + + + +Fajardo, et al. Standards Track [Page 29] + +RFC 6733 Diameter Base Protocol October 2012 + + +2.8.1. Relay Agents + + Relay agents are Diameter agents that accept requests and route + messages to other Diameter nodes based on information found in the + messages (e.g., the value of the Destination-Realm AVP Section 6.6). + This routing decision is performed using a list of supported realms + and known peers. This is known as the routing table, as is defined + further in Section 2.7. + + Relays may, for example, be used to aggregate requests from multiple + Network Access Servers (NASes) within a common geographical area + (Point of Presence, 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 they do not modify any other portion of a message. + Relays SHOULD NOT maintain session state but MUST maintain + transaction state. + + +------+ ---------> +------+ ---------> +------+ + | | 1. Request | | 2. Request | | + | NAS | | DRL | | HMS | + | | 4. Answer | | 3. Answer | | + +------+ <--------- +------+ <--------- +------+ + example.net example.net example.com + + Figure 2: Relaying of Diameter messages + + The example provided in Figure 2 depicts a request issued from a NAS, + which is an access device, for the user [email protected]. Prior to + issuing the request, the NAS performs a Diameter route lookup, using + "example.com" as the key, and determines that the message is to be + relayed to a DRL, which is a Diameter relay. The DRL performs the + same route lookup as the NAS, and relays the message to the HMS, + which is example.com's home server. The 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 the NAS using saved transaction + state. + + Since relays do not perform any application-level processing, they + provide relaying services for all Diameter applications; therefore, + they MUST advertise the Relay Application Id. +</pre> + +<p> +Requests are relayed by returning a <c>relay</c> tuple from a +&app_handle_request; callback.</p> + +<pre> + + + +Fajardo, et al. Standards Track [Page 30] + +RFC 6733 Diameter Base Protocol October 2012 + + +2.8.2. Proxy Agents + + Similar 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 provide + provisioning. + + Proxies may, for example, be used in call control centers or access + ISPs that provide outsourced connections; they can monitor the number + and type of ports in use and make allocation and admission decisions + according to their configuration. + + Since enforcing policies requires an understanding of the service + being provided, proxies MUST only advertise the Diameter applications + they support. +</pre> + +&nada; + +<pre> + +2.8.3. Redirect Agents + + Redirect agents are useful in scenarios where the Diameter routing + configuration needs to be centralized. An example is a redirect + agent that provides services to all members of a consortium, but does + not wish to be burdened with relaying all messages between realms. + 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 redirect agents 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 redirect + agents do not receive answer messages, they cannot maintain session + state. + + The example provided in Figure 3 depicts a request issued from the + access device, NAS, for the user [email protected]. The message is + forwarded by the NAS to its relay, DRL, which does not have a routing + entry in its Diameter routing table for example.com. The DRL has a + default route configured to DRD, which is a redirect agent that + returns a redirect notification to DRL, as well as the HMS' contact + information. Upon receipt of the redirect notification, the DRL + establishes a transport connection with the HMS, if one doesn't + already exist, and forwards the request to it. + + + + + + + + +Fajardo, et al. Standards Track [Page 31] + +RFC 6733 Diameter Base Protocol October 2012 + + + +------+ + | | + | DRD | + | | + +------+ + ^ | + 2. Request | | 3. Redirection + | | Notification + | v + +------+ ---------> +------+ ---------> +------+ + | | 1. Request | | 4. Request | | + | NAS | | DRL | | HMS | + | | 6. Answer | | 5. Answer | | + +------+ <--------- +------+ <--------- +------+ + example.net example.net example.com + + Figure 3: Redirecting a Diameter Message + + Since redirect agents do not perform any application-level + processing, they provide relaying services for all Diameter + applications; therefore, they MUST advertise the Relay Application + ID. +</pre> + +&nada; + +<pre> + +2.8.4. 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 session stateful and + MUST maintain transaction state. + + Translation of messages can only occur if the agent recognizes the + application of a particular request; therefore, translation agents + MUST only advertise their locally supported applications. + + +------+ ---------> +------+ ---------> +------+ + | | RADIUS Request | | Diameter Request | | + | NAS | | TLA | | HMS | + | | RADIUS Answer | | Diameter Answer | | + +------+ <--------- +------+ <--------- +------+ + example.net example.net example.com + + Figure 4: Translation of RADIUS to Diameter +</pre> + +&nada; + +<pre> + + + + +Fajardo, et al. Standards Track [Page 32] + +RFC 6733 Diameter Base Protocol October 2012 + + +2.9. Diameter Path Authorization + + As noted in Section 2.2, Diameter provides transmission-level + security for each connection using TLS/TCP and DTLS/SCTP. Therefore, + each connection can be authenticated and can be replay and integrity + protected. + + In addition to authenticating each connection, the entire session + MUST also be authorized. Before initiating a connection, a Diameter + peer MUST check that its peers are authorized to act in their roles. + For example, a Diameter peer may be authentic, but that does not mean + that it is authorized to act as a Diameter server advertising a set + of Diameter applications. + + Prior to bringing up a connection, authorization checks are performed + at each connection along the path. Diameter capabilities negotiation + (CER/CEA) also MUST be carried out, in order to determine what + Diameter applications are supported by each peer. Diameter sessions + MUST be routed only through authorized nodes that have advertised + support for the Diameter application required by the session. + + As noted in Section 6.1.9, a relay or proxy agent MUST append a + Route-Record AVP to all requests forwarded. The AVP contains the + identity of the peer from which the request was received. + + The home Diameter server, prior to authorizing a session, MUST check + the Route-Record AVPs to make sure that the route traversed by the + request is acceptable. For example, administrators within the home + realm may not wish to honor requests that have been routed through an + untrusted realm. By authorizing a request, the home Diameter server + is implicitly indicating its willingness to engage in the business + transaction as specified by any contractual relationship between the + server and the previous hop. A DIAMETER_AUTHORIZATION_REJECTED error + message (see Section 7.1.5) is sent if the route traversed by the + request is unacceptable. + + A home realm may also wish to check that each accounting request + message corresponds to a Diameter response authorizing the session. + Accounting requests without corresponding authorization responses + SHOULD be subjected to further scrutiny, as should accounting + requests indicating a difference between the requested and provided + service. + + Forwarding of an authorization response is considered evidence of a + willingness to take on financial risk relative to the session. A + local realm may wish to limit this exposure, for example, by + establishing credit limits for intermediate realms and refusing to + accept responses that would violate those limits. By issuing an + + + +Fajardo, et al. Standards Track [Page 33] + +RFC 6733 Diameter Base Protocol October 2012 + + + accounting request corresponding to the authorization response, the + local realm implicitly indicates its agreement to provide the service + indicated in the authorization response. If the service cannot be + provided by the local realm, then a DIAMETER_UNABLE_TO_COMPLY error + message MUST be sent within the accounting request; a Diameter client + receiving an authorization response for a service that it cannot + perform MUST NOT substitute an alternate service and then send + accounting requests for the alternate service instead. +</pre> + +&nada; + +<pre> + +3. 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Version | Message Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Command Flags | Command Code | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Application-ID | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Hop-by-Hop Identifier | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | End-to-End Identifier | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | AVPs ... + +-+-+-+-+-+-+-+-+-+-+-+-+- +</pre> + +<p> +The Diameter Header is represented by the <c>diameter_header</c> +record defined in <c>diameter.hrl</c>. +The <c>diameter_packet</c> record contains a <c>header</c> field whose +value will be a decoded <c>#diameter_header{}</c> for incoming +messages passed to &app_handle_request; and &app_handle_answer; +callbacks. +In the case of outgoing messages, diameter and the relevant +dictionary populate the Diameter Header appropriately, although +&app_prepare_request; and &app_handle_request; callbacks can modify +header values. +(Which can be useful in test.)</p> + +<pre> + + Version + + This Version field MUST be set to 1 to indicate Diameter Version + 1. + + Message Length + + The Message Length field is three octets and indicates the length + of the Diameter message including the header fields and the padded + AVPs. Thus, the Message Length field is always a multiple of 4. + + Command Flags + + The Command Flags field is eight bits. The following bits are + assigned: + + + + + + +Fajardo, et al. Standards Track [Page 34] + +RFC 6733 Diameter Base Protocol October 2012 + + + 0 1 2 3 4 5 6 7 + +-+-+-+-+-+-+-+-+ + |R P E T r r r r| + +-+-+-+-+-+-+-+-+ + + 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, relayed, or redirected. If + cleared, the message MUST be locally processed. + + E(rror) + + If set, the message contains a protocol error, and the message + will not conform to the CCF described for this command. + Messages with the 'E' bit set are commonly referred to as error + messages. This bit MUST NOT be set in request messages (see + Section 7.2). + + T(Potentially retransmitted message) + + This flag is set after a link failover procedure, to aid the + removal of duplicate requests. It is set when resending + requests not yet acknowledged, as an indication of a possible + duplicate due to a link failure. This bit MUST be cleared when + sending a request for the first time; otherwise, the sender + MUST set this flag. Diameter agents only need to be concerned + about the number of requests they send based on a single + received request; retransmissions by other entities need not be + tracked. Diameter agents that receive a request with the T + flag set, MUST keep the T flag set in the forwarded request. + This flag MUST NOT be set if an error answer message (e.g., a + protocol error) has been received for the earlier message. It + can be set only in cases where no answer has been received from + the server for a request, and the request has been sent again. + This flag MUST NOT be set in answer messages. + + r(eserved) + + These flag bits are reserved for future use; they MUST be set + to zero and ignored by the receiver. +</pre> + +<p> +Reserved bits are set to 0 in outgoing messages.</p> + +<pre> + + + + + + +Fajardo, et al. Standards Track [Page 35] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 3.1). Command Code + values 16,777,214 and 16,777,215 (hexadecimal values FFFFFE- + FFFFFF) are reserved for experimental use (see Section 11.2). + + Application-ID + + Application-ID is four octets and is used to identify for which + application the message is applicable. The application can be an + authentication application, an accounting application, or a + vendor-specific application. + + The value of the Application-ID field in the header MUST be the + same as any relevant Application-Id AVPs contained in the message. + + Hop-by-Hop Identifier + + The Hop-by-Hop Identifier is an unsigned 32-bit integer field (in + network byte order) that aids in matching requests and replies. + The sender MUST ensure that the Hop-by-Hop Identifier in a request + is unique on a given connection at any given time, and it 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 + + The End-to-End Identifier is an unsigned 32-bit integer field (in + network byte order) that is used to detect duplicate messages. + Upon reboot, implementations MAY set the high order 12 bits to + contain the low order 12 bits of current time, and the low order + 20 bits to a random value. Senders of request messages MUST + insert a unique identifier on each message. The identifier MUST + remain locally unique for a period of at least 4 minutes, even + across reboots. The originator of an answer message MUST ensure + that the End-to-End Identifier field contains the same value that + was found in the corresponding request. The End-to-End Identifier + MUST NOT be modified by Diameter agents of any kind. The + combination of the Origin-Host AVP (Section 6.3) and this field is + used to detect duplicates. Duplicate requests SHOULD cause the + same answer to be transmitted (modulo the Hop-by-Hop Identifier + + + +Fajardo, et al. Standards Track [Page 36] + +RFC 6733 Diameter Base Protocol October 2012 + + + field and any routing AVPs that may be present), and they MUST NOT + affect any state that was set when the original request was + processed. Duplicate answer messages that are to be locally + consumed (see Section 6.2) 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. +</pre> + +&nada; + +<pre> + +3.1. Command Codes + + Each command Request/Answer pair is assigned a Command Code, and the + sub-type (i.e., 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: + + Section + Command Name Abbrev. Code Reference + -------------------------------------------------------- + Abort-Session-Request ASR 274 8.5.1 + Abort-Session-Answer ASA 274 8.5.2 + Accounting-Request ACR 271 9.7.1 + Accounting-Answer ACA 271 9.7.2 + Capabilities-Exchange- CER 257 5.3.1 + Request + Capabilities-Exchange- CEA 257 5.3.2 + Answer + Device-Watchdog-Request DWR 280 5.5.1 + Device-Watchdog-Answer DWA 280 5.5.2 + Disconnect-Peer-Request DPR 282 5.4.1 + Disconnect-Peer-Answer DPA 282 5.4.2 + Re-Auth-Request RAR 258 8.3.1 + Re-Auth-Answer RAA 258 8.3.2 + Session-Termination- STR 275 8.4.1 + Request + Session-Termination- STA 275 8.4.2 + Answer +</pre> + +<p> +These messages are all defined in diameter's implementation of the +common dictionary in modules <c>diameter_gen_base_rfc6733</c> and +<c>diameter_gen_base_rfc3588</c>. +Corresponding record definitions are found in +<c>diameter_gen_base_rfc6733.hrl</c> and +<c>diameter_gen_base_rfc3588.hrl</c>.</p> + +<pre> + + + + + + + + + +Fajardo, et al. Standards Track [Page 37] + +RFC 6733 Diameter Base Protocol October 2012 + + +3.2. Command Code Format Specification + + Every Command Code defined MUST include a corresponding Command Code + Format (CCF) specification, which is used to define the AVPs that + MUST or MAY be present when sending the message. The following ABNF + specifies the CCF used in the definition: +</pre> + +<p> +The CCF is what is specified in the <c>@messages</c> section of the +&man_dict; format, except as noted below.</p> + +<pre> + + command-def = "<" command-name ">" "::=" diameter-message +</pre> + +<p> +Angle brackets are currently not allowed here. +This was a change between RFC 3588 and RFC 6733: the former disallowed +them in the grammar but included them in its own command definitions.</p> + +<pre> + + command-name = diameter-name + + diameter-name = ALPHA *(ALPHA / DIGIT / "-") + + diameter-message = header *fixed *required *optional + + header = "<Diameter-Header:" command-id + [r-bit] [p-bit] [e-bit] [application-id]">" + + application-id = 1*DIGIT + + 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, indicating that the message + ; is proxiable. + + e-bit = ", ERR" + ; If present, the 'E' bit in the Command + ; Flags is set, indicating that the answer + ; message contains a Result-Code AVP in + ; the "protocol error" class. + + fixed = [qual] "<" avp-spec ">" + ; Defines the fixed position of an AVP. + + required = [qual] "{" avp-spec "}" + ; The AVP MUST be present and can appear + ; anywhere in the message. + + + + + + +Fajardo, et al. Standards Track [Page 38] + +RFC 6733 Diameter Base Protocol October 2012 + + + optional = [qual] "[" avp-name "]" + ; The avp-name in the 'optional' rule cannot + ; evaluate to any AVP Name that is included + ; in a fixed or required rule. The AVP can + ; appear anywhere in the message. + ; + ; NOTE: "[" and "]" have a slightly different + ; meaning than in ABNF. 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'. + + qual = [min] "*" [max] + ; See ABNF conventions, RFC 5234, Section 4. + ; The absence of any qualifier depends on + ; whether it precedes a fixed, required, or + ; optional rule. If a fixed or required rule has + ; no qualifier, then exactly one such AVP MUST + ; be present. If an optional rule has no + ; qualifier, then 0 or 1 such AVP may be + ; present. If an optional rule has a qualifier, + ; then the value of min MUST be 0 if present. + + min = 1*DIGIT + ; The minimum number of times the element may + ; be present. If absent, the default value is 0 + ; for fixed and optional rules and 1 for + ; required rules. The value MUST be at least 1 + ; for required rules. + + max = 1*DIGIT + ; The maximum number of times the element may + ; be present. If absent, the default value is + ; infinity. A value of 0 implies the AVP MUST + ; NOT be present. + + 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, not otherwise listed in that Command Code + ; definition. The inclusion of this string + ; is recommended for all CCFs to allow for + ; extensibility. + + + + +Fajardo, et al. Standards Track [Page 39] + +RFC 6733 Diameter Base Protocol October 2012 + + + The following is a definition of a fictitious Command Code: + + Example-Request ::= < Diameter Header: 9999999, REQ, PXY > + { User-Name } + 1* { Origin-Host } + * [ AVP ] +</pre> + +&nada; + +<pre> + +3.3. Diameter Command Naming Conventions + + Diameter command names typically includes one or more English words + followed by the verb "Request" or "Answer". Each English word is + delimited by a hyphen. A three-letter acronym for both the request + and answer is also normally provided. + + An example is a message set used to terminate a session. The command + name is Session-Terminate-Request and Session-Terminate-Answer, while + the acronyms are STR and STA, respectively. + + Both the request and the answer for a given command share the same + Command Code. The request is identified by the R(equest) bit in the + Diameter header set to one (1), to ask that a particular action be + performed, such as authorizing a user or terminating a session. Once + the receiver has completed the request, it issues the corresponding + answer, which includes a result code that communicates one of the + following: + + o The request was successful + + o The request failed + + o An additional request has to be sent to provide information the + peer requires prior to returning a successful or failed answer. + + o The receiver could not process the request, but provides + information about a Diameter peer that is able to satisfy the + request, known as redirect. + + Additional information, encoded within AVPs, may also be included in + answer messages. +</pre> + +<p> +The &man_dict; format places no requirement on the naming of commands.</p> + +<pre> + +4. Diameter AVPs + + Diameter AVPs carry specific authentication, accounting, + authorization, and routing information as well as configuration + details for the request and reply. + + + + + + +Fajardo, et al. Standards Track [Page 40] + +RFC 6733 Diameter Base Protocol October 2012 + + + Each AVP of type OctetString MUST be padded to align on a 32-bit + boundary, while other AVP types align naturally. A number of zero- + valued bytes are added to the end of the AVP Data field until 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. AVP numbers 1 through 255 are reserved for + reuse of RADIUS attributes, without setting the Vendor-Id field. + AVP numbers 256 and above are used for Diameter, which are + allocated by IANA (see Section 11.1.1). + + AVP Flags + + The AVP Flags field informs the receiver how each attribute must + be handled. New Diameter applications SHOULD NOT define + additional AVP Flag bits. However, note that new Diameter + applications MAY define additional bits within the AVP header, and + an unrecognized bit SHOULD be considered an error. The sender of + the AVP MUST set 'R' (reserved) bits to 0 and the receiver SHOULD + ignore all 'R' (reserved) bits. The 'P' bit has been reserved for + future usage of end-to-end security. At the time of writing, + there are no end-to-end security mechanisms specified; therefore, + the 'P' bit SHOULD be set to 0. + + The 'M' bit, known as the Mandatory bit, indicates whether the + receiver of the AVP MUST parse and understand the semantics of the + AVP including its content. The receiving entity MUST return an + appropriate error message if it receives an AVP that has the M-bit + + + +Fajardo, et al. Standards Track [Page 41] + +RFC 6733 Diameter Base Protocol October 2012 + + + set but does not understand it. An exception applies when the AVP + is embedded within a Grouped AVP. See Section 4.4 for details. + Diameter relay and redirect agents MUST NOT reject messages with + unrecognized AVPs. + + The 'M' bit MUST be set according to the rules defined in the + application specification that introduces or reuses this AVP. + Within a given application, the M-bit setting for an AVP is + defined either for all command types or for each command type. + + AVPs with the 'M' bit cleared are informational only; a receiver + that receives a message with such an AVP that is not supported, or + whose value 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. + + AVP Length + + The AVP Length field is three octets, and indicates the number of + octets in this AVP including the AVP Code field, AVP Length field, + AVP Flags field, Vendor-ID field (if present), and the AVP Data + field. If a message is received with an invalid attribute length, + the message MUST be rejected. + +4.1.1. 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" + [ENTERPRISE] value, encoded in network byte order. Any vendors or + standardization organizations that are also treated like vendors + in the IANA-managed "SMI Network Management Private Enterprise + Codes" space wishing to implement a vendor-specific Diameter AVP + MUST use their own Vendor-ID along with their privately managed + AVP address space, guaranteeing that they will not collide with + any other vendor's vendor-specific AVP(s) or with future IETF + AVPs. + + + + + + +Fajardo, et al. Standards Track [Page 42] + +RFC 6733 Diameter Base Protocol October 2012 + + + A Vendor-ID value of zero (0) corresponds to the IETF-adopted AVP + values, as managed by IANA. Since the absence of the Vendor-ID + field implies that the AVP in question is not vendor specific, + implementations MUST NOT use the value of zero (0) for the + Vendor-ID field. + +4.2. Basic AVP Data Formats + + 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 Basic + AVP 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 are + not a multiple of 4 octets in length are followed by the necessary + padding so that the next AVP (if any) will start on a 32-bit + boundary. + + 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). + + + + + + + + +Fajardo, et al. Standards Track [Page 43] + +RFC 6733 Diameter Base Protocol October 2012 + + + Float32 + + This represents floating point values of single precision as + described by [FLOATPOINT]. The 32-bit value is transmitted in + network byte order. The AVP Length field MUST be set to 12 (16 if + the 'V' bit is enabled). + + Float64 + + This represents floating point values of double precision as + described by [FLOATPOINT]. The 64-bit value is transmitted in + network byte order. The AVP Length field MUST be set to 16 (20 if + the 'V' bit is enabled). + + Grouped + + The Data field is specified as a sequence of AVPs. These AVPs are + concatenated -- including their headers and padding -- in the + order in which they are specified and the result encapsulated in + the Data field. 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. Thus, the AVP Length field + of an AVP of type Grouped is always a multiple of 4. + +4.3. Derived AVP Data Formats + + In addition to using the Basic AVP Data Formats, applications may + define data formats derived from the Basic AVP Data Formats. An + application that defines new Derived AVP Data Formats MUST include + them in a section titled "Derived AVP Data Formats", using the same + format as the definitions below. Each new definition MUST be either + defined or listed with a reference to the RFC that defines the + format. + +4.3.1. Common Derived AVP Data Formats + + The following are commonly used Derived AVP Data Formats. + + Address + + The Address format is derived from the OctetString Basic AVP + Format. It is a discriminated union representing, for example, a + 32-bit (IPv4) [RFC0791] or 128-bit (IPv6) [RFC4291] address, most + significant octet first. The first two octets of the Address AVP + represent the AddressType, which contains an Address Family, + defined in [IANAADFAM]. The AddressType is used to discriminate + the content and format of the remaining octets. + + + + +Fajardo, et al. Standards Track [Page 44] + +RFC 6733 Diameter Base Protocol October 2012 + + + Time + + The Time format is derived from the OctetString Basic AVP Format. + The string MUST contain four octets, in the same format as the + first four bytes are in the NTP timestamp format. The NTP + timestamp format is defined in Section 3 of [RFC5905]. + + This represents 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. + Simple Network Time Protocol (SNTP) [RFC5905] describes a + procedure to extend the time to 2104. This procedure MUST be + supported by all Diameter nodes. + + UTF8String + + The UTF8String format is derived from the OctetString Basic AVP + 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 transformation format [RFC3629]. + + 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 encoding of a code + point into UTF-8 charset or are outside this range are prohibited. + + The use of control codes SHOULD be avoided. When it is necessary + to represent a new line, 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 charset is + identical to the US-ASCII charset. + + 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 AVP Length field of an UTF8String is measured in + octets not characters. + + + + +Fajardo, et al. Standards Track [Page 45] + +RFC 6733 Diameter Base Protocol October 2012 + + + DiameterIdentity + + The DiameterIdentity format is derived from the OctetString Basic + AVP Format. + + DiameterIdentity = FQDN/Realm + + The DiameterIdentity value is used to uniquely identify either: + + * A Diameter node for purposes of duplicate connection and + routing loop detection. + + * A Realm to determine whether messages can be satisfied locally + or whether they must be routed or redirected. + + When a DiameterIdentity value is used to identify a Diameter node, + the contents of the string MUST be the Fully Qualified Domain Name + (FQDN) of the Diameter node. If multiple Diameter nodes run on + the same host, each Diameter node MUST be assigned a unique + DiameterIdentity. If a Diameter node can be identified by several + FQDNs, a single FQDN should be picked at startup and used as the + only DiameterIdentity for that node, whatever the connection on + which it is sent. In this document, note that DiameterIdentity is + in ASCII form in order to be compatible with existing DNS + infrastructure. See Appendix D for interactions between the + Diameter protocol and Internationalized Domain Names (IDNs). + + DiameterURI + + The DiameterURI MUST follow the Uniform Resource Identifiers (RFC + 3986) syntax [RFC3986] rules specified below: + + "aaa://" FQDN [ port ] [ transport ] [ protocol ] + + ; No transport security + + "aaas://" FQDN [ port ] [ transport ] [ protocol ] + + ; Transport security used + + FQDN = < Fully Qualified Domain Name > + + + + + + + + + + +Fajardo, et al. Standards Track [Page 46] + +RFC 6733 Diameter Base Protocol October 2012 + + + port = ":" 1*DIGIT + + ; One of the ports used to listen for + ; incoming connections. + ; If absent, the default Diameter port + ; (3868) is assumed if no transport + ; security is used and port 5658 when + ; transport security (TLS/TCP and DTLS/SCTP) + ; is used. + + transport = ";transport=" transport-protocol + + ; One of the transports used to listen + ; for incoming connections. If absent, + ; the default protocol is assumed to be TCP. + ; UDP MUST NOT be used when the aaa-protocol + ; field is set to diameter. + + transport-protocol = ( "tcp" / "sctp" / "udp" ) + + protocol = ";protocol=" aaa-protocol + + ; If absent, the default AAA protocol + ; is Diameter. + + aaa-protocol = ( "diameter" / "radius" / "tacacs+" ) + + The following are examples of valid Diameter host identities: + + aaa://host.example.com;transport=tcp + aaa://host.example.com:6666;transport=tcp + aaa://host.example.com;protocol=diameter + aaa://host.example.com:6666;protocol=diameter + aaa://host.example.com:6666;transport=tcp;protocol=diameter + aaa://host.example.com:1813;transport=udp;protocol=radius + + Enumerated + + The Enumerated format is derived from the Integer32 Basic AVP + Format. The definition contains a list of valid values and their + interpretation and is described in the Diameter application + introducing the AVP. + + + + + + + + + +Fajardo, et al. Standards Track [Page 47] + +RFC 6733 Diameter Base Protocol October 2012 + + + IPFilterRule + + The IPFilterRule format is derived from the OctetString Basic AVP + Format and uses the ASCII charset. The rule syntax is a modified + subset of ipfw(8) from FreeBSD. Packets may be filtered based on + the following information that is associated with it: + + Direction (in or out) + Source and destination IP address (possibly masked) + Protocol + Source and destination port (lists or ranges) + TCP flags + IP fragment flag + IP options + ICMP types + + Rules for the appropriate direction are evaluated in order, with the + first matched rule terminating the evaluation. Each packet is + evaluated once. If no rule matches, the packet is dropped if the + last rule evaluated was a permit, and passed if the last rule was a + deny. + + IPFilterRule filters MUST follow the format: + + action dir proto from src to dst [options] + + action permit - Allow packets that match the rule. + deny - Drop packets that match the rule. + + dir "in" is from the terminal, "out" is to the + terminal. + + proto An IP protocol specified by number. The "ip" + keyword means any protocol will match. + + src and dst <address/mask> [ports] + + The <address/mask> may be specified as: + ipno An IPv4 or IPv6 number in dotted- + quad or canonical IPv6 form. Only + this exact IP number will match the + rule. + + + + + + + + + +Fajardo, et al. Standards Track [Page 48] + +RFC 6733 Diameter Base Protocol October 2012 + + + ipno/bits An IP number as above with a mask + width of the form 192.0.2.10/24. In + this case, all IP numbers from + 192.0.2.0 to 192.0.2.255 will match. + The bit width MUST be valid for the + IP version, and the IP number MUST + NOT have bits set beyond the mask. + For a match to occur, the same IP + version must be present in the + packet that was used in describing + the IP address. To test for a + particular IP version, the bits part + can be set to zero. The keyword + "any" is 0.0.0.0/0 or the IPv6 + equivalent. The keyword "assigned" + is the address or set of addresses + assigned to the terminal. For IPv4, + a typical first rule is often "deny + in ip! assigned". + + The sense of the match can be inverted by + preceding an address with the not modifier (!), + causing all other addresses to be matched + instead. This does not affect the selection of + port numbers. + + With the TCP, UDP, and SCTP protocols, optional + ports may be specified as: + + {port/port-port}[,ports[,...]] + + The '-' notation specifies a range of ports + (including boundaries). + + Fragmented packets that have a non-zero offset + (i.e., not the first fragment) will never match + a rule that has one or more port + specifications. See the frag option for + details on matching fragmented packets. + + options: + frag Match if the packet is a fragment and this is not + the first fragment of the datagram. frag may not + be used in conjunction with either tcpflags or + TCP/UDP port specifications. + + + + + + +Fajardo, et al. Standards Track [Page 49] + +RFC 6733 Diameter Base Protocol October 2012 + + + ipoptions spec + Match if the IP header contains the comma-separated + list of options specified in spec. The + supported IP options are: + + ssrr (strict source route), lsrr (loose source + route), rr (record packet route), and ts + (timestamp). The absence of a particular option + may be denoted with a '!'. + + tcpoptions spec + Match if the TCP header contains the comma-separated + list of options specified in spec. The + supported TCP options are: + + mss (maximum segment size), window (tcp window + advertisement), sack (selective ack), ts (rfc1323 + timestamp), and cc (rfc1644 t/tcp connection + count). The absence of a particular option may + be denoted with a '!'. + + established + TCP packets only. Match packets that have the RST + or ACK bits set. + + setup TCP packets only. Match packets that have the SYN + bit set but no ACK bit. + + + tcpflags spec + TCP packets only. Match if the TCP header + contains the comma-separated list of flags + specified in spec. The supported TCP flags are: + + fin, syn, rst, psh, ack, and urg. The absence of a + particular flag may be denoted with a '!'. A rule + that contains a tcpflags specification can never + match a fragmented packet that has a non-zero + offset. See the frag option for details on + matching fragmented packets. + + icmptypes types + ICMP packets only. Match if the ICMP type is in + the list types. The list may be specified as any + combination of ranges or individual types + separated by commas. Both the numeric values and + the symbolic values listed below can be used. The + supported ICMP types are: + + + +Fajardo, et al. Standards Track [Page 50] + +RFC 6733 Diameter Base Protocol October 2012 + + + echo reply (0), destination unreachable (3), + source quench (4), redirect (5), echo request + (8), router advertisement (9), router + solicitation (10), time-to-live exceeded (11), IP + header bad (12), timestamp request (13), + timestamp reply (14), information request (15), + information reply (16), address mask request (17), + and address mask reply (18). + + There is one kind of packet that the access device MUST always + discard, that is an IP fragment with a fragment offset of one. This + is a valid packet, but it only has one use, to try to circumvent + firewalls. + + An access device that is unable to interpret or apply a deny rule + MUST terminate the session. An access device that is unable to + interpret or apply a permit rule MAY apply a more restrictive rule. + An access device MAY apply deny rules of its own before the supplied + rules, for example to protect the access device owner's + infrastructure. + +4.4. 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 4.4. + + The AVP Code numbering space of all AVPs included in a Grouped AVP is + the same as for non-Grouped AVPs. Receivers of a Grouped AVP that + does not have the 'M' (mandatory) bit set and one or more of the + encapsulated AVPs within the group has the 'M' (mandatory) bit set + MAY simply be ignored if the Grouped AVP itself is unrecognized. The + rule applies even if the encapsulated AVP with its 'M' (mandatory) + bit set is further encapsulated within other sub-groups, i.e., other + Grouped AVPs embedded within the Grouped AVP. + + Every Grouped AVP definition MUST include a corresponding grammar, + using ABNF [RFC5234] (with modifications), as defined below. + + grouped-avp-def = "<" name ">" "::=" avp + + name-fmt = ALPHA *(ALPHA / DIGIT / "-") + + + + + + +Fajardo, et al. Standards Track [Page 51] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 + + header = "<" "AVP-Header:" avpcode [vendor] ">" + + avpcode = 1*DIGIT + ; The AVP Code assigned to the Grouped AVP. + + vendor = 1*DIGIT + ; The Vendor-ID assigned to the Grouped AVP. + ; If absent, the default value of zero is + ; used. + +4.4.1. 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 CCF grammar: + + Example-AVP ::= < AVP Header: 999999 > + { Origin-Host } + 1*{ Session-Id } + *[ AVP ] + + An Example-AVP with Grouped Data follows. + + The Origin-Host AVP (Section 6.3) 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" + + + + + + + + + + +Fajardo, et al. Standards Track [Page 52] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 hexadecimal form + since the format of these AVPs is not 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 that support the same set of AVPs. The encoding + example illustrates how padding is used and how length fields are + calculated. Also, note that AVPs may be present in the Grouped AVP + value that the receiver cannot interpret (here, the Recover-Policy + and Futuristic-Acct-Record AVPs). The length of the Example-AVP is + the sum of all the length of the member AVPs, including their + padding, plus the Example-AVP header size. + + + + + + + + + + + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 53] + +RFC 6733 Diameter Base Protocol October 2012 + + + This AVP would be encoded as follows: + + 0 1 2 3 4 5 6 7 + +-------+-------+-------+-------+-------+-------+-------+-------+ + 0 | Example AVP Header (AVP Code = 999999), Length = 496 | + +-------+-------+-------+-------+-------+-------+-------+-------+ + 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 = 49 | 'g' | 'r' | 'u' | 'm' | + +-------+-------+-------+-------+-------+-------+-------+-------+ + . . . + +-------+-------+-------+-------+-------+-------+-------+-------+ + 72 | 'F' | '3' | 'B' | '8' | '1' |Padding|Padding|Padding| + +-------+-------+-------+-------+-------+-------+-------+-------+ + 80 | Session-Id AVP Header (AVP Code = 263), Length = 50 | + +-------+-------+-------+-------+-------+-------+-------+-------+ + 88 | 'g' | 'r' | 'u' | 'm' | 'p' | '.' | 'e' | 'x' | + +-------+-------+-------+-------+-------+-------+-------+-------+ + . . . + +-------+-------+-------+-------+-------+-------+-------+-------+ + 120| '5' | '8' | ';' | '0' | 'A' | 'F' | '3' | 'B' | + +-------+-------+-------+-------+-------+-------+-------+-------+ + 128| '8' | '2' |Padding|Padding| Recovery-Policy Header (AVP | + +-------+-------+-------+-------+-------+-------+-------+-------+ + 136| Code = 8341), Length = 223 | 0x21 | 0x63 | 0xbc | 0x1d | + +-------+-------+-------+-------+-------+-------+-------+-------+ + 144| 0x0a | 0xd8 | 0x23 | 0x71 | 0xf6 | 0xbc | 0x09 | 0x48 | + +-------+-------+-------+-------+-------+-------+-------+-------+ + . . . + +-------+-------+-------+-------+-------+-------+-------+-------+ + 352| 0x8c | 0x7f | 0x92 |Padding| Futuristic-Acct-Record Header | + +-------+-------+-------+-------+-------+-------+-------+-------+ + 328|(AVP Code = 15930),Length = 137| 0xfe | 0x19 | 0xda | 0x58 | + +-------+-------+-------+-------+-------+-------+-------+-------+ + 336| 0x02 | 0xac | 0xd9 | 0x8b | 0x07 | 0xa5 | 0xb8 | 0xc6 | + +-------+-------+-------+-------+-------+-------+-------+-------+ + . . . + +-------+-------+-------+-------+-------+-------+-------+-------+ + 488| 0xe4 | 0x99 | 0x68 | 0xf8 | 0x41 |Padding|Padding|Padding| + +-------+-------+-------+-------+-------+-------+-------+-------+ + + + + + + + +Fajardo, et al. Standards Track [Page 54] + +RFC 6733 Diameter Base Protocol October 2012 + + +4.5. Diameter Base Protocol AVPs + + The following table describes the Diameter AVPs defined in the base + protocol, their AVP Code values, types, and possible flag values. + + Due to space constraints, the short form DiamIdent is used to + represent DiameterIdentity. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 55] + +RFC 6733 Diameter Base Protocol October 2012 + + + +----------+ + | AVP Flag | + | rules | + |----+-----| + AVP Section | |MUST | + Attribute Name Code Defined Data Type |MUST| NOT | + -----------------------------------------|----+-----| + Acct- 85 9.8.2 Unsigned32 | M | V | + Interim-Interval | | | + Accounting- 483 9.8.7 Enumerated | M | V | + Realtime-Required | | | + Acct- 50 9.8.5 UTF8String | M | V | + Multi-Session-Id | | | + Accounting- 485 9.8.3 Unsigned32 | M | V | + Record-Number | | | + Accounting- 480 9.8.1 Enumerated | M | V | + Record-Type | | | + Acct- 44 9.8.4 OctetString| M | V | + Session-Id | | | + Accounting- 287 9.8.6 Unsigned64 | M | V | + Sub-Session-Id | | | + Acct- 259 6.9 Unsigned32 | M | V | + Application-Id | | | + Auth- 258 6.8 Unsigned32 | M | V | + Application-Id | | | + Auth-Request- 274 8.7 Enumerated | M | V | + Type | | | + Authorization- 291 8.9 Unsigned32 | M | V | + Lifetime | | | + Auth-Grace- 276 8.10 Unsigned32 | M | V | + Period | | | + Auth-Session- 277 8.11 Enumerated | M | V | + State | | | + Re-Auth-Request- 285 8.12 Enumerated | M | V | + Type | | | + Class 25 8.20 OctetString| M | V | + Destination-Host 293 6.5 DiamIdent | M | V | + Destination- 283 6.6 DiamIdent | M | V | + Realm | | | + Disconnect-Cause 273 5.4.3 Enumerated | M | V | + Error-Message 281 7.3 UTF8String | | V,M | + Error-Reporting- 294 7.4 DiamIdent | | V,M | + Host | | | + Event-Timestamp 55 8.21 Time | M | V | + Experimental- 297 7.6 Grouped | M | V | + Result | | | + -----------------------------------------|----+-----| + + + + +Fajardo, et al. Standards Track [Page 56] + +RFC 6733 Diameter Base Protocol October 2012 + + + +----------+ + | AVP Flag | + | rules | + |----+-----| + AVP Section | |MUST | + Attribute Name Code Defined Data Type |MUST| NOT | + -----------------------------------------|----+-----| + Experimental- 298 7.7 Unsigned32 | M | V | + Result-Code | | | + Failed-AVP 279 7.5 Grouped | M | V | + Firmware- 267 5.3.4 Unsigned32 | | V,M | + Revision | | | + Host-IP-Address 257 5.3.5 Address | M | V | + Inband-Security | M | V | + -Id 299 6.10 Unsigned32 | | | + Multi-Round- 272 8.19 Unsigned32 | M | V | + Time-Out | | | + Origin-Host 264 6.3 DiamIdent | M | V | + Origin-Realm 296 6.4 DiamIdent | M | V | + Origin-State-Id 278 8.16 Unsigned32 | M | V | + Product-Name 269 5.3.7 UTF8String | | V,M | + Proxy-Host 280 6.7.3 DiamIdent | M | V | + Proxy-Info 284 6.7.2 Grouped | M | V | + Proxy-State 33 6.7.4 OctetString| M | V | + Redirect-Host 292 6.12 DiamURI | M | V | + Redirect-Host- 261 6.13 Enumerated | M | V | + Usage | | | + Redirect-Max- 262 6.14 Unsigned32 | M | V | + Cache-Time | | | + Result-Code 268 7.1 Unsigned32 | M | V | + Route-Record 282 6.7.1 DiamIdent | M | V | + Session-Id 263 8.8 UTF8String | M | V | + Session-Timeout 27 8.13 Unsigned32 | M | V | + Session-Binding 270 8.17 Unsigned32 | M | V | + Session-Server- 271 8.18 Enumerated | M | V | + Failover | | | + Supported- 265 5.3.6 Unsigned32 | M | V | + Vendor-Id | | | + Termination- 295 8.15 Enumerated | M | V | + Cause | | | + User-Name 1 8.14 UTF8String | M | V | + Vendor-Id 266 5.3.3 Unsigned32 | M | V | + Vendor-Specific- 260 6.11 Grouped | M | V | + Application-Id | | | + -----------------------------------------|----+-----| + + + + + + +Fajardo, et al. Standards Track [Page 57] + +RFC 6733 Diameter Base Protocol October 2012 + + +5. Diameter Peers + + This section describes how Diameter nodes establish connections and + communicate with peers. + +5.1. Peer Connections + + Connections between diameter peers are established using their valid + DiameterIdentity. A Diameter node initiating a connection to a peer + MUST know the peer's DiameterIdentity. Methods for discovering a + Diameter peer can be found in Section 5.2. + + Although a Diameter node may have many possible peers with which it + is able to communicate, it may not be economical to have an + established connection to all of them. At a minimum, a Diameter node + SHOULD have an established connection with two peers per realm, known + as the primary and secondary peers. Of course, a node MAY have + additional connections, if it is deemed necessary. Typically, all + messages for a realm are sent to the primary peer but, in the event + that failover procedures are invoked, any pending requests are sent + to the secondary peer. However, implementations are free to load + balance requests between a set of peers. + + Note that a given peer MAY act as a primary for a given realm while + acting as a secondary for another realm. + + When a peer is deemed suspect, which could occur for various reasons, + including not receiving a DWA within an allotted time frame, no new + requests should be forwarded to the peer, but failover procedures are + invoked. When an active peer is moved to this mode, additional + connections SHOULD be established to ensure that the necessary number + of active connections exists. + + There are two ways that a peer is removed from the suspect peer list: + + 1. The peer is no longer reachable, causing the transport connection + to be shut down. The peer is moved to the closed state. + + 2. Three watchdog messages are exchanged with accepted round-trip + times, and the connection to the peer is considered stabilized. + + In the event the peer being removed is either the primary or + secondary, an alternate peer SHOULD replace the deleted peer and + assume the role of either primary or secondary. + + + + + + + +Fajardo, et al. Standards Track [Page 58] + +RFC 6733 Diameter Base Protocol October 2012 + + +5.2. Diameter Peer Discovery + + Allowing for dynamic Diameter agent discovery makes possible simpler + and more robust deployment of Diameter services. In order to promote + interoperable implementations of Diameter peer discovery, the + following mechanisms (manual configuration and DNS) are described. + These are based on existing IETF standards. Both mechanisms MUST be + supported by all Diameter implementations; either MAY be used. + + There are two cases where Diameter peer 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 statically + (manually) configured Diameter agent locations. These will be + used if they exist and respond. + + 2. The Diameter implementation performs a NAPTR query for a server + in a particular realm. The Diameter implementation has to know, + in advance, in which realm to look for a Diameter agent. This + could be deduced, for example, from the 'realm' in an NAI on + which a Diameter implementation needed to perform a Diameter + operation. + + The NAPTR usage in Diameter follows the S-NAPTR DDDS application + [RFC3958] in which the SERVICE field includes tags for the + desired application and supported application protocol. The + application service tag for a Diameter application is 'aaa' and + the supported application protocol tags are 'diameter.tcp', + 'diameter.sctp', 'diameter.dtls', or 'diameter.tls.tcp' + [RFC6408]. + + The client can follow the resolution process defined by the + S-NAPTR DDDS [RFC3958] application to find a matching SRV, A, or + AAAA record of a suitable peer. The domain suffixes in the NAPTR + replacement field SHOULD match the domain of the original query. + An example can be found in Appendix B. + + 3. If no NAPTR records are found, the requester directly queries for + one of the following SRV records: for Diameter over TCP, use + "_diameter._tcp.realm"; for Diameter over TLS, use + "_diameters._tcp.realm"; for Diameter over SCTP, use + "_diameter._sctp.realm"; for Diameter over DTLS, use + "_diameters._sctp.realm". If SRV records are found, then the + requester can perform address record query (A RR's and/or AAAA + + + + +Fajardo, et al. Standards Track [Page 59] + +RFC 6733 Diameter Base Protocol October 2012 + + + RR's) for the target hostname specified in the SRV records + following the rules given in [RFC2782]. If no SRV records are + found, the requester gives up. + + If the server is using a site certificate, the domain name in the + NAPTR query and the domain name in the replacement field MUST both be + valid based on the site certificate handed out by the server in the + TLS/TCP and DTLS/SCTP or Internet Key Exchange Protocol (IKE) + exchange. Similarly, the domain name in the SRV query and the domain + name in the target in the SRV record MUST both be valid based on the + same site certificate. Otherwise, an attacker could modify the DNS + records to contain replacement values in a different domain, and the + client could not validate whether this was the desired behavior or + the result of an attack. + + Also, the Diameter peer MUST check to make sure that the discovered + peers are authorized to act in its role. Authentication via IKE or + TLS/TCP and DTLS/SCTP, or validation of DNS RRs via DNSSEC is not + sufficient to conclude this. For example, a web server may have + obtained a valid TLS/TCP and DTLS/SCTP certificate, and secured RRs + may be included in the DNS, but this does not imply that it is + authorized to act as a Diameter server. + + Authorization can be achieved, for example, by the configuration of a + Diameter server Certification Authority (CA). The server CA issues a + certificate to the Diameter server, which includes an Object + Identifier (OID) to indicate the subject is a Diameter server in the + Extended Key Usage extension [RFC5280]. This certificate is then + used during TLS/TCP, DTLS/SCTP, or IKE security negotiation. + However, note that, at the time of writing, no Diameter server + Certification Authorities exist. + + A dynamically discovered peer causes an entry in the peer table (see + Section 2.6) to be created. Note that entries created via DNS MUST + expire (or be refreshed) within the DNS Time to Live (TTL). If a + peer is discovered outside of the local realm, a routing table entry + (see Section 2.7) for the peer's realm is created. The routing table + entry's expiration MUST match the peer's expiration value. + +5.3. 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 5.6). This message allows the discovery + of a peer's identity and its capabilities (protocol version number, + the identifiers of supported Diameter applications, security + mechanisms, etc.). + + + + +Fajardo, et al. Standards Track [Page 60] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 Application Ids in order to + ensure that unrecognized commands and/or AVPs are not unnecessarily + sent to a peer. + + A receiver of a Capabilities-Exchange-Request (CER) message that 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 2.4) MUST be interpreted + as having common applications with the peer. + + The receiver of the Capabilities-Exchange-Request (CER) MUST + determine common applications by computing the intersection of its + own set of supported Application Ids against all of the + Application-Id AVPs (Auth-Application-Id, Acct-Application-Id, and + Vendor-Specific-Application-Id) present in the CER. The value of the + Vendor-Id AVP in the Vendor-Specific-Application-Id MUST NOT be used + during computation. The sender of the Capabilities-Exchange-Answer + (CEA) SHOULD include all of its supported applications as a hint to + the receiver regarding all of its application capabilities. + + Diameter implementations SHOULD first attempt to establish a TLS/TCP + and DTLS/SCTP connection prior to the CER/CEA exchange. This + protects the capabilities information of both peers. To support + older Diameter implementations that do not fully conform to this + document, the transport security MAY still be negotiated via an + Inband-Security AVP. In this case, the receiver of a Capabilities- + Exchange-Request (CER) message that does not have any security + mechanisms in common with the sender MUST return a Capabilities- + Exchange-Answer (CEA) with the Result-Code AVP set to + DIAMETER_NO_COMMON_SECURITY and SHOULD disconnect the transport layer + connection. + + CERs received from unknown peers MAY be silently discarded, or a CEA + MAY be issued with the Result-Code AVP set to DIAMETER_UNKNOWN_PEER. + In both cases, the transport connection is closed. If the local + policy permits receiving CERs from unknown hosts, a successful CEA + MAY be returned. If a CER from an unknown peer is answered with a + successful CEA, the lifetime of the peer entry is equal to the + lifetime of the transport connection. In case of a transport + failure, all the pending transactions destined to the unknown peer + can be discarded. + + The CER and CEA messages MUST NOT be proxied, redirected, or relayed. + + + + +Fajardo, et al. Standards Track [Page 61] + +RFC 6733 Diameter Base Protocol October 2012 + + + Since the CER/CEA messages cannot be proxied, it is still possible + that an upstream agent will receive a message for which it has no + available peers to handle the application that corresponds to the + Command Code. In such instances, the 'E' bit is set in the answer + message (Section 7) with the Result-Code AVP set to + DIAMETER_UNABLE_TO_DELIVER to inform the downstream agent 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 Id). + +5.3.1. 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 + exchange local capabilities. Upon detection of a transport failure, + this message MUST NOT be sent to an alternate peer. + + When Diameter is run over SCTP [RFC4960] or DTLS/SCTP [RFC6083], + which allow for connections to span multiple interfaces and 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 + + <CER> ::= < 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 ] + * [ Inband-Security-Id ] + * [ Acct-Application-Id ] + * [ Vendor-Specific-Application-Id ] + [ Firmware-Revision ] + * [ AVP ] + + + + + + + +Fajardo, et al. Standards Track [Page 62] + +RFC 6733 Diameter Base Protocol October 2012 + + +5.3.2. Capabilities-Exchange-Answer + + The Capabilities-Exchange-Answer (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 [RFC4960] or DTLS/SCTP [RFC6083], + which allow 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 + + <CEA> ::= < Diameter Header: 257 > + { Result-Code } + { Origin-Host } + { Origin-Realm } + 1* { Host-IP-Address } + { Vendor-Id } + { Product-Name } + [ Origin-State-Id ] + [ Error-Message ] + [ Failed-AVP ] + * [ Supported-Vendor-Id ] + * [ Auth-Application-Id ] + * [ Inband-Security-Id ] + * [ Acct-Application-Id ] + * [ Vendor-Specific-Application-Id ] + [ Firmware-Revision ] + * [ AVP ] + +5.3.3. Vendor-Id AVP + + The Vendor-Id AVP (AVP Code 266) is of type Unsigned32 and contains + the IANA "SMI Network Management Private Enterprise Codes" + [ENTERPRISE] value assigned to the Diameter Software vendor. It is + envisioned that the combination of the Vendor-Id, Product-Name + (Section 5.3.7), and Firmware-Revision (Section 5.3.4) AVPs may + provide useful debugging information. + + A Vendor-Id value of zero in the CER or CEA message is reserved and + indicates that this field is ignored. + + + + + + + + +Fajardo, et al. Standards Track [Page 63] + +RFC 6733 Diameter Base Protocol October 2012 + + +5.3.4. 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. + +5.3.5. Host-IP-Address AVP + + The Host-IP-Address AVP (AVP Code 257) is of type Address 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 [RFC4960] or + DTLS/SCTP [RFC6083] MUST be advertised in the CER and CEA messages by + including a Host-IP-Address AVP for each address. + +5.3.6. 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" + [ENTERPRISE] value assigned to a vendor other than the device vendor + but including the application 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 AVPs defined by the vendor identified + in this AVP. The value of this AVP MUST NOT be set to zero. + Multiple instances of this AVP containing the same value SHOULD NOT + be sent. + +5.3.7. 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. + +5.4. Disconnecting Peer Connections + + When a Diameter node disconnects one of its transport connections, + its peer cannot know the reason for the disconnect and will most + likely assume that a connectivity problem occurred or that the peer + has rebooted. In these cases, the peer may periodically attempt to + reconnect, as stated in Section 2.1. In the event that the + disconnect was a result of either a shortage of internal resources or + simply that the node in question has no intentions of forwarding any + Diameter messages to the peer in the foreseeable future, a periodic + + + + +Fajardo, et al. Standards Track [Page 64] + +RFC 6733 Diameter Base Protocol October 2012 + + + connection request would not be welcomed. The Disconnection-Reason + AVP contains the reason the Diameter node issued the Disconnect-Peer- + Request message. + + The Disconnect-Peer-Request message is used by a Diameter node to + inform its peer of its intent to disconnect the transport layer and + that the peer shouldn't reconnect unless it has a valid reason to do + so (e.g., message to be forwarded). Upon receipt of the message, the + Disconnect-Peer-Answer message is returned, which SHOULD contain an + error if messages have recently been forwarded, and are likely in + flight, which would otherwise cause a race condition. + + The receiver of the Disconnect-Peer-Answer message initiates the + transport disconnect. The sender of the Disconnect-Peer-Answer + message should be able to detect the transport closure and clean up + the connection. + +5.4.1. Disconnect-Peer-Request + + The Disconnect-Peer-Request (DPR), indicated by the Command Code set + to 282 and the Command Flags' 'R' bit set, is sent to a peer to + inform it of its intentions to shut down the transport connection. + Upon detection of a transport failure, this message MUST NOT be sent + to an alternate peer. + + Message Format + + <DPR> ::= < Diameter Header: 282, REQ > + { Origin-Host } + { Origin-Realm } + { Disconnect-Cause } + * [ AVP ] + +5.4.2. Disconnect-Peer-Answer + + The Disconnect-Peer-Answer (DPA), indicated by the Command Code set + to 282 and the Command Flags' 'R' bit cleared, is sent as a response + to the Disconnect-Peer-Request message. Upon receipt of this + message, the transport connection is shut down. + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 65] + +RFC 6733 Diameter Base Protocol October 2012 + + + Message Format + + <DPA> ::= < Diameter Header: 282 > + { Result-Code } + { Origin-Host } + { Origin-Realm } + [ Error-Message ] + [ Failed-AVP ] + * [ AVP ] + + +5.4.3. Disconnect-Cause AVP + + The Disconnect-Cause AVP (AVP Code 273) is of type Enumerated. A + Diameter node MUST include this AVP in the Disconnect-Peer-Request + message to inform the peer of the reason for its intention to shut + down the transport connection. The following values are supported: + + REBOOTING 0 + A scheduled reboot is imminent. A receiver of a DPR with + above result code MAY attempt reconnection. + + BUSY 1 + The peer's internal resources are constrained, and it has + determined that the transport connection needs to be closed. + A receiver of a DPR with above result code SHOULD NOT attempt + reconnection. + + DO_NOT_WANT_TO_TALK_TO_YOU 2 + The peer has determined that it does not see a need for the + transport connection to exist, since it does not expect any + messages to be exchanged in the near future. A receiver of a + DPR with above result code SHOULD NOT attempt reconnection. + +5.5. 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 + agents, 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. + + + + + + + + +Fajardo, et al. Standards Track [Page 66] + +RFC 6733 Diameter Base Protocol October 2012 + + +5.5.1. 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 (see Section 5.5.3). + Upon detection of a transport failure, this message MUST NOT be sent + to an alternate peer. + + Message Format + + <DWR> ::= < Diameter Header: 280, REQ > + { Origin-Host } + { Origin-Realm } + [ Origin-State-Id ] + * [ AVP ] + +5.5.2. Device-Watchdog-Answer + + 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 + + <DWA> ::= < Diameter Header: 280 > + { Result-Code } + { Origin-Host } + { Origin-Realm } + [ Error-Message ] + [ Failed-AVP ] + [ Origin-State-Id ] + * [ AVP ] + +5.5.3. Transport Failure Algorithm + + The transport failure algorithm is defined in [RFC3539]. All + Diameter implementations MUST support the algorithm defined in that + specification in order to be compliant to the Diameter base protocol. + +5.5.4. Failover and 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". + + + + + + +Fajardo, et al. Standards Track [Page 67] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 + is used to match the answer with the queued request. + + When a transport failure is detected, if possible, all messages in + the queue are sent to an alternate agent with the T flag set. On + booting a Diameter client or agent, the T flag is also set on any + remaining records in non-volatile storage that are still waiting to + be transmitted. An example of a case where it is not possible to + 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 answer message with the 'E' bit set and the + Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER. + + It is important to note that multiple identical requests or answers + 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". + +5.6. Peer State Machine + + 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. + + This state machine is closely coupled with the state machine + described in [RFC3539], which is used to open, close, failover, + probe, and reopen transport connections. In particular, note that + [RFC3539] requires the use of watchdog messages to probe connections. + For Diameter, DWR and DWA messages are to be used. + + The I- prefix is used to represent the initiator (connecting) + connection, while the R- prefix 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. + + + +Fajardo, et al. Standards Track [Page 68] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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. + + For TLS/TCP and DTLS/SCTP usage, a TLS/TCP and DTLS/SCTP handshake + SHOULD begin when both ends are in the closed state prior to any + Diameter message exchanges. The TLS/TCP and DTLS/SCTP connection + SHOULD be established before sending any CER or CEA message to secure + and protect the capabilities information of both peers. The TLS/TCP + and DTLS/SCTP connection SHOULD be disconnected when the state + machine moves to the closed state. When connecting to responders + that do not conform to this document (i.e., older Diameter + implementations that are not prepared to received TLS/TCP and DTLS/ + SCTP connections in the closed state), the initial TLS/TCP and DTLS/ + SCTP connection attempt will fail. The initiator MAY then attempt to + connect via TCP or SCTP and initiate the TLS/TCP and DTLS/SCTP + handshake when both ends are in the open state. If the handshake is + successful, all further messages will be sent via TLS/TCP and DTLS/ + SCTP. If the handshake fails, both ends move to the closed state. + + 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. + + + + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 69] + +RFC 6733 Diameter Base Protocol October 2012 + + + state event action next state + ----------------------------------------------------------------- + Closed Start I-Snd-Conn-Req Wait-Conn-Ack + R-Conn-CER R-Accept, R-Open + Process-CER, + 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-Open + R-Snd-CEA + 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 + 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-Snd-DPR Closing + R-Rcv-DPR R-Snd-DPA Closing + R-Peer-Disc R-Disc Closed + + + + + + +Fajardo, et al. Standards Track [Page 70] + +RFC 6733 Diameter Base Protocol October 2012 + + + I-Open Send-Message I-Snd-Message I-Open + I-Rcv-Message Process I-Open + I-Rcv-DWR Process-DWR, I-Open + I-Snd-DWA + I-Rcv-DWA Process-DWA I-Open + R-Conn-CER R-Reject I-Open + Stop I-Snd-DPR Closing + I-Rcv-DPR I-Snd-DPA Closing + I-Peer-Disc I-Disc Closed + + Closing I-Rcv-DPA I-Disc Closed + R-Rcv-DPA R-Disc Closed + Timeout Error Closed + I-Peer-Disc I-Disc Closed + R-Peer-Disc R-Disc Closed + +5.6.1. 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 host and port + determine the identity of a Diameter peer; the source port of an + incoming connection is arbitrary. Upon receipt of a CER, the + identity of the connecting peer can be uniquely determined from the + Origin-Host. + + For this reason, a Diameter peer must employ logic separate from the + state machine to receive connection requests, accept them, and await + the CER. Once the CER arrives on a new connection, the Origin-Host + that 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 a 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 a 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 above. + +5.6.2. Events + + Transitions and actions in the automaton are caused by events. In + this section, we will ignore the I- and R- prefixes, since the actual + event would be identical, but it would occur on one of two possible + connections. + + + +Fajardo, et al. Standards Track [Page 71] + +RFC 6733 Diameter Base Protocol October 2012 + + + Start The Diameter application has signaled that a + connection should be initiated with the peer. + + R-Conn-CER An acknowledgement is received stating that the + transport connection has been established, and the + associated CER has arrived. + + Rcv-Conn-Ack A positive acknowledgement is received confirming that + the transport connection is established. + + Rcv-Conn-Nack A negative acknowledgement was received stating that + the transport connection was not established. + + 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 a CEA, from the peer was + received. + + Peer-Disc A disconnection indication from the peer was received. + + Rcv-DPR A DPR message from the peer was received. + + Rcv-DPA A DPA message 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, DPR, DPA, DWR, or DWA + was received. + + Stop The Diameter application has signaled that a + connection should be terminated (e.g., on system + shutdown). + +5.6.3. 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- prefixes, + since the actual action would be identical, but it would occur on one + of two possible connections. + + + +Fajardo, et al. Standards Track [Page 72] + +RFC 6733 Diameter Base Protocol October 2012 + + + Snd-Conn-Req A transport connection is initiated with the peer. + + 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-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 shut down, 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. + + Snd-DPR A DPR message is sent to the peer. + + Snd-DPA A DPA message is sent to the peer. + + Disc The transport layer connection is disconnected, + and local resources are freed. + + Elect An election occurs (see Section 5.6.4 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. + + + + + + + +Fajardo, et al. Standards Track [Page 73] + +RFC 6733 Diameter Base Protocol October 2012 + + +5.6.4. The Election Process + + The election is performed on the responder. The responder compares + the Origin-Host received in the CER with its own Origin-Host as two + streams of octets. If the local Origin-Host lexicographically + succeeds the received Origin-Host, a Win-Election event is issued + locally. Diameter identities are in ASCII form; therefore, the + lexical comparison is consistent with DNS case insensitivity, where + octets that fall in the ASCII range 'a' through 'z' MUST compare + equally to their uppercase counterparts between 'A' and 'Z'. See + Appendix D for interactions between the Diameter protocol and + Internationalized Domain Name (IDNs). + + The winner of the election MUST close the connection it initiated. + Historically, maintaining the responder side of a connection was more + efficient than maintaining the initiator side. However, current + practices makes this distinction irrelevant. + +6. Diameter Message Processing + + This section describes how Diameter requests and answers are created + and processed. + +6.1. Diameter Request Routing Overview + + A request is sent towards its final destination using one of the + following three combinations of the Destination-Realm and + Destination-Host AVPs: + + o A request that is not able to be proxied (such as a CER) MUST NOT + contain either Destination-Realm or Destination-Host AVPs. + + o 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. For + Diameter clients, the value of the Destination-Realm AVP MAY be + extracted from the User-Name AVP, or other methods. + + o Otherwise, 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: + + o Authentication requests that span multiple round trips. + + + + +Fajardo, et al. Standards Track [Page 74] + +RFC 6733 Diameter Base Protocol October 2012 + + + o 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. + + o 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 only forward a request to a host described in + the Destination-Host AVP if the host in question is included in its + peer table (see Section 2.6). Otherwise, the request is routed based + on the Destination-Realm only (see Section 6.1.6). + + When a message is received, the message is processed in the following + order: + + o If the message is destined for the local host, the procedures + listed in Section 6.1.4 are followed. + + o If the message is intended for a Diameter peer with whom the local + host is able to directly communicate, the procedures listed in + Section 6.1.5 are followed. This is known as "Request + Forwarding". + + o The procedure listed in Section 6.1.6 is followed, which is known + as "Request Routing". + + o If none of the above are successful, an answer is returned with + the Result-Code set to DIAMETER_UNABLE_TO_DELIVER, with the 'E' + bit set. + + For routing of Diameter messages to work within an administrative + domain, all Diameter nodes within the realm MUST be peers. + + The overview contained in this section (6.1) is intended to provide + general guidelines to Diameter developers. Implementations are free + to use different methods than the ones described here as long as they + conform to the requirements specified in Sections 6.1.1 through + 6.1.9. See Section 7 for more details on error handling. + +6.1.1. 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: + + + + + +Fajardo, et al. Standards Track [Page 75] + +RFC 6733 Diameter Base Protocol October 2012 + + + o the Command Code is set to the appropriate value; + + o the 'R' bit is set; + + o the End-to-End Identifier is set to a locally unique value; + + o the Origin-Host and Origin-Realm AVPs MUST be set to the + appropriate values, used to identify the source of the message; + and + + o the Destination-Host and Destination-Realm AVPs MUST be set to the + appropriate values, as described in Section 6.1. + +6.1.2. Sending a Request + + When sending a request, originated either locally or as the result of + a forwarding or routing operation, the following procedures SHOULD be + followed: + + o The Hop-by-Hop Identifier SHOULD be set to a locally unique value. + + o 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. + +6.1.3. Receiving Requests + + A relay or proxy agent MUST check for forwarding loops when receiving + requests. A loop is detected if the server finds its own identity in + a Route-Record AVP. When such an event occurs, the agent MUST answer + with the Result-Code AVP set to DIAMETER_LOOP_DETECTED. + +6.1.4. Processing Local Requests + + A request is known to be for local consumption when one of the + following conditions occurs: + + o The Destination-Host AVP contains the local host's identity; + + o 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 + + o Both the Destination-Host and the Destination-Realm are not + present. + + + + + +Fajardo, et al. Standards Track [Page 76] + +RFC 6733 Diameter Base Protocol October 2012 + + + When a request is locally processed, the rules in Section 6.2 should + be used to generate the corresponding answer. + +6.1.5. Request Forwarding + + Request forwarding is done using the Diameter peer table. The + Diameter peer table contains all of the peers with which the local + node is able to directly communicate. + + 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. + +6.1.6. Request Routing + + Diameter request message routing is done via realms and Application + Ids. A Diameter message that may be forwarded by Diameter agents + (proxies, redirect agents, or relay agents) MUST include the target + realm in the Destination-Realm AVP. Request routing SHOULD rely on + the Destination-Realm AVP and the Application Id present in the + request message header to aid in the routing decision. 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 + applications, and they MAY have a list of externally supported realms + and applications. When a request is received that includes a realm + and/or application that is not locally supported, the message is + routed to the peer configured in the routing table (see Section 2.7). + + Realm names and Application Ids are the minimum supported routing + criteria, additional information may be needed to support redirect + semantics. + +6.1.7. Predictive Loop Avoidance + + Before forwarding or routing a request, Diameter agents, in addition + to performing the processing described in Section 6.1.3, SHOULD check + for the presence of a candidate route's peer identity in any of the + Route-Record AVPs. In the event of the agent detecting the presence + of a candidate route's peer identity in a Route-Record AVP, the agent + MUST ignore such a route for the Diameter request message and attempt + alternate routes if any exist. In case all the candidate routes are + eliminated by the above criteria, the agent SHOULD return a + DIAMETER_UNABLE_TO_DELIVER message. + + + + + +Fajardo, et al. Standards Track [Page 77] + +RFC 6733 Diameter Base Protocol October 2012 + + +6.1.8. Redirecting Requests + + When a redirect agent receives a request whose routing entry is set + to REDIRECT, it MUST reply with an answer message with the 'E' bit + set, 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 a separate + Redirect-Host AVP. + + +------------------+ + | Diameter | + | Redirect Agent | + +------------------+ + ^ | 2. command + 'E' bit + 1. Request | | Result-Code = + [email protected] | | DIAMETER_REDIRECT_INDICATION + + | | Redirect-Host AVP(s) + | v + +-------------+ 3. Request +-------------+ + | example.com |------------->| example.net | + | Relay | | Diameter | + | Agent |<-------------| Server | + +-------------+ 4. Answer +-------------+ + + Figure 5: Diameter Redirect Agent + + The receiver of an answer message with the 'E' bit set and the + Result-Code AVP set to DIAMETER_REDIRECT_INDICATION uses the Hop-by- + Hop Identifier in the Diameter header to identify the request in the + pending message queue (see Section 5.5.4) that is to be redirected. + If no transport connection exists with the new peer, one is created, + and the request is sent directly to it. + + Multiple Redirect-Host AVPs are allowed. The receiver of the answer + message with the 'E' bit set selects exactly one of these hosts as + the destination of the redirected message. + + When the Redirect-Host-Usage AVP included in the answer message has a + non-zero value, a route entry for the redirect indications is created + and cached by the receiver. The redirect usage for such a route + entry is set by the value of Redirect-Host-Usage AVP and the lifetime + of the cached route entry is set by Redirect-Max-Cache-Time AVP + value. + + It is possible that multiple redirect indications can create multiple + cached route entries differing only in their redirect usage and the + peer to forward messages to. As an example, two(2) route entries + that are created by two(2) redirect indications results in two(2) + + + +Fajardo, et al. Standards Track [Page 78] + +RFC 6733 Diameter Base Protocol October 2012 + + + cached routes for the same realm and Application Id. However, one + has a redirect usage of ALL_SESSION, where matching requests will be + forwarded to one peer; the other has a redirect usage of ALL_REALM, + where request are forwarded to another peer. Therefore, an incoming + request that matches the realm and Application Id of both routes will + need additional resolution. In such a case, a routing precedence + rule MUST be used against the redirect usage value to resolve the + contention. The precedence rule can be found in Section 6.13. + +6.1.9. Relaying and Proxying Requests + + A relay or proxy agent MUST append a Route-Record AVP to all requests + forwarded. The AVP contains the identity of the peer from which the + request was received. + + 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. + + A relay or proxy agent MAY include the Proxy-Info AVP in requests if + it requires access to any local state information when the + corresponding response is received. The Proxy-Info AVP has security + implications as state information is distributed to other entities. + As such, it is RECOMMENDED that the content of the Proxy-Info AVP be + protected with cryptographic mechanisms, for example, by using a + keyed message digest such as HMAC-SHA1 [RFC2104]. Such a mechanism, + however, requires the management of keys, although only locally at + the Diameter server. Still, a full description of the management of + the keys used to protect the Proxy-Info AVP is beyond the scope of + this document. Below is a list of common recommendations: + + o The keys should be generated securely following the randomness + recommendations in [RFC4086]. + + o The keys and cryptographic protection algorithms should be at + least 128 bits in strength. + + o The keys should not be used for any other purpose than generating + and verifying instances of the Proxy-Info AVP. + + o The keys should be changed regularly. + + o The keys should be changed if the AVP format or cryptographic + protection algorithms change. + + The message is then forwarded to the next hop, as identified in the + routing table. + + + + +Fajardo, et al. Standards Track [Page 79] + +RFC 6733 Diameter Base Protocol October 2012 + + + Figure 6 provides an example of message routing using the procedures + listed in these sections. + + (Origin-Host=nas.example.net) (Origin-Host=nas.example.net) + (Origin-Realm=example.net) (Origin-Realm=example.net) + (Destination-Realm=example.com) (Destination-Realm=example.com) + (Route-Record=nas.example.net) + +------+ ------> +------+ ------> +------+ + | | (Request) | | (Request) | | + | NAS +-------------------+ DRL +-------------------+ HMS | + | | | | | | + +------+ <------ +------+ <------ +------+ + example.net (Answer) example.net (Answer) example.com + (Origin-Host=hms.example.com) (Origin-Host=hms.example.com) + (Origin-Realm=example.com) (Origin-Realm=example.com) + + Figure 6: Routing of Diameter messages + + Relay and proxy agents are not required to perform full inspection of + incoming messages. At a minimum, validation of the message header + and relevant routing AVPs has to be done when relaying messages. + Proxy agents may optionally perform more in-depth message validation + for applications in which it is interested. + +6.2. Diameter Answer Processing + + When a 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: + + o The same Hop-by-Hop Identifier in the request is used in the + answer. + + o The local host's identity is encoded in the Origin-Host AVP. + + o The Destination-Host and Destination-Realm AVPs MUST NOT be + present in the answer message. + + o The Result-Code AVP is added with its value indicating success or + failure. + + o If the Session-Id is present in the request, it MUST be included + in the answer. + + o Any Proxy-Info AVPs in the request MUST be added to the answer + message, in the same order they were present in the request. + + + + +Fajardo, et al. Standards Track [Page 80] + +RFC 6733 Diameter Base Protocol October 2012 + + + o The 'P' bit is set to the same value as the one in the request. + + o The same End-to-End identifier in the request is used in the + answer. + + Note that the error messages (see Section 7) are also subjected to + the above processing rules. + +6.2.1. 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 + requests. It SHOULD ignore answers received that do not match a + known Hop-by-Hop Identifier. + +6.2.2. Relaying and Proxying Answers + + If the answer is for a request that 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 modify the Result-Code + AVP to contain the appropriate error in the message destined towards + the access device as well as include the Error-Reporting-Host AVP; it + MUST also issue an STR on behalf of the access device towards the + Diameter server. + + The agent MUST then send the answer to the host that it received the + original request from. + +6.3. Origin-Host AVP + + The Origin-Host AVP (AVP Code 264) is of type DiameterIdentity, and + it MUST be present in all Diameter messages. This AVP identifies the + endpoint that originated the Diameter message. Relay agents MUST NOT + modify this AVP. + + + + + +Fajardo, et al. Standards Track [Page 81] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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. + + This AVP SHOULD be placed as close to the Diameter header as + possible. + +6.4. Origin-Realm AVP + + The Origin-Realm AVP (AVP Code 296) is of type DiameterIdentity. + 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. + +6.5. 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. + +6.6. Destination-Realm AVP + + The Destination-Realm AVP (AVP Code 283) is of type DiameterIdentity + and contains the realm to which the message is to be routed. 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. + + The CCF for a request message that includes the Destination-Realm AVP + SHOULD list the Destination-Realm AVP as a required AVP (an AVP + indicated as {AVP}); otherwise, the message is inherently a non- + routable message. + + + + +Fajardo, et al. Standards Track [Page 82] + +RFC 6733 Diameter Base Protocol October 2012 + + + This AVP SHOULD be placed as close to the Diameter header as + possible. + +6.7. Routing AVPs + + The AVPs defined in this section are Diameter AVPs used for routing + purposes. These AVPs change as Diameter messages are processed by + agents. + +6.7.1. 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 received in + the Origin-Host of the Capabilities Exchange message. + +6.7.2. Proxy-Info AVP + + The Proxy-Info AVP (AVP Code 284) is of type Grouped. This AVP + contains the identity and local state information of the Diameter + node that creates and adds it to a message. The Grouped Data field + has the following CCF grammar: + + Proxy-Info ::= < AVP Header: 284 > + { Proxy-Host } + { Proxy-State } + * [ AVP ] + +6.7.3. 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. + +6.7.4. Proxy-State AVP + + The Proxy-State AVP (AVP Code 33) is of type OctetString. It + contains state information that would otherwise be stored at the + Diameter entity that created it. As such, this AVP MUST be treated + as opaque data by other Diameter entities. + +6.8. 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 2.4). If + present in a message other than CER and CEA, the value of the Auth- + Application-Id AVP MUST match the Application Id present in the + Diameter message header. + + + + +Fajardo, et al. Standards Track [Page 83] + +RFC 6733 Diameter Base Protocol October 2012 + + +6.9. 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 2.4). If present in a message other than + CER and CEA, the value of the Acct-Application-Id AVP MUST match the + Application Id present in the Diameter message header. + +6.10. Inband-Security-Id AVP + + The Inband-Security-Id AVP (AVP Code 299) is of type Unsigned32 and + is used in order to advertise support of the security portion of the + application. The use of this AVP in CER and CEA messages is NOT + RECOMMENDED. Instead, discovery of a Diameter entity's security + capabilities can be done either through static configuration or via + Diameter Peer Discovery as described in Section 5.2. + + The following values are supported: + + + NO_INBAND_SECURITY 0 + + This peer does not support TLS/TCP and DTLS/SCTP. This is the + default value, if the AVP is omitted. + + TLS 1 + + This node supports TLS/TCP [RFC5246] and DTLS/SCTP [RFC6083] + security. + +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. Exactly one instance of either Auth- + Application-Id or Acct-Application-Id AVP MUST be present. The + Application Id carried by either Auth-Application-Id or Acct- + Application-Id AVP MUST comply with vendor-specific Application Id + assignment described in Section 11.3. It MUST also match the + Application Id present in the Diameter header except when used in a + CER or CEA message. + + The Vendor-Id AVP is an informational AVP pertaining to the vendor + who may have authorship of the vendor-specific Diameter application. + It MUST NOT be used as a means of defining a completely separate + vendor-specific Application Id space. + + + + + +Fajardo, et al. Standards Track [Page 84] + +RFC 6733 Diameter Base Protocol October 2012 + + + The Vendor-Specific-Application-Id AVP SHOULD be placed as close to + the Diameter header as possible. + + AVP Format + + <Vendor-Specific-Application-Id> ::= < AVP Header: 260 > + { Vendor-Id } + [ Auth-Application-Id ] + [ Acct-Application-Id ] + + A Vendor-Specific-Application-Id AVP MUST contain exactly one of + either Auth-Application-Id or Acct-Application-Id. If a Vendor- + Specific-Application-Id is received without one of these two AVPs, + then the recipient SHOULD issue an answer with a Result-Code set to + DIAMETER_MISSING_AVP. The answer SHOULD also include a Failed-AVP, + which MUST contain an example of an Auth-Application-Id AVP and an + Acct-Application-Id AVP. + + If a Vendor-Specific-Application-Id is received that contains both + Auth-Application-Id and Acct-Application-Id, then the recipient MUST + issue an answer with Result-Code set to + DIAMETER_AVP_OCCURS_TOO_MANY_TIMES. The answer MUST also include a + Failed-AVP, which MUST contain the received Auth-Application-Id AVP + and Acct-Application-Id AVP. + +6.12. Redirect-Host AVP + + The Redirect-Host AVP (AVP Code 292) is of type DiameterURI. One or + more instances of this AVP MUST be present if the answer message's + 'E' bit is set and the Result-Code AVP is set to + DIAMETER_REDIRECT_INDICATION. + + Upon receiving the above, the receiving Diameter node SHOULD forward + the request directly to one of the hosts identified in these AVPs. + The server contained in the selected Redirect-Host AVP SHOULD be used + for all messages matching the criteria set by the Redirect-Host-Usage + AVP. + +6.13. Redirect-Host-Usage AVP + + The Redirect-Host-Usage AVP (AVP Code 261) is of type Enumerated. + This AVP MAY be present in answer messages whose 'E' bit is set and + the Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION. + + When present, this AVP provides hints about how the routing entry + resulting from the Redirect-Host is to be used. The following values + are supported: + + + + +Fajardo, et al. Standards Track [Page 85] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 SHOULD be sent to the host specified in the + Redirect-Host AVP. + + ALL_REALM 2 + + All messages destined for the realm requested SHOULD 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 + SHOULD be sent to the host specified in the Redirect-Host AVP. + + ALL_APPLICATION 4 + + All messages for the application requested SHOULD 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 + Redirect-Host SHOULD be sent to the host specified in the + Redirect-Host AVP. + + ALL_USER 6 + + All messages for the user requested SHOULD be sent to the host + specified in the Redirect-Host AVP. + + When multiple cached routes are created by redirect indications and + they differ only in redirect usage and peers to forward requests to + (see Section 6.1.8), a precedence rule MUST be applied to the + redirect usage values of the cached routes during normal routing to + resolve contentions that may occur. The precedence rule is the order + that dictate which redirect usage should be considered before any + other as they appear. The order is as follows: + + + + + + + +Fajardo, et al. Standards Track [Page 86] + +RFC 6733 Diameter Base Protocol October 2012 + + + 1. ALL_SESSION + + 2. ALL_USER + + 3. REALM_AND_APPLICATION + + 4. ALL_REALM + + 5. ALL_APPLICATION + + 6. ALL_HOST + +6.14. Redirect-Max-Cache-Time AVP + + The Redirect-Max-Cache-Time AVP (AVP Code 262) is of type Unsigned32. + This AVP MUST be present in answer messages whose 'E' bit is set, + whose Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION, and + whose 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, SHOULD be + cached. Note that once a host is no longer reachable, any associated + cache, peer, and routing table entries MUST be deleted. + +7. Error Handling + + There are two different types of errors in Diameter; protocol errors + and application errors. A protocol error is one that occurs at the + base protocol level and MAY require per-hop attention (e.g., a + message routing error). Application errors, on the other hand, + 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 + only be present in answer messages whose 'E' bit is set. When a + request message is received that causes a protocol error, an answer + message is returned with the 'E' bit set, 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. + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 87] + +RFC 6733 Diameter Base Protocol October 2012 + + + 1. Request +---------+ Link Broken + +-------------------------->|Diameter |----///----+ + | +---------------------| | v + +------+--+ | 2. answer + 'E' set | Relay 2 | +--------+ + |Diameter |<-+ (Unable to Forward) +---------+ |Diameter| + | | | Home | + | Relay 1 |--+ +---------+ | Server | + +---------+ | 3. Request |Diameter | +--------+ + +-------------------->| | ^ + | Relay 3 |-----------+ + +---------+ + + Figure 7: Example of Protocol Error Causing Answer Message + + Figure 7 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 + answer message is returned with the 'E' bit set and the Result-Code + AVP set to 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 8: Example of Application Error Answer Message + + Figure 8 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; + therefore, the message would be forwarded back to the originator of + the request. + + In the case where the answer message itself contains errors, any + related session SHOULD be terminated by sending an STR or ASR + message. The Termination-Cause AVP in the STR MAY be filled with the + appropriate value to indicate the cause of the error. An application + MAY also send an application-specific request instead of an STR or + ASR message to signal the error in the case where no state is + maintained or to allow for some form of error recovery with the + corresponding Diameter entity. + + + +Fajardo, et al. Standards Track [Page 88] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 as follows: + + o A request with 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. + + o A request with 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. + + o A received command that is missing AVPs that are defined as + required in the commands CCF; examples are AVPs indicated as + {AVP}. 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 as expected in the missing AVP. The created AVP + is then added to the Failed-AVP AVP. + + The Result-Code AVP describes the error that the Diameter node + encountered in its processing. In case there are multiple errors, + the Diameter node MUST report only the first error it encountered + (detected possibly in some implementation-dependent order). The + specific errors that can be described by this AVP are described in + the following section. + +7.1. Result-Code AVP + + The Result-Code AVP (AVP Code 268) is of type Unsigned32 and + indicates whether a particular request was completed successfully or + an error occurred. All Diameter answer messages in IETF-defined + Diameter application specifications MUST include one Result-Code AVP. + A non-successful Result-Code AVP (one containing a non-2xxx value + other than DIAMETER_REDIRECT_INDICATION) 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 11.3.2). Diameter provides + the following classes of errors, all identified by the thousands + digit in the decimal notation: + + + + + + + +Fajardo, et al. Standards Track [Page 89] + +RFC 6733 Diameter Base Protocol October 2012 + + + o 1xxx (Informational) + + o 2xxx (Success) + + o 3xxx (Protocol Errors) + + o 4xxx (Transient Failures) + + o 5xxx (Permanent Failure) + + An unrecognized class (one whose first digit is not defined in this + section) MUST be handled as a permanent failure. + +7.1.1. 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 requires multiple round trips, and a subsequent request needs + to be issued in order for access to be granted. + +7.1.2. 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. + +7.1.3. Protocol Errors + + 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 answer messages whose 'E' bit is set. + + + + +Fajardo, et al. Standards Track [Page 90] + +RFC 6733 Diameter Base Protocol October 2012 + + + DIAMETER_COMMAND_UNSUPPORTED 3001 + + This error code is used when a Diameter entity receives a message + with a Command Code that it does not support. + + DIAMETER_UNABLE_TO_DELIVER 3002 + + This error is given when Diameter cannot deliver the message to + the destination, either because no host within the realm + supporting the required application was available to process the + request or because the Destination-Host AVP was given without the + associated Destination-Realm AVP. + + DIAMETER_REALM_NOT_SERVED 3003 + + The intended realm of the request is not recognized. + + DIAMETER_TOO_BUSY 3004 + + When returned, a Diameter node SHOULD attempt to send the message + to an alternate peer. This error MUST only be used when a + specific server is requested, and it cannot provide the requested + service. + + DIAMETER_LOOP_DETECTED 3005 + + An agent detected a loop while trying to get the message to the + intended recipient. 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_REDIRECT_INDICATION 3006 + + A redirect agent 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 information has + been added to the response. When set, the Redirect-Host AVP MUST + be present. + + DIAMETER_APPLICATION_UNSUPPORTED 3007 + + A request was sent for an application that is not supported. + + DIAMETER_INVALID_HDR_BITS 3008 + + A request was received whose bits in the Diameter header were set + either to an invalid combination or to a value that is + inconsistent with the Command Code's definition. + + + +Fajardo, et al. Standards Track [Page 91] + +RFC 6733 Diameter Base Protocol October 2012 + + + DIAMETER_INVALID_AVP_BITS 3009 + + A request was received that included an AVP whose flag bits are + set to an unrecognized value or that is inconsistent with the + AVP's definition. + + DIAMETER_UNKNOWN_PEER 3010 + + A CER was received from an unknown peer. + +7.1.4. 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. + Note that these errors MUST be used in answer messages whose 'E' bit + is not set. + + 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. + + ELECTION_LOST 4003 + + The peer has determined that it has lost the election process and + has therefore disconnected the transport connection. + +7.1.5. 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. Note that these errors SHOULD be used in answer messages + whose 'E' bit is not set. In error conditions where it is not + possible or efficient to compose application-specific answer grammar, + answer messages with the 'E' bit set and which comply to the grammar + described in Section 7.2 MAY also be used for permanent errors. + + + + + + + + +Fajardo, et al. Standards Track [Page 92] + +RFC 6733 Diameter Base Protocol October 2012 + + + DIAMETER_AVP_UNSUPPORTED 5001 + + The peer received a message that contained an AVP that is not + recognized or supported and was marked with the 'M' (Mandatory) + bit. A Diameter message with this error MUST contain one or more + Failed-AVP AVPs containing the AVPs that caused the failure. + + DIAMETER_UNKNOWN_SESSION_ID 5002 + + The request contained an unknown Session-Id. + + DIAMETER_AUTHORIZATION_REJECTED 5003 + + 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 5004 + + The request contained an AVP with an invalid value in its data + portion. A Diameter message indicating this error MUST include + the offending AVPs within a Failed-AVP AVP. + + DIAMETER_MISSING_AVP 5005 + + 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 5006 + + A request was received that cannot be authorized because the user + has already expended allowed resources. An example of this error + condition is when a user that is restricted to one dial-up PPP + port attempts to establish a second PPP connection. + + DIAMETER_CONTRADICTING_AVPS 5007 + + The Home Diameter server has detected AVPs in the request that + contradicted each other, and it is not willing to provide service + to the user. The Failed-AVP AVP MUST be present, which contain + the AVPs that contradicted each other. + + + + + + +Fajardo, et al. Standards Track [Page 93] + +RFC 6733 Diameter Base Protocol October 2012 + + + DIAMETER_AVP_NOT_ALLOWED 5008 + + 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 5009 + + 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_NO_COMMON_APPLICATION 5010 + + This error is returned by a Diameter node that receives a CER + whereby no applications are common between the CER sending peer + and the CER receiving peer. + + DIAMETER_UNSUPPORTED_VERSION 5011 + + This error is returned when a request was received, whose version + number is unsupported. + + DIAMETER_UNABLE_TO_COMPLY 5012 + + This error is returned when a request is rejected for unspecified + reasons. + + DIAMETER_INVALID_BIT_IN_HEADER 5013 + + This error is returned when a reserved bit in the Diameter header + is set to one (1) or the bits in the Diameter header are set + incorrectly. + + DIAMETER_INVALID_AVP_LENGTH 5014 + + 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. In cases where the erroneous AVP length + value exceeds the message length or is less than the minimum AVP + header length, it is sufficient to include the offending AVP + header and a zero filled payload of the minimum required length + for the payloads data type. If the AVP is a Grouped AVP, the + Grouped AVP header with an empty payload would be sufficient to + indicate the offending AVP. In the case where the offending AVP + header cannot be fully decoded when the AVP length is less than + + + + +Fajardo, et al. Standards Track [Page 94] + +RFC 6733 Diameter Base Protocol October 2012 + + + the minimum AVP header length, it is sufficient to include an + offending AVP header that is formulated by padding the incomplete + AVP header with zero up to the minimum AVP header length. + + DIAMETER_INVALID_MESSAGE_LENGTH 5015 + + This error is returned when a request is received with an invalid + message length. + + DIAMETER_INVALID_AVP_BIT_COMBO 5016 + + The request contained an AVP with which is not allowed to have the + given value in the AVP Flags field. A Diameter message indicating + this error MUST include the offending AVPs within a Failed-AVP + AVP. + + DIAMETER_NO_COMMON_SECURITY 5017 + + This error is returned when a CER message is received, and there + are no common security mechanisms supported between the peers. A + Capabilities-Exchange-Answer (CEA) message MUST be returned with + the Result-Code AVP set to DIAMETER_NO_COMMON_SECURITY. + +7.2. Error Bit + + The 'E' (Error Bit) in the Diameter header is set when the request + caused a protocol-related error (see Section 7.1.3). A message with + the 'E' bit MUST NOT be sent as a response to an answer message. + Note that a message with the 'E' bit set is still subjected to the + processing rules defined in Section 6.2. When set, the answer + message will not conform to the CCF specification for the command; + instead, it and will conform to the following CCF: + + Message Format + + <answer-message> ::= < Diameter Header: code, ERR [, PXY] > + 0*1< Session-Id > + { Origin-Host } + { Origin-Realm } + { Result-Code } + [ Origin-State-Id ] + [ Error-Message ] + [ Error-Reporting-Host ] + [ Failed-AVP ] + [ Experimental-Result ] + * [ Proxy-Info ] + * [ AVP ] + + + + +Fajardo, et al. Standards Track [Page 95] + +RFC 6733 Diameter Base Protocol October 2012 + + + Note that the code used in the header is the same than the one found + in the request message, but with the 'R' bit cleared and the 'E' bit + set. The 'P' bit in the header is set to the same value as the one + found in the request message. + +7.3. Error-Message AVP + + 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 an environment + where error messages are processed automatically. It SHOULD NOT be + expected that the content of this AVP be parsed by network entities. + +7.4. 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 it MUST be set when the + Result-Code AVP indicates a failure. + +7.5. 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. A Diameter answer message SHOULD contain an + instance of the Failed-AVP AVP that corresponds to the error + indicated by the Result-Code AVP. For practical purposes, this + Failed-AVP would typically refer to the first AVP processing error + that a Diameter node encounters. + + 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 tables in Section 10) or the presence of two or + more occurrences of an AVP that is restricted to 0, 1, or 0-1 + occurrences. + + A Diameter message SHOULD 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 omitted AVP will be added. If the failure + reason is an invalid AVP length where the reported length is less + + + +Fajardo, et al. Standards Track [Page 96] + +RFC 6733 Diameter Base Protocol October 2012 + + + than the minimum AVP header length or greater than the reported + message length, a copy of the offending AVP header and a zero-filled + payload of the minimum required length SHOULD be added. + + In the case where the offending AVP is embedded within a Grouped AVP, + the Failed-AVP MAY contain the grouped AVP, which in turn contains + the single offending AVP. The same method MAY be employed if the + grouped AVP itself is embedded in yet another grouped AVP and so on. + In this case, the Failed-AVP MAY contain the grouped AVP hierarchy up + to the single offending AVP. This enables the recipient to detect + the location of the offending AVP when embedded in a group. + + AVP Format + + <Failed-AVP> ::= < AVP Header: 279 > + 1* {AVP} + +7.6. Experimental-Result AVP + + The Experimental-Result AVP (AVP Code 297) is of type Grouped, and + indicates whether a particular vendor-specific request was completed + successfully or whether an error occurred. This AVP has the + following structure: + + AVP Format + + Experimental-Result ::= < AVP Header: 297 > + { Vendor-Id } + { Experimental-Result-Code } + + The Vendor-Id AVP (see Section 5.3.3) in this grouped AVP identifies + the vendor responsible for the assignment of the result code that + follows. All Diameter answer messages defined in vendor-specific + applications MUST include either one Result-Code AVP or one + Experimental-Result AVP. + +7.7. Experimental-Result-Code AVP + + The Experimental-Result-Code AVP (AVP Code 298) is of type Unsigned32 + and contains a vendor-assigned value representing the result of + processing the request. + + It is recommended that vendor-specific result codes follow the same + conventions given for the Result-Code AVP regarding the different + types of result codes and the handling of errors (for non-2xxx + values). + + + + + +Fajardo, et al. Standards Track [Page 97] + +RFC 6733 Diameter Base Protocol October 2012 + + +8. Diameter User Sessions + + In general, Diameter can provide two different types of services to + applications. The first involves authentication and authorization, + and it can 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 implement network + resources for a finite amount of time, and it is willing to extend + the authorization via a future request, it MUST add the + Authorization- Lifetime AVP to the answer message. The + Authorization-Lifetime AVP defines the maximum number of seconds a + user MAY make use of the resources before another authorization + request is expected by the server. The Auth-Grace-Period AVP + contains the number of seconds following the expiration of the + Authorization-Lifetime, after which the server will release all state + information related to the user's session. Note that if payment for + services is expected by the serving realm from the user's home realm, + the Authorization-Lifetime AVP, combined with the Auth-Grace-Period + AVP, implies the maximum length of the session for which the home + realm is willing to be fiscally responsible. Services provided past + the expiration of the Authorization-Lifetime and Auth-Grace-Period + AVPs are the responsibility of the access device. Of course, the + actual cost of services rendered is clearly outside the scope of the + protocol. + + An access device that does not expect to send a re-authorization or a + session termination request to the server MAY include the Auth- + Session-State AVP with the value set to NO_STATE_MAINTAINED as a hint + to the server. If the server accepts the hint, it agrees that since + no session termination message will be received once service to the + user is terminated, it cannot maintain state for the session. If the + answer message from the server contains a different value in the + Auth-Session-State AVP (or the default value if the AVP is absent), + the access device MUST follow the server's directives. Note that the + value NO_STATE_MAINTAINED MUST NOT be set in subsequent re- + authorization requests and answers. + + + + +Fajardo, et al. Standards Track [Page 98] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 + session termination messages are not used, since a session is + signaled as being terminated by issuing an accounting stop message. + + Diameter may also be used for services that cannot be easily + categorized as authentication, authorization, or accounting (e.g., + certain Third Generation Partnership Project Internet Multimedia + System (3GPP IMS) interfaces). In such cases, the finite state + machine defined in subsequent sections may not be applicable. + Therefore, the application itself MAY need to define its own finite + state machine. However, such application-specific state machines + SHOULD follow the general state machine framework outlined in this + document such as the use of Session-Id AVPs and the use of STR/STA, + ASR/ASA messages for stateful sessions. + +8.1. Authorization Session State Machine + + This section contains a set of finite state machines, which represent + the life cycle of Diameter sessions and which MUST be observed by all + Diameter implementations that make 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 IPv4, NASREQ). + + There are four different authorization session state machines + supported in the Diameter base protocol. The first two describe a + session in which the server is maintaining session state, indicated + by the value of the Auth-Session-State AVP (or its absence). One + describes the session from a client perspective, the other from a + server perspective. The second two state machines are used when the + server does not maintain session state. Here again, one describes + the session from a client perspective, the other from a server + perspective. + + When a session is moved to the Idle state, any resources that were + allocated for the particular session must be released. Any event not + listed in the state machines MUST be considered an error condition, + and an answer, if applicable, MUST be returned to the originator of + the message. + + + +Fajardo, et al. Standards Track [Page 99] + +RFC 6733 Diameter Base Protocol October 2012 + + + In the case that an application does not support re-auth, the state + transitions related to server-initiated re-auth, when both client and + server sessions maintain state (e.g., Send RAR, Pending, Receive + RAA), MAY be ignored. + + In the state table, the event "Failure to send X" means that the + Diameter agent is unable to send command X to the desired + destination. This could be due to the peer being down or due to the + peer sending back a transient failure or temporary protocol error + notification DIAMETER_TOO_BUSY or DIAMETER_LOOP_DETECTED in the + Result-Code AVP of the corresponding Answer command. The event 'X + successfully sent' is the complement of 'Failure to send X'. + + The following state machine is observed by a client when state is + maintained on the server: + + CLIENT, STATEFUL + State Event Action New State + --------------------------------------------------------------- + Idle Client or device requests Send Pending + access service- + specific + auth req + + Idle ASR Received Send ASA Idle + for unknown session with + Result-Code = + UNKNOWN_ + SESSION_ID + + Idle RAR Received Send RAA Idle + for unknown session with + Result-Code = + UNKNOWN_ + SESSION_ID + + Pending Successful service-specific Grant Open + authorization answer Access + received with default + Auth-Session-State value + + 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 + + + +Fajardo, et al. Standards Track [Page 100] + +RFC 6733 Diameter Base Protocol October 2012 + + + Pending Failed service-specific Clean up Idle + authorization answer received + + Open User or client device Send Open + requests access to service service- + specific + auth req + + Open Successful service-specific Provide Open + authorization answer received service + + Open Failed service-specific Discon. Idle + authorization answer user/device + received. + + Open RAR received and client will Send RAA Open + perform subsequent re-auth with + Result-Code = + SUCCESS + + Open RAR received and client will Send RAA Idle + not perform subsequent with + re-auth Result-Code != + SUCCESS, + Discon. + user/device + + Open Session-Timeout expires on Send STR Discon + access device + + Open ASR received, Send ASA Discon + client will comply with + with request to end the Result-Code = + session = SUCCESS, + Send STR. + + Open ASR Received, Send ASA Open + client will not comply with + with request to end the Result-Code != + session != SUCCESS + + Open Authorization-Lifetime + Send STR Discon + Auth-Grace-Period expires on + access device + + Discon ASR received Send ASA Discon + + + + + +Fajardo, et al. Standards Track [Page 101] + +RFC 6733 Diameter Base Protocol October 2012 + + + Discon STA received Discon. Idle + user/device + + The following state machine is observed by a server when it is + maintaining state for the session: + + SERVER, STATEFUL + State Event Action New State + --------------------------------------------------------------- + Idle Service-specific authorization Send Open + request received, and successful + user is authorized service- + specific + answer + + Idle Service-specific authorization Send Idle + request received, and failed + user is not authorized service- + specific + answer + + Open Service-specific authorization Send Open + request received, and user successful + is authorized service- + specific + answer + + Open Service-specific authorization Send Idle + request received, and user failed + is not authorized service- + specific + answer, + Clean up + + Open Home server wants to confirm Send RAR Pending + authentication and/or + authorization of the user + + Pending Received RAA with a failed Clean up Idle + Result-Code + + Pending Received RAA with Result-Code Update Open + = SUCCESS session + + Open Home server wants to Send ASR Discon + terminate the service + + + + + +Fajardo, et al. Standards Track [Page 102] + +RFC 6733 Diameter Base Protocol October 2012 + + + Open Authorization-Lifetime (and Clean up Idle + Auth-Grace-Period) expires + on home server + + Open Session-Timeout expires on Clean up Idle + home server + + Discon Failure to send ASR Wait, Discon + resend ASR + + Discon ASR successfully sent and Clean up Idle + ASA Received with Result-Code + + Not ASA Received None No Change + Discon + + Any STR Received Send STA, Idle + Clean up + + The following state machine is observed by a client when state is not + maintained on the server: + + CLIENT, STATELESS + State Event Action New State + --------------------------------------------------------------- + Idle Client or device requests Send Pending + access service- + specific + auth req + + Pending Successful service-specific Grant Open + authorization answer access + received with Auth-Session- + State set to + NO_STATE_MAINTAINED + + Pending Failed service-specific Clean up Idle + authorization answer + received + + Open Session-Timeout expires on Discon. Idle + access device user/device + + Open Service to user is terminated Discon. Idle + user/device + + + + + + +Fajardo, et al. Standards Track [Page 103] + +RFC 6733 Diameter Base Protocol October 2012 + + + The following state machine is observed by a server when it is not + maintaining state for the session: + + SERVER, STATELESS + State Event Action New State + --------------------------------------------------------------- + Idle Service-specific authorization Send Idle + request received, and service- + successfully processed specific + answer + +8.2. Accounting Session State Machine + + The following state machines MUST be supported for applications that + have an accounting portion or that require only accounting services. + The first state machine is to be observed by clients. + + See Section 9.7 for Accounting Command Codes and Section 9.8 for + Accounting AVPs. + + The server side in the accounting state machine depends in some cases + on the particular application. The Diameter base protocol defines a + default state machine that MUST be followed by all applications that + have not specified other state machines. This is the second state + machine in this section described below. + + The default server side state machine requires the reception of + accounting records in any order and at any time, and it does not + place any standards requirement on the processing of these records. + Implementations of Diameter may perform checking, ordering, + correlation, fraud detection, and other tasks based on these records. + AVPs may need to be inspected as a part of these tasks. The tasks + can happen either immediately after record reception or in a post- + processing phase. However, as these tasks are typically application + or even policy dependent, they are not standardized by the Diameter + specifications. Applications MAY define requirements on when to + accept accounting records based on the used value of Accounting- + Realtime-Required AVP, credit-limit checks, and so on. + + However, the Diameter base protocol defines one optional server side + state machine that MAY be followed by applications that require + keeping track of the session state at the accounting server. Note + that such tracking is incompatible with the ability to sustain long + duration connectivity problems. Therefore, the use of this state + machine is recommended only in applications where the value of the + Accounting-Realtime-Required AVP is DELIVER_AND_GRANT; hence, + accounting connectivity problems are required to cause the serviced + user to be disconnected. Otherwise, records produced by the client + + + +Fajardo, et al. Standards Track [Page 104] + +RFC 6733 Diameter Base Protocol October 2012 + + + may be lost by the server, which no longer accepts them after the + connectivity is re-established. This state machine is the third + state machine in this section. The state machine is supervised by a + supervision session timer Ts, whose value should be reasonably higher + than the Acct_Interim_Interval value. Ts MAY be set to two times the + value of the Acct_Interim_Interval so as to avoid the accounting + session in the Diameter server to change to Idle state in case of + short transient network failure. + + Any event not listed in the state machines MUST be considered as an + error condition, and a corresponding answer, if applicable, MUST be + returned to the originator of the message. + + In the state table, the event "Failure to send" means that the + Diameter client is unable to communicate with the desired + destination. This could be due to the peer being down, or due to the + peer sending back a transient failure or temporary protocol error + notification DIAMETER_OUT_OF_SPACE, DIAMETER_TOO_BUSY, or + DIAMETER_LOOP_DETECTED in the Result-Code AVP of the Accounting + Answer command. + + The event "Failed answer" means that the Diameter client received a + non-transient failure notification in the Accounting Answer command. + + Note that the action "Disconnect user/dev" MUST also have an effect + on the authorization session state table, e.g., cause the STR message + to be sent, if the given application has both authentication/ + authorization and accounting portions. + + The states PendingS, PendingI, PendingL, PendingE, and PendingB stand + for pending states to wait for an answer to an accounting request + related to a Start, Interim, Stop, Event, or buffered record, + respectively. + + CLIENT, ACCOUNTING + State Event Action New State + --------------------------------------------------------------- + Idle Client or device requests Send PendingS + access accounting + start req. + + Idle Client or device requests Send PendingE + a one-time service accounting + event req + + Idle Records in storage Send PendingB + record + + + + +Fajardo, et al. Standards Track [Page 105] + +RFC 6733 Diameter Base Protocol October 2012 + + + PendingS Successful accounting Open + start answer received + + PendingS Failure to send and buffer Store Open + space available and real time Start + not equal to DELIVER_AND_GRANT Record + + PendingS Failure to send and no buffer Open + space available and real time + equal to GRANT_AND_LOSE + + PendingS Failure to send and no Disconnect Idle + buffer space available and user/dev + real time not equal to + GRANT_AND_LOSE + + PendingS Failed accounting start answer Open + received and real time equal + to GRANT_AND_LOSE + + PendingS Failed accounting start answer Disconnect Idle + received and real time not user/dev + equal to GRANT_AND_LOSE + + PendingS User service terminated Store PendingS + stop + record + + Open Interim interval elapses Send PendingI + accounting + interim + record + + Open User service terminated Send PendingL + accounting + stop req. + + PendingI Successful accounting interim Open + answer received + + PendingI Failure to send and (buffer Store Open + space available or old interim + record can be overwritten) record + and real time not equal to + DELIVER_AND_GRANT + + + + + + +Fajardo, et al. Standards Track [Page 106] + +RFC 6733 Diameter Base Protocol October 2012 + + + PendingI Failure to send and no buffer Open + space available and real time + equal to GRANT_AND_LOSE + + PendingI Failure to send and no Disconnect Idle + buffer space available and user/dev + real time not equal to + GRANT_AND_LOSE + + PendingI Failed accounting interim Open + answer received and real time + equal to GRANT_AND_LOSE + + PendingI Failed accounting interim Disconnect Idle + answer received and user/dev + real time not equal to + GRANT_AND_LOSE + + PendingI User service terminated Store PendingI + stop + record + PendingE Successful accounting Idle + event answer received + + PendingE Failure to send and buffer Store Idle + space available event + record + + PendingE Failure to send and no buffer Idle + space available + + PendingE Failed accounting event answer Idle + received + + PendingB Successful accounting answer Delete Idle + received record + + PendingB Failure to send Idle + + PendingB Failed accounting answer Delete Idle + received record + + PendingL Successful accounting Idle + stop answer received + + PendingL Failure to send and buffer Store Idle + space available stop + record + + + +Fajardo, et al. Standards Track [Page 107] + +RFC 6733 Diameter Base Protocol October 2012 + + + PendingL Failure to send and no buffer Idle + space available + + PendingL Failed accounting stop answer Idle + received + + + SERVER, STATELESS ACCOUNTING + State Event Action New State + --------------------------------------------------------------- + + Idle Accounting start request Send Idle + received and successfully accounting + processed. start + answer + + Idle Accounting event request Send Idle + received and successfully accounting + processed. event + answer + + Idle Interim record received Send Idle + and successfully processed. accounting + interim + answer + + Idle Accounting stop request Send Idle + received and successfully accounting + processed stop answer + + Idle Accounting request received; Send Idle + no space left to store accounting + records answer; + Result-Code = + OUT_OF_ + SPACE + + + + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 108] + +RFC 6733 Diameter Base Protocol October 2012 + + + SERVER, STATEFUL ACCOUNTING + State Event Action New State + --------------------------------------------------------------- + + Idle Accounting start request Send Open + received and successfully accounting + processed. start + answer; + Start Ts + + Idle Accounting event request Send Idle + received and successfully accounting + processed. event + answer + Idle Accounting request received; Send Idle + no space left to store accounting + records answer; + Result-Code = + OUT_OF_ + SPACE + + Open Interim record received Send Open + and successfully processed. accounting + interim + answer; + Restart Ts + + Open Accounting stop request Send Idle + received and successfully accounting + processed stop answer; + Stop Ts + + Open Accounting request received; Send Idle + no space left to store accounting + records answer; + Result-Code = + OUT_OF_ + SPACE; + Stop Ts + + Open Session supervision timer Ts Stop Ts Idle + expired + + + + + + + + + +Fajardo, et al. Standards Track [Page 109] + +RFC 6733 Diameter Base Protocol October 2012 + + +8.3. 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 prepaid 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 an RAR message with the 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 server-initiated re-auth is + supported, since some applications do not allow access devices to + prompt the user for re-auth. + +8.3.1. 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 + + <RAR> ::= < Diameter Header: 258, REQ, PXY > + < Session-Id > + { Origin-Host } + { Origin-Realm } + { Destination-Realm } + { Destination-Host } + { Auth-Application-Id } + { Re-Auth-Request-Type } + [ User-Name ] + [ Origin-State-Id ] + * [ Proxy-Info ] + * [ Route-Record ] + * [ AVP ] + +8.3.2. 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 it indicates the disposition + of the request. + + + + +Fajardo, et al. Standards Track [Page 110] + +RFC 6733 Diameter Base Protocol October 2012 + + + A successful RAA message MUST be followed by an application-specific + authentication and/or authorization message. + + Message Format + + <RAA> ::= < Diameter Header: 258, PXY > + < Session-Id > + { Result-Code } + { Origin-Host } + { Origin-Realm } + [ User-Name ] + [ Origin-State-Id ] + [ Error-Message ] + [ Error-Reporting-Host ] + [ Failed-AVP ] + * [ Redirect-Host ] + [ Redirect-Host-Usage ] + [ Redirect-Max-Cache-Time ] + * [ Proxy-Info ] + * [ AVP ] + +8.4. Session Termination + + It is necessary for a Diameter server that authorized a session, for + which it is maintaining state, to be 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. For sessions whose state is not being + maintained, this section is not used. + + 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 + + + +Fajardo, et al. Standards Track [Page 111] + +RFC 6733 Diameter Base Protocol October 2012 + + + modify an authorization answer, converting the result from success to + failure, prior to forwarding the message to the access device. If + the answer did not contain an Auth-Session-State AVP with the value + NO_STATE_MAINTAINED, 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 and the Auth- + Grace-Period AVPs expire without receipt of a re-authorization + request, 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. + +8.4.1. 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 a Diameter + client or by a Diameter proxy to inform the Diameter server that an + authenticated and/or authorized session is being terminated. + + Message Format + + <STR> ::= < Diameter Header: 275, REQ, PXY > + < Session-Id > + { Origin-Host } + { Origin-Realm } + { Destination-Realm } + { Auth-Application-Id } + { Termination-Cause } + [ User-Name ] + [ Destination-Host ] + * [ Class ] + [ Origin-State-Id ] + * [ Proxy-Info ] + * [ Route-Record ] + * [ AVP ] + + + + + + + +Fajardo, et al. Standards Track [Page 112] + +RFC 6733 Diameter Base Protocol October 2012 + + +8.4.2. 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 it 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 + + <STA> ::= < Diameter Header: 275, PXY > + < Session-Id > + { Result-Code } + { Origin-Host } + { Origin-Realm } + [ User-Name ] + * [ Class ] + [ Error-Message ] + [ Error-Reporting-Host ] + [ Failed-AVP ] + [ Origin-State-Id ] + * [ Redirect-Host ] + [ Redirect-Host-Usage ] + [ Redirect-Max-Cache-Time ] + * [ Proxy-Info ] + * [ AVP ] + +8.5. 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 + (ASR). + + For example, the Diameter server that originally authorized the + session may be required to cause that session to be stopped for lack + of credit or other reasons that were not anticipated when the session + was first authorized. + + 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 + + + +Fajardo, et al. Standards Track [Page 113] + +RFC 6733 Diameter Base Protocol October 2012 + + + respond with an Abort-Session-Answer, including a Result-Code AVP to + indicate what action it took. + +8.5.1. 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 Diameter + server or any Diameter proxy to the access device that is providing + session service, to request that the session identified by the + Session-Id be stopped. + + Message Format + + <ASR> ::= < Diameter Header: 274, REQ, PXY > + < Session-Id > + { Origin-Host } + { Origin-Realm } + { Destination-Realm } + { Destination-Host } + { Auth-Application-Id } + [ User-Name ] + [ Origin-State-Id ] + * [ Proxy-Info ] + * [ Route-Record ] + * [ AVP ] + +8.5.2. 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 + 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, the Result-Code is set to DIAMETER_SUCCESS. If the + session is not currently active, the Result-Code is set to + DIAMETER_UNKNOWN_SESSION_ID. If the access device does not stop the + session for any other reason, the Result-Code is set to + DIAMETER_UNABLE_TO_COMPLY. + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 114] + +RFC 6733 Diameter Base Protocol October 2012 + + + Message Format + + <ASA> ::= < Diameter Header: 274, PXY > + < Session-Id > + { Result-Code } + { Origin-Host } + { Origin-Realm } + [ User-Name ] + [ Origin-State-Id ] + [ Error-Message ] + [ Error-Reporting-Host ] + [ Failed-AVP ] + * [ Redirect-Host ] + [ Redirect-Host-Usage ] + [ Redirect-Max-Cache-Time ] + * [ Proxy-Info ] + * [ AVP ] + +8.6. Inferring Session Termination from Origin-State-Id + + The Origin-State-Id is used to allow detection of terminated sessions + for which no STR would have been issued, due to unanticipated + shutdown of an access device. + + A Diameter client or access device increments the value of the + Origin-State-Id every time it is started or powered up. The new + Origin-State-Id is then sent in the CER/CEA message immediately upon + connection to the server. The Diameter server receiving the new + Origin-State-Id can determine whether the sending Diameter client had + abruptly shut down by comparing the old value of the Origin-State-Id + it has kept for that specific client is less than the new value and + whether it has un-terminated sessions originating from that client. + + An access device can also include the Origin-State-Id in request + messages other than the CER if there are relays or proxies in between + the access device and the server. In this case, however, the server + cannot discover that the access device has been restarted unless and + until it receives a new request from it. Therefore, this mechanism + is more opportunistic across proxies and relays. + + The Diameter server may assume that all sessions that were active + prior to detection of a client restart have been terminated. The + Diameter server MAY clean up all session state associated with such + lost sessions, and it MAY also issue STRs for all such lost sessions + that were authorized on upstream servers, to allow session state to + be cleaned up globally. + + + + + +Fajardo, et al. Standards Track [Page 115] + +RFC 6733 Diameter Base Protocol October 2012 + + +8.7. Auth-Request-Type AVP + + The Auth-Request-Type AVP (AVP Code 274) is of type Enumerated and is + included in application-specific auth requests to inform the peers + whether a user is to be authenticated only, authorized only, or both. + Note any value other than both MAY cause RADIUS interoperability + issues. The following values are defined: + + AUTHENTICATE_ONLY 1 + + The request being sent is for authentication only, and it MUST + contain the relevant application-specific authentication AVPs that + are needed by the Diameter server to authenticate the user. + + AUTHORIZE_ONLY 2 + + The request being sent is for authorization only, and it MUST + contain the application-specific authorization AVPs that are + necessary to identify the service being requested/offered. + + AUTHORIZE_AUTHENTICATE 3 + + The request contains a request for both authentication and + authorization. The request MUST include both the relevant + application-specific authentication information and authorization + information necessary to identify the service being requested/ + offered. + +8.8. Session-Id AVP + + The Session-Id AVP (AVP Code 263) is of type UTF8String and is used + to identify a specific session (see Section 8). 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). + + 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 it 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 4.3.1). The remainder of the + Session-Id is delimited by a ";" character, and it MAY be any + + + +Fajardo, et al. Standards Track [Page 116] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 in NTP format [RFC5905], and the low 32 bits + MAY be initialized to zero. 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 it may include a + modem's device Id, a Layer 2 address, timestamp, etc. + + Example, in which there is no optional value: + + accesspoint7.example.com;1876543210;523 + + Example, in which there is an optional value: + + accesspoint7.example.com;1876543210;523;[email protected] + + The Session-Id is created by the Diameter application initiating the + session, which, in most cases, is done by the client. Note that a + Session-Id MAY be used for both the authentication, authorization, + and accounting commands of a given application. + +8.9. 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. 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. + + A value of zero (0) means that immediate re-auth is necessary by the + access device. The absence of this AVP, or a value of all ones + (meaning all bits in the 32-bit field are set to one) means no re- + auth is expected. + + + +Fajardo, et al. Standards Track [Page 117] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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. + + An Authorization-Lifetime AVP MAY be present in re-authorization + messages, and it contains the number of seconds the user is + authorized to receive service from the time the re-auth answer + message is received by the access device. + + This AVP MAY be provided by the client as a hint of the maximum + lifetime that it is willing to accept. The server MUST return a + value that is equal to, or smaller than, the one provided by the + client. + +8.10. Auth-Grace-Period AVP + + The Auth-Grace-Period AVP (AVP Code 276) is of type Unsigned32 and + contains the number of seconds the Diameter server will wait + following the expiration of the Authorization-Lifetime AVP before + cleaning up resources for the session. + +8.11. Auth-Session-State AVP + + The Auth-Session-State AVP (AVP Code 277) is of type Enumerated and + specifies whether state is maintained for a particular session. The + client MAY include this AVP in requests as a hint to the server, but + the value in the server's answer message is binding. The following + values are supported: + + STATE_MAINTAINED 0 + + This value is used to specify that session state is being + maintained, and the access device MUST issue a session termination + message when service to the user is terminated. This is the + default value. + + NO_STATE_MAINTAINED 1 + + This value is used to specify that no session termination messages + will be sent by the access device upon expiration of the + Authorization-Lifetime. + +8.12. Re-Auth-Request-Type AVP + + The Re-Auth-Request-Type AVP (AVP Code 285) is of type Enumerated and + is included in application-specific auth answers to inform the client + of the action expected upon expiration of the Authorization-Lifetime. + + + + +Fajardo, et al. Standards Track [Page 118] + +RFC 6733 Diameter Base Protocol October 2012 + + + If the answer message contains an Authorization-Lifetime AVP with a + positive value, the Re-Auth-Request-Type AVP MUST be present in an + answer message. The following values are defined: + + AUTHORIZE_ONLY 0 + + An authorization only re-auth is expected upon expiration of the + Authorization-Lifetime. This is the default value if the AVP is + not present in answer messages that include the Authorization- + Lifetime. + + AUTHORIZE_AUTHENTICATE 1 + + An authentication and authorization re-auth is expected upon + expiration of the Authorization-Lifetime. + +8.13. Session-Timeout AVP + + The Session-Timeout AVP (AVP Code 27) [RFC2865] is of type Unsigned32 + and contains the maximum number of seconds of service to be provided + to the user before termination of the session. When both the + Session-Timeout and the Authorization-Lifetime AVPs are present in an + answer message, the former MUST be equal to or greater than the value + of the latter. + + A session that terminates on an access device due to the expiration + of the Session-Timeout MUST cause an STR to be issued, unless both + the access device and the home server had previously agreed that no + session termination messages would be sent (see Section 8). + + A Session-Timeout AVP MAY be present in a re-authorization answer + message, and it contains the remaining number of seconds from the + beginning of the re-auth. + + 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 + timeout that it is willing to accept. However, the server MAY return + a value that is equal to, or smaller than, the one provided by the + client. + +8.14. User-Name AVP + + The User-Name AVP (AVP Code 1) [RFC2865] is of type UTF8String, which + contains the User-Name, in a format consistent with the NAI + specification [RFC4282]. + + + + +Fajardo, et al. Standards Track [Page 119] + +RFC 6733 Diameter Base Protocol October 2012 + + +8.15. 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 currently assigned values for this AVP can be + found in the IANA registry for Termination-Cause AVP Values + [IANATCV]. + +8.16. 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 + 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 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. + +8.17. Session-Binding AVP + + The Session-Binding AVP (AVP Code 270) is of type Unsigned32, and it + 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 and Session-Termination-Request messages + for this session MUST be sent to the same authorization server. + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 120] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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, if known, MUST be present in all + accounting messages for this session. + +8.18. 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 + 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. + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 121] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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. + +8.19. 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. + +8.20. Class AVP + + The Class AVP (AVP Code 25) is of type OctetString and is used 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 + 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. + +8.21. Event-Timestamp AVP + + The Event-Timestamp (AVP Code 55) is of type Time and MAY be included + in an Accounting-Request and Accounting-Answer messages to record the + time that the reported event occurred, in seconds since January 1, + 1900 00:00 UTC. + + + + +Fajardo, et al. Standards Track [Page 122] + +RFC 6733 Diameter Base Protocol October 2012 + + +9. Accounting + + This accounting protocol is based on a server directed model with + capabilities for real-time delivery of accounting information. + Several fault resilience methods [RFC2975] have been built into the + protocol in order minimize loss of accounting data in various fault + situations and under different assumptions about the capabilities of + the used devices. + +9.1. 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 [RFC2975], 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. + Note, however, that even if at the Diameter layer, accounting + requests are processed one by one; transport protocols used under + Diameter typically batch several requests in the same packet under + heavy traffic conditions. This may be sufficient for many + applications. + + 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 Acct-Interim-Interval and Accounting-Realtime-Required AVPs to + control the operation of the Diameter peer operating as a client. + The Acct-Interim-Interval AVP, when present, instructs the Diameter + node acting as a client to produce accounting records continuously + even during a session. Accounting-Realtime-Required AVP is used to + control the behavior of the client when the transfer of accounting + records from the Diameter client is delayed or unsuccessful. + + The Diameter accounting server MAY override the interim interval or + the real-time requirements by including the Acct-Interim-Interval or + Accounting-Realtime-Required AVP in the Accounting-Answer message. + When one of these AVPs is present, the latest value received SHOULD + be used in further accounting activities for the same session. + + + + + + +Fajardo, et al. Standards Track [Page 123] + +RFC 6733 Diameter Base Protocol October 2012 + + +9.2. Protocol Messages + + A Diameter node that receives a successful authentication and/or + authorization message from the Diameter server SHOULD collect + accounting information for the session. The Accounting-Request + message is used to transmit the accounting information to the + Diameter 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. The value of the Accounting-Realtime-Required + AVP received earlier for the session in question may indicate that + the user's session has to be terminated when a rejected Accounting- + Request message was received. + +9.3. Accounting Application Extension and Requirements + + Each Diameter application (e.g., NASREQ, Mobile IP) SHOULD define its + service-specific AVPs that MUST be present in the Accounting-Request + message in a section titled "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 that section. + + Applications have the option of using one or both of the following + accounting application extension models: + + Split Accounting Service + + The accounting message will carry the Application Id of the + Diameter base accounting application (see Section 2.4). + Accounting messages may be routed to Diameter nodes other than the + corresponding Diameter application. These nodes might be + centralized accounting servers that provide accounting service for + multiple different Diameter applications. These nodes MUST + advertise the Diameter base accounting Application Id during + capabilities exchange. + + Coupled Accounting Service + + The accounting message will carry the Application Id of the + application that is using it. The application itself will process + the received accounting records or forward them to an accounting + server. There is no accounting application advertisement required + during capabilities exchange, and the accounting messages will be + routed the same way as any of the other application messages. + + In cases where an application does not define its own accounting + service, it is preferred that the split accounting model be used. + + + +Fajardo, et al. Standards Track [Page 124] + +RFC 6733 Diameter Base Protocol October 2012 + + +9.4. Fault Resilience + + Diameter base protocol mechanisms are used to overcome small message + loss and network faults of a 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 the 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. Appendix C + discusses duplicate detection needs and implementation issues. + + 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 start sending the records in the non-volatile memory + to the accounting server with the appropriate modifications in + termination cause, session length, and other relevant information in + the records. + + A further application of this protocol may include AVPs to control + the maximum number of accounting records that may 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 the oldest, undelivered, or as 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. + +9.5. Accounting Records + + In all accounting records, the Session-Id AVP MUST be present; the + User-Name AVP MUST be present if it is available to the Diameter + client. + + 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 + + + + + +Fajardo, et al. Standards Track [Page 125] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 not directed interim + accounting to be enabled for the session, two accounting records MUST + be generated for each service of type session. When the initial + Accounting-Request 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 the authorization server has directed interim accounting to be + enabled, the Diameter client MUST produce additional records between + the START_RECORD and STOP_RECORD, marked INTERIM_RECORD. The + production of these records is directed by Acct-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 on an access device for any given + session. + + A particular value of Accounting-Sub-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_RECORDs and a single + STOP_RECORD. A particular Diameter application specification MUST + define the type of sequences that MUST be used. + +9.6. Correlation of Accounting Records + + If an application uses accounting messages, it can correlate + accounting records with a specific application session by using the + Session-Id of the particular application session in the accounting + messages. Accounting messages MAY also use a different Session-Id + from that of the application sessions, in which case, other session- + related information is needed to perform correlation. + + In cases where an application requires multiple accounting sub- + sessions, an Accounting-Sub-Session-Id AVP is used to differentiate + each sub-session. The Session-Id would remain constant for all sub- + sessions and is used to correlate all the sub-sessions to a + particular application session. Note that receiving a STOP_RECORD + + + + +Fajardo, et al. Standards Track [Page 126] + +RFC 6733 Diameter Base Protocol October 2012 + + + with no Accounting-Sub-Session-Id AVP when sub-sessions were + originally used in the START_RECORD messages implies that all sub- + sessions are terminated. + + There are also cases where an application needs to correlate multiple + application sessions into a single accounting record; the accounting + record may span multiple different Diameter applications and sessions + used by the same user at a given time. In such cases, the Acct- + Multi-Session-Id AVP is used. The Acct-Multi-Session-Id AVP SHOULD + be signaled by the server to the access device (typically, during + authorization) when it determines that a request belongs to an + existing session. The access device MUST then include the Acct- + Multi-Session-Id AVP in all subsequent accounting messages. + + The Acct-Multi-Session-Id AVP MAY include the value of the original + Session-Id. Its contents are implementation specific, but the MUST + be globally unique across other Acct-Multi-Session-Ids 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 it 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. + +9.7. Accounting Command Codes + + This section defines Command Code values that MUST be supported by + all Diameter implementations that provide accounting services. + +9.7.1. Accounting-Request + + The Accounting-Request (ACR) 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. + + In addition to the AVPs listed below, Accounting-Request messages + SHOULD include service-specific accounting AVPs. + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 127] + +RFC 6733 Diameter Base Protocol October 2012 + + + Message Format + + <ACR> ::= < Diameter Header: 271, REQ, PXY > + < Session-Id > + { Origin-Host } + { Origin-Realm } + { Destination-Realm } + { Accounting-Record-Type } + { Accounting-Record-Number } + [ Acct-Application-Id ] + [ Vendor-Specific-Application-Id ] + [ User-Name ] + [ Destination-Host ] + [ Accounting-Sub-Session-Id ] + [ Acct-Session-Id ] + [ Acct-Multi-Session-Id ] + [ Acct-Interim-Interval ] + [ Accounting-Realtime-Required ] + [ Origin-State-Id ] + [ Event-Timestamp ] + * [ Proxy-Info ] + * [ Route-Record ] + * [ AVP ] + +9.7.2. Accounting-Answer + + The Accounting-Answer (ACA) 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 as the corresponding request. + + Only the target Diameter server, known as the home Diameter server, + SHOULD respond with the Accounting-Answer command. + + In addition to the AVPs listed below, Accounting-Answer messages + SHOULD include service-specific accounting AVPs. + + + + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 128] + +RFC 6733 Diameter Base Protocol October 2012 + + + Message Format + + <ACA> ::= < Diameter Header: 271, PXY > + < Session-Id > + { Result-Code } + { Origin-Host } + { Origin-Realm } + { Accounting-Record-Type } + { Accounting-Record-Number } + [ Acct-Application-Id ] + [ Vendor-Specific-Application-Id ] + [ User-Name ] + [ Accounting-Sub-Session-Id ] + [ Acct-Session-Id ] + [ Acct-Multi-Session-Id ] + [ Error-Message ] + [ Error-Reporting-Host ] + [ Failed-AVP ] + [ Acct-Interim-Interval ] + [ Accounting-Realtime-Required ] + [ Origin-State-Id ] + [ Event-Timestamp ] + * [ Proxy-Info ] + * [ AVP ] + +9.8. Accounting AVPs + + This section contains AVPs that describe accounting usage information + related to a specific session. + +9.8.1. 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 it is the only record of the service. + + + + + + + + + +Fajardo, et al. Standards Track [Page 129] + +RFC 6733 Diameter Base Protocol October 2012 + + + START_RECORD 2 + + 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. + + 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 done by the Acct-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. + +9.8.2. Acct-Interim-Interval AVP + + The Acct-Interim-Interval AVP (AVP Code 85) 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 Acct-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 + + + + + +Fajardo, et al. Standards Track [Page 130] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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. + +9.8.3. 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. + +9.8.4. Acct-Session-Id AVP + + The Acct-Session-Id AVP (AVP Code 44) is of type OctetString is only + used when RADIUS/Diameter translation occurs. This AVP contains the + contents of the RADIUS Acct-Session-Id attribute. + +9.8.5. Acct-Multi-Session-Id AVP + + The Acct-Multi-Session-Id AVP (AVP Code 50) is of type UTF8String, + following the format specified in Section 8.8. The Acct-Multi- + Session-Id AVP is used to link multiple related accounting sessions, + where each session would have a unique Session-Id but the same Acct- + Multi-Session-Id AVP. This AVP MAY be returned by the Diameter + server in an authorization answer, and it MUST be used in all + accounting messages for the given session. + +9.8.6. Accounting-Sub-Session-Id AVP + + The Accounting-Sub-Session-Id AVP (AVP Code 287) is of type + Unsigned64 and contains the accounting sub-session identifier. The + combination of the Session-Id and this AVP MUST be unique per sub- + session, and the value of this AVP MUST be monotonically increased by + one for all new sub-sessions. The absence of this AVP implies no + sub-sessions are in use, with the exception of an Accounting-Request + whose Accounting-Record-Type is set to STOP_RECORD. A STOP_RECORD + message with no Accounting-Sub-Session-Id AVP present will signal the + termination of all sub-sessions for a given Session-Id. + + + +Fajardo, et al. Standards Track [Page 131] + +RFC 6733 Diameter Base Protocol October 2012 + + +9.8.7. Accounting-Realtime-Required AVP + + The Accounting-Realtime-Required AVP (AVP Code 483) is of type + Enumerated and is sent from the Diameter home authorization server to + the Diameter client or in the Accounting-Answer from the accounting + server. The client uses information in this AVP to decide what to do + if the sending of accounting records to the accounting server has + been temporarily prevented due to, for instance, a network problem. + + DELIVER_AND_GRANT 1 + + The AVP with Value field set to DELIVER_AND_GRANT means that the + service MUST only be granted as long as there is a connection to + an accounting server. Note that the set of alternative accounting + servers are treated as one server in this sense. Having to move + the accounting record stream to a backup server is not a reason to + discontinue the service to the user. + + GRANT_AND_STORE 2 + + The AVP with Value field set to GRANT_AND_STORE means that service + SHOULD be granted if there is a connection, or as long as records + can still be stored as described in Section 9.4. + + This is the default behavior if the AVP isn't included in the + reply from the authorization server. + + GRANT_AND_LOSE 3 + + The AVP with Value field set to GRANT_AND_LOSE means that service + SHOULD be granted even if the records cannot be delivered or + stored. + +10. AVP Occurrence Tables + + The following tables present the AVPs defined in this document and + specify in which Diameter messages they MAY or MAY NOT be present. + AVPs that occur only inside a Grouped AVP are not shown in these + tables. + + The tables use 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. + + + + + +Fajardo, et al. Standards Track [Page 132] + +RFC 6733 Diameter Base Protocol October 2012 + + + 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 one 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. + +10.1. 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|DPR|DPA|DWR|DWA|RAR|RAA|ASR|ASA|STR|STA| + --------------------+---+---+---+---+---+---+---+---+---+---+---+---+ + Acct-Interim- |0 |0 |0 |0 |0 |0 |0-1|0 |0 |0 |0 |0 | + Interval | | | | | | | | | | | | | + Accounting-Realtime-|0 |0 |0 |0 |0 |0 |0-1|0 |0 |0 |0 |0 | + Required | | | | | | | | | | | | | + Acct-Application-Id |0+ |0+ |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Auth-Application-Id |0+ |0+ |0 |0 |0 |0 |1 |0 |1 |0 |1 |0 | + Auth-Grace-Period |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Auth-Request-Type |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Auth-Session-State |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Authorization- |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Lifetime | | | | | | | | | | | | | + Class |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0+ |0+ | + Destination-Host |0 |0 |0 |0 |0 |0 |1 |0 |1 |0 |0-1|0 | + Destination-Realm |0 |0 |0 |0 |0 |0 |1 |0 |1 |0 |1 |0 | + Disconnect-Cause |0 |0 |1 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Error-Message |0 |0-1|0 |0-1|0 |0-1|0 |0-1|0 |0-1|0 |0-1| + Error-Reporting-Host|0 |0 |0 |0 |0 |0 |0 |0-1|0 |0-1|0 |0-1| + Failed-AVP |0 |0-1|0 |0-1|0 |0-1|0 |0-1|0 |0-1|0 |0-1| + Firmware-Revision |0-1|0-1|0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Host-IP-Address |1+ |1+ |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Inband-Security-Id |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Multi-Round-Time-Out|0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + + + + + + + + + + +Fajardo, et al. Standards Track [Page 133] + +RFC 6733 Diameter Base Protocol October 2012 + + + Origin-Host |1 |1 |1 |1 |1 |1 |1 |1 |1 |1 |1 |1 | + Origin-Realm |1 |1 |1 |1 |1 |1 |1 |1 |1 |1 |1 |1 | + Origin-State-Id |0-1|0-1|0 |0 |0-1|0-1|0-1|0-1|0-1|0-1|0-1|0-1| + Product-Name |1 |1 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Proxy-Info |0 |0 |0 |0 |0 |0 |0+ |0+ |0+ |0+ |0+ |0+ | + Redirect-Host |0 |0 |0 |0 |0 |0 |0 |0+ |0 |0+ |0 |0+ | + Redirect-Host-Usage |0 |0 |0 |0 |0 |0 |0 |0-1|0 |0-1|0 |0-1| + Redirect-Max-Cache- |0 |0 |0 |0 |0 |0 |0 |0-1|0 |0-1|0 |0-1| + Time | | | | | | | | | | | | | + Result-Code |0 |1 |0 |1 |0 |1 |0 |1 |0 |1 |0 |1 | + Re-Auth-Request-Type|0 |0 |0 |0 |0 |0 |1 |0 |0 |0 |0 |0 | + Route-Record |0 |0 |0 |0 |0 |0 |0+ |0 |0+ |0 |0+ |0 | + Session-Binding |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Session-Id |0 |0 |0 |0 |0 |0 |1 |1 |1 |1 |1 |1 | + Session-Server- |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Failover | | | | | | | | | | | | | + Session-Timeout |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Supported-Vendor-Id |0+ |0+ |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Termination-Cause |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 |1 |0 | + User-Name |0 |0 |0 |0 |0 |0 |0-1|0-1|0-1|0-1|0-1|0-1| + Vendor-Id |1 |1 |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Vendor-Specific- |0+ |0+ |0 |0 |0 |0 |0 |0 |0 |0 |0 |0 | + Application-Id | | | | | | | | | | | | | + --------------------+---+---+---+---+---+---+---+---+---+---+---+---+ + +10.2. 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. These + AVP occurrence requirements are guidelines, which may be expanded, + and/or overridden by application-specific requirements in the + Diameter applications documents. + + + + + + + + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 134] + +RFC 6733 Diameter Base Protocol October 2012 + + + +-----------+ + | Command | + | Code | + +-----+-----+ + Attribute Name | ACR | ACA | + ------------------------------+-----+-----+ + Acct-Interim-Interval | 0-1 | 0-1 | + Acct-Multi-Session-Id | 0-1 | 0-1 | + Accounting-Record-Number | 1 | 1 | + Accounting-Record-Type | 1 | 1 | + Acct-Session-Id | 0-1 | 0-1 | + Accounting-Sub-Session-Id | 0-1 | 0-1 | + Accounting-Realtime-Required | 0-1 | 0-1 | + Acct-Application-Id | 0-1 | 0-1 | + Auth-Application-Id | 0 | 0 | + Class | 0+ | 0+ | + Destination-Host | 0-1 | 0 | + Destination-Realm | 1 | 0 | + Error-Reporting-Host | 0 | 0+ | + Event-Timestamp | 0-1 | 0-1 | + Failed-AVP | 0 | 0-1 | + Origin-Host | 1 | 1 | + Origin-Realm | 1 | 1 | + Proxy-Info | 0+ | 0+ | + Route-Record | 0+ | 0 | + Result-Code | 0 | 1 | + Session-Id | 1 | 1 | + Termination-Cause | 0 | 0 | + User-Name | 0-1 | 0-1 | + Vendor-Specific-Application-Id| 0-1 | 0-1 | + ------------------------------+-----+-----+ + +11. IANA Considerations + + This section provides guidance to the Internet Assigned Numbers + Authority (IANA) regarding registration of values related to the + Diameter protocol, in accordance with [RFC5226]. Existing IANA + registries and assignments put in place by RFC 3588 remain the same + unless explicitly updated or deprecated in this section. + +11.1. AVP Header + + As defined in Section 4, the AVP header contains three fields that + require IANA namespace management: the AVP Code, Vendor-ID, and Flags + fields. + + + + + + +Fajardo, et al. Standards Track [Page 135] + +RFC 6733 Diameter Base Protocol October 2012 + + +11.1.1. AVP Codes + + There are multiple namespaces. Vendors can have their own AVP Codes + namespace that will be identified by their Vendor-ID (also known as + Enterprise-Number), and they control the assignments of their vendor- + specific AVP Codes within their own namespace. The absence of a + Vendor-ID or a Vendor-ID value of zero (0) identifies the IETF AVP + Codes namespace, which is under IANA control. The AVP Codes and + sometimes possible values in an AVP are controlled and maintained by + IANA. AVP Code 0 is not used. AVP Codes 1-255 are managed + separately as RADIUS Attribute Types. Where a Vendor-Specific AVP is + implemented by more than one vendor, allocation of global AVPs should + be encouraged instead. + + AVPs may be allocated following Expert Review (by a Designated + Expert) with Specification Required [RFC5226]. A block allocation + (release of more than three AVPs at a time for a given purpose) + requires IETF Review [RFC5226]. + +11.1.2. AVP Flags + + Section 4.1 describes the existing AVP Flags. The remaining bits can + only be assigned via a Standards Action [RFC5226]. + +11.2. Diameter Header + +11.2.1. Command Codes + + For the Diameter header, the Command Code namespace allocation has + changed. The new allocation rules are as follows: + + The Command Code values 256 - 8,388,607 (0x100 to 0x7fffff) are + for permanent, standard commands, allocated by IETF Review + [RFC5226]. + + The values 8,388,608 - 16,777,213 (0x800000 - 0xfffffd) are + reserved for vendor-specific Command Codes, to be allocated on a + First Come, First Served basis by IANA [RFC5226]. The request to + IANA for a Vendor-Specific Command Code SHOULD include a reference + to a publicly available specification that documents the command + in sufficient detail to aid in interoperability between + independent implementations. If the specification cannot be made + publicly available, the request for a vendor-specific Command Code + MUST include the contact information of persons and/or entities + responsible for authoring and maintaining the command. + + + + + + +Fajardo, et al. Standards Track [Page 136] + +RFC 6733 Diameter Base Protocol October 2012 + + + The values 16,777,214 and 16,777,215 (hexadecimal values 0xfffffe + - 0xffffff) are reserved for experimental commands. As these + codes are only for experimental and testing purposes, no guarantee + is made for interoperability between Diameter peers using + experimental commands. + +11.2.2. Command Flags + + Section 3 describes the existing Command Flags field. The remaining + bits can only be assigned via a Standards Action [RFC5226]. + +11.3. AVP Values + + For AVP values, the Experimental-Result-Code AVP value allocation has + been added; see Section 11.3.1. The old AVP value allocation rule, + IETF Consensus, has been updated to IETF Review as per [RFC5226], and + affected AVPs are listed as reminders. + +11.3.1. Experimental-Result-Code AVP + + Values for this AVP are purely local to the indicated vendor, and no + IANA registry is maintained for them. + +11.3.2. Result-Code AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.3. Accounting-Record-Type AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.4. Termination-Cause AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.5. Redirect-Host-Usage AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.6. Session-Server-Failover AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.7. Session-Binding AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + + + + + +Fajardo, et al. Standards Track [Page 137] + +RFC 6733 Diameter Base Protocol October 2012 + + +11.3.8. Disconnect-Cause AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.9. Auth-Request-Type AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.10. Auth-Session-State AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.11. Re-Auth-Request-Type AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.12. Accounting-Realtime-Required AVP Values + + New values are available for assignment via IETF Review [RFC5226]. + +11.3.13. Inband-Security-Id AVP (code 299) + + The use of this AVP has been deprecated. + +11.4. _diameters Service Name and Port Number Registration + + IANA has registered the "_diameters" service name and assigned port + numbers for TLS/TCP and DTLS/SCTP according to the guidelines given + in [RFC6335]. + + Service Name: _diameters + + Transport Protocols: TCP, SCTP + + Assignee: IESG <[email protected]> + + Contact: IETF Chair <[email protected]> + + Description: Diameter over TLS/TCP and DTLS/SCTP + + Reference: RFC 6733 + + Port Number: 5868, from the User Range + + + + + + + + +Fajardo, et al. Standards Track [Page 138] + +RFC 6733 Diameter Base Protocol October 2012 + + +11.5. SCTP Payload Protocol Identifiers + + Two SCTP payload protocol identifiers have been registered in the + SCTP Payload Protocol Identifiers registry: + + + Value | SCTP Payload Protocol Identifier + -------|----------------------------------- + 46 | Diameter in a SCTP DATA chunk + 47 | Diameter in a DTLS/SCTP DATA chunk + + +11.6. S-NAPTR Parameters + + The following tag has been registered in the S-NAPTR Application + Protocol Tags registry: + + Tag | Protocol + -------------------|--------- + diameter.dtls.sctp | DTLS/SCTP + +12. 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. + + 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 Realm Names, and the address of the peer to which the + message must be forwarded. 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 + connection exists. The recommended value is 30 seconds. + + + +Fajardo, et al. Standards Track [Page 139] + +RFC 6733 Diameter Base Protocol October 2012 + + +13. Security Considerations + + The Diameter base protocol messages SHOULD be secured by using TLS + [RFC5246] or DTLS/SCTP [RFC6083]. Additional security mechanisms + such as IPsec [RFC4301] MAY also be deployed to secure connections + between peers. However, all Diameter base protocol implementations + MUST support the use of TLS/TCP and DTLS/SCTP, and the Diameter + protocol MUST NOT be used without one of TLS, DTLS, or IPsec. + + If a Diameter connection is to be protected via TLS/TCP and DTLS/SCTP + or IPsec, then TLS/TCP and DTLS/SCTP or IPsec/IKE SHOULD begin prior + to any Diameter message exchange. All security parameters for TLS/ + TCP and DTLS/SCTP or IPsec are configured independent of the Diameter + protocol. All Diameter messages will be sent through the TLS/TCP and + DTLS/SCTP or IPsec connection after a successful setup. + + For TLS/TCP and DTLS/SCTP connections to be established in the open + state, the CER/CEA exchange MUST include an Inband-Security-ID AVP + with a value of TLS/TCP and DTLS/SCTP. The TLS/TCP and DTLS/SCTP + handshake will begin when both ends successfully reach the open + state, after completion of the CER/CEA exchange. If the TLS/TCP and + DTLS/SCTP handshake is successful, all further messages will be sent + via TLS/TCP and DTLS/SCTP. If the handshake fails, both ends MUST + move to the closed state. See Section 13.1 for more details. + +13.1. TLS/TCP and DTLS/SCTP Usage + + Diameter nodes using TLS/TCP and DTLS/SCTP for security MUST mutually + authenticate as part of TLS/TCP and DTLS/SCTP session establishment. + In order to ensure mutual authentication, the Diameter node acting as + the TLS/TCP and DTLS/SCTP server MUST request a certificate from the + Diameter node acting as TLS/TCP and DTLS/SCTP client, and the + Diameter node acting as the TLS/TCP and DTLS/SCTP client MUST be + prepared to supply a certificate on request. + + Diameter nodes MUST be able to negotiate the following TLS/TCP and + DTLS/SCTP cipher suites: + + TLS_RSA_WITH_RC4_128_MD5 + TLS_RSA_WITH_RC4_128_SHA + TLS_RSA_WITH_3DES_EDE_CBC_SHA + + Diameter nodes SHOULD be able to negotiate the following TLS/TCP and + DTLS/SCTP cipher suite: + + TLS_RSA_WITH_AES_128_CBC_SHA + + + + + +Fajardo, et al. Standards Track [Page 140] + +RFC 6733 Diameter Base Protocol October 2012 + + + Note that it is quite possible that support for the + TLS_RSA_WITH_AES_128_CBC_SHA cipher suite will be REQUIRED at some + future date. Diameter nodes MAY negotiate other TLS/TCP and DTLS/ + SCTP cipher suites. + + If public key certificates are used for Diameter security (for + example, with TLS), the value of the expiration times in the routing + and peer tables MUST NOT be greater than the expiry time in the + relevant certificates. + +13.2. Peer-to-Peer Considerations + + As with any peer-to-peer protocol, proper configuration of the trust + model within a Diameter peer is essential to security. When + certificates are used, it is necessary to configure the root + certificate authorities trusted by the Diameter peer. These root CAs + are likely to be unique to Diameter usage and distinct from the root + CAs that might be trusted for other purposes such as Web browsing. + In general, it is expected that those root CAs will be configured so + as to reflect the business relationships between the organization + hosting the Diameter peer and other organizations. As a result, a + Diameter peer will typically not be configured to allow connectivity + with any arbitrary peer. With certificate authentication, Diameter + peers may not be known beforehand and therefore peer discovery may be + required. + +13.3. AVP Considerations + + Diameter AVPs often contain security-sensitive data; for example, + user passwords and location data, network addresses and cryptographic + keys. The following AVPs defined in this document are considered to + be security-sensitive: + + o Acct-Interim-Interval + + o Accounting-Realtime-Required + + o Acct-Multi-Session-Id + + o Accounting-Record-Number + + o Accounting-Record-Type + + o Accounting-Session-Id + + o Accounting-Sub-Session-Id + + o Class + + + +Fajardo, et al. Standards Track [Page 141] + +RFC 6733 Diameter Base Protocol October 2012 + + + o Session-Id + + o Session-Binding + + o Session-Server-Failover + + o User-Name + + Diameter messages containing these or any other AVPs considered to be + security-sensitive MUST only be sent protected via mutually + authenticated TLS or IPsec. In addition, those messages MUST NOT be + sent via intermediate nodes unless there is end-to-end security + between the originator and recipient or the originator has locally + trusted configuration that indicates that end-to-end security is not + needed. For example, end-to-end security may not be required in the + case where an intermediary node is known to be operated as part of + the same administrative domain as the endpoints so that an ability to + successfully compromise the intermediary would imply a high + probability of being able to compromise the endpoints as well. Note + that no end-to-end security mechanism is specified in this document. + +14. References + +14.1. Normative References + + [FLOATPOINT] + Institute of Electrical and Electronics Engineers, "IEEE + Standard for Binary Floating-Point Arithmetic, ANSI/IEEE + Standard 754-1985", August 1985. + + [IANAADFAM] + IANA, "Address Family Numbers", + <http://www.iana.org/assignments/address-family-numbers>. + + [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, + September 1981. + + [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, + RFC 793, September 1981. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode + for Internationalized Domain Names in Applications + (IDNA)", RFC 3492, March 2003. + + + + + +Fajardo, et al. Standards Track [Page 142] + +RFC 6733 Diameter Base Protocol October 2012 + + + [RFC3539] Aboba, B. and J. Wood, "Authentication, Authorization and + Accounting (AAA) Transport Profile", RFC 3539, June 2003. + + [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO + 10646", STD 63, RFC 3629, November 2003. + + [RFC3958] Daigle, L. and A. Newton, "Domain-Based Application + Service Location Using SRV RRs and the Dynamic Delegation + Discovery Service (DDDS)", RFC 3958, January 2005. + + [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform + Resource Identifier (URI): Generic Syntax", STD 66, + RFC 3986, January 2005. + + [RFC4004] Calhoun, P., Johansson, T., Perkins, C., Hiller, T., and + P. McCann, "Diameter Mobile IPv4 Application", RFC 4004, + August 2005. + + [RFC4005] Calhoun, P., Zorn, G., Spence, D., and D. Mitton, + "Diameter Network Access Server Application", RFC 4005, + August 2005. + + [RFC4006] Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J. + Loughney, "Diameter Credit-Control Application", RFC 4006, + August 2005. + + [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness + Requirements for Security", BCP 106, RFC 4086, June 2005. + + [RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The + Network Access Identifier", RFC 4282, December 2005. + + [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing + Architecture", RFC 4291, February 2006. + + [RFC4960] Stewart, R., "Stream Control Transmission Protocol", + RFC 4960, September 2007. + + [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an + IANA Considerations Section in RFCs", BCP 26, RFC 5226, + May 2008. + + [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", STD 68, RFC 5234, January 2008. + + [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security + (TLS) Protocol Version 1.2", RFC 5246, August 2008. + + + + +Fajardo, et al. Standards Track [Page 143] + +RFC 6733 Diameter Base Protocol October 2012 + + + [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., + Housley, R., and W. Polk, "Internet X.509 Public Key + Infrastructure Certificate and Certificate Revocation List + (CRL) Profile", RFC 5280, May 2008. + + [RFC5729] Korhonen, J., Jones, M., Morand, L., and T. Tsou, + "Clarifications on the Routing of Diameter Requests Based + on the Username and the Realm", RFC 5729, December 2009. + + [RFC5890] Klensin, J., "Internationalized Domain Names for + Applications (IDNA): Definitions and Document Framework", + RFC 5890, August 2010. + + [RFC5891] Klensin, J., "Internationalized Domain Names in + Applications (IDNA): Protocol", RFC 5891, August 2010. + + [RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram + Transport Layer Security (DTLS) for Stream Control + Transmission Protocol (SCTP)", RFC 6083, January 2011. + + [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer + Security Version 1.2", RFC 6347, January 2012. + + [RFC6408] Jones, M., Korhonen, J., and L. Morand, "Diameter + Straightforward-Naming Authority Pointer (S-NAPTR) Usage", + RFC 6408, November 2011. + +14.2. Informative References + + [ENTERPRISE] IANA, "SMI Network Management Private Enterprise + Codes", + <http://www.iana.org/assignments/enterprise-numbers>. + + [IANATCV] IANA, "Termination-Cause AVP Values (code 295)", + <http://www.iana.org/assignments/aaa-parameters/ + aaa-parameters.xml#aaa-parameters-16>. + + [RFC1492] Finseth, C., "An Access Control Protocol, Sometimes + Called TACACS", RFC 1492, July 1993. + + [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", + STD 51, RFC 1661, July 1994. + + [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: + Keyed-Hashing for Message Authentication", RFC 2104, + February 1997. + + + + + +Fajardo, et al. Standards Track [Page 144] + +RFC 6733 Diameter Base Protocol October 2012 + + + [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR + for specifying the location of services (DNS SRV)", + RFC 2782, February 2000. + + [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, + "Remote Authentication Dial In User Service (RADIUS)", + RFC 2865, June 2000. + + [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. + + [RFC2869] Rigney, C., Willats, W., and P. Calhoun, "RADIUS + Extensions", RFC 2869, June 2000. + + [RFC2881] Mitton, D. and M. Beadles, "Network Access Server + Requirements Next Generation (NASREQNG) NAS Model", + RFC 2881, July 2000. + + [RFC2975] Aboba, B., Arkko, J., and D. Harrington, "Introduction + to Accounting Management", RFC 2975, October 2000. + + [RFC2989] Aboba, B., Calhoun, P., Glass, S., Hiller, T., McCann, + P., Shiino, H., Walsh, P., Zorn, G., Dommety, G., + Perkins, C., Patil, B., Mitton, D., Manning, S., + Beadles, M., Chen, X., Sivalingham, S., Hameed, A., + Munson, M., Jacobs, S., Lim, B., Hirschman, B., Hsu, + R., Koo, H., Lipford, M., Campbell, E., Xu, Y., Baba, + S., and E. Jaques, "Criteria for Evaluating AAA + Protocols for Network Access", RFC 2989, November 2000. + + [RFC3162] Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", + RFC 3162, August 2001. + + [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and + H. Levkowetz, "Extensible Authentication Protocol + (EAP)", RFC 3748, June 2004. + + [RFC4301] Kent, S. and K. Seo, "Security Architecture for the + Internet Protocol", RFC 4301, December 2005. + + [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review + and Recommendations for Internationalized Domain Names + (IDNs)", RFC 4690, September 2006. + + [RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B. + Aboba, "Dynamic Authorization Extensions to Remote + Authentication Dial In User Service (RADIUS)", + RFC 5176, January 2008. + + + + +Fajardo, et al. Standards Track [Page 145] + +RFC 6733 Diameter Base Protocol October 2012 + + + [RFC5461] Gont, F., "TCP's Reaction to Soft Errors", RFC 5461, + February 2009. + + [RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, + "Network Time Protocol Version 4: Protocol and + Algorithms Specification", RFC 5905, June 2010. + + [RFC5927] Gont, F., "ICMP Attacks against TCP", RFC 5927, + July 2010. + + [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and + S. Cheshire, "Internet Assigned Numbers Authority + (IANA) Procedures for the Management of the Service + Name and Transport Protocol Port Number Registry", + BCP 165, RFC 6335, August 2011. + + [RFC6737] Kang, J. and G. Zorn, "The Diameter Capabilities Update + Application", RFC 6737, October 2012. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Fajardo, et al. Standards Track [Page 146] + +RFC 6733 Diameter Base Protocol October 2012 + + +Appendix A. Acknowledgements + +A.1. This Document + + The authors would like to thank the following people that have + provided proposals and contributions to this document: + + To Vishnu Ram and Satendra Gera for their contributions on + capabilities updates, predictive loop avoidance, as well as many + other technical proposals. To Tolga Asveren for his insights and + contributions on almost all of the proposed solutions incorporated + into this document. To Timothy Smith for helping on the capabilities + Update and other topics. To Tony Zhang for providing fixes to + loopholes on composing Failed-AVPs as well as many other issues and + topics. To Jan Nordqvist for clearly stating the usage of + Application Ids. To Anders Kristensen for providing needed technical + opinions. To David Frascone for providing invaluable review of the + document. To Mark Jones for providing clarifying text on vendor + command codes and other vendor-specific indicators. To Victor + Pascual and Sebastien Decugis for new text and recommendations on + SCTP/DTLS. To Jouni Korhonen for taking over the editing task and + resolving last bits from versions 27 through 29. + + Special thanks to the Diameter extensibility design team, which + helped resolve the tricky question of mandatory AVPs and ABNF + semantics. The members of this team are as follows: + + Avi Lior, Jari Arkko, Glen Zorn, Lionel Morand, Mark Jones, Tolga + Asveren, Jouni Korhonen, and Glenn McGregor. + + Special thanks also to people who have provided invaluable comments + and inputs especially in resolving controversial issues: + + Glen Zorn, Yoshihiro Ohba, Marco Stura, Stephen Farrel, Pete Resnick, + Peter Saint-Andre, Robert Sparks, Krishna Prasad, Sean Turner, Barry + Leiba, and Pasi Eronen. + + Finally, we would like to thank the original authors of this + document: + + Pat Calhoun, John Loughney, Jari Arkko, Erik Guttman, and Glen Zorn. + + Their invaluable knowledge and experience has given us a robust and + flexible AAA protocol that many people have seen great value in + adopting. We greatly appreciate their support and stewardship for + the continued improvements of Diameter as a protocol. We would also + like to extend our gratitude to folks aside from the authors who have + + + + +Fajardo, et al. Standards Track [Page 147] + +RFC 6733 Diameter Base Protocol October 2012 + + + assisted and contributed to the original version of this document. + Their efforts significantly contributed to the success of Diameter. + +A.2. RFC 3588 + + 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, Jonathan Wood, and Bernard Aboba provided + invaluable assistance in working out transport issues and this was + also the case with Steven Bellovin 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 + comments as a result of a thorough review of the spec. + + The authors would also like to acknowledge the following people for + their contribution in the development of the Diameter protocol: + + Allan C. Rubens, Haseeb Akhtar, William Bulley, Stephen Farrell, + David Frascone, Daniel C. Fox, Lol Grant, Ignacio Goyret, Nancy + Greene, Peter Heitman, Fredrik Johansson, Mark Jones, Martin Julien, + Bob Kopacz, Paul Krumviede, Fergal Ladley, Ryan Moats, Victor Muslin, + Kenneth Peirce, John Schnizlein, Sumit Vakil, John R. Vollbrecht, and + Jeff Weisberg. + + Finally, Pat Calhoun would like to thank Sun Microsystems since most + of the effort put into this document was done while he was in their + employ. + +Appendix B. S-NAPTR Example + + As an example, consider a client that wishes to resolve aaa: + ex1.example.com. The client performs a NAPTR query for that domain, + and the following NAPTR records are returned: + + ;; order pref flags service regexp replacement + IN NAPTR 50 50 "s" "aaa:diameter.tls.tcp" "" + _diameter._tls.ex1.example.com + IN NAPTR 100 50 "s" "aaa:diameter.tcp" "" + _aaa._tcp.ex1.example.com + IN NAPTR 150 50 "s" "aaa:diameter.sctp" "" + _diameter._sctp.ex1.example.com + + This indicates that the server supports TLS, TCP, and SCTP in that + order. If the client supports TLS, TLS will be used, targeted to a + + + +Fajardo, et al. Standards Track [Page 148] + +RFC 6733 Diameter Base Protocol October 2012 + + + host determined by an SRV lookup of _diameter._tls.ex1.example.com. + That lookup would return: + + ;; Priority Weight Port Target + IN SRV 0 1 5060 server1.ex1.example.com + IN SRV 0 2 5060 server2.ex1.example.com + + As an alternative example, a client that wishes to resolve aaa: + ex2.example.com. The client performs a NAPTR query for that domain, + and the following NAPTR records are returned: + + ;; order pref flags service regexp replacement + IN NAPTR 150 50 "a" "aaa:diameter.tls.tcp" "" + server1.ex2.example.com + IN NAPTR 150 50 "a" "aaa:diameter.tls.tcp" "" + server2.ex2.example.com + + This indicates that the server supports TCP available at the returned + host names. + +Appendix C. Duplicate Detection + + As described in Section 9.4, accounting record duplicate detection is + based on session identifiers. Duplicates can appear for various + reasons: + + o Failover to an alternate server. Where close to real-time + performance is required, failover thresholds need to be kept low. + This may lead to an increased likelihood of duplicates. Failover + can occur at the client or within Diameter agents. + + o Failure of a client or agent after sending a record from non- + volatile memory, but prior to receipt of an application-layer ACK + and deletion of the record to be sent. This will result in + retransmission of the record soon after the client or agent has + rebooted. + + o Duplicates received from RADIUS gateways. Since the + retransmission behavior of RADIUS is not defined within [RFC2865], + the likelihood of duplication will vary according to the + implementation. + + o Implementation problems and misconfiguration. + + The T flag is used as an indication of an application-layer + retransmission event, e.g., due to failover to an alternate server. + It is defined only for request messages sent by Diameter clients or + agents. For instance, after a reboot, a client may not know whether + + + +Fajardo, et al. Standards Track [Page 149] + +RFC 6733 Diameter Base Protocol October 2012 + + + it has already tried to send the accounting records in its non- + volatile memory before the reboot occurred. Diameter servers MAY use + the T flag as an aid when processing requests and detecting duplicate + messages. However, servers that do this MUST ensure that duplicates + are found even when the first transmitted request arrives at the + server after the retransmitted request. It can be used only in cases + where no answer has been received from the server for a request and + the request is sent again, (e.g., due to a failover to an alternate + peer, due to a recovered primary peer or due to a client re-sending a + stored record from non-volatile memory such as after reboot of a + client or agent). + + In some cases, the Diameter accounting server can delay the duplicate + detection and accounting record processing until a post-processing + phase takes place. At that time records are likely to be sorted + according to the included User-Name and duplicate elimination is easy + in this case. In other situations, it may be necessary to perform + real-time duplicate detection, such as when credit limits are imposed + or real-time fraud detection is desired. + + In general, only generation of duplicates due to failover or re- + sending of records in non-volatile storage can be reliably detected + by Diameter clients or agents. In such cases, the Diameter client or + agents can mark the message as a possible duplicate by setting the T + flag. Since the Diameter server is responsible for duplicate + detection, it can choose whether or not to make use of the T flag, in + order to optimize duplicate detection. Since the T flag does not + affect interoperability, and it may not be needed by some servers, + generation of the T flag is REQUIRED for Diameter clients and agents, + but it MAY be implemented by Diameter servers. + + As an example, it can be usually be assumed that duplicates appear + within a time window of longest recorded network partition or device + fault, perhaps a day. So only records within this time window need + to be looked at in the backward direction. Secondly, hashing + techniques or other schemes, such as the use of the T flag in the + received messages, may be used to eliminate the need to do a full + search even in this set except for rare cases. + + The following is an example of how the T flag may be used by the + server to detect duplicate requests. + + A Diameter server MAY check the T flag of the received message to + determine if the record is a possible duplicate. If the T flag is + set in the request message, the server searches for a duplicate + within a configurable duplication time window backward and + forward. This limits database searching to those records where + the T flag is set. In a well-run network, network partitions and + + + +Fajardo, et al. Standards Track [Page 150] + +RFC 6733 Diameter Base Protocol October 2012 + + + device faults will presumably be rare events, so this approach + represents a substantial optimization of the duplicate detection + process. During failover, it is possible for the original record + to be received after the T-flag-marked record, due to differences + in network delays experienced along the path by the original and + duplicate transmissions. The likelihood of this occurring + increases as the failover interval is decreased. In order to be + able to detect duplicates that are out of order, the Diameter + server should use backward and forward time windows when + performing duplicate checking for the T-flag-marked request. For + example, in order to allow time for the original record to exit + the network and be recorded by the accounting server, the Diameter + server can delay processing records with the T flag set until a + time period TIME_WAIT + RECORD_PROCESSING_TIME has elapsed after + the closing of the original transport connection. After this time + period, it may check the T-flag-marked records against the + database with relative assurance that the original records, if + sent, have been received and recorded. + +Appendix D. Internationalized Domain Names + + To be compatible with the existing DNS infrastructure and simplify + host and domain name comparison, Diameter identities (FQDNs) are + represented in ASCII form. This allows the Diameter protocol to fall + in-line with the DNS strategy of being transparent from the effects + of Internationalized Domain Names (IDNs) by following the + recommendations in [RFC4690] and [RFC5890]. Applications that + provide support for IDNs outside of the Diameter protocol but + interacting with it SHOULD use the representation and conversion + framework described in [RFC5890], [RFC5891], and [RFC3492]. +</pre> + +</section> |