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<!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>connect_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.
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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"
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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 | | |
-----------------------------------------|----+-----|
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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.).
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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.
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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 ]
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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.
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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
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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.
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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.
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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".
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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:
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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.
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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.
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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)
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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.
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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.
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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.
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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.
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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.
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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.
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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:
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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:
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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.
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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.
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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:
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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.
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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.
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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.
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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.
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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
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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 ]
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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
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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).
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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.
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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 ]
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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
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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.
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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.
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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
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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.
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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.
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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].
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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.
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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.
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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.
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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.
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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.
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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
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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
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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.
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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.
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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.
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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
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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.
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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.
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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 |
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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.
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+-----------+
| 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.
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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.
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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].
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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
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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.
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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
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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]
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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
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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
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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
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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
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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>
