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<rfc category="std" ipr="full3978" docName="draft-ietf-dime-rfc3588bis-10.txt">
<front>
<title abbrev="Diameter Base Protocol">Diameter Base Protocol</title>
<author role="editor" initials="V." surname="Fajardo" fullname="Victor Fajardo">
<organization>Toshiba America Research</organization>
<address>
<postal>
<street>One Telcordia Drive, 1S-222</street>
<city>Piscataway</city>
<region>NJ</region>
<code>08854</code>
<country>USA</country>
</postal>
<phone>1 908-421-1845</phone>
<email>vfajardo@tari.toshiba.com</email>
</address>
</author>
<author initials="J." surname="Arkko" fullname="Jari Arkko">
<organization>Ericsson Research</organization>
<address>
<postal>
<street>02420 Jorvas</street>
<city></city>
<region></region>
<code></code>
<country>Finland</country>
</postal>
<phone>+358 40 5079256</phone>
<email>jari.arkko@ericsson.com</email>
</address>
</author>
<author initials="J." surname="Loughney" fullname="John Loughney">
<organization>Nokia Research Center</organization>
<address>
<postal>
<street>955 Page Mill Road</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94304</code>
<country>US</country>
</postal>
<phone>1-650-283-8068</phone>
<email>john.loughney@nokia.com</email>
</address>
</author>
<author initials="G." surname="Zorn" fullname="Glenn Zorn">
<organization>NetCube</organization>
<address>
<postal>
<street>1310 East Thomas Street, #306</street>
<city>Seattle</city>
<region>WA</region>
<code>98102</code>
<country>US</country>
</postal>
<phone></phone>
<email>glenzorn@comcast.net</email>
</address>
</author>
<date year="2008" />
<area>Network Working Group</area>
<workgroup>DIME</workgroup>
<keyword>RFC 3588</keyword>
<abstract>
<t>The Diameter base protocol is intended to provide an Authentication,
Authorization and Accounting (AAA) framework for applications such as
network access or IP mobility. Diameter is also intended to work in
both local Authentication, Authorization & Accounting and roaming
situations. This document specifies the message format, transport,
error reporting, accounting and security services to be used by all
Diameter applications. The Diameter base application needs to be
supported by all Diameter implementations.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>Authentication, Authorization and Accounting (AAA) protocols such as
TACACS
<xref target="RFC1492" /> and RADIUS
<xref target="RFC2865" /> were initially deployed to provide dial-up PPP
<xref target="RFC1661" /> and terminal server access. Over time, with
the growth of the Internet and the introduction of new access technologies
(including wireless, DSL, Mobile IP and Ethernet), both the amount and
complexity of processing performed by routers and network access servers
(NAS) have increased, putting new demands on AAA protocols.</t>
<t>Network access requirements for AAA protocols are summarized in
<xref target="RFC2989" />. These include:
<vspace blankLines="1" />
<list style="hanging">
<t hangText="Failover">
<vspace blankLines="1" />
<xref target="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. This is described in Section 5.5
and
<xref target="RFC3539" />.</t>
<t hangText="Transmission-level security">
<vspace blankLines="1" />
<xref target="RFC2865" /> defines an application-layer authentication
and integrity scheme that is required only for use with Response
packets. While
<xref target="RFC2869" /> defines an additional authentication and
integrity mechanism, use is only required during Extensible
Authentication Protocol (EAP) sessions. While attribute-hiding is
supported,
<xref target="RFC2865" /> does not provide support for per-packet
confidentiality. In accounting,
<xref target="RFC2866" /> assumes that replay protection is provided
by the backend billing server, rather than within the protocol
itself.
<vspace blankLines="1" />While <xref target="RFC3162"/> defines the use of IPsec
with RADIUS, support for IPsec is not required. Since within
<xref target="RFC4306" /> authentication occurs only within Phase 1
prior to the establishment of IPsec SAs in Phase 2, it is typically
not possible to define separate trust or authorization schemes for
each application. This limits the usefulness of IPsec in inter-domain
AAA applications (such as roaming) where it may be desirable to
define a distinct certificate hierarchy for use in a AAA deployment.
In order to provide universal support for transmission-level
security, and enable both intra- and inter-domain AAA deployments,
Diameter provides support for TLS. Security is discussed in Section 13.
<vspace blankLines="1" /></t>
<t hangText="Reliable transport">
<vspace blankLines="1" />
<vspace blankLines="1" />RADIUS runs over UDP, and does not define
retransmission behavior; as a result, reliability varies between
implementations. As described in
<xref target="RFC2975" />, this is a major issue in accounting, where
packet loss may translate directly into revenue loss. In order to
provide well defined transport behavior, Diameter runs over reliable
transport mechanisms (TCP, SCTP) as defined in
<xref target="RFC3539" />.
<vspace blankLines="1" /></t>
<t hangText="Agent support">
<vspace blankLines="1" />
<xref target="RFC2865" /> 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.
<vspace blankLines="1" /></t>
<t hangText="Server-initiated messages">
<vspace blankLines="1" />While RADIUS server-initiated messages are
defined in
<xref target="RFC3576" />, support is optional. This makes it
difficult to implement features such as unsolicited disconnect or
reauthentication/reauthorization on demand across a heterogeneous
deployment. Support for server-initiated messages is mandatory in
Diameter, and is described in Section 8.
<vspace blankLines="1" /></t>
<t hangText="Transition support">
<vspace blankLines="1" />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, described in
<xref target="RFC4005" />, enables Diameter support to be added to
legacy networks, by addition of a gateway or server speaking both
RADIUS and Diameter.
<vspace blankLines="1" />In addition to addressing the above
requirements, Diameter also provides support for the following:
<vspace blankLines="1" /></t>
<t hangText="Capability negotiation">
<vspace blankLines="1" />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).
<vspace blankLines="1" /></t>
<t hangText="Peer discovery and configuration">
<vspace blankLines="1" />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
<xref target="RFC2865" />. Through DNS, Diameter enables dynamic
discovery of peers. Derivation of dynamic session keys is enabled via
transmission-level security.
<vspace blankLines="1" /></t>
</list></t>
<t>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
within embedded devices, given improvements in processor speeds and the
widespread availability of embedded TLS implementations.</t>
<section anchor="Protocol" title="Diameter Protocol">
<t>The Diameter base protocol provides the following facilities:
<list style="symbols">
<t>Delivery of AVPs (attribute value pairs)</t>
<t>Capabilities negotiation</t>
<t>Error notification</t>
<t>Extensibility, through addition of new applications, commands and AVPs
(required in
<xref target="RFC2989" />).</t>
<t>Basic services necessary for applications, such as handling of
user sessions or accounting</t>
</list></t>
<t>All data delivered by the protocol is in the form of an AVP. Some
of these AVP values are used by the Diameter protocol itself, while
others deliver data associated with particular applications that
employ Diameter. AVPs may be added arbitrarily to Diameter messages,
so long as the requirements of a message's ABNF are met and the ABNF
allows for it. AVPs are used by the base Diameter protocol to support
the following required features:
<list style="symbols">
<t>Transporting of user authentication information, for the
purposes of enabling the Diameter server to authenticate the
user.</t>
<t>Transporting of service specific authorization information,
between client and servers, allowing the peers to decide whether a
user's access request should be granted.</t>
<t>Exchanging resource usage information, which MAY be used for
accounting purposes, capacity planning, etc.</t>
<t>Relaying, proxying and redirecting of Diameter messages through
a server hierarchy.</t>
</list></t>
<t>The Diameter base protocol provides the minimum requirements
needed for a AAA protocol, as required by
<xref target="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
<xref target="RFC4004" />, or network access
<xref target="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. At this time the focus of Diameter is 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 2.4 for more information on Diameter applications.</t>
<t>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.</t>
<t>The Diameter protocol also supports server-initiated messages,
such as a request to abort service to a particular user.</t>
<section anchor="desc" title="Description of the Document Set">
<t>Currently, the Diameter specification consists of an updated
version of the base protocol specification (this document),
Transport Profile <xref target="RFC3539" /> and applications: Mobile IPv4
<xref target="RFC4004" />, NASREQ <xref target="RFC4005" />,
Credit Control <xref target="RFC4006" />,
EAP <xref target="RFC4072" /> and
SIP <xref target="RFC4740" />. Note that this document deprecates
<xref target="RFC3588" />. A summary of the base protocol updates included in
this document can be found in <xref target="updates" />.</t>
<t>The Transport Profile document
<xref target="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.</t>
<t>The Mobile IPv4
<xref target="RFC4004" /> application defines a Diameter application
that allows a Diameter server to perform AAA functions for Mobile
IPv4 services to a mobile node.</t>
<t>The NASREQ
<xref target="RFC4005" /> application defines a Diameter Application
that allows a Diameter server to be used in a PPP/SLIP Dial-Up and
Terminal Server Access environment. Consideration was given for
servers that need to perform protocol conversion between Diameter
and RADIUS.</t>
<t>The Credit Control
<xref target="RFC4006" /> application defines a Diameter Application
that can be used to implement real-time credit-control for a variety
of end user services such as network access, SIP services, messaging
services, and download services. It provides a general solution to
real-time cost and credit-control.</t>
<t>The EAP
<xref target="RFC4072" /> application defines a Diameter Application
that can be used to carry EAP packets between the Network Access
Server (NAS) working as an EAP authenticator and a back-end
authentication server. The Diameter EAP application is based on
NASREQ and intended for a similar environment.</t>
<t>The SIP
<xref target="RFC4740" /> application defines a Diameter Application
that allows a Diameter client to request authentication and authorization
information to a Diameter server for SIP-based IP multimedia services
(see SIP <xref target="RFC3261" />).</t>
<t>In summary, this document defines the base protocol
specification for AAA, which includes support for accounting. The
applications documents describe applications that use this base
specification for Authentication, Authorization and
Accounting.</t>
</section>
<section anchor="convention" title="Conventions Used in This Document">
<t>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 <xref target="RFC2119"/>.</t>
</section>
<section anchor="updates" title="Changes from RFC3588">
<t>This document deprecates <xref target="RFC3588" /> but is fully backward
compatible with that document. The changes introduced in this document
focuses on fixing issues that has surfaced during implementation of
<xref target="RFC3588"/>. An overview of some the major changes are shown below.
</t><t>
<list style="symbols">
<t>Simplified Security Requirements. The use of a secured transport for
exchanging diameter messages remains mandatory. However, TLS has become
the primary method of securing diameter and IPSec is a secondary alternative.
See <xref target="seccons"/> for details. Along with this, support for the End-to-End security
framework (E2ESequence AVP and 'P'-bit in the AVP header) has also been deprecated.</t>
<t>Diameter Extensibility Changes. This includes fixes to the diameter extensibility
specification (<xref target="ext"/> and others) to better aid diameter application designers.
It also includes allocation of vendor specific command code space. The new
specification relaxes the allocation of command codes for
vendor specific uses. See <xref target="comcod"/> for details.</t>
<t>Application Id Usage. Clarify the proper use of Application Id information
which can be found in multiple places within a diameter message. This includes
co-relating Application Ids found in the message headers and AVPs.
These changes also clearly specifies the proper Application Id value to use
for specific base protocol messages (ASR/ASA, STR/STA) as well as clarifying
the content and use of Vendor-Specific-Application-Id.</t>
<t>Routing Fixes. For general routing, specifies much more clearly what information
(AVPs and Application Id) can be used for making routing decisions.
Prioritization of redirect routing criterias when multiple route entries
are found via redirects has also been added (See <xref target="RHUAVP"/> for details).</t>
<t>Simplification of Diameter Peer Discovery. The diameter discovery
process now supports only well known discovery schemes. The rest has been
deprecated. (See <xref target="PeerDis"/> for details).</t>
</list>
</t>
<t>There are many other many miscellaneous fixes that has been
introduced in this document that may not be considered significant but they are
important nonetheless. Examples are removal of obselete types, fixes to
command ABNFs, fixes state machine, clarification on election process,
message validation, fixes to Failed-AVP and Result-Code AVP values etc. A comprehensive
list of changes is now shown here for practical reasons. Though,
that can be generated via a diff comparison between this document
and <xref target="RFC3588"/>.
</t>
</section>
</section>
<section anchor="ext" title="Approach to Extensibility">
<t>The Diameter protocol is designed to be extensible, using several
mechanisms, including:
<list style="symbols">
<t>Defining new AVP values</t>
<t>Creating new AVPs</t>
<t>Creating new commands</t>
<t>Creating new authentication/authorization applications</t>
<t>Creating new accounting applications</t>
<t>Application authentication procedures</t>
</list></t>
<t>Reuse of existing AVP values, AVPs, commands and Diameter applications are
strongly recommended. Reuse simplifies standardization and implementation and
avoids potential interoperability issues.</t>
<section anchor="define" title=" Defining New AVP Values">
<t>New applications should attempt to reuse AVPs defined in
existing applications when possible, as opposed to creating new
AVPs. For AVPs of type Enumerated, an application may require a new
value to communicate some service-specific information.</t>
<t>In order to allocate a new AVP value for a standards track AVP,
a request MUST be sent to IANA <xref target="RFC2434" />, along with
an explanation of the new AVP value. IANA considerations for AVP
values are discussed in Section 11.4.</t>
</section>
<section anchor="create" title=" Creating New AVPs">
<t>When no existing AVP can be reused, a new AVP should be created.
The new AVP being defined MUST use one of the data types listed in
Section 4.2 or 4.3. If an appropriate derived data type is already
defined, it SHOULD be used instead of the base data type to encourage
reusability and good design practice.</t>
<t>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).</t>
<t>In order to create a new standards track AVP, a request MUST be sent
to IANA with a reference to the specification that defines the AVP.
IANA considerations for AVPs are discussed in Section 11.1.1.</t>
</section>
<section anchor="createcmd" title=" Creating New Commands">
<t>A new command should only be created when no suitable command can
be reused from an existing application. A new command MUST result in
the definition of a new application. In order to create a new command,
a request MUST be sent to IANA. The IANA considerations for commands
are discussed in Section 11.2.1.</t>
</section>
<section anchor="auth"
title=" Creating New Authentication Applications">
<t>Every Diameter application specification MUST have an IANA
assigned Application Id (see <xref target="appl" /> and
<xref target="Appid" />).</t>
<t>Should a new Diameter usage scenario find itself unable to fit
within an existing application without requiring major changes to
the specification, it may be desirable to create a new Diameter
application. Major changes to an application include:
<list style="symbols">
<t>Adding new AVPs to the command, which have the "M" bit
set.</t>
<t>Requiring a command that has a different number of round trips
to satisfy a request (e.g., application foo has a command that
requires one round trip, but new application bar has a command
that requires two round trips to complete).</t>
<t>Adding support for an authentication method requiring
definition of new AVPs for use with the application. Since a new
EAP authentication method can be supported within Diameter
without requiring new AVPs, addition of EAP methods does not
require the creation of a new authentication application.</t>
</list></t>
<t>Creation of a new application should be viewed as a last resort.
An implementation MAY add arbitrary non-mandatory AVPs to a
command defined in an application, including vendor-specific AVPs
without needing to define a new application. This can be done if
the commands ABNF allows for it. Please refer to Section 11.1.1 for
details.</t>
<t>In order to justify allocation of a new Application Id,
Diameter applications MUST define one Command Code, add new
mandatory AVPs to the ABNF or significantly change the state
machine or processing rules of an existing application.</t>
<t>The expected AVPs MUST be defined in an ABNF
<xref target="RFC4234"/> grammar (see Section 3.2). If the Diameter
application has accounting requirements, it MUST also specify the
AVPs that are to be present in the Diameter Accounting messages
(see Section 9.3). However, just because a new authentication
Application Id is required, does not imply that a new accounting
Application Id is required.</t>
<t>When possible, a new Diameter application SHOULD reuse existing
Diameter AVPs, in order to avoid defining multiple AVPs that carry
similar information.</t>
</section>
<section anchor="acc" title=" Creating New Accounting Applications">
<t>There are services that only require Diameter accounting. Such
services need to define the AVPs carried in the Accounting-Request
(ACR)/ Accounting-Answer (ACA) messages, but do not need to define
new command codes. An implementation MAY add arbitrary
non-mandatory AVPs (AVPs with the "M" bit not set) to any command
defined in an application, including vendor-specific AVPs, without
needing to define a new accounting application. Please refer to
Section 11.1.1 for details.</t>
<t>Application Ids are still required for Diameter
capability exchange. Every Diameter accounting application
specification MUST have an IANA assigned Application Id
(see Section 2.4) or a vendor specific Application Id.</t>
<t>Every Diameter implementation MUST support accounting. Basic
accounting support is sufficient to handle any application that
uses the ACR/ACA commands defined in this document, as long as no
new mandatory AVPs are added. A mandatory AVP is defined as one
which has the "M" bit set when sent within an accounting command,
regardless of whether it is required or optional within the ABNF
for the accounting application.</t>
<t>The creation of a new accounting application should be viewed as
a last resort and MUST NOT be used unless a new command or
additional mechanisms (e.g., application defined state machine) is
defined within the application, or new mandatory AVPs are added to
the ABNF.</t>
<t>Within an accounting command, setting the "M" bit implies that a
backend server (e.g., billing server) or the accounting server
itself MUST understand the AVP in order to compute a correct bill.
If the AVP is not relevant to the billing process, when the AVP is
included within an accounting command, it MUST NOT have the "M" bit
set, even if the "M" bit is set when the same AVP is used within
other Diameter commands (i.e., authentication/authorization
commands).</t>
<t>A DIAMETER base accounting implementation MUST be configurable
to advertise supported accounting applications in order to prevent
the accounting server from accepting accounting requests for
unbillable services. The combination of the home domain and the
accounting Application Id can be used in order to route the request
to the appropriate accounting server.</t>
<t>When possible, a new Diameter accounting application SHOULD
attempt to reuse existing AVPs, in order to avoid defining multiple
AVPs that carry similar information.</t>
<t>If the base accounting is used without any mandatory AVPs, new
commands or additional mechanisms (e.g., application defined state
machine), then the base protocol defined standard accounting
Application Id (Section 2.4) MUST be used in ACR/ACA commands.</t>
</section>
<section anchor="app" title="Application Authentication Procedures">
<t>When possible, applications SHOULD be designed such that new
authentication methods MAY be added without requiring changes to
the application. This MAY require that new AVP values be assigned
to represent the new authentication transform, or any other scheme
that produces similar results. When possible, authentication
frameworks, such as Extensible Authentication Protocol
<xref target="RFC3748" />, SHOULD be used.</t>
</section>
</section>
<section anchor="term" title="Terminology">
<t>
<list style="hanging">
<t hangText="AAA">
<vspace blankLines="1" />Authentication, Authorization and Accounting.
<vspace blankLines="1" /></t>
<t hangText=" Accounting">
<vspace blankLines="1" />The act of collecting information on
resource usage for the purpose of capacity planning, auditing,
billing or cost allocation.
<vspace blankLines="1" /></t>
<t hangText=" Accounting Record">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="Authentication">
<vspace blankLines="1" />The act of verifying the identity of
an entity (subject).
<vspace blankLines="1" /></t>
<t hangText="Authorization">
<vspace blankLines="1" />The act of determining whether a
requesting entity (subject) will be allowed access to a resource
(object).
<vspace blankLines="1" /></t>
<t hangText="AVP">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="Broker">
<vspace blankLines="1" />A broker is a business term commonly used in
AAA infrastructures. A broker is either a relay, proxy or
redirect agent, and MAY be operated by roaming consortiums.
Depending on the business model, a broker may either choose to
deploy relay agents or proxy agents.
<vspace blankLines="1" /></t>
<t hangText="Diameter Agent">
<vspace blankLines="1" />A Diameter Agent is a Diameter node
that provides either relay, proxy, redirect or translation
services.
<vspace blankLines="1" /></t>
<t hangText="Diameter Client">
<vspace blankLines="1" />A Diameter Client is a device at
the edge of the network that performs access control. An example
of a Diameter client is a Network Access Server (NAS) or a
Foreign Agent (FA). By its very nature, a Diameter Client MUST
support Diameter client applications in addition to the base
protocol.
<vspace blankLines="1" /></t>
<t hangText="Diameter Node">
<vspace blankLines="1" />A Diameter node is a host process
that implements the Diameter protocol, and acts either as a
Client, Agent or Server.
<vspace blankLines="1" /></t>
<t hangText=" Diameter Peer">
<vspace blankLines="1" />A Diameter Peer is a Diameter Node
to which a given Diameter Node has a direct transport connection.
<vspace blankLines="1" /></t>
<t hangText=" Diameter Server">
<vspace blankLines="1" />A Diameter Server is one that
handles authentication, authorization and accounting requests for
a particular realm. By its very nature, a Diameter Server MUST
support Diameter server applications in addition to the base protocol.
<vspace blankLines="1" /></t>
<t hangText="Downstream">
<vspace blankLines="1" />Downstream is used to identify the
direction of a particular Diameter message from the home server
towards the access device.
<vspace blankLines="1" /></t>
<t hangText="Home Realm">
<vspace blankLines="1" />A Home Realm is the administrative
domain with which the user maintains an account relationship.
<vspace blankLines="1" /></t>
<t hangText="Home Server"><vspace blankLines="1" />
A Diameter Server which serves the Home Realm.
<vspace blankLines="1" /></t>
<t hangText="Interim accounting">
<vspace blankLines="1" />An interim accounting message
provides a snapshot of usage during a user's session. It is
typically implemented in order to provide for partial accounting
of a user's session in the case of a device reboot or other
network problem prevents the reception of a session summary
message or session record.
<vspace blankLines="1" /></t>
<t hangText="Local Realm">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="Multi-session">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="Network Access Identifier">
<vspace blankLines="1" />The Network Access
Identifier, or NAI
<xref target="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.
<vspace blankLines="1" /></t>
<t hangText="Proxy Agent or Proxy">
<vspace blankLines="1" />In addition to forwarding
requests and responses, proxies make policy decisions relating to
resource usage and provisioning. This is typically accomplished
by tracking the state of NAS devices. While proxies typically do
not respond to client Requests prior to receiving a Response from
the server, they may originate Reject messages in cases where
policies are violated. As a result, proxies need to understand
the semantics of the messages passing through them, and may not
support all Diameter applications.
<vspace blankLines="1" /></t>
<t hangText="Realm">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="Real-time Accounting">
<vspace blankLines="1" />Real-time accounting involves
the processing of information on resource usage within a defined
time window. Time constraints are typically imposed in order to
limit financial risk.
<vspace blankLines="1" /></t>
<t hangText="Relay Agent or Relay">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText=" Redirect Agent">
<vspace blankLines="1" />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 proxy agents, redirect agents do not
keep state with respect to sessions or NAS resources.
<vspace blankLines="1" /></t>
<t hangText=" Roaming Relationships">
<vspace blankLines="1" />Roaming relationships
include relationships between companies and ISPs, relationships
among peer ISPs within a roaming consortium, and relationships
between an ISP and a roaming consortium.
<vspace blankLines="1" /></t>
<t hangText=" Session">
<vspace blankLines="1" />A session is a related progression of
events devoted to a particular activity. Each application SHOULD
provide guidelines as to when a session begins and ends. All
Diameter packets with the same Session-Identifier are considered
to be part of the same session.
<vspace blankLines="1" /></t>
<t hangText="Session state">
<vspace blankLines="1" />A stateful agent is one that
maintains session state information, by keeping track of all
authorized active sessions. Each authorized session is bound to a
particular service, and its state is considered active either
until it is notified otherwise, or by expiration.
<vspace blankLines="1" /></t>
<t hangText=" Sub-session">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="Transaction state">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText=" Translation Agent">
<vspace blankLines="1" />A translation agent is a
stateful Diameter node that performs protocol translation between
Diameter and another AAA protocol, such as RADIUS.
<vspace blankLines="1" /></t>
<t hangText="Transport Connection">
<vspace blankLines="1" />A transport connection is a
TCP or SCTP connection existing directly between two Diameter
peers, otherwise known as a Peer- to-Peer Connection.
<vspace blankLines="1" /></t>
<t hangText="Upstream">
<vspace blankLines="1" />Upstream is used to identify the direction
of a particular Diameter message from the access device towards
the home server.
<vspace blankLines="1" /></t>
<t hangText=" User">
<vspace blankLines="1" />The entity requesting or using some resource,
in support of which a Diameter client has generated a request.
<vspace blankLines="1" /></t>
</list>
</t>
</section>
</section>
<section anchor="overview" title="Protocol Overview">
<t>The base Diameter protocol may be used by itself for accounting
applications, but for use in authentication and authorization it is
always extended for a particular application. Two Diameter applications
are defined by companion documents: NASREQ
<xref target="RFC4005" />, Mobile IPv4
<xref target="RFC4004" />. These applications are introduced in this
document but specified elsewhere. Additional Diameter applications MAY
be defined in the future (see Section 11.3).</t>
<t>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.,
NASREQ and/or Mobile IPv4. A Diameter Client that does not support both
NASREQ and Mobile IPv4, MUST be referred to as "Diameter X Client"
where X is the application which it supports, and not a "Diameter
Client".</t>
<t>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 that does not support both
NASREQ and Mobile IPv4, MUST be referred to as "Diameter X Server"
where X is the application which it supports, and not a "Diameter
Server".</t>
<t>Diameter Relays and redirect agents are, by definition, protocol
transparent, and MUST transparently support the Diameter base protocol,
which includes accounting, and all Diameter applications.</t>
<t>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 which does not support also both
NASREQ and Mobile IPv4, MUST be referred to as "Diameter X Proxy" where
X is the application which it supports, and not a "Diameter Proxy".</t>
<t>The base Diameter protocol concerns itself with capabilities
negotiation, how messages are sent and how peers may eventually be
abandoned. The base protocol also defines certain rules that apply to
all exchanges of messages between Diameter nodes.</t>
<t>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.</t>
<t>The initial request for authentication and/or authorization of a
user would include the Session-Id. The Session-Id is then used in all
subsequent messages to identify the user's session (see Section 8 for
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 an error occurred. The specific behavior of the Diameter
server or client receiving a request depends on the Diameter
application employed.</t>
<t>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.</t>
<section anchor="trans" title="Transport">
<t>Transport profile is defined in
<xref target="RFC3539" />.</t>
<t>The base Diameter protocol is run on port 3868 of both TCP
<xref target="RFC793" /> and SCTP
<xref target="RFC2960" /> transport protocols.</t>
<t>Diameter clients MUST support either TCP or SCTP, while agents and
servers MUST support both. Future versions of this specification MAY
mandate that clients support SCTP.</t>
<t>A Diameter node MAY initiate connections from a source port other
than the one that it declares it accepts incoming connections on, and
MUST be prepared to receive connections on port 3868. 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.</t>
<t>When no transport connection exists with a peer, an attempt to
connect SHOULD be periodically made. This behavior is handled via the
Tc timer, 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.</t>
<t>When connecting to a peer and either zero or more transports are
specified, SCTP SHOULD be tried first, followed by TCP. See Section
5.2 for more information on peer discovery.</t>
<t>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.
Diameter implementations SHOULD also be able to interpret a reset
from the transport and timed-out connection attempts. If Diameter
receives data up from TCP 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).</t>
<section anchor="sctp" title="SCTP Guidelines">
<t>The following are guidelines for Diameter implementations that
support SCTP:
<vspace blankLines="1" />
<list style="numbers">
<t>For interoperability: All Diameter nodes MUST be prepared to
receive Diameter messages on any SCTP stream in the
association.</t>
<t>To prevent blocking: All Diameter nodes SHOULD utilize all
SCTP streams available to the association to prevent
head-of-the-line blocking.</t>
</list></t>
</section>
</section>
<section anchor="sec" title="Securing Diameter Messages">
<t>Connections between Diameter peers SHOULD be protected by TLS.
All Diameter base protocol implementations MUST support the use of TLS.
If desired, additional security measures that are transparent
to and independent of Diameter, such as IPSec <xref target="RFC4301"/>, can
be deployed to secure connections between peers. The Diameter protocol
MUST NOT be used without any security mechanism.</t>
</section>
<section anchor="comp" title="Diameter Application Compliance">
<t>Application Ids are advertised during the capabilities
exchange phase (see Section 5.3). For a given application,
advertising support of an application implies that the sender
supports all command codes, and the AVPs specified in the associated
ABNFs, described in the specification.</t>
<t>An implementation MAY add arbitrary non-mandatory AVPs to a
command defined in an application, including vendor-specific AVPs
only if the commands ABNF allows for it. Please refer to Section 11.1.1
for details.</t>
</section>
<section anchor="appl" title="Application Identifiers">
<t>Each Diameter application MUST have an IANA assigned Application
Id (see Section 11.3). 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.</t>
<t>The following Application Id values are defined:
<artwork>
Diameter Common Messages 0
NASREQ 1 [RFC4005]
Mobile-IP 2 [RFC4004]
Diameter Base Accounting 3
Relay 0xffffffff
</artwork>
</t>
<t>Relay and redirect agents MUST advertise the Relay Application
Identifier, while all other Diameter nodes MUST advertise locally
supported applications. The receiver of a Capabilities Exchange
message advertising Relay service MUST assume that the sender
supports all current and future applications.</t>
<t>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.</t>
</section>
<section anchor="conn" title="Connections vs. Sessions">
<t>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.</t>
<t>A connection is a transport level connection between two peers,
used to send and receive Diameter messages. A session is a logical
concept at the application layer, and is shared between an access
device and a server, and is identified via the Session-Id AVP.</t>
<t>
<figure anchor="Figure1" title="Diameter connections and sessions">
<artwork>
+--------+ +-------+ +--------+
| Client | | Relay | | Server |
+--------+ +-------+ +--------+
<----------> <---------->
peer connection A peer connection B
<----------------------------->
User session x
</artwork>
</figure>
</t>
<t>In the example provided in <xref target="Figure1" />, peer connection
A is established between the Client and its local 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.</t>
<t>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).</t>
</section>
<section anchor="peer" title="Peer Table">
<t>The Diameter Peer Table is used in message forwarding, and
referenced by the Routing Table. A Peer Table entry contains
the following fields:</t>
<list style="hanging">
<t hangText="Host identity">
<vspace blankLines="1" />Following the conventions described for
the DiameterIdentity derived AVP data format in Section 4.4. This
field contains the contents of the Origin-Host (Section 6.3) AVP
found in the CER or CEA message.
<vspace blankLines="1" /></t>
<t hangText="StatusT">
<vspace blankLines="1" />This is the state of the peer entry, and MUST
match one of the values listed in Section 5.6.
<vspace blankLines="1" /></t>
<t hangText="Static or Dynamic">
<vspace blankLines="1" />Specifies whether a peer entry was
statically configured, or dynamically discovered.
<vspace blankLines="1" /></t>
<t hangText="Expiration time">
<vspace blankLines="1" />Specifies the time at which dynamically
discovered peer table entries are to be either refreshed, or expired.
<vspace blankLines="1" /></t>
<t hangText="TLS Enabled">
<vspace blankLines="1" />Specifies whether TLS is to be used when
communicating with the peer.
<vspace blankLines="1" /></t>
</list>
<t>Additional security information, when needed (e.g., keys,
certificates)</t>
</section>
<section anchor="realm" title="Routing Table">
<t>All Realm-Based routing lookups are performed against what is
commonly known as the Routing Table (see Section 12). A
Routing Table Entry contains the following fields:</t>
<list style="hanging">
<t hangText="Realm Name">
<vspace blankLines="1" />This is the field that is typically used as
a primary key in the routing table lookups. Note that some
implementations perform their lookups based on
longest-match-from-the-right on the realm rather than requiring an
exact match.
<vspace blankLines="1" /></t>
<t hangText="Application Identifier">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="Local Action">
<vspace blankLines="1" />The Local Action field is used to identify
how a message should be treated. The following actions are supported:
<vspace blankLines="1" />
<list style="numbers">
<t>LOCAL - Diameter messages that resolve to a route entry with the
Local Action set to Local can be satisfied locally, and do not need
to be routed to another server.</t>
<t>RELAY - All Diameter messages that fall within this category
MUST be routed to a next hop server, without modifying any
non-routing AVPs. See Section 6.1.9 for relaying guidelines</t>
<t>PROXY - All Diameter messages that fall within this category
MUST be routed to a next hop server. The local server MAY apply its
local policies to the message by including new AVPs to the message
prior to routing. See Section 6.1.9 for proxying guidelines.</t>
<t>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 6.1.9 for
redirect guidelines.</t>
</list></t>
<t hangText="Server Identifier">
<vspace blankLines="1" />One or more servers the message is to
be routed to. These servers MUST also be present in the Peer table.
When the Local Action is set to RELAY or PROXY, this field contains
the identity of the server(s) the message must be routed to. When the
Local Action field is set to REDIRECT, this field contains the
identity of one or more servers the message should be redirected
to.</t>
<t hangText="Static or Dynamic">
<vspace blankLines="1" />Specifies whether a route entry was
statically configured, or dynamically discovered.</t>
<t hangText="Expiration time">
<vspace blankLines="1" />Specifies the time which a dynamically
discovered route table entry expires.</t>
</list>
<t>It is important to note that Diameter agents MUST support at least
one of the LOCAL, RELAY, PROXY or REDIRECT modes of operation. Agents
do not need to support all modes of operation in order to conform
with the protocol specification, but MUST follow the protocol
compliance guidelines in Section 2. Relay agents MUST NOT reorder
AVPs, and proxies MUST NOT reorder AVPs.</t>
<t>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.</t>
<t>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.</t>
</section>
<section anchor="role" title="Role of Diameter Agents">
<t>In addition to client and servers, the Diameter protocol
introduces relay, proxy, redirect, and translation agents, each of
which is defined in Section 1.3. These Diameter agents are useful for
several reasons:
<list style="symbols">
<t>They can distribute administration of systems to a configurable
grouping, including the maintenance of security associations.</t>
<t>They can be used for concentration of requests from an number of
co-located or distributed NAS equipment sets to a set of like user
groups.</t>
<t>They can do value-added processing to the requests or
responses.</t>
<t>They can be used for load balancing.</t>
<t>A complex network will have multiple authentication sources,
they can sort requests and forward towards the correct target.</t>
</list></t>
<t>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.</t>
<t>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.</t>
<t>A stateful agent is one that maintains session state information;
by keeping track of all authorized active sessions. Each authorized
session is bound to a particular service, and its state is considered
active either until it is notified otherwise, or by expiration. Each
authorized session has an expiration, which is communicated by
Diameter servers via the Session-Timeout AVP.</t>
<t>Maintaining session state MAY be useful in certain applications,
such as:
<list style="symbols">
<t>Protocol translation (e.g., RADIUS <-> Diameter)</t>
<t>Limiting resources authorized to a particular user</t>
<t>Per user or transaction auditing</t>
</list></t>
<t>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.</t>
<section anchor="relay" title="Relay Agents">
<t>Relay Agents are Diameter agents that accept requests and route
messages to other Diameter nodes based on information found in the
messages (e.g., Destination-Realm). 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.</t>
<t>Relays MAY be used to aggregate requests from multiple Network
Access Servers (NASes) within a common geographical area (POP). The
use of Relays is advantageous since it eliminates the need for
NASes to be configured with the necessary security information they
would otherwise require to communicate with Diameter servers in
other realms. Likewise, this reduces the configuration load on
Diameter servers that would otherwise be necessary when NASes are
added, changed or deleted.</t>
<t>Relays modify Diameter messages by inserting and removing
routing information, but do not modify any other portion of a
message. Relays SHOULD NOT maintain session state but MUST maintain
transaction state.
<figure anchor="Figure2" title="Relaying of Diameter messages">
<artwork>
+------+ ---------> +------+ ---------> +------+
| | 1. Request | | 2. Request | |
| NAS | | DRL | | HMS |
| | 4. Answer | | 3. Answer | |
+------+ <--------- +------+ <--------- +------+
example.net example.net example.com
</artwork>
</figure></t>
<t>The example provided in <xref target="Figure2" /> depicts a request issued from
NAS, which is an access device, for the user bob@example.com. Prior
to issuing the request, NAS performs a Diameter route lookup, using
"example.com" as the key, and determines that the message is to be
relayed to DRL, which is a Diameter Relay. DRL performs the same
route lookup as NAS, and relays the message to HMS, which is
example.com's Home Diameter Server. HMS identifies that the request
can be locally supported (via the realm), processes the
authentication and/or authorization request, and replies with an
answer, which is routed back to NAS using saved transaction
state.</t>
<t>Since Relays do not perform any application level processing,
they provide relaying services for all Diameter applications, and
therefore MUST advertise the Relay Application Id.</t>
</section>
<section anchor="PA" title="Proxy Agents">
<t>Similarly to relays, proxy agents route Diameter messages using
the Diameter Routing Table. However, they differ since they modify
messages to implement policy enforcement. This requires that
proxies maintain the state of their downstream peers (e.g., access
devices) to enforce resource usage, provide admission control, and
provisioning.</t>
<t>Proxies MAY be used in call control centers or access ISPs that
provide outsourced connections, they can monitor the number and
types of ports in use, and make allocation and admission decisions
according to their configuration.</t>
<t>Proxies that wish to limit resources MUST maintain session
state. All proxies MUST maintain transaction state.</t>
<t>Since enforcing policies requires an understanding of the
service being provided, Proxies MUST only advertise the Diameter
applications they support.</t>
</section>
<section anchor="RA" title="Redirect Agents">
<t>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.</t>
<t>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. Further, since redirect agents never relay requests, they
are not required to maintain transaction state.</t>
<t>The example provided in <xref target="Figure3" /> depicts a request issued from
the access device, NAS, for the user bob@example.com. The message
is forwarded by the NAS to its relay, DRL, which does not have a
routing entry in its Diameter Routing Table for example.com. DRL
has a default route configured to DRD, which is a redirect agent
that returns a redirect notification to DRL, as well as HMS'
contact information. Upon receipt of the redirect notification, DRL
establishes a transport connection with HMS, if one doesn't already
exist, and forwards the request to it.
<figure anchor="Figure3" title="Redirecting a Diameter Message">
<artwork>
+------+
| |
| DRD |
| |
+------+
^ |
2. Request | | 3. Redirection
| | Notification
| v
+------+ ---------> +------+ ---------> +------+
| | 1. Request | | 4. Request | |
| NAS | | DRL | | HMS |
| | 6. Answer | | 5. Answer | |
+------+ <--------- +------+ <--------- +------+
example.net example.net example.com
</artwork>
</figure></t>
<t>Since redirect agents do not perform any application level
processing, they provide relaying services for all Diameter
applications, and therefore MUST advertise the Relay Application
Identifier.</t>
</section>
<section anchor="TA" title="Translation Agents">
<t>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.</t>
<t>Given that the Diameter protocol introduces the concept of
long-lived authorized sessions, translation agents MUST be session
stateful and MUST maintain transaction state.</t>
<t>Translation of messages can only occur if the agent recognizes
the application of a particular request, and therefore translation
agents MUST only advertise their locally supported applications.
<figure anchor="Figure4" title="Translation of RADIUS to Diameter">
<artwork>
+------+ ---------> +------+ ---------> +------+
| | RADIUS Request | | Diameter Request | |
| NAS | | TLA | | HMS |
| | RADIUS Answer | | Diameter Answer | |
+------+ <--------- +------+ <--------- +------+
example.net example.net example.com
</artwork>
</figure></t>
</section>
</section>
<section anchor="DPA" title="Diameter Path Authorization">
<t>As noted in Section 2.2, Diameter provides transmission level
security for each connection using TLS. Therefore, each connection can
be authenticated, replay and integrity protected.</t>
<t>In addition to authenticating each connection, each connection
as well as 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.</t>
<t>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.</t>
<t>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 the request was received from.</t>
<t>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 the 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.</t>
<t>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.</t>
<t>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 which would violate those limits. By
issuing an 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.</t>
</section>
</section>
<section anchor="DH" title="Diameter Header">
<t>A summary of the Diameter header format is shown below. The fields
are transmitted in network byte order.
<artwork>
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
</artwork>
</t>
<t>
<list style="hanging">
<t hangText="Version">
<vspace blankLines="1" />This Version field MUST be set to 1 to
indicate Diameter Version 1.</t>
<t hangText=" Message Length">
<vspace blankLines="1" />The Message Length field is three
octets and indicates the length of the Diameter message including
the header fields.</t>
<t hangText="Command Flags">
<vspace blankLines="1" />The Command Flags field is eight bits.
The following bits are assigned:
<artwork>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|R P E T r r r r|
+-+-+-+-+-+-+-+-+
</artwork>
<list style="hanging">
<t hangText="R(equest)">
<vspace blankLines="1" />If set, the message is a request. If
cleared, the message is an answer.
<vspace blankLines="1" /></t>
<t hangText="P(roxiable)">
<vspace blankLines="1" />If set, the message MAY be proxied,
relayed or redirected. If cleared, the message MUST be locally
processed.
<vspace blankLines="1" /></t>
<t hangText="E(rror)">
<vspace blankLines="1" />If set, the message contains a protocol
error, and the message will not conform to the ABNF 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.
<vspace blankLines="1" /></t>
<t hangText="T(Potentially re-transmitted message)">
<vspace blankLines="1" />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 is
sent again. This flag MUST NOT be set in answer messages.
<vspace blankLines="1" /></t>
<t hangText="r(eserved)">
<vspace blankLines="1" />These flag bits are reserved for future
use, and MUST be set to zero, and ignored by the receiver.</t>
</list></t>
<t hangText="Command-Code">
<vspace blankLines="1" />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
11.2.1).
<vspace blankLines="1" />Command-Code values 16,777,214 and
16,777,215 (hexadecimal values FFFFFE -FFFFFF) are reserved for
experimental use (See Section 11.3).</t>
<t hangText=" Application-ID">
<vspace blankLines="1" />Application-ID is four octets and is
used to identify to which application the message is applicable
for. The application can be an authentication application, an
accounting application or a vendor specific application. See
Section 11.3 for the possible values that the application-id may
use.
<vspace blankLines="1" />The application-id in the header MUST
be the same as what is contained in any relevant application-id
AVPs contained in the message.</t>
<t hangText="Hop-by-Hop Identifier">
<vspace blankLines="1" />The Hop-by-Hop Identifier is an
unsigned 32-bit integer field (in network byte order) and 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 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.
<vspace blankLines="1" /></t>
<t hangText="End-to-End Identifier">
<vspace blankLines="1" />The End-to-End Identifier is an
unsigned 32-bit integer field (in network byte order) and 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 (see 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 field
and any routing AVPs that may be present), and 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.
<vspace blankLines="1" /></t>
<t hangText="AVPs">
<vspace blankLines="1" />AVPs are a method of encapsulating information
relevant to the Diameter message. See Section 4 for more
information on AVPs.</t>
</list>
</t>
<section anchor="CC" title="Command Codes">
<t>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.
<vspace blankLines="1" /></t>
<t>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:
<artwork>
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
</artwork></t>
</section>
<section anchor="CCABNF" title="Command Code ABNF specification">
<t>Every Command Code defined MUST include a corresponding ABNF
specification, which is used to define the AVPs that MUST or MAY be
present. The following format is used in the definition:
<artwork>
command-def = command-name "::=" diameter-message
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.
optional = [qual] "[" avp-name "]"
; The avp-name in the 'optional' rule cannot
; evaluate to any AVP Name which is included
; in a fixed or required rule. The AVP can
; appear anywhere in the message.
qual = [min] "*" [max]
; See ABNF conventions, RFC 4234 Section 6.6.
; The absence of any qualifiers 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.
;
; NOTE: "[" and "]" have a different meaning
; than in ABNF (see the optional rule, above).
; These braces cannot be used to express
; optional fixed rules (such as an optional
; ICV at the end). To do this, the convention
; is '0*1fixed'.
min = 1*DIGIT
; The minimum number of times the element may
; be present. The default value is zero.
max = 1*DIGIT
; The maximum number of times the element may
; be present. The default value is infinity. A
; value of zero 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 following is a definition of a fictitious command code:
Example-Request ::= < Diameter Header: 9999999, REQ, PXY >
{ User-Name }
* { Origin-Host }
* [ AVP
</artwork></t>
</section>
<section anchor="DCNC" title="Diameter Command Naming Conventions">
<t>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.</t>
<t>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.</t>
<t>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:
<list style="symbols">
<t>The request was successful</t>
<t>The request failed</t>
<t>An additional request MUST be sent to provide information the
peer requires prior to returning a successful or failed answer.</t>
<t>The receiver could not process the request, but provides
information about a Diameter peer that is able to satisfy the
request, known as redirect.</t>
</list></t>
<t>Additional information, encoded within AVPs, MAY also be included
in answer messages.
<vspace blankLines="1" /></t>
</section>
</section>
<section anchor="AVP" title="Diameter AVPs">
<t>Diameter AVPs carry specific authentication, accounting,
authorization and routing information as well as
configuration details for the request and reply.</t>
<t>Some AVPs MAY be listed more than once. The effect of such an AVP is
specific, and is specified in each case by the AVP description.</t>
<t>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 till a word
boundary is reached. The length of the padding is not reflected in the
AVP Length field.</t>
<section anchor="AVPHeader" title="AVP Header">
<t>The fields in the AVP header MUST be sent in network byte order.
The format of the header is:
<artwork>
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 r r r r r r| AVP Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-ID (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
</artwork></t>
<t>
<list style="hanging">
<t hangText="AVP Code">
<vspace blankLines="1" />The AVP Code, combined with the Vendor-Id
field, identifies the attribute uniquely. AVP numbers 1 through
255 are reserved for backward compatibility with RADIUS, without
setting the Vendor-Id field. AVP numbers 256 and above are used
for Diameter, which are allocated by IANA (see Section 11.1).
<vspace blankLines="1" /></t>
<t hangText="AVP Flags">
<vspace blankLines="1" />The AVP Flags field informs the receiver
how each attribute must be handled. The 'r' (reserved) bits are
unused and SHOULD be set to 0. Note that subsequent Diameter
applications MAY define additional bits within the AVP Header,
and an unrecognized bit SHOULD be considered an error. The 'P' bit
indicates the need for encryption for end-to-end security. Note
that the 'P' bit has been deprecated and MUST be to zero(0) when
sending an AVP and ingnored on receipt of an AVP.
<vspace blankLines="1" />The 'M' Bit, known as the Mandatory bit,
indicates whether support of the AVP is required. If an AVP with
the 'M' bit set is received by a Diameter client, server, proxy,
or translation agent and either the AVP or its value is
unrecognized, the message MUST be rejected. An exception to this
rule 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.
<vspace blankLines="1" />The 'M' bit MUST be set according to the
rules defined for the AVP containing it. In order to preserve
interoperability, a Diameter implementation MUST be able to
exclude from a Diameter message any Mandatory AVP which is
neither defined in the base Diameter protocol nor in any of the
Diameter Application specifications governing the message in
which it appears. It MAY do this in one of the following ways:
<list style="numbers">
<t>If a message is rejected because it
contains a Mandatory AVP which is neither defined in the base
Diameter standard nor in any of the Diameter Application
specifications governing the message in which it appears, the
implementation may resend the message without the AVP, possibly
inserting additional standard AVPs instead.</t>
<t>A configuration option may be
provided on a system wide, per peer, or per realm basis that
would allow/prevent particular Mandatory AVPs to be sent. Thus an
administrator could change the configuration to avoid
interoperability problems.</t>
</list>
<vspace blankLines="1" />Diameter implementations are required to
support all Mandatory AVPs which are allowed by the message's
formal syntax and defined either in the base Diameter standard or
in one of the Diameter Application specifications governing the
message.
<vspace blankLines="1" />AVPs with the 'M' bit cleared are
informational only and 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.
<vspace blankLines="1" />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.
<vspace blankLines="1" />Unless otherwise noted, AVPs will have
the following default AVP Flags field settings:
<vspace blankLines="1" />The 'M' bit MUST be set. The 'V' bit
MUST NOT be set.</t>
<t hangText="AVP Length">
<vspace blankLines="1" />The AVP Length field is three octets,
and indicates the number of octets in this AVP including the AVP
Code, AVP Length, AVP Flags, Vendor-ID field (if present) and the
AVP data. If a message is received with an invalid attribute
length, the message SHOULD be rejected.</t>
</list>
</t>
<section anchor="opt" title="Optional Header Elements">
<t>The AVP Header contains one optional field. This field is only
present if the respective bit-flag is enabled.
<vspace blankLines="1" />
<list style="hanging">
<t hangText="Vendor-ID">
<vspace blankLines="1" />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"
<xref target="RFC3232" /> value, encoded in network byte order.
Any vendor wishing to implement a vendor-specific Diameter AVP
MUST use their own Vendor-ID along with their privately managed
AVP address space, guaranteeing that they will not collide with
any other vendor's vendor-specific AVP(s), nor with future IETF
applications.
<vspace blankLines="1" />A vendor ID value of zero (0)
corresponds to the IETF adopted AVP values, as managed by the
IANA. Since the absence of the vendor ID field implies that the
AVP in question is not vendor specific, implementations MUST NOT
use the zero (0) vendor ID.</t>
</list></t>
</section>
</section>
<section anchor="AVPDF" title="Basic AVP Data Formats">
<t>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.
<vspace blankLines="1" />
<list style="hanging">
<t hangText="OctetString">
<vspace blankLines="1" />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 four-octets in length is
followed by the necessary padding so that the next AVP (if any)
will start on a 32-bit boundary.
<vspace blankLines="1" /></t>
<t hangText="Integer32">
<vspace blankLines="1" />32 bit signed value, in network byte order.
The AVP Length field MUST be set to 12 (16 if the 'V' bit is
enabled).
<vspace blankLines="1" /></t>
<t hangText="Integer64">
<vspace blankLines="1" />64 bit signed value, in network byte order.
The AVP Length field MUST be set to 16 (20 if the 'V' bit is
enabled).
<vspace blankLines="1" /></t>
<t hangText="Unsigned32">
<vspace blankLines="1" />32 bit unsigned value, in network byte
order. The AVP Length field MUST be set to 12 (16 if the 'V' bit is
enabled).
<vspace blankLines="1" /></t>
<t hangText="Unsigned64">
<vspace blankLines="1" />64 bit unsigned value, in network byte
order. The AVP Length field MUST be set to 16 (20 if the 'V' bit is
enabled).
<vspace blankLines="1" /></t>
<t hangText="Float32">
<vspace blankLines="1" />This represents floating point values of
single precision as described by
<xref target="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).
<vspace blankLines="1" /></t>
<t hangText="Float64">
<vspace blankLines="1" />This represents floating point values of
double precision as described by
<xref target="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).
<vspace blankLines="1" /></t>
<t hangText="Grouped">
<vspace blankLines="1" />The Data field is specified as a sequence of
AVPs. Each of these AVPs follows - in the order in which they are
specified - including their headers and padding. The AVP Length
field is set to 8 (12 if the 'V' bit is enabled) plus the total
length of all included AVPs, including their headers and padding.
Thus the AVP length field of an AVP of type Grouped is always a
multiple of 4.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="DerivedAVP" title="Derived AVP Data Formats">
<t>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 AVP Derived Data Formats MUST include
them in a section entitled "AVP Derived 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.</t>
<t>The below AVP Derived Data Formats are commonly used by
applications.
<vspace blankLines="1" />
<list style="hanging">
<t hangText="Address">
<vspace blankLines="1" />The Address format is derived from the
OctetString AVP Base Format. It is a discriminated union,
representing, for example a 32-bit (IPv4)
<xref target="RFC791" /> or 128-bit (IPv6)
<xref target="RFC4291" /> address, most significant octet first. The
first two octets of the Address AVP represents the AddressType,
which contains an Address Family defined in
<xref target="IANAADFAM" />. The AddressType is used to
discriminate the content and format of the remaining octets.
<vspace blankLines="1" /></t>
<t hangText="Time">
<vspace blankLines="1" />The Time format is derived from the OctetString
AVP Base 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 chapter 3 of
<xref target="RFC4330" />.
<vspace blankLines="1" />This represents the number of seconds
since 0h on 1 January 1900 with respect to the Coordinated
Universal Time (UTC).
<vspace blankLines="1" />On 6h 28m 16s UTC, 7 February 2036 the
time value will overflow. SNTP
<xref target="RFC4330" /> describes a procedure to extend the time
to 2104. This procedure MUST be supported by all DIAMETER nodes.
<vspace blankLines="1" /></t>
<t hangText="UTF8String">
<vspace blankLines="1" />The UTF8String format is derived from the
OctetString AVP Base Format. This is a human readable string
represented using the ISO/IEC IS 10646-1 character set, encoded as
an OctetString using the UTF-8 <xref target="RFC3629"/> transformation format
described in RFC 3629.
<vspace blankLines="1" />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.
<vspace blankLines="1" />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.
<vspace blankLines="1" />The use of leading or trailing white space
SHOULD be avoided.
<vspace blankLines="1" />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.
<vspace blankLines="1" />For information encoded in 7-bit US-ASCII,
the UTF-8 charset is identical to the US-ASCII charset.
<vspace blankLines="1" />UTF-8 may require multiple bytes to
represent a single character / code point; thus the length of an
UTF8String in octets may be different from the number of characters
encoded.
<vspace blankLines="1" />Note that the AVP Length field of an
UTF8String is measured in octets, not characters.</t>
<t hangText="DiameterIdentity">
<vspace blankLines="1" />The DiameterIdentity format is
derived from the OctetString AVP Base Format.
<artwork>
DiameterIdentity = FQDN
</artwork>
<vspace blankLines="1" />DiameterIdentity value is used to uniquely
identify a Diameter node for purposes of duplicate connection and
routing loop detection.
<vspace blankLines="1" />The contents of the string MUST be the
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 it is
sent on. Note that in this document, DiameterIdentity is in ASCII
form in order to be compatible with existing DNS infrastructure.
See <xref target="appIDNA" /> for interactions between the Diameter
protocol and Internationalized Domain Name (IDNs).
<vspace blankLines="1" /></t>
<t hangText="DiameterURI">
<vspace blankLines="1" />The DiameterURI MUST follow the Uniform
Resource Identifiers (URI) syntax
<xref target="RFC3986" /> rules specified below:
<artwork>
"aaa://" FQDN [ port ] [ transport ] [ protocol ]
; No transport security
"aaas://" FQDN [ port ] [ transport ] [ protocol ]
; Transport security used
FQDN = Fully Qualified Host Name
port = ":" 1*DIGIT
; One of the ports used to listen for
; incoming connections.
; If absent,
; the default Diameter port (3868) is
; assumed.
transport = ";transport=" transport-protocol
; One of the transports used to listen
; for incoming connections. If absent,
; the default SCTP [RFC2960] protocol is
; assumed. 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
</artwork></t>
<t hangText="Enumerated">
<vspace blankLines="1" />Enumerated is derived from the Integer32
AVP Base Format. The definition contains a list of valid values and
their interpretation and is described in the Diameter application
introducing the AVP.
<vspace blankLines="1" /></t>
<t hangText="IPFilterRule">
<vspace blankLines="1" />The IPFilterRule format is derived from the
OctetString AVP Base 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:
<artwork>
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
</artwork>
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.
<vspace blankLines="1" />IPFilterRule filters MUST follow the
format:
<artwork>
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.
ipno/bits An IP number as above with a mask
width of the form 1.2.3.4/24. In
this case, all IP numbers from
1.2.3.0 to 1.2.3.255 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.
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:
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).
</artwork>
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.
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor=" GroupedAVP" title=" Grouped AVP Values">
<t>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.</t>
<t>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.</t>
<t>Every Grouped AVP defined MUST include a corresponding grammar,
using ABNF
<xref target="RFC4234" /> (with modifications), as defined below.
<artwork>
grouped-avp-def = name "::=" avp
name-fmt = ALPHA *(ALPHA / DIGIT / "-")
name = name-fmt
; The name has to be the name of an AVP,
; defined in the base or extended Diameter
; specifications.
avp = header [ *fixed] [ *required] [ *optional]
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.
</artwork></t>
<section anchor="ePG" title="Example AVP with a Grouped Data type">
<t>The Example-AVP (AVP Code 999999) is of type Grouped and is used
to clarify how Grouped AVP values work. The Grouped Data field has
the following ABNF grammar:
<artwork>
Example-AVP ::= < AVP Header: 999999 >
{ Origin-Host }
1*{ Session-Id }
*[ AVP ]
An Example-AVP with Grouped Data follows.
The Origin-Host AVP is required (Section 6.3). In this case:
Origin-Host = "example.com".
One or more Session-Ids must follow. Here there are two:
Session-Id =
"grump.example.com:33041;23432;893;0AF3B81"
Session-Id =
"grump.example.com:33054;23561;2358;0AF3B82"
optional AVPs included are
Recovery-Policy = <binary>
2163bc1d0ad82371f6bc09484133c3f09ad74a0dd5346d54195a7cf0b35
2cabc881839a4fdcfbc1769e2677a4c1fb499284c5f70b48f58503a45c5
c2d6943f82d5930f2b7c1da640f476f0e9c9572a50db8ea6e51e1c2c7bd
f8bb43dc995144b8dbe297ac739493946803e1cee3e15d9b765008a1b2a
cf4ac777c80041d72c01e691cf751dbf86e85f509f3988e5875dc905119
26841f00f0e29a6d1ddc1a842289d440268681e052b30fb638045f7779c
1d873c784f054f688f5001559ecff64865ef975f3e60d2fd7966b8c7f92
Futuristic-Acct-Record = <binary>
fe19da5802acd98b07a5b86cb4d5d03f0314ab9ef1ad0b67111ff3b90a0
57fe29620bf3585fd2dd9fcc38ce62f6cc208c6163c008f4258d1bc88b8
17694a74ccad3ec69269461b14b2e7a4c111fb239e33714da207983f58c
41d018d56fe938f3cbf089aac12a912a2f0d1923a9390e5f789cb2e5067
d3427475e49968f841
</artwork></t>
<t>The data for the optional AVPs is represented in hex since the
format of these AVPs is neither known at the time of definition of
the Example-AVP group, nor (likely) at the time when the example
instance of this AVP is interpreted - except by Diameter
implementations which support the same set of AVPs. The encoding
example illustrates how padding is used and how length fields are
calculated. Also note that AVPs may be present in the Grouped AVP
value which the receiver cannot interpret (here, the Recover-Policy
and Futuristic-Acct-Record AVPs). 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.
<vspace blankLines="1" /></t>
<t>This AVP would be encoded as follows:
<artwork>
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|
+-------+-------+-------+-------+-------+-------+-------+-------+
</artwork></t>
</section>
</section>
<section anchor="DBAVP" title="Diameter Base Protocol AVPs">
<t>The following table describes the Diameter AVPs defined in the
base protocol, their AVP Code values, types, possible flag values.</t>
<t>Due to space constraints, the short form DiamIdent is used to
represent DiameterIdentity.
<artwork>
+---------------------+
| AVP Flag rules |
|----+-----+----+-----|
AVP Section | | |SHLD| MUST|
Attribute Name Code Defined Data Type |MUST| MAY | NOT| 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 | | | | |
Accounting- 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 | | | | |
-----------------------------------------|----+-----+----+-----|
</artwork>
<artwork>
+---------------------+
| AVP Flag rules |
|----+-----+----+-----|
AVP Section | | |SHLD| MUST|
Attribute Name Code Defined Data Type |MUST| MAY | NOT| 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 | | | | |
-----------------------------------------|----+-----+----+-----|
</artwork></t>
</section>
</section>
<section anchor="DPeers" title="Diameter Peers">
<t>This section describes how Diameter nodes establish connections and
communicate with peers.</t>
<section anchor="PC" title="Peer Connections">
<t>Although a Diameter node may have many possible peers that it is
able to communicate with, 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.</t>
<t>Note that a given peer MAY act as a primary for a given realm,
while acting as a secondary for another realm.</t>
<t>When a peer is deemed suspect, which could occur for various
reasons, including not receiving a DWA within an allotted timeframe,
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.</t>
<t>There are two ways that a peer is removed from the suspect peer
list:
<vspace blankLines="1" />
<list style="numbers">
<t>The peer is no longer reachable, causing the transport
connection to be shutdown. The peer is moved to the closed
state.</t>
<t>Three watchdog messages are exchanged with accepted round trip
times, and the connection to the peer is considered stabilized.</t>
</list></t>
<t>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.</t>
</section>
<section anchor="PeerDis" title="Diameter Peer Discovery">
<t>Allowing for dynamic Diameter agent discovery will make it
possible for simpler and more robust deployment of Diameter services.
In order to promote interoperable implementations of Diameter peer
discovery, the following mechanisms are described. These are based on
existing IETF standards. The first option (manual configuration) MUST
be supported by all DIAMETER nodes, while the latter option
(DNS) MAY be supported.</t>
<t>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:
<vspace blankLines="1" />
<list style="numbers">
<t>The Diameter implementation consults its list of static
(manually) configured Diameter agent locations. These will be used
if they exist and respond.
<vspace blankLines="1" /></t>
<t>The Diameter implementation performs a NAPTR query for a server
in a particular realm. The Diameter implementation has to know in
advance which realm to look for a Diameter agent in. This could be
deduced, for example, from the 'realm' in a NAI that a Diameter
implementation needed to perform a Diameter operation on.
<list style="symbols">
<t>The services relevant for the task of transport protocol
selection are those with NAPTR service fields with values
"AAA+D2x", where x is a letter that corresponds to a transport
protocol supported by the domain. This specification defines D2T
for TCP and D2S for SCTP. We also establish an IANA registry for
NAPTR service name to transport protocol mappings.
<vspace blankLines="1" />These NAPTR records provide a mapping
from a domain, to the SRV record for contacting a server with the
specific transport protocol in the NAPTR services field. The
resource record will contain an empty regular expression and a
replacement value, which is the SRV record for that particular
transport protocol. If the server supports multiple transport
protocols, there will be multiple NAPTR records, each with a
different service value. As per
<xref target="RFC3403" />, the client discards any records whose
services fields are not applicable. For the purposes of this
specification, several rules are defined.
<vspace blankLines="1" /></t>
<t>A client MUST discard any service fields that identify a
resolution service whose value is not "D2X", for values of X that
indicate transport protocols supported by the client. The NAPTR
processing as described in <xref target="RFC3403"/> will result in discovery of
the most preferred transport protocol of the server that is
supported by the client, as well as an SRV record for the server.
<vspace blankLines="1" />The domain suffixes in the NAPTR
replacement field SHOULD match the domain of the original query.
<vspace blankLines="1" /></t>
</list></t>
<t>If no NAPTR records are found, the requester queries for those
address records for the destination address,
'_diameter._sctp'.realm or '_diameter._tcp'.realm. Address records
include A RR's, AAAA RR's or other similar records, chosen
according to the requestor's network protocol capabilities. If the
DNS server returns no address records, the requestor gives up.
<vspace blankLines="1" />If the server is using a site certificate,
the domain name in the 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 or 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 that this was the desired behavior, or the result of an
attack
<vspace blankLines="1" />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, or validation of DNS RRs via DNSSEC
is not sufficient to conclude this. For example, a web server may
have obtained a valid TLS 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.
<vspace blankLines="1" />Authorization can be achieved for example,
by configuration of a Diameter Server CA. Alternatively this can be
achieved by definition of OIDs within TLS or IKE certificates so as
to signify Diameter Server authorization.
<vspace blankLines="1" /></t>
</list></t>
<t>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 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.</t>
</section>
<section anchor="CE" title="Capabilities Exchange">
<t>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, supported Diameter applications, security mechanisms,
etc.)</t>
<t>The receiver only issues commands to its peers that have
advertised support for the Diameter application that defines the
command. A Diameter node MUST cache the supported applications in
order to ensure that unrecognized commands and/or AVPs are not
unnecessarily sent to a peer.</t>
<t>A receiver of a Capabilities-Exchange-Req (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.</t>
<t>The receiver of the Capabilities-Exchange-Request (CER) MUST
determine common applications by computing the intersection of
its own set of supported Application Id against all of the
application indentifier 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.</t>
<t>Similarly, a receiver of a Capabilities-Exchange-Req (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.</t>
<t>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.</t>
<t>The CER and CEA messages MUST NOT be proxied, redirected or
relayed.</t>
<t>Since the CER/CEA messages cannot be proxied, it is still possible
that an upstream agent receives 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 (see Section 7.) with the Result-Code AVP set to
DIAMETER_UNABLE_TO_DELIVER to inform the downstream to take action
(e.g., re-routing request to an alternate peer).</t>
<t>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).</t>
<section anchor="CER" title="Capabilities-Exchange-Request">
<t>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.</t>
<t>When Diameter is run over SCTP
<xref target="RFC2960" />, which allows 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.
<artwork>
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 ]
</artwork></t>
</section>
<section anchor="CEA" title="Capabilities-Exchange-Answer">
<t>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.</t>
<t>When Diameter is run over SCTP
<xref target="RFC2960" />, which allows 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.
<artwork>
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 ]
</artwork></t>
</section>
<section anchor="vendor" title="Vendor-Id AVP">
<t>The Vendor-Id AVP (AVP Code 266) is of type Unsigned32 and
contains the IANA "SMI Network Management Private Enterprise Codes"
<xref target="RFC3232" /> value assigned to the vendor of the
Diameter device. It is envisioned that the combination of the
Vendor-Id, Product-Name (Section 5.3.7) and the Firmware-Revision
(Section 5.3.4) AVPs may provide useful debugging information.</t>
<t>A Vendor-Id value of zero in the CER or CEA messages is reserved
and indicates that this field is ignored.</t>
</section>
<section anchor="firmware" title="Firmware-Revision AVP">
<t>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.</t>
<t>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.</t>
</section>
<section anchor="hostavp" title="Host-IP-Address AVP">
<t>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
<xref target="RFC2960" /> MUST be advertised in the CER and CEA
messages by including a Host-IP- Address AVP for each address. This
AVP MUST ONLY be used in the CER and CEA messages.</t>
</section>
<section anchor="supvenavp" title="Supported-Vendor-Id AVP">
<t>The Supported-Vendor-Id AVP (AVP Code 265) is of type Unsigned32
and contains the IANA "SMI Network Management Private Enterprise
Codes"
<xref target="RFC3232" /> 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 SHOULD NOT be set to zero.
Multiple instances of this AVP containing the same value SHOULD NOT be
sent.</t>
</section>
<section anchor="prodavp" title="Product-Name AVP">
<t>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.</t>
</section>
</section>
<section anchor="discon" title="Disconnecting Peer connections">
<t>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
connection request would not be welcomed. The Disconnection-Reason
AVP contains the reason the Diameter node issued the
Disconnect-Peer-Request message.</t>
<t>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 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.</t>
<t>The receiver of the Disconnect-Peer-Answer initiates the transport
disconnect. The sender of the Disconnect-Peer-Answer should be able
to detect the transport closure and cleanup the connection.</t>
<section anchor="req" title="Disconnect-Peer-Request">
<t>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 its intentions to shutdown the transport connection. Upon
detection of a transport failure, this message MUST NOT be sent to
an alternate peer.
<artwork>
Message Format
<DPR> ::= < Diameter Header: 282, REQ >
{ Origin-Host }
{ Origin-Realm }
{ Disconnect-Cause }
</artwork>
</t>
</section>
<section anchor="ans" title=" Disconnect-Peer-Answer">
<t>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 shutdown.
<artwork>
Message Format
<DPA> ::= < Diameter Header: 282 >
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
[ Error-Message ]
[ Failed-AVP ]
</artwork>
</t>
</section>
<section anchor="cau" title=" Disconnect-Cause AVP">
<t>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
shutdown the transport connection. The following values are
supported:
<artwork>
REBOOTING 0
A scheduled reboot is imminent. Receiver of 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.
Receiver of 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. Receiver of DPR
with above result code SHOULD NOT attempt reconnection.
</artwork></t>
</section>
</section>
<section anchor="transfa" title="Transport Failure Detection">
<t>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.</t>
<section anchor="wat" title="Device-Watchdog-Request">
<t>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.
<artwork>
Message Format
<DWR> ::= < Diameter Header: 280, REQ >
{ Origin-Host }
{ Origin-Realm }
[ Origin-State-Id ]
</artwork></t>
</section>
<section anchor="devi" title="Device-Watchdog-Answer">
<t>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.
<artwork>
Message Format
<DWA> ::= < Diameter Header: 280 >
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
[ Error-Message ]
[ Failed-AVP ]
[ Origin-State-Id ]
</artwork></t>
</section>
<section anchor="transalg" title=" Transport Failure Algorithm">
<t>The transport failure algorithm is defined in
<xref target="RFC3539" />. All Diameter implementations MUST
support the algorithm defined in the specification in order to be
compliant to the Diameter base protocol.</t>
</section>
<section anchor="fail" title="Failover and Failback Procedures">
<t>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.</t>
<t>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.</t>
<t>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
records still remaining to be transmitted in non-volatile storage.
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.</t>
<t>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.</t>
<t>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.</t>
</section>
</section>
<section anchor="peerst" title="Peer State Machine">
<t>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.</t>
<t>This state machine is closely coupled with the state machine
described in
<xref target="RFC3539" />, which is used to open, close, failover,
probe, and reopen transport connections. Note in particular that
<xref target="RFC3539" /> requires the use of watchdog messages to
probe connections. For Diameter, DWR and DWA messages are to be
used.</t>
<t>I- is used to represent the initiator (connecting) connection,
while the R- is used to represent the responder (listening)
connection. The lack of a prefix indicates that the event or action
is the same regardless of the connection on which the event
occurred.</t>
<t>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.</t>
<t>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.</t>
<t>For TLS usage, a TLS handshake will begin when both ends are in
the open state. If the TLS handshake is successful, all further
messages will be sent via TLS. If the handshake fails, both ends move
to the closed state.</t>
<t>The state machine constrains only the behavior of a Diameter
implementation as seen by Diameter peers through events on the
wire.</t>
<t>Any implementation that produces equivalent results is considered
compliant.
<artwork>
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, Closed
R-Disc
R-Peer-Disc R-Disc Closed
R-Rcv-CER R-Snd-CEA R-Open
R-Rcv-CEA Process-CEA R-Open
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, Closed
I-Disc
I-Peer-Disc I-Disc Closed
I-Rcv-CER I-Snd-CEA I-Open
I-Rcv-CEA Process-CEA I-Open
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
</artwork></t>
<section anchor="inc" title="Incoming connections">
<t>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; and the source port of
an incoming connection is arbitrary. Upon receipt of CER, the
identity of the connecting peer can be uniquely determined from
Origin-Host.</t>
<t>For this reason, a Diameter peer must employ logic separate from
the state machine to receive connection requests, accept them, and
await CER. Once CER arrives on a new connection, the Origin-Host
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.</t>
<t>The logic that handles incoming connections SHOULD close and
discard the connection if any message other than CER arrives, or if
an implementation-defined timeout occurs prior to receipt of
CER.</t>
<t>Because handling of incoming connections up to and including
receipt of CER requires logic, separate from that of any individual
state machine associated with a particular peer, it is described
separately in this section rather than in the state machine
above.</t>
</section>
<section anchor="eve" title="Events">
<t>Transitions and actions in the automaton are caused by events.
In this section, we will ignore the -I and -R prefix, since the
actual event would be identical, but would occur on one of two
possible connections.
<artwork>
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 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).
</artwork></t>
</section>
<section anchor="act" title="Actions">
<t>Actions in the automaton are caused by events and typically
indicate the transmission of packets and/or an action to be taken
on the connection. In this section we will ignore the I- and
R-prefix, since the actual action would be identical, but would
occur on one of two possible connections.
<artwork>
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 shutdown, and any
local resources are freed.
Error The transport layer connection is disconnected, either
politely or abortively, in response to an error
condition. Local resources are freed.
Process-CEA A received CEA is processed.
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.
</artwork></t>
</section>
<section anchor="elep" title="The Election Process">
<t>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 upper-case counterparts
between 'A' and 'Z'. See <xref target="appIDNA" /> for interactions
between the Diameter protocol and Internationalized Domain Name (IDNs).</t>
<t>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.</t>
</section>
<section anchor="capUp" title="Capabilities Update">
<t>A Diameter node MUST initiate peer capabilities update by
sending a Capabilities-Exchange-Req (CER) to all its peers
which supports peer capabilities update and is in OPEN
state. The receiver of CER in open state MUST process and
reply to the CER as a described in <xref target="CE" />. The CEA
which the receiver sends MUST contain its latest
capabilities. Note that peers which successfully process
the peer capabilities update SHOULD also update their
routing tables to reflect the change. The receiver of
the CEA, with a Result-Code AVP other than DIAMETER_SUCCESS,
initiates the transport disconnect. The peer may periodically
attempt to reconnect, as stated in <xref target="trans" />.</t>
<t>Peer capabilities update in the open state SHOULD be
limited to the advertisement of the new list of supported
applications and MUST preclude re-negotiation of security
mechanism or other capabilities. If any capabilities change
happens in the node (e.g. change in security mechanisms),
other than a change in the supported applications, the
node SHOULD gracefully terminate (setting the
Disconnect-Cause AVP value to REBOOTING) and re-establish
the diameter connections to all the peers.</t>
</section>
</section>
</section>
<section anchor="DMP" title="Diameter message processing">
<t>This section describes how Diameter requests and answers are created
and processed.</t>
<section anchor="rout" title="Diameter Request Routing Overview">
<t>A request is sent towards its final destination using a
combination of the Destination-Realm and Destination-Host AVPs, in
one of these three combinations:
<list style="symbols">
<t>a request that is not able to be proxied (such as CER) MUST NOT
contain either Destination-Realm or Destination-Host AVPs.</t>
<t>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.</t>
<t>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.</t>
</list></t>
<t>The Destination-Host AVP is used as described above when the
destination of the request is fixed, which includes:
<list style="symbols">
<t>Authentication requests that span multiple round trips</t>
<t>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.</t>
<t>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.</t>
</list></t>
<t>Note that an agent can forward a request to a host described in
the Destination-Host AVP only if the host in question is included in
its peer table (see Section 2.7). Otherwise, the request is routed
based on the Destination-Realm only (see Sections 6.1.6).</t>
<t>The Destination-Realm AVP MUST be present if the message is
proxiable. A message that MUST NOT be forwarded by Diameter
agents (proxies, redirects or relays) MUST NOT include the
Destination-Realm in its ABNF. For Diameter clients, the value of
the Destination-Realm AVP MAY be extracted from the User-Name AVP,
or other application-specific methods.</t>
<t>When a message is received, the message is processed in the
following order:
<list style="symbols">
<t>If the message is destined for the local host, the procedures
listed in Section 6.1.4 are followed.</t>
<t>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.</t>
<t>The procedures listed in Section 6.1.6 are followed, which is
known as Request Routing.</t>
<t>If none of the above is successful, an answer is returned with
the Result-Code set to DIAMETER_UNABLE_TO_DELIVER, with the E-bit
set.</t>
</list></t>
<t>For routing of Diameter messages to work within an administrative
domain, all Diameter nodes within the realm MUST be peers.</t>
<t>Note the processing rules contained in this section are intended
to be used as general guidelines to Diameter developers. Certain
implementations MAY use different methods than the ones described
here, and still comply with the protocol specification. See Section 7
for more detail on error handling.</t>
<section anchor="origi" title="Originating a Request">
<t>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:
<list style="symbols">
<t>the Command-Code is set to the appropriate value</t>
<t>the 'R' bit is set</t>
<t>the End-to-End Identifier is set to a locally unique value</t>
<t>the Origin-Host and Origin-Realm AVPs MUST be set to the
appropriate values, used to identify the source of the
message</t>
<t>the Destination-Host and Destination-Realm AVPs MUST be set to
the appropriate values as described in Section 6.1.</t>
</list></t>
</section>
<section anchor="send" title="Sending a Request">
<t>When sending a request, originated either locally, or as the
result of a forwarding or routing operation, the following
procedures MUST be followed:
<list style="symbols">
<t>the Hop-by-Hop Identifier should be set to a locally unique
value.</t>
<t>The message should be saved in the list of pending
requests.</t>
</list></t>
<t>Other actions to perform on the message based on the
particular role the agent is playing are described in the
following sections.</t>
</section>
<section anchor="RR" title="Receiving Requests">
<t>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.</t>
</section>
<section anchor="PLR" title="Processing Local Requests">
<t>A request is known to be for local consumption when one of the
following conditions occur:
<list style="symbols">
<t>The Destination-Host AVP contains the local host's
identity,</t>
<t>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</t>
<t>Both the Destination-Host and the Destination-Realm are not
present.</t>
</list></t>
<t>When a request is locally processed, the rules in Section 6.2
should be used to generate the corresponding answer.</t>
</section>
<section anchor="RF" title="Request Forwarding">
<t>Request forwarding is done using the Diameter Peer Table. The
Diameter peer table contains all of the peers that the local node
is able to directly communicate with.</t>
<t>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.</t>
</section>
<section anchor="RRo" title="Request Routing">
<t>Diameter request message routing is done via realms and
applications. A Diameter message that may be forwarded by
Diameter agents (proxies, redirects or relays) 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.</t>
<t>Diameter agents MAY have a list of locally supported realms and
applications, and 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).</t>
<t>Realm names and Application Ids are the minimum supported
routing criteria, additional routing information maybe needed to support
redirect semantics.</t>
</section>
<section anchor="preL" title="Predictive Loop Avoidance">
<t>Before forwarding or routing a request, Diameter agents, in
addition to processing done in Section 6.1.3, SHOULD check
for the presence of candidate route's peer identity in any
of the Route-Record AVPs. In an event of the agent detecting
the presence of a candidate route's peer identity in a
Route-Record AVP, the agent MUST ignore such route for the
Diameter request message and attempt alternate routes if any.
In case all the candidate routes are eliminated by the above
criteria, the agent SHOULD return DIAMETER_UNABLE_TO_DELIVER
message.</t>
</section>
<section anchor="ReR" title="Redirecting requests">
<t>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
separate Redirect-Host AVP.
<figure anchor="Figure5" title="Diameter Redirect Agent">
<artwork>
+------------------+
| Diameter |
| Redirect Agent |
+------------------+
^ | 2. command + 'E' bit
1. Request | | Result-Code =
joe@example.com | | DIAMETER_REDIRECT_INDICATION +
| | Redirect-Host AVP(s)
| v
+-------------+ 3. Request +-------------+
| example.com |------------->| example.net |
| Relay | | Diameter |
| Agent |<-------------| Server |
+-------------+ 4. Answer +-------------+
</artwork>
</figure></t>
<t>The receiver of the answer message with the 'E' bit set, and the
Result-Code AVP set to DIAMETER_REDIRECT_INDICATION uses the
hop-by- hop field in the Diameter header to identify the request in
the pending message queue (see Section 5.3) that is to be
redirected. If no transport connection exists with the new agent,
one is created, and the request is sent directly to it.</t>
<t>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.</t>
<t>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
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.</t>
<t>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) cached routes
for the same realm and Application Id. However, one has a redirect
usage of ALL_SESSION where matching request will be forwarded to one
peer and 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 againt the redirect
usage value to resolve the contention. The precedence rule can be found
in Section 6.13.</t>
</section>
<section anchor="ReRr" title="Relaying and Proxying Requests">
<t>A relay or proxy agent MUST append a Route-Record AVP to all
requests forwarded. The AVP contains the identity of the peer the
request was received from.</t>
<t>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.</t>
<t>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. Proxy-Info AVP has certain
security implications and SHOULD contain an embedded HMAC with a
node-local key. Alternatively, it MAY simply use local storage to
store state information.</t>
<t>The message is then forwarded to the next hop, as identified in
the Routing Table.</t>
<t><xref target="Figure6" /> provides an example of message routing using the
procedures listed in these sections.
<figure anchor="Figure6" title="Routing of Diameter messages">
<artwork>
(Origin-Host=nas.mno.net) (Origin-Host=nas.mno.net)
(Origin-Realm=mno.net) (Origin-Realm=mno.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)
</artwork>
</figure></t>
<t>Relay agents do not require full validation of incoming messages.
At a minimum, validation of the message header and relevant routing
AVPs has to be done when relaying messages.</t>
</section>
</section>
<section anchor="DAP" title="Diameter Answer Processing">
<t>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:
<list style="symbols">
<t>The same Hop-by-Hop identifier in the request is used in the
answer.</t>
<t>The local host's identity is encoded in the Origin-Host AVP.</t>
<t>The Destination-Host and Destination-Realm AVPs MUST NOT be
present in the answer message.</t>
<t>The Result-Code AVP is added with its value indicating success
or failure.</t>
<t>If the Session-Id is present in the request, it MUST be included
in the answer.</t>
<t>Any Proxy-Info AVPs in the request MUST be added to the answer
message, in the same order they were present in the request.</t>
<t>The 'P' bit is set to the same value as the one in the
request.</t>
<t>The same End-to-End identifier in the request is used in the
answer.</t>
</list></t>
<t>Note that the error messages (see Section 7.3) are also subjected
to the above processing rules.</t>
<section anchor="PRA" title=" Processing received Answers">
<t>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.</t>
</section>
<section anchor="RPA" title="Relaying and Proxying Answers">
<t>If the answer is for a request which was proxied or relayed, the
agent MUST restore the original value of the Diameter header's Hop-
by-Hop Identifier field.</t>
<t>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.</t>
<t>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 and it MUST issue an STR on behalf of the
access device.</t>
<t>The agent MUST then send the answer to the host that it received
the original request from.</t>
</section>
</section>
<section anchor="OHAVP" title="Origin-Host AVP">
<t>The Origin-Host AVP (AVP Code 264) is of type DiameterIdentity,
and MUST be present in all Diameter messages. This AVP identifies the
endpoint that originated the Diameter message. Relay agents MUST NOT
modify this AVP.</t>
<t>The value of the Origin-Host AVP is guaranteed to be unique within
a single host.</t>
<t>Note that the Origin-Host AVP may resolve to more than one address
as the Diameter peer may support more than one address.</t>
<t>This AVP SHOULD be placed as close to the Diameter header as
possible.</t>
</section>
<section anchor="ORAVP" title="Origin-Realm AVP">
<t>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.</t>
<t>This AVP SHOULD be placed as close to the Diameter header as
possible.</t>
</section>
<section anchor="DHAVP" title="Destination-Host AVP">
<t>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.</t>
<t>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.</t>
<t>This AVP SHOULD be placed as close to the Diameter header as
possible.</t>
</section>
<section anchor="DRAVP" title="Destination-Realm AVP">
<t>The Destination-Realm AVP (AVP Code 283) is of type
DiameterIdentity, and contains the realm the message is to be routed
to. The Destination-Realm AVP MUST NOT be present in Answer messages.
Diameter Clients insert the realm portion of the User-Name AVP.
Diameter servers initiating a request message use the value of the
Origin-Realm AVP from a previous message received from the intended
target host (unless it is known a priori). When present, the
Destination-Realm AVP is used to perform message routing
decisions.</t>
<t>Request messages whose ABNF does not list the Destination-Realm
AVP as a mandatory AVP are inherently non-routable messages.</t>
<t>This AVP SHOULD be placed as close to the Diameter header as
possible.</t>
</section>
<section anchor="RAVP" title="Routing AVPs">
<t>The AVPs defined in this section are Diameter AVPs used for
routing purposes. These AVPs change as Diameter messages are
processed by agents.</t>
<section anchor="RRAVP" title="Route-Record AVP">
<t>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.</t>
</section>
<section anchor="PIAVP" title="Proxy-Info AVP">
<t>The Proxy-Info AVP (AVP Code 284) is of type Grouped. The
Grouped Data field has the following ABNF grammar:
<artwork>
Proxy-Info ::= < AVP Header: 284 >
{ Proxy-Host }
{ Proxy-State }
* [ AVP ]
</artwork></t>
</section>
<section anchor="PHAVP" title="Proxy-Host AVP">
<t>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.</t>
</section>
<section anchor="PSAVP" title="Proxy-State AVP">
<t>The Proxy-State AVP (AVP Code 33) is of type OctetString, and
contains state local information, and MUST be treated as opaque
data.</t>
</section>
</section>
<section anchor="authAVP" title="Auth-Application-Id AVP">
<t>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.</t>
</section>
<section anchor="AAAVP" title="Acct-Application-Id AVP">
<t>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.</t>
</section>
<section anchor="InAVP" title="Inband-Security-Id AVP">
<t>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.</t>
<t>Currently, the following values are supported, but there is ample
room to add new security Ids.
<vspace blankLines="1" />
<list style="hanging">
<t hangText="NO_INBAND_SECURITY 0">
<vspace blankLines="1" />This peer does not support TLS.
This is the default value, if the AVP is omitted.</t>
<t hangText="TLS 1">
<vspace blankLines="1" />This node supports TLS security, as defined by
<xref target="RFC4346" />.</t>
</list></t>
</section>
<section anchor="VSVP" title="Vendor-Specific-Application-Id AVP">
<t>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 Sec 11.3. It
MUST also match the Application Id present in the diameter
header except when used in a CER or CEA messages.</t>
<t>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.</t>
<t>This AVP MUST also be present as the first AVP in all experimental
commands defined in the vendor-specific application.</t>
<t>This AVP SHOULD be placed as close to the Diameter header as
possible.
<artwork>
AVP Format
<Vendor-Specific-Application-Id> ::= < AVP Header: 260 >
{ Vendor-Id }
[ Auth-Application-Id ]
[ Acct-Application-Id ]
</artwork></t>
<t>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 any 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.</t>
<t>If a Vendor-Specific-Application-Id is received that contains both
Auth-Application-Id and Acct-Application-Id, then the recipient SHOULD
issue an answer with Result-Code set to DIAMETER_AVP_OCCURS_TOO_MANY_TIMES.
The answer SHOULD also include a Failed-AVP which MUST contain the received
Auth-Application-Id AVP and Acct-Application-Id AVP.
</t>
</section>
<section anchor="RHAVP" title="Redirect-Host AVP">
<t>One or more of 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.</t>
<t>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 pertaining to this session.</t>
</section>
<section anchor="RHUAVP" title="Redirect-Host-Usage AVP">
<t>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.</t>
<t>When present, this AVP dictates how the routing entry resulting
from the Redirect-Host is to be used. The following values are
supported:
<vspace blankLines="1" />
<list style="hanging">
<t hangText="DONT_CACHE 0">
<vspace blankLines="1" />The host specified in the Redirect-Host
AVP should not be cached. This is the default value.
<vspace blankLines="1" /></t>
<t hangText="ALL_SESSION 1">
<vspace blankLines="1" />All messages within the same session,
as defined by the same value of the Session-ID AVP MAY be sent to
the host specified in the Redirect-Host AVP.
<vspace blankLines="1" /></t>
<t hangText="ALL_REALM 2">
<vspace blankLines="1" />All messages destined for the realm
requested MAY be sent to the host specified in the Redirect-Host
AVP.
<vspace blankLines="1" /></t>
<t hangText="REALM_AND_APPLICATION 3">
<vspace blankLines="1" />All messages for the
application requested to the realm specified MAY be sent to the
host specified in the Redirect-Host AVP.</t>
<t hangText="ALL_APPLICATION 4">
<vspace blankLines="1" />All messages for the application
requested MAY be sent to the host specified in the Redirect-Host
AVP.
<vspace blankLines="1" /></t>
<t hangText="ALL_HOST 5">
<vspace blankLines="1" />All messages that would be sent to the
host that generated the Redirect-Host MAY be sent to the host
specified in the Redirect- Host AVP.
<vspace blankLines="1" /></t>
<t hangText="ALL_USER 6">
<vspace blankLines="1" />All messages for the user requested MAY be
sent to the host specified in the Redirect-Host AVP.
<vspace blankLines="1" /></t>
</list></t>
<vspace blankLines="1" />
<t>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:
<vspace blankLines="1" />
<list style="numbers">
<t>ALL_SESSION</t>
<t>ALL_USER</t>
<t>REALM_AND_APPLICATION</t>
<t>ALL_REALM</t>
<t>ALL_APPLICATION</t>
<t>ALL_HOST</t>
</list></t>
</section>
<section anchor="ReM" title="Redirect-Max-Cache-Time AVP">
<t>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, the Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION
and the Redirect-Host-Usage AVP set to a non-zero value.</t>
<t>This AVP contains the maximum number of seconds the peer and route
table entries, created as a result of the Redirect-Host, will be
cached. Note that once a host created due to a redirect indication is
no longer reachable, any associated peer and routing table entries
MUST be deleted.</t>
</section>
</section>
<section anchor="EH" title="Error Handling">
<t>There are two different types of errors in Diameter; protocol and
application errors. A protocol error is one that occurs at the base
protocol level, and MAY require per hop attention (e.g., message
routing error). Application errors, on the other hand, generally occur
due to a problem with a function specified in a Diameter application
(e.g., user authentication, Missing AVP).</t>
<t>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.
<figure anchor="Figure7"
title="Example of Protocol Error causing answer message">
<artwork>
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 |-----------+
+---------+
</artwork>
</figure></t>
<t><xref target="Figure7" /> 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.
<figure anchor="Figure8"
title="Example of Application Error Answer message">
<artwork>
+---------+ 1. Request +---------+ 2. Request +---------+
| Access |------------>|Diameter |------------>|Diameter |
| | | | | Home |
| Device |<------------| Relay |<------------| Server |
+---------+ 4. Answer +---------+ 3. Answer +---------+
(Missing AVP) (Missing AVP)
</artwork>
</figure></t>
<t><xref target="Figure8" /> provides an example of a Diameter message that caused an
application error. When application errors occur, the Diameter entity
reporting the error clears the 'R' bit in the Command Flags, and adds
the Result-Code AVP with the proper value. Application errors do not
require any proxy or relay agent involvement, and therefore the message
would be forwarded back to the originator of the request.</t>
<t>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:
<list style="symbols">
<t>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.</t>
<t>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.</t>
<t>A command is received with an AVP that is omitted, yet is
mandatory according to the command's ABNF. The receiver issues an
answer with the Result-Code set to DIAMETER_MISSING_AVP, and creates
an AVP with the AVP Code and other fields set as expected in the
missing AVP. The created AVP is then added to the Failed- AVP AVP.</t>
</list></t>
<t>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.
<vspace blankLines="1" /></t>
<section anchor="ReAVP" title="Result-Code AVP">
<t>The Result-Code AVP (AVP Code 268) is of type Unsigned32 and
indicates whether a particular request was completed successfully or
whether an error occurred. All Diameter answer messages defined in
IETF applications 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.
<vspace blankLines="1" /></t>
<t>The Result-Code data field contains an IANA-managed 32-bit address
space representing errors (see Section 11.4). Diameter provides the
following classes of errors, all identified by the thousands digit in
the decimal notation:
<list style="symbols">
<t>1xxx (Informational)</t>
<t>2xxx (Success)</t>
<t>3xxx (Protocol Errors)</t>
<t>4xxx (Transient Failures)</t>
<t>5xxx (Permanent Failure)</t>
</list></t>
<t>A non-recognized class (one whose first digit is not defined in
this section) MUST be handled as a permanent failure.</t>
<section anchor="If" title="Informational">
<t>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.
<vspace blankLines="1" />
<list style="hanging">
<t hangText="DIAMETER_MULTI_ROUND_AUTH 1001">
<vspace blankLines="1" />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.</t>
</list></t>
</section>
<section anchor="suc" title="Success">
<t>Errors that fall within the Success category are used to inform
a peer that a request has been successfully completed.
<vspace blankLines="1" />
<list style="hanging">
<t hangText="DIAMETER_SUCCESS 2001">
<vspace blankLines="1" />The Request was successfully
completed.</t>
<t hangText="DIAMETER_LIMITED_SUCCESS 2002">
<vspace blankLines="1" />When returned, the
request was successfully completed, but additional processing is
required by the application in order to provide service to the
user.</t>
</list></t>
</section>
<section anchor="PEr" title="Protocol Errors">
<t>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 and
only these errors MUST only be used in answer messages whose
'E' bit is set. To provide backward compatibility with
existing implementations that follow <xref target='RFC3588' />,
some of the error values that have previously been used in
this category by <xref target='RFC3588' /> will not be re-used.
Therefore the error values enumerated here may be non-sequential.
<vspace blankLines="1" />
<list style="hanging">
<!--- 3001 is left blank for backwards compatibility -->
<t hangText="DIAMETER_UNABLE_TO_DELIVER 3002">
<vspace blankLines="1" />This error is given
when Diameter can not 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
Destination-Host AVP was given without the associated
Destination-Realm AVP.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_REALM_NOT_SERVED 3003">
<vspace blankLines="1" />The intended realm
of the request is not recognized.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_TOO_BUSY 3004">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_LOOP_DETECTED 3005">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_REDIRECT_INDICATION 3006">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_APPLICATION_UNSUPPORTED 3007">
<vspace blankLines="1" />A request was
sent for an application that is not supported.
<vspace blankLines="1" /></t>
<!--- 3008 is left blank for backwards compatibility -->
<!--- 3009 is left blank for backwards compatibility -->
<!--- 3010 is left blank for backwards compatibility -->
<t hangText="DIAMETER_INVALID_BIT_IN_HEADER 3011">
<vspace blankLines="1" />This error is returned when a
reserved bit in the Diameter header is set
to one (1) or the bits in the Diameter header defined in Sec 3
are set incorrectly.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_INVALID_MESSAGE_LENGTH 3012">
<vspace blankLines="1" />This error is
returned when a request is received with an invalid message
length.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="TE" title="Transient Failures">
<t>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.
<vspace blankLines="1" />
<list style="hanging">
<t hangText="DIAMETER_AUTHENTICATION_REJECTED 4001">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_OUT_OF_SPACE 4002">
<vspace blankLines="1" />A Diameter node received
the accounting request but was unable to commit it to stable
storage due to a temporary lack of space.
<vspace blankLines="1" /></t>
<t hangText="ELECTION_LOST 4003">
<vspace blankLines="1" />The peer has determined that it
has lost the election process and has therefore disconnected the
transport connection.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="PF" title="Permanent Failures">
<t>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 then answer messages with E-bit set and complying to the
grammar described in 7.2 MAY also be used for permanent errors.</t>
<t>To provide backward compatibility with existing implementations
that follow <xref target='RFC3588' />, some of the error values that
have previously been used in this category by <xref target='RFC3588' />
will not be re-used. Therefore the error values enumerated here maybe
non-sequential.</t>
<vspace blankLines="1" />
<list style="hanging">
<t hangText="DIAMETER_AVP_UNSUPPORTED 5001">
<vspace blankLines="1" />The peer received a
message that contained an AVP that is not recognized or supported
and was marked with the Mandatory bit. A Diameter message with
this error MUST contain one or more Failed- AVP AVP containing
the AVPs that caused the failure.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_UNKNOWN_SESSION_ID 5002">
<vspace blankLines="1" />The request
contained an unknown Session-Id.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_AUTHORIZATION_REJECTED 5003">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_INVALID_AVP_VALUE 5004">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_MISSING_AVP 5005">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_RESOURCES_EXCEEDED 5006">
<vspace blankLines="1" />A request was
received that cannot be authorized because the user has already
expended allowed resources. An example of this error condition is
a user that is restricted to one dial-up PPP port, attempts to
establish a second PPP connection.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_CONTRADICTING_AVPS 5007">
<vspace blankLines="1" />The Home Diameter
server has detected AVPs in the request that contradicted each
other, and is not willing to provide service to the user. The
Failed-AVP AVPs MUST be present which contains the AVPs that
contradicted each other.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_AVP_NOT_ALLOWED 5008">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_AVP_OCCURS_TOO_MANY_TIMES 5009">
<vspace blankLines="1" />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
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_NO_COMMON_APPLICATION 5010">
<vspace blankLines="1" />This error is returned by a Diameter node
that is not acting as a relay when it receives a CER which advertises
a set of applications that it does not support.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_UNSUPPORTED_VERSION 5011">
<vspace blankLines="1" />This error is
returned when a request was received, whose version number is
unsupported.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_UNABLE_TO_COMPLY 5012">
<vspace blankLines="1" />This error is
returned when a request is rejected for unspecified reasons.
<vspace blankLines="1" /></t>
<!--- 5013 is left blank for backwards compatibility -->
<t hangText="DIAMETER_INVALID_AVP_LENGTH 5014">
<vspace blankLines="1" />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 avp length is less
than 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.
<vspace blankLines="1" /></t>
<!--- 5015 is left blank for backwards compatibility -->
<!--- 5016 is left blank for backwards compatibility -->
<t hangText="DIAMETER_NO_COMMON_SECURITY 5017">
<vspace blankLines="1" />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) MUST be returned with the
Result-Code AVP set to DIAMETER_NO_COMMON_SECURITY.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_UNKNOWN_PEER 5018">
<vspace blankLines="1" />A CER was received from
an unknown peer.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_COMMAND_UNSUPPORTED 5019">
<vspace blankLines="1" />The Request
contained a Command-Code that the receiver did not recognize or
support. This MUST be used when a Diameter node receives an
experimental command that it does not understand.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_INVALID_HDR_BITS 5020">
<vspace blankLines="1" />A request was
received whose bits in the Diameter header were either set to an
invalid combination, or to a value that is inconsistent with the
command code's definition.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_INVALID_AVP_BITS 5021">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
</list>
</section>
</section>
<section anchor="EB" title="Error Bit">
<t>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 ABNF specification for the command, and will
instead conform to the following ABNF:
<artwork>
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 ]
* [ Proxy-Info ]
* [ AVP ]
</artwork></t>
<t>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.</t>
</section>
<section anchor="EmAVP" title="Error-Message AVP">
<t>The Error-Message AVP (AVP Code 281) is of type UTF8String. It MAY
accompany a Result-Code AVP as a human readable error message. The
Error-Message AVP is not intended to be useful in real-time, and
SHOULD NOT be expected to be parsed by network entities.</t>
</section>
<section anchor="ERHAV" title="Error-Reporting-Host AVP">
<t>The Error-Reporting-Host AVP (AVP Code 294) is of type
DiameterIdentity. This AVP contains the identity of the Diameter host
that sent the Result-Code AVP to a value other than 2001 (Success),
only if the host setting the Result-Code is different from the one
encoded in the Origin-Host AVP. This AVP is intended to be used for
troubleshooting purposes, and MUST be set when the Result- Code AVP
indicates a failure.</t>
</section>
<section anchor="failedavp" title="Failed-AVP AVP">
<t>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 message SHOULD contain only one
Failed-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.</t>
<t>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 which is restricted to 0, 1, or
0-1 occurrences.</t>
<t>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
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.</t>
<t>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 heirarchy up to the single offending
AVP. This enables the recipient to detect the location of the offending AVP
when embedded in a group.</t>
<t>AVP Format
<artwork>
<Failed-AVP> ::= < AVP Header: 279 >
1* {AVP}
</artwork></t>
</section>
<section anchor="exp" title="Experimental-Result AVP">
<t>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. Its Data field has the
following ABNF grammar:
<vspace blankLines="1" />AVP Format
<artwork>
Experimental-Result ::= < AVP Header: 297 >
{ Vendor-Id }
{ Experimental-Result-Code }
</artwork></t>
<t>The Vendor-Id AVP (see Section 5.3.3) in this grouped AVP
identifies the vendor responsible for the assignment of the result
code which follows. All Diameter answer messages defined in
vendor-specific applications MUST include either one Result-Code AVP
or one Experimental-Result AVP.</t>
</section>
<section anchor="expavp" title="Experimental-Result-Code AVP">
<t>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.</t>
<t>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).</t>
</section>
</section>
<section anchor="DUS" title="Diameter User Sessions">
<t>In general, Diameter can provide two different types of services to
applications. The first involves authentication and authorization, and
can optionally make use of accounting. The second only makes use of
accounting.</t>
<t>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.</t>
<t>When a Diameter server authorizes a user to use 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 the home realm is willing to be fiscally responsible for.
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.</t>
<t>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.</t>
<t>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 is used to terminate user sessions. These
are used to allow servers that maintain state information to free
resources.</t>
<t>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.</t>
<t>Diameter may also be used for services that cannot be easily
categorized as authentication, authorization or accounting (e.g.,
certain 3GPP IMS interfaces). In such cases, the finite state machine
defined in subsequent sections may not be applicable. Therefore, the
applications itself MAY need to define its own finite state machine.
However, such application specific state machines MUST comply
with general Diameter user session requirements such co-relating all
message exchanges via Session-Id AVP.</t>
<section anchor="authses" title="Authorization Session State Machine">
<t>This section contains a set of finite state machines, representing
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).</t>
<t>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.</t>
<t>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 as an error
condition, and an answer, if applicable, MUST be returned to the
originator of the message.</t>
<t>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 maintains state (e.g., Send RAR, Pending, Receive RAA)
MAY be ignored.</t>
<t>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'.</t>
<t>The following state machine is observed by a client when state is
maintained on the server:
<artwork>
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
Pending Failed Service-specific Cleanup 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 session Result-Code
= SUCCESS,
Send STR.
Open ASR Received, Send ASA Open
client will not comply with with
request to end the session Result-Code
!= SUCCESS
Open Authorization-Lifetime + Send STR Discon
Auth-Grace-Period expires on
access device
Discon ASR Received Send ASA Discon
Discon STA Received Discon. Idle
user/device
</artwork></t>
<t>The following state machine is observed by a server when it is
maintaining state for the session:
<artwork>
SERVER, STATEFUL
State Event Action New State
-------------------------------------------------------------
Idle Service-specific authorization Send Open
request received, and successful
user is authorized serv.
specific
answer
Idle Service-specific authorization Send Idle
request received, and failed serv.
user is not authorized specific
answer
Open Service-specific authorization Send Open
request received, and user successful
is authorized serv. specific
answer
Open Service-specific authorization Send Idle
request received, and user failed serv.
is not authorized specific
answer,
Cleanup
Open Home server wants to confirm Send RAR Pending
authentication and/or
authorization of the user
Pending Received RAA with a failed Cleanup Idle
Result-Code
Pending Received RAA with Result-Code Update Open
= SUCCESS session
Open Home server wants to Send ASR Discon
terminate the service
Open Authorization-Lifetime (and Cleanup Idle
Auth-Grace-Period) expires
on home server.
Open Session-Timeout expires on Cleanup Idle
home server
Discon Failure to send ASR Wait, Discon
resend ASR
Discon ASR successfully sent and Cleanup Idle
ASA Received with Result-Code
Not ASA Received None No Change.
Discon
Any STR Received Send STA, Idle
Cleanup.
</artwork></t>
<t>The following state machine is observed by a client when state is
not maintained on the server:
<artwork>
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 Cleanup 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
</artwork></t>
<t>The following state machine is observed by a server when it is not
maintaining state for the session:
<artwork>
SERVER, STATELESS
State Event Action New State
-------------------------------------------------------------
Idle Service-specific authorization Send serv. Idle
request received, and specific
successfully processed answer
</artwork></t>
</section>
<section anchor="accses" title="Accounting Session State Machine">
<t>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.</t>
<t>See Section 9.7 for Accounting Command Codes and Section 9.8 for
Accounting AVPs.</t>
<t>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.</t>
<t>The default server side state machine requires the reception of
accounting records in any order and at any time, and 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.
Both base Diameter AVPs as well as application specific AVPs MAY 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 limits checks, and so on.</t>
<t>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, and hence
accounting connectivity problems are required to cause the serviced
user to be disconnected. Otherwise, records produced by the client
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, which the 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.</t>
<t>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.</t>
<t>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.</t>
<t>The event 'Failed answer' means that the Diameter client received
a non-transient failure notification in the Accounting Answer
command.</t>
<t>Note that the action 'Disconnect user/dev' MUST have an effect
also to 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.</t>
<t>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.
<artwork>
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
PendingS Successful accounting Open
start answer received
PendingS Failure to send and buffer Store Open
space available and realtime Start
not equal to DELIVER_AND_GRANT Record
PendingS Failure to send and no buffer Open
space available and realtime
equal to GRANT_AND_LOSE
PendingS Failure to send and no buffer Disconnect Idle
space available and realtime user/dev
not equal to
GRANT_AND_LOSE
PendingS Failed accounting start answer Open
received and realtime equal
to GRANT_AND_LOSE
PendingS Failed accounting start answer Disconnect Idle
received and realtime 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 record interim
can be overwritten) and record
realtime not equal to
DELIVER_AND_GRANT
PendingI Failure to send and no buffer Open
space available and realtime
equal to GRANT_AND_LOSE
PendingI Failure to send and no buffer Disconnect Idle
space available and realtime user/dev
not equal to GRANT_AND_LOSE
PendingI Failed accounting interim Open
answer received and realtime
equal to GRANT_AND_LOSE
PendingI Failed accounting interim Disconnect Idle
answer received and realtime user/dev
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
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
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
</artwork></t>
</section>
<section anchor="srvini" title="Server-Initiated Re-Auth">
<t>A Diameter server may initiate a re-authentication and/or re-
authorization service for a particular session by issuing a Re-Auth-
Request (RAR).</t>
<t>For example, for pre-paid services, the Diameter server that
originally authorized a session may need some confirmation that the
user is still using the services.</t>
<t>An access device that receives a RAR message with Session-Id equal
to a currently active session MUST initiate a re-auth towards the
user, if the service supports this particular feature. Each Diameter
application MUST state whether service-initiated re-auth is
supported, since some applications do not allow access devices to
prompt the user for re-auth.</t>
<section anchor="reauthreq" title="Re-Auth-Request">
<t>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.</t>
<t>
<artwork>
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 ]
</artwork>
</t>
</section>
<section anchor="reauthans" title="Re-Auth-Answer">
<t>The Re-Auth-Answer (RAA), indicated by the Command-Code set to
258 and the message flags' 'R' bit clear, is sent in response to
the RAR. The Result-Code AVP MUST be present, and indicates the
disposition of the request.</t>
<t>A successful RAA message MUST be followed by an
application-specific authentication and/or authorization
message.</t>
<t>
<artwork>
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 ]
</artwork>
</t>
</section>
</section>
<section anchor="sester" title="Session Termination">
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>It is also possible that a session that was authorized is never
actually started due to action of a proxy. For example, a proxy may
modify an authorization answer, converting the result from success to
failure, prior to forwarding the message to the access device. 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.</t>
<t>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.</t>
<t>A Diameter server also MUST clean up resources when the Session-
Timeout expires, or when the Authorization-Lifetime and the Auth-
Grace-Period AVPs expires 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.</t>
<section anchor="sesterreq" title="Session-Termination-Request">
<t>The Session-Termination-Request (STR), indicated by the
Command-Code set to 275 and the Command Flags' 'R' bit set, is sent
by the access device to inform the Diameter Server that an
authenticated and/or authorized session is being terminated.</t>
<t>
<artwork>
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 ]
</artwork>
</t>
</section>
<section anchor="sesterans" title="Session-Termination-Answer">
<t>The Session-Termination-Answer (STA), indicated by the
Command-Code set to 275 and the message flags' 'R' bit clear, is
sent by the Diameter Server to acknowledge the notification that
the session has been terminated. The Result-Code AVP MUST be
present, and MAY contain an indication that an error occurred while
servicing the STR.</t>
<t>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.</t>
<t>
<artwork>
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 ]
</artwork>
</t>
</section>
</section>
<section anchor="Abses" title="Aborting a Session">
<t>A Diameter server may request that the access device stop
providing service for a particular session by issuing an
Abort-Session-Request (ASR).</t>
<t>For example, the Diameter server that originally authorized the
session may be required to cause that session to be stopped for
credit or other reasons that were not anticipated when the session
was first authorized. On the other hand, an operator may maintain a
management server for the purpose of issuing ASRs to administratively
remove users from the network.</t>
<t>An access device that receives an ASR with Session-ID equal to a
currently active session MAY stop the session. Whether the access
device stops the session or not is implementation- and/or
configuration-dependent. For example, an access device may honor ASRs
from certain agents only. In any case, the access device MUST respond
with an Abort-Session-Answer, including a Result-Code AVP to indicate
what action it took.</t>
<t>Note that if the access device does stop the session upon receipt
of an ASR, it issues an STR to the authorizing server (which may or
may not be the agent issuing the ASR) just as it would if the session
were terminated for any other reason.</t>
<section anchor="Absesre" title="Abort-Session-Request">
<t>The Abort-Session-Request (ASR), indicated by the Command-Code
set to 274 and the message flags' 'R' bit set, may be sent by any
server to the access device that is providing session service, to
request that the session identified by the Session-Id be
stopped.</t>
<t>
<artwork>
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 ]
</artwork>
</t>
</section>
<section anchor="Absesans" title="Abort-Session-Answer">
<t>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.</t>
<t>If the session identified by Session-Id in the ASR was
successfully terminated, Result-Code is set to DIAMETER_SUCCESS. If
the session is not currently active, Result-Code is set to
DIAMETER_UNKNOWN_SESSION_ID. If the access device does not stop the
session for any other reason, Result-Code is set to
DIAMETER_UNABLE_TO_COMPLY.</t>
<t>
<artwork>
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 ]
</artwork>
</t>
</section>
</section>
<section anchor="Iinfsester"
title="Inferring Session Termination from Origin-State-Id">
<t>Origin-State-Id is used to allow rapid detection of terminated
sessions for which no STR would have been issued, due to
unanticipated shutdown of an access device.</t>
<t>By including Origin-State-Id in CER/CEA messages, an access device
allows a next-hop server to determine immediately upon connection
whether the device has lost its sessions since the last
connection.</t>
<t>By including Origin-State-Id in request messages, an access device
also allows a server with which it communicates via proxy to make
such a determination. However, a server that is not directly
connected with the access device will not discover that the access
device has been restarted unless and until it receives a new request
from the access device. Thus, use of this mechanism across proxies is
opportunistic rather than reliable, but useful nonetheless.</t>
<t>When a Diameter server receives an Origin-State-Id that is greater
than the Origin-State-Id previously received from the same issuer, it
may assume that the issuer has lost state since the previous message
and that all sessions that were active under the lower Origin-State-
Id have been terminated. The Diameter server MAY clean up all session
state associated with such lost sessions, and MAY also issues STRs
for all such lost sessions that were authorized on upstream servers,
to allow session state to be cleaned up globally.</t>
</section>
<section anchor="authreqty" title="Auth-Request-Type AVP">
<t>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:
<vspace blankLines="1" />
<list style="hanging">
<t hangText="AUTHENTICATE_ONLY 1">
<vspace blankLines="1" />The request being sent is for
authentication only, and MUST contain the relevant application
specific authentication AVPs that are needed by the Diameter server
to authenticate the user.
<vspace blankLines="1" /></t>
<t hangText="AUTHORIZE_ONLY 2">
<vspace blankLines="1" />The request being sent is for
authorization only, and MUST contain the application specific
authorization AVPs that are necessary to identify the service being
requested/offered.
<vspace blankLines="1" /></t>
<t hangText="AUTHORIZE_AUTHENTICATE 3">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="sesavp" title="Session-Id AVP">
<t>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).</t>
<t>The Session-Id MUST be globally and eternally unique, as it is
meant to uniquely identify a user session without reference to any
other information, and may be needed to correlate historical
authentication information with accounting information. The
Session-Id includes a mandatory portion and an implementation-defined
portion; a recommended format for the implementation-defined portion
is outlined below.</t>
<t>The Session-Id MUST begin with the sender's identity encoded in
the DiameterIdentity type (see Section 4.4). The remainder of the
Session-Id is delimited by a ";" character, and MAY be any sequence
that the client can guarantee to be eternally unique; however, the
following format is recommended, (square brackets [] indicate an
optional element):
<artwork>
<DiameterIdentity>;<high 32 bits>;<low 32 bits>[;<optional value>]
</artwork></t>
<t><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
<xref target="RFC4330" />, 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.</t>
<t>
<artwork>
<optional value> is implementation specific but may include a modem's
device Id, a layer 2 address, timestamp, etc.
Example, in which there is no optional value:
accesspoint7.acme.com;1876543210;523
Example, in which there is an optional value:
accesspoint7.acme.com;1876543210;523;mobile@200.1.1.88
</artwork>
</t>
<t>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 authorization and accounting
commands of a given application.</t>
</section>
<section anchor="authzav" title="Authorization-Lifetime AVP">
<t>The Authorization-Lifetime AVP (AVP Code 291) is of type
Unsigned32 and contains the maximum number of seconds of service to
be provided to the user before the user is to be re-authenticated
and/or re- authorized. Great care should be taken when the
Authorization- Lifetime value is determined, since a low, non-zero,
value could create significant Diameter traffic, which could congest
both the network and the agents.</t>
<t>A value of zero (0) means that immediate re-auth is necessary by
the access device. This is typically used in cases where multiple
authentication methods are used, and a successful auth response with
this AVP set to zero is used to signal that the next authentication
method is to be immediately initiated. 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.</t>
<t>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.</t>
<t>An Authorization-Lifetime AVP MAY be present in re-authorization
messages, and 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.</t>
<t>This AVP MAY be provided by the client as a hint of the maximum
lifetime 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.</t>
</section>
<section anchor="authgra" title="Auth-Grace-Period AVP">
<t>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.</t>
</section>
<section anchor="authsesst" title="Auth-Session-State AVP">
<t>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:
<vspace blankLines="1" />
<list style="hanging">
<t hangText="STATE_MAINTAINED 0">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="NO_STATE_MAINTAINED 1">
<vspace blankLines="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.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="rarta" title="Re-Auth-Request-Type AVP">
<t>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. 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:
<vspace blankLines="1" />
<list style="hanging">
<t hangText="AUTHORIZE_ONLY 0">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="AUTHORIZE_AUTHENTICATE 1">
<vspace blankLines="1" />An authentication and
authorization re-auth is expected upon expiration of the
Authorization-Lifetime.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="sestav" title="Session-Timeout AVP">
<t>The Session-Timeout AVP (AVP Code 27)
<xref target="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.</t>
<t>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 8.11).</t>
<t>A Session-Timeout AVP MAY be present in a re-authorization answer
message, and contains the remaining number of seconds from the
beginning of the re-auth.</t>
<t>A value of zero, or the absence of this AVP, means that this
session has an unlimited number of seconds before termination.</t>
<t>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.</t>
</section>
<section anchor="usrav" title="User-Name AVP">
<t>The User-Name AVP (AVP Code 1)
<xref target="RFC2865" /> is of type UTF8String, which contains the
User-Name, in a format consistent with the NAI specification
<xref target="RFC4282" />.</t>
</section>
<section anchor="tcavav" title="Termination-Cause AVP">
<t>The Termination-Cause AVP (AVP Code 295) is of type Enumerated,
and is used to indicate the reason why a session was terminated on
the access device. The following values are defined:
<vspace blankLines="1" />
<list style="hanging">
<t hangText="DIAMETER_LOGOUT 1">
<vspace blankLines="1" />The user initiated a disconnect
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_SERVICE_NOT_PROVIDED 2">
<vspace blankLines="1" />This value is used
when the user disconnected prior to the receipt of the
authorization answer message.
<vspace blankLines="1" /></t>
<t hangText="DIAMETER_BAD_ANSWER 3">
<vspace blankLines="1" />This value indicates that the
authorization answer received by the access device was not
processed successfully.
<vspace blankLines="1" /></t>
<t hangText=" DIAMETER_ADMINISTRATIVE 4">
<vspace blankLines="1" />The user was not granted
access, or was disconnected, due to administrative reasons, such as
the receipt of a Abort-Session-Request message.
<vspace blankLines="1" /></t>
<t hangText=" DIAMETER_LINK_BROKEN 5">
<vspace blankLines="1" />The communication to the user
was abruptly disconnected.
<vspace blankLines="1" /></t>
<t hangText=" DIAMETER_AUTH_EXPIRED 6">
<vspace blankLines="1" />The user's access was
terminated since its authorized session time has expired.
<vspace blankLines="1" /></t>
<t hangText=" DIAMETER_USER_MOVED 7">
<vspace blankLines="1" />The user is receiving services
from another access device.
<vspace blankLines="1" /></t>
<t hangText=" DIAMETER_SESSION_TIMEOUT 8">
<vspace blankLines="1" />The user's session has
timed out, and service has been terminated.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="origist" title="Origin-State-Id AVP">
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
<section anchor="sesbiav" title="Session-Binding AVP">
<t>The Session-Binding AVP (AVP Code 270) is of type Unsigned32, and
MAY be present in application-specific authorization answer messages.
If present, this AVP MAY inform the Diameter client that all future
application-specific re-auth messages for this session MUST be sent
to the same authorization server. This AVP MAY also specify that a
Session-Termination-Request message for this session MUST be sent to
the same authorizing server.</t>
<t>This field is a bit mask, and the following bits have been
defined:
<vspace blankLines="1" />
<list style="hanging">
<t hangText="RE_AUTH 1">
<vspace blankLines="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.
<vspace blankLines="1" /></t>
<t hangText="STR 2">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="ACCOUNTING 4">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="sesfail" title="Session-Server-Failover AVP">
<t>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.</t>
<t>The following values are supported:
<vspace blankLines="1" />
<list style="hanging">
<t hangText="REFUSE_SERVICE 0">
<vspace blankLines="1" />If either the re-auth or the STR
message delivery fails, terminate service with the user, and do not
attempt any subsequent attempts.
<vspace blankLines="1" /></t>
<t hangText="TRY_AGAIN 1">
<vspace blankLines="1" />If either the re-auth or the STR message
delivery fails, resend the failed message without the
Destination-Host AVP present.
<vspace blankLines="1" /></t>
<t hangText="ALLOW_SERVICE 2">
<vspace blankLines="1" />If re-auth message delivery fails,
assume that re-authorization succeeded. If STR message delivery
fails, terminate the session.
<vspace blankLines="1" /></t>
<t hangText="TRY_AGAIN_ALLOW_SERVICE 3">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="mulrouti" title="Multi-Round-Time-Out AVP">
<t>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.</t>
</section>
<section anchor="classav" title="Class AVP">
<t>The Class AVP (AVP Code 25) is of type OctetString and is used to
by Diameter servers to return state information to the access device.
When one or more Class AVPs are present in application-specific
authorization answer messages, they MUST be present in subsequent
re-authorization, session termination and accounting messages. Class
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.</t>
</section>
<section anchor="evttsav" title="Event-Timestamp AVP">
<t>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.</t>
</section>
</section>
<section anchor="accg" title="Accounting">
<t>This accounting protocol is based on a server directed model with
capabilities for real-time delivery of accounting information. Several
fault resilience methods
<xref target="RFC2975" /> have been built in to the protocol in order
minimize loss of accounting data in various fault situations and under
different assumptions about the capabilities of the used devices.</t>
<section anchor="sdm" title="Server Directed Model">
<t>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.</t>
<t>As discussed in
<xref target="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.</t>
<t>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.</t>
<t>The Diameter accounting server MAY override the interim interval
or the realtime 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.</t>
</section>
<section anchor="prm" title="Protocol Messages">
<t>A Diameter node that receives a successful authentication and/or
authorization messages from the Home AAA server MUST collect
accounting information for the session. The Accounting-Request
message is used to transmit the accounting information to the Home
AAA server, which MUST reply with the Accounting-Answer message to
confirm reception. The Accounting-Answer message includes the
Result-Code AVP, which MAY indicate that an error was present in the
accounting message. A rejected Accounting-Request message MAY cause
the user's session to be terminated, depending on the value of the
Accounting-Realtime-Required AVP received earlier for the session in
question.</t>
<t>Each Diameter Accounting protocol message MAY be compressed, in
order to reduce network bandwidth usage. If TLS is used to secure
the Diameter session, then TLS compression <xref target="RFC4346" />
MAY be used.</t>
</section>
<section anchor="appdoc" title="Accounting Application Extension and Requirements">
<t>Each Diameter application (e.g., NASREQ, MobileIP), MUST define
their Service-Specific AVPs that MUST be present in the
Accounting-Request message in a section entitled "Accounting AVPs".
The application MUST assume that the AVPs described in this document
will be present in all Accounting messages, so only their respective
service-specific AVPs need to be defined in this section.</t>
<t>Applications have the option of using one or both
of the following accounting application extension models:
</t>
<list style="hanging">
<t hangText="Split Accounting Service"><vspace blankLines="1" />
The accounting message will carry the Application Id
of the Diameter base accounting application (see <xref target="appl"/>).
Accounting messages maybe 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. <vspace blankLines="1" />
</t>
<t hangText="Coupled Accounting Service"><vspace blankLines="1" />
The accounting messages 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 as any of the other
application messages.
</t>
<t>In cases where an application does not define its own accounting
service, it is preferred that the split accounting model be used.</t>
</list>
</section>
<section anchor="falre" title="Fault Resilience">
<t>Diameter Base protocol mechanisms are used to overcome small
message loss and network faults of temporary nature.</t>
<t>Diameter peers acting as clients MUST implement the use of
failover to guard against server failures and certain network
failures. Diameter peers acting as agents or related off-line
processing systems MUST detect duplicate accounting records caused by
the sending of same record to several servers and duplication of
messages in transit. This detection MUST be based on the inspection
of the Session-Id and Accounting-Record-Number AVP pairs. <xref target="appDD" />
discusses duplicate detection needs and implementation issues.</t>
<t>Diameter clients MAY have non-volatile memory for the safe storage
of accounting records over reboots or extended network failures,
network partitions, and server failures. If such memory is available,
the client SHOULD store new accounting records there as soon as the
records are created and until a positive acknowledgement of their
reception from the Diameter Server has been received. Upon a reboot,
the client MUST starting sending the records in the non-volatile
memory to the accounting server with appropriate modifications in
termination cause, session length, and other relevant information in
the records.</t>
<t>A further application of this protocol may include AVPs to control
how many accounting records may at most be stored in the Diameter
client without committing them to the non-volatile memory or
transferring them to the Diameter server.</t>
<t>The client SHOULD NOT remove the accounting data from any of its
memory areas before the correct Accounting-Answer has been received.
The client MAY remove oldest, undelivered or yet unacknowledged
accounting data if it runs out of resources such as memory. It is an
implementation dependent matter for the client to accept new sessions
under this condition.</t>
</section>
<section anchor="acccrec" title="Accounting Records">
<t>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.</t>
<t>Different types of accounting records are sent depending on the
actual type of accounted service and the authorization server's
directions for interim accounting. If the accounted service is a
one-time event, meaning that the start and stop of the event are
simultaneous, then the Accounting-Record-Type AVP MUST be present and
set to the value EVENT_RECORD.</t>
<t>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.</t>
<t>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.</t>
<t>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_RECORD and a
single STOP_RECORD. A particular Diameter application specification
MUST define the type of sequences that MUST be used.</t>
</section>
<section anchor="coacccrec" title="Correlation of Accounting Records">
<t>The Diameter protocol's Session-Id AVP, which is globally unique
(see Section 8.8), is used during the authorization phase to identify
a particular session. Services that do not require any authorization
still use the Session-Id AVP to identify sessions. Accounting
messages MAY use a different Session-Id from that sent in
authorization messages. Specific applications MAY require different a
Session-ID for accounting messages.</t>
<t>However, there are certain applications that require multiple
accounting sub-sessions. Such applications would send messages with a
constant Session-Id AVP, but a different Accounting-Sub-Session-Id
AVP. In these cases, correlation is performed using the Session-Id.
It is important to note that receiving a STOP_RECORD 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.</t>
<t>Furthermore, there are certain applications where a user receives
service from different access devices (e.g., Mobile IPv4), each with
their own unique Session-Id. In such cases, the Acct-Multi-Session-
Id AVP is used for correlation. During authorization, a server that
determines that a request is for an existing session SHOULD include
the Acct-Multi-Session-Id AVP, which the access device MUST include
in all subsequent accounting messages.</t>
<t>The Acct-Multi-Session-Id AVP MAY include the value of the
original Session-Id. It's contents are implementation specific, but
MUST be globally unique across other Acct-Multi-Session-Id, and MUST
NOT change during the life of a session.</t>
<t>A Diameter application document MUST define the exact concept of a
session that is being accounted, and MAY define the concept of a
multi-session. For instance, the NASREQ DIAMETER application treats a
single PPP connection to a Network Access Server as one session, and
a set of Multilink PPP sessions as one multi-session.</t>
</section>
<section anchor="acccomm" title="Accounting Command-Codes">
<t>This section defines Command-Code values that MUST be supported by
all Diameter implementations that provide Accounting services.</t>
<section anchor="accrst" title="Accounting-Request">
<t>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.</t>
<t>One of Acct-Application-Id and Vendor-Specific-Application-Id
AVPs MUST be present. If the Vendor-Specific-Application-Id grouped
AVP is present, it MUST include an Acct-Application-Id AVP.</t>
<t>The AVP listed below SHOULD include service specific accounting
AVPs, as described in Section 9.3.</t>
<t>
<artwork>
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 ]
</artwork>
</t>
</section>
<section anchor="accanswr" title="Accounting-Answer">
<t>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.</t>
<t>Only the target Diameter Server, known as the home Diameter
Server, SHOULD respond with the Accounting-Answer command.</t>
<t>One of Acct-Application-Id and Vendor-Specific-Application-Id
AVPs MUST be present. If the Vendor-Specific-Application-Id grouped
AVP is present, it MUST contain an Acct-Application-Id AVP.</t>
<t>The AVP listed below SHOULD include service specific accounting
AVPs, as described in Section 9.3.</t>
<t>
<artwork>
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 ]
</artwork>
</t>
</section>
</section>
<section anchor="accavp" title="Accounting AVPs">
<t>This section contains AVPs that describe accounting usage
information related to a specific session.</t>
<section anchor="accrecty" title="Accounting-Record-Type AVP">
<t>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:
<vspace blankLines="1" />
<list style="hanging">
<t hangText="EVENT_RECORD 1">
<vspace blankLines="1" />An Accounting Event Record is used
to indicate that a one-time event has occurred (meaning that the
start and end of the event are simultaneous). This record
contains all information relevant to the service, and is the only
record of the service.
<vspace blankLines="1" /></t>
<t hangText="START_RECORD 2">
<vspace blankLines="1" />An Accounting Start, Interim, and
Stop Records are used to indicate that a service of a measurable
length has been given. An Accounting Start Record is used to
initiate an accounting session, and contains accounting
information that is relevant to the initiation of the session.
<vspace blankLines="1" /></t>
<t hangText="INTERIM_RECORD 3">
<vspace blankLines="1" />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.
<vspace blankLines="1" /></t>
<t hangText="STOP_RECORD 4">
<vspace blankLines="1" />An Accounting Stop Record is sent to
terminate an accounting session and contains cumulative
accounting information relevant to the existing session.
<vspace blankLines="1" /></t>
</list></t>
</section>
<section anchor="accinter" title="Acct-Interim-Interval AVP">
<t>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:
<vspace blankLines="1" />
<list style="numbers">
<t>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.
<vspace blankLines="1" /></t>
<t>The inclusion of the AVP with Value field set to a non-zero
value means that INTERIM_RECORD records MUST be produced between
the START_RECORD and STOP_RECORD records. The Value field of this
AVP is the nominal interval between these records in seconds. The
Diameter node that originates the accounting information, known
as the client, MUST produce the first INTERIM_RECORD record
roughly at the time when this nominal interval has elapsed from
the START_RECORD, the next one again as the interval has elapsed
once more, and so on until the session ends and a STOP_RECORD
record is produced.
<vspace blankLines="1" />
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.</t>
</list></t>
</section>
<section anchor="accrecnum" title=" Accounting-Record-Number AVP">
<t>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.</t>
</section>
<section anchor="accidavp" title="Acct-Session-Id AVP">
<t>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.</t>
</section>
<section anchor="accmulti" title="Acct-Multi-Session-Id AVP">
<t>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 together 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
MUST be used in all accounting messages for the given session.</t>
</section>
<section anchor="accsub" title="Accounting-Sub-Session-Id AVP">
<t>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.</t>
</section>
<section anchor="accreal" title=" Accounting-Realtime-Required AVP">
<t>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.
<vspace blankLines="1" />
<list style="hanging">
<t hangText="DELIVER_AND_GRANT 1">
<vspace blankLines="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.
<vspace blankLines="1" /></t>
<t hangText="GRANT_AND_STORE 2">
<vspace blankLines="1" />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.
<vspace blankLines="1" />This is the default behavior if the AVP
isn't included in the reply from the authorization server.
<vspace blankLines="1" /></t>
<t hangText="GRANT_AND_LOSE 3">
<vspace blankLines="1" />The AVP with Value field set to
GRANT_AND_LOSE means that service SHOULD be granted even if the
records can not be delivered or stored.
<vspace blankLines="1" /></t>
</list></t>
</section>
</section>
</section>
<section anchor="avpocc" title="AVP Occurrence Table">
<t>The following tables presents the AVPs defined in this document, and
specifies in which Diameter messages they MAY be present or not.
AVPs that occur only inside a Grouped AVP are not shown in this table.</t>
<t>The table uses the following symbols:
<vspace blankLines="1" />
<list>
<t>0 The AVP MUST NOT be present in the message.</t>
<t>0+ Zero or more instances of the AVP MAY be present in the
message.</t>
<t>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.</t>
<t>1 One instance of the AVP MUST be present in the message.</t>
<t>1+ At least one instance of the AVP MUST be present in the
message.</t>
</list></t>
<section anchor="bapr" title="Base Protocol Command AVP Table">
<t>The table in this section is limited to the non-accounting Command
Codes defined in this specification.
<artwork>
+-----------------------------------------------+
| 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+ |0 |0+ |0 |0+ |0 |0+ |0 |0+ |0 |0+ |
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 |
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 | | | | | | | | | | | | |
--------------------+---+---+---+---+---+---+---+---+---+---+---+---+
</artwork></t>
</section>
<section anchor="accevtabr" title="Accounting AVP Table">
<t>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.
<artwork>
+-----------+
| 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 |
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 |
------------------------------+-----+-----+
</artwork></t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values related to the
Diameter protocol, in accordance with BCP 26
<xref target="RFC2434" />. The following policies are used here with
the meanings defined in BCP 26: "Private Use", "First Come First
Served", "Expert Review", "Specification Required", "IETF Consensus",
"Standards Action".</t>
<t>This section explains the criteria to be used by the IANA for
assignment of numbers within namespaces defined within this
document.</t>
<t>Diameter is not intended as a general purpose protocol, and
allocations SHOULD NOT be made for purposes unrelated to
authentication, authorization or accounting.</t>
<t>For registration requests where a Designated Expert should be
consulted, the responsible IESG area director should appoint the
Designated Expert. For Designated Expert with Specification Required,
the request is posted to the DIME WG mailing list (or, if it has been
disbanded, a successor designated by the Area Director) for comment and
review, and MUST include a pointer to a public specification. Before a
period of 30 days has passed, the Designated Expert will either approve
or deny the registration request and publish a notice of the decision
to the DIME WG mailing list or its successor. A denial notice MUST be
justified by an explanation and, in the cases where it is possible,
concrete suggestions on how the request can be modified so as to become
acceptable.</t>
<section anchor="avphdr" title="AVP Header">
<t>As defined in Section 4, the AVP header contains three fields that
requires IANA namespace management; the AVP Code, Vendor-ID and Flags
field.</t>
<section anchor="avpcod" title="AVP Codes">
<t>The AVP Code namespace is used to identify attributes. There are
multiple namespaces. Vendors can have their own AVP Codes namespace
which 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
IANA controlled AVP Codes namespace. The AVP Codes and sometimes
also possible values in an AVP are controlled and maintained by
IANA.</t>
<t>AVP Code 0 is not used. AVP Codes 1-255 are managed separately
as RADIUS Attribute Types
<xref target="RADTYPE" />. This document defines the AVP Codes
257-274, 276-285, 287, 291-300, 480, 483 and 485-486. See Section
4.5 for the assignment of the namespace in this specification.</t>
<t>AVPs may be allocated following Designated Expert with
Specification Required
<xref target="RFC2434" />. Release of blocks of AVPs (more than 3
at a time for a given purpose) should require IETF Consensus.</t>
<t>Note that Diameter defines a mechanism for Vendor-Specific AVPs,
where the Vendor-Id field in the AVP header is set to a non-zero
value. Vendor-Specific AVPs codes are for Private Use and should be
encouraged instead of allocation of global attribute types, for
functions specific only to one vendor's implementation of Diameter,
where no interoperability is deemed useful. Where a Vendor-Specific
AVP is implemented by more than one vendor, allocation of global
AVPs should be encouraged instead.</t>
</section>
<section anchor="avpfla" title="AVP Flags">
<t>There are 8 bits in the AVP Flags field of the AVP header,
defined in Section 4. This document assigns bit 0 ('V'endor
Specific), bit 1 ('M'andatory) and bit 2 ('P'rotected). The
remaining bits should only be assigned via a Standards Action
<xref target="RFC2434" />.</t>
</section>
</section>
<section anchor="diahdr" title="Diameter Header">
<t>As defined in Section 3, the Diameter header contains two fields
that require IANA namespace management; Command Code and Command
Flags.</t>
<section anchor="comcod" title="Command Codes">
<t>The Command Code namespace is used to identify Diameter
commands. The values 0-255 (0x00-0xff) are reserved for RADIUS
backward compatibility, and are defined as "RADIUS Packet Type Codes"
in <xref target="RADTYPE" />. Values 256 - 8,388,607 (0x100 to 0x7fffff)
are for permanent, standard commands, allocated by IETF Consensus
<xref target="RFC2434" />. This document defines the Command Codes 257,
258, 271, 274-275, 280 and 282. See Section 3.1 for the assignment
of the namespace in this specification.</t>
<t>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 <xref target="RFC2434" />. The request to IANA for
a Vendor-Specific Command Code SHOULD include a reference to a publicly
available specification which 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.</t>
<t>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, as outlined in
<xref target="IANA-EXP" />.</t>
</section>
<section anchor="comfl" title="Command Flags">
<t>There are eight bits in the Command Flags field of the Diameter
header. This document assigns bit 0 ('R'equest), bit 1 ('P'roxy),
bit 2 ('E'rror) and bit 3 ('T'). Bits 4 through 7 MUST only be
assigned via a Standards Action
<xref target="RFC2434" />.</t>
</section>
</section>
<section anchor="Appid" title="Application Identifiers">
<t>As defined in <xref target="appl" />, the Application Id is used to
identify a specific Diameter Application. There are standards-track
Application Ids and vendor specific Application Ids.</t>
<t>IANA
<xref target="RFC2434" /> has assigned the range 0x00000001 to
0x00ffffff for standards-track applications; and 0x01000000 -
0xfffffffe for vendor specific applications, on a first-come,
first-served basis. The following values are allocated.
<artwork>
Diameter Common Messages 0
NASREQ 1 [RFC4005]
Mobile-IP 2 [RFC4004]
Diameter Base Accounting 3
Relay 0xffffffff
</artwork></t>
<t>Assignment of standards-track Application Ids are by Designated
Expert with Specification Required
<xref target="RFC2434" />.</t>
<t>Both Auth-Application-Id and Acct-Application-Id AVPs use the
same Application Id space. A diameter node advertising
itself as a relay agent MUST set either Application-Id or
Acct-Application-Id to 0xffffffff.</t>
<t>Vendor-Specific Application Ids, are for Private Use.
Vendor-Specific Application Ids are assigned on a First Come,
First Served basis by IANA.</t>
</section>
<section anchor="avpval" title="AVP Values">
<t>Certain AVPs in Diameter define a list of values with various
meanings. For attributes other than those specified in this section,
adding additional values to the list can be done on a First Come,
First Served basis by IANA.</t>
<section anchor="recoav" title="Result-Code AVP Values">
<t>As defined in Section 7.1, the Result-Code AVP (AVP Code 268)
defines the values 1001, 2001-2002, 3001-3012, 4001-4003 and
5001-5021.</t>
<t>All remaining values are available for assignment via IETF
Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="accrtav" title="Accounting-Record-Type AVP Values">
<t>As defined in Section 9.8.1, the Accounting-Record-Type AVP (AVP
Code 480) defines the values 1-4. All remaining values are
available for assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="tercas" title="Termination-Cause AVP Values">
<t>As defined in Section 8.15, the Termination-Cause AVP (AVP Code
295) defines the values 1-8. All remaining values are available for
assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="redho" title="Redirect-Host-Usage AVP Values">
<t>As defined in Section 6.13, the Redirect-Host-Usage AVP (AVP
Code 261) defines the values 0-5. All remaining values are
available for assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="sesfa" title="Session-Server-Failover AVP Values">
<t>As defined in Section 8.18, the Session-Server-Failover AVP (AVP
Code 271) defines the values 0-3. All remaining values are
available for assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="sesbiavpva" title="Session-Binding AVP Values">
<t>As defined in Section 8.17, the Session-Binding AVP (AVP Code
270) defines the bits 1-4. All remaining bits are available for
assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="disca" title="Disconnect-Cause AVP Values">
<t>As defined in Section 5.4.3, the Disconnect-Cause AVP (AVP Code
273) defines the values 0-2. All remaining values are available for
assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="aurta" title="Auth-Request-Type AVP Values">
<t>As defined in Section 8.7, the Auth-Request-Type AVP (AVP Code
274) defines the values 1-3. All remaining values are available for
assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="auses" title="Auth-Session-State AVP Values">
<t>As defined in Section 8.11, the Auth-Session-State AVP (AVP Code
277) defines the values 0-1. All remaining values are available for
assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="reau" title="Re-Auth-Request-Type AVP Values">
<t>As defined in Section 8.12, the Re-Auth-Request-Type AVP (AVP
Code 285) defines the values 0-1. All remaining values are
available for assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="accrr"
title="Accounting-Realtime-Required AVP Values">
<t>As defined in Section 9.8.7, the Accounting-Realtime-Required
AVP (AVP Code 483) defines the values 1-3. All remaining values are
available for assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
<section anchor="inbasec" title="Inband-Security-Id AVP (code 299)">
<t>As defined in Section 6.10, the Inband-Security-Id AVP (AVP Code
299) defines the values 0-1. All remaining values are available for
assignment via IETF Consensus
<xref target="RFC2434" />.</t>
</section>
</section>
<section anchor="ditc" title="Diameter TCP/SCTP Port Numbers">
<t>The IANA has assigned TCP and SCTP port number 3868 to
Diameter.</t>
</section>
<section anchor="napserv" title="NAPTR Service Fields">
<t>The registration in the RFC MUST include the following
information:</t>
<t>Service Field: The service field being registered. An example
for a new fictitious transport protocol called NCTP might be
"AAA+D2N".</t>
<t>Protocol: The specific transport protocol associated with that
service field. This MUST include the name and acronym for the
protocol, along with reference to a document that describes the
transport protocol. For example - "New Connectionless Transport
Protocol (NCTP), RFC XYZ".</t>
<t>Name and Contact Information: The name, address, email address and
telephone number for the person performing the registration.</t>
<t>The following values have been placed into the registry:
<artwork>
Services Field Protocol
AAA+D2T TCP
AAA+D2S SCTP
</artwork></t>
</section>
</section>
<section anchor="diprcpa"
title="Diameter protocol related configurable parameters">
<t>This section contains the configurable parameters that are found
throughout this document:
<list style="hanging">
<t hangText="Diameter Peer">
<vspace blankLines="1" />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.</t>
<t hangText="Routing Table">
<vspace blankLines="1" />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 to. The routing
table MAY also include a "default route", which is typically used for
all messages that cannot be locally processed.</t>
<t hangText="Tc timer">
<vspace blankLines="1" />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.</t>
</list></t>
</section>
<section anchor="seccons" title="Security Considerations">
<t>The Diameter base protocol messages SHOULD be secured by using TLS
<xref target="RFC4346" />. Additional security measures that are transparent
to and independent of Diameter, such as IPSec <xref target="RFC4301"/>, can
also be deployed to secure connections between peers.</t>
<t>During deployment, connections between Diameter nodes SHOULD be
protected by TLS. All Diameter base protocol implementations
MUST support the use of TLS. The Diameter protocol MUST NOT be used
without any security mechanism.</t>
<t>If a Diameter connection is to be protected via TLS, then the CER/CEA
exchange MUST include an Inband-Security-ID AVP with a value of TLS.
For TLS usage, a TLS handshake will begin when both ends are in the
open state, after completion of the CER/CEA exchange. If the TLS
handshake is successful, all further messages will be sent via TLS. If
the handshake fails, both ends move to the closed state. See Sections 13.1
for more details.</t>
<section anchor="TLSus" title="TLS Usage">
<t>A Diameter node that initiates a connection to another Diameter
node acts as a TLS client according to
<xref target="RFC4346" />, and a Diameter node that accepts a
connection acts as a TLS server. Diameter nodes implementing TLS for
security MUST mutually authenticate as part of TLS session
establishment. In order to ensure mutual authentication, the Diameter
node acting as TLS server MUST request a certificate from the
Diameter node acting as TLS client, and the Diameter node acting as
TLS client MUST be prepared to supply a certificate on request.</t>
<t>Diameter nodes MUST be able to negotiate the following TLS cipher
suites:
<artwork>
TLS_RSA_WITH_RC4_128_MD5
TLS_RSA_WITH_RC4_128_SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA
</artwork></t>
<t>Diameter nodes SHOULD be able to negotiate the following TLS
cipher suite:
<artwork>
TLS_RSA_WITH_AES_128_CBC_SHA
</artwork></t>
<t>Diameter nodes MAY negotiate other TLS cipher suites.</t>
<t>Upon receiving the peers certificate, Diameter nodes SHOULD further
validate the identity of the peer by matching the received Origin-Host
and/or Origin-Realm in the CER and CEA exchange against the content of
the peers certificate. Diameter peer hostname and/or realm validation
can be performed in the following order:
<list style="symbols">
<t>If one ore more 'Subject Alternate Name (subjectAltName)' extension
of type dNSName is present in the certificate (See <xref target="RFC3280" />),
then the Origin-Host value can be used to find a matching extension.</t>
<t>If there are no matches found, then the Origin-Realm value can be
used to find a matching subjectAltName extension.</t>
<t>Otherwise, the Origin-Host value should be found within the
'Common Name (CN)' field in the Subject field of the certificate
(See <xref target="RFC3280" />).</t>
</list></t>
<t>Identity validation MAY be omitted by a Diameter node if the information
contained in the certificate cannot be co-related or mapped to the
Origin-Host and Origin-Realm presented by a peer. However, the Diameter
node SHOULD have external information or other means to validate the
identity of a peer.
</t>
</section>
<section anchor="ptpcos" title="Peer-to-Peer Considerations">
<t>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.</t>
</section>
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor="FLOATPOINT">
<front>
<title abbrev="ieee">IEEE Standard for Binary Floating-Point
Arithmetic, ANSI/IEEE Standard 754-1985</title>
<author>
<organization abbrev="ieee">Institute of Electrical and Electronics
Engineers</organization>
</author>
<date month="August" year="1985" />
</front>
</reference>
<reference anchor="IANAADFAM">
<front>
<title>Address Family Numbers</title>
<author>
<organization abbrev="IANA">IANA,</organization>
</author>
<date month="" year="" />
</front>
<seriesInfo name=""
value="http://www.iana.org/assignments/address-family-numbers" />
</reference>
<reference anchor="RADTYPE">
<front>
<title>RADIUS Types</title>
<author>
<organization abbrev="IANA">IANA,</organization>
</author>
<date month="" year="" />
</front>
<seriesInfo name=""
value="http://www.iana.org/assignments/radius-types" />
</reference>
<reference anchor="RFC791">
<front>
<title>Internet Protocol</title>
<author fullname="Postel.J" initials="J" surname="Postel">
<organization />
</author>
<date month="September" year="1981" />
</front>
<seriesInfo name="RFC" value="791" />
</reference>
<reference anchor="RFC793">
<front>
<title>Transmission Control Protocol</title>
<author fullname="Postel.J" initials="J" surname="Postel">
<organization />
</author>
<date month="January" year="1981" />
</front>
<seriesInfo name="RFC" value="793" />
</reference>
&AAATRANS;
&AAAMIP4;
&AAANASREQ;
&AAACC;
&AAAEAP;
&AAASIP;
&ABNF;
&DIAMETER;
&EAP;
&IANA;
&IKE;
&IPV6;
&KEYWORDS;
&NAI;
&NAPTR;
&SIP;
&SCTP;
&TLS;
&URI;
&UTF8;
&X509;
&IDNA;
&NGREP;
&PUNYC;
</references>
<references title="Informational References">
&AAAREQ;
&ACCMGMT;
&ASSIGNNO;
&DYNAUTH;
&PPP;
&RADACCT;
&RADEXT;
&RADIUS;
&RADIUSV6;
&SECARCH;
&SNTP;
&TACACS;
&RIDNA;
<reference anchor="IANA-EXP">
<front>
<title>Assigning Experimental and Testing Numbers Considered Useful,
Work in Progress.</title>
<author fullname="T. Narten" initials="T" surname="Narten">
<organization />
</author>
<date month="" year="" />
</front>
</reference>
</references>
<section anchor="acks" title="Acknowledgements">
<t>The authors would like to thank the following people that have
provided proposals and contributions to this document:</t>
<t>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 Updates and other topics.
To Tony Zhang for providing fixes to loop holes 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.</t>
<t>Special thanks also to people who have provided invaluable comments
and inputs especially in resolving controversial issues:</t>
<t>Glen Zorn, Yoshihiro Ohba, Marco Stura, and Pasi Eronen.</t>
<t>Finally, we would like to thank the original authors of this document:</t>
<t>Pat Calhoun, John Loughney, Jari Arkko, Erik Guttman and Glen Zorn.</t>
<t>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
assisted and contributed to the original version of this document.
Their efforts significantly contributed to the success of Diameter.</t>
</section>
<section anchor="appNAPTR" title="NAPTR Example">
<t>As an example, consider a client that wishes to resolve
aaa:ex.com. The client performs a NAPTR query for that domain, and
the following NAPTR records are returned:
<artwork>
;; order pref flags service regexp replacement
IN NAPTR 50 50 "s" "AAA+D2S" ""
_diameter._sctp.example.com IN NAPTR 100 50 "s" "AAA+D2T"
"" _aaa._tcp.example.com
</artwork></t>
<t>This indicates that the server supports SCTP, and TCP, in that
order. If the client supports over SCTP, SCTP will be used, targeted
to a host determined by an SRV lookup of _diameter._sctp.ex.com. That
lookup would return:
<artwork>
;; Priority Weight Port Target
IN SRV 0 1 5060 server1.example.com IN SRV 0
2 5060 server2.example.com
</artwork></t>
</section>
<section anchor="appDD" title="Duplicate Detection">
<t>As described in Section 9.4, accounting record duplicate detection
is based on session identifiers. Duplicates can appear for various
reasons:
<list style="symbols">
<t>Failover to an alternate server. Where close to real-time
performance is required, failover thresholds need to be kept low
and this may lead to an increased likelihood of duplicates.
Failover can occur at the client or within Diameter agents.</t>
<t>Failure of a client or agent after sending of a record from non-
volatile memory, but prior to receipt of an application layer ACK
and deletion of the record. record to be sent. This will result in
retransmission of the record soon after the client or agent has
rebooted.</t>
<t>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.</t>
<t>Implementation problems and misconfiguration.</t>
</list></t>
<t>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
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).</t>
<t>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.</t>
<t>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 possible duplicate by setting the T
flag. Since the Diameter server is responsible for duplicate
detection, it can choose to make use of the T flag or not, in order
to optimize duplicate detection. Since the T flag does not affect
interoperability, and may not be needed by some servers, generation
of the T flag is REQUIRED for Diameter clients and agents, but MAY be
implemented by Diameter servers.</t>
<t>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.</t>
<t>The following is an example of how the T flag may be used by the
server to detect duplicate requests.
<vspace blankLines="1" />
<list>
<t>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 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 out
of order duplicates, 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 has expired,
then 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.</t>
</list></t>
</section>
<section anchor="appIDNA" title="Internationalized Domain Names">
<t>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 recommnedations in <xref target="RFC4690" /> and
<xref target="RFC3490" />. Applications that provide support for IDNs outside
of the Diameter protocol but interacting with it SHOULD use the representation
and conversion framework described in <xref target="RFC3490" />, <xref target="RFC3491" />
and <xref target="RFC3492" />.
</t>
</section>
</back>
</rfc>
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