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Diameter
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... RADIUS] 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
...
... packet loss may translate directly into revenue loss. In order to
provide well defined transport behavior, Diameter runs over
reliable transport mechanisms (TCP ...
... 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.
...
... deployment. Support for server-initiated messages is mandatory in
Diameter, and is described in Section 8.
Auditability
...
... data object security is not mandatory within
Diameter, these capabilities are supported, and are described in
[AAACMS].
...
... be deployed in the same network. Initially, it is expected that
Diameter will be deployed within new network devices, as well as
within gateways ...
... gateways enabling communication between legacy RADIUS
devices and Diameter agents. This capability, described in
[NASREQ ...
... agents. This capability, described in
[NASREQ], enables Diameter support to be added to legacy networks,
by addition of a gateway ...
... In addition to addressing the above requirements, Diameter also
provides support for the following:
...
... 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
...
... temporally unique as required in [RADIUS]. Through DNS, Diameter
enables dynamic discovery of peers. Derivation of dynamic session
keys is enabled via transmission-level security ...
... layer security
(Section 13) features, Diameter addresses these limitations and
provides for secure and scalable roaming ...
... 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
...
... Diameter Protocol ...
...
The Diameter base protocol provides the following facilities:
...
... AVP. Some of
these AVP values are used by the Diameter protocol itself, while
others deliver data associated with particular applications that
employ Diameter ...
... Diameter protocol itself, while
others deliver data associated with particular applications that
employ Diameter. AVPs may be added arbitrarily to Diameter messages,
...
... employ Diameter. AVPs may be added arbitrarily to Diameter messages,
so long as the required AVPs are included and AVPs ...
... explicitly excluded are not included. AVPs are used by the base
Diameter protocol to support the following required features:
- Transporting of user authentication ...
... - Transporting of user authentication information, for the purposes
of enabling the Diameter server to authenticate the user.
- Transporting of service ...
... accounting purposes, capacity planning, etc.
- Relaying, proxying and redirecting of Diameter messages through a
server hierarchy.
...
... be used by itself for accounting purposes only, or it may be used
with a Diameter application, such as Mobile IPv4 [DIAMMIP], or
...
... 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 ...
... 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 ...
... 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 ...
...
Any node can initiate a request. In that sense, Diameter is a peer-
to-peer protocol. In this document, a Diameter Client ...
... 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 ...
... Diameter
client generates Diameter messages to request authentication,
authorization, and accounting services for the user. A Diameter ...
... Diameter messages to request authentication,
authorization, and accounting services for the user. A Diameter
agent is a node ...
... proxies, redirects and relay agents. A
Diameter server performs authentication and/or authorization of the
...
... 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.
...
... acting as a server for others.
The Diameter protocol also supports server-initiated messages, such
as a request to abort service to a particular user.
...
...
Currently, the Diameter specification consists of a base
specification (this document), Transport Profile ...
... 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 ...
... The Mobile IPv4 [DIAMMIP] application defines a Diameter application
that allows a Diameter server to perform AAA ...
... DIAMMIP] application defines a Diameter application
that allows a Diameter server to perform AAA functions for Mobile
IPv4 services ...
... The NASREQ [NASREQ] application defines a Diameter Application that
allows a Diameter server to be used in a PPP ...
... NASREQ] application defines a Diameter Application that
allows a Diameter server to be used in a PPP/SLIP Dial-Up ...
... Terminal Server Access environment. Consideration was given for
servers that need to perform protocol conversion between Diameter and
RADIUS.
...
...
The Diameter protocol is designed to be extensible, using several
mechanisms, including:
...
... Reuse of existing AVP values, AVPs and Diameter applications are
strongly recommended. Reuse simplifies standardization and
implementation and avoids potential interoperability ...
... Application Identifier.
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 ...
... 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:
- Adding new AVPs ...
... AVPs for use with the application. Since a new EAP
authentication method can be supported within Diameter without
requiring new AVPs, addition of EAP ...
... In order to justify allocation of a new application identifier,
Diameter applications MUST define one Command Code, or add new
mandatory AVPs to the ABNF ...
... ABNF [ABNF] grammar (see
Section 3.2). If the Diameter application has accounting
requirements, it MUST also specify the AVPs that are to be present in
...
... 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
...
... accounting application id is required.
When possible, a new Diameter application SHOULD reuse existing
Diameter AVPs ...
... When possible, a new Diameter application SHOULD reuse existing
Diameter AVPs, in order to avoid defining multiple AVPs that carry
...
...
Application Identifiers are still required for Diameter capability
exchange. Every Diameter accounting ...
... Identifiers are still required for Diameter capability
exchange. Every Diameter accounting application specification MUST
have an IANA ...
... Application Identifier.
Every Diameter implementation MUST support accounting. Basic
accounting ...
... if the "M" bit is set when the same AVP is used within other Diameter
commands (i.e., authentication/authorization commands).
...
... authorization commands).
A DIAMETER base accounting implementation MUST be configurable to
advertise supported accounting ...
... accounting server.
When possible, a new Diameter accounting application SHOULD attempt
to reuse existing AVPs ...
... AVP
The Diameter protocol consists of a header followed by one or more
Attribute-Value-Pairs (AVPs ...
... A Diameter Agent is a Diameter node that provides either relay,
proxy, redirect or translation services ...
... network that
performs access control. An example of a Diameter client is a
Network Access Server ...
... Diameter Node
A Diameter node is a host process that implements the Diameter
protocol, and acts either as a Client ...
... A Diameter node is a host process that implements the Diameter
protocol, and acts either as a Client, Agent or Server.
...
... Diameter Peer
A Diameter Peer is a Diameter Node to which a given Diameter Node
has a direct transport connection ...
... A Diameter Peer is a Diameter Node to which a given Diameter Node
has a direct transport connection.
...
... Diameter Security Exchange
A Diameter Security Exchange is a process through which two
Diameter nodes ...
... Diameter Security Exchange is a process through which two
Diameter nodes establish end-to-end security.
...
... authorization and accounting requests for a particular realm. By
its very nature, a Diameter Server MUST support Diameter
applications in addition to the base protocol.
...
... accounting requests for a particular realm. By
its very nature, a Diameter Server MUST support Diameter
applications in addition to the base protocol.
...
... Downstream is used to identify the direction of a particular
Diameter message from the home server towards the access device.
...
... proxy are involved, this
hop-by-hop security does not protect the entire Diameter user
session. End-to-end security ...
... session. End-to-end security is security between two Diameter
nodes, possibly communicating through Diameter Agents. This
...
... End-to-end security is security between two Diameter
nodes, possibly communicating through Diameter Agents. This
security ...
... Agents. This
security protects the entire Diameter communications path from the
originating Diameter node to the terminating Diameter node ...
... security protects the entire Diameter communications path from the
originating Diameter node to the terminating Diameter node.
...
... Diameter communications path from the
originating Diameter node to the terminating Diameter node.
Home Realm ...
... NAI [NAI], is used in the
Diameter protocol to extract a user's identity and realm. The
identity ...
... proxies need to understand the semantics of the
messages passing through them, and may not support all Diameter
applications.
Realm
...
... 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
...
... routing AVPs, and are
capable of handling any Diameter application or message type.
Since relays make decisions based on information in routing ...
... association between two endpoints in
a Diameter session which allows the endpoints to communicate with
...
... particular activity. Each application SHOULD provide guidelines
as to when a session begins and ends. All Diameter packets with
the same Session-Identifier ...
... Agent
A translation agent is a stateful Diameter node that performs
protocol translation between Diameter ...
... Diameter node that performs
protocol translation between Diameter and another AAA protocol,
such as RADIUS ...
... SCTP connection existing
directly between two Diameter peers, otherwise known as a Peer-
to-Peer Connection.
...
... Upstream is used to identify the direction of a particular
Diameter message from the access device towards the home server.
...
... The entity requesting or using some resource, in support of which
a Diameter client has generated a request.
...
...
The base Diameter protocol may be used by itself for accounting
applications, but for use in authentication ...
... authentication and authorization it is
always extended for a particular application. Two Diameter
applications are defined by companion documents: NASREQ [NASREQ],
...
... Mobile IPv4 [DIAMMIP]. These applications are introduced in this
document but specified elsewhere. Additional Diameter applications
MAY be defined in the future (see Section 11.3).
...
... MAY be defined in the future (see Section 11.3).
Diameter Clients MUST support the base protocol, which includes
...
... 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.,
...
... both NASREQ and Mobile IPv4, MUST be referred to as "Diameter X
Client" where X is the application which it supports, and not a
...
... 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 ...
... NASREQ and/or Mobile IPv4. A Diameter Server that does not support
both NASREQ and Mobile IPv4 ...
... 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 ...
... Diameter X
Server" where X is the application which it supports, and not a
"Diameter Server".
Diameter ...
... Diameter Server".
Diameter Relays and redirect agents are, by definition, protocol
transparent, and MUST transparently support the Diameter ...
... 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 ...
... base protocol, which includes
accounting. In addition, they MUST fully support each Diameter
application that is needed to implement proxied services, e.g.,
NASREQ ...
... 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
...
... Proxy".
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.
Communication between Diameter ...
... Diameter nodes.
Communication between Diameter peers begins with one peer sending a
message to another Diameter peer. The set of AVPs ...
... 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 ...
... 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 ...
...
set to indicate an error occurred. The specific behavior of the
Diameter server or client receiving a request depends on the Diameter
application ...
... Diameter server or client receiving a request depends on the Diameter
application employed.
Session ...
... Session-Timeout
AVP, and according to rules established in a particular Diameter
application.
...
... connections on port 3868. A given
Diameter instance of the peer state machine MUST NOT use more than
one transport connection ...
... 5.2 for more information on peer discovery.
Diameter implementations SHOULD be able to interpret ICMP protocol
port ...
... 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 ...
... connection attempts.
If Diameter receives data up from TCP that cannot be parsed or
identified as a Diameter ...
... 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 ...
...
1. For interoperability: All Diameter nodes MUST be prepared to
receive Diameter messages on any SCTP stream ...
... interoperability: All Diameter nodes MUST be prepared to
receive Diameter messages on any SCTP stream in the association.
...
... association.
2. To prevent blocking: All Diameter nodes SHOULD utilize all SCTP
streams available to the association ...
... Securing Diameter Messages ...
... Diameter servers MUST support TLS and IPsec. The Diameter protocol
MUST NOT be used without any security mechanism (TLS ...
... Diameter Application Compliance ...
...
Each Diameter application MUST have an IANA assigned Application
Identifier (see Section 11.3). The base protocol ...
... Application Identifier since its support is mandatory. During the
capabilities exchange, Diameter nodes inform their peers of locally
supported applications. Furthermore, all Diameter messages contain
...
... capabilities exchange, Diameter nodes inform their peers of locally
supported applications. Furthermore, all Diameter messages contain
an Application Identifier, which is used in the message forwarding
...
... 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
...
... supports all current and future applications.
Diameter relay and proxy agents are responsible for finding an
...
... transport level connection between two peers, used
to send and receive Diameter messages. A session is a logical
concept at the application layer ...
... connection and a session, and that
Diameter messages for multiple sessions are all multiplexed through a
single connection ...
...
The Diameter Peer Table is used in message forwarding, and referenced
by the Realm Routing Table ...
... vendor id and an application id.
For all IETF standards track Diameter applications, the vendor id
is zero. A route entry ...
... treated. The following actions are supported:
1. 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.
2. RELAY - All Diameter messages that fall within this category
MUST be routed to a next hop server, without modifying any
...
...
3. PROXY - All Diameter messages that fall within this category
MUST be routed to a next hop server. The local server MAY
...
... proxying guidelines.
4. REDIRECT - Diameter messages that fall within this category
MUST have the identity of the home Diameter server ...
... 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 6.1.7
...
... entry expires.
It is important to note that Diameter agents MUST support at least
one of the LOCAL, RELAY, PROXY ...
...
In addition to client and servers, the Diameter protocol introduces
relay, proxy, redirect, and translation agents ...
... proxy, redirect, and translation agents, each of which is
defined in Section 1.3. These Diameter agents are useful for several
reasons:
...
... 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
...
... authorized session has an expiration, which is communicated by
Diameter servers via the Session-Timeout AVP.
...
... - Protocol translation (e.g., RADIUS <-> Diameter)
- Limiting resources authorized to a particular user
...
... transaction auditing
A Diameter agent MAY act in a stateful manner for some requests and
be stateless ...
... 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 ...
... agents that accept requests and route
messages to other Diameter nodes based on information found in the
messages (e.g., Destination-Realm). This routing ...
... 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
...
... 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,
...
... deleted.
Relays modify Diameter messages by inserting and removing routing
information, but do not modify any other portion of a message.
...
... example.net example.net example.com
Figure 2: Relaying of Diameter messages
The example provided in Figure 2 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
...
... 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 ...
... 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 ...
... Since Relays do not perform any application level processing, they
provide relaying services for all Diameter applications, and
therefore MUST advertise the Relay Application Identifier.
...
... route Diameter messages using the
Diameter Routing Table. However, they differ since they modify
messages to implement policy enforcement. This requires that proxies ...
...
Redirect agents are useful in scenarios where the Diameter routing
configuration needs to be centralized. An example is a redirect
...
... 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
...
... 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 ...
... example.net example.net example.com
Figure 3: Redirecting a Diameter Message
Since redirect agents ...
... agents do not perform any application level
processing, they provide relaying services for all Diameter
applications, and therefore MUST advertise the Relay Application
Identifier.
...
... agent is a device that provides translation between two
protocols (e.g., RADIUS<->Diameter, TACACS+<->Diameter). Translation
...
... RADIUS<->Diameter, TACACS+<->Diameter). Translation
agents are likely to be used as aggregation ...
... 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.
...
... systems to be migrated at a slower pace.
Given that the Diameter protocol introduces the concept of long-lived
authorized sessions, translation agents ...
... +------+ ---------> +------+ ---------> +------+
| | RADIUS Request | | Diameter Request | |
| NAS | | TLA | | HMS |
...
... NAS | | TLA | | HMS |
| | RADIUS Answer | | Diameter Answer | |
+------+ <--------- +------+ <--------- +------+
example.net example.net example.com
...
... subject of
standardization, may be applied by next hop Diameter peer or by
destination realm. For example, where TLS ...
... end-to-end security.
It is strongly RECOMMENDED that all Diameter implementations support
end-to-end security.
...
... Diameter Path Authorization ...
...
As noted in Section 2.2, Diameter requires transmission level
security to be used on each connection ...
... 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 ...
... 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 ...
... 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.
...
... may be authentic, but that does not mean that it is authorized to act
as a Diameter Server advertising a set of Diameter applications.
Prior to bringing up a connection ...
... authorization checks are performed
at each connection along the path. Diameter capabilities negotiation
(CER ...
... (CER/CEA) also MUST be carried out, in order to determine what
Diameter applications are supported by each peer. Diameter sessions
...
... 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 ...
... MUST be routed only through authorized nodes that have advertised
support for the Diameter application required by the session.
...
... identity of the peer the request was received from.
The home Diameter server, prior to authorizing a session, MUST check
the Route-Record ...
... 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
...
... 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 ...
... home realm may also wish to check that each accounting request
message corresponds to a Diameter response authorizing the session.
Accounting requests ...
... Diameter agent, on receiving a Diameter response
authorizing a session, MUST check the Route-Record ...
... 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 ...
... DIAMETER_UNABLE_TO_COMPLY error
message MUST be sent within the accounting request; a Diameter client
receiving ...
...
A summary of the Diameter header format is shown below. The fields
are transmitted in network byte order ...
... The Message Length field is three octets and indicates the length
of the Diameter message including the header fields.
...
... 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
...
... 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
...
... End-to-End Identifier
MUST NOT be modified by Diameter agents of any kind. The
combination of the Origin-Host ...
... AVPs are a method of encapsulating information relevant to the
Diameter message. See Section 4 for more information on AVPs.
...
... 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:
...
... present. The following format is used in the definition:
command-def = command-name "::=" diameter-message
command-name = diameter ...
... ; The avp-spec has to be an AVP Name, defined
; in the base or extended Diameter
; specifications.
...
... The following is a definition of a fictitious command code:
Example-Request ::= < "Diameter-Header: 9999999, REQ, PXY >
{ User-Name ...
... Diameter Command Naming Conventions ...
...
Diameter command names typically includes one or more English words
followed by the verb Request or Answer. Each English word is
delimited by a hyphen. A three-letter acronym ...
... 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 ...
... - The receiver could not process the request, but provides
information about a Diameter peer that is able to satisfy the
request, known as redirect.
...
... Vendor-Id
field. AVP numbers 256 and above are used for Diameter, which are
allocated by IANA (see Section 11.1).
...
... 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 ...
... 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. Diameter Relay and redirect agents MUST NOT reject
messages with unrecognized AVPs ...
... AVP
containing it. In order to preserve interoperability, a Diameter
implementation MUST be able to exclude from a Diameter message any
...
... 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 ...
... 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
...
... 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:
...
... 1) 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
...
... 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 ...
... interoperability problems.
Diameter implementations are required to support all Mandatory
AVPs which are allowed by the message's formal syntax ...
... 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.
...
... formal syntax and defined
either in the base Diameter standard or in one of the Diameter
Application specifications governing the message.
AVPs ...
... SNTP [SNTP] describes a procedure to extend the time to 2104.
This procedure MUST be supported by all DIAMETER nodes.
UTF8String
...
... FQDN
DiameterIdentity value is used to uniquely identify a Diameter
node for purposes of duplicate connection and routing loop
...
...
The contents of the string MUST be the FQDN of the Diameter node.
If multiple Diameter nodes run on the same host ...