| Network Working Group | V. Fajardo, Ed. |
| Internet-Draft | Telcordia Technologies |
| Obsoletes: 3588 5719 (if approved) | J. Arkko |
| Intended status: Standards Track | Ericsson Research |
| Expires: November 06, 2012 | J. Loughney |
| Nokia Research Center | |
| G. Zorn, Ed. | |
| Network Zen | |
| May 07, 2012 |
Diameter Base Protocol
draft-ietf-dime-rfc3588bis-33.txt
The Diameter base protocol is intended to provide an Authentication, Authorization and Accounting (AAA) framework for applications such as network access or IP mobility in both local and roaming situations. This document specifies the message format, transport, error reporting, accounting and security services used by all Diameter applications. The Diameter base protocol as defined in this document obsoletes RFC 3588 and RFC 5719 and must be supported by all new Diameter implementations.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 06, 2012.
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Authentication, Authorization and Accounting (AAA) protocols such as TACACS [RFC1492] and RADIUS [RFC2865] were initially deployed to provide dial-up PPP [RFC1661] and terminal server access. Over time, AAA support was needed on many new access technologies, the scale and complexity of AAA networks grew, and AAA was also used on new applications (such as voice over IP). This lead to new demands on AAA protocols.
Network access requirements for AAA protocols are summarized in [RFC2989]. These include:
In addition to addressing the above requirements, Diameter also provides support for the following:
Over time, the capabilities of Network Access Server (NAS) devices have increased substantially. As a result, while Diameter is a considerably more sophisticated protocol than RADIUS, it remains feasible to implement it within embedded devices.
The Diameter base protocol provides the following facilities:
All data delivered by the protocol is in the form of AVPs. Some of these AVP values are used by the Diameter protocol itself, while others deliver data associated with particular applications that employ Diameter. AVPs may be arbitrarily added to Diameter messages, the only restriction being that the Command Code Format specification Section 3.2 is satisfied. AVPs are used by the base Diameter protocol to support the following required features:
The Diameter base protocol satisfies the minimum requirements for an AAA protocol, as specified by [RFC2989]. The base protocol may be used by itself for accounting purposes only, or it may be used with a Diameter application, such as Mobile IPv4 [RFC4004], or network access [RFC4005]. It is also possible for the base protocol to be extended for use in new applications, via the addition of new commands or AVPs. The initial focus of Diameter was network access and accounting applications. A truly generic AAA protocol used by many applications might provide functionality not provided by Diameter. Therefore, it is imperative that the designers of new applications understand their requirements before using Diameter. See Section 1.3.4 for more information on Diameter applications.
Any node can initiate a request. In that sense, Diameter is a peer-to-peer protocol. In this document, a Diameter Client is a device at the edge of the network that performs access control, such as a Network Access Server (NAS) or a Foreign Agent (FA). A Diameter client generates Diameter messages to request authentication, authorization, and accounting services for the user. A Diameter agent is a node that does not provide local user authentication or authorization services; agents include proxies, redirects and relay agents. A Diameter server performs authentication and/or authorization of the user. A Diameter node may act as an agent for certain requests while acting as a server for others.
The Diameter protocol also supports server-initiated messages, such as a request to abort service to a particular user.
The Diameter specification consists of an updated version of the base protocol specification (this document) and the Transport Profile [RFC3539]. This document obsoletes both RFC 3588 and RFC 5719. A summary of the base protocol updates included in this document can be found in Section 1.1.3.
This document defines the base protocol specification for AAA, which includes support for accounting. There are also a myriad of applications documents describing applications that use this base specification for Authentication, Authorization and Accounting. These application documents specify how to use the Diameter protocol within the context of their application.
The Transport Profile document [RFC3539] discusses transport layer issues that arise with AAA protocols and recommendations on how to overcome these issues. This document also defines the Diameter failover algorithm and state machine.
Clarifications on the Routing of Diameter Request based on Username and the Realm [RFC5729] defines specific behavior on how to route requests based on the content of the User-Name AVP (Attribute Value Pair).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
This document obsoletes RFC 3588 but is fully backward compatible with that document. The changes introduced in this document focus on fixing issues that have surfaced during implementation of Diameter [RFC3588]. An overview of some the major changes are given below.
There are many other many miscellaneous fixes that have been introduced in this document that may not be considered significant but they are important nonetheless. Examples are removal of obsolete types, fixes to the state machine, clarification of the election process, message validation, fixes to Failed-AVP and Result-Code AVP values, etc. All of the errata previously filed against RFC 3588 have been fixed. A comprehensive list of changes is not shown here for practical reasons.
The Diameter protocol is designed to be extensible, using several mechanisms, including:
From the point of view of extensibility Diameter authentication, authorization and accounting applications are treated in the same way.
Note: Protocol designers should try to re-use existing functionality, namely AVP values, AVPs, commands, and Diameter applications. Reuse simplifies standardization and implementation. To avoid potential interoperability issues it is important to ensure that the semantics of the re-used features are well understood. Given that Diameter can also carry RADIUS attributes as Diameter AVPs, such re-use considerations apply also to existing RADIUS attributes that may be useful in a Diameter application.
In order to allocate a new AVP value for AVPs defined in the Diameter Base protocol, the IETF needs to approve a new RFC that describes the AVP value. IANA considerations for these AVP values are discussed in Section 11.3.
The allocation of AVP values for other AVPs is guided by the IANA considerations of the document that defines those AVPs. Typically, allocation of new values for an AVP defined in an IETF RFC would require IETF Review [RFC5226], whereas values for vendor-specific AVPs can be allocated by the vendor.
A new AVP being defined MUST use one of the data types listed in Section 4.2 or Section 4.3. If an appropriate derived data type is already defined, it SHOULD be used instead of a base data type to encourage reusability and good design practice.
In the event that a logical grouping of AVPs is necessary, and multiple "groups" are possible in a given command, it is recommended that a Grouped AVP be used (see Section 4.4).
The creation of new AVPs can happen in various ways. The recommended approach is to define a new general-purpose AVP in a standards track RFC approved by the IETF. However, as described in Section 11.1.1 there are also other mechanisms.
A new Command Code MUST be allocated when required AVPs (those indicated as {AVP} in the CCF definition) are added to, deleted from or redefined in (for example, by changing a required AVP into an optional one) an existing command.
Furthermore, if the transport characteristics of a command are changed (for example, with respect to the number of round trips required) a new Command Code MUST be registered.
A change to the CCF of a command, such as described above, MUST result in the definition of a new Command Code. This subsequently leads to the need to define a new Diameter Application for any application that will use that new Command.
The IANA considerations for command codes are discussed in Section 3.1.
Every Diameter application specification MUST have an IANA assigned Application Id (see Section 2.4). The managed Application Id space is flat and there is no relationship between different Diameter applications with respect to their Application Ids. As such, there is no versioning support provided by these application Ids itself; every Diameter application is a standalone application. If the application has a relationship with other Diameter applications, such a relationship is not known to Diameter.
Before describing the rules for creating new Diameter applications it is important to discuss the semantics of the AVP occurrences as stated in the CCF and the M-bit flag (Section 4.1) for an AVP. There is no relationship imposed between the two; they are set independently.
Section 11.1.1 for details.
It is the decision of the protocol designer when to develop a new Diameter application rather than extending Diameter in other ways. However, a new Diameter application MUST be created when one or more of the following criteria are met:
If the CCF definition of a command allows it, an implementation may add arbitrary optional AVPs with the M-bit cleared (including vendor-specific AVPs) to that command without needing to define a new application. Please refer to
The base Diameter protocol concerns itself with establishing connections to peers, capabilities negotiation, how messages are sent and routed through peers, and how the connections are eventually torn down. The base protocol also defines certain rules that apply to all message exchanges between Diameter nodes.
Communication between Diameter peers begins with one peer sending a message to another Diameter peer. The set of AVPs included in the message is determined by a particular Diameter application. One AVP that is included to reference a user's session is the Session-Id.
The initial request for authentication and/or authorization of a user would include the Session-Id AVP. The Session-Id is then used in all subsequent messages to identify the user's session (see Section 8 for 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.
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.
The base Diameter protocol may be used by itself for accounting applications. For authentication and authorization, it is always extended for a particular application.
Diameter Clients MUST support the base protocol, which includes accounting. In addition, they MUST fully support each Diameter application that is needed to implement the client's service, e.g., NASREQ and/or Mobile IPv4. A Diameter Client MUST be referred to as "Diameter X Client" where X is the application which it supports, and not a "Diameter Client".
Diameter Servers MUST support the base protocol, which includes accounting. In addition, they MUST fully support each Diameter application that is needed to implement the intended service, e.g., NASREQ and/or Mobile IPv4. A Diameter Server MUST be referred to as "Diameter X Server" where X is the application which it supports, and not a "Diameter Server".
Diameter Relays and redirect agents are transparent to the Diameter applications but they MUST support the Diameter base protocol, which includes accounting, and all Diameter applications.
Diameter proxies MUST support the base protocol, which includes accounting. In addition, they MUST fully support each Diameter application that is needed to implement proxied services, e.g., NASREQ and/or Mobile IPv4. A Diameter proxy MUST be referred to as "Diameter X Proxy" where X is the application which it supports, and not a "Diameter Proxy".
The Diameter Transport profile is defined in [RFC3539].
The base Diameter protocol is run on port 3868 for both TCP [RFC793] and SCTP [RFC4960]. For TLS [RFC5246] and DTLS [RFC6347], a Diameter node that initiate a connection prior to any message exchanges MUST run on port <TBD>. It is assumed that TLS is run on top of TCP when it is used and DTLS is run on top of SCTP when it is used.
If the Diameter peer does not support receiving TLS/TCP and DTLS/SCTP connections on port <TBD> (i.e., the peer complies only with [RFC3588]), then the initiator MAY revert to using TCP or SCTP on port 3868. Note that this scheme is kept only for the purpose of backward compatibility and that there are inherent security vulnerabilities when the initial CER/CEA messages are sent unprotected (see Section 5.6).
Diameter clients MUST support either TCP or SCTP; agents and servers SHOULD support both.
A Diameter node MAY initiate connections from a source port other than the one that it declares it accepts incoming connections on, and MUST always be prepared to receive connections on port 3868 for TCP or SCTP and port <TBD> for TLS/TCP and DTLS/SCTP connections. When DNS-based peer discovery (Section 5.2) is used, the port numbers received from SRV records take precedence over the default ports (3868 and <TBD>).
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.
When no transport connection exists with a peer, an attempt to connect SHOULD be periodically made. This behavior is handled via the Tc timer (see Section 12 for details), whose recommended value is 30 seconds. There are certain exceptions to this rule, such as when a peer has terminated the transport connection stating that it does not wish to communicate.
When connecting to a peer and either zero or more transports are specified, TLS SHOULD be tried first, followed by DTLS, then by TCP and finally by SCTP. See Section 5.2 for more information on peer discovery.
Diameter implementations SHOULD be able to interpret ICMP protocol port unreachable messages as explicit indications that the server is not reachable, subject to security policy on trusting such messages. Further guidance regarding the treatment of ICMP errors can be found in [RFC5927] and [RFC5461]. Diameter implementations SHOULD also be able to interpret a reset from the transport and timed-out connection attempts. If Diameter receives data from the lower layer that cannot be parsed or identified as a Diameter error made by the peer, the stream is compromised and cannot be recovered. The transport connection MUST be closed using a RESET call (send a TCP RST bit) or an SCTP ABORT message (graceful closure is compromised).
Diameter messages SHOULD be mapped into SCTP streams in a way that avoids head-of-the-line (HOL) blocking. Among different ways of performing the mapping that fulfill this requirement it is RECOMMENDED that a Diameter node sends every Diameter message (request or response) over the stream zero with the unordered flag set. However, Diameter nodes MAY select and implement other design alternatives for avoiding HOL blocking such as using multiple streams with the unordered flag cleared (as originally instructed in RFC3588). On the receiving side, a Diameter entity MUST be ready to receive Diameter messages over any stream and it is free to return responses over a different stream. This way, both sides manage the available streams in the sending direction, independently of the streams chosen by the other side to send a particular Diameter message. These messages can be out-of-order and belong to different Diameter sessions.
Out-of-order delivery has special concerns during a connection establishment and termination. When a connection is established, the responder side sends a CEA message and moves to R-Open state as specified in Section 5.6. If an application message is sent shortly after the CEA and delivered out-of-order, the initiator side, still in Wait-I-CEA state, will discard the application message and close the connection. In order to avoid this race condition, the receiver side SHOULD NOT use out-of-order delivery methods until the first message has been received from the initiator, proving that it has moved to I-Open state. To trigger such message, the receiver side could send a DWR immediatly after sending CEA. Upon reception of the corresponding DWA, the receiver side should start using out-of-order delivery methods to counter the HOL blocking.
Another race condition may occur when DPR and DPA messages are used. Both DPR and DPA are small in size, thus they may be delivered faster to the peer than application messages when out-of-order delivery mechanism is used. Therefore, it is possible that a DPR/DPA exchange completes while application messages are still in transit, resulting to a loss of these messages. An implementation could mitigate this race condition, for example, using timers and wait for a short period of time for pending application level messages to arrive before proceeding to disconnect the transport connection. Eventually, lost messages are handled by the retransmission mechanism described in Section 5.5.4.
A Diameter agent SHOULD use dedicated payload protocol identifiers (PPID) for clear text and encrypted SCTP DATA chunks instead of only using the unspecified payload protocol identifier (value 0). For this purpose two PPID values are allocated. The PPID value <TBD2> is for Diameter messages in clear text SCTP DATA chunks and the PPID value <TBD3> is for Diameter messages in protected DTLS/SCTP DATA chunks.
Connections between Diameter peers SHOULD be protected by TLS/TCP and DTLS/SCTP. All Diameter base protocol implementations MUST support the use of TLS/TCP and DTLS/SCTP. If desired, alternative security mechanisms that are independent of Diameter, such as IPsec [RFC4301], can be deployed to secure connections between peers. The Diameter protocol MUST NOT be used without one of TLS, DTLS or IPsec.
Application Ids are advertised during the capabilities exchange phase (see Section 5.3). Advertising support of an application implies that the sender supports the functionality specified in the respective Diameter application specification.
Implementations MAY add arbitrary optional AVPs with the M-bit cleared (including vendor-specific AVPs) to a command defined in an application, but only if the command's CCF syntax specification allows for it. Please refer to Section 11.1.1 for details.
Each Diameter application MUST have an IANA assigned Application Id. The base protocol does not require an Application Id since its support is mandatory. During the capabilities exchange, Diameter nodes inform their peers of locally supported applications. Furthermore, all Diameter messages contain an Application Id, which is used in the message forwarding process.
Diameter Common Messages 0
Diameter Base Accounting 3
Relay 0xffffffff
The following Application Id values are defined:
Relay and redirect agents MUST advertise the Relay Application Identifier, while all other Diameter nodes MUST advertise locally supported applications. The receiver of a Capabilities Exchange message advertising Relay service MUST assume that the sender supports all current and future applications.
Diameter relay and proxy agents are responsible for finding an upstream server that supports the application of a particular message. If none can be found, an error message is returned with the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER.
This section attempts to provide the reader with an understanding of the difference between connection and session, which are terms used extensively throughout this document.
A connection refers to a transport level connection between two peers that is used to send and receive Diameter messages. A session is a logical concept at the application layer existing between the Diameter client and the Diameter server; it is identified via the Session-Id AVP.
+--------+ +-------+ +--------+
| Client | | Relay | | Server |
+--------+ +-------+ +--------+
<----------> <---------->
peer connection A peer connection B
<----------------------------->
User session x
In the example provided in Figure 2, peer connection A is established between the Client and the Relay. Peer connection B is established between the Relay and the Server. User session X spans from the Client via the Relay to the Server. Each "user" of a service causes an auth request to be sent, with a unique session identifier. Once accepted by the server, both the client and the server are aware of the session.
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).
The Diameter Peer Table is used in message forwarding, and referenced by the Routing Table. A Peer Table entry contains the following fields:
Additional security information, when needed (e.g., keys, certificates).
All Realm-Based routing lookups are performed against what is commonly known as the Routing Table (see Section 12). Each Routing Table entry contains the following fields:
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 and proxies MUST NOT reorder AVPs.
The routing table MAY include a default entry that MUST be used for any requests not matching any of the other entries. The routing table MAY consist of only such an entry.
When a request is routed, the target server MUST have advertised the Application Id (see Section 2.4) for the given message, or have advertised itself as a relay or proxy agent. Otherwise, an error is returned with the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER.
In addition to clients and servers, the Diameter protocol introduces relay, proxy, redirect, and translation agents, each of which is defined in Section 1.2. Diameter agents are useful for several reasons:
The Diameter protocol requires that agents maintain transaction state, which is used for failover purposes. Transaction state implies that upon forwarding a request, its Hop-by-Hop identifier is saved; the field is replaced with a locally unique identifier, which is restored to its original value when the corresponding answer is received. The request's state is released upon receipt of the answer. A stateless agent is one that only maintains transaction state.
The Proxy-Info AVP allows stateless agents to add local state to a Diameter request, with the guarantee that the same state will be present in the answer. However, the protocol's failover procedures require that agents maintain a copy of pending requests.
A stateful agent is one that maintains session state information by keeping track of all authorized active sessions. Each authorized session is bound to a particular service, and its state is considered active either until the agent is notified otherwise, or the session expires. Each authorized session has an expiration, which is communicated by Diameter servers via the Session-Timeout AVP.
Maintaining session state may be useful in certain applications, such as:
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.
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.
Relays may, for example, 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.
+------+ ---------> +------+ ---------> +------+
| | 1. Request | | 2. Request | |
| NAS | | DRL | | HMS |
| | 4. Answer | | 3. Answer | |
+------+ <--------- +------+ <--------- +------+
example.net example.net example.com
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.
The example provided in Figure 3 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.
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.
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.
Proxies may, for example, 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.
Since enforcing policies requires an understanding of the service being provided, Proxies MUST only advertise the Diameter applications they support.
Redirect agents are useful in scenarios where the Diameter routing configuration needs to be centralized. An example is a redirect agent that provides services to all members of a consortium, but does not wish to be burdened with relaying all messages between realms. This scenario is advantageous since it does not require that the consortium provide routing updates to its members when changes are made to a member's infrastructure.
Since redirect agents do not relay messages, and only return an answer with the information necessary for Diameter agents to communicate directly, they do not modify messages. Since redirect agents do not receive answer messages, they cannot maintain session state.
+------+
| |
| DRD |
| |
+------+
^ |
2. Request | | 3. Redirection
| | Notification
| v
+------+ ---------> +------+ ---------> +------+
| | 1. Request | | 4. Request | |
| NAS | | DRL | | HMS |
| | 6. Answer | | 5. Answer | |
+------+ <--------- +------+ <--------- +------+
example.net example.net example.com
The example provided in Figure 4 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.
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.
A translation agent is a device that provides translation between two protocols (e.g., RADIUS<->Diameter, TACACS+<->Diameter). Translation agents are likely to be used as aggregation servers to communicate with a Diameter infrastructure, while allowing for the embedded systems to be migrated at a slower pace.
Given that the Diameter protocol introduces the concept of long-lived authorized sessions, translation agents MUST be session stateful and MUST maintain transaction state.
+------+ ---------> +------+ ---------> +------+
| | RADIUS Request | | Diameter Request | |
| NAS | | TLA | | HMS |
| | RADIUS Answer | | Diameter Answer | |
+------+ <--------- +------+ <--------- +------+
example.net example.net example.com
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.
As noted in Section 2.2, Diameter provides transmission level security for each connection using TLS/TCP and DTLS/SCTP. Therefore, each connection can be authenticated, replay and integrity protected.
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.
Prior to bringing up a connection, authorization checks are performed at each connection along the path. Diameter capabilities negotiation (CER/CEA) also MUST be carried out, in order to determine what Diameter applications are supported by each peer. Diameter sessions MUST be routed only through authorized nodes that have advertised support for the Diameter application required by the session.
As noted in Section 6.1.9, a relay or proxy agent MUST append a Route-Record AVP to all requests forwarded. The AVP contains the identity of the peer the request was received from.
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.
A home realm may also wish to check that each accounting request message corresponds to a Diameter response authorizing the session. Accounting requests without corresponding authorization responses SHOULD be subjected to further scrutiny, as should accounting requests indicating a difference between the requested and provided service.
Forwarding of an authorization response is considered evidence of a willingness to take on financial risk relative to the session. A local realm may wish to limit this exposure, for example, by establishing credit limits for intermediate realms and refusing to accept responses 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.
A summary of the Diameter header format is shown below. The fields are transmitted in network byte order.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| command flags | Command-Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Application-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop-by-Hop Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End-to-End Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVPs ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|R P E T r r r r|
+-+-+-+-+-+-+-+-+
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.
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
Every Diameter message MUST contain a command code in its header's Command-Code field, which is used to determine the action that is to be taken for a particular message. The following Command Codes are defined in the Diameter base protocol:
command-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.
;
; NOTE: "[" and "]" have a slightly different
; meaning than in ABNF. These braces
; cannot be used to express optional fixed rules
; (such as an optional ICV at the end). To do
; this, the convention is '0*1fixed'.
qual = [min] "*" [max]
; See ABNF conventions, RFC 5234, Section 4.
; The absence of any 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.
min = 1*DIGIT
; The minimum number of times the element may
; be present. If absent, the default value is zero
; for fixed and optional rules and one for
; required rules. The value MUST be at least one
; for required rules.
max = 1*DIGIT
; The maximum number of times the element may
; be present. If absent, the default value is
; infinity. A value of 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 inclusion of this string
; is recommended for all CCFs to allow for
; extensibility.
The following is a definition of a fictitious command code:
Example-Request ::= < Diameter Header: 9999999, REQ, PXY >
{ User-Name }
1* { Origin-Host }
* [ AVP ]
Every Command Code defined MUST include a corresponding Command Code Format (CCF) specification, which is used to define the AVPs that MUST or MAY be present when sending the message. The following ABNF specifies the CCF used in the definition:
Diameter command names typically includes one or more English words followed by the verb Request or Answer. Each English word is delimited by a hyphen. A three-letter acronym for both the request and answer is also normally provided.
An example is a message set used to terminate a session. The command name is Session-Terminate-Request and Session-Terminate-Answer, while the acronyms are STR and STA, respectively.
Both the request and the answer for a given command share the same command code. The request is identified by the R(equest) bit in the Diameter header set to one (1), to ask that a particular action be performed, such as authorizing a user or terminating a session. Once the receiver has completed the request it issues the corresponding answer, which includes a result code that communicates one of the following:
Additional information, encoded within AVPs, may also be included in answer messages.
Diameter AVPs carry specific authentication, accounting, authorization and routing information as well as configuration details for the request and reply.
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.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V M P r r r r r| AVP Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-ID (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
The fields in the AVP header MUST be sent in network byte order. The format of the header is:
The AVP Header contains one optional field. This field is only present if the respective bit-flag is enabled.
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.
In addition to using the Basic AVP Data Formats, applications may define data formats derived from the Basic AVP Data Formats. An application that defines new Derived AVP Data Formats MUST include them in a section entitled "Derived AVP Data Formats", using the same format as the definitions below. Each new definition MUST be either defined or listed with a reference to the RFC that defines the format.
DiameterIdentity = FQDN/Realm
"aaa://" FQDN [ port ] [ transport ] [ protocol ]
; No transport security
"aaas://" FQDN [ port ] [ transport ] [ protocol ]
; Transport security used
FQDN = < Fully Qualified Domain Name >
port = ":" 1*DIGIT
; One of the ports used to listen for
; incoming connections.
; If absent, the default Diameter port
; (3868) is assumed if no transport
; security is used and port <TBD> when
; transport security (TLS/TCP and DTLS/SCTP)
; is used.
transport = ";transport=" transport-protocol
; One of the transports used to listen
; for incoming connections. If absent,
; the default protocol is assumed to be TCP.
; UDP MUST NOT be used when the aaa-protocol
; field is set to diameter.
transport-protocol = ( "tcp" / "sctp" / "udp" )
protocol = ";protocol=" aaa-protocol
; If absent, the default AAA protocol
; is Diameter.
aaa-protocol = ( "diameter" / "radius" / "tacacs+" )
The following are examples of valid Diameter host identities:
aaa://host.example.com;transport=tcp
aaa://host.example.com:6666;transport=tcp
aaa://host.example.com;protocol=diameter
aaa://host.example.com:6666;protocol=diameter
aaa://host.example.com:6666;transport=tcp;protocol=diameter
aaa://host.example.com:1813;transport=udp;protocol=radius
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
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 192.0.2.10/24. In
this case, all IP numbers from
192.0.2.0 to 192.0.2.255 will match.
The bit width MUST be valid for the
IP version and the IP number MUST
NOT have bits set beyond the mask.
For a match to occur, the same IP
version must be present in the
packet that was used in describing
the IP address. To test for a
particular IP version, the bits part
can be set to zero. The keyword
"any" is 0.0.0.0/0 or the IPv6
equivalent. The keyword "assigned"
is the address or set of addresses
assigned to the terminal. For IPv4,
a typical first rule is often "deny
in ip! assigned"
The sense of the match can be inverted by
preceding an address with the not modifier (!),
causing all other addresses to be matched
instead. This does not affect the selection of
port numbers.
With the TCP, UDP and SCTP protocols, optional
ports may be specified as:
{port/port-port}[,ports[,...]]
The '-' notation specifies a range of ports
(including boundaries).
Fragmented packets that have a non-zero offset
(i.e., not the first fragment) will never match
a rule that has one or more port
specifications. See the frag option for
details on matching fragmented packets.
options:
frag Match if the packet is a fragment and this is not
the first fragment of the datagram. frag may not
be used in conjunction with either tcpflags or
TCP/UDP port specifications.
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).
The following are commonly used Derived AVP Data Formats.
The Diameter protocol allows AVP values of type 'Grouped'. This implies that the Data field is actually a sequence of AVPs. It is possible to include an AVP with a Grouped type within a Grouped type, that is, to nest them. AVPs within an AVP of type Grouped have the same padding requirements as non-Grouped AVPs, as defined in Section 4.4.
The AVP Code numbering space of all AVPs included in a Grouped AVP is the same as for non-grouped AVPs. Receivers of a Grouped AVP that does not have the 'M' (mandatory) bit set and one or more of the encapsulated AVPs within the group has the 'M' (mandatory) bit set MAY simply be ignored if the Grouped AVP itself is unrecognized. The rule applies even if the encapsulated AVP with its 'M' (mandatory) bit set is further encapsulated within other sub-groups; i.e. other Grouped AVPs embedded within the Grouped AVP.
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.
Every Grouped AVP defined MUST include a corresponding grammar, using CCF [RFC5234] (with modifications), as defined below.
Example-AVP ::= < AVP Header: 999999 >
{ Origin-Host }
1*{ Session-Id }
*[ AVP ]
An Example-AVP with Grouped Data follows.
The Origin-Host AVP (Section 6.3) is required. In this case:
Origin-Host = "example.com".
One or more Session-Ids must follow. Here there are two:
Session-Id =
"grump.example.com:33041;23432;893;0AF3B81"
Session-Id =
"grump.example.com:33054;23561;2358;0AF3B82"
optional AVPs included are
Recovery-Policy = <binary>
2163bc1d0ad82371f6bc09484133c3f09ad74a0dd5346d54195a7cf0b35
2cabc881839a4fdcfbc1769e2677a4c1fb499284c5f70b48f58503a45c5
c2d6943f82d5930f2b7c1da640f476f0e9c9572a50db8ea6e51e1c2c7bd
f8bb43dc995144b8dbe297ac739493946803e1cee3e15d9b765008a1b2a
cf4ac777c80041d72c01e691cf751dbf86e85f509f3988e5875dc905119
26841f00f0e29a6d1ddc1a842289d440268681e052b30fb638045f7779c
1d873c784f054f688f5001559ecff64865ef975f3e60d2fd7966b8c7f92
Futuristic-Acct-Record = <binary>
fe19da5802acd98b07a5b86cb4d5d03f0314ab9ef1ad0b67111ff3b90a0
57fe29620bf3585fd2dd9fcc38ce62f6cc208c6163c008f4258d1bc88b8
17694a74ccad3ec69269461b14b2e7a4c111fb239e33714da207983f58c
41d018d56fe938f3cbf089aac12a912a2f0d1923a9390e5f789cb2e5067
d3427475e49968f841
The Example-AVP (AVP Code 999999) is of type Grouped and is used to clarify how Grouped AVP values work. The Grouped Data field has the following CCF grammar:
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.
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|
+-------+-------+-------+-------+-------+-------+-------+-------+
This AVP would be encoded as follows:
The following table describes the Diameter AVPs defined in the base protocol, their AVP Code values, types, possible flag values.
+----------+
| AVP Flag |
| rules |
|----+-----|
AVP Section | |MUST |
Attribute Name Code Defined Data Type |MUST| NOT |
-----------------------------------------|----+-----|
Acct- 85 9.8.2 Unsigned32 | M | V |
Interim-Interval | | |
Accounting- 483 9.8.7 Enumerated | M | V |
Realtime-Required | | |
Acct- 50 9.8.5 UTF8String | M | V |
Multi-Session-Id | | |
Accounting- 485 9.8.3 Unsigned32 | M | V |
Record-Number | | |
Accounting- 480 9.8.1 Enumerated | M | V |
Record-Type | | |
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 | | |
-----------------------------------------|----+-----|
+----------+
| AVP Flag |
| rules |
|----+-----|
AVP Section | |MUST |
Attribute Name Code Defined Data Type |MUST| NOT |
-----------------------------------------|----+-----|
Experimental- 298 7.7 Unsigned32 | M | V |
Result-Code | | |
Failed-AVP 279 7.5 Grouped | M | V |
Firmware- 267 5.3.4 Unsigned32 | | V,M |
Revision | | |
Host-IP-Address 257 5.3.5 Address | M | V |
Inband-Security | M | V |
-Id 299 6.10 Unsigned32 | | |
Multi-Round- 272 8.19 Unsigned32 | M | V |
Time-Out | | |
Origin-Host 264 6.3 DiamIdent | M | V |
Origin-Realm 296 6.4 DiamIdent | M | V |
Origin-State-Id 278 8.16 Unsigned32 | M | V |
Product-Name 269 5.3.7 UTF8String | | V,M |
Proxy-Host 280 6.7.3 DiamIdent | M | V |
Proxy-Info 284 6.7.2 Grouped | M | V |
Proxy-State 33 6.7.4 OctetString| M | V |
Redirect-Host 292 6.12 DiamURI | M | V |
Redirect-Host- 261 6.13 Enumerated | M | V |
Usage | | |
Redirect-Max- 262 6.14 Unsigned32 | M | V |
Cache-Time | | |
Result-Code 268 7.1 Unsigned32 | M | V |
Route-Record 282 6.7.1 DiamIdent | M | V |
Session-Id 263 8.8 UTF8String | M | V |
Session-Timeout 27 8.13 Unsigned32 | M | V |
Session-Binding 270 8.17 Unsigned32 | M | V |
Session-Server- 271 8.18 Enumerated | M | V |
Failover | | |
Supported- 265 5.3.6 Unsigned32 | M | V |
Vendor-Id | | |
Termination- 295 8.15 Enumerated | M | V |
Cause | | |
User-Name 1 8.14 UTF8String | M | V |
Vendor-Id 266 5.3.3 Unsigned32 | M | V |
Vendor-Specific- 260 6.11 Grouped | M | V |
Application-Id | | |
-----------------------------------------|----+-----|
Due to space constraints, the short form DiamIdent is used to represent DiameterIdentity.
This section describes how Diameter nodes establish connections and communicate with peers.
Connections between diameter peers are established using their valid DiameterIdentity. A Diameter node initiating a connection to a peer MUST know the peers DiameterIdentity. Methods for discovering a Diameter peer can be found in Section 5.2.
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.
Note that a given peer MAY act as a primary for a given realm, while acting as a secondary for another realm.
When a peer is deemed suspect, which could occur for various reasons, including not receiving a DWA within an allotted 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.
There are two ways that a peer is removed from the suspect peer list:
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.
Allowing for dynamic Diameter agent discovery makes possible simpler and more robust deployment of Diameter services. In order to promote interoperable implementations of Diameter peer discovery, the following mechanisms (manual configuration and DNS) are described. These are based on existing IETF standards. Both mechanisms MUST be supported by all Diameter implementations; either MAY be used.
There are two cases where Diameter peer discovery may be performed. The first is when a Diameter client needs to discover a first-hop Diameter agent. The second case is when a Diameter agent needs to discover another agent - for further handling of a Diameter operation. In both cases, the following 'search order' is recommended:
If the server is using a site certificate, the domain name in the NAPTR query and the domain name in the replacement field MUST both be valid based on the site certificate handed out by the server in the TLS/TCP and DTLS/SCTP or 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.
Also, the Diameter Peer MUST check to make sure that the discovered peers are authorized to act in its role. Authentication via IKE or TLS/TCP and DTLS/SCTP, or validation of DNS RRs via DNSSEC is not sufficient to conclude this. For example, a web server may have obtained a valid TLS/TCP and DTLS/SCTP certificate, and secured RRs may be included in the DNS, but this does not imply that it is authorized to act as a Diameter Server.
Authorization can be achieved for example, by configuration of a Diameter Server Certification Authority (CA). The Server CA issues a certificate to the Diameter Server, which includes an Object Identifier (OID) to indicate the subject is a Diameter Server in the Extended Key Usage extension [RFC5280]. This certificate is then used during TLS/TCP, DTLS/SCTP, or IKE security negotiation. Note, however, that at the time of writing no Diameter Server Certification Authorities exist.
A dynamically discovered peer causes an entry in the Peer Table (see Section 2.6) to be created. Note that entries created via DNS MUST expire (or be refreshed) within the DNS 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.
When two Diameter peers establish a transport connection, they MUST exchange the Capabilities Exchange messages, as specified in the peer state machine (see Section 5.6). This message allows the discovery of a peer's identity and its capabilities (protocol version number, the identifiers of supported Diameter applications, security mechanisms, etc.)
The receiver only issues commands to its peers that have advertised support for the Diameter application that defines the command. A Diameter node MUST cache the supported Application Ids in order to ensure that unrecognized commands and/or AVPs are not unnecessarily sent to a peer.
A receiver of a Capabilities-Exchange-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.
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 identifier AVPs (Auth-Application-Id, Acct-Application-Id and Vendor-Specific-Application-Id) present in the CER. The value of the Vendor-Id AVP in the Vendor-Specific-Application-Id MUST NOT be used during computation. The sender of the Capabilities-Exchange-Answer (CEA) SHOULD include all of its supported applications as a hint to the receiver regarding all of its application capabilities.
Diameter implementations SHOULD first attempt to establish a TLS/TCP and DTLS/SCTP connection prior to the CER/CEA exchange. This protects the capabilities information of both peers. To support older Diameter implementations that do not fully conform to this document, the transport security MAY still be negotiated via Inband-Security AVP. In this case, the 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.
CERs received from unknown peers MAY be silently discarded, or a CEA MAY be issued with the Result-Code AVP set to DIAMETER_UNKNOWN_PEER. In both cases, the transport connection is closed. If the local policy permits receiving CERs from unknown hosts, a successful CEA MAY be returned. If a CER from an unknown peer is answered with a successful CEA, the lifetime of the peer entry is equal to the lifetime of the transport connection. In case of a transport failure, all the pending transactions destined to the unknown peer can be discarded.
The CER and CEA messages MUST NOT be proxied, redirected or relayed.
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 (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).
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).
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.
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 ]
When Diameter is run over SCTP [RFC4960] or DTLS/SCTP [RFC6083], which allow for connections to span multiple interfaces and multiple IP addresses, the Capabilities-Exchange-Request message MUST contain one Host-IP-Address AVP for each potential IP address that MAY be locally used when transmitting Diameter messages.
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.
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 ]
When Diameter is run over SCTP [RFC4960] or DTLS/SCTP [RFC6083], which allow connections to span multiple interfaces, hence, multiple IP addresses, the Capabilities-Exchange-Answer message MUST contain one Host-IP-Address AVP for each potential IP address that MAY be locally used when transmitting Diameter messages.
The Vendor-Id AVP (AVP Code 266) is of type Unsigned32 and contains the IANA "SMI Network Management Private Enterprise Codes" [ENTERPRISE] value assigned to the Diameter Software vendor. It is envisioned that the combination of the Vendor-Id, Product-Name (Section 5.3.7) and the Firmware-Revision (Section 5.3.4) AVPs may provide useful debugging information.
A Vendor-Id value of zero in the CER or CEA messages is reserved and indicates that this field is ignored.
The Firmware-Revision AVP (AVP Code 267) is of type Unsigned32 and is used to inform a Diameter peer of the firmware revision of the issuing device.
For devices that do not have a firmware revision (general purpose computers running Diameter software modules, for instance), the revision of the Diameter software module may be reported instead.
The Host-IP-Address AVP (AVP Code 257) is of type Address and is used to inform a Diameter peer of the sender's IP address. All source addresses that a Diameter node expects to use with SCTP [RFC4960] or DTLS/SCTP [RFC6083] MUST be advertised in the CER and CEA messages by including a Host-IP-Address AVP for each address.
The Supported-Vendor-Id AVP (AVP Code 265) is of type Unsigned32 and contains the IANA "SMI Network Management Private Enterprise Codes" [ENTERPRISE] value assigned to a vendor other than the device vendor but including the application vendor. This is used in the CER and CEA messages in order to inform the peer that the sender supports (a subset of) the vendor-specific AVPs defined by the vendor identified in this AVP. The value of this AVP MUST NOT be set to zero. Multiple instances of this AVP containing the same value SHOULD NOT be sent.
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.
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.
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.
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.
Message Format
<DPR> ::= < Diameter Header: 282, REQ >
{ Origin-Host }
{ Origin-Realm }
{ Disconnect-Cause }
* [ AVP ]
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.
Message Format
<DPA> ::= < Diameter Header: 282 >
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
[ Error-Message ]
[ Failed-AVP ]
* [ AVP ]
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.
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.
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:
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.
Message Format
<DWR> ::= < Diameter Header: 280, REQ >
{ Origin-Host }
{ Origin-Realm }
[ Origin-State-Id ]
* [ AVP ]
The Device-Watchdog-Request (DWR), indicated by the Command-Code set to 280 and the Command Flags' 'R' bit set, is sent to a peer when no traffic has been exchanged between two peers (see Section 5.5.3). Upon detection of a transport failure, this message MUST NOT be sent to an alternate peer.
Message Format
<DWA> ::= < Diameter Header: 280 >
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
[ Error-Message ]
[ Failed-AVP ]
[ Origin-State-Id ]
* [ AVP ]
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.
The transport failure algorithm is defined in [RFC3539]. All Diameter implementations MUST support the algorithm defined in the specification in order to be compliant to the Diameter base protocol.
In the event that a transport failure is detected with a peer, it is necessary for all pending request messages to be forwarded to an alternate agent, if possible. This is commonly referred to as failover.
In order for a Diameter node to perform failover procedures, it is necessary for the node to maintain a pending message queue for a given peer. When an answer message is received, the corresponding request is removed from the queue. The Hop-by-Hop Identifier field is used to match the answer with the queued request.
When a transport failure is detected, if possible all messages in the queue are sent to an alternate agent with the T flag set. On booting a Diameter client or agent, the T flag is also set on any 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.
It is important to note that multiple identical requests or answers MAY be received as a result of a failover. The End-to-End Identifier field in the Diameter header along with the Origin-Host AVP MUST be used to identify duplicate messages.
As described in Section 2.1, a connection request should be periodically attempted with the failed peer in order to re-establish the transport connection. Once a connection has been successfully established, messages can once again be forwarded to the peer. This is commonly referred to as failback.
This section contains a finite state machine that MUST be observed by all Diameter implementations. Each Diameter node MUST follow the state machine described below when communicating with each peer. Multiple actions are separated by commas, and may continue on succeeding lines, as space requires. Similarly, state and next state may also span multiple lines, as space requires.
This state machine is closely coupled with the state machine described in [RFC3539], which is used to open, close, failover, probe, and reopen transport connections. Note in particular that [RFC3539] requires the use of watchdog messages to probe connections. For Diameter, DWR and DWA messages are to be used.
I- is used to represent the initiator (connecting) connection, while the R- is used to represent the responder (listening) connection. The lack of a prefix indicates that the event or action is the same regardless of the connection on which the event occurred.
The stable states that a state machine may be in are Closed, I-Open and R-Open; all other states are intermediate. Note that I-Open and R-Open are equivalent except for whether the initiator or responder transport connection is used for communication.
A CER message is always sent on the initiating connection immediately after the connection request is successfully completed. In the case of an election, one of the two connections will shut down. The responder connection will survive if the Origin-Host of the local Diameter entity is higher than that of the peer; the initiator connection will survive if the peer's Origin-Host is higher. All subsequent messages are sent on the surviving connection. Note that the results of an election on one peer are guaranteed to be the inverse of the results on the other.
For TLS/TCP and DTLS/SCTP usage, TLS/TCP and DTLS/SCTP handshake SHOULD begin when both ends are in the closed state prior to any Diameter message exchanges. The TLS/TCP and DTLS/SCTP connection SHOULD be established before sending any CER or CEA message to secure and protect the capabilities information of both peers. The TLS/TCP and DTLS/SCTP connection SHOULD be disconnected when the state machine moves to the closed state. When connecting to responders that do not conform to this document (i.e. older Diameter implementations that are not prepared to received TLS/TCP and DTLS/SCTP connections in the closed state), the initial TLS/TCP and DTLS/SCTP connection attempt will fail. The initiator MAY then attempt to connect via TCP or SCTP and initiate the TLS/TCP and DTLS/SCTP handshake when both ends are in the open state. If the handshake is successful, all further messages will be sent via TLS/TCP and DTLS/SCTP. If the handshake fails, both ends move to the closed state.
The state machine constrains only the behavior of a Diameter implementation as seen by Diameter peers through events on the wire.
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
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
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
Any implementation that produces equivalent results is considered compliant.
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.
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.
The logic that handles incoming connections SHOULD close and discard the connection if any message other than CER arrives, or if an implementation-defined timeout occurs prior to receipt of CER.
Because handling of incoming connections up to and including receipt of CER requires logic, separate from that of any individual state machine associated with a particular peer, it is described separately in this section rather than in the state machine above.
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).
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.
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.
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.
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 Appendix Appendix D for interactions between the Diameter protocol and Internationalized Domain Name (IDNs).
The winner of the election MUST close the connection it initiated. Historically, maintaining the responder side of a connection was more efficient than maintaining the initiator side. However, current practices makes this distinction irrelevant.
This section describes how Diameter requests and answers are created and processed.
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:
The Destination-Host AVP is used as described above when the destination of the request is fixed, which includes:
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 2.6). Otherwise, the request is routed based on the Destination-Realm only (see Section 6.1.6).
When a message is received, the message is processed in the following order:
For routing of Diameter messages to work within an administrative domain, all Diameter nodes within the realm MUST be peers.
The overview contained in this section (6.1) is intended to provide general guidelines to Diameter developers. Implementations are free to use different methods than the ones described here as long as they conform to the requirements specified in Sections 6.1.1 through 6.1.9. See Section 7 for more detail on error handling.
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:
When sending a request, originated either locally, or as the result of a forwarding or routing operation, the following procedures SHOULD be followed:
Other actions to perform on the message based on the particular role the agent is playing are described in the following sections.
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.
A request is known to be for local consumption when one of the following conditions occur:
When a request is locally processed, the rules in Section 6.2 should be used to generate the corresponding answer.
Request forwarding is done using the Diameter Peer Table. The Diameter peer table contains all of the peers that the local node is able to directly communicate with.
When a request is received, and the host encoded in the Destination-Host AVP is one that is present in the peer table, the message SHOULD be forwarded to the peer.
Diameter request message routing is done via realms and application identifiers. A Diameter message that may be forwarded by Diameter agents (proxies, redirect or relay agents) MUST include the target realm in the Destination-Realm AVP. Request routing SHOULD rely on the Destination-Realm AVP and the Application Id present in the request message header to aid in the routing decision. The realm MAY be retrieved from the User-Name AVP, which is in the form of a Network Access Identifier (NAI). The realm portion of the NAI is inserted in the Destination-Realm AVP.
Diameter agents MAY have a list of locally supported realms and applications, and MAY have a list of externally supported realms and applications. When a request is received that includes a realm and/or application that is not locally supported, the message is routed to the peer configured in the Routing Table (see Section 2.7).
Realm names and Application Ids are the minimum supported routing criteria, additional information may be needed to support redirect semantics.
Before forwarding or routing a request Diameter agents, in addition to performing the processing described in Section 6.1.3, SHOULD check for the presence of 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.
+------------------+
| 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 +-------------+
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.
The receiver of an answer message with the 'E' bit set and the Result-Code AVP set to DIAMETER_REDIRECT_INDICATION uses the Hop-by-Hop Identifier in the Diameter header to identify the request in the pending message queue (see Section 5.5.4) that is to be redirected. If no transport connection exists with the new agent, one is created, and the request is sent directly to it.
Multiple Redirect-Host AVPs are allowed. The receiver of the answer message with the 'E' bit set selects exactly one of these hosts as the destination of the redirected message.
When the Redirect-Host-Usage AVP included in the answer message has a non-zero value, a route entry for the redirect indications is created and cached by the receiver. The redirect usage for such route entry is set by the value of Redirect-Host-Usage AVP and the lifetime of the cached route entry is set by Redirect-Max-Cache-Time AVP value.
It is possible that multiple redirect indications can create multiple cached route entries differing only in their redirect usage and the peer to forward messages to. As an example, two(2) route entries that are created by two(2) redirect indications results in two(2) 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 against the redirect usage value to resolve the contention. The precedence rule can be found in Section 6.13.
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.
The Hop-by-Hop identifier in the request is saved, and replaced with a locally unique value. The source of the request is also saved, which includes the IP address, port and protocol.
A relay or proxy agent MAY include the Proxy-Info AVP in requests if it requires access to any local state information when the corresponding response is received. The Proxy-Info AVP has security implications as state information is distributed to other entities. As such, it is RECOMMENDED that the content of the Proxy-Info AVP be protected with cryptographic mechanisms, for example by using a keyed message digest such as HMAC-SHA1 [RFC2104]. Such a mechanism, however, requires the management of keys, although only locally at the Diameter server. Still, a full description of the management of the keys used to protect the Proxy-Info AVP is beyond the scope of this document. Below is a list of common recommendations:
The message is then forwarded to the next hop, as identified in the Routing Table.
(Origin-Host=nas.example.net) (Origin-Host=nas.example.net)
(Origin-Realm=example.net) (Origin-Realm=example.net)
(Destination-Realm=example.com) (Destination-
Realm=example.com)
(Route-Record=nas.example.net)
+------+ ------> +------+ ------> +------+
| | (Request) | | (Request) | |
| NAS +-------------------+ DRL +-------------------+ HMS |
| | | | | |
+------+ <------ +------+ <------ +------+
example.net (Answer) example.net (Answer) example.com
(Origin-Host=hms.example.com) (Origin-Host=hms.example.com)
(Origin-Realm=example.com) (Origin-Realm=example.com)
Figure 31 provides an example of message routing using the procedures listed in these sections.
Relay and proxy agents are not required to perform full inspection of incoming messages. At a minimum, validation of the message header and relevant routing AVPs has to be done when relaying messages. Proxy agents may optionally perform more in-depth message validation for applications it is interested in.
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:
Note that the error messages (see Section 7) are also subjected to the above processing rules.
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.
If the answer is for a request which was proxied or relayed, the agent MUST restore the original value of the Diameter header's Hop- by-Hop Identifier field.
If the last Proxy-Info AVP in the message is targeted to the local Diameter server, the AVP MUST be removed before the answer is forwarded.
If a relay or proxy agent receives an answer with a Result-Code AVP indicating a failure, it MUST NOT modify the contents of the AVP. Any additional local errors detected SHOULD be logged, but not reflected in the Result-Code AVP. If the agent receives an answer message with a Result-Code AVP indicating success, and it wishes to modify the AVP to indicate an error, it MUST 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 towards the Diameter server.
The agent MUST then send the answer to the host that it received the original request from.
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.
The value of the Origin-Host AVP is guaranteed to be unique within a single host.
Note that the Origin-Host AVP may resolve to more than one address as the Diameter peer may support more than one address.
This AVP SHOULD be placed as close to the Diameter header as possible.
The Origin-Realm AVP (AVP Code 296) is of type DiameterIdentity. This AVP contains the Realm of the originator of any Diameter message and MUST be present in all messages.
This AVP SHOULD be placed as close to the Diameter header as possible.
The Destination-Host AVP (AVP Code 293) is of type DiameterIdentity. This AVP MUST be present in all unsolicited agent initiated messages, MAY be present in request messages, and MUST NOT be present in Answer messages.
The absence of the Destination-Host AVP will cause a message to be sent to any Diameter server supporting the application within the realm specified in Destination-Realm AVP.
This AVP SHOULD be placed as close to the Diameter header as possible.
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.
The CCF for a request message that includes the Destination-Realm AVP SHOULD list the Destination-Realm AVP as a required AVP (an AVP indicated as {AVP}) otherwise the message is inherently a non-routable message.
This AVP SHOULD be placed as close to the Diameter header as possible.
The AVPs defined in this section are Diameter AVPs used for routing purposes. These AVPs change as Diameter messages are processed by agents.
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.
Proxy-Info ::= < AVP Header: 284 >
{ Proxy-Host }
{ Proxy-State }
* [ AVP ]
The Proxy-Info AVP (AVP Code 284) is of type Grouped. This AVP contains the identity and local state information of the Diameter node that creates and adds it to a message. The Grouped Data field has the following CCF grammar:
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.
The Proxy-State AVP (AVP Code 33) is of type OctetString. It contains state information that would otherwise be stored at the Diameter entity that created it. As such, this AVP MUST be treated as opaque data by other Diameter entities.
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.
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.
The Inband-Security-Id AVP (AVP Code 299) is of type Unsigned32 and is used in order to advertise support of the security portion of the application. The use of this AVP in CER and CEA messages is NOT RECCOMENDED. Instead, discovery of a Diameter entities security capabilities can be done either through static configuration or via Diameter Peer Discovery as described in Section 5.2.
The following values are supported:
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 message.
The Vendor-Id AVP is an informational AVP pertaining to the vendor who may have authorship of the vendor-specific Diameter application. It MUST NOT be used as a means of defining a completely separate vendor-specific Application Id space.
AVP Format
<Vendor-Specific-Application-Id> ::= < AVP Header: 260 >
{ Vendor-Id }
[ Auth-Application-Id ]
[ Acct-Application-Id ]
The Vendor-Specific-Application-Id AVP SHOULD be placed as close to the Diameter header as possible.
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.
If a Vendor-Specific-Application-Id is received that contains both Auth-Application-Id and Acct-Application-Id, then the recipient MUST issue an answer with Result-Code set to DIAMETER_AVP_OCCURS_TOO_MANY_TIMES. The answer MUST also include a Failed-AVP which MUST contain the received Auth-Application-Id AVP and Acct-Application-Id AVP.
The Redirect-Host AVP (AVP Code 292) is of type DiameterURI. 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.
Upon receiving the above, the receiving Diameter node SHOULD forward the request directly to one of the hosts identified in these AVPs. The server contained in the selected Redirect-Host AVP SHOULD be used for all messages matching the criteria set by the Redirect-Host-Usage AVP.
The Redirect-Host-Usage AVP (AVP Code 261) is of type Enumerated. This AVP MAY be present in answer messages whose 'E' bit is set and the Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION.
When present, this AVP provides a hints about how the routing entry resulting from the Redirect-Host is to be used. The following values are supported:
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:
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.
This AVP contains the maximum number of seconds the peer and route table entries, created as a result of the Redirect-Host, SHOULD be cached. Note that once a host is no longer reachable, any associated cache, peer and routing table entries MUST be deleted.
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).
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 |-----------+
+---------+
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.
+---------+ 1. Request +---------+ 2. Request +---------+
| Access |------------>|Diameter |------------>|Diameter |
| | | | | Home |
| Device |<------------| Relay |<------------| Server |
+---------+ 4. Answer +---------+ 3. Answer +---------+
(Missing AVP) (Missing AVP)
Figure 34 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 35 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.
In the case where the answer message itself contains errors, any related session SHOULD be terminated by sending an STR or ASR message. The Termination-Cause AVP in the STR MAY be filled with the appropriate value to indicate the cause of the error. An application MAY also send an application-specific request instead of STR or ASR to signal the error in the case where no state is maintained or to allow for some form of error recovery with the corresponding Diameter entity.
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:
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.
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 in IETF defined Diameter application specification MUST include one Result-Code AVP. A non-successful Result-Code AVP (one containing a non 2xxx value other than DIAMETER_REDIRECT_INDICATION) MUST include the Error-Reporting-Host AVP if the host setting the Result-Code AVP is different from the identity encoded in the Origin-Host AVP.
The Result-Code data field contains an IANA-managed 32-bit address space representing errors (see Section 11.3.2). Diameter provides the following classes of errors, all identified by the thousands digit in the decimal notation:
A non-recognized class (one whose first digit is not defined in this section) MUST be handled as a permanent failure.
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.
Errors that fall within the Success category are used to inform a peer that a request has been successfully completed.
Errors that fall within the Protocol Error category SHOULD be treated on a per-hop basis, and Diameter proxies MAY attempt to correct the error, if it is possible. Note that these errors MUST only be used in answer messages whose 'E' bit is set.
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.
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.
Message Format
<answer-message> ::= < Diameter Header: code, ERR [, PXY] >
0*1< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Result-Code }
[ Origin-State-Id ]
[ Error-Message ]
[ Error-Reporting-Host ]
[ Failed-AVP ]
[ Experimental-Result ]
* [ Proxy-Info ]
* [ AVP ]
The 'E' (Error Bit) in the Diameter header is set when the request caused a protocol-related error (see Section 7.1.3). A message with the 'E' bit MUST NOT be sent as a response to an answer message. Note that a message with the 'E' bit set is still subjected to the processing rules defined in Section 6.2. When set, the answer message will not conform to the CCF specification for the command, and will instead conform to the following CCF:
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.
The Error-Message AVP (AVP Code 281) is of type UTF8String. It MAY accompany a Result-Code AVP as a human readable error message. The Error-Message AVP is not intended to be useful in an environment where error messages are processed automatically. It SHOULD NOT be expected that the content of this AVP is parsed by network entities.
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.
The Failed-AVP AVP (AVP Code 279) is of type Grouped and provides debugging information in cases where a request is rejected or not fully processed due to erroneous information in a specific AVP. The value of the Result-Code AVP will provide information on the reason for the Failed-AVP AVP. A Diameter answer message SHOULD contain 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.
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.
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.
In the case where the offending AVP is embedded within a grouped AVP, the Failed-AVP MAY contain the grouped AVP which in turn contains the single offending AVP. The same method MAY be employed if the grouped AVP itself is embedded in yet another grouped AVP and so on. In this case, the Failed-AVP MAY contain the grouped AVP hierarchy up to the single offending AVP. This enables the recipient to detect the location of the offending AVP when embedded in a group.
<Failed-AVP> ::= < AVP Header: 279 >
1* {AVP}
AVP Format
Experimental-Result ::= < AVP Header: 297 >
{ Vendor-Id }
{ Experimental-Result-Code }
The Experimental-Result AVP (AVP Code 297) is of type Grouped, and indicates whether a particular vendor-specific request was completed successfully or whether an error occurred. This AVP has the following structure:
AVP Format
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.
The Experimental-Result-Code AVP (AVP Code 298) is of type Unsigned32 and contains a vendor-assigned value representing the result of processing the request.
It is recommended that vendor-specific result codes follow the same conventions given for the Result-Code AVP regarding the different types of result codes and the handling of errors (for non 2xxx values).
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.
When a service makes use of the authentication and/or authorization portion of an application, and a user requests access to the network, the Diameter client issues an auth request to its local server. The auth request is defined in a service-specific Diameter application (e.g., NASREQ). The request contains a Session-Id AVP, which is used in subsequent messages (e.g., subsequent authorization, accounting, etc) relating to the user's session. The Session-Id AVP is a means for the client and servers to correlate a Diameter message with a user session.
When a Diameter server authorizes a user to use network resources 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.
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.
The base protocol does not include any authorization request messages, since these are largely application-specific and are defined in a Diameter application document. However, the base protocol does define a set of messages that are used to terminate user sessions. These are used to allow servers that maintain state information to free resources.
When a service only makes use of the Accounting portion of the Diameter protocol, even in combination with an application, the Session-Id is still used to identify user sessions. However, the session termination messages are not used, since a session is signaled as being terminated by issuing an accounting stop message.
Diameter may also be used for services that cannot be easily categorized as authentication, authorization or accounting (e.g., certain 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 SHOULD follow the general state machine framework outlined in this document such as the use of Session-Id AVPs and the use of STR/STA, ASR/ASA messages for stateful sessions.
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).
There are four different authorization session state machines supported in the Diameter base protocol. The first two describe a session in which the server is maintaining session state, indicated by the value of the Auth-Session-State AVP (or its absence). One describes the session from a client perspective, the other from a server perspective. The second two state machines are used when the server does not maintain session state. Here again, one describes the session from a client perspective, the other from a server perspective.
When a session is moved to the Idle state, any resources that were allocated for the particular session must be released. Any event not listed in the state machines MUST be considered as an error condition, and an answer, if applicable, MUST be returned to the originator of the message.
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 session maintains state (e.g., Send RAR, Pending, Receive RAA) MAY be ignored.
In the state table, the event 'Failure to send X' means that the Diameter agent is unable to send command X to the desired destination. This could be due to the peer being down, or due to the peer sending back a transient failure or temporary protocol error notification DIAMETER_TOO_BUSY or DIAMETER_LOOP_DETECTED in the Result-Code AVP of the corresponding Answer command. The event 'X successfully sent' is the complement of 'Failure to send X'.
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 Result-Code =
session = SUCCESS,
Send STR.
Open ASR Received, Send ASA Open
client will not comply with
with request to end the Result-Code !=
session != SUCCESS
Open Authorization-Lifetime + Send STR Discon
Auth-Grace-Period expires on
access device
Discon ASR Received Send ASA Discon
Discon STA Received Discon. Idle
user/device
The following state machine is observed by a client when state is maintained on the server:
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.
The following state machine is observed by a server when it is maintaining state for the session:
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
The following state machine is observed by a client when state is not maintained on the server:
SERVER, STATELESS
State Event Action New State
---------------------------------------------------------------
Idle Service-specific authorization Send serv. Idle
request received, and specific
successfully processed answer
The following state machine is observed by a server when it is not maintaining state for the session:
The following state machines MUST be supported for applications that have an accounting portion or that require only accounting services. The first state machine is to be observed by clients.
See Section 9.7 for Accounting Command Codes and Section 9.8 for Accounting AVPs.
The server side in the accounting state machine depends in some cases on the particular application. The Diameter base protocol defines a default state machine that MUST be followed by all applications that have not specified other state machines. This is the second state machine in this section described below.
The default server side state machine requires the reception of accounting records in any order and at any time, and does not place any standards requirement on the processing of these records. Implementations of Diameter may perform checking, ordering, correlation, fraud detection, and other tasks based on these records. AVPs may need to be inspected as a part of these tasks. The tasks can happen either immediately after record reception or in a post-processing phase. However, as these tasks are typically application or even policy dependent, they are not standardized by the Diameter specifications. Applications MAY define requirements on when to accept accounting records based on the used value of Accounting-Realtime-Required AVP, credit limits checks, and so on.
However, the Diameter base protocol defines one optional server side state machine that MAY be followed by applications that require keeping track of the session state at the accounting server. Note that such tracking is incompatible with the ability to sustain long duration connectivity problems. Therefore, the use of this state machine is recommended only in applications where the value of the Accounting-Realtime-Required AVP is DELIVER_AND_GRANT, 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.
Any event not listed in the state machines MUST be considered as an error condition, and a corresponding answer, if applicable, MUST be returned to the originator of the message.
In the state table, the event 'Failure to send' means that the Diameter client is unable to communicate with the desired destination. This could be due to the peer being down, or due to the peer sending back a transient failure or temporary protocol error notification DIAMETER_OUT_OF_SPACE, DIAMETER_TOO_BUSY, or DIAMETER_LOOP_DETECTED in the Result-Code AVP of the Accounting Answer command.
The event 'Failed answer' means that the Diameter client received a non-transient failure notification in the Accounting Answer command.
Note that the action 'Disconnect user/dev' MUST 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.
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 Disconnect Idle
buffer space available and user/dev
realtime 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 interim
record can be overwritten) record
and 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 Disconnect Idle
buffer space available and user/dev
realtime 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 user/dev
realtime 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
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.
A Diameter server may initiate a re-authentication and/or re- authorization service for a particular session by issuing a Re-Auth- Request (RAR).
For example, for pre-paid services, the Diameter server that originally authorized a session may need some confirmation that the user is still using the services.
An access device that receives a RAR message with Session-Id equal to a currently active session MUST initiate a re-auth towards the user, if the service supports this particular feature. Each Diameter application MUST state whether server-initiated re-auth is supported, since some applications do not allow access devices to prompt the user for re-auth.
The Re-Auth-Request (RAR), indicated by the Command-Code set to 258 and the message flags' 'R' bit set, may be sent by any server to the access device that is providing session service, to request that the user be re-authenticated and/or re-authorized.
Message Format
<RAR> ::= < Diameter Header: 258, REQ, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Destination-Host }
{ Auth-Application-Id }
{ Re-Auth-Request-Type }
[ User-Name ]
[ Origin-State-Id ]
* [ Proxy-Info ]
* [ Route-Record ]
* [ AVP ]
The Re-Auth-Answer (RAA), indicated by the Command-Code set to 258 and the message flags' 'R' bit clear, is sent in response to the RAR. The Result-Code AVP MUST be present, and indicates the disposition of the request.
A successful RAA message MUST be followed by an application-specific authentication and/or authorization message.
Message Format
<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 ]
It is necessary for a Diameter server that authorized a session, for which it is maintaining state, to be notified when that session is no longer active, both for tracking purposes as well as to allow stateful agents to release any resources that they may have provided for the user's session. For sessions whose state is not being maintained, this section is not used.
When a user session that required Diameter authorization terminates, the access device that provided the service MUST issue a Session-Termination-Request (STR) message to the Diameter server that authorized the service, to notify it that the session is no longer active. An STR MUST be issued when a user session terminates for any reason, including user logoff, expiration of Session-Timeout, administrative action, termination upon receipt of an Abort-Session- Request (see below), orderly shutdown of the access device, etc.
The access device also MUST issue an STR for a session that was authorized but never actually started. This could occur, for example, due to a sudden resource shortage in the access device, or because the access device is unwilling to provide the type of service requested in the authorization, or because the access device does not support a mandatory AVP returned in the authorization, etc.
It is also possible that a session that was authorized is never actually started due to action of a proxy. For example, a proxy may modify an authorization answer, converting the result from success to failure, prior to forwarding the message to the access device. If the answer did not contain an Auth-Session-State AVP with the value NO_STATE_MAINTAINED, a proxy that causes an authorized session not to be started MUST issue an STR to the Diameter server that authorized the session, since the access device has no way of knowing that the session had been authorized.
A Diameter server that receives an STR message MUST clean up resources (e.g., session state) associated with the Session-Id specified in the STR, and return a Session-Termination-Answer.
A Diameter server also MUST clean up resources when the Session- Timeout expires, or when the Authorization-Lifetime and the Auth- Grace-Period AVPs 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.
The Session-Termination-Request (STR), indicated by the Command-Code set to 275 and the Command Flags' 'R' bit set, is sent by a Diameter client or by a Diameter proxy to inform the Diameter Server that an authenticated and/or authorized session is being terminated.
Message Format
<STR> ::= < Diameter Header: 275, REQ, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Auth-Application-Id }
{ Termination-Cause }
[ User-Name ]
[ Destination-Host ]
* [ Class ]
[ Origin-State-Id ]
* [ Proxy-Info ]
* [ Route-Record ]
* [ AVP ]
The Session-Termination-Answer (STA), indicated by the Command-Code set to 275 and the message flags' 'R' bit clear, is sent by the Diameter Server to acknowledge the notification that the session has been terminated. The Result-Code AVP MUST be present, and MAY contain an indication that an error occurred while servicing the STR.
Upon sending or receipt of the STA, the Diameter Server MUST release all resources for the session indicated by the Session-Id AVP. Any intermediate server in the Proxy-Chain MAY also release any resources, if necessary.
Message Format
<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 ]
A Diameter server may request that the access device stop providing service for a particular session by issuing an Abort-Session-Request (ASR).
For example, the Diameter server that originally authorized the session may be required to cause that session to be stopped for lack of credit or other reasons that were not anticipated when the session was first authorized.
An access device that receives an ASR with Session-ID equal to a currently active session MAY stop the session. Whether the access device stops the session or not is implementation- and/or configuration-dependent. For example, an access device may honor ASRs from certain agents only. In any case, the access device MUST respond with an Abort-Session-Answer, including a Result-Code AVP to indicate what action it took.
The Abort-Session-Request (ASR), indicated by the Command-Code set to 274 and the message flags' 'R' bit set, may be sent by any Diameter server or any Diameter proxy to the access device that is providing session service, to request that the session identified by the Session-Id be stopped.
Message Format
<ASR> ::= < Diameter Header: 274, REQ, PXY >
< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Destination-Host }
{ Auth-Application-Id }
[ User-Name ]
[ Origin-State-Id ]
* [ Proxy-Info ]
* [ Route-Record ]
* [ AVP ]
The Abort-Session-Answer (ASA), indicated by the Command-Code set to 274 and the message flags' 'R' bit clear, is sent in response to the ASR. The Result-Code AVP MUST be present, and indicates the disposition of the request.
If the session identified by Session-Id in the ASR was successfully terminated, Result-Code is set to DIAMETER_SUCCESS. If the session is not currently active, Result-Code is set to DIAMETER_UNKNOWN_SESSION_ID. If the access device does not stop the session for any other reason, Result-Code is set to DIAMETER_UNABLE_TO_COMPLY.
Message Format
<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 ]
The Origin-State-Id is used to allow detection of terminated sessions for which no STR would have been issued, due to unanticipated shutdown of an access device.
A Diameter client or access device increments the value of the Origin-State-Id every time it is started or powered-up. The new Origin-State-Id is then sent in the CER/CEA message immediately upon connection to the server. The Diameter server receiving the new Origin-State-Id can determine whether the sending Diameter client had abruptly shutdown by comparing the old value of the Origin-State-Id it has kept for that specific client is less than the new value and whether it has un-terminated sessions originating from that client.
An access device can also include the Origin-State-Id in request messages other than CER if there are relays or proxies in between the access device and the server. In this case, however, the server cannot discover that the access device has been restarted unless and until it receives a new request from it. Therefore this mechanism is more opportunistic across proxies and relays.
The Diameter server may assume that all sessions that were active prior to detection of a client restart have been terminated. The Diameter server MAY clean up all session state associated with such lost sessions, and MAY also issues STRs for all such lost sessions that were authorized on upstream servers, to allow session state to be cleaned up globally.
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:
The Session-Id AVP (AVP Code 263) is of type UTF8String and is used to identify a specific session (see Section 8). All messages pertaining to a specific session MUST include only one Session-Id AVP and the same value MUST be used throughout the life of a session. When present, the Session-Id SHOULD appear immediately following the Diameter Header (see Section 3).
The Session-Id MUST be globally and eternally unique, as it is meant to uniquely identify a user session without reference to any other information, and 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.
<DiameterIdentity>;<high 32 bits>;<low 32 bits>[;<optional value>]
The Session-Id MUST begin with the sender's identity encoded in the DiameterIdentity type (see Section 4.3.1). The remainder of the Session-Id is delimited by a ";" character, and 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):
<high 32 bits> and <low 32 bits> are decimal representations of the high and low 32 bits of a monotonically increasing 64-bit value. The 64-bit value is rendered in two part to simplify formatting by 32-bit processors. At startup, the high 32 bits of the 64-bit value MAY be initialized to the time in NTP format [RFC5905], and the low 32 bits MAY be initialized to zero. This will for practical purposes eliminate the possibility of overlapping Session-Ids after a reboot, assuming the reboot process takes longer than a second. Alternatively, an implementation MAY keep track of the increasing value in non-volatile memory.
<optional value> is implementation specific but may include a modem's
device Id, a layer 2 address, timestamp, etc.
Example, in which there is no optional value:
accesspoint7.example.com;1876543210;523
Example, in which there is an optional value:
accesspoint7.example.com;1876543210;523;mobile@200.1.1.88
The Session-Id is created by the Diameter application initiating the session, which in most cases is done by the client. Note that a Session-Id MAY be used for both the authentication, authorization and accounting commands of a given application.
The Authorization-Lifetime AVP (AVP Code 291) is of type Unsigned32 and contains the maximum number of seconds of service to be provided to the user before the user is to be re-authenticated and/or re-authorized. Care should be taken when the Authorization-Lifetime value is determined, since a low, non-zero, value could create significant Diameter traffic, which could congest both the network and the agents.
A value of zero (0) means that immediate re-auth is necessary by the access device. The absence of this AVP, or a value of all ones (meaning all bits in the 32 bit field are set to one) means no re-auth is expected.
If both this AVP and the Session-Timeout AVP are present in a message, the value of the latter MUST NOT be smaller than the Authorization-Lifetime AVP.
An Authorization-Lifetime AVP MAY be present in re-authorization messages, and contains the number of seconds the user is authorized to receive service from the time the re-auth answer message is received by the access device.
This AVP MAY be provided by the client as a hint of the maximum lifetime that it is willing to accept. The server MUST return a value that is equal to, or smaller, than the one provided by the client.
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.
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:
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:
The Session-Timeout AVP (AVP Code 27) [RFC2865] is of type Unsigned32 and contains the maximum number of seconds of service to be provided to the user before termination of the session. When both the Session-Timeout and the Authorization-Lifetime AVPs are present in an answer message, the former MUST be equal to or greater than the value of the latter.
A session that terminates on an access device due to the expiration of the Session-Timeout MUST cause an STR to be issued, unless both the access device and the home server had previously agreed that no session termination messages would be sent (see Section 8).
A Session-Timeout AVP MAY be present in a re-authorization answer message, and contains the remaining number of seconds from the beginning of the re-auth.
A value of zero, or the absence of this AVP, means that this session has an unlimited number of seconds before termination.
This AVP MAY be provided by the client as a hint of the maximum timeout that it is willing to accept. However, the server MAY return a value that is equal to, or smaller, than the one provided by the client.
The User-Name AVP (AVP Code 1) [RFC2865] is of type UTF8String, which contains the User-Name, in a format consistent with the NAI specification [RFC4282].
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:
The Origin-State-Id AVP (AVP Code 278), of type Unsigned32, is a monotonically increasing value that is advanced whenever a Diameter entity restarts with loss of previous state, for example upon reboot. Origin-State-Id MAY be included in any Diameter message, including CER.
A Diameter entity issuing this AVP MUST create a higher value for this AVP each time its state is reset. A Diameter entity MAY set Origin-State-Id to the time of startup, or it MAY use an incrementing counter retained in non-volatile memory across restarts.
The Origin-State-Id, if present, MUST reflect the state of the entity indicated by Origin-Host. If a proxy modifies Origin-Host, it MUST either remove Origin-State-Id or modify it appropriately as well. Typically, Origin-State-Id is used by an access device that always starts up with no active sessions; that is, any session active prior to restart will have been lost. By including Origin-State-Id in a message, it allows other Diameter entities to infer that sessions associated with a lower Origin-State-Id are no longer active. If an access device does not intend for such inferences to be made, it MUST either not include Origin-State-Id in any message, or set its value to 0.
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 and Session-Termination-Request messages for this session MUST be sent to the same authorization server.
This field is a bit mask, and the following bits have been defined:
The Session-Server-Failover AVP (AVP Code 271) is of type Enumerated, and MAY be present in application-specific authorization answer messages that either do not include the Session-Binding AVP or include the Session-Binding AVP with any of the bits set to a zero value. If present, this AVP MAY inform the Diameter client that if a re-auth or STR message fails due to a delivery problem, the Diameter client SHOULD issue a subsequent message without the Destination-Host AVP. When absent, the default value is REFUSE_SERVICE.
The following values are supported:
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.
The Class AVP (AVP Code 25) is of type OctetString and is used by Diameter servers to return state information to the access device. When one or more Class AVPs are present in application-specific authorization answer messages, they MUST be present in subsequent re-authorization, session termination and accounting messages. Class AVPs found in a re-authorization answer message override the ones found in any previous authorization answer message. Diameter server implementations SHOULD NOT return Class AVPs that require more than 4096 bytes of storage on the Diameter client. A Diameter client that receives Class AVPs whose size exceeds local available storage MUST terminate the session.
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.
This accounting protocol is based on a server directed model with capabilities for real-time delivery of accounting information. Several fault resilience methods [RFC2975] have been built 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.
The server directed model means that the device generating the accounting data gets information from either the authorization server (if contacted) or the accounting server regarding the way accounting data shall be forwarded. This information includes accounting record timeliness requirements.
As discussed in [RFC2975], real-time transfer of accounting records is a requirement, such as the need to perform credit limit checks and fraud detection. Note that batch accounting is not a requirement, and is therefore not supported by Diameter. Should batched accounting be required in the future, a new Diameter application will need to be created, or it could be handled using another protocol. Note, however, that even if at the Diameter layer accounting requests are processed one by one, transport protocols used under Diameter typically batch several requests in the same packet under heavy traffic conditions. This may be sufficient for many applications.
The authorization server (chain) directs the selection of proper transfer strategy, based on its knowledge of the user and relationships of roaming partnerships. The server (or agents) uses the Acct-Interim-Interval and Accounting-Realtime-Required AVPs to control the operation of the Diameter peer operating as a client. The Acct-Interim-Interval AVP, when present, instructs the Diameter node acting as a client to produce accounting records continuously even during a session. Accounting-Realtime-Required AVP is used to control the behavior of the client when the transfer of accounting records from the Diameter client is delayed or unsuccessful.
The Diameter accounting server MAY override the interim interval or the 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.
A Diameter node that receives a successful authentication and/or authorization messages from the Diameter server SHOULD collect accounting information for the session. The Accounting-Request message is used to transmit the accounting information to the Diameter server, which MUST reply with the Accounting-Answer message to confirm reception. The Accounting-Answer message includes the Result-Code AVP, which MAY indicate that an error was present in the accounting message. The value of the Accounting-Realtime-Required AVP received earlier for the session in question may indicate that the user's session has to be terminated when a rejected Accounting-Request message was received.
Each Diameter application (e.g., NASREQ, MobileIP), SHOULD 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 that section.
Applications have the option of using one or both of the following accounting application extension models:
In cases where an application does not define its own accounting service, it is preferred that the split accounting model be used.
Diameter Base protocol mechanisms are used to overcome small message loss and network faults of temporary nature.
Diameter peers acting as clients MUST implement the use of failover to guard against server failures and certain network failures. Diameter peers acting as agents or related off-line processing systems MUST detect duplicate accounting records caused by the sending of the same record to several servers and duplication of messages in transit. This detection MUST be based on the inspection of the Session-Id and Accounting-Record-Number AVP pairs. Appendix Appendix C discusses duplicate detection needs and implementation issues.
Diameter clients MAY have non-volatile memory for the safe storage of accounting records over reboots or extended network failures, network partitions, and server failures. If such memory is available, the client SHOULD store new accounting records there as soon as the records are created and until a positive acknowledgement of their reception from the Diameter Server has been received. Upon a reboot, the client MUST 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.
A further application of this protocol may include AVPs to control how many accounting records may at most be stored in the Diameter client without committing them to the non-volatile memory or transferring them to the Diameter server.
The client SHOULD NOT remove the accounting data from any of its memory areas before the correct Accounting-Answer has been received. The client MAY remove oldest, undelivered or yet unacknowledged accounting data if it runs out of resources such as memory. It is an implementation dependent matter for the client to accept new sessions under this condition.
In all accounting records, the Session-Id AVP MUST be present; the User-Name AVP MUST be present if it is available to the Diameter client.
Different types of accounting records are sent depending on the actual type of accounted service and the authorization server's directions for interim accounting. If the accounted service is a one-time event, meaning that the start and stop of the event are simultaneous, then the Accounting-Record-Type AVP MUST be present and set to the value EVENT_RECORD.
If the accounted service is of a measurable length, then the AVP MUST use the values START_RECORD, STOP_RECORD, and possibly, INTERIM_RECORD. If the authorization server has not directed interim accounting to be enabled for the session, two accounting records MUST be generated for each service of type session. When the initial Accounting-Request for a given session is sent, the Accounting- Record-Type AVP MUST be set to the value START_RECORD. When the last Accounting-Request is sent, the value MUST be STOP_RECORD.
If the authorization server has directed interim accounting to be enabled, the Diameter client MUST produce additional records between the START_RECORD and STOP_RECORD, marked INTERIM_RECORD. The production of these records is directed by Acct-Interim-Interval as well as any re-authentication or re-authorization of the session. The Diameter client MUST overwrite any previous interim accounting records that are locally stored for delivery, if a new record is being generated for the same session. This ensures that only one pending interim record can exist on an access device for any given session.
A particular value of Accounting-Sub-Session-Id MUST appear only in one sequence of accounting records from a Diameter client, except for the purposes of retransmission. The one sequence that is sent MUST be either one record with Accounting-Record-Type AVP set to the value EVENT_RECORD, or several records starting with one having the value START_RECORD, followed by zero or more INTERIM_RECORD and a single STOP_RECORD. A particular Diameter application specification MUST define the type of sequences that MUST be used.
If an application uses accounting messages, it can correlate accounting records with a specific application session by using the Session-Id of the particular application session in the accounting messages. Accounting messages MAY also use a different Session-Id from that of the application sessions in which case other session related information is needed to perform correlation.
In cases where an application requires multiple accounting sub-session, an Accounting-Sub-Session-Id AVP is used to differentiate each sub-session. The Session-Id would remain constant for all sub-sessions and is be used to correlate all the sub-sessions to a particular application session. 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.
There are also cases where an application needs to correlate multiple application sessions into a single accounting record; the accounting record may span multiple different Diameter applications and sessions used by the same user at a given time. In such cases, the Acct-Multi-Session-Id AVP is used. The Acct-Multi-Session-Id AVP SHOULD be signaled by the server to the access device (typically during authorization) when it determines that a request belongs to an existing session. The access device MUST then include the Acct-Multi-Session-Id AVP in all subsequent accounting messages.
The Acct-Multi-Session-Id AVP MAY include the value of the original Session-Id. 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.
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.
This section defines Command-Code values that MUST be supported by all Diameter implementations that provide Accounting services.
The Accounting-Request (ACR) command, indicated by the Command-Code field set to 271 and the Command Flags' 'R' bit set, is sent by a Diameter node, acting as a client, in order to exchange accounting information with a peer.
In addition to the AVPs listed below, Accounting-Request messages SHOULD include service-specific accounting AVPs.
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 ]
The Accounting-Answer (ACA) command, indicated by the Command-Code field set to 271 and the Command Flags' 'R' bit cleared, is used to acknowledge an Accounting-Request command. The Accounting-Answer command contains the same Session-Id as the corresponding request.
Only the target Diameter Server, known as the home Diameter Server, SHOULD respond with the Accounting-Answer command.
In addition to the AVPs listed below, Accounting-Answer messages SHOULD include service-specific accounting AVPs.
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 ]
This section contains AVPs that describe accounting usage information related to a specific session.
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:
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:
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.
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.
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.
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.
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.
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.
The table uses the following symbols:
+-----------------------------------------------+
| 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 | | | | | | | | | | | | |
--------------------+---+---+---+---+---+---+---+---+---+---+---+---+
The table in this section is limited to the non-accounting Command Codes defined in this specification.
+-----------+
| 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 |
------------------------------+-----+-----+
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.
This section provides guidance to the Internet Assigned Numbers Authority (IANA) regarding registration of values related to the Diameter protocol, in accordance with [RFC5226]. Existing IANA registries and assignments put in place by [RFC3588] remain the same unless explicitly updated or deprecated in this section.
As defined in Section 4, the AVP header contains three fields that requires IANA namespace management; the AVP Code, Vendor-ID and Flags field.
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. AVP Code 0 is not used. AVP Codes 1-255 are managed separately as RADIUS Attribute Types. Where a Vendor-Specific AVP is implemented by more than one vendor, allocation of global AVPs should be encouraged instead.
AVPs may be allocated following Expert Review (or Designated Expert) with Specification Required [RFC5226]. A block allocation (release of more than 3 AVPs at a time for a given purpose) requires IETF Review.
Section 4.1 describes the existing AVP Flags. The remaining bits can only be assigned via a Standards Action [RFC5226].
For the Diameter Header, the command code namespace allocation has changed. The new allocation rules are as follows:
Section 3 describes the existing Command Flag field. The remaining bits can only be assigned via a Standards Action [RFC5226].
For AVP values, the Experimental-Result-Code AVP value allocation has been added, see Section 11.3.1. The old AVP value allocation rule IETF Consensus has been updated to IETF Review as per [RFC5226] and affected AVPs are listed as reminders.
Values for this AVP are purely local to the indicated vendor, and no IANA registry is maintained for them.
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
New values are available for assignment via IETF Review [RFC5226].
The use of this AVP has been deprecated.
This section requests the IANA to register the "_diameter" service name and assign port numbers for TLS/TCP and DTLS/SCTP according to the guidelines given in Cotton, et al. [RFC6335].
Value | SCTP Payload Protocol Identifier -------|----------------------------------- <TBD2> | Diameter in a SCTP DATA chunk <TBD3> | Diameter in a DTLS/SCTP DATA chunk
Two SCTP payload protocol identifiers are registered in SCTP Payload Protocol Identifier registry:
Tag | Protocol -------------------|--------- diameter.dtls.sctp | DTLS/SCTP
This document also registers the following S-NAPTR Application Protocol Tags registry:
This section contains the configurable parameters that are found throughout this document:
The Diameter base protocol messages SHOULD be secured by using TLS [RFC5246] or DTLS/SCTP [RFC6083]. Additional security mechanisms such as IPsec [RFC4301] MAY also be deployed to secure connections between peers. However, all Diameter base protocol implementations MUST support the use of TLS/TCP and DTLS/SCTP and the Diameter protocol MUST NOT be used without one of TLS, DTLS or IPsec.
If a Diameter connection is to be protected via TLS/TCP and DTLS/SCTP or IPsec, then TLS/TCP and DTLS/SCTP or IPsec/IKE SHOULD begin prior to any Diameter message exchange. All security parameters for TLS/TCP and DTLS/SCTP or IPsec are configured independent of the Diameter protocol. All Diameter messages will be sent through the TLS/TCP and DTLS/SCTP or IPsec connection after a successful setup.
For TLS/TCP and DTLS/SCTP connections to be established in the open state, the CER/CEA exchange MUST include an Inband-Security-ID AVP with a value of TLS/TCP and DTLS/SCTP. The TLS/TCP and DTLS/SCTP handshake will begin when both ends successfully reached the open state, after completion of the CER/CEA exchange. If the TLS/TCP and DTLS/SCTP handshake is successful, all further messages will be sent via TLS/TCP and DTLS/SCTP. If the handshake fails, both ends MUST move to the closed state. See Section 13.1 for more details.
Diameter nodes using TLS/TCP and DTLS/SCTP for security MUST mutually authenticate as part of TLS/TCP and DTLS/SCTP session establishment. In order to ensure mutual authentication, the Diameter node acting as the TLS/TCP and DTLS/SCTP server MUST request a certificate from the Diameter node acting as TLS/TCP and DTLS/SCTP client, and the Diameter node acting as the TLS/TCP and DTLS/SCTP client MUST be prepared to supply a certificate on request.
TLS_RSA_WITH_RC4_128_MD5
TLS_RSA_WITH_RC4_128_SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA
Diameter nodes MUST be able to negotiate the following TLS/TCP and DTLS/SCTP cipher suites:
TLS_RSA_WITH_AES_128_CBC_SHA
Diameter nodes SHOULD be able to negotiate the following TLS/TCP and DTLS/SCTP cipher suite:
Note that that it is quite possible that support for the TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite will be REQUIRED at some future date. Diameter nodes MAY negotiate other TLS/TCP and DTLS/SCTP cipher suites.
If public key certificates are used for Diameter security (for example, with TLS), the value of the expiration times in the routing and peer tables MUST NOT be greater than the expiry time in the relevant certificates.
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.
Diameter AVPs often contain security-sensitive data; for example, user passwords and location data, network addresses and cryptographic keys. The Diameter messages containing such AVPs MUST only be sent protected via mutually authenticated TLS or IPsec. In addition, those messages SHOULD NOT be sent via intermediate nodes that would expose the sensitive data at those nodes except in cases where an intermediary is known to be operated as part of the same administrative domain as the endpoints so that an ability to successfully compromise the intermediary would imply a high probability of being able to compromise the endpoints as well.
The authors would like to thank the following people that have provided proposals and contributions to this document:
To Vishnu Ram and Satendra Gera for their contributions on Capabilities Updates, and Predictive Loop Avoidance as well as many other technical proposals. To Tolga Asveren for his insights and contributions on almost all of the proposed solutions incorporated into this document. To Timothy Smith for helping on the Capabilities Update and other topics. To Tony Zhang for providing fixes to 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. To Jouni Korhonen for taking over the editing task and resolving last bits from -27 through -29.
Special thanks to the Diameter extensibility design team which helped resolve the tricky question of mandatory AVPs and ABNF semantics. The members of this team are as follows:
Avi Lior, Jari Arkko, Glen Zorn, Lionel Morand, Mark Jones, Tolga Asveren Jouni Korhonen, Glenn McGregor.
Special thanks also to people who have provided invaluable comments and inputs especially in resolving controversial issues:
Glen Zorn, Yoshihiro Ohba, Marco Stura, Stephen Farrel, Pete Resnick, Peter Saint-Andre, Robert Sparks, Krishna Prasad, Sean Turner, Barry Leiba and Pasi Eronen.
Finally, we would like to thank the original authors of this document:
Pat Calhoun, John Loughney, Jari Arkko, Erik Guttman and Glen Zorn.
Their invaluable knowledge and experience has given us a robust and flexible AAA protocol that many people have seen great value in adopting. We greatly appreciate their support and stewardship for the continued improvements of Diameter as a protocol. We would also like to extend our gratitude to folks aside from the authors who have assisted and contributed to the original version of this document. Their efforts significantly contributed to the success of Diameter.
The authors would like to thank Nenad Trifunovic, Tony Johansson and Pankaj Patel for their participation in the pre-IETF Document Reading Party. Allison Mankin, Jonathan Wood and Bernard Aboba provided invaluable assistance in working out transport issues, and similarly with Steven Bellovin in the security area.
Paul Funk and David Mitton were instrumental in getting the Peer State Machine correct, and our deep thanks go to them for their time.
Text in this document was also provided by Paul Funk, Mark Eklund, Mark Jones and Dave Spence. Jacques Caron provided many great comments as a result of a thorough review of the spec.
The authors would also like to acknowledge the following people for their contribution in the development of the Diameter protocol:
Allan C. Rubens, Haseeb Akhtar, William Bulley, Stephen Farrell, David Frascone, Daniel C. Fox, Lol Grant, Ignacio Goyret, Nancy Greene, Peter Heitman, Fredrik Johansson, Mark Jones, Martin Julien, Bob Kopacz, Paul Krumviede, Fergal Ladley, Ryan Moats, Victor Muslin, Kenneth Peirce, John Schnizlein, Sumit Vakil, John R. Vollbrecht and Jeff Weisberg.
Finally, Pat Calhoun would like to thank Sun Microsystems since most of the effort put into this document was done while he was in their employ.
;; order pref flags service regexp replacement
IN NAPTR 50 50 "s" "aaa:diameter.tls.tcp" ""
_diameter._tls.ex1.example.com
IN NAPTR 100 50 "s" "aaa:diameter.tcp" ""
_aaa._tcp.ex1.example.com
IN NAPTR 150 50 "s" "aaa:diameter.sctp" ""
_diameter._sctp.ex1.example.com
As an example, consider a client that wishes to resolve aaa:ex1.example.com. The client performs a NAPTR query for that domain, and the following NAPTR records are returned:
;; Priority Weight Port Target
IN SRV 0 1 5060 server1.ex1.example.com
IN SRV 0 2 5060 server2.ex1.example.com
This indicates that the server supports TLS, TCP and SCTP in that order. If the client supports TLS, TLS will be used, targeted to a host determined by an SRV lookup of _diameter._tls.ex1.example.com. That lookup would return:
;; order pref flags service regexp replacement
IN NAPTR 150 50 "a" "aaa:diameter.tls.tcp" ""
server1.ex2.example.com
IN NAPTR 150 50 "a" "aaa:diameter.tls.tcp" ""
server2.ex2.example.com
As an alternative example, a client that wishes to resolve aaa:ex2.example.com. The client performs a NAPTR query for that domain, and the following NAPTR records are returned:
This indicates that the server supports TCP available at the returned host names.
As described in Section 9.4, accounting record duplicate detection is based on session identifiers. Duplicates can appear for various reasons:
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).
In some cases the Diameter accounting server can delay the duplicate detection and accounting record processing until a post-processing phase takes place. At that time records are likely to be sorted according to the included User-Name and duplicate elimination is easy in this case. In other situations it may be necessary to perform real-time duplicate detection, such as when credit limits are imposed or real-time fraud detection is desired.
In general, only generation of duplicates due to failover or re- sending of records in non-volatile storage can be reliably detected by Diameter clients or agents. In such cases the Diameter client or agents can mark the message as 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.
As an example, it can be usually be assumed that duplicates appear within a time window of longest recorded network partition or device fault, perhaps a day. So only records within this time window need to be looked at in the backward direction. Secondly, hashing techniques or other schemes, such as the use of the T flag in the received messages, may be used to eliminate the need to do a full search even in this set except for rare cases.
The following is an example of how the T flag may be used by the server to detect duplicate requests.
To be compatible with the existing DNS infrastructure and simplify host and domain name comparison, Diameter identities (FQDNs) are represented in ASCII form. This allows the Diameter protocol to fall in-line with the DNS strategy of being transparent from the effects of Internationalized Domain Names (IDNs) by following the recommendations in [RFC4690] and [RFC5890]. Applications that provide support for IDNs outside of the Diameter protocol but interacting with it SHOULD use the representation and conversion framework described in [RFC5890], [RFC5891] and [RFC3492].