RFC 3588
Diameter Base Protocol
5. Diameter Peers
This section describes how Diameter nodes establish connections and communicate with peers.5.1. Peer Connections
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: 1. The peer is no longer reachable, causing the transport connection to be shutdown. The peer is moved to the closed state. 2. Three watchdog messages are exchanged with accepted round trip times, and the connection to the peer is considered stabilized. In the event the peer being removed is either the primary or secondary, an alternate peer SHOULD replace the deleted peer, and assume the role of either primary or secondary.5.2. Diameter Peer Discovery
Allowing for dynamic Diameter agent discovery will make it possible for simpler and more robust deployment of Diameter services. In order to promote interoperable implementations of Diameter peer discovery, the following mechanisms are described. These are based
on existing IETF standards. The first option (manual configuration)
MUST be supported by all DIAMETER nodes, while the latter two options
(SRVLOC and DNS) MAY be supported.
There are two cases where Diameter peer discovery may be performed.
The first is when a Diameter client needs to discover a first-hop
Diameter agent. The second case is when a Diameter agent needs to
discover another agent - for further handling of a Diameter
operation. In both cases, the following 'search order' is
recommended:
1. The Diameter implementation consults its list of static (manually)
configured Diameter agent locations. These will be used if they
exist and respond.
2. The Diameter implementation uses SLPv2 [SLP] to discover Diameter
services. The Diameter service template [TEMPLATE] is included in
Appendix A.
It is recommended that SLPv2 security be deployed (this requires
distributing keys to SLPv2 agents). This is discussed further in
Appendix A. SLPv2 security SHOULD be used (requiring distribution
of keys to SLPv2 agents) in order to ensure that discovered peers
are authorized for their roles. SLPv2 is discussed further in
Appendix A.
3. The Diameter implementation performs a NAPTR query for a server in
a particular realm. The Diameter implementation has to know in
advance which realm to look for a Diameter agent in. This could
be deduced, for example, from the 'realm' in a NAI that a Diameter
implementation needed to perform a Diameter operation on.
3.1 The services relevant for the task of transport protocol
selection are those with NAPTR service fields with values
"AAA+D2x", where x is a letter that corresponds to a transport
protocol supported by the domain. This specification defines
D2T for TCP and D2S for SCTP. We also establish an IANA
registry for NAPTR service name to transport protocol
mappings.
These NAPTR records provide a mapping from a domain, to the
SRV record for contacting a server with the specific transport
protocol in the NAPTR services field. The resource record
will contain an empty regular expression and a replacement
value, which is the SRV record for that particular transport
protocol. If the server supports multiple transport
protocols, there will be multiple NAPTR records, each with a
different service value. As per RFC 2915 [NAPTR], the client
discards any records whose services fields are not applicable.
For the purposes of this specification, several rules are
defined.
3.2 A client MUST discard any service fields that identify a
resolution service whose value is not "D2X", for values of X
that indicate transport protocols supported by the client.
The NAPTR processing as described in RFC 2915 will result in
discovery of the most preferred transport protocol of the
server that is supported by the client, as well as an SRV
record for the server.
The domain suffixes in the NAPTR replacement field SHOULD
match the domain of the original query.
4. If no NAPTR records are found, the requester queries for those
address records for the destination address,
'_diameter._sctp'.realm or '_diameter._tcp'.realm. Address
records include A RR's, AAAA RR's or other similar records, chosen
according to the requestor's network protocol capabilities. If
the DNS server returns no address records, the requestor gives up.
If the server is using a site certificate, the domain name in the
query and the domain name in the replacement field MUST both be
valid based on the site certificate handed out by the server in
the TLS or IKE exchange. Similarly, the domain name in the SRV
query and the domain name in the target in the SRV record MUST
both be valid based on the same site certificate. Otherwise, an
attacker could modify the DNS records to contain replacement
values in a different domain, and the client could not validate
that this was the desired behavior, or the result of an attack
Also, the Diameter Peer MUST check to make sure that the
discovered peers are authorized to act in its role.
Authentication via IKE or TLS, or validation of DNS RRs via DNSSEC
is not sufficient to conclude this. For example, a web server may
have obtained a valid TLS certificate, and secured RRs may be
included in the DNS, but this does not imply that it is authorized
to act as a Diameter Server.
Authorization can be achieved for example, by configuration of a
Diameter Server CA. Alternatively this can be achieved by
definition of OIDs within TLS or IKE certificates so as to signify
Diameter Server authorization.
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.5.3. Capabilities Exchange
When two Diameter peers establish a transport connection, they MUST exchange the Capabilities Exchange messages, as specified in the peer state machine (see Section 5.6). This message allows the discovery of a peer's identity and its capabilities (protocol version number, 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 applications 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. Similarly, a receiver of a Capabilities-Exchange-Req (CER) message that does not have any security mechanisms in common with the sender MUST return a Capabilities-Exchange-Answer (CEA) with the Result-Code AVP set to DIAMETER_NO_COMMON_SECURITY, and SHOULD disconnect the transport layer connection. 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 (see Section 7.) with the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER to inform the downstream to take action (e.g., re-routing request to an alternate peer). 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 Identifier).5.3.1. Capabilities-Exchange-Request
The Capabilities-Exchange-Request (CER), indicated by the Command- Code set to 257 and the Command Flags' 'R' bit set, is sent to exchange local capabilities. Upon detection of a transport failure, this message MUST NOT be sent to an alternate peer. When Diameter is run over SCTP [SCTP], which allows for connections to span multiple interfaces and multiple IP addresses, the Capabilities-Exchange-Request message MUST contain one Host-IP- Address AVP for each potential IP address that MAY be locally used when transmitting Diameter messages. 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 ]5.3.2. Capabilities-Exchange-Answer
The Capabilities-Exchange-Answer (CEA), indicated by the Command-Code set to 257 and the Command Flags' 'R' bit cleared, is sent in response to a CER message.
When Diameter is run over SCTP [SCTP], which allows connections to span multiple interfaces, hence, multiple IP addresses, the Capabilities-Exchange-Answer message MUST contain one Host-IP-Address AVP for each potential IP address that MAY be locally used when transmitting Diameter messages. Message Format <CEA> ::= < Diameter Header: 257 > { Result-Code } { Origin-Host } { Origin-Realm } 1* { Host-IP-Address } { Vendor-Id } { Product-Name } [ Origin-State-Id ] [ Error-Message ] * [ Failed-AVP ] * [ Supported-Vendor-Id ] * [ Auth-Application-Id ] * [ Inband-Security-Id ] * [ Acct-Application-Id ] * [ Vendor-Specific-Application-Id ] [ Firmware-Revision ] * [ AVP ]5.3.3. Vendor-Id AVP
The Vendor-Id AVP (AVP Code 266) is of type Unsigned32 and contains the IANA "SMI Network Management Private Enterprise Codes" [ASSIGNNO] value assigned to the vendor of the Diameter application. In combination with the Supported-Vendor-Id AVP (Section 5.3.6), this MAY be used in order to know which vendor specific attributes may be sent to the peer. It is also 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 very useful debugging information. A Vendor-Id value of zero in the CER or CEA messages is reserved and indicates that this field is ignored.5.3.4. Firmware-Revision AVP
The Firmware-Revision AVP (AVP Code 267) is of type Unsigned32 and is used to inform a Diameter peer of the firmware revision of the issuing device.
For devices that do not have a firmware revision (general purpose computers running Diameter software modules, for instance), the revision of the Diameter software module may be reported instead.5.3.5. Host-IP-Address AVP
The Host-IP-Address AVP (AVP Code 257) is of type Address and is used to inform a Diameter peer of the sender's IP address. All source addresses that a Diameter node expects to use with SCTP [SCTP] MUST be advertised in the CER and CEA messages by including a Host-IP- Address AVP for each address. This AVP MUST ONLY be used in the CER and CEA messages.5.3.6. Supported-Vendor-Id AVP
The Supported-Vendor-Id AVP (AVP Code 265) is of type Unsigned32 and contains the IANA "SMI Network Management Private Enterprise Codes" [ASSIGNNO] value assigned to a vendor other than the device 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.5.3.7. Product-Name AVP
The Product-Name AVP (AVP Code 269) is of type UTF8String, and contains the vendor assigned name for the product. The Product-Name AVP SHOULD remain constant across firmware revisions for the same product.5.4. Disconnecting Peer connections
When a Diameter node disconnects one of its transport connections, its peer cannot know the reason for the disconnect, and will most likely assume that a connectivity problem occurred, or that the peer has rebooted. In these cases, the peer may periodically attempt to reconnect, as stated in Section 2.1. In the event that the disconnect was a result of either a shortage of internal resources, or simply that the node in question has no intentions of forwarding any Diameter messages to the peer in the foreseeable future, a periodic 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.5.4.1. Disconnect-Peer-Request
The Disconnect-Peer-Request (DPR), indicated by the Command-Code set to 282 and the Command Flags' 'R' bit set, is sent to a peer to inform 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 <DPR> ::= < Diameter Header: 282, REQ > { Origin-Host } { Origin-Realm } { Disconnect-Cause }5.4.2. Disconnect-Peer-Answer
The Disconnect-Peer-Answer (DPA), indicated by the Command-Code set to 282 and the Command Flags' 'R' bit cleared, is sent as a response to the Disconnect-Peer-Request message. Upon receipt of this message, the transport connection is shutdown. Message Format <DPA> ::= < Diameter Header: 282 > { Result-Code } { Origin-Host } { Origin-Realm } [ Error-Message ] * [ Failed-AVP ]5.4.3. Disconnect-Cause AVP
The Disconnect-Cause AVP (AVP Code 273) is of type Enumerated. A Diameter node MUST include this AVP in the Disconnect-Peer-Request message to inform the peer of the reason for its intention to shutdown the transport connection. The following values are supported:
REBOOTING 0
A scheduled reboot is imminent.
BUSY 1
The peer's internal resources are constrained, and it has
determined that the transport connection needs to be closed.
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.
5.5. Transport Failure Detection
Given the nature of the Diameter protocol, it is recommended that
transport failures be detected as soon as possible. Detecting such
failures will minimize the occurrence of messages sent to unavailable
agents, resulting in unnecessary delays, and will provide better
failover performance. The Device-Watchdog-Request and Device-
Watchdog-Answer messages, defined in this section, are used to pro-
actively detect transport failures.
5.5.1. Device-Watchdog-Request
The Device-Watchdog-Request (DWR), indicated by the Command-Code set
to 280 and the Command Flags' 'R' bit set, is sent to a peer when no
traffic has been exchanged between two peers (see Section 5.5.3).
Upon detection of a transport failure, this message MUST NOT be sent
to an alternate peer.
Message Format
<DWR> ::= < Diameter Header: 280, REQ >
{ Origin-Host }
{ Origin-Realm }
[ Origin-State-Id ]
5.5.2. Device-Watchdog-Answer
The Device-Watchdog-Answer (DWA), indicated by the Command-Code set
to 280 and the Command Flags' 'R' bit cleared, is sent as a response
to the Device-Watchdog-Request message.
Message Format
<DWA> ::= < Diameter Header: 280 >
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
[ Error-Message ]
* [ Failed-AVP ]
[ Original-State-Id ]
5.5.3. Transport Failure Algorithm
The transport failure algorithm is defined in [AAATRANS]. All
Diameter implementations MUST support the algorithm defined in the
specification in order to be compliant to the Diameter base protocol.
5.5.4. Failover and Failback Procedures
In the event that a transport failure is detected with a peer, it is
necessary for all pending request messages to be forwarded to an
alternate agent, if possible. This is commonly referred to as
failover.
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.5.6. Peer State Machine
This section contains a finite state machine that MUST be observed by all Diameter implementations. Each Diameter node MUST follow the state machine described below when communicating with each peer. Multiple actions are separated by commas, and may continue on succeeding lines, as space requires. Similarly, state and next state may also span multiple lines, as space requires. This state machine is closely coupled with the state machine described in [AAATRANS], which is used to open, close, failover, probe, and reopen transport connections. Note in particular that [AAATRANS] 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 usage, a TLS handshake will begin when both ends are in the open state. If the TLS handshake is successful, all further messages will be sent via TLS. If the handshake fails, both ends move to the closed state. The state machine constrains only the behavior of a Diameter implementation as seen by Diameter peers through events on the wire.
Any implementation that produces equivalent results is considered
compliant.
state event action next state
-----------------------------------------------------------------
Closed Start I-Snd-Conn-Req Wait-Conn-Ack
R-Conn-CER R-Accept, R-Open
Process-CER,
R-Snd-CEA
Wait-Conn-Ack I-Rcv-Conn-Ack I-Snd-CER Wait-I-CEA
I-Rcv-Conn-Nack Cleanup Closed
R-Conn-CER R-Accept, Wait-Conn-Ack/
Process-CER Elect
Timeout Error Closed
Wait-I-CEA I-Rcv-CEA Process-CEA I-Open
R-Conn-CER R-Accept, Wait-Returns
Process-CER,
Elect
I-Peer-Disc I-Disc Closed
I-Rcv-Non-CEA Error Closed
Timeout Error Closed
Wait-Conn-Ack/ I-Rcv-Conn-Ack I-Snd-CER,Elect Wait-Returns
Elect I-Rcv-Conn-Nack R-Snd-CEA R-Open
R-Peer-Disc R-Disc Wait-Conn-Ack
R-Conn-CER R-Reject Wait-Conn-Ack/
Elect
Timeout Error Closed
Wait-Returns Win-Election I-Disc,R-Snd-CEA R-Open
I-Peer-Disc I-Disc, R-Open
R-Snd-CEA
I-Rcv-CEA R-Disc I-Open
R-Peer-Disc R-Disc Wait-I-CEA
R-Conn-CER R-Reject Wait-Returns
Timeout Error Closed
R-Open Send-Message R-Snd-Message R-Open
R-Rcv-Message Process R-Open
R-Rcv-DWR Process-DWR, R-Open
R-Snd-DWA
R-Rcv-DWA Process-DWA R-Open
R-Conn-CER R-Reject R-Open
Stop R-Snd-DPR Closing
R-Rcv-DPR R-Snd-DPA, Closed
R-Disc
R-Peer-Disc R-Disc Closed
R-Rcv-CER R-Snd-CEA R-Open
R-Rcv-CEA Process-CEA R-Open
I-Open Send-Message I-Snd-Message I-Open
I-Rcv-Message Process I-Open
I-Rcv-DWR Process-DWR, I-Open
I-Snd-DWA
I-Rcv-DWA Process-DWA I-Open
R-Conn-CER R-Reject I-Open
Stop I-Snd-DPR Closing
I-Rcv-DPR I-Snd-DPA, Closed
I-Disc
I-Peer-Disc I-Disc Closed
I-Rcv-CER I-Snd-CEA I-Open
I-Rcv-CEA Process-CEA I-Open
Closing I-Rcv-DPA I-Disc Closed
R-Rcv-DPA R-Disc Closed
Timeout Error Closed
I-Peer-Disc I-Disc Closed
R-Peer-Disc R-Disc Closed
5.6.1. Incoming connections
When a connection request is received from a Diameter peer, it is
not, in the general case, possible to know the identity of that peer
until a CER is received from it. This is because host and port
determine the identity of a Diameter peer; 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.
5.6.2. Events
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. 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).
5.6.3. Actions
Actions in the automaton are caused by events and typically indicate the transmission of packets and/or an action to be taken on the connection. In this section we will ignore the I- and R-prefix, since the actual action 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.5.6.4. The Election Process
The election is performed on the responder. The responder compares the Origin-Host received in the CER sent by its peer with its own Origin-Host. If the local Diameter entity's Origin-Host is higher than the peer's, a Win-Election event is issued locally. The comparison proceeds by considering the shorter OctetString to be padded with zeros so that it length is the same as the length of the longer, then performing an octet-by-octet unsigned comparison with the first octet being most significant. Any remaining octets are assumed to have value 0x80.6. Diameter message processing
This section describes how Diameter requests and answers are created and processed.6.1. Diameter Request Routing Overview
A request is sent towards its final destination using a combination of the Destination-Realm and Destination-Host AVPs, in one of these three combinations: - a request that is not able to be proxied (such as CER) MUST NOT contain either Destination-Realm or Destination-Host AVPs. - a request that needs to be sent to a home server serving a specific realm, but not to a specific server (such as the first request of a series of round-trips), MUST contain a Destination- Realm AVP, but MUST NOT contain a Destination-Host AVP. - otherwise, a request that needs to be sent to a specific home server among those serving a given realm, MUST contain both the Destination-Realm and Destination-Host AVPs. The Destination-Host AVP is used as described above when the destination of the request is fixed, which includes: - Authentication requests that span multiple round trips - A Diameter message that uses a security mechanism that makes use of a pre-established session key shared between the source and the final destination of the message.
- Server initiated messages that MUST be received by a specific
Diameter client (e.g., access device), such as the Abort-Session-
Request message, which is used to request that a particular user's
session be terminated.
Note that an agent can forward a request to a host described in the
Destination-Host AVP only if the host in question is included in its
peer table (see Section 2.7). Otherwise, the request is routed based
on the Destination-Realm only (see Sections 6.1.6).
The Destination-Realm AVP MUST be present if the message is
proxiable. Request messages that may be forwarded by Diameter agents
(proxies, redirects or relays) MUST also contain an Acct-
Application-Id AVP, an Auth-Application-Id AVP or a Vendor-Specific-
Application-Id AVP. A message that MUST NOT be forwarded by Diameter
agents (proxies, redirects or relays) MUST not include the
Destination-Realm in its ABNF. The value of the Destination-Realm
AVP MAY be extracted from the User-Name AVP, or other application-
specific methods.
When a message is received, the message is processed in the following
order:
1. If the message is destined for the local host, the procedures
listed in Section 6.1.4 are followed.
2. If the message is intended for a Diameter peer with whom the local
host is able to directly communicate, the procedures listed in
Section 6.1.5 are followed. This is known as Request Forwarding.
3. The procedures listed in Section 6.1.6 are followed, which is
known as Request Routing.
4. If none of the above is successful, an answer is returned with the
Result-Code set to DIAMETER_UNABLE_TO_DELIVER, with the E-bit set.
For routing of Diameter messages to work within an administrative
domain, all Diameter nodes within the realm MUST be peers.
Note the processing rules contained in this section are intended to
be used as general guidelines to Diameter developers. Certain
implementations MAY use different methods than the ones described
here, and still comply with the protocol specification. See Section
7 for more detail on error handling.
6.1.1. Originating a Request
When creating a request, in addition to any other procedures described in the application definition for that specific request, the following procedures MUST be followed: - the Command-Code is set to the appropriate value - the 'R' bit is set - the End-to-End Identifier is set to a locally unique value - the Origin-Host and Origin-Realm AVPs MUST be set to the appropriate values, used to identify the source of the message - the Destination-Host and Destination-Realm AVPs MUST be set to the appropriate values as described in Section 6.1. - an Acct-Application-Id AVP, an Auth-Application-Id or a Vendor- Specific-Application-Id AVP must be included if the request is proxiable.6.1.2. Sending a Request
When sending a request, originated either locally, or as the result of a forwarding or routing operation, the following procedures MUST be followed: - the Hop-by-Hop Identifier should be set to a locally unique value - The message should be saved in the list of pending requests. Other actions to perform on the message based on the particular role the agent is playing are described in the following sections.6.1.3. Receiving Requests
A relay or proxy agent MUST check for forwarding loops when receiving requests. A loop is detected if the server finds its own identity in a Route-Record AVP. When such an event occurs, the agent MUST answer with the Result-Code AVP set to DIAMETER_LOOP_DETECTED.6.1.4. Processing Local Requests
A request is known to be for local consumption when one of the following conditions occur: - The Destination-Host AVP contains the local host's identity,
- The Destination-Host AVP is not present, the Destination-Realm AVP
contains a realm the server is configured to process locally, and
the Diameter application is locally supported, or
- Both the Destination-Host and the Destination-Realm are not
present.
When a request is locally processed, the rules in Section 6.2 should
be used to generate the corresponding answer.
6.1.5. Request Forwarding
Request forwarding is done using the Diameter Peer Table. The
Diameter peer table contains all of the peers 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.
6.1.6. Request Routing
Diameter request message routing is done via realms and applications.
A Diameter message that may be forwarded by Diameter agents (proxies,
redirects or relays) MUST include the target realm in the
Destination-Realm AVP and one of the application identification AVPs
Auth-Application-Id, Acct-Application-Id or Vendor-Specific-
Application-Id. 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 Realm Routing Table (see Section
2.7).
6.1.7. Redirecting requests
When a redirect agent receives a request whose routing entry is set
to REDIRECT, it MUST reply with an answer message with the 'E' bit
set, while maintaining the Hop-by-Hop Identifier in the header, and
include the Result-Code AVP to DIAMETER_REDIRECT_INDICATION. Each of
the servers associated with the routing entry are added in separate
Redirect-Host AVP.
+------------------+ | 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 +-------------+ Figure 5: Diameter Redirect Agent The receiver of the answer message with the 'E' bit set, and the Result-Code AVP set to DIAMETER_REDIRECT_INDICATION uses the hop-by- hop field in the Diameter header to identify the request in the pending message queue (see Section 5.3) that is to be redirected. If no transport connection exists with the new agent, one is created, and the request is sent directly to it. 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.6.1.8. Relaying and Proxying Requests
A relay or proxy agent MUST append a Route-Record AVP to all requests forwarded. The AVP contains the identity of the peer 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. Proxy-Info AVP has certain security implications and SHOULD contain an embedded HMAC with a node-local key. Alternatively, it MAY simply use local storage to store state information. The message is then forwarded to the next hop, as identified in the Realm Routing Table.
Figure 6 provides an example of message routing using the procedures listed in these sections. (Origin-Host=nas.mno.net) (Origin-Host=nas.mno.net) (Origin-Realm=mno.net) (Origin-Realm=mno.net) (Destination-Realm=example.com) (Destination- Realm=example.com) (Route-Record=nas.example.net) +------+ ------> +------+ ------> +------+ | | (Request) | | (Request) | | | NAS +-------------------+ DRL +-------------------+ HMS | | | | | | | +------+ <------ +------+ <------ +------+ example.net (Answer) example.net (Answer) example.com (Origin-Host=hms.example.com) (Origin-Host=hms.example.com) (Origin-Realm=example.com) (Origin-Realm=example.com) Figure 6: Routing of Diameter messages6.2. Diameter Answer Processing
When a request is locally processed, the following procedures MUST be applied to create the associated answer, in addition to any additional procedures that MAY be discussed in the Diameter application defining the command: - The same Hop-by-Hop identifier in the request is used in the answer. - The local host's identity is encoded in the Origin-Host AVP. - The Destination-Host and Destination-Realm AVPs MUST NOT be present in the answer message. - The Result-Code AVP is added with its value indicating success or failure. - If the Session-Id is present in the request, it MUST be included in the answer. - Any Proxy-Info AVPs in the request MUST be added to the answer message, in the same order they were present in the request. - The 'P' bit is set to the same value as the one in the request. - The same End-to-End identifier in the request is used in the answer.
Note that the error messages (see Section 7.3) are also subjected to the above processing rules.6.2.1. Processing received Answers
A Diameter client or proxy MUST match the Hop-by-Hop Identifier in an answer received against the list of pending requests. The corresponding message should be removed from the list of pending requests. It SHOULD ignore answers received that do not match a known Hop-by-Hop Identifier.6.2.2. Relaying and Proxying Answers
If the answer is for a request 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. The agent MUST then send the answer to the host that it received the original request from.6.3. Origin-Host AVP
The Origin-Host AVP (AVP Code 264) is of type DiameterIdentity, and 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. 6.106.4. Origin-Realm AVP
The Origin-Realm AVP (AVP Code 296) is of type DiameterIdentity. This AVP contains the Realm of the originator of any Diameter message and MUST be present in all messages. This AVP SHOULD be placed as close to the Diameter header as possible.6.5. Destination-Host AVP
The Destination-Host AVP (AVP Code 293) is of type DiameterIdentity. This AVP MUST be present in all unsolicited agent initiated messages, MAY be present in request messages, and MUST NOT be present in Answer messages. The absence of the Destination-Host AVP will cause a message to be sent to any Diameter server supporting the application within the realm specified in Destination-Realm AVP. This AVP SHOULD be placed as close to the Diameter header as possible.6.6. Destination-Realm AVP
The Destination-Realm AVP (AVP Code 283) is of type DiameterIdentity, and contains the realm 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. Request messages whose ABNF does not list the Destination-Realm AVP as a mandatory AVP are inherently non-routable messages. This AVP SHOULD be placed as close to the Diameter header as possible.6.7. Routing AVPs
The AVPs defined in this section are Diameter AVPs used for routing purposes. These AVPs change as Diameter messages are processed by agents, and therefore MUST NOT be protected by end-to-end security.
6.7.1. Route-Record AVP
The Route-Record AVP (AVP Code 282) is of type DiameterIdentity. The identity added in this AVP MUST be the same as the one received in the Origin-Host of the Capabilities Exchange message.6.7.2. Proxy-Info AVP
The Proxy-Info AVP (AVP Code 284) is of type Grouped. The Grouped Data field has the following ABNF grammar: Proxy-Info ::= < AVP Header: 284 > { Proxy-Host } { Proxy-State } * [ AVP ]6.7.3. Proxy-Host AVP
The Proxy-Host AVP (AVP Code 280) is of type DiameterIdentity. This AVP contains the identity of the host that added the Proxy-Info AVP.6.7.4. Proxy-State AVP
The Proxy-State AVP (AVP Code 33) is of type OctetString, and contains state local information, and MUST be treated as opaque data.6.8. Auth-Application-Id AVP
The Auth-Application-Id AVP (AVP Code 258) is of type Unsigned32 and is used in order to advertise support of the Authentication and Authorization portion of an application (see Section 2.4). The Auth-Application-Id MUST also be present in all Authentication and/or Authorization messages that are defined in a separate Diameter specification and have an Application ID assigned.6.9. Acct-Application-Id AVP
The Acct-Application-Id AVP (AVP Code 259) is of type Unsigned32 and is used in order to advertise support of the Accounting portion of an application (see Section 2.4). The Acct-Application-Id MUST also be present in all Accounting messages. Exactly one of the Auth- Application-Id and Acct-Application-Id AVPs MAY be present.6.10. Inband-Security-Id AVP
The Inband-Security-Id AVP (AVP Code 299) is of type Unsigned32 and is used in order to advertise support of the Security portion of the application.
Currently, the following values are supported, but there is ample
room to add new security Ids.
NO_INBAND_SECURITY 0
This peer does not support TLS. This is the default value, if the
AVP is omitted.
TLS 1
This node supports TLS security, as defined by [TLS].
6.11. Vendor-Specific-Application-Id AVP
The Vendor-Specific-Application-Id AVP (AVP Code 260) is of type
Grouped and is used to advertise support of a vendor-specific
Diameter Application. Exactly one of the Auth-Application-Id and
Acct-Application-Id AVPs MAY be present.
This AVP MUST also be present as the first AVP in all experimental
commands defined in the vendor-specific application.
This AVP SHOULD be placed as close to the Diameter header as
possible.
AVP Format
<Vendor-Specific-Application-Id> ::= < AVP Header: 260 >
1* [ Vendor-Id ]
0*1{ Auth-Application-Id }
0*1{ Acct-Application-Id }
6.12. Redirect-Host AVP
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 pertaining to this session.
6.13. Redirect-Host-Usage AVP
The Redirect-Host-Usage AVP (AVP Code 261) is of type Enumerated.
This AVP MAY be present in answer messages whose 'E' bit is set and
the Result-Code AVP is set to DIAMETER_REDIRECT_INDICATION.
When present, this AVP dictates how the routing entry resulting from
the Redirect-Host is to be used. The following values are supported:
DONT_CACHE 0
The host specified in the Redirect-Host AVP should not be cached.
This is the default value.
ALL_SESSION 1
All messages within the same session, as defined by the same value
of the Session-ID AVP MAY be sent to the host specified in the
Redirect-Host AVP.
ALL_REALM 2
All messages destined for the realm requested MAY be sent to the
host specified in the Redirect-Host AVP.
REALM_AND_APPLICATION 3
All messages for the application requested to the realm specified
MAY be sent to the host specified in the Redirect-Host AVP.
ALL_APPLICATION 4
All messages for the application requested MAY be sent to the host
specified in the Redirect-Host AVP.
ALL_HOST 5
All messages that would be sent to the host that generated the
Redirect-Host MAY be sent to the host specified in the Redirect-
Host AVP.
ALL_USER 6
All messages for the user requested MAY be sent to the host
specified in the Redirect-Host AVP.
6.14. Redirect-Max-Cache-Time AVP
The Redirect-Max-Cache-Time AVP (AVP Code 262) is of type Unsigned32.
This AVP MUST be present in answer messages whose 'E' bit is set, 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, will be
cached. Note that once a host created due to a redirect indication
is no longer reachable, any associated peer and routing table entries
MUST be deleted.
6.15. E2E-Sequence AVP
The E2E-Sequence AVP (AVP Code 300) provides anti-replay protection for end to end messages and is of type grouped. It contains a random value (an OctetString with a nonce) and counter (an Integer). For each end-to-end peer with which a node communicates (or remembers communicating) a different nonce value MUST be used and the counter is initiated at zero and increases by one each time this AVP is emitted to that peer. This AVP MUST be included in all messages which use end-to-end protection (e.g., CMS signing or encryption).7. Error Handling
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). 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 +---------+ Link Broken +-------------------------->|Diameter |----///----+ | +---------------------| | v +------+--+ | 2. answer + 'E' set | Relay 2 | +--------+ |Diameter |<-+ (Unable to Forward) +---------+ |Diameter| | | | Home | | Relay 1 |--+ +---------+ | Server | +---------+ | 3. Request |Diameter | +--------+ +-------------------->| | ^ | Relay 3 |-----------+ +---------+ Figure 7: Example of Protocol Error causing answer message Figure 7 provides an example of a message forwarded upstream by a Diameter relay. When the message is received by Relay 2, and it detects that it cannot forward the request to the home server, an answer message is returned with the 'E' bit set and the Result-Code AVP set to DIAMETER_UNABLE_TO_DELIVER. Given that this error falls
within the protocol error category, Relay 1 would take special action, and given the error, attempt to route the message through its alternate Relay 3. +---------+ 1. Request +---------+ 2. Request +---------+ | Access |------------>|Diameter |------------>|Diameter | | | | | | Home | | Device |<------------| Relay |<------------| Server | +---------+ 4. Answer +---------+ 3. Answer +---------+ (Missing AVP) (Missing AVP) Figure 8: Example of Application Error Answer message Figure 8 provides an example of a Diameter message that caused an application error. When application errors occur, the Diameter entity reporting the error clears the 'R' bit in the Command Flags, and adds the Result-Code AVP with the proper value. Application errors do not require any proxy or relay agent involvement, and therefore the message would be forwarded back to the originator of the request. 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: - An unrecognized AVP is received with the 'M' bit (Mandatory bit) set, causes an answer to be sent with the Result-Code AVP set to DIAMETER_AVP_UNSUPPORTED, and the Failed-AVP AVP containing the offending AVP. - An AVP that is received with an unrecognized value causes an answer to be returned with the Result-Code AVP set to DIAMETER_INVALID_AVP_VALUE, with the Failed-AVP AVP containing the AVP causing the error. - A command is received with an AVP that is omitted, yet is mandatory according to the command's ABNF. The receiver issues an answer with the Result-Code set to DIAMETER_MISSING_AVP, and creates an AVP with the AVP Code and other fields set as expected in the missing AVP. The created AVP is then added to the Failed- AVP AVP. The Result-Code AVP describes the error that the Diameter node encountered in its processing. In case there are multiple errors, the Diameter node MUST report only the first error it encountered
(detected possibly in some implementation dependent order). The specific errors that can be described by this AVP are described in the following section.7.1. Result-Code AVP
The Result-Code AVP (AVP Code 268) is of type Unsigned32 and indicates whether a particular request was completed successfully or whether an error occurred. All Diameter answer messages defined in IETF applications MUST include one Result-Code AVP. A non-successful Result-Code AVP (one containing a non 2xxx value other than DIAMETER_REDIRECT_INDICATION) MUST include the Error-Reporting-Host AVP if the host setting the Result-Code AVP is different from the identity encoded in the Origin-Host AVP. The Result-Code data field contains an IANA-managed 32-bit address space representing errors (see Section 11.4). Diameter provides the following classes of errors, all identified by the thousands digit in the decimal notation: - 1xxx (Informational) - 2xxx (Success) - 3xxx (Protocol Errors) - 4xxx (Transient Failures) - 5xxx (Permanent Failure) A non-recognized class (one whose first digit is not defined in this section) MUST be handled as a permanent failure.7.1.1. Informational
Errors that fall within this category are used to inform the requester that a request could not be satisfied, and additional action is required on its part before access is granted. DIAMETER_MULTI_ROUND_AUTH 1001 This informational error is returned by a Diameter server to inform the access device that the authentication mechanism being used requires multiple round trips, and a subsequent request needs to be issued in order for access to be granted.7.1.2. Success
Errors that fall within the Success category are used to inform a peer that a request has been successfully completed. DIAMETER_SUCCESS 2001 The Request was successfully completed.
DIAMETER_LIMITED_SUCCESS 2002
When returned, the request was successfully completed, but
additional processing is required by the application in order to
provide service to the user.
7.1.3. Protocol Errors
Errors that fall within the Protocol Error category SHOULD be treated
on a per-hop basis, and Diameter proxies MAY attempt to correct the
error, if it is possible. Note that these and only these errors MUST
only be used in answer messages whose 'E' bit is set.
DIAMETER_COMMAND_UNSUPPORTED 3001
The Request contained a Command-Code that the receiver did not
recognize or support. This MUST be used when a Diameter node
receives an experimental command that it does not understand.
DIAMETER_UNABLE_TO_DELIVER 3002
This error is given when Diameter can not deliver the message to
the destination, either because no host within the realm
supporting the required application was available to process the
request, or because Destination-Host AVP was given without the
associated Destination-Realm AVP.
DIAMETER_REALM_NOT_SERVED 3003
The intended realm of the request is not recognized.
DIAMETER_TOO_BUSY 3004
When returned, a Diameter node SHOULD attempt to send the message
to an alternate peer. This error MUST only be used when a
specific server is requested, and it cannot provide the requested
service.
DIAMETER_LOOP_DETECTED 3005
An agent detected a loop while trying to get the message to the
intended recipient. The message MAY be sent to an alternate peer,
if one is available, but the peer reporting the error has
identified a configuration problem.
DIAMETER_REDIRECT_INDICATION 3006
A redirect agent has determined that the request could not be
satisfied locally and the initiator of the request should direct
the request directly to the server, whose contact information has
been added to the response. When set, the Redirect-Host AVP MUST
be present.
DIAMETER_APPLICATION_UNSUPPORTED 3007
A request was sent for an application that is not supported.
DIAMETER_INVALID_HDR_BITS 3008
A request was received whose bits in the Diameter header were
either set to an invalid combination, or to a value that is
inconsistent with the command code's definition.
DIAMETER_INVALID_AVP_BITS 3009
A request was received that included an AVP whose flag bits are
set to an unrecognized value, or that is inconsistent with the
AVP's definition.
DIAMETER_UNKNOWN_PEER 3010
A CER was received from an unknown peer.
7.1.4. Transient Failures
Errors that fall within the transient failures category are used
to inform a peer that the request could not be satisfied at the
time it was received, but MAY be able to satisfy the request in
the future.
DIAMETER_AUTHENTICATION_REJECTED 4001
The authentication process for the user failed, most likely due to
an invalid password used by the user. Further attempts MUST only
be tried after prompting the user for a new password.
DIAMETER_OUT_OF_SPACE 4002
A Diameter node received the accounting request but was unable to
commit it to stable storage due to a temporary lack of space.
ELECTION_LOST 4003
The peer has determined that it has lost the election process and
has therefore disconnected the transport connection.
7.1.5. Permanent Failures
Errors that fall within the permanent failures category are used
to inform the peer that the request failed, and should not be
attempted again.
DIAMETER_AVP_UNSUPPORTED 5001
The peer received a message that contained an AVP that is not
recognized or supported and was marked with the Mandatory bit. A
Diameter message with this error MUST contain one or more Failed-
AVP AVP containing the AVPs that caused the failure.
DIAMETER_UNKNOWN_SESSION_ID 5002
The request contained an unknown Session-Id.
DIAMETER_AUTHORIZATION_REJECTED 5003
A request was received for which the user could not be authorized.
This error could occur if the service requested is not permitted
to the user.
DIAMETER_INVALID_AVP_VALUE 5004
The request contained an AVP with an invalid value in its data
portion. A Diameter message indicating this error MUST include
the offending AVPs within a Failed-AVP AVP.
DIAMETER_MISSING_AVP 5005
The request did not contain an AVP that is required by the Command
Code definition. If this value is sent in the Result-Code AVP, a
Failed-AVP AVP SHOULD be included in the message. The Failed-AVP
AVP MUST contain an example of the missing AVP complete with the
Vendor-Id if applicable. The value field of the missing AVP
should be of correct minimum length and contain zeroes.
DIAMETER_RESOURCES_EXCEEDED 5006
A request was received that cannot be authorized because the user
has already expended allowed resources. An example of this error
condition is a user that is restricted to one dial-up PPP port,
attempts to establish a second PPP connection.
DIAMETER_CONTRADICTING_AVPS 5007
The Home Diameter server has detected AVPs in the request that
contradicted each other, and is not willing to provide service to
the user. One or more Failed-AVP AVPs MUST be present, containing
the AVPs that contradicted each other.
DIAMETER_AVP_NOT_ALLOWED 5008
A message was received with an AVP that MUST NOT be present. The
Failed-AVP AVP MUST be included and contain a copy of the
offending AVP.
DIAMETER_AVP_OCCURS_TOO_MANY_TIMES 5009
A message was received that included an AVP that appeared more
often than permitted in the message definition. The Failed-AVP
AVP MUST be included and contain a copy of the first instance of
the offending AVP that exceeded the maximum number of occurrences
DIAMETER_NO_COMMON_APPLICATION 5010
This error is returned when a CER message is received, and there
are no common applications supported between the peers.
DIAMETER_UNSUPPORTED_VERSION 5011
This error is returned when a request was received, whose version
number is unsupported.
DIAMETER_UNABLE_TO_COMPLY 5012
This error is returned when a request is rejected for unspecified
reasons.
DIAMETER_INVALID_BIT_IN_HEADER 5013
This error is returned when an unrecognized bit in the Diameter
header is set to one (1).
DIAMETER_INVALID_AVP_LENGTH 5014
The request contained an AVP with an invalid length. A Diameter
message indicating this error MUST include the offending AVPs
within a Failed-AVP AVP.
DIAMETER_INVALID_MESSAGE_LENGTH 5015
This error is returned when a request is received with an invalid
message length.
DIAMETER_INVALID_AVP_BIT_COMBO 5016
The request contained an AVP with which is not allowed to have the
given value in the AVP Flags field. A Diameter message indicating
this error MUST include the offending AVPs within a Failed-AVP
AVP.
DIAMETER_NO_COMMON_SECURITY 5017
This error is returned when a CER message is received, and there
are no common security mechanisms supported between the peers. A
Capabilities-Exchange-Answer (CEA) MUST be returned with the
Result-Code AVP set to DIAMETER_NO_COMMON_SECURITY.
7.2. Error Bit
The 'E' (Error Bit) in the Diameter header is set when the request
caused a protocol-related error (see Section 7.1.3). A message with
the 'E' bit MUST NOT be sent as a response to an answer message.
Note that a message with the 'E' bit set is still subjected to the
processing rules defined in Section 6.2. When set, the answer
message will not conform to the ABNF specification for the command,
and will instead conform to the following ABNF:
Message Format
<answer-message> ::= < Diameter Header: code, ERR [PXY] >
0*1< Session-Id >
{ Origin-Host }
{ Origin-Realm }
{ Result-Code }
[ Origin-State-Id ]
[ Error-Reporting-Host ]
[ Proxy-Info ]
* [ AVP ]
Note that the code used in the header is the same than the one found
in the request message, but with the 'R' bit cleared and the 'E' bit
set. The 'P' bit in the header is set to the same value as the one
found in the request message.
7.3. Error-Message AVP
The Error-Message AVP (AVP Code 281) is of type UTF8String. It MAY
accompany a Result-Code AVP as a human readable error message. The
Error-Message AVP is not intended to be useful in real-time, and
SHOULD NOT be expected to be parsed by network entities.
7.4. Error-Reporting-Host AVP
The Error-Reporting-Host AVP (AVP Code 294) is of type
DiameterIdentity. This AVP contains the identity of the Diameter
host that sent the Result-Code AVP to a value other than 2001
(Success), only if the host setting the Result-Code is different from
the one encoded in the Origin-Host AVP. This AVP is intended to be
used for troubleshooting purposes, and MUST be set when the Result-
Code AVP indicates a failure.
7.5. Failed-AVP AVP
The Failed-AVP AVP (AVP Code 279) is of type Grouped and provides
debugging information in cases where a request is rejected or not
fully processed due to erroneous information in a specific AVP. The
value of the Result-Code AVP will provide information on the reason
for the Failed-AVP AVP.
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 MAY 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.
AVP Format
<Failed-AVP> ::= < AVP Header: 279 >
1* {AVP}
7.6. Experimental-Result AVP
The Experimental-Result AVP (AVP Code 297) is of type Grouped, and
indicates whether a particular vendor-specific request was completed
successfully or whether an error occurred. Its Data field has the
following ABNF grammar:
AVP Format
Experimental-Result ::= < AVP Header: 297 >
{ Vendor-Id }
{ Experimental-Result-Code }
The Vendor-Id AVP (see Section 5.3.3) in this grouped AVP identifies
the vendor responsible for the assignment of the result code which
follows. All Diameter answer messages defined in vendor-specific
applications MUST include either one Result-Code AVP or one
Experimental-Result AVP.
7.7. Experimental-Result-Code AVP
The Experimental-Result-Code AVP (AVP Code 298) is of type Unsigned32
and contains a vendor-assigned value representing the result of
processing the request.
It is recommended that vendor-specific result codes follow the same
conventions given for the Result-Code AVP regarding the different
types of result codes and the handling of errors (for non 2xxx
values).
(page 90 continued on part 4)
