| Diameter Maintenance and Extensions (DIME) | J. Korhonen, Ed. |
| Internet-Draft | Broadcom |
| Intended status: Standards Track | S. Donovan, Ed. |
| Expires: April 30, 2015 | B. Campbell |
| Oracle | |
| L. Morand | |
| Orange Labs | |
| October 27, 2014 |
Diameter Overload Indication Conveyance
draft-ietf-dime-ovli-04.txt
This specification documents a Diameter Overload Control (DOC) base solution and the dissemination of the overload report information.
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 RFC 2119 [RFC2119].
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 April 30, 2015.
Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.
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This specification defines a base solution for Diameter Overload Control (DOC), referred to as Diameter Overload Indication Conveyance (DOIC). The requirements for the solution are described and discussed in the corresponding design requirements document [RFC7068]. Note that the overload control solution defined in this specification does not address all the requirements listed in [RFC7068]. A number of overload control related features are left for the future specifications. See Appendix A for a list of extensions that are currently being considered. See Appendix C for an analysis of the conformance to the requirements specified in [RFC7068].
The solution defined in this specification addresses Diameter overload control between Diameter nodes that support the DOIC solution. Furthermore, the solution which is designed to apply to existing and future Diameter applications, requires no changes to the Diameter base protocol [RFC6733] and is deployable in environments where some Diameter nodes do not implement the Diameter overload control solution defined in this specification.
The Diameter Overload Information Conveyance (DOIC) solution allows Diameter nodes to request other nodes to perform overload abatement actions, that is, actions to reduce the load offered to the overloaded node or realm.
A Diameter node that supports DOIC is known as a "DOIC node". Any Diameter node can act as a DOIC node, including clients, servers, and agents. DOIC nodes are further divided into "Reporting Nodes" and "Reacting Nodes." A reporting node requests overload abatement by sending an Overload Report (OLR) to one or more reacting nodes.
A reacting node acts upon OLRs, and performs whatever actions are needed to fulfil the abatement requests included in the OLRs. A Reporting node may report overload on its own behalf, or on behalf of other (typically upstream) nodes. Likewise, a reacting node may perform overload abatement on its own behalf, or on behalf of other (typically downstream) nodes.
A node's role as a DOIC node is independent of its Diameter role. For example, Diameter Relay and Proxy Agents may act as DOIC nodes, even though they are not endpoints in the Diameter sense. Since Diameter enables bi-directional applications, where Diameter Servers can send requests towards Diameter Clients, a given Diameter node can simultaneously act as a reporting node and a reacting node.
Likewise, a relay or proxy agent may act as a reacting node from the perspective of upstream nodes, and a reporting node from the perspective of downstream nodes.
DOIC nodes do not generate new messages to carry DOIC related information. Rather, they "piggyback" DOIC information over existing Diameter messages by inserting new AVPs into existing Diameter requests and responses. Nodes indicate support for DOIC, and any needed DOIC parameters by inserting an OC_Supported_Features AVP (Section 6.2) into existing requests and responses. Reporting nodes send OLRs by inserting OC-OLR AVPs (Section 6.3).
A given OLR applies to the Diameter realm and application of the Diameter message that carries it. If a reporting node supports more than one realm and/or application, it reports independently for each combination of realm and application. Similarly, the OC-Supported-Features AVP applies to the realm and application of the enclosing message. This implies that a node may support DOIC for one application and/or realm, but not another, and may indicate different DOIC parameters for each application and realm for which it supports DOIC.
Reacting nodes perform overload abatement according to an agreed-upon abatement algorithm. An abatement algorithm defines the meaning of the parameters of an OLR and the procedures required for overload abatement. This document specifies a single must-support algorithm, namely the "loss" algorithm (Section 5). Future specifications may introduce new algorithms.
Overload conditions may vary in scope. For example, a single Diameter node may be overloaded, in which case reacting nodes may reasonably attempt to send requests to other destinations or via other agents. On the other hand, an entire Diameter realm may be overloaded, in which case such attempts would do harm. DOIC OLRs have a concept of "report type" (Section 6.6), where the type defines such behaviors. Report types are extensible. This document defines report types for overload of a specific server, and for overload of an entire realm.
A report of type host is sent to indicate the overload of a specific server for the application-id indicated in the transaction. When receiving an OLR of type host, a reacting node applies overload abatement to what is referred to in this document as host-routed requests. This is the set of requests that the reacting node knows will be served by a particular host, either due to the presence of a Destination-Host AVP, or by some other local knowledge on the part of the reacting node. The reacting node applies overload abatement on those host-routed requests which the reacting node knows will be served by the server that matches the Origin-Host AVP of the received message that contained the received OLR of type host.
A report type of realm is sent to indicate the overload of all servers in a realm for the application-id. When receiving an OLR of type realm, a reacting node applies overload abatement to what is referred to in this document as realm-routed requests. This is the set of requests that are not host-routed as defined in the previous paragraph.
While a reporting node sends OLRs to "adjacent" reacting nodes, nodes that are "adjacent" for DOIC purposes may not be adjacent from a Diameter, or transport, perspective. For example, one or more Diameter agents that do not support DOIC may exist between a given pair of reporting and reacting nodes, as long as those agents pass unknown AVPs through unchanged. The report types described in this document can safely pass through non-supporting agents. This may not be true for report types defined in future specifications. Documents that introduce new report types MUST describe any limitations on their use across non-supporting agents.
The overload control AVPs defined in this specification have been designed to be piggybacked on top of existing application messages. This is made possible by adding overload control top-level AVPs, the OC-OLR AVP and the OC-Supported-Features AVP, as optional AVPs into existing commands when the corresponding Command Code Format (CCF) specification allows adding new optional AVPs (see Section 1.3.4 of [RFC6733]).
Reacting nodes indicate support for DOIC by including the OC-Supported-Features AVP in all request messages originated or relayed by the reacting node.
Reporting nodes indicate support for DOIC by including the OC-Supported-Features AVP in all answer messages originated or relayed by the reporting node. Reporting nodes also include overload reports using the OC-OLR AVP in answer messages.
Note that the overload control solution does not have fixed server and client roles. The DOIC node role is determined based on the message type: whether the message is a request (i.e. sent by a "reacting node") or an answer (i.e. send by a "reporting node"). Therefore, in a typical "client-server" deployment, the Diameter Client MAY report its overload condition to the Diameter Server for any Diameter Server initiated message exchange. An example of such is the Diameter Server requesting a re-authentication from a Diameter Client.
The DOIC solution supports the ability for Diameter nodes to determine if other nodes in the path of a request support the solution. This capability is referred to as DOIC Capability Announcement (DCA) and is separate from Diameter Capability Exchange.
The DCA solution uses the OC-Supported-Features AVPs to indicate the Diameter overload features supported.
The first node in the path of a Diameter request that supports the DOIC solution inserts the OC-Supported-Feature AVP in the request message. This includes an indication that it supports the loss overload abatement algorithm defined in this specification (see Section 5). This ensures that there is at least one commonly supported overload abatement algorithm between the reporting node and the reacting nodes in the path of the request.
The reporting node inserts the OC-Supported-Feature AVP in all answer messages to requests that contained the OC-Supported-Feature AVP. The contents of the reporting node's OC-Supported-Feature AVP indicate the set of Diameter overload features supported by the reporting node with one exception.
The reporting node only includes an indication of support for one overload abatement algorithm. This is the algorithm that the reporting node intends to use should it enter an overload condition or requests to use while it actually is in an overload condition. Reacting nodes can use the indicated overload abatement algorithm to prepare for possible overload reports and must use the indicated overload abatement algorithm if traffic reduction is actually requested.
The individual features supported by the DOIC nodes are indicated in the OC-Feature-Vector AVP. Any semantics associated with the features will be defined in extension specifications that introduce the features.
The DCA mechanism must also support the scenario where the set of features supported by the sender of a request and by agents in the path of a request differ. In this case, the agent updates the OC-Supported-Feature AVP to reflect the mixture of the two sets of supported features.
As with DOIC Capability Announcement, Overload Condition Reporting uses new AVPs (Section 6.3) to indicate an overload condition.
The OC-OLR AVP is referred to as an overload report. The OC-OLR AVP includes the type of report, a sequence number, the length of time that the report is valid and abatement algorithm specific AVPs.
Two types of overload reports are defined in this document, host reports and realm reports.
A report of type host is sent to indicate the overload of a specific Diameter node for the application-id indicated in the transaction. When receiving an OLR of type host, a reacting node applies overload abatement to what is referred to in this document as host-routed requests. This is the set of requests that the reacting node knows will be served by a particular host, either due to the presence of a Destination-Host AVP, or by some other local knowledge on the part of the reacting node. The reacting node applies overload abatement on those host-routed requests which the reacting node knows will be served by the server that matches the Origin-Host AVP of the received message that contained the received OLR of type host.
Realm reports apply to realm-routed requests for a specific realm as indicated in the Destination-Realm AVP.
Reporting nodes are responsible for determining the need for a reduction of traffic. The method for making this determination is implementation specific and depend on the type of overload report being generated. A host report, for instance, will generally be generated by tracking utilization of resources required by the host to handle transactions for the Diameter application. A realm report will generally impact the traffic sent to multiple hosts and, as such, will typically require tracking the capacity of the servers able to handle realm-routed requests for the application.
Once a reporting node determines the need for a reduction in traffic, it uses the DOIC defined AVPs to report on the condition. These AVPs are included in answer messages sent or relayed by the reporting node. The reporting node indicates the overload abatement algorithm that is to be used to handle the traffic reduction in the OC-Supported-Features AVP. The OC-OLR AVP is used to communicate information about the requested reduction.
Reacting nodes, upon receipt of an overload report, are responsible for applying the abatement algorithm to traffic impacted by the overload report. The method used for that abatement is dependent on the abatement algorithm. The loss abatement algorithm is defined in this document (Section 5). Other abatement algorithms can be defined in extensions to the DOIC solutions.
As the conditions that lead to the generation of the overload report change the reporting node can send new overload reports requesting greater reduction if the condition gets worse or less reduction if the condition improves. The reporting node sends an overload report with a duration of zero to indicate that the overload condition has ended and use of the abatement algorithm is no longer needed.
The reacting node also determines when the overload report expires based on the OC-Validity-Duration AVP in the overload report and stops applying the abatement algorithm when the report expires.
The DOIC solution is designed to be extensible. This extensibility is based on existing Diameter based extensibility mechanisms.
There are multiple categories of extensions that are expected. This includes the definition of new overload abatement algorithms, the definition of new report types and new definitions of the scope of messages impacted by an overload report.
The DOIC solution uses the OC-Supported-Features AVP for DOIC nodes to communicate supported features. The specific features supported by the DOIC node are indicated in the OC-Feature-Vector AVP. DOIC extensions must define new values for the OC-Feature-Vector AVP. DOIC extensions also have the ability to add new AVPs to the OC-Supported-Features AVP, if additional information about the new feature is required.
Reporting nodes use the OC-OLR AVP to communicate overload occurrences. This AVP can also be extended to add new AVPs allowing a reporting nodes to communicate additional information about handling an overload condition.
If necessary, new extensions can also define new top-level AVPs. It is, however, recommended that DOIC extensions use the OC-Supported-Features and OC-OLR to carry all DOIC related AVPs.
Figure 1 illustrates the simplified architecture for Diameter overload information conveyance.
Realm X Same or other Realms
<--------------------------------------> <---------------------->
+--^-----+ : (optional) :
|Diameter| : :
|Server A|--+ .--. : +---^----+ : .--.
+--------+ | _( `. : |Diameter| : _( `. +---^----+
+--( )--:-| Agent |-:--( )--|Diameter|
+--------+ | ( ` . ) ) : +-----^--+ : ( ` . ) ) | Client |
|Diameter|--+ `--(___.-' : : `--(___.-' +-----^--+
|Server B| : :
+---^----+ : :
End-to-end Overload Indication
1) <----------------------------------------------->
Diameter Application Y
Overload Indication A Overload Indication A'
2) <----------------------> <---------------------->
standard base protocol standard base protocol
Figure 1: Simplified architecture choices for overload indication delivery
In Figure 1, the Diameter overload indication can be conveyed (1) end-to-end between servers and clients or (2) between servers and Diameter agent inside the realm and then between the Diameter agent and the clients.
This section outlines the normative behavior associated with the DOIC solution.
This section defines DOIC Capability Announcement (DCA) behavior.
A reacting node MUST include the OC-Supported-Features AVP in all request messages.
A reacting node MAY include the OC-Feature-Vector AVP with an indication of the loss algorithm. A reacting node MUST include the OC-Feature-Vector AVP to indicate support for abatement algorithms in addition to the loss algorithm.
A reacting node SHOULD indicate support for all other DOIC features it supports.
An OC-Supported-Features AVP in answer messages indicates there is a reporting node for the transaction. The reacting node MAY take action based on the features indicated in the OC-Feature-Vector AVP.
Upon receipt of a request message, a reporting node determines if there is a reacting node for the transaction based on the presence of the OC-Supported-Features AVP.
If the request message contains an OC-Supported-Features AVP then the reporting node MUST include the OC-Supported-Features AVP in the answer message for that transaction.
The reporting node MUST NOT include the OC-Supported-Features AVP, OC-OLR AVP or any other overload control AVPs defined in extension drafts in response messages for transactions where the request message does not include the OC-Supported-Features AVP. Lack of the OC-Supported-Features AVP in the request message indicates that there is no reacting node for the transaction.
Based on the content of the OC-Supported-Features AVP in the request message, the reporting node knows what overload control functionality is supported by the reacting node. The reporting node then acts accordingly for the subsequent answer messages it initiates.
The reporting node MUST indicate support for one and only one abatement algorithm in the OC-Feature-Vector AVP. The abatement algorithm included MUST be from the set of abatement algorithms contained in the request message's OC-Supported-Features AVP. The abatement algorithm included MUST indicate the abatement algorithm the reporting node wants the reacting node to use when the reporting node enters an overload condition.
For an ongoing overload state, a reacting node MUST keep the algorithm that was selected by the reporting node in further requests towards the reporting node. The reporting node SHOULD NOT change the selected algorithm during a period of time that it is in an overload condition and, as a result, is sending OC-OLR AVPs in answer messages.
The reporting node SHOULD indicate support for other DOIC features defined in extension drafts that it supports and that apply to the transaction.
Diameter agents that support DOIC MUST ensure that all messages have the OC-Supporting-Features AVP. If a message handled by the DOIC agent does not include the OC-Supported-Features AVP then the DOIC agent inserts the AVP. If the message already has the AVP then the agent either leaves it unchanged in the relayed message or modifies it to reflect a mixed set of DOIC features.
An agent MAY modify the OC-Supported-Features AVP carried in answer messages.
Both reacting and reporting nodes maintain Overload Control State (OCS) for active overload conditions.
A reacting node SHOULD maintain the following OCS per supported Diameter application:
A host-type OCS entry is identified by the pair of Application-Id and Host-Id.
A realm-type OCS entry is identified by the pair of Application-Id and Realm-Id.
The host-type and realm-type OCS entries MAY include the following information (the actual information stored is an implementation decision):
A reporting node SHOULD maintain OCS entries per supported Diameter application, per supported (and eventually selected) Abatement Algorithm and per report-type.
An OCS entry is identified by the pair of Application-Id and Abatement Algorithm.
The OCS entry for a given pair of Application and Abatement Algorithm MAY include the information (the actual information stored is an implementation decision):
When a reacting node receives an OC-OLR AVP, it MUST determine if it is for an existing or new overload condition.
The OLR is for an existing overload condition if the reacting node has an OCS that matches the received OLR.
For a host report-type this means it matches the app-id and host-id in an existing host OCS entry.
For a realm report-type this means it matches the app-id and realm-id in an existing realm OCS entry.
If the OLR is for an existing overload condition then it MUST determine if the OLR is a retransmission or an update to the existing OLR.
If the sequence number for the received OLR is greater than the sequence number stored in the matching OCS entry then the reacting node MUST update the matching OCS entry.
If the sequence number for the received OLR is less than or equal to the sequence number in the matching OCS entry then the reacting node MUST silently ignore the received OLR. The matching OCS MUST NOT be updated in this case.
If the received OLR is for a new overload condition then the reacting node MUST generate a new OCS entry for the overload condition.
For a host report-type this means it creates on OCS entry with the app-id of the application-id in the received message and host-id of the Origin-Host in the received message.
For a realm report-type this means it creates on OCS entry with the app-id of the application-id in the received message and realm-id of the Origin-Realm in the received message.
If the received OLR contains a validity duration of zero (“0”) then the reacting node MUST update the OCS entry as being expired.
The reacting node does not delete an OCS when receiving an answer message that does not contain an OC-OLR AVP (i.e. absence of OLR means “no change”).
A reporting node SHOULD create a new OCS entry when entering an overload condition.
When generating a new OCS entry the sequence number MAY be set to any value if there is no unexpired overload report for previous overload conditions sent to any reacting node for the same application and report-type.
When generating sequence numbers for new overload conditions, the new sequence number MUST be greater than any sequence number in an active (unexpired) overload report previously sent by the reporting node. This property MUST hold over a reboot of the reporting node.
The reporting node MUST update an OCS entry when it needs to adjust the validity duration of the overload condition at reacting nodes.
A reporting node MUST NOT update the abatement algorithm in an active OCS entry.
A reporting node MUST update an OCS entry when it wishes to adjust any abatement algorithm specific parameters, including the reduction percentage used for the Loss abatement algorithm.
The reporting node MUST update the sequence number associated with the OCS entry anytime the contents of the OCS entry are changed. This will result in a new sequence number being sent to reacting nodes, instructing the reacting nodes to process the OC-OLR AVP.
A reporting node SHOULD update an OCS entry with a validity duration of zero ("0") when the overload condition ends.
The reporting node MUST keep an OCS entry with a validity duration of zero ("0") for a period of time long enough to ensure that any non-expired reacting node's OCS entry created as a result of the overload condition in the reporting node is deleted.
When a reacting node sends a request it MUST determine if that request matches an active OCS.
If the request matches and active OCS then the reacting node MUST apply abatement treatment on the request. The abatement treatment applied depends on the abatement algorithm stored in the OCS.
For the Loss abatement algorithm defined in this specification, see Section 5 for the abatement logic applied.
If the abatement treatment results in throttling of the request and if the reacting node is an agent then the agent MUST send an appropriate error as defined in section Section 7.
In the case that the OCS entry validity duration expires or has a validity duration of zero ("0"), meaning that it the reporting node has explicitly signaled the end of the overload condition then abatement associated with the overload abatement MUST be ended in a controlled fashion.
The operation on the reporting node is straight forward.
If there is an active OCS entry then the reporting node SHOULD include the OC-OLR AVP in all answer messages to requests that contain the OC-Supported-Features AVP and that match the active OCS entry.
The contents of the OC-OLR AVP MUST contain all information necessary for the abatement algorithm indicated in the OC-Supported-Features AVP that is also included in the answer message.
A reporting node MAY choose to not resend an overload report to a reacting node if it can guarantee that this overload report is already active in the reacting node.
A reporting node MUST NOT send overload reports of a type that has not been advertised as supported by the reacting node.
A reporting node MAY rely on the OC-Validity-Duration AVP values for the implicit overload control state cleanup on the reacting node. However, it is RECOMMENDED that the reporting node always explicitly indicates the end of a overload condition.
The reporting node SHOULD indicate the end of an overload occurrence by sending a new OLR with OC-Validity-Duration set to a value of zero ("0"). The reporting node SHOULD ensure that all reacting nodes receive the updated overload report.
When a reporting node sends an OLR, it effectively delegates any necessary throttling to downstream nodes. Therefore, the reporting node SHOULD NOT apply throttling to the set of messages to which the OLR applies. That is, the same candidate set of messages SHOULD NOT be throttled multiple times.
However, when the reporting node sends and OLR downstream, it MAY still be responsible to apply other abatement methods such as diversion. The reporting node might also need to throttle requests for reasons other then overload. For example, an agent or server might have a configured rate limit for each client, and throttle requests that exceed that limit, even if such requests had already been candidates for throttling by downstream nodes.
This document assumes that there is a single source for realm-reports for a given realm, or that if multiple nodes can send realm reports, that each such node has full knowledge of the overload state of the entire realm. A reacting node cannot distinguish between receiving realm-reports from a single node, or from multiple nodes.
The overload control solution can be extended, e.g. with new traffic abatement algorithms, new report types or other new functionality.
When defining a new extension a new feature bit MUST be defined for the OC-Feature-Vector. This feature bit is used to communicate support for the new feature.
The extension MAY define new AVPs for use in DOIC Capability Announcement and for use in DOIC Overload reporting. These new AVPs SHOULD be defined to be extensions to the OC-Supported-Features and OC-OLR AVPs defined in this document.
It should be noted that [RFC6733] defined Grouped AVP extension mechanisms apply. This allows, for example, defining a new feature that is mandatory to be understood even when piggybacked on an existing application.
The handling of feature bits in the OC-Feature-Vector AVP that are not associated with overload abatement algorithms MUST be specified by the extensions that define the features.
When defining new report type values, the corresponding specification MUST define the semantics of the new report types and how they affect the OC-OLR AVP handling. The specification MUST also reserve a corresponding new feature bit in the OC-Feature-Vector AVP.
The OC-OLR AVP can be expanded with optional sub-AVPs only if a legacy DOIC implementation can safely ignore them without breaking backward compatibility for the given OC-Report-Type AVP value. If the new sub-AVPs imply new semantics for handling the indicated report type, then a new OC-Report-Type AVP value MUST be defined.
New features (feature bits in the OC-Feature-Vector AVP) and report types (in the OC-Report-Type AVP) MUST be registered with IANA. As with any Diameter specification, new AVPs MUST also be registered with IANA. See Section 8 for the required procedures.
This section documents the Diameter overload loss abatement algorithm.
The DOIC specification supports the ability for multiple overload abatement algorithms to be specified. The abatement algorithm used for any instance of overload is determined by the Diameter Overload Capability Announcement process documented in Section 4.1.
The loss algorithm described in this section is the default algorithm that must be supported by all Diameter nodes that support DOIC.
The loss algorithm is designed to be a straightforward and stateless overload abatement algorithm. It is used by reporting nodes to request a percentage reduction in the amount of traffic sent. The traffic impacted by the requested reduction depends on the type of overload report.
Reporting nodes use a strategy of applying abatement logic to the requested percentage of request messages sent (or handled in the case of agents) by the reacting node that are impacted by the overload report.
From a conceptual level, the logic at the reacting node could be outlined as follows.
The method a reporting nodes uses to determine the amount of traffic reduction required to address an overload condition is an implementation decision.
When a reporting node that has selected the loss abatement algorithm determines the need to request a traffic reduction it includes an OC-OLR AVP in response messages as described in Section 4.2.3.
The reporting node MUST indicate a percentage reduction in the OC-Reduction-Percentage AVP.
The reporting node MAY change the reduction percentage in subsequent overload reports. When doing so the reporting node must conform to overload report handing specified in Section 4.2.3.
When the reporting node determines it no longer needs a reduction in traffic the reporting node SHOULD send an overload report indicating the overload report is no longer valid, as specified in Section 4.2.3.
The method a reacting node uses to determine which request messages are given abatement treatment is an implementation decision.
When receiving an OC-OLR in an answer message where the algorithm indicated in the OC-Supported-Features AVP is the loss algorithm, the reacting node MUST apply abatement treatment to the requested percentage of request messages sent.
When applying overload abatement treatment for the load abatement algorithm, the reacting node MUST abate, either by throttling or diversion, the requested percentage of requests that would have otherwise been sent to the reporting host or realm.
If reacting node comes out of the 100 percent traffic reduction as a result of the overload report timing out, the following concerns are RECOMMENDED to be applied. The reacting node sending the traffic should be conservative and, for example, first send "probe" messages to learn the overload condition of the overloaded node before converging to any traffic amount/rate decided by the sender. Similar concerns apply in all cases when the overload report times out unless the previous overload report stated 0 percent reduction.
If the reacting node does not receive an OLR in messages sent to the formerly overloaded node then the reacting node SHOULD slowly increase the rate of traffic sent to the overloaded node.
It is suggested that the reacting node decrease the amount of traffic given abatement treatment by 20% each second until the reduction is completely removed and no traffic is given abatement treatment.
This section describes the encoding and semantics of the Diameter Overload Indication Attribute Value Pairs (AVPs) defined in this document.
A new application specification can incorporate the overload control mechanism specified in this document by making it mandatory to implement for the application and referencing this specification normatively. It is the responsibility of the Diameter application designers to define how overload control mechanisms works on that application.
The OC-Supported-Features AVP (AVP code TBD1) is type of Grouped and serves two purposes. First, it announces a node's support for the DOIC solution in general. Second, it contains the description of the supported DOIC features of the sending node. The OC-Supported-Features AVP MUST be included in every Diameter request message a DOIC supporting node sends.
OC-Supported-Features ::= < AVP Header: TBD1 >
[ OC-Feature-Vector ]
* [ AVP ]
The OC-Feature-Vector sub-AVP is used to announce the DOIC features supported by the DOIC node, in the form of a flag bits field in which each bit announces one feature or capability supported by the node (see Section 6.2). The absence of the OC-Feature-Vector AVP indicates that only the default traffic abatement algorithm described in this specification is supported.
The OC-Feature-Vector AVP (AVP code TBD6) is type of Unsigned64 and contains a 64 bit flags field of announced capabilities of a DOIC node. The value of zero (0) is reserved.
The following capabilities are defined in this document:
The OC-OLR AVP (AVP code TBD2) is type of Grouped and contains the information necessary to convey an overload report on an overload condition at the reporting node. The OC-OLR AVP does not explicitly contain all information needed by the reacting node to decide whether a subsequent request must undergo a throttling process with the received reduction percentage. The value of the OC-Report-Type AVP within the OC-OLR AVP indicates which implicit information is relevant for this decision (see Section 6.6). The application the OC-OLR AVP applies to is the same as the Application-Id found in the Diameter message header. The host or realm the OC-OLR AVP concerns is determined from the Origin-Host AVP and/or Origin-Realm AVP found in the encapsulating Diameter command. The OC-OLR AVP is intended to be sent only by a reporting node.
OC-OLR ::= < AVP Header: TBD2 >
< OC-Sequence-Number >
< OC-Report-Type >
[ OC-Reduction-Percentage ]
[ OC-Validity-Duration ]
* [ AVP ]
Note that if a Diameter command were to contain multiple OC-OLR AVPs they all MUST have different OC-Report-Type AVP value. OC-OLR AVPs with unknown values SHOULD be silently discarded by reacting nodes and the event SHOULD be logged.
The OC-Sequence-Number AVP (AVP code TBD3) is type of Unsigned64. Its usage in the context of overload control is described in Section 4.2.
From the functionality point of view, the OC-Sequence-Number AVP MUST be used as a non-volatile increasing counter for a sequence of overload reports between two DOIC nodes for the same overload occurrence. The sequence number is only required to be unique between two DOIC nodes. Sequence numbers are treated in a uni-directional manner, i.e. two sequence numbers on each direction between two DOIC nodes are not related or correlated.
The OC-Validity-Duration AVP (AVP code TBD4) is type of Unsigned32 and indicates in milliseconds the validity time of the overload report. The number of milliseconds is measured after reception of the first OC-OLR AVP with a given value of OC-Sequence-Number AVP. The default value for the OC-Validity-Duration AVP is 5000 (i.e., 5 seconds). When the OC-Validity-Duration AVP is not present in the OC-OLR AVP, the default value applies. Validity duration with values above 86400 (i.e.; 24 hours) MUST NOT be used. Invalid duration values are treated as if the OC-Validity-Duration AVP were not present and result in the default value being used.
Editor's note: There is an open discussion on whether to have an upper limit on the OC-Validity-Duration value, beyond that which can be indicated by an Unsigned32.
A timeout of the overload report has specific concerns that need to be taken into account by the DOIC node acting on the earlier received overload report(s). Section 6.7 discusses the impacts of timeout in the scope of the traffic abatement algorithms.
The OC-Report-Type AVP (AVP code TBD5) is type of Enumerated. The value of the AVP describes what the overload report concerns. The following values are initially defined:
The OC-Report-Type AVP is envisioned to be useful for situations where a reacting node needs to apply different overload treatments for different overload contexts. For example, the reacting node(s) might need to throttle differently requests sent to a specific server (identified by the Destination-Host AVP in the request) and requests that can be handled by any server in a realm.
The OC-Reduction-Percentage AVP (AVP code TBD8) is type of Unsigned32 and describes the percentage of the traffic that the sender is requested to reduce, compared to what it otherwise would send. The OC-Reduction-Percentage AVP applies to the default (loss) algorithm specified in this specification. However, the AVP can be reused for future abatement algorithms, if its semantics fit into the new algorithm.
The value of the Reduction-Percentage AVP is between zero (0) and one hundred (100). Values greater than 100 are ignored. The value of 100 means that all traffic is to be throttled, i.e. the reporting node is under a severe load and ceases to process any new messages. The value of 0 means that the reporting node is in a stable state and has no need for the reacting node to apply any traffic abatement. The default value of the OC-Reduction-Percentage AVP is 0. When the OC-Reduction-Percentage AVP is not present in the overload report, the default value applies.
+---------+
|AVP flag |
|rules |
+----+----+
AVP Section | |MUST|
Attribute Name Code Defined Value Type |MUST| NOT|
+--------------------------------------------------+----+----+
|OC-Supported-Features TBD1 x.x Grouped | | V |
+--------------------------------------------------+----+----+
|OC-OLR TBD2 x.x Grouped | | V |
+--------------------------------------------------+----+----+
|OC-Sequence-Number TBD3 x.x Unsigned64 | | V |
+--------------------------------------------------+----+----+
|OC-Validity-Duration TBD4 x.x Unsigned32 | | V |
+--------------------------------------------------+----+----+
|OC-Report-Type TBD5 x.x Enumerated | | V |
+--------------------------------------------------+----+----+
|OC-Reduction | | |
| -Percentage TBD8 x.x Unsigned32 | | V |
+--------------------------------------------------+----+----+
|OC-Feature-Vector TBD6 x.x Unsigned64 | | V |
+--------------------------------------------------+----+----+
As described in the Diameter base protocol [RFC6733], the M-bit setting for a given AVP is relevant to an application and each command within that application that includes the AVP.
The Diameter overload control AVPs SHOULD always be sent with the M-bit cleared when used within existing Diameter applications to avoid backward compatibility issues. Otherwise, when reused in newly defined Diameter applications, the DOC related AVPs SHOULD have the M-bit set.
When a DOIC node rejects a Diameter request due to overload, the DOIC node MUST select an appropriate error response code. This determination is made based on the probability of the request succeeding if retried on a different path.
A reporting node rejecting a Diameter request due to an overload condition SHOULD send a DIAMETER-TOO-BUSY error response, if it can assume that the same request may succeed on a different path.
If a reporting node knows or assumes that the same request will not succeed on a different path, DIAMETER_UNABLE_TO_COMPLY error response SHOULD be used. Retrying would consume valuable resources during an occurrence of overload.
New AVPs defined by this specification are listed in Section 6. All AVP codes allocated from the 'Authentication, Authorization, and Accounting (AAA) Parameters' AVP Codes registry.
Two new registries are needed under the 'Authentication, Authorization, and Accounting (AAA) Parameters' registry.
Section 6.2 defines a new "Overload Control Feature Vector" registry including the initial assignments. New values can be added into the registry using the Specification Required policy [RFC5226]. See Section 6.2 for the initial assignment in the registry.
Section 6.6 defines a new "Overload Report Type" registry with its initial assignments. New types can be added using the Specification Required policy [RFC5226].
This mechanism gives Diameter nodes the ability to request that downstream nodes send fewer Diameter requests. Nodes do this by exchanging overload reports that directly affect this reduction. This exchange is potentially subject to multiple methods of attack, and has the potential to be used as a Denial-of-Service (DoS) attack vector.
Overload reports may contain information about the topology and current status of a Diameter network. This information is potentially sensitive. Network operators may wish to control disclosure of overload reports to unauthorized parties to avoid its use for competitive intelligence or to target attacks.
Diameter does not include features to provide end-to-end authentication, integrity protection, or confidentiality. This may cause complications when sending overload reports between non-adjacent nodes.
The Diameter protocol involves transactions in the form of requests and answers exchanged between clients and servers. These clients and servers may be peers, that is,they may share a direct transport (e.g. TCP or SCTP) connection, or the messages may traverse one or more intermediaries, known as Diameter Agents. Diameter nodes use TLS, DTLS, or IPSec to authenticate peers, and to provide confidentiality and integrity protection of traffic between peers. Nodes can make authorization decisions based on the peer identities authenticated at the transport layer.
When agents are involved, this presents an effectively hop-by-hop trust model. That is, a Diameter client or server can authorize an agent for certain actions, but it must trust that agent to make appropriate authorization decisions about its peers, and so on.
Since confidentiality and integrity protection occurs at the transport layer. Agents can read, and perhaps modify, any part of a Diameter message, including an overload report.
There are several ways an attacker might attempt to exploit the overload control mechanism. An unauthorized third party might inject an overload report into the network. If this third party is upstream of an agent, and that agent fails to apply proper authorization policies, downstream nodes may mistakenly trust the report. This attack is at least partially mitigated by the assumption that nodes include overload reports in Diameter answers but not in requests. This requires an attacker to have knowledge of the original request in order to construct a response. Therefore, implementations SHOULD validate that an answer containing an overload report is a properly constructed response to a pending request prior to acting on the overload report.
A similar attack involves an otherwise authorized Diameter node that sends an inappropriate overload report. For example, a server for the realm "example.com" might send an overload report indicating that a competitor's realm "example.net" is overloaded. If other nodes act on the report, they may falsely believe that "example.net" is overloaded, effectively reducing that realm's capacity. Therefore, it's critical that nodes validate that an overload report received from a peer actually falls within that peer's responsibility before acting on the report or forwarding the report to other peers. For example, an overload report from a peer that applies to a realm not handled by that peer is suspect.
An attacker might use the information in an overload report to assist in certain attacks. For example, an attacker could use information about current overload conditions to time a DoS attack for maximum effect, or use subsequent overload reports as a feedback mechanism to learn the results of a previous or ongoing attack.
Diameter overload reports can cause a node to cease sending some or all Diameter requests for an extended period. This makes them a tempting vector for DoS tacks. Furthermore, since Diameter is almost always used in support of other protocols, a DoS attack on Diameter is likely to impact those protocols as well. Therefore, Diameter nodes MUST NOT honor or forward overload reports from unauthorized or otherwise untrusted sources.
When a Diameter node sends an overload report, it cannot assume that all nodes will comply. A non-compliant node might continue to send requests with no reduction in load. Requirement 28 [RFC7068] indicates that the overload control solution cannot assume that all Diameter nodes in a network are necessarily trusted, and that malicious nodes not be allowed to take advantage of the overload control mechanism to get more than their fair share of service.
In the absence of an overload control mechanism, Diameter nodes need to implement strategies to protect themselves from floods of requests, and to make sure that a disproportionate load from one source does not prevent other sources from receiving service. For example, a Diameter server might reject a certain percentage of requests from sources that exceed certain limits. Overload control can be thought of as an optimization for such strategies, where downstream nodes never send the excess requests in the first place. However, the presence of an overload control mechanism does not remove the need for these other protection strategies.
The lack of end-to-end security features makes it far more difficult to establish trust in overload reports that originate from non-adjacent nodes. Any agents in the message path may insert or modify overload reports. Nodes must trust that their adjacent peers perform proper checks on overload reports from their peers, and so on, creating a transitive-trust requirement extending for potentially long chains of nodes. Network operators must determine if this transitive trust requirement is acceptable for their deployments. Nodes supporting Diameter overload control MUST give operators the ability to select which peers are trusted to deliver overload reports, and whether they are trusted to forward overload reports from non-adjacent nodes.
The lack of end-to-end confidentiality protection means that any Diameter agent in the path of an overload report can view the contents of that report. In addition to the requirement to select which peers are trusted to send overload reports, operators MUST be able to select which peers are authorized to receive reports. A node MUST not send an overload report to a peer not authorized to receive it. Furthermore, an agent MUST remove any overload reports that might have been inserted by other nodes before forwarding a Diameter message to a peer that is not authorized to receive overload reports.
At the time of this writing, the DIME working group is studying requirements for adding end-to-end security [I-D.ietf-dime-e2e-sec-req] features to Diameter. These features, when they become available, might make it easier to establish trust in non-adjacent nodes for overload control purposes. Readers should be reminded, however, that the overload control mechanism encourages Diameter agents to modify AVPs in, or insert additional AVPs into, existing messages that are originated by other nodes. If end-to-end security is enabled, there is a risk that such modification could violate integrity protection. The details of using any future Diameter end-to-end security mechanism with overload control will require careful consideration, and are beyond the scope of this document.
The following people contributed substantial ideas, feedback, and discussion to this document:
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC5226] | Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. |
| [RFC5905] | Mills, D., Martin, J., Burbank, J. and W. Kasch, "Network Time Protocol Version 4: Protocol and Algorithms Specification", RFC 5905, June 2010. |
| [RFC6733] | Fajardo, V., Arkko, J., Loughney, J. and G. Zorn, "Diameter Base Protocol", RFC 6733, October 2012. |
| [Cx] | 3GPP, , "ETSI TS 129 229 V11.4.0", August 2013. |
| [I-D.ietf-dime-e2e-sec-req] | Tschofenig, H., Korhonen, J., Zorn, G. and K. Pillay, "Diameter AVP Level Security: Scenarios and Requirements", Internet-Draft draft-ietf-dime-e2e-sec-req-00, September 2013. |
| [PCC] | 3GPP, , "ETSI TS 123 203 V11.12.0", December 2013. |
| [RFC4006] | Hakala, H., Mattila, L., Koskinen, J-P., Stura, M. and J. Loughney, "Diameter Credit-Control Application", RFC 4006, August 2005. |
| [RFC5729] | Korhonen, J., Jones, M., Morand, L. and T. Tsou, "Clarifications on the Routing of Diameter Requests Based on the Username and the Realm", RFC 5729, December 2009. |
| [RFC7068] | McMurry, E. and B. Campbell, "Diameter Overload Control Requirements", RFC 7068, November 2013. |
| [S13] | 3GPP, , "ETSI TS 129 272 V11.9.0", December 2012. |
The base solution for the overload control does not cover all possible use cases. A number of solution aspects were intentionally left for future specification and protocol work.
This specification describes only means for a simple loss based algorithm. Future algorithms can be added using the designed solution extension mechanism. The new algorithms need to be registered with IANA. See Sections 6.1 and 8 for the required IANA steps.
This specification focuses on Diameter endpoint (server or client) overload. A separate extension will be required to outline the handling of the case of agent overload.
The proposal was made to add a new Error Diagnostic AVP to supplement the error responces to be able to indicate that overload was the reason for the rejection of the message.
Non supporting agents
Topology hiding interactions
This section contains the result of an analysis of the DOIC solutions conformance to the requirements defined in [RFC7068].
To be completed.
This section outlines considerations to be taken into account when integrating the DOIC solution into Diameter applications.
The following is a classification of Diameter applications and request types. This discussion is meant to document factors that play into decisions made by the Diameter identity responsible for handling overload reports.
Section 8.1 of [RFC6733] defines two state machines that imply two types of applications, session-less and session-based applications. The primary difference between these types of applications is the lifetime of Session-Ids.
For session-based applications, the Session-Id is used to tie multiple requests into a single session.
The Credit-Control application defined in [RFC4006] is an example of a Diameter session-based application.
In session-less applications, the lifetime of the Session-Id is a single Diameter transaction, i.e. the session is implicitly terminated after a single Diameter transaction and a new Session-Id is generated for each Diameter request.
For the purposes of this discussion, session-less applications are further divided into two types of applications:
The handling of overload reports must take the type of application into consideration, as discussed in Appendix D.2.
This section discusses considerations for mitigating overload reported by a Diameter entity. This discussion focuses on the type of application. Appendix D.3 discusses considerations for handling various request types when the target server is known to be in an overloaded state.
These discussions assume that the strategy for mitigating the reported overload is to reduce the overall workload sent to the overloaded entity. The concept of applying overload treatment to requests targeted for an overloaded Diameter entity is inherent to this discussion. The method used to reduce offered load is not specified here but could include routing requests to another Diameter entity known to be able to handle them, or it could mean rejecting certain requests. For a Diameter agent, rejecting requests will usually mean generating appropriate Diameter error responses. For a Diameter client, rejecting requests will depend upon the application. For example, it could mean giving an indication to the entity requesting the Diameter service that the network is busy and to try again later.
The request classes identified in Appendix D.3 have implications on decisions about which requests should be throttled first. The following list of request treatment regarding throttling is provided as guidelines for application designers when implementing the Diameter overload control mechanism described in this document. The exact behavior regarding throttling is a matter of local policy, unless specifically defined for the application.