| Diameter Maintenance and Extensions (DIME) | J. Korhonen, Ed. |
| Internet-Draft | Broadcom |
| Intended status: Standards Track | S. Donovan, Ed. |
| Expires: February 7, 2016 | B. Campbell |
| Oracle | |
| L. Morand | |
| Orange Labs | |
| August 6, 2015 |
Diameter Overload Indication Conveyance
draft-ietf-dime-ovli-09.txt
This specification defines a base solution for Diameter overload control, referred to as Diameter Overload Indication Conveyance (DOIC).
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This Internet-Draft will expire on February 7, 2016.
Copyright (c) 2015 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, referred to as Diameter Overload Indication Conveyance (DOIC), based on the requirements identified in [RFC7068].
This specification addresses Diameter overload control between Diameter nodes that support the DOIC solution. 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.
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.
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 future specifications. See Appendix A for a list of extensions that are currently being considered.
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].
RFC 2119 [RFC2119] interpretation does not apply for the above listed words when they are not used in all-caps format.
The Diameter Overload Information Conveyance (DOIC) solution allows Diameter nodes to request other Diameter 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 Diameter Clients, Diameter Servers, and Diameter Agents. DOIC nodes are further divided into "Reporting Nodes" and "Reacting Nodes." A reporting node requests overload abatement by sending Overload Reports (OLR).
A reacting node acts upon OLRs, and performs whatever actions are needed to fulfill the abatement requests included in the OLRs. A Reporting node may report overload on its own behalf, or on behalf of other nodes. Likewise, a reacting node may perform overload abatement on its own behalf, or on behalf of other nodes.
A Diameter node's role as a DOIC node is independent of its Diameter role. For example, Diameter 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 both a reporting node and a reacting node.
Likewise, a Diameter 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 7.2) into existing requests and responses. Reporting nodes send OLRs by inserting OC-OLR AVPs (Section 7.3).
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 some of the parameters of an OLR and the procedures required for overload abatement. An overload abatement algorithm separates Diameter requests into two sets. The first set contains the requests that are to undergo overload abatement treatment of either throttling or diversion. The second set contains the requests that are to be given normal routing treatment. This document specifies a single must-support algorithm, namely the "loss" algorithm (Section 6). 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 attempt to send requests to other destinations. 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 7.6), where the type defines such behaviors. Report types are extensible. This document defines report types for overload of a specific host, and for overload of an entire realm.
DOIC works through non supporting Diameter Agents that properly pass unknown AVPs unchanged.
There is no new Diameter application defined to carry overload related AVPs. 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 the optional overload control AVPs OC-OLR and OC-Supported-Features into existing commands.
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 that are in response to a request that contained the OC-Supported-Features AVP. Reporting nodes may 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., sent 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 mechanism 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-Features AVP in the request message.
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 OC-Feature-Vector AVP will always contain an indication of support for the loss overload abatement algorithm defined in this specification (see Section 6). This ensures that a reporting node always supports at least one of the advertized abatement algorithms received in a request messages.
The reporting node inserts the OC-Supported-Features AVP in all answer messages to requests that contained the OC-Supported-Features AVP. The contents of the reporting node's OC-Supported-Features AVP indicate the set of Diameter overload features supported by the reporting node. This specification defines one exception - the reporting node only includes an indication of support for one overload abatement algorithm, independent of the number of overload abatement algorithms actually supported by the reacting node. The overload abatement algorithm indicated is the algorithm that the reporting node intends to use should it enter 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 DCA mechanism must also allow 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 can update the OC- Supported-Features AVP to reflect the mixture of the two sets of supported features.
As with DOIC capability announcement, overload condition reporting uses new AVPs (Section 7.3) 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_REPORT" is sent to indicate the overload of a specific host, identified by the Origin-Host AVP of the message containing the OLR, for the application-id indicated in the transaction. When receiving an OLR of type "HOST_REPORT", a reacting node applies overload abatement treatment to the host-routed requests identified by the overload abatement algorithm (see definition in Section 2) sent for this application to the overloaded host.
A report of type "REALM_REPORT" is sent to indicate the overload of a realm for the application-id indicated in the transaction. The overloaded realm is identified by the Destination-Realm AVP of the message containing the OLR. When receiving an OLR of type "REALM_REPORT", a reacting node applies overload abatement treatment to realm-routed requests identified by the overload abatement algorithm (see definition in Section 2) sent for this application to the overloaded realm.
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.
Reporting nodes are responsible for determining the need for a reduction of traffic. The method for making this determination is implementation specific and depends on the type of overload report being generated. A host-report might be generated by tracking use of resources required by the host to handle transactions for the Diameter application. A realm-report generally impacts the traffic sent to multiple hosts and, as such, requires tracking the capacity of all servers able to handle realm-routed requests for the application and realm.
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, apply the overload abatement algorithm to traffic impacted by the overload report. The method used to determine the requests that are to receive overload abatement treatment is dependent on the abatement algorithm. The loss abatement algorithm is defined in this document (Section 6). Other abatement algorithms can be defined in extensions to the DOIC solution.
Two types of overload abatement treatment are defined, diversion and throttling. Reacting nodes are responsible for determining which treatment is appropriate for individual requests.
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 abatement 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.
Note that erroneous overload reports can be used for DoS attacks. This includes the ability to indicate that a significant reduction in traffic, up to and including a request for no traffic, should be sent to a reporting node. As such, care should be taken to verify the sender of overload reports.
The DOIC solution is designed to be extensible. This extensibility is based on existing Diameter based extensibility mechanisms, along with the DOIC capability announcement mechanism.
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 the definition of new scopes of messages impacted by an overload report.
A DOIC node communicates supported features by including them in the OC-Feature-Vector AVP, as a sub-AVP of OC-Supported-Features. Any non-backwards compatible DOIC extensions 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.
Overload reports can also be extended by adding new sub-AVPs to the OC-OLR AVP, allowing reporting nodes to communicate additional information about handling an overload condition.
If necessary, new extensions can also define new AVPs that are not part of the OC-Supported-Features and OC-OLR group AVPs. It is, however, recommended that DOIC extensions use the OC-Supported-Features AVP and OC-OLR AVP 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) <----------------------> <---------------------->
Diameter Application Y Diameter Application Y
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 for the DOIC solution.
This section defines DOIC Capability Announcement (DCA) behavior.
A reacting node MUST include the OC-Supported-Features AVP in all requests. It MAY include the OC-Feature-Vector AVP, as a sub-avp of OC-Supported-Features. If it does so, it MUST indicate support for the "loss" algorithm. If the reacting node is configured to support features (including other algorithms) in addition to the loss algorithm, it MUST indicate such support in an OC-Feature-Vector AVP.
An OC-Supported-Features AVP in answer messages indicates there is a reporting node for the transaction. The reacting node MAY take action, for example creating state for some stateful abatement algorithm, based on the features indicated in the OC-Feature-Vector AVP.
Reacting nodes need to be prepared for the reporting node to change selected algorithms. This can happen at any time, including when the reporting node has sent an active overload report. The reacting node can minimize the potential for changes by modifying the advertised abatement algorithms sent to an overloaded reporting node to the currently selected algorithm and loss (or just loss if it is the currently selected algorithm). This has the effect of limiting the potential change in abatement algorithm from the currently selected algorithm to loss, avoiding changes to more complex abatement algorithms that require state to operate properly.
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 in the request message.
If the request message contains an OC-Supported-Features AVP then a reporting node MUST include the OC-Supported-Features AVP in the answer message for that transaction.
A 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.
A reporting node knows what overload control functionality is supported by the reacting node based on the content or absence of the OC-Feature-Vector AVP within the OC-Supported-Features AVP in the request message.
A reporting node MUST A reporting node MUST select a single abatement algorithm in the OC-Feature-Vector AVP. The abatement algorithm selected MUST indicate the abatement algorithm the reporting node wants the reacting node to use when the reporting node enters an overload condition.
The abatement algorithm selected MUST be from the set of abatement algorithms contained in the request message's OC-Feature-Vector AVP.
A reporting node that selects the loss algorithm may do so by including the OC-Feature-Vector AVP with an explicit indication of the loss algorithm, or it MAY omit OC-Feature-Vector. If it selects a different algorithm, it MUST include the OC-Feature-Vector AVP with an explicit indication of the selected algorithm.
The reporting node SHOULD indicate support for other DOIC features defined in extension drafts that it supports and that apply to the transaction. It does so using the OC-Feature-Vector AVP.
Diameter Agents that support DOIC can ensure that all messages relayed by the agent contain the OC-Supported-Features AVP.
A Diameter Agent MAY take on reacting node behavior for Diameter endpoints that do not support the DOIC solution. A Diameter Agent detects that a Diameter endpoint does not support DOIC reacting node behavior when there is no OC-Supported-Features AVP in a request message.
For a Diameter Agent to be a reacting node for a non-supporting Diameter endpoint, the Diameter Agent MUST include the OC-Supported-Features AVP in request messages it relays that do not contain the OC-Supported-Features AVP.
A Diameter Agent MAY take on reporting node behavior for Diameter endpoints that do not support the DOIC solution. The Diameter Agent MUST have visibility to all traffic destined for the non-supporting host in order to become the reporting node for the Diameter endpoint. A Diameter Agent detects that a Diameter endpoint does not support DOIC reporting node behavior when there is no OC-Supported-Features AVP in an answer message for a transaction that contained the OC-Supported-Features AVP in the request message.
If a request already has the OC-Supported-Features AVP, a Diameter agent MAY modify it to reflect the features appropriate for the transaction. Otherwise, the agent relays the OC-Supported-Features AVP without change.
If the Diameter Agent changes the OC-Supported-Features AVP in a request message then it is likely it will also need to modify the OC-Supported-Features AVP in the answer message for the transaction. A Diameter Agent MAY modify the OC-Supported-Features AVP carried in answer messages.
When making changes to the OC-Supported-Features or OC-OLR AVPs, the Diameter Agent needs to ensure consistency in its behavior with both upstream and downstream DOIC nodes.
Both reacting and reporting nodes maintain Overload Control State (OCS) for active overload conditions. The following sections define behavior associated with that OCS.
The contents of the OCS in the reporting node and in the reacting node represent logical constructs. The actual internal physical structure of the state included in the OCS is an implementation decision.
A reacting node maintains the following OCS per supported Diameter application:
A host-type OCS entry is identified by the pair of application-id and the node's DiameterIdentity.
A realm-type OCS entry is identified by the pair of application-id and realm.
The host-type and realm-type OCS entries include the following information (the actual information stored is an implementation decision):
A reporting node maintains OCS entries per supported Diameter application, per supported (and eventually selected) Abatement Algorithm and per report-type.
An OCS entry is identified by the tuple of Application-Id, Report-Type and Abatement Algorithm and includes the following 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.
When receiving an answer message with multiple OLRs of different supported report types, a reacting node MUST process each received OLR.
The OLR is for an existing overload condition if a reacting node has an OCS that matches the received OLR.
For a host-report this means it matches the application-id and the host's DiameterIdentity in an existing host OCS entry.
For a realm-report this means it matches the application-id and the realm in an existing realm OCS entry.
If the OLR is for an existing overload condition then a reacting node 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 a 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 a reacting node MUST silently ignore the received OLR. The matching OCS MUST NOT be updated in this case.
If the reacting node determines that the sequence number has rolled over then the reacting node MUST update the matching OCS entry. This can be determined by recognizing that the number has changed from something close to the maximum value in the OC-Sequence-Number AVP to something close to the minimum value in the OC-Sequence-Number AVP.
If the received OLR is for a new overload condition then a reacting node MUST generate a new OCS entry for the overload condition.
For a host-report this means a reacting node creates on OCS entry with the application-id in the received message and DiameterIdentity of the Origin-Host in the received message.
For a realm-report this means a reacting node creates on OCS entry with the application-id in the received message and realm of the Origin-Realm in the received message.
If the received OLR contains a validity duration of zero (“0”) then a 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 SHOULD be set to zero ("0").
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 for the same application and report-type previously sent by the reporting node. This property MUST hold over a reboot of the reporting node.
A 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 update an OCS entry when it wishes to adjust any abatement algorithm specific parameters, including, for example, the reduction percentage used for the Loss abatement algorithm.
A reporting node MUST increment 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 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.
A 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 an active OCS then the reacting node MUST use the overload abatement algorithm indicated in the OCS to determine if the request is to receive overload abatement treatment.
For the Loss abatement algorithm defined in this specification, see Section 6 for the overload abatement algorithm logic applied.
If the overload abatement algorithm selects the request for overload abatement treatment then the reacting node MUST apply overload abatement treatment on the request. The abatement treatment applied depends on the context of the request.
If diversion abatement treatment is possible (i.e., a different path for the request can be selected where the overloaded node is not part of the different path), then the reacting node SHOULD apply diversion abatement treatment to the request. The reacting node MUST apply throttling abatement treatment to requests identified for abatement treatment when diversion treatment is not possible or was not applied.
If the overload 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 8.
Diameter endpoints that throttle requests need to do so according to the rules of the client application. Those rules will vary by application, and are beyond the scope of this document.
In the case that the OCS entry indicated no traffic was to be sent to the overloaded entity and the validity duration expires then overload abatement associated with the overload report MUST be ended in a controlled fashion.
If there is an active OCS entry then a reporting node SHOULD include the OC-OLR AVP in all answers to requests that contain the OC-Supported-Features AVP and that match the active OCS entry.
The contents of the OC-OLR AVP depend on the selected algorithm.
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 SHOULD explicitly 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.
A reporting node MAY rely on the OC-Validity-Duration AVP values for the implicit overload control state cleanup on the reacting node.
When a reporting node sends an OLR, it effectively delegates any necessary throttling to downstream nodes. If the reporting node also locally throttles the same set of messages, the overall number of throttled requests may be higher than intended. Therefore, before applying local message throttling, a reporting node needs to check if these messages match existing OCS entries, indicating that these messages have survived throttling applied by downstream nodes that have received the related OLR.
However, even if the set of messages match existing OCS entries, the reporting node can still apply other abatement methods such as diversion. The reporting node might also need to throttle requests for reasons other than 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. The reporting node also has the option to send new OLRs requesting greater reductions in traffic, reducing the need for local throttling.
A reporting node SHOULD decrease requested overload abatement treatment in a controlled fashion to avoid oscillations in traffic.
The DOIC solution can be extended. Types of potential extensions include new traffic abatement algorithms, new report types or other new functionality.
When defining a new extension that requires new normative behavior, the specification must define a new feature 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 or OC-OLR AVPs defined in this document.
[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.
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 OC-Supported-Feature and OC-OLR AVPs 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. Any new sub-AVPs must not require that the M-bit be set.
Documents that introduce new report types must describe any limitations on their use across non-supporting agents.
As with any Diameter specification, RFC6733 requires all new AVPs to be registered with IANA. See Section 9 for the required procedures. New features (feature bits in the OC-Feature-Vector AVP) and report types (in the OC-Report-Type AVP) MUST be registered with IANA.
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 5.1.
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 request the stateless reduction of the number of requests by an indicated percentage. This percentage reduction is in comparison to the number of messages the node otherwise would send, regardless of how many requests the node might have sent in the past.
From a conceptual level, the logic at the reacting node could be outlined as follows.
The method a reporting node 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 reduction in traffic, it includes an OC-OLR AVP in answer messages as described in Section 5.2.3.
When sending the OC-OLR AVP, 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 5.2.3.
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.
If reacting node comes out of the 100 percent traffic reduction, meaning it has received an OLR indicating that no traffic should be sent, as a result of the overload report timing out 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.
This section describes the encoding and semantics of the Diameter Overload Indication Attribute Value Pairs (AVPs) defined in this document.
Refer to section 4 of [RFC6733] for more information on AVPs and AVP data types.
The OC-Supported-Features AVP (AVP code TBD1) is of type 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 AVP (AVP code TBD2) is of type Unsigned64 and contains a 64 bit flags field of announced capabilities of a DOIC node. The value of zero (0) is reserved.
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. The absence of the OC-Feature-Vector AVP in request messages indicates that only the default traffic abatement algorithm described in this specification is supported. The absence of the OC- Feature-Vector AVP in answer messages indicates that the default traffic abatement algorithm described in this specification is selected (while other traffic abatement algorithms may be supported), and no features other than abatement algorithms are supported.
The following capabilities are defined in this document:
The OC-OLR AVP (AVP code TBD3) is of type Grouped and contains the information necessary to convey an overload report on an overload condition at the reporting node. 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 ]
The OC-Sequence-Number AVP (AVP code TBD4) is of type Unsigned64. Its usage in the context of overload control is described in Section 5.2.
From the functionality point of view, the OC-Sequence-Number AVP is used as a non-volatile increasing counter for a sequence of overload reports between two DOIC nodes for the same overload occurrence. 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 TBD5) is of type Unsigned32 and indicates in seconds the validity time of the overload report. The number of seconds 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 30 seconds. When the OC-Validity-Duration AVP is not present in the OC-OLR AVP, the default value applies. The maximum value for the OC-Validity-Duration AVP is 86,400 seconds (24 hours). If the value received in the OC-Validity-Duration is greater than the maximum value then the default value applies.
The OC-Report-Type AVP (AVP code TBD6) is of type Enumerated. The value of the AVP describes what the overload report concerns. The following values are initially defined:
The OC-Reduction-Percentage AVP (AVP code TBD7) is of type 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.
+---------+
|AVP flag |
|rules |
+----+----+
AVP Section | |MUST|
Attribute Name Code Defined Value Type |MUST| NOT|
+--------------------------------------------------+----+----+
|OC-Supported-Features TBD1 7.1 Grouped | | V |
+--------------------------------------------------+----+----+
|OC-Feature-Vector TBD2 7.2 Unsigned64 | | V |
+--------------------------------------------------+----+----+
|OC-OLR TBD3 7.3 Grouped | | V |
+--------------------------------------------------+----+----+
|OC-Sequence-Number TBD4 7.4 Unsigned64 | | V |
+--------------------------------------------------+----+----+
|OC-Validity-Duration TBD5 7.5 Unsigned32 | | V |
+--------------------------------------------------+----+----+
|OC-Report-Type TBD6 7.6 Enumerated | | V |
+--------------------------------------------------+----+----+
|OC-Reduction | | |
| -Percentage TBD7 7.7 Unsigned32 | | V |
+--------------------------------------------------+----+----+
As described in the Diameter base protocol [RFC6733], the M-bit usage for a given AVP in a given command may be defined by the application.
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 7. All AVP codes are 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.
A new "Overload Control Feature Vector" registry is required. The registry must contain the following:
See Section 7.2 for the initial Feature Vector Value in the registry. This specification is the specification defining the value. New values can be added into the registry using the Specification Required policy. [RFC5226].
A new "Overload Report Type" registry is required. The registry must contain the following:
See Section 7.6 for the initial assignment in the registry. New types can be added using the Specification Required policy [RFC5226].
DOIC gives Diameter nodes the ability to request that downstream nodes send fewer Diameter requests. Nodes do this by exchanging overload reports that directly effect 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. For instance, a series of injected realm OLRs with a requested reduction percentage of 100% could be used to completely eliminate any traffic from being sent to that realm.
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 transitive 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 an answer. Such an answer would also need to arrive at a Diameter node via a protected transport connection. Therefore, implementations MUST validate that an answer containing an overload report is a properly constructed response to a pending request prior to acting on the overload report, and that the answer was received via an appropriate transport connection.
A similar attack involves a compromised but otherwise authorized 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. This may require out-of-band, non Diameter agreements and/or mechanisms.
Diameter overload reports, especially realm-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 attacks. 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. In the worst case, where the Diameter application is being used for access control into an IP network, a coordinated DOS attack could result in the blockage of all traffic into that network. Therefore, Diameter nodes MUST NOT honor or forward OLRs received from peers that are not trusted to send them.
An attacker might use the information in an OLR to assist in DoS attacks. For example, an attacker could use information about current overload conditions to time an attack for maximum effect, or use subsequent overload reports as a feedback mechanism to learn the results of a previous or ongoing attack. Operators need the ability to ensure that OLRs are not leaked to untrusted parties.
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 throttle 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.
When a Diameter node sends an overload report, it cannot assume that all nodes will comply, even if they indicate support for DOIC. A non-compliant node might continue to send requests with no reduction in load. Such non-compliance could be done accidentally, or maliciously to gain an unfair advantage over compliant nodes. Requirement 28 [RFC7068] indicates that the overload control solution cannot assume that all Diameter nodes in a network are trusted. It also requires that malicious nodes not be allowed to take advantage of the overload control mechanism to get more than their fair share of service.
The lack of end-to-end integrity features makes it difficult to establish trust in overload reports received 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. DOIC nodes MUST strip DOIC AVPs from messages received from peers that are not trusted for DOIC purposes.
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.
It is expected that work on end-to-end Diameter security 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 allows 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, DOI 10.17487/RFC2119, March 1997. |
| [RFC5226] | Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008. |
| [RFC6733] | Fajardo, V., Arkko, J., Loughney, J. and G. Zorn, "Diameter Base Protocol", RFC 6733, DOI 10.17487/RFC6733, 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-01, October 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, DOI 10.17487/RFC4006, August 2005. |
| [RFC7068] | McMurry, E. and B. Campbell, "Diameter Overload Control Requirements", RFC 7068, DOI 10.17487/RFC7068, 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. The following sub-sections define some of the potential extensions to the DOIC solution.
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 7.1 and 9 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.
This specification indicates the use of existing error messages when nodes reject requests due to overload. There is an expectation that additional error codes or AVPs will be defined in a separate specification to indicate that overload was the reason for the rejection of the message.
Non-Supporting Agents
Topology Hiding Interactions
Inter Realm/Administrative Domain Considerations
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 entity 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 C.2.
This section discusses considerations for mitigating overload reported by a Diameter entity. This discussion focuses on the type of application. Appendix C.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 C.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.