Internet DRAFT - draft-ietf-dime-ovli
draft-ietf-dime-ovli
Diameter Maintenance and Extensions (DIME) J. Korhonen, Ed.
Internet-Draft Broadcom
Intended status: Standards Track S. Donovan, Ed.
Expires: February 20, 2016 B. Campbell
Oracle
L. Morand
Orange Labs
August 19, 2015
Diameter Overload Indication Conveyance
draft-ietf-dime-ovli-10.txt
Abstract
This specification defines a base solution for Diameter overload
control, referred to as Diameter Overload Indication Conveyance
(DOIC).
Status of This Memo
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Abbreviations . . . . . . . . . . . . . . . . 3
3. Conventions Used in This Document . . . . . . . . . . . . . . 5
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Piggybacking . . . . . . . . . . . . . . . . . . . . . . 6
4.2. DOIC Capability Announcement . . . . . . . . . . . . . . 7
4.3. DOIC Overload Condition Reporting . . . . . . . . . . . . 9
4.4. DOIC Extensibility . . . . . . . . . . . . . . . . . . . 11
4.5. Simplified Example Architecture . . . . . . . . . . . . . 11
5. Solution Procedures . . . . . . . . . . . . . . . . . . . . . 12
5.1. Capability Announcement . . . . . . . . . . . . . . . . . 12
5.1.1. Reacting Node Behavior . . . . . . . . . . . . . . . 13
5.1.2. Reporting Node Behavior . . . . . . . . . . . . . . . 13
5.1.3. Agent Behavior . . . . . . . . . . . . . . . . . . . 14
5.2. Overload Report Processing . . . . . . . . . . . . . . . 15
5.2.1. Overload Control State . . . . . . . . . . . . . . . 15
5.2.2. Reacting Node Behavior . . . . . . . . . . . . . . . 19
5.2.3. Reporting Node Behavior . . . . . . . . . . . . . . . 20
5.3. Protocol Extensibility . . . . . . . . . . . . . . . . . 22
6. Loss Algorithm . . . . . . . . . . . . . . . . . . . . . . . 22
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 23
6.2. Reporting Node Behavior . . . . . . . . . . . . . . . . . 23
6.3. Reacting Node Behavior . . . . . . . . . . . . . . . . . 24
7. Attribute Value Pairs . . . . . . . . . . . . . . . . . . . . 24
7.1. OC-Supported-Features AVP . . . . . . . . . . . . . . . . 25
7.2. OC-Feature-Vector AVP . . . . . . . . . . . . . . . . . . 25
7.3. OC-OLR AVP . . . . . . . . . . . . . . . . . . . . . . . 25
7.4. OC-Sequence-Number AVP . . . . . . . . . . . . . . . . . 26
7.5. OC-Validity-Duration AVP . . . . . . . . . . . . . . . . 26
7.6. OC-Report-Type AVP . . . . . . . . . . . . . . . . . . . 26
7.7. OC-Reduction-Percentage AVP . . . . . . . . . . . . . . . 27
7.8. Attribute Value Pair flag rules . . . . . . . . . . . . . 27
8. Error Response Codes . . . . . . . . . . . . . . . . . . . . 28
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
9.1. AVP codes . . . . . . . . . . . . . . . . . . . . . . . . 28
9.2. New registries . . . . . . . . . . . . . . . . . . . . . 29
10. Security Considerations . . . . . . . . . . . . . . . . . . . 29
10.1. Potential Threat Modes . . . . . . . . . . . . . . . . . 30
10.2. Denial of Service Attacks . . . . . . . . . . . . . . . 31
10.3. Non-Compliant Nodes . . . . . . . . . . . . . . . . . . 31
10.4. End-to End-Security Issues . . . . . . . . . . . . . . . 32
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 33
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
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12.1. Normative References . . . . . . . . . . . . . . . . . . 33
12.2. Informative References . . . . . . . . . . . . . . . . . 34
Appendix A. Issues left for future specifications . . . . . . . 34
A.1. Additional traffic abatement algorithms . . . . . . . . . 34
A.2. Agent Overload . . . . . . . . . . . . . . . . . . . . . 34
A.3. New Error Diagnostic AVP . . . . . . . . . . . . . . . . 35
Appendix B. Deployment Considerations . . . . . . . . . . . . . 35
Appendix C. Considerations for Applications Integrating the DOIC
Solution . . . . . . . . . . . . . . . . . . . . . . 35
C.1. Application Classification . . . . . . . . . . . . . . . 35
C.2. Application Type Overload Implications . . . . . . . . . 36
C.3. Request Transaction Classification . . . . . . . . . . . 38
C.4. Request Type Overload Implications . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40
1. Introduction
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.
2. Terminology and Abbreviations
Abatement
Reaction to receipt of an overload report resulting in a reduction
in traffic sent to the reporting node. Abatement actions include
diversion and throttling.
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Abatement Algorithm
An extensible method requested by reporting nodes and used by
reacting nodes to reduce the amount of traffic sent during an
occurrence of overload control.
Diversion
An overload abatement treatment where the reacting node selects
alternate destinations or paths for requests.
Host-Routed Requests
Requests that a reacting node knows will be served by a particular
host, either due to the presence of a Destination-Host Attribute
Value Pair (AVP), or by some other local knowledge on the part of
the reacting node.
Overload Control State (OCS)
Internal state maintained by a reporting or reacting node
describing occurrences of overload control.
Overload Report (OLR)
Overload control information for a particular overload occurrence
sent by a reporting node.
Reacting Node
A Diameter node that acts upon an overload report.
Realm-Routed Requests
Requests that a reacting node does not know which host will
service the request.
Reporting Node
A Diameter node that generates an overload report. (This may or
may not be the overloaded node.)
Throttling
An abatement treatment that limits the number of requests sent by
the reacting node. Throttling can include a Diameter Client
choosing to not send requests, or a Diameter Agent or Server
rejecting requests with appropriate error responses. In both
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cases the result of the throttling is a permanent rejection of the
transaction.
3. Conventions Used in This Document
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.
4. Solution Overview
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
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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.
4.1. Piggybacking
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.
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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.
4.2. DOIC Capability Announcement
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.
Note: As discussed elsewhere in the document, agents in the path
of the request can modify the OC-Supported-Features AVP.
Note: The DOIC solution must support deployments where Diameter
Clients and/or Diameter Servers do not support the DOIC solution.
In this scenario, Diameter Agents that support the DOIC solution
may handle overload abatement for the non-supporting Diameter
nodes. In this case the DOIC agent will insert the OC-Supported-
Features AVP in requests that do not already contain one, telling
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the reporting node that there is a DOIC node that will handle
overload abatement. For transactions where there was an OC-
Supporting-Features AVP in the request, the agent will insert the
OC-Supported-Features AVP in answers, telling the reacting node
that there is a reporting node.
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.
Note that the loss algorithm defined in this document is a
stateless abatement algorithm. As a result it does not require
any actions by reacting nodes prior to the receipt of an overload
report. Stateful abatement algorithms that base the abatement
logic on a history of request messages sent might require reacting
nodes to maintain state in advance of receiving an overload report
to ensure that the overload reports can be properly handled.
While it should only be done in exceptional circumstances and not
during an active occurrence of overload, a reacting node that wishes
to transition to a different abatement algorithm can stop advertising
support for the algorithm indicated by the reporting node, as long as
support for the loss algorithm is always advertised.
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.
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Note: The logic to determine if the content of the OC-Supported-
Features AVP should be changed is out-of-scope for this document,
as is the logic to determine the content of a modified OC-
Supported-Features AVP. These are left to implementation
decisions. Care must be taken not to introduce interoperability
issues for downstream or upstream DOIC nodes. As such, the agent
must act as a fully compliant reporting node to the downstream
reacting node and as a fully compliant reacting node to the
upstream reporting node.
4.3. DOIC Overload Condition Reporting
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.
Note: Known issues exist if multiple sources for overload reports
which apply to the same Diameter entity exist. Reacting nodes
have no way of determining the source and, as such, will treat
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them as coming from a single source. Variance in sequence numbers
between the two sources can then cause incorrect overload
abatement treatment to be applied for indeterminate periods of
time.
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
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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.
4.4. DOIC Extensibility
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.
4.5. Simplified Example Architecture
Figure 1 illustrates the simplified architecture for Diameter
overload information conveyance.
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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.
5. Solution Procedures
This section outlines the normative behavior for the DOIC solution.
5.1. Capability Announcement
This section defines DOIC Capability Announcement (DCA) behavior.
Note: This specification assumes that changes in DOIC node
capabilities are relatively rare events that occur as a result of
administrative action. Reacting nodes ought to minimize changes
that force the reporting node to change the features being used,
especially during active overload conditions. But even if
reacting nodes avoid such changes, reporting nodes still have to
be prepared for them to occur. For example, differing
capabilities between multiple reacting nodes may still force a
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reporting node to select different features on a per-transaction
basis.
5.1.1. Reacting Node 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.
Note: The loss abatement algorithm does not require stateful
behavior when there is no active overload report.
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.
5.1.2. Reporting Node Behavior
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.
Note: Capability announcement is done on a per transaction basis.
The reporting node cannot assume that the capabilities announced
by a reacting node will be the same between transactions.
A reporting node MUST NOT include the OC-Supported-Features AVP, OC-
OLR AVP or any other overload control AVPs defined in extension
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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 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.
Note: Not all DOIC features will apply to all Diameter
applications or deployment scenarios. The features included in
the OC-Feature-Vector AVP are based on local reporting node
policy.
5.1.3. Agent Behavior
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.
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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.
For instance, if the agent supports a superset of the features
reported by the reacting node then the agent might choose, based
on local policy, to advertise that superset of features to the
reporting node.
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.
5.2. Overload Report Processing
5.2.1. Overload Control State
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.
5.2.1.1. Overload Control State for Reacting Nodes
A reacting node maintains the following OCS per supported Diameter
application:
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o A host-type OCS entry for each Destination-Host to which it sends
host-type requests and
o A realm-type OCS entry for each Destination-Realm to which it
sends realm-type requests.
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):
o Sequence number (as received in OC-OLR, see Section 7.3)
o Time of expiry (derived from OC-Validity-Duration AVP received in
the OC-OLR AVP and time of reception of the message carrying OC-
OLR AVP)
o Selected Abatement Algorithm (as received in the OC-Supported-
Features AVP)
o Abatement Algorithm specific input data (as received in the OC-OLR
AVP, for example, OC-Reduction-Percentage for the Loss abatement
algorithm)
5.2.1.2. Overload Control State for Reporting Nodes
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):
o Sequence number
o Validity Duration
o Expiration Time
o Algorithm specific input data (for example, the Reduction
Percentage for the Loss Abatement Algorithm)
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5.2.1.3. Reacting Node Maintenance of Overload Control State
When a reacting node receives an OC-OLR AVP, it MUST determine if it
is for an existing or new overload condition.
Note: For the remainder of this section the term OLR refers to the
combination of the contents of the received OC-OLR AVP and the
abatement algorithm indicated in the received OC-Supported-
Features AVP.
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.
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Note: This solution assumes that the Origin-Host AVP in the answer
message included by the reporting node is not changed along the
path to the reacting node.
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.
Note: It is not necessarily appropriate to delete the OCS entry,
as there is recommended behavior that the reacting node slowly
returns to full traffic when ending an overload abatement period.
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").
5.2.1.4. Reporting Node Maintenance of Overload Control State
A reporting node SHOULD create a new OCS entry when entering an
overload condition.
Note: If a reporting node knows through absence of the OC-
Supported-Features AVP in received messages that there are no
reacting nodes supporting DOIC then the reporting node can choose
to not create OCS entries.
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.
Note: One way of addressing this over a reboot of a reporting node
is to use a time stamp for the first overload condition that
occurs after the report and to start using sequences beginning
with zero for subsequent overload conditions.
A reporting node MUST update an OCS entry when it needs to adjust the
validity duration of the overload condition at reacting nodes.
For instance, if a reporting node wishes to instruct reacting
nodes to continue overload abatement for a longer period of time
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than originally communicated. This also applies if the reporting
node wishes to shorten the period of time that overload abatement
is to continue.
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.
For instance, if a reporting node wishes to change the reduction
percentage either higher, if the overload condition has worsened,
or lower, if the overload condition has improved, then the
reporting node would update the appropriate OCS entry.
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.
Note: If a reporting node knows that the OCS entries in the
reacting nodes are near expiration then the reporting node might
decide not to send an OLR with a validity duration of zero.
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.
5.2.2. Reacting Node Behavior
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.
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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.
Note: This only addresses the case where there are two defined
abatement treatments, diversion and throttling. Any extension
that defines a new abatement treatment must also define the
interaction of the new abatement treatment with existing
treatments.
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.
5.2.3. Reporting Node Behavior
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.
Note: A request matches if the application-id in the request
matches the application-id in any active OCS entry and if the
report-type in the OCS entry matches a report-type supported by
the reporting node as indicated in the OC-Supported-Features AVP.
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.
Note: In some cases (e.g., when there are one or more agents in
the path between reporting and reacting nodes, or when overload
reports are discarded by reacting nodes) a reporting node may not
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be able to guarantee that the reacting node has received the
report.
A reporting node MUST NOT send overload reports of a type that has
not been advertised as supported by the reacting node.
Note: A reacting node implicitly advertises support for the host
and realm report types by including the OC-Supported-Features AVP
in the request. Support for other report types will be explicitly
indicated by new feature bits in the OC-Feature-Vector AVP.
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.
Note: All OLRs sent have an expiration time calculated by adding
the validity-duration contained in the OLR to the time the message
was sent. Transit time for the OLR can be safely ignored. The
reporting node can ensure that all reacting nodes have received
the OLR by continuing to send it in answer messages until the
expiration time for all OLRs sent for that overload condition have
expired.
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.
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For example, it might wait some period of time after overload ends
before terminating the OLR, or it might send a series of OLRs
indicating progressively less overload severity.
5.3. Protocol Extensibility
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.
6. Loss Algorithm
This section documents the Diameter overload loss abatement
algorithm.
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6.1. Overview
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.
1. An overload report is received and the associated OCS is either
saved or updated (if required) by the reacting node.
2. A new Diameter request is generated by the application running on
the reacting node.
3. The reacting node determines that an active overload report
applies to the request, as indicated by the corresponding OCS
entry.
4. The reacting node determines if overload abatement treatment
should be applied to the request. One approach that could be
taken for each request is to select a uniformly selected random
number between 1 and 100. If the random number is less than or
equal to the indicated reduction percentage then the request is
given abatement treatment, otherwise the request is given normal
routing treatment.
6.2. Reporting Node Behavior
The method a reporting node uses to determine the amount of traffic
reduction required to address an overload condition is an
implementation decision.
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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.
6.3. Reacting Node Behavior
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.
Note: The loss algorithm is a stateless algorithm. As a result,
the reacting node does not guarantee that there will be an
absolute reduction in traffic sent. Rather, it guarantees that
the requested percentage of new requests will be given abatement
treatment.
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.
The goal of this behavior is to reduce the probability of overload
condition thrashing where an immediate transition from 100%
reduction to 0% reduction results in the reporting node moving
quickly back into an overload condition.
7. Attribute Value Pairs
This section describes the encoding and semantics of the Diameter
Overload Indication Attribute Value Pairs (AVPs) defined in this
document.
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Refer to section 4 of [RFC6733] for more information on AVPs and AVP
data types.
7.1. OC-Supported-Features AVP
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 ]
7.2. 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:
OLR_DEFAULT_ALGO (0x0000000000000001)
When this flag is set by the a DOIC reacting node it means that
the default traffic abatement (loss) algorithm is supported. When
this flag is set by a DOIC reporting node it means that the loss
algorithm will be used for requested overload abatement.
7.3. OC-OLR AVP
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
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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 ]
7.4. OC-Sequence-Number 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.
7.5. OC-Validity-Duration AVP
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.
7.6. OC-Report-Type AVP
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:
HOST_REPORT 0 The overload report is for a host. Overload abatement
treatment applies to host-routed requests.
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REALM_REPORT 1 The overload report is for a realm. Overload
abatement treatment applies to realm-routed requests.
7.7. OC-Reduction-Percentage AVP
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.
7.8. Attribute Value Pair flag rules
+---------+
|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.
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8. Error Response Codes
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.
Note: This only applies for DOIC nodes that are not the originator
of the request.
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.
For instance, if the request arrived at the reporting node without
a Destination-Host AVP then the reporting node might determine
that there is an alternative Diameter node that could successfully
process the request and that retrying the transaction would not
negatively impact the reporting node. DIAMETER_TOO_BUSY would be
sent in this case.
If the request arrived at the reporting node with a Destination-
Host AVP populated with its own Diameter identity then the
reporting node can assume that retrying the request would result
in it coming to the same reporting node.
DIAMETER_UNABLE_TO_COMPLY would be sent in this case.
A second example is when an agent that supports the DOIC solution
is performing the role of a reacting node for a non-supporting
client. Requests that are rejected as a result of DOIC throttling
by the agent in this scenario would generally be rejected with a
DIAMETER_UNABLE_TO_COMPLY response code.
9. IANA Considerations
9.1. AVP codes
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.
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9.2. New registries
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:
Feature Vector Value Name
Feature Vector Value
Specification - the specification that defines the new value.
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:
Report Type Value Name
Report Type Value
Specification - the specification that defines the new value.
See Section 7.6 for the initial assignment in the registry. New
types can be added using the Specification Required policy [RFC5226].
10. Security Considerations
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.
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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.
10.1. Potential Threat Modes
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
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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.
This attack is partially mitigated by the fact that the
application, as well as host and realm, for a given OLR is
determined implicitly by respective AVPs in the enclosing answer.
If a reporting node modifies any of those AVPs, the enclosing
transaction will also be affected.
10.2. Denial of Service Attacks
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.
10.3. Non-Compliant Nodes
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
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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.
10.4. End-to End-Security Issues
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.
A DOIC node cannot always automatically detect that a peer also
supports DOIC. For example, a node might have a peer that is a
non-supporting agent. If nodes on the other side of that agent
send OC-Supported-Features AVPs, the agent is likely to forward
them as unknown AVPs. Messages received across the non-supporting
agent may be indistinguishable from messages received across a
DOIC supporting agent, giving the false impression that the non-
supporting agent actually supports DOIC. This complicates the
transitive-trust nature of DOIC. Operators need to be careful to
avoid situations where a non-supporting agent is mistakenly
trusted to enforce DOIC related authorization policies.
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
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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.
11. Contributors
The following people contributed substantial ideas, feedback, and
discussion to this document:
o Eric McMurry
o Hannes Tschofenig
o Ulrich Wiehe
o Jean-Jacques Trottin
o Maria Cruz Bartolome
o Martin Dolly
o Nirav Salot
o Susan Shishufeng
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[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,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
Ed., "Diameter Base Protocol", RFC 6733,
DOI 10.17487/RFC6733, October 2012,
<http://www.rfc-editor.org/info/rfc6733>.
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12.2. Informative References
[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",
draft-ietf-dime-e2e-sec-req-01 (work in progress), 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,
<http://www.rfc-editor.org/info/rfc4006>.
[RFC7068] McMurry, E. and B. Campbell, "Diameter Overload Control
Requirements", RFC 7068, DOI 10.17487/RFC7068, November
2013, <http://www.rfc-editor.org/info/rfc7068>.
[S13] 3GPP, , "ETSI TS 129 272 V11.9.0", December 2012.
Appendix A. Issues left for future specifications
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.
A.1. Additional traffic abatement algorithms
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.
A.2. Agent Overload
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.
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A.3. New Error Diagnostic AVP
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.
Appendix B. Deployment Considerations
Non-Supporting Agents
Due to the way that realm-routed requests are handled in Diameter
networks with the server selection for the request done by an
agent, network operators should enable DOIC at agents that perform
server selection first.
Topology Hiding Interactions
There exist proxies that implement what is referred to as Topology
Hiding. This can include cases where the agent modifies the
Origin-Host in answer messages. The behavior of the DOIC solution
is not well understood when this happens. As such, the DOIC
solution does not address this scenario.
Inter Realm/Administrative Domain Considerations
There are likely to be special considerations for handling DOIC
signaling across administrative boundaries. This includes
considerations for whether or not information included in the DOIC
signaling should be sent across those boundaries. In addition
consideration should be taken as to whether or not a reacting node
in one realm can be trusted to implement the requested overload
abatement handling for overload reports received from a separately
administered realm.
Appendix C. Considerations for Applications Integrating the DOIC
Solution
This section outlines considerations to be taken into account when
integrating the DOIC solution into Diameter applications.
C.1. Application Classification
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.
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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:
Stateless Applications:
Requests within a stateless application have no relationship to
each other. The 3GPP defined S13 application is an example of a
stateless application [S13], where only a Diameter command is
defined between a client and a server and no state is maintained
between two consecutive transactions.
Pseudo-Session Applications:
Applications that do not rely on the Session-Id AVP for
correlation of application messages related to the same session
but use other session-related information in the Diameter requests
for this purpose. The 3GPP defined Cx application [Cx] is an
example of a pseudo-session application.
The handling of overload reports must take the type of application
into consideration, as discussed in Appendix C.2.
C.2. Application Type Overload Implications
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
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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.
Stateless Applications:
By definition there is no relationship between individual requests
in a stateless application. As a result, when a request is sent
or relayed to an overloaded Diameter entity - either a Diameter
Server or a Diameter Agent - the sending or relaying entity can
choose to apply the overload treatment to any request targeted for
the overloaded entity.
Pseudo-Session Applications:
For pseudo-session applications, there is an implied ordering of
requests. As a result, decisions about which requests towards an
overloaded entity to reject could take the command code of the
request into consideration. This generally means that
transactions later in the sequence of transactions should be given
more favorable treatment than messages earlier in the sequence.
This is because more work has already been done by the Diameter
network for those transactions that occur later in the sequence.
Rejecting them could result in increasing the load on the network
as the transactions earlier in the sequence might also need to be
repeated.
Session-Based Applications:
Overload handling for session-based applications must take into
consideration the work load associated with setting up and
maintaining a session. As such, the entity sending requests
towards an overloaded Diameter entity for a session-based
application might tend to reject new session requests prior to
rejecting intra-session requests. In addition, session ending
requests might be given a lower probability of being rejected as
rejecting session ending requests could result in session status
being out of sync between the Diameter clients and servers.
Application designers that would decide to reject mid-session
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requests will need to consider whether the rejection invalidates
the session and any resulting session cleanup procedures.
C.3. Request Transaction Classification
Independent Request:
An independent request is not correlated to any other requests
and, as such, the lifetime of the session-id is constrained to an
individual transaction.
Session-Initiating Request:
A session-initiating request is the initial message that
establishes a Diameter session. The ACR message defined in
[RFC6733] is an example of a session-initiating request.
Correlated Session-Initiating Request:
There are cases when multiple session-initiated requests must be
correlated and managed by the same Diameter server. It is notably
the case in the 3GPP PCC architecture [PCC], where multiple
apparently independent Diameter application sessions are actually
correlated and must be handled by the same Diameter server.
Intra-Session Request:
An intra-session request is a request that uses the same Session-
Id than the one used in a previous request. An intra-session
request generally needs to be delivered to the server that handled
the session creating request for the session. The STR message
defined in [RFC6733] is an example of an intra-session request.
Pseudo-Session Requests:
Pseudo-session requests are independent requests and do not use
the same Session-Id but are correlated by other session-related
information contained in the request. There exists Diameter
applications that define an expected ordering of transactions.
This sequencing of independent transactions results in a pseudo
session. The AIR, MAR and SAR requests in the 3GPP defined Cx
[Cx] application are examples of pseudo-session requests.
C.4. Request Type Overload Implications
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
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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.
Independent Requests:
Independent requests can generally be given equal treatment when
making throttling decisions, unless otherwise indicated by
application requirements or local policy.
Session-Initiating Requests:
Session-initiating requests often represent more work than
independent or intra-session requests. Moreover, session-
initiating requests are typically followed by other session-
related requests. Since the main objective of the overload
control is to reduce the total number of requests sent to the
overloaded entity, throttling decisions might favor allowing
intra-session requests over session-initiating requests. In the
absence of local policies or application specific requirements to
the contrary, Individual session-initiating requests can be given
equal treatment when making throttling decisions.
Correlated Session-Initiating Requests:
A Request that results in a new binding, where the binding is used
for routing of subsequent session-initiating requests to the same
server, represents more work load than other requests. As such,
these requests might be throttled more frequently than other
request types.
Pseudo-Session Requests:
Throttling decisions for pseudo-session requests can take into
consideration where individual requests fit into the overall
sequence of requests within the pseudo session. Requests that are
earlier in the sequence might be throttled more aggressively than
requests that occur later in the sequence.
Intra-Session Requests:
There are two types of intra-sessions requests, requests that
terminate a session and the remainder of intra-session requests.
Implementers and operators may choose to throttle session-
terminating requests less aggressively in order to gracefully
terminate sessions, allow cleanup of the related resources (e.g.,
session state) and avoid the need for additional intra-session
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requests. Favoring session-termination requests may reduce the
session management impact on the overloaded entity. The default
handling of other intra-session requests might be to treat them
equally when making throttling decisions. There might also be
application level considerations whether some request types are
favored over others.
Authors' Addresses
Jouni Korhonen (editor)
Broadcom
Porkkalankatu 24
Helsinki FIN-00180
Finland
Email: jouni.nospam@gmail.com
Steve Donovan (editor)
Oracle
7460 Warren Parkway
Frisco, Texas 75034
United States
Email: srdonovan@usdonovans.com
Ben Campbell
Oracle
7460 Warren Parkway
Frisco, Texas 75034
United States
Email: ben@nostrum.com
Lionel Morand
Orange Labs
38/40 rue du General Leclerc
Issy-Les-Moulineaux Cedex 9 92794
France
Phone: +33145296257
Email: lionel.morand@orange.com
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