Diameter Overload Indication Conveyance
draft-ietf-dime-ovli-04
The information below is for an old version of the document.
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| Authors | Jouni Korhonen , Steve Donovan , Ben Campbell , Lionel Morand | ||
| Last updated | 2014-10-27 | ||
| Replaces | draft-docdt-dime-ovli | ||
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draft-ietf-dime-ovli-04
Diameter Maintenance and Extensions (DIME) J. Korhonen, Ed.
Internet-Draft Broadcom
Intended status: Standards Track S. Donovan, Ed.
Expires: April 30, 2015 B. Campbell
Oracle
L. Morand
Orange Labs
October 27, 2014
Diameter Overload Indication Conveyance
draft-ietf-dime-ovli-04.txt
Abstract
This specification documents a Diameter Overload Control (DOC) base
solution and the dissemination of the overload report information.
Requirements
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].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 30, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Abbreviations . . . . . . . . . . . . . . . . 3
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Piggybacking Principle . . . . . . . . . . . . . . . . . 7
3.2. DOIC Capability Announcement . . . . . . . . . . . . . . 8
3.3. DOIC Overload Condition Reporting . . . . . . . . . . . . 9
3.4. DOIC Extensibility . . . . . . . . . . . . . . . . . . . 10
3.5. Simplified Example Architecture . . . . . . . . . . . . . 11
4. Solution Procedures . . . . . . . . . . . . . . . . . . . . . 12
4.1. Capability Announcement . . . . . . . . . . . . . . . . . 12
4.1.1. Reacting Node Behavior . . . . . . . . . . . . . . . 12
4.1.2. Reporting Node Behavior . . . . . . . . . . . . . . . 12
4.1.3. Agent Behavior . . . . . . . . . . . . . . . . . . . 13
4.2. Overload Report Processing . . . . . . . . . . . . . . . 14
4.2.1. Overload Control State . . . . . . . . . . . . . . . 14
4.2.2. Reacting Node Behavior . . . . . . . . . . . . . . . 18
4.2.3. Reporting Node Behavior . . . . . . . . . . . . . . . 18
4.3. Protocol Extensibility . . . . . . . . . . . . . . . . . 20
5. Loss Algorithm . . . . . . . . . . . . . . . . . . . . . . . 21
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2. Reporting Node Behavior . . . . . . . . . . . . . . . . . 22
5.3. Reacting Node Behavior . . . . . . . . . . . . . . . . . 22
6. Attribute Value Pairs . . . . . . . . . . . . . . . . . . . . 23
6.1. OC-Supported-Features AVP . . . . . . . . . . . . . . . . 23
6.2. OC-Feature-Vector AVP . . . . . . . . . . . . . . . . . . 24
6.3. OC-OLR AVP . . . . . . . . . . . . . . . . . . . . . . . 24
6.4. OC-Sequence-Number AVP . . . . . . . . . . . . . . . . . 25
6.5. OC-Validity-Duration AVP . . . . . . . . . . . . . . . . 25
6.6. OC-Report-Type AVP . . . . . . . . . . . . . . . . . . . 25
6.7. OC-Reduction-Percentage AVP . . . . . . . . . . . . . . . 26
6.8. Attribute Value Pair flag rules . . . . . . . . . . . . . 27
7. Error Response Codes . . . . . . . . . . . . . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
8.1. AVP codes . . . . . . . . . . . . . . . . . . . . . . . . 28
8.2. New registries . . . . . . . . . . . . . . . . . . . . . 28
9. Security Considerations . . . . . . . . . . . . . . . . . . . 29
9.1. Potential Threat Modes . . . . . . . . . . . . . . . . . 29
9.2. Denial of Service Attacks . . . . . . . . . . . . . . . . 30
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9.3. Non-Compliant Nodes . . . . . . . . . . . . . . . . . . . 30
9.4. End-to End-Security Issues . . . . . . . . . . . . . . . 31
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 32
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
11.1. Normative References . . . . . . . . . . . . . . . . . . 32
11.2. Informative References . . . . . . . . . . . . . . . . . 32
Appendix A. Issues left for future specifications . . . . . . . 33
A.1. Additional traffic abatement algorithms . . . . . . . . . 33
A.2. Agent Overload . . . . . . . . . . . . . . . . . . . . . 33
A.3. New Error Diagnostic AVP . . . . . . . . . . . . . . . . 33
Appendix B. Deployment Considerations . . . . . . . . . . . . . 34
Appendix C. Requirements Conformance Analysis . . . . . . . . . 34
Appendix D. Considerations for Applications Integrating the DOIC
Solution . . . . . . . . . . . . . . . . . . . . . . 34
D.1. Application Classification . . . . . . . . . . . . . . . 34
D.2. Application Type Overload Implications . . . . . . . . . 35
D.3. Request Transaction Classification . . . . . . . . . . . 36
D.4. Request Type Overload Implications . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
1. Introduction
This specification defines a base solution for Diameter Overload
Control (DOC), referred to as Diameter Overload Indication Conveyance
(DOIC). The requirements for the solution are described and
discussed in the corresponding design requirements document
[RFC7068]. Note that the overload control solution defined in this
specification does not address all the requirements listed in
[RFC7068]. A number of overload control related features are left
for the future specifications. See Appendix A for a list of
extensions that are currently being considered. See Appendix C for
an analysis of the conformance to the requirements specified in
[RFC7068].
The solution defined in this specification addresses Diameter
overload control between Diameter nodes that support the DOIC
solution. Furthermore, the solution which is designed to apply to
existing and future Diameter applications, requires no changes to the
Diameter base protocol [RFC6733] and is deployable in environments
where some Diameter nodes do not implement the Diameter overload
control solution defined in this specification.
2. Terminology and Abbreviations
Abatement
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Reaction to receipt of an overload report resulting in a reduction
in traffic sent to the reporting node. Abatement actions include
diversion and throttling.
Abatement Algorithm
An mechanism requested by reporting nodes and used by reacting
nodes to reduce the amount of traffic sent during an occurrence of
overload control.
Diversion
Abatement of traffic sent to a reporting node by a reacting node
in response to receipt of an overload report. The abatement is
achieved by diverting traffic from the reporting node to another
Diameter node that is able to process the request.
Host-Routed Request
The set of requests that a reacting node knows will be served by a
particular host, either due to the presence of a Destination-Host
AVP, or by some other local knowledge on the part of the reacting
node.
Overload Control State (OCS)
Reporting and reacting node internally maintained state describing
occurrences of overload control.
Overload Report (OLR)
Information sent by a reporting node indicating the start,
continuation or end of an occurrence of overload control.
Reacting Node
A Diameter node that acts upon an overload report.
Realm-Routed Request
The set of requests that a reacting node does not know the host
that will service the request.
Reporting Node
A Diameter node that generates an overload report. (This may or
may not be the overloaded node.)
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Throttling
Throttling is the reduction of the number of requests sent to an
entity. Throttling can include a Diameter Client or Diameter
Server dropping requests, or a Diameter Agent rejecting requests
with appropriate error responses. In extreme cases reporting
nodes can also throttle requests when the requested reductions in
traffic does not sufficiently address the overload scenario.
3. Solution Overview
The Diameter Overload Information Conveyance (DOIC) solution allows
Diameter nodes to request other nodes to perform overload abatement
actions, that is, actions to reduce the load offered to the
overloaded node or realm.
A Diameter node that supports DOIC is known as a "DOIC node". Any
Diameter node can act as a DOIC node, including clients, servers, and
agents. DOIC nodes are further divided into "Reporting Nodes" and
"Reacting Nodes." A reporting node requests overload abatement by
sending an Overload Report (OLR) to one or more reacting nodes.
A reacting node acts upon OLRs, and performs whatever actions are
needed to fulfil the abatement requests included in the OLRs. A
Reporting node may report overload on its own behalf, or on behalf of
other (typically upstream) nodes. Likewise, a reacting node may
perform overload abatement on its own behalf, or on behalf of other
(typically downstream) nodes.
A node's role as a DOIC node is independent of its Diameter role.
For example, Diameter Relay and Proxy Agents may act as DOIC nodes,
even though they are not endpoints in the Diameter sense. Since
Diameter enables bi-directional applications, where Diameter Servers
can send requests towards Diameter Clients, a given Diameter node can
simultaneously act as a reporting node and a reacting node.
Likewise, a relay or proxy agent may act as a reacting node from the
perspective of upstream nodes, and a reporting node from the
perspective of downstream nodes.
DOIC nodes do not generate new messages to carry DOIC related
information. Rather, they "piggyback" DOIC information over existing
Diameter messages by inserting new AVPs into existing Diameter
requests and responses. Nodes indicate support for DOIC, and any
needed DOIC parameters by inserting an OC_Supported_Features AVP
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(Section 6.2) into existing requests and responses. Reporting nodes
send OLRs by inserting OC-OLR AVPs (Section 6.3).
A given OLR applies to the Diameter realm and application of the
Diameter message that carries it. If a reporting node supports more
than one realm and/or application, it reports independently for each
combination of realm and application. Similarly, the OC-Supported-
Features AVP applies to the realm and application of the enclosing
message. This implies that a node may support DOIC for one
application and/or realm, but not another, and may indicate different
DOIC parameters for each application and realm for which it supports
DOIC.
Reacting nodes perform overload abatement according to an agreed-upon
abatement algorithm. An abatement algorithm defines the meaning of
the parameters of an OLR and the procedures required for overload
abatement. This document specifies a single must-support algorithm,
namely the "loss" algorithm (Section 5). Future specifications may
introduce new algorithms.
Overload conditions may vary in scope. For example, a single
Diameter node may be overloaded, in which case reacting nodes may
reasonably attempt to send requests to other destinations or via
other agents. On the other hand, an entire Diameter realm may be
overloaded, in which case such attempts would do harm. DOIC OLRs
have a concept of "report type" (Section 6.6), where the type defines
such behaviors. Report types are extensible. This document defines
report types for overload of a specific server, and for overload of
an entire realm.
A report of type host is sent to indicate the overload of a specific
server for the application-id indicated in the transaction. When
receiving an OLR of type host, a reacting node applies overload
abatement to what is referred to in this document as host-routed
requests. This is the set of requests that the reacting node knows
will be served by a particular host, either due to the presence of a
Destination-Host AVP, or by some other local knowledge on the part of
the reacting node. The reacting node applies overload abatement on
those host-routed requests which the reacting node knows will be
served by the server that matches the Origin-Host AVP of the received
message that contained the received OLR of type host.
A report type of realm is sent to indicate the overload of all
servers in a realm for the application-id. When receiving an OLR of
type realm, a reacting node applies overload abatement to what is
referred to in this document as realm-routed requests. This is the
set of requests that are not host-routed as defined in the previous
paragraph.
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While a reporting node sends OLRs to "adjacent" reacting nodes, nodes
that are "adjacent" for DOIC purposes may not be adjacent from a
Diameter, or transport, perspective. For example, one or more
Diameter agents that do not support DOIC may exist between a given
pair of reporting and reacting nodes, as long as those agents pass
unknown AVPs through unchanged. The report types described in this
document can safely pass through non-supporting agents. This may not
be true for report types defined in future specifications. Documents
that introduce new report types MUST describe any limitations on
their use across non-supporting agents.
3.1. Piggybacking Principle
The overload control AVPs defined in this specification have been
designed to be piggybacked on top of existing application messages.
This is made possible by adding overload control top-level AVPs, the
OC-OLR AVP and the OC-Supported-Features AVP, as optional AVPs into
existing commands when the corresponding Command Code Format (CCF)
specification allows adding new optional AVPs (see Section 1.3.4 of
[RFC6733]).
Reacting nodes indicate support for DOIC by including the OC-
Supported-Features AVP in all request messages originated or relayed
by the reacting node.
Reporting nodes indicate support for DOIC by including the OC-
Supported-Features AVP in all answer messages originated or relayed
by the reporting node. Reporting nodes also include overload reports
using the OC-OLR AVP in answer messages.
Note: There is no new Diameter application defined to carry
overload related AVPs. The DOIC AVPs are carried in existing
Diameter application messages.
Note that the overload control solution does not have fixed server
and client roles. The DOIC node role is determined based on the
message type: whether the message is a request (i.e. sent by a
"reacting node") or an answer (i.e. send by a "reporting node").
Therefore, in a typical "client-server" deployment, the Diameter
Client MAY report its overload condition to the Diameter Server for
any Diameter Server initiated message exchange. An example of such
is the Diameter Server requesting a re-authentication from a Diameter
Client.
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3.2. 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 solution uses the OC-Supported-Features AVPs to indicate the
Diameter overload features supported.
The first node in the path of a Diameter request that supports the
DOIC solution inserts the OC-Supported-Feature AVP in the request
message. This includes an indication that it supports the loss
overload abatement algorithm defined in this specification (see
Section 5). This ensures that there is at least one commonly
supported overload abatement algorithm between the reporting node and
the reacting nodes in the path of the request.
DOIC must support deployments where Diameter Clients and/or
Diameter Servers do not support the DOIC solution. In this
scenario, it is assumed that Diameter Agents that support the DOIC
solution will handle overload abatement for the non supporting
Diameter nodes. In this case the DOIC agent will insert the OC-
Supporting-Features AVP in requests that do not already contain
one, telling the reporting node that there is a DOIC node that
will handle overload abatement.
The reporting node inserts the OC-Supported-Feature AVP in all answer
messages to requests that contained the OC-Supported-Feature AVP.
The contents of the reporting node's OC-Supported-Feature AVP
indicate the set of Diameter overload features supported by the
reporting node with one exception.
The reporting node only includes an indication of support for one
overload abatement algorithm. This is the algorithm that the
reporting node intends to use should it enter an overload condition
or requests to use while it actually is in an overload condition.
Reacting nodes can use the indicated overload abatement algorithm to
prepare for possible overload reports and must use the indicated
overload abatement algorithm if traffic reduction is actually
requested.
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
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nodes to maintain state to ensure that overload reports can be
properly handled.
The individual features supported by the DOIC nodes are indicated in
the OC-Feature-Vector AVP. Any semantics associated with the
features will be defined in extension specifications that introduce
the features.
The DCA mechanism must also support the scenario where the set of
features supported by the sender of a request and by agents in the
path of a request differ. In this case, the agent updates the OC-
Supported-Feature AVP to reflect the mixture of the two sets of
supported features.
The logic to determine the content of the modified OC-Supported-
Feature AVP is out-of-scope for this specification and is left to
implementation decisions. Care must be taken not to introduce
interoperability issues for downstream or upstream DOIC nodes.
3.3. DOIC Overload Condition Reporting
As with DOIC Capability Announcement, Overload Condition Reporting
uses new AVPs (Section 6.3) to indicate an overload condition.
The OC-OLR AVP is referred to as an overload report. The OC-OLR AVP
includes the type of report, a sequence number, the length of time
that the report is valid and abatement algorithm specific AVPs.
Two types of overload reports are defined in this document, host
reports and realm reports.
A report of type host is sent to indicate the overload of a specific
Diameter node for the application-id indicated in the transaction.
When receiving an OLR of type host, a reacting node applies overload
abatement to what is referred to in this document as host-routed
requests. This is the set of requests that the reacting node knows
will be served by a particular host, either due to the presence of a
Destination-Host AVP, or by some other local knowledge on the part of
the reacting node. The reacting node applies overload abatement on
those host-routed requests which the reacting node knows will be
served by the server that matches the Origin-Host AVP of the received
message that contained the received OLR of type host.
Realm reports apply to realm-routed requests for a specific realm as
indicated in the Destination-Realm AVP.
Reporting nodes are responsible for determining the need for a
reduction of traffic. The method for making this determination is
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implementation specific and depend on the type of overload report
being generated. A host report, for instance, will generally be
generated by tracking utilization of resources required by the host
to handle transactions for the Diameter application. A realm report
will generally impact the traffic sent to multiple hosts and, as
such, will typically require tracking the capacity of the servers
able to handle realm-routed requests for the application.
Once a reporting node determines the need for a reduction in traffic,
it uses the DOIC defined AVPs to report on the condition. These AVPs
are included in answer messages sent or relayed by the reporting
node. The reporting node indicates the overload abatement algorithm
that is to be used to handle the traffic reduction in the OC-
Supported-Features AVP. The OC-OLR AVP is used to communicate
information about the requested reduction.
Reacting nodes, upon receipt of an overload report, are responsible
for applying the abatement algorithm to traffic impacted by the
overload report. The method used for that abatement is dependent on
the abatement algorithm. The loss abatement algorithm is defined in
this document (Section 5). Other abatement algorithms can be defined
in extensions to the DOIC solutions.
As the conditions that lead to the generation of the overload report
change the reporting node can send new overload reports requesting
greater reduction if the condition gets worse or less reduction if
the condition improves. The reporting node sends an overload report
with a duration of zero to indicate that the overload condition has
ended and use of the abatement algorithm is no longer needed.
The reacting node also determines when the overload report expires
based on the OC-Validity-Duration AVP in the overload report and
stops applying the abatement algorithm when the report expires.
3.4. DOIC Extensibility
The DOIC solution is designed to be extensible. This extensibility
is based on existing Diameter based extensibility mechanisms.
There are multiple categories of extensions that are expected. This
includes the definition of new overload abatement algorithms, the
definition of new report types and new definitions of the scope of
messages impacted by an overload report.
The DOIC solution uses the OC-Supported-Features AVP for DOIC nodes
to communicate supported features. The specific features supported
by the DOIC node are indicated in the OC-Feature-Vector AVP. DOIC
extensions must define new values for the OC-Feature-Vector AVP.
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DOIC extensions also have the ability to add new AVPs to the OC-
Supported-Features AVP, if additional information about the new
feature is required.
Reporting nodes use the OC-OLR AVP to communicate overload
occurrences. This AVP can also be extended to add new AVPs allowing
a reporting nodes to communicate additional information about
handling an overload condition.
If necessary, new extensions can also define new top-level AVPs. It
is, however, recommended that DOIC extensions use the OC-Supported-
Features and OC-OLR to carry all DOIC related AVPs.
3.5. Simplified Example Architecture
Figure 1 illustrates the simplified architecture for Diameter
overload information conveyance.
Realm X Same or other Realms
<--------------------------------------> <---------------------->
+--^-----+ : (optional) :
|Diameter| : :
|Server A|--+ .--. : +---^----+ : .--.
+--------+ | _( `. : |Diameter| : _( `. +---^----+
+--( )--:-| Agent |-:--( )--|Diameter|
+--------+ | ( ` . ) ) : +-----^--+ : ( ` . ) ) | Client |
|Diameter|--+ `--(___.-' : : `--(___.-' +-----^--+
|Server B| : :
+---^----+ : :
End-to-end Overload Indication
1) <----------------------------------------------->
Diameter Application Y
Overload Indication A Overload Indication A'
2) <----------------------> <---------------------->
standard base protocol standard base protocol
Figure 1: Simplified architecture choices for overload indication
delivery
In Figure 1, the Diameter overload indication can be conveyed (1)
end-to-end between servers and clients or (2) between servers and
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Diameter agent inside the realm and then between the Diameter agent
and the clients.
4. Solution Procedures
This section outlines the normative behavior associated with the DOIC
solution.
4.1. Capability Announcement
This section defines DOIC Capability Announcement (DCA) behavior.
4.1.1. Reacting Node Behavior
A reacting node MUST include the OC-Supported-Features AVP in all
request messages.
A reacting node MAY include the OC-Feature-Vector AVP with an
indication of the loss algorithm. A reacting node MUST include the
OC-Feature-Vector AVP to indicate support for abatement algorithms in
addition to the loss algorithm.
A reacting node SHOULD indicate support for all other DOIC features
it supports.
Not all DOIC features will necessarily apply to all transactions.
For instance, there may be a future extension that only applies to
session based applications. A reacting node that supports this
extension can choose to not include it for non session based
applications.
An OC-Supported-Features AVP in answer messages indicates there is a
reporting node for the transaction. The reacting node MAY take
action based on the features indicated in the OC-Feature-Vector AVP.
Note that the loss abatement algorithm is the only feature
described in this document and it does not require action to be
taken when there is an active overload report. This behavior is
described in Section 4.2 and Section 5.
4.1.2. 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.
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If the request message contains an OC-Supported-Features AVP then the
reporting node MUST include the OC-Supported-Features AVP in the
answer message for that transaction.
The reporting node MUST NOT include the OC-Supported-Features AVP,
OC-OLR AVP or any other overload control AVPs defined in extension
drafts in response messages for transactions where the request
message does not include the OC-Supported-Features AVP. Lack of the
OC-Supported-Features AVP in the request message indicates that there
is no reacting node for the transaction.
Based on the content of the OC-Supported-Features AVP in the request
message, the reporting node knows what overload control functionality
is supported by the reacting node. The reporting node then acts
accordingly for the subsequent answer messages it initiates.
The reporting node MUST indicate support for one and only one
abatement algorithm in the OC-Feature-Vector AVP. The abatement
algorithm included MUST be from the set of abatement algorithms
contained in the request message's OC-Supported-Features AVP. The
abatement algorithm included MUST indicate the abatement algorithm
the reporting node wants the reacting node to use when the reporting
node enters an overload condition.
For an ongoing overload state, a reacting node MUST keep the
algorithm that was selected by the reporting node in further requests
towards the reporting node. The reporting node SHOULD NOT change the
selected algorithm during a period of time that it is in an overload
condition and, as a result, is sending OC-OLR AVPs in answer
messages.
The reporting node SHOULD indicate support for other DOIC features
defined in extension drafts that it supports and that apply to the
transaction.
Note that 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.
4.1.3. Agent Behavior
Diameter agents that support DOIC MUST ensure that all messages have
the OC-Supporting-Features AVP. If a message handled by the DOIC
agent does not include the OC-Supported-Features AVP then the DOIC
agent inserts the AVP. If the message already has the AVP then the
agent either leaves it unchanged in the relayed message or modifies
it to reflect a mixed set of DOIC features.
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An agent MAY modify the OC-Supported-Features AVP carried in answer
messages.
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 agent modifies the OC-Supported-Features AVP sent to the
reporting node then it might also need to modify the OC-Supported-
Features AVP sent to a reacting node in the subsequent answer
message, as it cannot send an indication of support for features
that are not supported by the reacting node.
Editor's note: There is an open issue on the wording around agent
behavior in this case that needs to be resolved prior to finishing
this document.
4.2. Overload Report Processing
4.2.1. Overload Control State
Both reacting and reporting nodes maintain Overload Control State
(OCS) for active overload conditions.
4.2.1.1. Overload Control State for Reacting Nodes
A reacting node SHOULD maintain the following OCS per supported
Diameter application:
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
Host-Id.
A realm-type OCS entry is identified by the pair of Application-Id
and Realm-Id.
The host-type and realm-type OCS entries MAY include the following
information (the actual information stored is an implementation
decision):
o Sequence number (as received in OC-OLR)
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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 OC-Supported-Features
AVP)
o Abatement Algorithm specific input data (as received within the
OC-OLR AVP, for example, OC-Reduction-Percentage for the Loss
abatement algorithm)
4.2.1.2. Overload Control State for Reporting Nodes
A reporting node SHOULD maintain OCS entries per supported Diameter
application, per supported (and eventually selected) Abatement
Algorithm and per report-type.
An OCS entry is identified by the pair of Application-Id and
Abatement Algorithm.
The OCS entry for a given pair of Application and Abatement Algorithm
MAY include the information (the actual information stored is an
implementation decision):
o Report type
o Sequence number
o Validity Duration
o Expiration Time
o Algorithm specific input data (for example, the Reduction
Percentage for the Loss Abatement Algorithm)
4.2.1.3. 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.
For the remainder of this section the term OLR referres to the
combination of the contents of the received OC-OLR AVP and the
abatement algorithm indicated in the received OC-Supported-
Features AVP.
The OLR is for an existing overload condition if the reacting node
has an OCS that matches the received OLR.
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For a host report-type this means it matches the app-id and host-id
in an existing host OCS entry.
For a realm report-type this means it matches the app-id and realm-id
in an existing realm OCS entry.
If the OLR is for an existing overload condition then it MUST
determine if the OLR is a retransmission or an update to the existing
OLR.
If the sequence number for the received OLR is greater than the
sequence number stored in the matching OCS entry then the reacting
node MUST update the matching OCS entry.
If the sequence number for the received OLR is less than or equal to
the sequence number in the matching OCS entry then the reacting node
MUST silently ignore the received OLR. The matching OCS MUST NOT be
updated in this case.
If the received OLR is for a new overload condition then the reacting
node MUST generate a new OCS entry for the overload condition.
For a host report-type this means it creates on OCS entry with the
app-id of the application-id in the received message and host-id of
the Origin-Host in the received message.
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-type this means it creates on OCS entry with the
app-id of the application-id in the received message and realm-id of
the Origin-Realm in the received message.
If the received OLR contains a validity duration of zero ("0") then
the reacting node MUST update the OCS entry as being expired.
Note that 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").
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4.2.1.4. Reporting Node Maintenance of Overload Control State
A reporting node SHOULD create a new OCS entry when entering an
overload condition.
If the 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 MAY be set to any
value if there is no unexpired overload report for previous overload
conditions sent to any reacting node for the same application and
report-type.
When generating sequence numbers for new overload conditions, the new
sequence number MUST be greater than any sequence number in an active
(unexpired) overload report previously sent by the reporting node.
This property MUST hold over a reboot of the reporting node.
The reporting node MUST update an OCS entry when it needs to adjust
the validity duration of the overload condition at reacting nodes.
For instance, if the reporting node wishes to instruct reacting
nodes to continue overload abatement for a longer period of time
that 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 NOT update the abatement algorithm in an active
OCS entry.
A reporting node MUST update an OCS entry when it wishes to adjust
any abatement algorithm specific parameters, including the reduction
percentage used for the Loss abatement algorithm.
For instance, if the 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.
The reporting node MUST update the sequence number associated with
the OCS entry anytime the contents of the OCS entry are changed.
This will result in a new sequence number being sent to reacting
nodes, instructing the reacting nodes to process the OC-OLR AVP.
A reporting node SHOULD update an OCS entry with a validity duration
of zero ("0") when the overload condition ends.
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If the reporting node knows that the OCS entries in the reacting
nodes are near expiration then the reporting node can decide to
delete the OCS entry.
The reporting node MUST keep an OCS entry with a validity duration of
zero ("0") for a period of time long enough to ensure that any non-
expired reacting node's OCS entry created as a result of the overload
condition in the reporting node is deleted.
4.2.2. Reacting Node Behavior
When a reacting node sends a request it MUST determine if that
request matches an active OCS.
If the request matches and active OCS then the reacting node MUST
apply abatement treatment on the request. The abatement treatment
applied depends on the abatement algorithm stored in the OCS.
For the Loss abatement algorithm defined in this specification, see
Section 5 for the abatement logic applied.
If the abatement treatment results in throttling of the request and
if the reacting node is an agent then the agent MUST send an
appropriate error as defined in section Section 7.
In the case that the OCS entry validity duration expires or has a
validity duration of zero ("0"), meaning that it the reporting node
has explicitly signaled the end of the overload condition then
abatement associated with the overload abatement MUST be ended in a
controlled fashion.
4.2.3. Reporting Node Behavior
The operation on the reporting node is straight forward.
If there is an active OCS entry then the reporting node SHOULD
include the OC-OLR AVP in all answer messages to requests that
contain the OC-Supported-Features AVP and that match the active OCS
entry.
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 MUST contain all information necessary
for the abatement algorithm indicated in the OC-Supported-Features
AVP that is also included in the answer message.
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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) the reporting node may
not 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 that a reacting node advertises support for the host and
realm report types by including the OC-Supported-Features AVP in
the request. Support for other report types must be explicitly
indicated by new feature bits in the OC-Feature-Vector AVP.
A reporting node MAY rely on the OC-Validity-Duration AVP values for
the implicit overload control state cleanup on the reacting node.
However, it is RECOMMENDED that the reporting node always explicitly
indicates the end of a overload condition.
The reporting node SHOULD indicate the end of an overload occurrence
by sending a new OLR with OC-Validity-Duration set to a value of zero
("0"). The reporting node SHOULD ensure that all reacting nodes
receive the updated overload report.
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. Therefore, the reporting
node SHOULD NOT apply throttling to the set of messages to which the
OLR applies. That is, the same candidate set of messages SHOULD NOT
be throttled multiple times.
However, when the reporting node sends and OLR downstream, it MAY
still be responsible to apply other abatement methods such as
diversion. The reporting node might also need to throttle requests
for reasons other then overload. For example, an agent or server
might have a configured rate limit for each client, and throttle
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requests that exceed that limit, even if such requests had already
been candidates for throttling by downstream nodes.
This document assumes that there is a single source for realm-reports
for a given realm, or that if multiple nodes can send realm reports,
that each such node has full knowledge of the overload state of the
entire realm. A reacting node cannot distinguish between receiving
realm-reports from a single node, or from multiple nodes.
Editor's Note: There is not yet consensus on the above two
paragraphs. Two alternatives are under consideration --
synchronization of sequence numbers and attribution of reports.
If no consensus is reached then it will be left to be addressed as
an extension.
4.3. Protocol Extensibility
The overload control solution can be extended, e.g. with new traffic
abatement algorithms, new report types or other new functionality.
When defining a new extension a new feature bit MUST be defined for
the OC-Feature-Vector. This feature bit is used to communicate
support for the new feature.
The extension MAY define new AVPs for use in DOIC Capability
Announcement and for use in DOIC Overload reporting. These new AVPs
SHOULD be defined to be extensions to the OC-Supported-Features and
OC-OLR AVPs defined in this document.
It should be noted that [RFC6733] defined Grouped AVP extension
mechanisms apply. This allows, for example, defining a new feature
that is mandatory to be understood even when piggybacked on an
existing application.
The handling of feature bits in the OC-Feature-Vector AVP that are
not associated with overload abatement algorithms MUST be specified
by the extensions that define the features.
When defining new report type values, the corresponding specification
MUST define the semantics of the new report types and how they affect
the OC-OLR AVP handling. The specification MUST also reserve a
corresponding new feature bit in the OC-Feature-Vector AVP.
The OC-OLR AVP can be expanded with optional sub-AVPs only if a
legacy DOIC implementation can safely ignore them without breaking
backward compatibility for the given OC-Report-Type AVP value. If
the new sub-AVPs imply new semantics for handling the indicated
report type, then a new OC-Report-Type AVP value MUST be defined.
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New features (feature bits in the OC-Feature-Vector AVP) and report
types (in the OC-Report-Type AVP) MUST be registered with IANA. As
with any Diameter specification, new AVPs MUST also be registered
with IANA. See Section 8 for the required procedures.
5. Loss Algorithm
This section documents the Diameter overload loss abatement
algorithm.
5.1. 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 4.1.
The loss algorithm described in this section is the default algorithm
that must be supported by all Diameter nodes that support DOIC.
The loss algorithm is designed to be a straightforward and stateless
overload abatement algorithm. It is used by reporting nodes to
request a percentage reduction in the amount of traffic sent. The
traffic impacted by the requested reduction depends on the type of
overload report.
Reporting nodes use a strategy of applying abatement logic to the
requested percentage of request messages sent (or handled in the case
of agents) by the reacting node that are impacted by the overload
report.
From a conceptual level, the logic at the reacting node could be
outlined as follows.
1. An overload report is received and the associated overload state
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 abatement should be applied to
the request. One approach that could be taken for each request
is to select a random number between 1 and 100. If the random
number is less than the indicated reduction percentage then the
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request is given abatement treatment, otherwise the request is
given normal routing treatment.
5.2. Reporting Node Behavior
The method a reporting nodes uses to determine the amount of traffic
reduction required to address an overload condition is an
implementation decision.
When a reporting node that has selected the loss abatement algorithm
determines the need to request a traffic reduction it includes an OC-
OLR AVP in response messages as described in Section 4.2.3.
The reporting node MUST indicate a percentage reduction in the OC-
Reduction-Percentage AVP.
The reporting node MAY change the reduction percentage in subsequent
overload reports. When doing so the reporting node must conform to
overload report handing specified in Section 4.2.3.
When the reporting node determines it no longer needs a reduction in
traffic the reporting node SHOULD send an overload report indicating
the overload report is no longer valid, as specified in
Section 4.2.3.
5.3. 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.
When applying overload abatement treatment for the load abatement
algorithm, the reacting node MUST abate, either by throttling or
diversion, the requested percentage of requests that would have
otherwise been sent to the reporting host or realm.
If reacting node comes out of the 100 percent traffic reduction as a
result of the overload report timing out, the following concerns are
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RECOMMENDED to be applied. The reacting node sending the traffic
should be conservative and, for example, first send "probe" messages
to learn the overload condition of the overloaded node before
converging to any traffic amount/rate decided by the sender. Similar
concerns apply in all cases when the overload report times out unless
the previous overload report stated 0 percent reduction.
If the reacting node does not receive an OLR in messages sent to the
formerly overloaded node then the reacting node SHOULD slowly
increase the rate of traffic sent to the overloaded node.
It is suggested that the reacting node decrease the amount of traffic
given abatement treatment by 20% each second until the reduction is
completely removed and no traffic is given abatement treatment.
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.
6. Attribute Value Pairs
This section describes the encoding and semantics of the Diameter
Overload Indication Attribute Value Pairs (AVPs) defined in this
document.
A new application specification can incorporate the overload control
mechanism specified in this document by making it mandatory to
implement for the application and referencing this specification
normatively. It is the responsibility of the Diameter application
designers to define how overload control mechanisms works on that
application.
6.1. OC-Supported-Features AVP
The OC-Supported-Features AVP (AVP code TBD1) is type of Grouped and
serves two purposes. First, it announces a node's support for the
DOIC solution in general. Second, it contains the description of the
supported DOIC features of the sending node. The OC-Supported-
Features AVP MUST be included in every Diameter request message a
DOIC supporting node sends.
OC-Supported-Features ::= < AVP Header: TBD1 >
[ OC-Feature-Vector ]
* [ AVP ]
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The OC-Feature-Vector sub-AVP is used to announce the DOIC features
supported by the DOIC node, in the form of a flag bits field in which
each bit announces one feature or capability supported by the node
(see Section 6.2). The absence of the OC-Feature-Vector AVP
indicates that only the default traffic abatement algorithm described
in this specification is supported.
6.2. OC-Feature-Vector AVP
The OC-Feature-Vector AVP (AVP code TBD6) is type of Unsigned64 and
contains a 64 bit flags field of announced capabilities of a DOIC
node. The value of zero (0) is reserved.
The following capabilities are defined in this document:
OLR_DEFAULT_ALGO (0x0000000000000001)
When this flag is set by the DOIC node it means that the default
traffic abatement (loss) algorithm is supported.
6.3. OC-OLR AVP
The OC-OLR AVP (AVP code TBD2) is type of Grouped and contains the
information necessary to convey an overload report on an overload
condition at the reporting node. The OC-OLR AVP does not explicitly
contain all information needed by the reacting node to decide whether
a subsequent request must undergo a throttling process with the
received reduction percentage. The value of the OC-Report-Type AVP
within the OC-OLR AVP indicates which implicit information is
relevant for this decision (see Section 6.6). The application the
OC-OLR AVP applies to is the same as the Application-Id found in the
Diameter message header. The host or realm the OC-OLR AVP concerns
is determined from the Origin-Host AVP and/or Origin-Realm AVP found
in the encapsulating Diameter command. The OC-OLR AVP is intended to
be sent only by a reporting node.
OC-OLR ::= < AVP Header: TBD2 >
< OC-Sequence-Number >
< OC-Report-Type >
[ OC-Reduction-Percentage ]
[ OC-Validity-Duration ]
* [ AVP ]
Note that if a Diameter command were to contain multiple OC-OLR AVPs
they all MUST have different OC-Report-Type AVP value. OC-OLR AVPs
with unknown values SHOULD be silently discarded by reacting nodes
and the event SHOULD be logged.
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6.4. OC-Sequence-Number AVP
The OC-Sequence-Number AVP (AVP code TBD3) is type of Unsigned64.
Its usage in the context of overload control is described in
Section 4.2.
From the functionality point of view, the OC-Sequence-Number AVP MUST
be used as a non-volatile increasing counter for a sequence of
overload reports between two DOIC nodes for the same overload
occurrence. The sequence number is only required to be unique
between two DOIC nodes. Sequence numbers are treated in a uni-
directional manner, i.e. two sequence numbers on each direction
between two DOIC nodes are not related or correlated.
6.5. OC-Validity-Duration AVP
The OC-Validity-Duration AVP (AVP code TBD4) is type of Unsigned32
and indicates in milliseconds the validity time of the overload
report. The number of milliseconds is measured after reception of
the first OC-OLR AVP with a given value of OC-Sequence-Number AVP.
The default value for the OC-Validity-Duration AVP is 5000 (i.e., 5
seconds). When the OC-Validity-Duration AVP is not present in the
OC-OLR AVP, the default value applies. Validity duration with values
above 86400 (i.e.; 24 hours) MUST NOT be used. Invalid duration
values are treated as if the OC-Validity-Duration AVP were not
present and result in the default value being used.
Editor's note: There is an open discussion on whether to have an
upper limit on the OC-Validity-Duration value, beyond that which can
be indicated by an Unsigned32.
A timeout of the overload report has specific concerns that need to
be taken into account by the DOIC node acting on the earlier received
overload report(s). Section 6.7 discusses the impacts of timeout in
the scope of the traffic abatement algorithms.
6.6. OC-Report-Type AVP
The OC-Report-Type AVP (AVP code TBD5) is type of Enumerated. The
value of the AVP describes what the overload report concerns. The
following values are initially defined:
0 A host report. The overload treatment should apply to requests
for which all of the following conditions are true:
Either the Destination-Host AVP is present in the request and its
value matches the value of the Origin-Host AVP of the received
message that contained the OC-OLR AVP; or the Destination-Host is
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not present in the request but the value of the peer identity
associated with the connection used to send the request matches
the value of the Origin-Host AVP of the received message that
contained the OC-OLR AVP.
The value of the Destination-Realm AVP in the request matches the
value of the Origin-Realm AVP of the received message that
contained the OC-OLR AVP.
The value of the Application-ID in the Diameter Header of the
request matches the value of the Application-ID of the Diameter
Header of the received message that contained the OC-OLR AVP.
1 A realm report. The overload treatment should apply to requests
for which all of the following conditions are true:
The Destination-Host AVP is absent in the requestand the value of
the peer identity associated with the connection used to send the
request does not match a server that could serve the request.
The value of the Destination-Realm AVP in the request matches the
value of the Origin-Realm AVP of the received message that
contained the OC-OLR AVP.
The value of the Application-ID in the Diameter Header of the
request matches the value of the Application-ID of the Diameter
Header of the received message that contained the OC-OLR AVP.
The OC-Report-Type AVP is envisioned to be useful for situations
where a reacting node needs to apply different overload treatments
for different overload contexts. For example, the reacting node(s)
might need to throttle differently requests sent to a specific server
(identified by the Destination-Host AVP in the request) and requests
that can be handled by any server in a realm.
6.7. OC-Reduction-Percentage AVP
The OC-Reduction-Percentage AVP (AVP code TBD8) is type of Unsigned32
and describes the percentage of the traffic that the sender is
requested to reduce, compared to what it otherwise would send. The
OC-Reduction-Percentage AVP applies to the default (loss) algorithm
specified in this specification. However, the AVP can be reused for
future abatement algorithms, if its semantics fit into the new
algorithm.
The value of the Reduction-Percentage AVP is between zero (0) and one
hundred (100). Values greater than 100 are ignored. The value of
100 means that all traffic is to be throttled, i.e. the reporting
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node is under a severe load and ceases to process any new messages.
The value of 0 means that the reporting node is in a stable state and
has no need for the reacting node to apply any traffic abatement.
The default value of the OC-Reduction-Percentage AVP is 0. When the
OC-Reduction-Percentage AVP is not present in the overload report,
the default value applies.
6.8. Attribute Value Pair flag rules
+---------+
|AVP flag |
|rules |
+----+----+
AVP Section | |MUST|
Attribute Name Code Defined Value Type |MUST| NOT|
+--------------------------------------------------+----+----+
|OC-Supported-Features TBD1 x.x Grouped | | V |
+--------------------------------------------------+----+----+
|OC-OLR TBD2 x.x Grouped | | V |
+--------------------------------------------------+----+----+
|OC-Sequence-Number TBD3 x.x Unsigned64 | | V |
+--------------------------------------------------+----+----+
|OC-Validity-Duration TBD4 x.x Unsigned32 | | V |
+--------------------------------------------------+----+----+
|OC-Report-Type TBD5 x.x Enumerated | | V |
+--------------------------------------------------+----+----+
|OC-Reduction | | |
| -Percentage TBD8 x.x Unsigned32 | | V |
+--------------------------------------------------+----+----+
|OC-Feature-Vector TBD6 x.x Unsigned64 | | V |
+--------------------------------------------------+----+----+
As described in the Diameter base protocol [RFC6733], the M-bit
setting for a given AVP is relevant to an application and each
command within that application that includes the AVP.
The Diameter overload control AVPs SHOULD always be sent with the
M-bit cleared when used within existing Diameter applications to
avoid backward compatibility issues. Otherwise, when reused in newly
defined Diameter applications, the DOC related AVPs SHOULD have the
M-bit set.
7. 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
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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.
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.
For instance, 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.
8. IANA Considerations
8.1. AVP codes
New AVPs defined by this specification are listed in Section 6. All
AVP codes allocated from the 'Authentication, Authorization, and
Accounting (AAA) Parameters' AVP Codes registry.
8.2. New registries
Two new registries are needed under the 'Authentication,
Authorization, and Accounting (AAA) Parameters' registry.
Section 6.2 defines a new "Overload Control Feature Vector" registry
including the initial assignments. New values can be added into the
registry using the Specification Required policy [RFC5226]. See
Section 6.2 for the initial assignment in the registry.
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Section 6.6 defines a new "Overload Report Type" registry with its
initial assignments. New types can be added using the Specification
Required policy [RFC5226].
9. Security Considerations
This mechanism gives Diameter nodes the ability to request that
downstream nodes send fewer Diameter requests. Nodes do this by
exchanging overload reports that directly affect this reduction.
This exchange is potentially subject to multiple methods of attack,
and has the potential to be used as a Denial-of-Service (DoS) attack
vector.
Overload reports may contain information about the topology and
current status of a Diameter network. This information is
potentially sensitive. Network operators may wish to control
disclosure of overload reports to unauthorized parties to avoid its
use for competitive intelligence or to target attacks.
Diameter does not include features to provide end-to-end
authentication, integrity protection, or confidentiality. This may
cause complications when sending overload reports between non-
adjacent nodes.
9.1. 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 hop-by-hop
trust model. That is, a Diameter client or server can authorize an
agent for certain actions, but it must trust that agent to make
appropriate authorization decisions about its peers, and so on.
Since confidentiality and integrity protection occurs at the
transport layer. Agents can read, and perhaps modify, any part of a
Diameter message, including an overload report.
There are several ways an attacker might attempt to exploit the
overload control mechanism. An unauthorized third party might inject
an overload report into the network. If this third party is upstream
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of an agent, and that agent fails to apply proper authorization
policies, downstream nodes may mistakenly trust the report. This
attack is at least partially mitigated by the assumption that nodes
include overload reports in Diameter answers but not in requests.
This requires an attacker to have knowledge of the original request
in order to construct a response. Therefore, implementations SHOULD
validate that an answer containing an overload report is a properly
constructed response to a pending request prior to acting on the
overload report.
A similar attack involves an otherwise authorized Diameter node that
sends an inappropriate overload report. For example, a server for
the realm "example.com" might send an overload report indicating that
a competitor's realm "example.net" is overloaded. If other nodes act
on the report, they may falsely believe that "example.net" is
overloaded, effectively reducing that realm's capacity. Therefore,
it's critical that nodes validate that an overload report received
from a peer actually falls within that peer's responsibility before
acting on the report or forwarding the report to other peers. For
example, an overload report from a peer that applies to a realm not
handled by that peer is suspect.
An attacker might use the information in an overload report to assist
in certain attacks. For example, an attacker could use information
about current overload conditions to time a DoS attack for maximum
effect, or use subsequent overload reports as a feedback mechanism to
learn the results of a previous or ongoing attack.
9.2. Denial of Service Attacks
Diameter overload reports can cause a node to cease sending some or
all Diameter requests for an extended period. This makes them a
tempting vector for DoS tacks. Furthermore, since Diameter is almost
always used in support of other protocols, a DoS attack on Diameter
is likely to impact those protocols as well. Therefore, Diameter
nodes MUST NOT honor or forward overload reports from unauthorized or
otherwise untrusted sources.
9.3. Non-Compliant Nodes
When a Diameter node sends an overload report, it cannot assume that
all nodes will comply. A non-compliant node might continue to send
requests with no reduction in load. Requirement 28 [RFC7068]
indicates that the overload control solution cannot assume that all
Diameter nodes in a network are necessarily trusted, and that
malicious nodes not be allowed to take advantage of the overload
control mechanism to get more than their fair share of service.
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In the absence of an overload control mechanism, Diameter nodes need
to implement strategies to protect themselves from floods of
requests, and to make sure that a disproportionate load from one
source does not prevent other sources from receiving service. For
example, a Diameter server might reject a certain percentage of
requests from sources that exceed certain limits. Overload control
can be thought of as an optimization for such strategies, where
downstream nodes never send the excess requests in the first place.
However, the presence of an overload control mechanism does not
remove the need for these other protection strategies.
9.4. End-to End-Security Issues
The lack of end-to-end security features makes it far more difficult
to establish trust in overload reports that originate from non-
adjacent nodes. Any agents in the message path may insert or modify
overload reports. Nodes must trust that their adjacent peers perform
proper checks on overload reports from their peers, and so on,
creating a transitive-trust requirement extending for potentially
long chains of nodes. Network operators must determine if this
transitive trust requirement is acceptable for their deployments.
Nodes supporting Diameter overload control MUST give operators the
ability to select which peers are trusted to deliver overload
reports, and whether they are trusted to forward overload reports
from non-adjacent nodes.
The lack of end-to-end confidentiality protection means that any
Diameter agent in the path of an overload report can view the
contents of that report. In addition to the requirement to select
which peers are trusted to send overload reports, operators MUST be
able to select which peers are authorized to receive reports. A node
MUST not send an overload report to a peer not authorized to receive
it. Furthermore, an agent MUST remove any overload reports that
might have been inserted by other nodes before forwarding a Diameter
message to a peer that is not authorized to receive overload reports.
At the time of this writing, the DIME working group is studying
requirements for adding end-to-end security
[I-D.ietf-dime-e2e-sec-req] features to Diameter. These features,
when they become available, might make it easier to establish trust
in non-adjacent nodes for overload control purposes. Readers should
be reminded, however, that the overload control mechanism encourages
Diameter agents to modify AVPs in, or insert additional AVPs into,
existing messages that are originated by other nodes. If end-to-end
security is enabled, there is a risk that such modification could
violate integrity protection. The details of using any future
Diameter end-to-end security mechanism with overload control will
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require careful consideration, and are beyond the scope of this
document.
10. 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
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
[RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
"Diameter Base Protocol", RFC 6733, October 2012.
11.2. Informative References
[Cx] 3GPP, , "ETSI TS 129 229 V11.4.0", August 2013.
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[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-00 (work in progress),
September 2013.
[PCC] 3GPP, , "ETSI TS 123 203 V11.12.0", December 2013.
[RFC4006] Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J.
Loughney, "Diameter Credit-Control Application", RFC 4006,
August 2005.
[RFC5729] Korhonen, J., Jones, M., Morand, L., and T. Tsou,
"Clarifications on the Routing of Diameter Requests Based
on the Username and the Realm", RFC 5729, December 2009.
[RFC7068] McMurry, E. and B. Campbell, "Diameter Overload Control
Requirements", RFC 7068, November 2013.
[S13] 3GPP, , "ETSI TS 129 272 V11.9.0", December 2012.
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.
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 6.1 and 8 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.
A.3. New Error Diagnostic AVP
The proposal was made to add a new Error Diagnostic AVP to supplement
the error responces to be able to indicate that overload was the
reason for the rejection of the message.
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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, it is recommended that deployments enable all agents that
do server selection to support the DOIC solution prior to enabling
the DOIC solution in the Diameter network.
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.
Appendix C. Requirements Conformance Analysis
This section contains the result of an analysis of the DOIC solutions
conformance to the requirements defined in [RFC7068].
To be completed.
Appendix D. Considerations for Applications Integrating the DOIC
Solution
This section outlines considerations to be taken into account when
integrating the DOIC solution into Diameter applications.
D.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 identity responsible for
handling overload reports.
Section 8.1 of [RFC6733] defines two state machines that imply two
types of applications, session-less and session-based applications.
The primary difference between these types of applications is the
lifetime of Session-Ids.
For session-based applications, the Session-Id is used to tie
multiple requests into a single session.
The Credit-Control application defined in [RFC4006] is an example of
a Diameter session-based application.
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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 D.2.
D.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 D.3 discusses considerations for handling
various request types when the target server is known to be in an
overloaded state.
These discussions assume that the strategy for mitigating the
reported overload is to reduce the overall workload sent to the
overloaded entity. The concept of applying overload treatment to
requests targeted for an overloaded Diameter entity is inherent to
this discussion. The method used to reduce offered load is not
specified here but could include routing requests to another Diameter
entity known to be able to handle them, or it could mean rejecting
certain requests. For a Diameter agent, rejecting requests will
usually mean generating appropriate Diameter error responses. For a
Diameter client, rejecting requests will depend upon the application.
For example, it could mean giving an indication to the entity
requesting the Diameter service that the network is busy and to try
again later.
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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
requests will need to consider whether the rejection invalidates
the session and any resulting session clean-up procedures.
D.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:
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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 requests.
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.
D.4. Request Type Overload Implications
The request classes identified in Appendix D.3 have implications on
decisions about which requests should be throttled first. The
following list of request treatment regarding throttling is provided
as guidelines for application designers when implementing the
Diameter overload control mechanism described in this document. The
exact behavior regarding throttling is a matter of local policy,
unless specifically defined for the application.
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:
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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.
Implementors and operators may choose to throttle session-
terminating requests less aggressively in order to gracefully
terminate sessions, allow clean-up of the related resources (e.g.
session state) and avoid the need for additional intra-session
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
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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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