Diameter Agent Overload and the Peer Overload Report
RFC 8581

Internet Engineering Task Force (IETF)                        S. Donovan
Request for Comments: 8581                                        Oracle
Updates: 7683                                                August 2019
Category: Standards Track
ISSN: 2070-1721

          Diameter Agent Overload and the Peer Overload Report

Abstract

   This specification documents an extension to the Diameter Overload
   Indication Conveyance (DOIC), a base solution for Diameter overload
   defined in RFC 7683.  The extension defines the Peer Overload report
   type.  The initial use case for the peer report is the handling of
   occurrences of overload of a Diameter Agent.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8581.

Copyright Notice

   Copyright (c) 2019 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
   (https://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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Terminology and Abbreviations . . . . . . . . . . . . . . . .   4
   4.  Peer-Report Use Cases . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Diameter Agent Overload Use Cases . . . . . . . . . . . .   5
       4.1.1.  Single Agent  . . . . . . . . . . . . . . . . . . . .   5
       4.1.2.  Redundant Agents  . . . . . . . . . . . . . . . . . .   6
       4.1.3.  Agent Chains  . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Diameter Endpoint Use Cases . . . . . . . . . . . . . . .   8
       4.2.1.  Hop-by-Hop Abatement Algorithms . . . . . . . . . . .   8
   5.  Interaction Between Host/Realm and Peer Overload Reports  . .   9
   6.  Peer-Report Behavior  . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Capability Announcement . . . . . . . . . . . . . . . . .   9
       6.1.1.  Reacting-Node Behavior  . . . . . . . . . . . . . . .   9
       6.1.2.  Reporting-Node Behavior . . . . . . . . . . . . . . .   9
     6.2.  Peer Overload Report Handling . . . . . . . . . . . . . .  10
       6.2.1.  Overload Control State  . . . . . . . . . . . . . . .  10
       6.2.2.  Reporting-Node Maintenance of Peer-Report OCS . . . .  11
       6.2.3.  Reacting-Node Maintenance of Peer-Report OCS  . . . .  12
       6.2.4.  Peer-Report Reporting-Node Behavior . . . . . . . . .  13
       6.2.5.  Peer-Report Reacting-Node Behavior  . . . . . . . . .  13
   7.  Peer-Report AVPs  . . . . . . . . . . . . . . . . . . . . . .  14
     7.1.  OC-Supported-Features AVP . . . . . . . . . . . . . . . .  14
       7.1.1.  OC-Feature-Vector AVP . . . . . . . . . . . . . . . .  15
       7.1.2.  OC-Peer-Algo AVP  . . . . . . . . . . . . . . . . . .  15
     7.2.  OC-OLR AVP  . . . . . . . . . . . . . . . . . . . . . . .  15
       7.2.1.  OC-Report-Type AVP  . . . . . . . . . . . . . . . . .  16
     7.3.  SourceID AVP  . . . . . . . . . . . . . . . . . . . . . .  16
     7.4.  Attribute-Value Pair Flag Rules . . . . . . . . . . . . .  16
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     10.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  18
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  19

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1.  Introduction

   This specification documents an extension to the Diameter Overload
   Indication Conveyance (DOIC), a base solution for Diameter overload
   [RFC7683].  The extension defines the Peer Overload report type.  The
   initial use case for the peer report is the handling of occurrences
   of overload of a Diameter Agent.

   This document defines the behavior of Diameter nodes when Diameter
   Agents enter an overload condition and send an Overload report
   requesting a reduction of traffic.  It also defines a new Overload
   report type, the Peer Overload report type, which is used for
   handling agent overload conditions.  The Peer Overload report type is
   defined in a generic fashion so that it can also be used for other
   Diameter overload scenarios.

   The base Diameter overload specification [RFC7683] addresses the
   handling of overload when a Diameter endpoint (a Diameter Client or
   Diameter Server as defined in [RFC6733]) becomes overloaded.

   In the base specification, the goal is to handle abatement of the
   overload occurrence as close to the source of the Diameter traffic as
   feasible.  When possible, this is done at the originator of the
   traffic, generally referred to as a Diameter Client.  A Diameter
   Agent might also handle the overload mitigation.  For instance, a
   Diameter Agent might handle Diameter overload mitigation when it
   knows that a Diameter Client does not support the DOIC extension.

   This document extends the base Diameter endpoint overload
   specification to address the case when Diameter Agents become
   overloaded.  Just as is the case with other Diameter nodes, i.e.,
   Diameter Clients and Diameter Servers, surges in Diameter traffic can
   cause a Diameter Agent to be asked to handle more Diameter traffic
   than it was configured to handle.  For a more detailed discussion of
   what can cause the overload of Diameter nodes, refer to the Diameter
   overload requirements [RFC7068].

   This document defines a new Overload report type to communicate
   occurrences of agent overload.  This report type works for the
   Diameter overload loss abatement algorithm defined in [RFC7683] and
   is expected to work for other overload abatement algorithms defined
   in extensions to the DOIC solution.

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2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Terminology and Abbreviations

   AVP

      Attribute-Value Pair

   Diameter Node

      A Diameter Client, Diameter Server, or Diameter Agent [RFC6733]

   Diameter Endpoint

      A Diameter Client or Diameter Server [RFC6733]

   Diameter Agent

      A Diameter node that provides relay, proxy, redirect, or
      translation services [RFC6733]

   Reporting Node

      A DOIC node that sends an Overload report in a Diameter answer
      message

   Reacting Node

      A DOIC node that receives and acts on a DOIC Overload report

   DOIC Node

      A Diameter node that supports the DOIC solution defined in
      [RFC7683]

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4.  Peer-Report Use Cases

   This section outlines representative use cases for the peer report
   used to communicate agent overload.

   There are two primary classes of use cases currently identified:
   those involving the overload of agents, and those involving the
   overload of Diameter endpoints.  In both cases, the goal is to use an
   overload algorithm that controls traffic sent towards peers.

4.1.  Diameter Agent Overload Use Cases

   The peer report needs to support the use cases described below.

   In the figures in this section, elements labeled "c" are Diameter
   Clients, elements labeled "a" are Diameter Agents, and elements
   labeled "s" are Diameter Servers.

4.1.1.  Single Agent

   This use case is illustrated in Figure 1.  In this case, the client
   sends all traffic through the single agent.  If there is a failure in
   the agent, then the client is unable to send Diameter traffic toward
   the server.

                              +-+    +-+    +-+
                              |c|----|a|----|s|
                              +-+    +-+    +-+

                                 Figure 1

   A more likely case for the use of agents is illustrated in Figure 2.
   In this case, there are multiple servers behind the single agent.
   The client sends all traffic through the agent, and the agent
   determines how to distribute the traffic to the servers based on
   local routing and load distribution policy.

                                            +-+
                                          --|s|
                              +-+    +-+ /  +-+
                              |c|----|a|-   ...
                              +-+    +-+ \  +-+
                                          --|s|
                                            +-+

                                 Figure 2

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   In both of these cases, the occurrence of overload in the single
   agent must by handled by the client similarly to as if the client
   were handling the overload of a directly connected server.  When the
   agent becomes overloaded, it will insert an Overload report in answer
   messages flowing to the client.  This Overload report will contain a
   requested reduction in the amount of traffic sent to the agent.  The
   client will apply overload abatement behavior as defined in the base
   Diameter overload specification [RFC7683] or in the extension
   document that defines the indicated overload abatement algorithm.
   This will result in the throttling of the abated traffic that would
   have been sent to the agent, as there is no alternative route.  The
   client sends an appropriate error response to the originator of the
   request.

4.1.2.  Redundant Agents

   Figure 3 and Figure 4 illustrate a second, and more likely, type of
   deployment scenario involving agents.  In both of these cases, the
   client has Diameter connections to two agents.

   Figure 3 illustrates a client that has a primary connection to one of
   the agents (agent a1) and a secondary connection to the other agent
   (agent a2).  In this scenario, under normal circumstances, the client
   will use the primary connection for all traffic.  The secondary
   connection is used when there is a failure scenario of some sort.

                                     +--+   +-+
                                   --|a1|---|s|
                              +-+ /  +--+\ /+-+
                              |c|-        x
                              +-+ .  +--+/ \+-+
                                   ..|a2|---|s|
                                     +--+   +-+

                                 Figure 3

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   The second case, in Figure 4, illustrates the case where the
   connections to the agents are both actively used.  In this case, the
   client will have local distribution policy to determine the traffic
   sent through each client.

                                     +--+   +-+
                                   --|a1|---|s|
                              +-+ /  +--+\ /+-+
                              |c|-        x
                              +-+ \  +--+/ \+-+
                                   --|a2|---|s|
                                     +--+   +-+

                                 Figure 4

   In the case where one of the agents in the above scenarios become
   overloaded, the client should reduce the amount of traffic sent to
   the overloaded agent by the amount requested.  This traffic should
   instead be routed through the non-overloaded agent.  For example,
   assume that the overloaded agent requests a reduction of 10 percent.
   The client should send 10 percent of the traffic that would have been
   routed to the overloaded agent through the non-overloaded agent.

   When the client has both an active and a standby connection to the
   two agents, then an alternative strategy for responding to an
   Overload report from an agent is to change the standby connection to
   active.  This will result in all traffic being routed through the new
   active connection.

   In the case where both agents are reporting overload, the client may
   need to start decreasing the total traffic sent to the agents.  This
   would be done in a similar fashion as that discussed in
   Section 4.1.1.  The amount of traffic depends on the combined
   reduction requested by the two agents.

4.1.3.  Agent Chains

   There are also deployment scenarios where there can be multiple
   Diameter Agents between Diameter Clients and Diameter Servers.  An
   example of this type of deployment is when there are Diameter Agents
   between administrative domains.

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   Figure 5 illustrates one such network deployment case.  Note that
   while this figure shows a maximum of two agents being involved in a
   Diameter transaction, it is possible for more than two agents to be
   in the path of a transaction.

                                +---+     +---+   +-+
                              --|a11|-----|a21|---|s|
                         +-+ /  +---+ \ / +---+\ /+-+
                         |c|-          x        x
                         +-+ \  +---+ / \ +---+/ \+-+
                              --|a12|-----|a22|---|s|
                                +---+     +---+   +-+

                                 Figure 5

   The handling of overload for one or both agents, a11 or a12 in this
   case, is equivalent to that discussed in Section 4.1.2.

   The overload of agents a21 and a22 must be handled by the previous-
   hop agents.  As such, agents a11 and a12 must handle the overload
   mitigation logic when receiving an Agent Overload report from agents
   a21 and a22.

   The handling of Peer Overload reports is similar to that discussed in
   Section 4.1.2.  If the overload can be addressed using diversion,
   then this approach should be taken.

   If both of the agents have requested a reduction in traffic, then the
   previous-hop agent must start throttling the appropriate number of
   transactions.  When throttling requests, an agent uses the same error
   responses as defined in the base DOIC specification [RFC7683].

4.2.  Diameter Endpoint Use Cases

   This section outlines use cases for the Peer Overload report
   involving Diameter Clients and Diameter Servers.

4.2.1.  Hop-by-Hop Abatement Algorithms

   It is envisioned that abatement algorithms will be defined that will
   support the option for Diameter endpoints to send peer reports.  For
   instance, it is envisioned that one usage scenario for the rate
   algorithm [RFC8582] will involve abatement being done on a hop-by-hop
   basis.

   This rate-deployment scenario would involve Diameter endpoints
   generating peer reports and selecting the rate algorithm for
   abatement of overload conditions.

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5.  Interaction Between Host/Realm and Peer Overload Reports

   It is possible for both an agent and an endpoint in the path of a
   transaction to be overloaded at the same time.  When this occurs,
   Diameter entities need to handle multiple Overload reports.  In this
   scenario, the reacting node should first handle the throttling of the
   overloaded Host or Realm.  Any messages that survive throttling due
   to Host or Realm reports should then go through abatement for the
   Peer Overload report.  In this scenario, when doing abatement on the
   peer report, the reacting node SHOULD take into consideration the
   number of messages already throttled by the handling of the host/
   realm report abatement.

      Note: The goal is to avoid traffic oscillations that might result
      from throttling of messages for both the host/realm Overload
      reports and the PEER Overload reports.  This is especially a
      concern if both reports indicate the loss abatement algorithm.

6.  Peer-Report Behavior

   This section defines the normative behavior associated with the Peer-
   Report extension to the DOIC solution.

6.1.  Capability Announcement

6.1.1.  Reacting-Node Behavior

   When sending a Diameter request, a DOIC node that supports the
   OC_PEER_REPORT feature (as defined in Section 7.1.1) MUST include in
   the OC-Supported-Features AVP an OC-Feature-Vector AVP with the
   OC_PEER_REPORT bit set.

   When sending a request, a DOIC node that supports the OC_PEER_REPORT
   feature MUST include a SourceID AVP in the OC-Supported-Features AVP
   with its own DiameterIdentity.

   When a Diameter Agent relays a request that includes a SourceID AVP
   in the OC-Supported-Features AVP, if the Diameter Agent supports the
   OC_PEER_REPORT feature, then it MUST remove the received SourceID AVP
   and replace it with a SourceID AVP containing its own
   DiameterIdentity.

6.1.2.  Reporting-Node Behavior

   When receiving a request, a DOIC node that supports the
   OC_PEER_REPORT feature MUST update transaction state with an
   indication of whether or not the peer from which the request was
   received supports the OC_PEER_REPORT feature.

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      Note: The transaction state is used when the DOIC node is acting
      as a peer-report reporting node and needs to send OC-OLR AVP
      reports of type "PEER-REPORT" in answer messages.  The Peer
      Overload reports are only included in answer messages being sent
      to peers that support the OC_PEER_REPORT feature.

   The peer supports the OC_PEER_REPORT feature if the received request
   contains an OC-Supported-Features AVP with the OC-Feature-Vector with
   the OC_PEER_REPORT feature bit set and with a SourceID AVP with a
   value that matches the DiameterIdentity of the peer from which the
   request was received.

   When an agent relays an answer message, a reporting node that
   supports the OC_PEER_REPORT feature MUST strip any SourceID AVP from
   the OC-Supported-Features AVP.

   When sending an answer message, a reporting node that supports the
   OC_PEER_REPORT feature MUST determine if the peer to which the answer
   is to be sent supports the OC_PEER_REPORT feature.

   If the peer supports the OC_PEER_REPORT feature, then the reporting
   node MUST indicate support for the feature in the OC-Supported-
   Features AVP.

   If the peer supports the OC_PEER_REPORT feature, then the reporting
   node MUST insert the SourceID AVP in the OC-Supported-Features AVP in
   the answer message.

   If the peer supports the OC_PEER_REPORT feature, then the reporting
   node MUST insert the OC-Peer-Algo AVP in the OC-Supported-Features
   AVP.  The OC-Peer-Algo AVP MUST indicate the overload abatement
   algorithm that the reporting node wants the reacting nodes to use
   should the reporting node send a Peer Overload report as a result of
   becoming overloaded.

6.2.  Peer Overload Report Handling

   This section defines the behavior for the handling of Overload
   reports of type "PEER-REPORT".

6.2.1.  Overload Control State

   This section describes the Overload Control State (OCS) that might be
   maintained by both the peer-report reporting node and the peer-report
   reacting node.

   This is an extension of the OCS handling defined in [RFC7683].

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6.2.1.1.  Reporting-Node Peer-Report OCS

   A DOIC node that supports the OC_PEER_REPORT feature SHOULD maintain
   Reporting-Node OCS, as defined in [RFC7683] and extended here.

   If different abatement-specific contents are sent to each peer, then
   the reporting node MUST maintain a separate reporting-node peer-
   report OCS entry per peer, to which a Peer Overload report is sent.

      Note: The rate-overload abatement algorithm allows for different
      rates to be sent to each peer.

6.2.1.2.  Reacting-Node Peer-Report OCS

   In addition to OCS maintained as defined in [RFC7683], a reacting
   node that supports the OC_PEER_REPORT feature maintains the following
   OCS per supported Diameter application:

      A peer-report OCS entry for each peer to which it sends requests

   A peer-report OCS entry is identified by both the Application-ID and
   the peer's DiameterIdentity.

   The peer-report OCS entry includes the following information (the
   actual information stored is an implementation decision):

      Sequence number (as received in the OC-OLR AVP)

      Time of expiry (derived from the OC-Validity-Duration AVP received
      in the OC-OLR AVP and time of reception of the message carrying
      the OC-OLR AVP)

      Selected abatement algorithm (as received in the OC-Supported-
      Features AVP)

      Input data that is specific to the abatement algorithm (as
      received in the OC-OLR AVP, e.g., OC-Reduction-Percentage for the
      loss abatement algorithm)

6.2.2.  Reporting-Node Maintenance of Peer-Report OCS

   All rules for managing the reporting-node OCS entries defined in
   [RFC7683] apply to the peer report.

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6.2.3.  Reacting-Node Maintenance of Peer-Report OCS

   When a reacting node receives an OC-OLR AVP with a report type of
   "PEER-REPORT", it MUST determine if the report was generated by the
   Diameter peer from which the report was received.

   If a reacting node receives an OC-OLR AVP of type "PEER-REPORT" and
   the SourceID matches the DiameterIdentity of the Diameter peer from
   which the response message was received, then the report was
   generated by a Diameter peer.

   If a reacting node receives an OC-OLR AVP of type "PEER-REPORT" and
   the SourceID does not match the DiameterIdentity of the Diameter peer
   from which the response message was received, then the reacting node
   MUST ignore the Overload report.

      Note: Under normal circumstances, a Diameter node will not add a
      peer report when sending to a peer that does not support this
      extension.  This requirement is to handle the case where peer
      reports are erroneously or maliciously inserted into response
      messages.

   If the peer report was received from a Diameter peer, then the
   reacting node MUST determine if it is for an existing or new overload
   condition.

   The peer report is for an existing overload condition if the reacting
   node has an OCS that matches the received peer report.  For a peer
   report, this means it matches the Application-ID and the peer's
   DiameterIdentity in an existing OCS entry.

   If the peer report is for an existing overload condition, then it
   MUST determine if the peer report is a retransmission or an update to
   the existing OLR.

   If the sequence number for the received peer report 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 peer report is less than or
   equal to the sequence number in the matching OCS entry, then the
   reacting node MUST silently ignore the received peer report.  The
   matching OCS MUST NOT be updated in this case.

   If the received peer report is for a new overload condition, then the
   reacting node MUST generate a new OCS entry for the overload
   condition.

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   For a peer report, this means it creates an OCS entry with a
   DiameterIdentity from the SourceID AVP in the received OC-OLR AVP.

   If the received peer report contains a validity duration of zero
   ("0"), then the reacting node MUST update the OCS entry as being
   expired.

   The reacting node does not delete an OCS when receiving an answer
   message that does not contain an OC-OLR AVP (i.e., the absence of OLR
   means "no change").

   The reacting node sets the abatement algorithm based on the OC-Peer-
   Algo AVP in the received OC-Supported-Features AVP.

6.2.4.  Peer-Report Reporting-Node Behavior

   When there is an existing reporting-node peer-report OCS entry, the
   reporting node MUST include an OC-OLR AVP with a report type of
   "PEER-REPORT" using the contents of the reporting-node peer-report
   OCS entry in all answer messages sent by the reporting node to peers
   that support the OC_PEER_REPORT feature.

      Note: The reporting node determines if a peer supports the
      OC_PEER_REPORT feature based on the indication recorded in the
      reporting node's transaction state.

   The reporting node MUST include its DiameterIdentity in the SourceID
   AVP in the OC-OLR AVP.  This is used by DOIC nodes that support the
   OC_PEER_REPORT feature to determine if the report was received from a
   Diameter peer.

   The reporting agent must follow all other overload reporting-node
   behaviors outlined in the DOIC specification.

6.2.5.  Peer-Report Reacting-Node Behavior

   A reacting node supporting this extension MUST support the receipt of
   multiple Overload reports in a single message.  The message might
   include a Host Overload report, a Realm Overload report, and/or a
   Peer Overload report.

   When a reacting node sends a request, it MUST determine if that
   request matches an active OCS.

   In all cases, if the reacting node is an agent, then it MUST strip
   the Peer-Report OC-OLR AVP from the message.

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   If the request matches an active OCS, then the reacting node MUST
   apply abatement treatment to the request.  The abatement treatment
   applied depends on the abatement algorithm indicated in the OCS.

   For Peer Overload Reports, the preferred abatement treatment is
   diversion.  As such, the reacting node SHOULD attempt to divert
   requests identified as needing abatement to other peers.

   If there is not sufficient capacity to divert abated traffic, then
   the reacting node MUST throttle the necessary requests to fit within
   the available capacity of the peers able to handle the requests.

   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 response as defined in [RFC7683].

   In the case that the OCS entry validity duration expires or has a
   validity duration of zero ("0"), meaning that if the reporting node
   has explicitly signaled the end of the overload condition, then
   abatement associated with the OCS entry MUST be ended in a controlled
   fashion.

7.  Peer-Report AVPs

7.1.  OC-Supported-Features AVP

   This extension adds a new feature to the OC-Feature-Vector AVP.  This
   feature indication shows support for handling of Peer Overload
   reports.  Peer Overload reports are used by agents to indicate the
   need for overload abatement handling by the agent's peer.

   A supporting node must also include the SourceID AVP in the
   OC-Supported-Features capability AVP.

   This AVP contains the DiameterIdentity of the node that supports the
   OC_PEER_REPORT feature.  This AVP is used to determine if support for
   the Peer Overload report is in an adjacent node.  The value of this
   AVP should be the same Diameter identity used as part of the Diameter
   Capabilities Exchange procedure defined in [RFC7683].

   This extension also adds the OC-Peer-Algo AVP to the OC-Supported-
   Features AVP.  This AVP is used by a reporting node to indicate the
   abatement algorithm it will use for Peer Overload reports.

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    OC-Supported-Features ::= < AVP Header: 621 >
                              [ OC-Feature-Vector ]
                              [ SourceID ]
                              [ OC-Peer-Algo]
                            * [ AVP ]

7.1.1.  OC-Feature-Vector AVP

   The Peer-Report feature defines a new feature bit for the OC-Feature-
   Vector AVP.

   OC_PEER_REPORT (0x0000000000000010)

      When this flag is set by a DOIC node, it indicates that the DOIC
      node supports the Peer Overload report type.

7.1.2.  OC-Peer-Algo AVP

   The OC-Peer-Algo AVP (AVP code 648) is of type Unsigned64 and
   contains a 64-bit flags field of announced capabilities for a DOIC
   node.  The value of zero ("0") is reserved.

   Feature bits defined for the OC-Feature-Vector AVP and associated
   with overload abatement algorithms are reused for this AVP.

7.2.  OC-OLR AVP

   This extension makes no changes to the OC_Sequence_Number or
   OC_Validity_Duration AVPs in the OC-OLR AVP.  These AVPs can also be
   used in Peer Overload reports.

   The OC_PEER_REPORT feature extends the base Diameter overload
   specification by defining a new Overload report type of "PEER-
   REPORT".  See Section 7.6 of [RFC7683] for a description of the
   OC-Report-Type AVP.

   The peer report MUST also include the Diameter identity of the agent
   that generated the report.  This is necessary to handle the case
   where there is a non-supporting agent between the reporting node and
   the reacting node.  Without the indication of the agent that
   generated the peer report, the reacting node could erroneously assume
   that the report applied to the non-supporting node.  This could, in
   turn, result in unnecessary traffic being either diverted or
   throttled.

   The SourceID AVP is used in the OC-OLR AVP to carry this
   DiameterIdentity.

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      OC-OLR ::= < AVP Header: 623 >
                 < OC-Sequence-Number >
                 < OC-Report-Type >
                 [ OC-Reduction-Percentage ]
                 [ OC-Validity-Duration ]
                 [ SourceID ]
               * [ AVP ]

7.2.1.  OC-Report-Type AVP

   The following new report type is defined for the OC-Report-Type AVP.

   PEER_REPORT 2:  The overload treatment should apply to all requests
      bound for the peer identified in the Overload report.  If the peer
      identified in the peer report is not a peer to the reacting
      endpoint, then the peer report should be stripped and not acted
      upon.

7.3.  SourceID AVP

   The SourceID AVP (AVP code 649) is of type DiameterIdentity and is
   inserted by a Diameter node to indicate the source of the AVP in
   which it is a part.

   In the case of peer reports, the SourceID AVP indicates the node that
   supports this feature (in the OC-Supported-Features AVP) or the node
   that generates an overload report with a report type of "PEER-REPORT"
   (in the OC-OLR AVP).

   It contains the DiameterIdentity of the inserting node.  This is used
   by other Diameter nodes to determine the node that inserted the
   enclosing AVP that contains the SourceID AVP.

7.4.  Attribute-Value Pair Flag Rules

                                                             +---------+
                                                             |AVP flag |
                                                             |rules    |
                                                             +----+----+
                             AVP   Section                   |    |MUST|
     Attribute Name          Code  Defined Value Type        |MUST| NOT|
    +--------------------------------------------------------+----+----+
    |OC-Peer-Algo            648    7.1.2  Unsigned64        |    | V  |
    |SourceID                649    7.3    DiameterIdentity  |    | V  |
    +--------------------------------------------------------+----+----+

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8.  IANA Considerations

   IANA has registered the following values in the "Authentication,
   Authorization, and Accounting (AAA) Parameters" registry:

      Two new AVP codes are defined in Section 7.4.

      Note that the values used for the OC-Peer-Algo AVP are a subset of
      the "OC-Feature-Vector AVP Values (code 622)" registry.  Only the
      values in that registry that apply to overload abatement
      algorithms apply to the OC-Peer-Algo AVP.

      A new OC-Feature-Vector AVP value is defined in Section 7.1.1.

      A new OC-Report-Type AVP value is defined in Section 7.2.1.

9.  Security Considerations

   Agent overload is an extension to the base Diameter Overload
   mechanism.  As such, all of the security considerations outlined in
   [RFC7683] apply to the agent overload scenarios.

   It is possible that the malicious insertion of an peer report could
   have a bigger impact on a Diameter network as agents can be
   concentration points in a Diameter network.  Where an endpoint report
   would impact the traffic sent to a single Diameter Server, for
   example, a peer report could throttle all traffic to the Diameter
   network.

   This impact is amplified in a Diameter agent that sits at the edge of
   a Diameter network that serves as the entry point from all other
   Diameter networks.

   The impacts of this attack, as well as the mitigation strategies, are
   the same as those outlined in [RFC7683].

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10.  References

10.1.  Normative References

   [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
              Ed., "Diameter Base Protocol", RFC 6733,
              DOI 10.17487/RFC6733, October 2012,
              <https://www.rfc-editor.org/info/rfc6733>.

   [RFC7683]  Korhonen, J., Ed., Donovan, S., Ed., Campbell, B., and L.
              Morand, "Diameter Overload Indication Conveyance",
              RFC 7683, DOI 10.17487/RFC7683, October 2015,
              <https://www.rfc-editor.org/info/rfc7683>.

   [RFC8582]  Donovan, S., Ed. and E. Noel, "Diameter Overload Rate
              Control", RFC 8582, DOI 10.17487/RFC8582, August 2019,
              <https://www.rfc-editor.org/info/rfc8582>.

10.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7068]  McMurry, E. and B. Campbell, "Diameter Overload Control
              Requirements", RFC 7068, DOI 10.17487/RFC7068, November
              2013, <https://www.rfc-editor.org/info/rfc7068>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Acknowledgements

   The author would like to thank Adam Roach and Eric McMurry for the
   work done in defining a comprehensive Diameter overload solution in
   draft-roach-dime-overload-ctrl-03.txt.

   The author would also like to thank Ben Campbell for his insights and
   review of early versions of this document.

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Author's Address

   Steve Donovan
   Oracle
   7460 Warren Parkway, Suite 300
   Frisco, Texas  75034
   United States of America

   Email: srdonovan@usdonovans.com

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