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+Internet Engineering Task Force (IETF)                        E. McMurry
+Request for Comments: 7068                                   B. Campbell
+Category: Informational                                           Oracle
+ISSN: 2070-1721                                            November 2013
+
+
+                 Diameter Overload Control Requirements
+
+Abstract
+
+   When a Diameter server or agent becomes overloaded, it needs to be
+   able to gracefully reduce its load, typically by advising clients to
+   reduce traffic for some period of time.  Otherwise, it must continue
+   to expend resources parsing and responding to Diameter messages,
+   possibly resulting in a progressively severe overload condition.  The
+   existing Diameter mechanisms are not sufficient for managing overload
+   conditions.  This document describes the limitations of the existing
+   mechanisms.  Requirements for new overload management mechanisms are
+   also provided.
+
+Status of This Memo
+
+   This document is not an Internet Standards Track specification; it is
+   published for informational purposes.
+
+   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).  Not all documents
+   approved by the IESG are a candidate for any level of Internet
+   Standard; see Section 2 of RFC 5741.
+
+   Information about the current status of this document, any errata,
+   and how to provide feedback on it may be obtained at
+   http://www.rfc-editor.org/info/rfc7068.
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+McMurry & Campbell            Informational                     [Page 1]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
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+Copyright Notice
+
+   Copyright (c) 2013 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
+   (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.
+
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+McMurry & Campbell            Informational                     [Page 2]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+Table of Contents
+
+   1. Introduction ....................................................4
+      1.1. Documentation Conventions ..................................4
+      1.2. Causes of Overload .........................................5
+      1.3. Effects of Overload ........................................6
+      1.4. Overload vs. Network Congestion ............................6
+      1.5. Diameter Applications in a Broader Network .................7
+   2. Overload Control Scenarios ......................................7
+      2.1. Peer-to-Peer Scenarios .....................................8
+      2.2. Agent Scenarios ...........................................10
+      2.3. Interconnect Scenario .....................................14
+   3. Diameter Overload Case Studies .................................15
+      3.1. Overload in Mobile Data Networks ..........................15
+      3.2. 3GPP Study on Core Network Overload .......................16
+   4. Existing Mechanisms ............................................17
+   5. Issues with the Current Mechanisms .............................18
+      5.1. Problems with Implicit Mechanism ..........................18
+      5.2. Problems with Explicit Mechanisms .........................18
+   6. Extensibility and Application Independence .....................19
+   7. Solution Requirements ..........................................20
+      7.1. General ...................................................20
+      7.2. Performance ...............................................21
+      7.3. Heterogeneous Support for Solution ........................22
+      7.4. Granular Control ..........................................23
+      7.5. Priority and Policy .......................................23
+      7.6. Security ..................................................23
+      7.7. Flexibility and Extensibility .............................24
+   8. Security Considerations ........................................25
+      8.1. Access Control ............................................25
+      8.2. Denial-of-Service Attacks .................................26
+      8.3. Replay Attacks ............................................26
+      8.4. Man-in-the-Middle Attacks .................................26
+      8.5. Compromised Hosts .........................................27
+   9. References .....................................................27
+      9.1. Normative References ......................................27
+      9.2. Informative References ....................................27
+   Appendix A. Contributors ..........................................29
+   Appendix B. Acknowledgements ......................................29
+
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+McMurry & Campbell            Informational                     [Page 3]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+1.  Introduction
+
+   A Diameter [RFC6733] node is said to be overloaded when it has
+   insufficient resources to successfully process all of the Diameter
+   requests that it receives.  When a node becomes overloaded, it needs
+   to be able to gracefully reduce its load, typically by advising
+   clients to reduce traffic for some period of time.  Otherwise, it
+   must continue to expend resources parsing and responding to Diameter
+   messages, possibly resulting in a progressively severe overload
+   condition.  The existing mechanisms provided by Diameter are not
+   sufficient for managing overload conditions.  This document describes
+   the limitations of the existing mechanisms and provides requirements
+   for new overload management mechanisms.
+
+   This document draws on the work done on SIP overload control
+   ([RFC5390], [RFC6357]) as well as on experience gained via overload
+   handling in Signaling System No. 7 (SS7) networks and studies done by
+   the Third Generation Partnership Project (3GPP) (Section 3).
+
+   Diameter is not typically an end-user protocol; rather, it is
+   generally used as one component in support of some end-user activity.
+
+   For example, a SIP server might use Diameter to authenticate and
+   authorize user access.  Overload in the Diameter backend
+   infrastructure will likely impact the experience observed by the end
+   user in the SIP application.
+
+   The impact of Diameter overload on the client application (a client
+   application may use the Diameter protocol and other protocols to do
+   its job) is beyond the scope of this document.
+
+   This document presents non-normative descriptions of causes of
+   overload, along with related scenarios and studies.  Finally, it
+   offers a set of normative requirements for an improved overload
+   indication mechanism.
+
+1.1.  Documentation Conventions
+
+   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 defined in [RFC2119], with the
+   exception that they are not intended for interoperability of
+   implementations.  Rather, they are used to describe requirements
+   towards future specifications where the interoperability requirements
+   will be defined.
+
+   The terms "client", "server", "agent", "node", "peer", "upstream",
+   and "downstream" are used as defined in [RFC6733].
+
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+
+McMurry & Campbell            Informational                     [Page 4]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
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+1.2.  Causes of Overload
+
+   Overload occurs when an element, such as a Diameter server or agent,
+   has insufficient resources to successfully process all of the traffic
+   it is receiving.  Resources include all of the capabilities of the
+   element used to process a request, including CPU processing, memory,
+   I/O, and disk resources.  It can also include external resources such
+   as a database or DNS server, in which case the CPU, processing,
+   memory, I/O, and disk resources of those elements are effectively
+   part of the logical element processing the request.
+
+   External resources can include upstream Diameter nodes; for example,
+   a Diameter agent can become effectively overloaded if one or more
+   upstream nodes are overloaded.
+
+   A Diameter node can become overloaded due to request levels that
+   exceed its capacity, a reduction of available resources (for example,
+   a local or upstream hardware failure), or a combination of the two.
+
+   Overload can occur for many reasons, including:
+
+   Inadequate capacity:  When designing Diameter networks, that is,
+      application-layer multi-node Diameter deployments, it can be very
+      difficult to predict all scenarios that may cause elevated
+      traffic.  It may also be more costly to implement support for some
+      scenarios than a network operator may deem worthwhile.  This
+      results in the likelihood that a Diameter network will not have
+      adequate capacity to handle all situations.
+
+   Dependency failures:  A Diameter node can become overloaded because a
+      resource on which it depends has failed or become overloaded,
+      greatly reducing the logical capacity of the node.  In these
+      cases, even minimal traffic might cause the node to go into
+      overload.  Examples of such dependency overloads include DNS
+      servers, databases, disks, and network interfaces that have failed
+      or become overloaded.
+
+   Component failures:  A Diameter node can become overloaded when it is
+      a member of a cluster of servers that each share the load of
+      traffic and one or more of the other members in the cluster fail.
+      In this case, the remaining nodes take over the work of the failed
+      nodes.  Normally, capacity planning takes such failures into
+      account, and servers are typically run with enough spare capacity
+      to handle failure of another node.  However, unusual failure
+      conditions can cause many nodes to fail at once.  This is often
+      the case with software failures, where a bad packet or bad
+      database entry hits the same bug in a set of nodes in a cluster.
+
+
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+McMurry & Campbell            Informational                     [Page 5]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
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+   Network-initiated traffic flood:  Certain access network events can
+      precipitate floods of Diameter signaling traffic.  For example,
+      operational changes can trigger avalanche restarts, or frequent
+      radio overlay handovers can generate excessive authorization
+      requests.  Failure of a Diameter proxy may also result in a large
+      amount of signaling as connections and sessions are reestablished.
+
+   Subscriber-initiated traffic flood:  Large gatherings of subscribers
+      or events that result in many subscribers interacting with the
+      network in close time proximity can result in Diameter signaling
+      traffic floods.  For example, the finale of a large fireworks show
+      could be immediately followed by many subscribers posting
+      messages, pictures, and videos concentrated on one portion of a
+      network.  Subscriber devices such as smartphones may use
+      aggressive registration strategies that generate unusually high
+      Diameter traffic loads.
+
+   DoS attacks:  An attacker wishing to disrupt service in the network
+      can cause a large amount of traffic to be launched at a target
+      element.  This can be done from a central source of traffic or
+      through a distributed DoS attack.  In all cases, the volume of
+      traffic well exceeds the capacity of the element, sending the
+      system into overload.
+
+1.3.  Effects of Overload
+
+   Modern Diameter networks, composed of application-layer multi-node
+   deployments of Diameter elements, may operate at very large
+   transaction volumes.  If a Diameter node becomes overloaded or, even
+   worse, fails completely, a large number of messages may be lost very
+   quickly.  Even with redundant servers, many messages can be lost in
+   the time it takes for failover to complete.  While a Diameter client
+   or agent should be able to retry such requests, an overloaded peer
+   may cause a sudden large increase in the number of transactions
+   needing to be retried, rapidly filling local queues or otherwise
+   contributing to local overload.  Therefore, Diameter devices need to
+   be able to shed load before critical failures can occur.
+
+1.4.  Overload vs. Network Congestion
+
+   This document uses the term "overload" to refer to application-layer
+   overload at Diameter nodes.  This is distinct from "network
+   congestion", that is, congestion that occurs at the lower networking
+   layers that may impact the delivery of Diameter messages between
+   nodes.  This document recognizes that element overload and network
+   congestion are interrelated, and that overload can contribute to
+   network congestion and vice versa.
+
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+McMurry & Campbell            Informational                     [Page 6]
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+RFC 7068         Diameter Overload Control Requirements    November 2013
+
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+   Network congestion issues are better handled by the transport
+   protocols.  Diameter uses TCP and the Stream Control Transmission
+   Protocol (SCTP), both of which include congestion management
+   features.  Analysis of whether those features are sufficient for
+   transport-level congestion between Diameter nodes and of any work to
+   further mitigate network congestion is out of scope for both this
+   document and the work proposed by it.
+
+1.5.  Diameter Applications in a Broader Network
+
+   Most elements using Diameter applications do not use Diameter
+   exclusively.  It is important to realize that overload of an element
+   can be caused by a number of factors that may be unrelated to the
+   processing of Diameter or Diameter applications.
+
+   An element that doesn't use Diameter exclusively needs to be able to
+   signal to Diameter peers that it is experiencing overload regardless
+   of the cause of the overload, since the overload will affect that
+   element's ability to process Diameter transactions.  If the element
+   communicates with protocols other than Diameter, it may also need to
+   signal the overload situation on these protocols, depending on its
+   function and the architecture of the network and application for
+   which it is providing services.  Whether that is necessary can only
+   be decided within the context of that architecture and use cases.
+   This specification details the requirements for a mechanism for
+   signaling overload with Diameter; this mechanism provides Diameter
+   nodes the ability to inform their Diameter peers of overload,
+   mitigating that part of the issue.  Diameter nodes may need to use
+   this, as well as other mechanisms, to solve their broader overload
+   issues.  Indicating overload on protocols other than Diameter is out
+   of scope for this document and for the work proposed by it.
+
+2.  Overload Control Scenarios
+
+   Several Diameter deployment scenarios exist that may impact overload
+   management.  The following scenarios help motivate the requirements
+   for an overload management mechanism.
+
+   These scenarios are by no means exhaustive and are in general
+   simplified for the sake of clarity.  In particular, this document
+   assumes for the sake of clarity that the client sends Diameter
+   requests to the server, and the server sends responses to the client,
+   even though Diameter supports bidirectional applications.  Each
+   direction in such an application can be modeled separately.
+
+   In a large-scale deployment, many of the nodes represented in these
+   scenarios would be deployed as clusters of servers.  This document
+   assumes that such a cluster is responsible for managing its own
+
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+McMurry & Campbell            Informational                     [Page 7]
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+RFC 7068         Diameter Overload Control Requirements    November 2013
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+   internal load-balancing and overload management so that it appears as
+   a single Diameter node.  That is, other Diameter nodes can treat it
+   as a single, monolithic node for the purposes of overload management.
+
+   These scenarios do not illustrate the client application.  As
+   mentioned in Section 1, Diameter is not typically an end-user
+   protocol; rather, it is generally used in support of some other
+   client application.  These scenarios do not consider the impact of
+   Diameter overload on the client application.
+
+2.1.  Peer-to-Peer Scenarios
+
+   This section describes Diameter peer-to-peer scenarios, that is,
+   scenarios where a Diameter client talks directly with a Diameter
+   server, without the use of a Diameter agent.
+
+   Figure 1 illustrates the simplest possible Diameter relationship.
+   The client and server share a one-to-one peer-to-peer relationship.
+   If the server becomes overloaded, either because the client exceeds
+   the server's capacity or because the server's capacity is reduced due
+   to some resource dependency, the client needs to reduce the amount of
+   Diameter traffic it sends to the server.  Since the client cannot
+   forward requests to another server, it must either queue requests
+   until the server recovers or itself become overloaded in the context
+   of the client application and other protocols it may also use.
+
+                            +------------------+
+                            |                  |
+                            |                  |
+                            |     Server       |
+                            |                  |
+                            +--------+---------+
+                                     |
+                                     |
+                            +--------+---------+
+                            |                  |
+                            |                  |
+                            |     Client       |
+                            |                  |
+                            +------------------+
+
+                   Figure 1: Basic Peer-to-Peer Scenario
+
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+McMurry & Campbell            Informational                     [Page 8]
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+RFC 7068         Diameter Overload Control Requirements    November 2013
+
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+   Figure 2 shows a similar scenario, except in this case the client has
+   multiple servers that can handle work for a specific realm and
+   application.  If Server 1 becomes overloaded, the client can forward
+   traffic to Server 2.  Assuming that Server 2 has sufficient reserve
+   capacity to handle the forwarded traffic, the client should be able
+   to continue serving client application protocol users.  If Server 1
+   is approaching overload, but can still handle some number of new
+   requests, it needs to be able to instruct the client to forward a
+   subset of its traffic to Server 2.
+
+               +------------------+     +------------------+
+               |                  |     |                  |
+               |                  |     |                  |
+               |     Server 1     |     |     Server 2     |
+               |                  |     |                  |
+               +--------+-`.------+     +------.'+---------+
+                            `.               .'
+                              `.           .'
+                                `.       .'
+                                  `.   .'
+                            +-------`.'--------+
+                            |                  |
+                            |                  |
+                            |     Client       |
+                            |                  |
+                            +------------------+
+
+              Figure 2: Multiple-Server Peer-to-Peer Scenario
+
+   Figure 3 illustrates a peer-to-peer scenario with multiple Diameter
+   realm and application combinations.  In this example, Server 2 can
+   handle work for both applications.  Each application might have
+   different resource dependencies.  For example, a server might need to
+   access one database for Application A and another for Application B.
+   This creates a possibility that Server 2 could become overloaded for
+   Application A but not for Application B, in which case the client
+   would need to divert some part of its Application A requests to
+   Server 1, but the client should not divert any Application B
+   requests.  This requires that Server 2 be able to distinguish between
+   applications when it indicates an overload condition to the client.
+
+   On the other hand, it's possible that the servers host many
+   applications.  If Server 2 becomes overloaded for all applications,
+   it would be undesirable for it to have to notify the client
+   separately for each application.  Therefore, it also needs a way to
+   indicate that it is overloaded for all possible applications.
+
+
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+McMurry & Campbell            Informational                     [Page 9]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
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+   +---------------------------------------------+
+   | Application A       +----------------------+----------------------+
+   |+------------------+ |  +----------------+  |  +------------------+|
+   ||                  | |  |                |  |  |                  ||
+   ||                  | |  |                |  |  |                  ||
+   ||     Server 1     | |  |    Server 2    |  |  |     Server 3     ||
+   ||                  | |  |                |  |  |                  ||
+   |+--------+---------+ |  +-------+--------+  |  +-+----------------+|
+   |         |           |          |           |    |                 |
+   +---------+-----------+----------+-----------+    |                 |
+             |           |          |                |                 |
+             |           |          |                |  Application B  |
+             |           +----------+----------------+-----------------+
+             ``-.._                 |                |
+                   `-..__           |            _.-''
+                        `--._       |        _.-''
+                             ``-._  |   _.-''
+                            +-----`-.-''-----+
+                            |                |
+                            |                |
+                            |     Client     |
+                            |                |
+                            +----------------+
+
+           Figure 3: Multiple-Application Peer-to-Peer Scenario
+
+2.2.  Agent Scenarios
+
+   This section describes scenarios that include a Diameter agent, in
+   the form of either a Diameter relay or Diameter proxy.  These
+   scenarios do not consider Diameter redirect agents, since they are
+   more readily modeled as end servers.  The examples have been kept
+   simple deliberately, to illustrate basic concepts.  Significantly
+   more complicated topologies are possible with Diameter, including
+   multiple intermediate agents in a path connected in a variety
+   of ways.
+
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+McMurry & Campbell            Informational                    [Page 10]
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+RFC 7068         Diameter Overload Control Requirements    November 2013
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+   Figure 4 illustrates a simple Diameter agent scenario with a single
+   client, agent, and server.  In this case, overload can occur at the
+   server, at the agent, or both.  But in most cases, client behavior is
+   the same whether overload occurs at the server or at the agent.  From
+   the client's perspective, server overload and agent overload are the
+   same thing.
+
+                           +------------------+
+                           |                  |
+                           |                  |
+                           |     Server       |
+                           |                  |
+                           +--------+---------+
+                                    |
+                                    |
+                           +--------+---------+
+                           |                  |
+                           |                  |
+                           |      Agent       |
+                           |                  |
+                           +--------+---------+
+                                    |
+                                    |
+                           +--------+---------+
+                           |                  |
+                           |                  |
+                           |     Client       |
+                           |                  |
+                           +------------------+
+
+                      Figure 4: Basic Agent Scenario
+
+   Figure 5 shows an agent scenario with multiple servers.  If Server 1
+   becomes overloaded but Server 2 has sufficient reserve capacity, the
+   agent may be able to transparently divert some or all Diameter
+   requests originally bound for Server 1 to Server 2.
+
+   In most cases, the client does not have detailed knowledge of the
+   Diameter topology upstream of the agent.  If the agent uses dynamic
+   discovery to find eligible servers, the set of eligible servers may
+   not be enumerable from the perspective of the client.  Therefore, in
+   most cases the agent needs to deal with any upstream overload issues
+   in a way that is transparent to the client.  If one server notifies
+   the agent that it has become overloaded, the notification should not
+   be passed back to the client in a way that the client could
+   mistakenly perceive the agent itself as being overloaded.  If the set
+
+
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+McMurry & Campbell            Informational                    [Page 11]
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+RFC 7068         Diameter Overload Control Requirements    November 2013
+
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+   of all possible destinations upstream of the agent no longer has
+   sufficient capacity for incoming load, the agent itself becomes
+   effectively overloaded.
+
+   On the other hand, there are cases where the client needs to be able
+   to select a particular server from behind an agent.  For example, if
+   a Diameter request is part of a multiple-round-trip authentication,
+   or is otherwise part of a Diameter "session", it may have a
+   Destination-Host Attribute-Value Pair (AVP) that requires that the
+   request be served by Server 1.  Therefore, the agent may need to
+   inform a client that a particular upstream server is overloaded or
+   otherwise unavailable.  Note that there can be many ways a server can
+   be specified, which may have different implications (e.g., by IP
+   address, by host name, etc).
+
+              +------------------+     +------------------+
+              |                  |     |                  |
+              |                  |     |                  |
+              |     Server 1     |     |     Server 2     |
+              |                  |     |                  |
+              +--------+-`.------+     +------.'+---------+
+                           `.               .'
+                             `.           .'
+                               `.       .'
+                                 `.   .'
+                           +-------`.'--------+
+                           |                  |
+                           |                  |
+                           |     Agent        |
+                           |                  |
+                           +--------+---------+
+                                    |
+                                    |
+                                    |
+                           +--------+---------+
+                           |                  |
+                           |                  |
+                           |     Client       |
+                           |                  |
+                           +------------------+
+
+                 Figure 5: Multiple-Server Agent Scenario
+
+
+
+
+
+
+
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+McMurry & Campbell            Informational                    [Page 12]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
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+   Figure 6 shows a scenario where an agent routes requests to a set of
+   servers for more than one Diameter realm and application.  In this
+   scenario, if Server 1 becomes overloaded or unavailable while
+   Server 2 still has available capacity, the agent may effectively
+   operate at reduced capacity for Application A but at full capacity
+   for Application B.  Therefore, the agent needs to be able to report
+   that it is overloaded for one application but not for another.
+
+   +--------------------------------------------+
+   | Application A       +----------------------+----------------------+
+   |+------------------+ |  +----------------+  |  +------------------+|
+   ||                  | |  |                |  |  |                  ||
+   ||                  | |  |                |  |  |                  ||
+   ||     Server 1     | |  |    Server 2    |  |  |     Server 3     ||
+   ||                  | |  |                |  |  |                  ||
+   |+---------+--------+ |  +-------+--------+  |  +--+---------------+|
+   |          |          |          |           |     |                |
+   +----------+----------+----------+-----------+     |                |
+              |          |          |                 |                |
+              |          |          |                 | Application B  |
+              |          +----------+-----------------+----------------+
+              |                     |                 |
+               ``--.__              |                _.
+                      ``-.__        |          __.--''
+                            `--.._  |    _..--'
+                            +----``-+.''-----+
+                            |                |
+                            |                |
+                            |    Agent       |
+                            |                |
+                            +-------+--------+
+                                    |
+                                    |
+                            +-------+--------+
+                            |                |
+                            |                |
+                            |    Client      |
+                            |                |
+                            +----------------+
+
+               Figure 6: Multiple-Application Agent Scenario
+
+
+
+
+
+
+
+
+
+
+McMurry & Campbell            Informational                    [Page 13]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+2.3.  Interconnect Scenario
+
+   Another scenario to consider when looking at Diameter overload is
+   that of multiple network operators using Diameter components
+   connected through an interconnect service, e.g., using IPX (IP Packet
+   eXchange).  IPX [IR.34] is an Inter-Operator IP Backbone that
+   provides a roaming interconnection network between mobile operators
+   and service providers.  IPX is also used to transport Diameter
+   signaling between operators [IR.88].  Figure 7 shows two network
+   operators with an interconnect network between them.  There could be
+   any number of these networks between any two network operators'
+   networks.
+
+               +-------------------------------------------+
+               |               Interconnect                |
+               |                                           |
+               |   +--------------+      +--------------+  |
+               |   |   Server 3   |------|   Server 4   |  |
+               |   +--------------+      +--------------+  |
+               |         .'                      `.        |
+               +------.-'--------------------------`.------+
+                    .'                               `.
+                 .-'                                   `.
+   ------------.'-----+                             +----`.-------------
+         +----------+ |                             | +----------+
+         | Server 1 | |                             | | Server 2 |
+         +----------+ |                             | +----------+
+                      |                             |
+   Network Operator 1 |                             | Network Operator 2
+   -------------------+                             +-------------------
+
+                Figure 7: Two-Network Interconnect Scenario
+
+   The characteristics of the information that an operator would want to
+   share over such a connection are different from the information
+   shared between components within a network operator's network.  For
+   example, network operators may not want to convey topology or
+   operational information; this would in turn limit how much overload
+   and loading information can be sent.  For the interconnect scenario
+   shown in Figure 7, Server 2 may want to signal overload to Server 1,
+   to affect traffic coming from Network Operator 1.
+
+   This case is distinct from those internal to a network operator's
+   network, where there may be many more elements in a more complicated
+   topology.  Also, the elements in the interconnect network may not
+   support Diameter overload control, and the network operators may not
+   want the interconnect network to use overload or loading information.
+   They may only want the information to pass through the interconnect
+
+
+
+McMurry & Campbell            Informational                    [Page 14]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   network without further processing or action by the interconnect
+   network, even if the elements in the interconnect network do support
+   Diameter overload control.
+
+3.  Diameter Overload Case Studies
+
+3.1.  Overload in Mobile Data Networks
+
+   As the number of smartphone devices that are Third Generation (3G)
+   and Long Term Evolution (LTE) enabled continues to expand in mobile
+   networks, there have been situations where high signaling traffic
+   load led to overload events at the Diameter-based Home Location
+   Registers (HLRs) and/or Home Subscriber Servers (HSS) [TR23.843].
+   The root causes of the HLR overload events were manifold but included
+   hardware failure and procedural errors.  The result was high
+   signaling traffic load on the HLR and HSS.
+
+   The 3GPP architecture [TS23.002] makes extensive use of Diameter.  It
+   is used for mobility management [TS29.272], the IP Multimedia
+   Subsystem (IMS) [TS29.228], and policy and charging control
+   [TS29.212], as well as other functions.  The details of the
+   architecture are out of scope for this document, but it is worth
+   noting that there are quite a few Diameter applications, some with
+   quite large amounts of Diameter signaling in deployed networks.
+
+   The 3GPP specifications do not currently address overload for
+   Diameter applications or provide a load control mechanism equivalent
+   to those provided in the more traditional SS7 elements in the Global
+   System for Mobile Communications (GSM); see [TS29.002].  The
+   capabilities specified in the 3GPP standards do not adequately
+   address the abnormal condition where excessively high signaling
+   traffic load situations are experienced.
+
+   Smartphones, which comprise an increasingly large percentage of
+   mobile devices, contribute much more heavily, relative to
+   non-smartphones, to the continuation of a registration surge, due to
+   their very aggressive registration algorithms.  Smartphone behavior
+   contributes to network loading and can contribute to overload
+   conditions.  The aggressive smartphone logic is designed to:
+
+   a.  always have voice and data registration, and
+
+   b.  constantly try to be on 3G or LTE data (and thus on 3G voice or
+       Voice over LTE (VoLTE) [IR.92]) for their added benefits.
+
+   Non-smartphones typically have logic to wait for a time period after
+   registering successfully on voice and data.
+
+
+
+
+McMurry & Campbell            Informational                    [Page 15]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   The aggressive smartphone registration is problematic in two ways:
+
+   o  first, by generating excessive signaling load towards the HSS that
+      is ten times the load from a non-smartphone, and
+
+   o  second, by causing continual registration attempts when a network
+      failure affects registrations through the 3G data network.
+
+3.2.  3GPP Study on Core Network Overload
+
+   A study in the 3GPP System Aspects working group 2 (SA2) on core
+   network overload has produced the technical report [TR23.843].  This
+   enumerates several causes of overload in mobile core networks,
+   including portions that are signaled using Diameter.  [TR23.843] is a
+   work in progress and is not complete.  However, it is useful for
+   pointing out scenarios and the general need for an overload control
+   mechanism for Diameter.
+
+   It is common for mobile networks to employ more than one radio
+   technology and to do so in an overlay fashion with multiple
+   technologies present in the same location (such as 2nd or 3rd
+   generation mobile technologies, along with LTE).  This presents
+   opportunities for traffic storms when issues occur on one overlay and
+   not another as all devices that had been on the overlay with issues
+   switch.  This causes a large amount of Diameter traffic as locations
+   and policies are updated.
+
+   Another scenario called out by this study is a flood of registration
+   and mobility management events caused by some element in the core
+   network failing.  This flood of traffic from end nodes falls under
+   the network-initiated traffic flood category.  There is likely to
+   also be traffic resulting directly from the component failure in this
+   case.  A similar flood can occur when elements or components recover
+   as well.
+
+   Subscriber-initiated traffic floods are also indicated in this study
+   as an overload mechanism where a large number of mobile devices are
+   attempting to access services at the same time, such as in response
+   to an entertainment event or a catastrophic event.
+
+   While this 3GPP study is concerned with the broader effects of these
+   scenarios on wireless networks and their elements, they have
+   implications specifically for Diameter signaling.  One of the goals
+   of this document is to provide guidance for a core mechanism that can
+   be used to mitigate the scenarios called out by this study.
+
+
+
+
+
+
+McMurry & Campbell            Informational                    [Page 16]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+4.  Existing Mechanisms
+
+   Diameter offers both implicit and explicit mechanisms for a Diameter
+   node to learn that a peer is overloaded or unreachable.  The implicit
+   mechanism is simply the lack of responses to requests.  If a client
+   fails to receive a response in a certain time period, it assumes that
+   the upstream peer is unavailable or is overloaded to the point of
+   effective unavailability.  The watchdog mechanism [RFC3539] ensures
+   that transaction responses occur at a certain rate even when there is
+   otherwise little or no other Diameter traffic.
+
+   The explicit mechanism can involve specific protocol error responses,
+   where an agent or server tells a downstream peer that it is either
+   too busy to handle a request (DIAMETER_TOO_BUSY) or unable to route a
+   request to an upstream destination (DIAMETER_UNABLE_TO_DELIVER)
+   perhaps because that destination itself is overloaded to the point of
+   unavailability.
+
+   Another explicit mechanism, a DPR (Disconnect-Peer-Request) message,
+   can be sent with a Disconnect-Cause of BUSY.  This signals the
+   sender's intent to close the transport connection and requests that
+   the client not reconnect.
+
+   Once a Diameter node learns via one of these mechanisms that an
+   upstream peer has become overloaded, it can then attempt to take
+   action to reduce the load.  This usually means forwarding traffic to
+   an alternate destination, if available.  If no alternate destination
+   is available, the node must either reduce the number of messages it
+   originates (in the case of a client) or inform the client to reduce
+   traffic (in the case of an agent).
+
+   Diameter requires the use of a congestion-managed transport layer,
+   currently TCP or SCTP, to mitigate network congestion.  It is
+   expected that these transports manage network congestion and that
+   issues with transport (e.g., congestion propagation and window
+   management) are managed at that level.  But even with a congestion-
+   managed transport, a Diameter node can become overloaded at the
+   Diameter protocol or application layers due to the causes described
+   in Section 1.2, and congestion-managed transports do not provide
+   facilities (and are at the wrong level) to handle server overload.
+   Transport-level congestion management is also not sufficient to
+   address overload in cases of multi-hop and multi-destination
+   signaling.
+
+
+
+
+
+
+
+
+McMurry & Campbell            Informational                    [Page 17]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+5.  Issues with the Current Mechanisms
+
+   The currently available Diameter mechanisms for indicating an
+   overload condition are not adequate to avoid service outages due to
+   overload.  This inadequacy may, in turn, contribute to broader
+   impacts resulting from overload due to unresponsive Diameter nodes
+   causing application-layer or transport-layer retransmissions.  In
+   particular, they do not allow a Diameter agent or server to shed load
+   as it approaches overload.  At best, a node can only indicate that it
+   needs to entirely stop receiving requests, i.e., that it has
+   effectively failed.  Even that is problematic due to the inability to
+   indicate durational validity on the transient errors available in the
+   base Diameter protocol.  Diameter offers no mechanism to allow a node
+   to indicate different overload states for different categories of
+   messages, for example, if it is overloaded for one Diameter
+   application but not another.
+
+5.1.  Problems with Implicit Mechanism
+
+   The implicit mechanism doesn't allow an agent or server to inform the
+   client of a problem until it is effectively too late to do anything
+   about it.  The client does not know that it needs to take action
+   until the upstream node has effectively failed.  A Diameter node has
+   no opportunity to shed load early to avoid collapse in the first
+   place.
+
+   Additionally, the implicit mechanism cannot distinguish between
+   overload of a Diameter node and network congestion.  Diameter treats
+   the failure to receive an answer as a transport failure.
+
+5.2.  Problems with Explicit Mechanisms
+
+   The Diameter specification is ambiguous on how a client should handle
+   receipt of a DIAMETER_TOO_BUSY response.  The base specification
+   [RFC6733] indicates that the sending client should attempt to send
+   the request to a different peer.  It makes no suggestion that the
+   receipt of a DIAMETER_TOO_BUSY response should affect future Diameter
+   messages in any way.
+
+   The Authentication, Authorization, and Accounting (AAA) Transport
+   Profile [RFC3539] recommends that a AAA node that receives a "Busy"
+   response failover all remaining requests to a different agent or
+   server.  But while the Diameter base specification explicitly depends
+   on [RFC3539] to define transport behavior, it does not refer to
+   [RFC3539] in the description of behavior on receipt of a
+   DIAMETER_TOO_BUSY error.  There's a strong likelihood that at least
+   some implementations will continue to send Diameter requests to an
+   upstream peer even after receiving a DIAMETER_TOO_BUSY error.
+
+
+
+McMurry & Campbell            Informational                    [Page 18]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   BCP 41 [RFC2914] describes, among other things, how end-to-end
+   application behavior can help avoid congestion collapse.  In
+   particular, an application should avoid sending messages that will
+   never be delivered or processed.  The DIAMETER_TOO_BUSY behavior as
+   described in the Diameter base specification fails at this, since if
+   an upstream node becomes overloaded, a client attempts each request
+   and does not discover the need to failover the request until the
+   initial attempt fails.
+
+   The situation is improved if implementations follow the [RFC3539]
+   recommendation to keep state about upstream peer overload.  But even
+   then, the Diameter specification offers no guidance on how long a
+   client should wait before retrying the overloaded destination.  If an
+   agent or server supports multiple realms and/or applications,
+   DIAMETER_TOO_BUSY offers no way to indicate that it is overloaded for
+   one application but not another.  A DIAMETER_TOO_BUSY error can only
+   indicate overload at a "whole server" scope.
+
+   Agent processing of a DIAMETER_TOO_BUSY response is also problematic
+   as described in the base specification.  DIAMETER_TOO_BUSY is defined
+   as a protocol error.  If an agent receives a protocol error, it may
+   either handle it locally or forward the response back towards the
+   downstream peer.  If a downstream peer receives the DIAMETER_TOO_BUSY
+   response, it may stop sending all requests to the agent for some
+   period of time, even though the agent may still be able to deliver
+   requests to other upstream peers.
+
+   DIAMETER_UNABLE_TO_DELIVER errors, or using DPR with cause code BUSY,
+   also have no mechanisms for specifying the scope or cause of the
+   failure, or the durational validity.
+
+   The issues with error responses described in [RFC6733] extend beyond
+   the particular issues for overload control and have been addressed in
+   an ad hoc fashion by various implementations.  Addressing these in a
+   standard way would be a useful exercise, but it is beyond the scope
+   of this document.
+
+6.  Extensibility and Application Independence
+
+   Given the variety of scenarios in which Diameter elements can be
+   deployed and the variety of roles they can fulfill with Diameter and
+   other technologies, a single algorithm for handling overload may not
+   be sufficient.  For purposes of this discussion, an algorithm is
+   inclusive of behavior for control of overload but does not encompass
+   the general mechanism for transporting control information.  This
+   effort cannot anticipate all possible future scenarios and roles.
+   Extensibility, particularly of algorithms used to deal with overload,
+   will be important to cover these cases.
+
+
+
+McMurry & Campbell            Informational                    [Page 19]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   Similarly, the scopes to which overload information may apply may
+   include cases that have not yet been considered.  Extensibility in
+   this area will also be important.
+
+   The basic mechanism is intended to be application independent, that
+   is, a Diameter node can use it across any existing and future
+   Diameter applications and expect reasonable results.  Certain
+   Diameter applications might, however, benefit from application-
+   specific behavior over and above the mechanism's defaults.  For
+   example, an application specification might specify relative
+   priorities of messages or selection of a specific overload control
+   algorithm.
+
+7.  Solution Requirements
+
+   This section proposes requirements for an improved mechanism to
+   control Diameter overload, with the goals of addressing the issues
+   described in Section 5 and supporting the scenarios described in
+   Section 2.  These requirements are stated primarily in terms of
+   individual node behavior to inform the design of the improved
+   mechanism; solution designers should keep in mind that the overall
+   goal is improved overall system behavior across all the nodes
+   involved, not just improved behavior from specific individual nodes.
+
+7.1.  General
+
+   REQ 1:  The solution MUST provide a communication method for Diameter
+           nodes to exchange load and overload information.
+
+   REQ 2:  The solution MUST allow Diameter nodes to support overload
+           control regardless of which Diameter applications they
+           support.  Diameter clients and agents must be able to use the
+           received load and overload information to support graceful
+           behavior during an overload condition.  Graceful behavior
+           under overload conditions is best described by REQ 3.
+
+   REQ 3:  The solution MUST limit the impact of overload on the overall
+           useful throughput of a Diameter server, even when the
+           incoming load on the network is far in excess of its
+           capacity.  The overall useful throughput under load is the
+           ultimate measure of the value of a solution.
+
+   REQ 4:  Diameter allows requests to be sent from either side of a
+           connection, and either side of a connection may have need to
+           provide its overload status.  The solution MUST allow each
+           side of a connection to independently inform the other of its
+           overload status.
+
+
+
+
+McMurry & Campbell            Informational                    [Page 20]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   REQ 5:  Diameter allows nodes to determine their peers via dynamic
+           discovery or manual configuration.  The solution MUST work
+           consistently without regard to how peers are determined.
+
+   REQ 6:  The solution designers SHOULD seek to minimize the amount of
+           new configuration required in order to work.  For example, it
+           is better to allow peers to advertise or negotiate support
+           for the solution, rather than to require that this knowledge
+           be configured at each node.
+
+7.2.  Performance
+
+   REQ 7:  The solution and any associated default algorithm(s) MUST
+           ensure that the system remains stable.  At some point after
+           an overload condition has ended, the solution MUST enable
+           capacity to stabilize and become equal to what it would be in
+           the absence of an overload condition.  Note that this also
+           requires that the solution MUST allow nodes to shed load
+           without introducing non-converging oscillations during or
+           after an overload condition.
+
+   REQ 8:  Supporting nodes MUST be able to distinguish current overload
+           information from stale information.
+
+   REQ 9:  The solution MUST function across fully loaded as well as
+           quiescent transport connections.  This is partially derived
+           from the requirement for stability in REQ 7.
+
+   REQ 10: Consumers of overload information MUST be able to determine
+           when the overload condition improves or ends.
+
+   REQ 11: The solution MUST be able to operate in networks of different
+           sizes.
+
+   REQ 12: When a single network node fails, goes into overload, or
+           suffers from reduced processing capacity, the solution MUST
+           make it possible to limit the impact of the affected node on
+           other nodes in the network.  This helps to prevent a small-
+           scale failure from becoming a widespread outage.
+
+   REQ 13: The solution MUST NOT introduce substantial additional work
+           for a node in an overloaded state.  For example, a
+           requirement for an overloaded node to send overload
+           information every time it received a new request would
+           introduce substantial work.
+
+
+
+
+
+
+McMurry & Campbell            Informational                    [Page 21]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   REQ 14: Some scenarios that result in overload involve a rapid
+           increase of traffic with little time between normal levels
+           and levels that induce overload.  The solution SHOULD provide
+           for rapid feedback when traffic levels increase.
+
+   REQ 15: The solution MUST NOT interfere with the congestion control
+           mechanisms of underlying transport protocols.  For example, a
+           solution that opened additional TCP connections when the
+           network is congested would reduce the effectiveness of the
+           underlying congestion control mechanisms.
+
+7.3.  Heterogeneous Support for Solution
+
+   REQ 16: The solution is likely to be deployed incrementally.  The
+           solution MUST support a mixed environment where some, but not
+           all, nodes implement it.
+
+   REQ 17: In a mixed environment with nodes that support the solution
+           and nodes that do not, the solution MUST NOT result in
+           materially less useful throughput during overload as would
+           have resulted if the solution were not present.  It SHOULD
+           result in less severe overload in this environment.
+
+   REQ 18: In a mixed environment of nodes that support the solution and
+           nodes that do not, the solution MUST NOT preclude elements
+           that support overload control from treating elements that do
+           not support overload control in an equitable fashion relative
+           to those that do.  Users and operators of nodes that do not
+           support the solution MUST NOT unfairly benefit from the
+           solution.  The solution specification SHOULD provide guidance
+           to implementors for dealing with elements not supporting
+           overload control.
+
+   REQ 19: It MUST be possible to use the solution between nodes in
+           different realms and in different administrative domains.
+
+   REQ 20: Any explicit overload indication MUST be clearly
+           distinguishable from other errors reported via Diameter.
+
+   REQ 21: In cases where a network node fails, is so overloaded that it
+           cannot process messages, or cannot communicate due to a
+           network failure, it may not be able to provide explicit
+           indications of the nature of the failure or its levels of
+           overload.  The solution MUST result in at least as much
+           useful throughput as would have resulted if the solution were
+           not in place.
+
+
+
+
+
+McMurry & Campbell            Informational                    [Page 22]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+7.4.  Granular Control
+
+   REQ 22: The solution MUST provide a way for a node to throttle the
+           amount of traffic it receives from a peer node.  This
+           throttling SHOULD be graded so that it can be applied
+           gradually as offered load increases.  Overload is not a
+           binary state; there may be degrees of overload.
+
+   REQ 23: The solution MUST provide sufficient information to enable a
+           load-balancing node to divert messages that are rejected or
+           otherwise throttled by an overloaded upstream node to other
+           upstream nodes that are the most likely to have sufficient
+           capacity to process them.
+
+   REQ 24: The solution MUST provide a mechanism for indicating load
+           levels, even when not in an overload condition, to assist
+           nodes in making decisions to prevent overload conditions from
+           occurring.
+
+7.5.  Priority and Policy
+
+   REQ 25: The base specification for the solution SHOULD offer general
+           guidance on which message types might be desirable to send or
+           process over others during times of overload, based on
+           application-specific considerations.  For example, it may be
+           more beneficial to process messages for existing sessions
+           ahead of new sessions.  Some networks may have a requirement
+           to give priority to requests associated with emergency
+           sessions.  Any normative or otherwise detailed definition of
+           the relative priorities of message types during an overload
+           condition will be the responsibility of the application
+           specification.
+
+   REQ 26: The solution MUST NOT prevent a node from prioritizing
+           requests based on any local policy, so that certain requests
+           are given preferential treatment, given additional
+           retransmission, not throttled, or processed ahead of others.
+
+7.6.  Security
+
+   REQ 27: The solution MUST NOT provide new vulnerabilities to
+           malicious attack or increase the severity of any existing
+           vulnerabilities.  This includes vulnerabilities to DoS and
+           DDoS attacks as well as replay and man-in-the-middle attacks.
+           Note that the Diameter base specification [RFC6733] lacks
+           end-to-end security, and this must be considered (see
+           Security Considerations in this document (Section 8)).  Note
+
+
+
+
+McMurry & Campbell            Informational                    [Page 23]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+           that this requirement was expressed at a high level so as to
+           not preclude any particular solution.  Is is expected that
+           the solution will address this in more detail.
+
+   REQ 28: The solution MUST NOT depend on being deployed in
+           environments where all Diameter nodes are completely trusted.
+           It SHOULD operate as effectively as possible in environments
+           where other nodes are malicious; this includes preventing
+           malicious nodes from obtaining more than a fair share of
+           service.  Note that this does not imply any responsibility on
+           the solution to detect, or take countermeasures against,
+           malicious nodes.
+
+   REQ 29: It MUST be possible for a supporting node to make
+           authorization decisions about what information will be sent
+           to peer nodes based on the identity of those nodes.  This
+           allows a domain administrator who considers the load of their
+           nodes to be sensitive information to restrict access to that
+           information.  Of course, in such cases, there is no
+           expectation that the solution itself will help prevent
+           overload from that peer node.
+
+   REQ 30: The solution MUST NOT interfere with any Diameter-compliant
+           method that a node may use to protect itself from overload
+           from non-supporting nodes or from denial-of-service attacks.
+
+7.7.  Flexibility and Extensibility
+
+   REQ 31: There are multiple situations where a Diameter node may be
+           overloaded for some purposes but not others.  For example,
+           this can happen to an agent or server that supports multiple
+           applications, or when a server depends on multiple external
+           resources, some of which may become overloaded while others
+           are fully available.  The solution MUST allow Diameter nodes
+           to indicate overload with sufficient granularity to allow
+           clients to take action based on the overloaded resources
+           without unreasonably forcing available capacity to go unused.
+           The solution MUST support specification of overload
+           information with granularities of at least "Diameter node",
+           "realm", and "Diameter application" and MUST allow
+           extensibility for others to be added in the future.
+
+   REQ 32: The solution MUST provide a method for extending the
+           information communicated and the algorithms used for overload
+           control.
+
+
+
+
+
+
+McMurry & Campbell            Informational                    [Page 24]
+
+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   REQ 33: The solution MUST provide a default algorithm that is
+           mandatory to implement.
+
+   REQ 34: The solution SHOULD provide a method for exchanging overload
+           and load information between elements that are connected by
+           intermediaries that do not support the solution.
+
+8.  Security Considerations
+
+   A Diameter overload control mechanism is primarily concerned with the
+   load-related and overload-related behavior of nodes in a Diameter
+   network, and the information used to affect that behavior.  Load and
+   overload information is shared between nodes and directly affects the
+   behavior, and thus the information is potentially vulnerable to a
+   number of methods of attack.
+
+   Load and overload information may also be sensitive from both
+   business and network protection viewpoints.  Operators of Diameter
+   equipment want to control the visibility of load and overload
+   information to keep it from being used for competitive intelligence
+   or for targeting attacks.  It is also important that the Diameter
+   overload control mechanism not introduce any way in which any other
+   information carried by Diameter is sent inappropriately.
+
+   Note that the Diameter base specification [RFC6733] lacks end-to-end
+   security, making it difficult for non-adjacent nodes to verify the
+   authenticity and ownership of load and overload information.
+   Authentication of load and overload information helps to alleviate
+   several of the security issues listed in this section.
+
+   This document includes requirements intended to mitigate the effects
+   of attacks and to protect the information used by the mechanism.
+   This section discusses potential security considerations for overload
+   control solutions.  This discussion provides the motivation for
+   several normative requirements described in Section 7.  The
+   discussion includes specific references to the normative requirements
+   that apply for each issue.
+
+8.1.  Access Control
+
+   To control the visibility of load and overload information, sending
+   should be subject to some form of authentication and authorization of
+   the receiver.  It is also important to the receivers that they are
+   confident the load and overload information they receive is from a
+   legitimate source.  REQ 28 requires that the solution work without
+   assuming that all Diameter nodes in a network are trusted for the
+   purposes of exchanging overload and load information.  REQ 29
+   requires that the solution let nodes restrict unauthorized parties
+
+
+
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+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   from seeing overload information.  Note that this implies a certain
+   amount of configurability on the nodes supporting the Diameter
+   overload control mechanism.
+
+8.2.  Denial-of-Service Attacks
+
+   An overload control mechanism provides a very attractive target for
+   denial-of-service attacks.  A small number of messages may effect a
+   large service disruption by falsely reporting overload conditions.
+   Alternately, attacking servers nearing, or in, overload may also be
+   facilitated by disrupting their overload indications, potentially
+   preventing them from mitigating their overload condition.
+
+   A design goal for the Diameter overload control mechanism is to
+   minimize or eliminate the possibility of using the mechanism for this
+   type of attack.  More strongly, REQ 27 forbids the solution from
+   introducing new vulnerabilities to malicious attack.  Additionally,
+   REQ 30 stipulates that the solution not interfere with other
+   mechanisms used for protection against denial-of-service attacks.
+
+   As the intent of some denial-of-service attacks is to induce overload
+   conditions, an effective overload control mechanism should help to
+   mitigate the effects of such an attack.
+
+8.3.  Replay Attacks
+
+   An attacker that has managed to obtain some messages from the
+   overload control mechanism may attempt to affect the behavior of
+   nodes supporting the mechanism by sending those messages at
+   potentially inopportune times.  In addition to time shifting, replay
+   attacks may send messages to other nodes as well (target shifting).
+
+   A design goal for the Diameter overload control solution is to
+   minimize or eliminate the possibility of causing disruption by using
+   a replay attack on the Diameter overload control mechanism.
+   (Allowing a replay attack using the overload control solution would
+   violate REQ 27.)
+
+8.4.  Man-in-the-Middle Attacks
+
+   By inserting themselves between two nodes supporting the Diameter
+   overload control mechanism, an attacker may potentially both access
+   and alter the information sent between those nodes.  This can be used
+   for information gathering for business intelligence and attack
+   targeting, as well as direct attacks.
+
+
+
+
+
+
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+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   REQs 27, 28, and 29 imply a need to prevent man-in-the-middle attacks
+   on the overload control solution.  A transport using Transport Layer
+   Security (TLS) and/or IPsec may be desirable for this purpose.
+
+8.5.  Compromised Hosts
+
+   A compromised host that supports the Diameter overload control
+   mechanism could be used for information gathering as well as for
+   sending malicious information to any Diameter node that would
+   normally accept information from it.  While it is beyond the scope of
+   the Diameter overload control mechanism to mitigate any operational
+   interruption to the compromised host, REQs 28 and 29 imply a need to
+   minimize the impact that a compromised host can have on other nodes
+   through the use of the Diameter overload control mechanism.  Of
+   course, a compromised host could be used to cause damage in a number
+   of other ways.  This is out of scope for a Diameter overload control
+   mechanism.
+
+9.  References
+
+9.1.  Normative References
+
+   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
+               Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [RFC6733]   Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
+               "Diameter Base Protocol", RFC 6733, October 2012.
+
+   [RFC2914]   Floyd, S., "Congestion Control Principles", BCP 41,
+               RFC 2914, September 2000.
+
+   [RFC3539]   Aboba, B. and J. Wood, "Authentication, Authorization and
+               Accounting (AAA) Transport Profile", RFC 3539, June 2003.
+
+9.2.  Informative References
+
+   [RFC5390]   Rosenberg, J., "Requirements for Management of Overload
+               in the Session Initiation Protocol", RFC 5390,
+               December 2008.
+
+   [RFC6357]   Hilt, V., Noel, E., Shen, C., and A. Abdelal, "Design
+               Considerations for Session Initiation Protocol (SIP)
+               Overload Control", RFC 6357, August 2011.
+
+   [TR23.843]  3GPP, "Study on Core Network (CN) overload solutions",
+               TR 23.843 1.2.0, Work in Progress, October 2013.
+
+
+
+
+
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+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+   [IR.34]     GSMA, "Inter-Service Provider IP Backbone Guidelines",
+               IR 34 9.1, May 2013.
+
+   [IR.88]     GSMA, "LTE Roaming Guidelines", IR 88 9.0, January 2013.
+
+   [IR.92]     GSMA, "IMS Profile for Voice and SMS", IR 92 7.0,
+               March 2013.
+
+   [TS23.002]  3GPP, "Network Architecture", TS 23.002 12.2.0,
+               June 2013.
+
+   [TS29.272]  3GPP, "Evolved Packet System (EPS); Mobility Management
+               Entity (MME) and Serving GPRS Support Node (SGSN) related
+               interfaces based on Diameter protocol", TS 29.272 12.2.0,
+               September 2013.
+
+   [TS29.212]  3GPP, "Policy and Charging Control (PCC) over Gx/Sd
+               reference point", TS 29.212 12.2.0, September 2013.
+
+   [TS29.228]  3GPP, "IP Multimedia (IM) Subsystem Cx and Dx interfaces;
+               Signalling flows and message contents", TS 29.228 12.0.0,
+               September 2013.
+
+   [TS29.002]  3GPP, "Mobile Application Part (MAP) specification",
+               TS 29.002 12.2.0, September 2013.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
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+RFC 7068         Diameter Overload Control Requirements    November 2013
+
+
+Appendix A.  Contributors
+
+   Significant contributions to this document were made by Adam Roach
+   and Eric Noel.
+
+Appendix B.  Acknowledgements
+
+   Review of, and contributions to, this specification by Martin Dolly,
+   Carolyn Johnson, Jianrong Wang, Imtiaz Shaikh, Jouni Korhonen, Robert
+   Sparks, Dieter Jacobsohn, Janet Gunn, Jean-Jacques Trottin, Laurent
+   Thiebaut, Andrew Booth, and Lionel Morand were most appreciated.  We
+   would like to thank them for their time and expertise.
+
+Authors' Addresses
+
+   Eric McMurry
+   Oracle
+   17210 Campbell Rd.
+   Suite 250
+   Dallas, TX  75252
+   US
+
+   EMail: [email protected]
+
+
+   Ben Campbell
+   Oracle
+   17210 Campbell Rd.
+   Suite 250
+   Dallas, TX  75252
+   US
+
+   EMail: [email protected]
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
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+