RFC 8903

Internet Engineering Task Force (IETF)                        R. Dobbins
Request for Comments: 8903                                Netscout, Inc.
Category: Informational                                       D. Migault
ISSN: 2070-1721                                                 Ericsson
                                                            R. Moskowitz
                                                          HTT Consulting
                                                               N. Teague
                                              Iron Mountain Data Centers
                                                                  L. Xia
                                                            K. Nishizuka
                                                      NTT Communications
                                                                May 2021

                Use Cases for DDoS Open Threat Signaling


   The DDoS Open Threat Signaling (DOTS) effort is intended to provide
   protocols to facilitate interoperability across disparate DDoS
   Mitigation solutions.  This document presents sample use cases that
   describe the interactions expected between the DOTS components as
   well as DOTS messaging exchanges.  These use cases are meant to
   identify the interacting DOTS components, how they collaborate, and
   what the typical information to be exchanged is.

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 candidates for any level of Internet
   Standard; see 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

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology and Acronyms
   3.  Use Cases
     3.1.  Upstream DDoS Mitigation by an Upstream Internet Transit
     3.2.  DDoS Mitigation by a Third-Party DDoS Mitigation Service
     3.3.  DDoS Orchestration
   4.  Security Considerations
   5.  IANA Considerations
   6.  Informative References

   Authors' Addresses

1.  Introduction

   At the time of writing, distributed denial-of-service (DDoS) attack
   mitigation solutions are largely based upon siloed, proprietary
   communications schemes with vendor lock-in as a side effect.  This
   can result in the configuration, provisioning, operation, and
   activation of these solutions being a highly manual and often time-
   consuming process.  Additionally, coordinating multiple DDoS
   Mitigation solutions simultaneously is fraught with both technical
   and process-related hurdles.  This greatly increases operational
   complexity, which in turn can degrade the efficacy of mitigations
   that are generally highly dependent on a timely reaction by the

   The DDoS Open Threat Signaling (DOTS) effort is intended to specify
   protocols that facilitate interoperability between diverse DDoS
   Mitigation solutions and ensure greater integration in terms of
   attack detection, mitigation requests, and attack characterization

   As DDoS solutions are broadly heterogeneous among vendors, the
   primary goal of DOTS is to provide high-level interaction amongst
   differing DDoS solutions, such as detecting DDoS attacks, initiating/
   terminating DDoS Mitigation assistance, or requesting the status of a
   DDoS Mitigation.

   This document provides sample use cases that provided input for the
   requirements [RFC8612] and design of the DOTS protocols
   [RFC8782][RFC8783].  The use cases are not exhaustive, and future use
   cases are expected to emerge as DOTS is adopted and evolves.

2.  Terminology and Acronyms

   This document makes use of the same terminology and definitions as
   [RFC8612].  In addition, it uses the terms defined below:

   DDoS Mitigation System (DMS):
      A system that performs DDoS Mitigation.  The DDoS Mitigation
      System may be composed of a cluster of hardware and/or software
      resources but could also involve an orchestrator that may make
      decisions, such as outsourcing some or all of the mitigation to
      another DDoS Mitigation System.

   DDoS Mitigation:
      The action performed by the DDoS Mitigation System.

   DDoS Mitigation Service:
      Designates a service provided to a customer to mitigate DDoS
      attacks.  Each service subscription usually involve Service Level
      Agreement (SLA) that has to be met.  It is the responsibility of
      the DDoS Service provider to instantiate the DDoS Mitigation
      System to meet these SLAs.

   DDoS Mitigation Service Provider:
      Designates the administrative entity providing the DDoS Mitigation

   Internet Transit Provider (ITP):
      Designates the entity that delivers the traffic to a customer
      network.  It can be an Internet Service Provider (ISP) or an
      upstream entity delivering the traffic to the ISP.

3.  Use Cases

3.1.  Upstream DDoS Mitigation by an Upstream Internet Transit Provider

   This use case describes how an enterprise or a residential customer
   network may take advantage of a pre-existing relation with its ITP in
   order to mitigate a DDoS attack targeting its network.

   For clarity of discussion, the targeted network is indicated as an
   enterprise network, but the same scenario applies to any downstream
   network, including residential and cloud hosting networks.

   As the ITP provides connectivity to the enterprise network, it is
   already on the path of the inbound and outbound traffic of the
   enterprise network and is well aware of the networking parameters
   associated with the enterprise network WAN connectivity.  This eases
   both the configuration and the instantiation of a DDoS Mitigation

   This section considers two kinds of DDoS Mitigation Service between
   an enterprise network and an ITP:

   *  The upstream ITP may instantiate a DMS upon receiving a request
      from the enterprise network.  This typically corresponds to a case
      when the enterprise network is under attack.

   *  On the other hand, the ITP may identify an enterprise network as
      the source of an attack and send a mitigation request to the
      enterprise DMS to mitigate this at the source.

   The two scenarios, though different, have similar interactions
   between the DOTS client and server.  For the sake of simplicity, only
   the first scenario will be detailed in this section.  Nevertheless,
   the second scenario is also in scope for DOTS.

   In the first scenario, as depicted in Figure 1, an enterprise network
   with self-hosted Internet-facing properties such as web servers,
   authoritative DNS servers, and Voice over IP (VoIP) servers has a DMS
   deployed to protect those servers and applications from DDoS attacks.
   In addition to on-premise DDoS defense capabilities, the enterprise
   has contracted with its ITP for DDoS Mitigation Services when attacks
   threaten to overwhelm the bandwidth of their WAN link(s).

       +------------------+        +------------------+
       | Enterprise       |        | Upstream         |
       | Network          |        | Internet Transit |
       |                  |        | Provider         |
       |      +--------+  |        |             DDoS Attack
       |      | DDoS   |  | <=================================
       |      | Target |  | <=================================
       |      +--------+  |        |  +------------+  |
       |                  | +-------->| DDoS       |  |
       |                  | |      |S | Mitigation |  |
       |                  | |      |  | System     |  |
       |                  | |      |  +------------+  |
       |                  | |      |                  |
       |                  | |      |                  |
       |                  | |      |                  |
       |  +------------+  | |      |                  |
       |  | DDoS       |<---+      |                  |
       |  | Mitigation |C |        |                  |
       |  | System     |  |        |                  |
       |  +------------+  |        |                  |
       +------------------+        +------------------+

          * C is for DOTS client functionality
          * S is for DOTS server functionality

        Figure 1: Upstream Internet Transit Provider DDoS Mitigation

   The enterprise DMS is configured such that if the incoming Internet
   traffic volume exceeds 50% of the provisioned upstream Internet WAN
   link capacity, the DMS will request DDoS Mitigation assistance from
   the upstream transit provider.  More sophisticated detection means
   may be considered as well.

   The requests to trigger, manage, and finalize a DDoS Mitigation
   between the enterprise DMS and the ITP are made using DOTS.  The
   enterprise DMS implements a DOTS client while the ITP implements a
   DOTS server, which is integrated with their DMS in this example.

   When the enterprise DMS locally detects an inbound DDoS attack
   targeting its resources (e.g., servers, hosts, or applications), it
   immediately begins a DDoS Mitigation.

   During the course of the attack, the inbound traffic volume to the
   enterprise network exceeds the 50% threshold, and the enterprise DMS
   escalates the DDoS Mitigation.  The enterprise DMS DOTS client
   signals to the DOTS server on the upstream ITP to initiate DDoS
   Mitigation.  The DOTS server replies to the DOTS client that it can
   serve this request, and mitigation is initiated on the ITP network by
   the ITP DMS.

   Over the course of the attack, the DOTS server of the ITP
   periodically informs the DOTS client on the mitigation status,
   statistics related to DDoS attack traffic mitigation, and related
   information.  Once the DDoS attack has ended or decreased to a
   certain level that the enterprise DMS might handle by itself, the
   DOTS server signals the enterprise DMS DOTS client that the attack
   has subsided.

   The DOTS client on the enterprise DMS then requests that the ITP
   terminate the DDoS Mitigation.  The DOTS server on the ITP receives
   this request and, once the mitigation has ended, confirms the end of
   upstream DDoS Mitigation to the enterprise DMS DOTS client.

   The following is an overview of the DOTS communication model for this
   use case:

   1.  A DDoS attack is initiated against resources of a network
       organization (here, the enterprise), which has deployed a DOTS-
       capable DMS -- typically a DOTS client.

   2.  The enterprise DMS detects, classifies, and begins the DDoS

   3.  The enterprise DMS determines that its capacity and/or capability
       to mitigate the DDoS attack is insufficient and sends a DOTS DDoS
       Mitigation request via its DOTS client to one or more DOTS
       servers residing on the upstream ITP.

   4.  The DOTS server, which receives the DOTS Mitigation request,
       determines that it has been configured to honor requests from the
       requesting DOTS client and does so by orchestrating its own DMS.

   5.  While the DDoS Mitigation is active, the DOTS server regularly
       transmits DOTS DDoS Mitigation status updates to the DOTS client.

   6.  Informed by the DOTS server status update that the attack has
       ended or subsided, the DOTS client transmits a DOTS DDoS
       Mitigation termination request to the DOTS server.

   7.  The DOTS server terminates DDoS Mitigation and sends the
       notification to the DOTS client.

   Note that communications between the enterprise DOTS client and the
   upstream ITP DOTS server may take place in band within the main
   Internet WAN link between the enterprise and the ITP; out of band via
   a separate, dedicated wireline network link utilized solely for DOTS
   signaling; or out of band via some other form of network connectivity
   such as third-party wireless 4G network connectivity.

   Note also that a DOTS client that sends a DOTS Mitigation request may
   also be triggered by a network admin that manually confirms the
   request to the upstream ITP, in which case the request may be sent
   from an application such as a web browser or a dedicated mobile

   Note also that when the enterprise is multihomed and connected to
   multiple upstream ITPs, each ITP is only able to provide a DDoS
   Mitigation Service for the traffic it transits.  As a result, the
   enterprise network may be required to coordinate the various DDoS
   Mitigation Services associated with each link.  More multihoming
   considerations are discussed in [DOTS-MULTIHOMING].

3.2.  DDoS Mitigation by a Third-Party DDoS Mitigation Service Provider

   This use case differs from the previous use case described in
   Section 3.1 in that the DDoS Mitigation Service is not provided by an
   upstream ITP.  In other words, as represented in Figure 2, the
   traffic is not forwarded through the DDoS Mitigation Service Provider
   by default.  In order to steer the traffic to the DDoS Mitigation
   Service Provider, some network configuration changes are required.
   As such, this use case is likely to apply to large enterprises or
   large data centers but, as for the other use cases, is not
   exclusively limited to them.

   Another typical scenario for this use case is for there to be a
   relationship between DDoS Mitigation Service Providers, forming an
   overlay of DMS.  When a DDoS Mitigation Service Provider mitigating a
   DDoS attack reaches its resource capacity, it may choose to delegate
   the DDoS Mitigation to another DDoS Mitigation Service Provider.

      +------------------+        +------------------+
      | Enterprise       |        | Upstream         |
      | Network          |        | Internet Transit |
      |                  |        | Provider         |
      |      +--------+  |        |             DDoS Attack
      |      | DDoS   |  | <=================================
      |      | Target |  | <=================================
      |      +--------+  |        |                  |
      |                  |        |                  |
      |                  |        +------------------+
      |                  |
      |                  |        +------------------+
      |                  |        | DDoS Mitigation  |
      |                  |        | Service Provider |
      |                  |        |                  |
      |  +------------+  |        |  +------------+  |
      |  | DDoS       |<------------>| DDoS       |  |
      |  | Mitigation |C |        | S| Mitigation |  |
      |  | System     |  |        |  | System     |  |
      |  +------------+  |        |  +------------+  |
      +------------------+        +------------------+

          * C is for DOTS client functionality
          * S is for DOTS server functionality

       Figure 2: DDoS Mitigation between an Enterprise Network and a
                Third-Party DDoS Mitigation Service Provider

   In this scenario, an enterprise network has entered into a
   prearranged DDoS Mitigation assistance agreement with one or more
   third-party DDoS Mitigation Service Providers in order to ensure that
   sufficient DDoS Mitigation capacity and/or capabilities may be
   activated in the event that a given DDoS attack threatens to
   overwhelm the ability of the enterprise or any other given DMS to
   mitigate the attack on its own.

   The prearrangement typically includes agreement on the mechanisms
   used to redirect the traffic to the DDoS Mitigation Service Provider,
   as well as the mechanism to re-inject the traffic back to the
   Enterprise Network.  Redirection to the DDoS Mitigation Service
   Provider typically involves BGP prefix announcement or DNS
   redirection, while re-injection of the scrubbed traffic to the
   enterprise network may be performed via tunneling mechanisms (e.g.,
   GRE).  The exact mechanisms used for traffic steering are out of
   scope of DOTS but will need to be prearranged, while in some contexts
   such changes could be detected and considered as an attack.

   In some cases, the communication between the enterprise DOTS client
   and the DOTS server of the DDoS Mitigation Service Provider may go
   through the ITP carrying the DDoS attack, which would affect the
   communication.  On the other hand, the communication between the DOTS
   client and DOTS server may take a path that is not undergoing a DDoS

     +------------------+        +------------------+
     | Enterprise       |        | Upstream         |
     | Network          |        | Internet Transit |
     |                  |        | Provider         |
     |      +--------+  |        |             DDoS Attack
     |      | DDoS   |  |<----------------+         | ++====
     |      | Target |  |    Mitigated    |         | || ++=
     |      +--------+  |        |        |         | || ||
     |                  |        |        |         | || ||
     |                  |        +--------|---------+ || ||
     |                  |                 |           || ||
     |                  |        +--------|---------+ || ||
     |                  |        | DDoS Mitigation  | || ||
     |                  |        | Service Provider | || ||
     |                  |        |        |         | || ||
     |  +------------+  |        |  +------------+  | || ||
     |  | DDoS       |<------------>| DDoS       |  | || ||
     |  | mitigation |C |        |S | mitigation |<===++ ||
     |  | system     |  |        |  | system     |<======++
     |  +------------+  |        |  +------------+  |
     +------------------+        +------------------+

          * C is for DOTS client functionality
          * S is for DOTS server functionality

        Figure 3: Redirection to a DDoS Mitigation Service Provider

   When the enterprise network is under attack or at least is reaching
   its capacity or ability to mitigate a given DDoS attack, the DOTS
   client sends a DOTS request to the DDoS Mitigation Service Provider
   to initiate network traffic diversion -- as represented in Figure 3
   -- and DDoS Mitigation activities.  Ongoing attack and mitigation
   status messages may be passed between the enterprise network and the
   DDoS Mitigation Service Provider using DOTS.  If the DDoS attack has
   stopped or the severity of the attack has subsided, the DOTS client
   can request that the DDoS Mitigation Service Provider terminate the
   DDoS Mitigation.

3.3.  DDoS Orchestration

   In this use case, one or more DDoS telemetry systems or monitoring
   devices monitor a network -- typically an ISP network, an enterprise
   network, or a data center.  Upon detection of a DDoS attack, these
   DDoS telemetry systems alert an orchestrator in charge of
   coordinating the various DMSs within the domain.  The DDoS telemetry
   systems may be configured to provide required information, such as a
   preliminary analysis of the observation, to the orchestrator.

   The orchestrator analyzes the various sets of information it receives
   from DDoS telemetry systems and initiates one or more DDoS Mitigation
   strategies.  For example, the orchestrator could select the DMS in
   the enterprise network or one provided by the ITP.

   DMS selection and DDoS Mitigation techniques may depend on the type
   of the DDoS attack.  In some cases, a manual confirmation or
   selection may also be required to choose a proposed strategy to
   initiate a DDoS Mitigation.  The DDoS Mitigation may consist of
   multiple steps such as configuring the network or updating already-
   instantiated DDoS Mitigation functions.  Eventually, the coordination
   of the mitigation may involve external DDoS Mitigation resources such
   as a transit provider or a third-party DDoS Mitigation Service

   The communication used to trigger a DDoS Mitigation between the DDoS
   telemetry and monitoring systems and the orchestrator is performed
   using DOTS.  The DDoS telemetry system implements a DOTS client while
   the orchestrator implements a DOTS server.

   The communication between a network administrator and the
   orchestrator is also performed using DOTS.  The network administrator
   uses, for example, a web interface that interacts with a DOTS client,
   while the orchestrator implements a DOTS server.

   The communication between the orchestrator and the DMSs is performed
   using DOTS.  The orchestrator implements a DOTS client while the DMSs
   implement a DOTS server.

   The configuration aspects of each DMS, as well as the instantiations
   of DDoS Mitigation functions or network configuration, are not part
   of DOTS.  Similarly, the discovery of available DDoS Mitigation
   functions is not part of DOTS and, as such, is out of scope.

          | network  |C            (Enterprise Network)
          | admini-  |<-+
          | strator  |  |
          +----------+  |
          +----------+  | S+--------------+     +-----------+
          |telemetry/|  +->|              |C   S| DDoS      |+
          |monitoring|<--->| Orchestrator |<--->| mitigation||
          |systems   |C   S|              |<-+  | systems   ||
          +----------+     +--------------+C |  +-----------+|
                                             |    +----------+
             (Internet Transit Provider)     |
                                             |  +-----------+
                                             | S| DDoS      |+
                                             +->| mitigation||
                                                | systems   ||
          * C is for DOTS client functionality    +----------+
          * S is for DOTS server functionality

                        Figure 4: DDoS Orchestration

   The DDoS telemetry systems monitor various aspects of the network
   traffic and perform some measurement tasks.

   These systems are configured so that when an event or some
   measurement indicators reach a predefined level, their associated
   DOTS client sends a DOTS mitigation request to the orchestrator DOTS
   server.  The DOTS mitigation request may be associated with some
   optional mitigation hints to let the orchestrator know what has
   triggered the request.  In particular, it is possible for something
   that looks like an attack locally to one telemetry system is not
   actually an attack when seen from the broader scope (e.g., of the

   Upon receipt of the DOTS mitigation request from the DDoS telemetry
   system, the orchestrator DOTS server responds with an acknowledgment
   to avoid retransmission of the request for mitigation.  The
   orchestrator may begin collecting additional fine-grained and
   specific information from various DDoS telemetry systems in order to
   correlate the measurements and provide an analysis of the event.
   Eventually, the orchestrator may ask for additional information from
   the DDoS telemetry system; however, the collection of this
   information is out of scope of DOTS.

   The orchestrator may be configured to start a DDoS Mitigation upon
   approval from a network administrator.  The analysis from the
   orchestrator is reported to the network administrator via, for
   example, a web interface.  If the network administrator decides to
   start the mitigation, the network administrator triggers the DDoS
   Mitigation request using, for example, a web interface of a DOTS
   client communicating to the orchestrator DOTS server.  This request
   is expected to be associated with a context that provides sufficient
   information to the orchestrator DOTS server to infer, elaborate, and
   coordinate the appropriate DDoS Mitigation.

   Upon receiving a request to mitigate a DDoS attack aimed at a target,
   the orchestrator may evaluate the volume of the attack as well as the
   value that the target represents.  The orchestrator may select the
   DDoS Mitigation Service Provider based on the attack severity.  It
   may also coordinate the DDoS Mitigation performed by the DDoS
   Mitigation Service Provider with some other tasks such as, for
   example, moving the target to another network so new sessions will
   not be impacted.  The orchestrator requests a DDoS Mitigation by the
   selected DMSs via its DOTS client, as described in Section 3.1.

   The orchestrator DOTS client is notified that the DDoS Mitigation is
   effective by the selected DMSs.  The orchestrator DOTS server returns
   this information to the network administrator.

   Similarly, when the DDoS attack has stopped, the orchestrator DOTS
   client is notified and the orchestrator's DOTS server indicates the
   end of the DDoS Mitigation to the DDoS telemetry systems as well as
   to the network administrator.

   In addition to the DDoS orchestration shown in Figure 4, the selected
   DMS can return a mitigation request to the orchestrator as an
   offloading.  For example, when the DDoS attack becomes severe and the
   DMS's utilization rate reaches its maximum capacity, the DMS can send
   mitigation requests with additional hints, such as its blocked
   traffic information, to the orchestrator.  Then the orchestrator can
   take further actions such as requesting forwarding nodes (e.g.,
   routers) to filter the traffic.  In this case, the DMS implements a
   DOTS client while the orchestrator implements a DOTS server.  Similar
   to other DOTS use cases, the offloading scenario assumes that some
   validation checks are followed by the DMS, the orchestrator, or both
   (e.g., avoid exhausting the resources of the forwarding nodes or
   inadvertent disruption of legitimate services).  These validation
   checks are part of the mitigation and are therefore out of the scope
   of the document.

4.  Security Considerations

   The document does not describe any protocol, though there are still a
   few high-level security considerations to discuss.

   DOTS is at risk from three primary attacks: DOTS agent impersonation,
   traffic injection, and signaling blocking.

   Impersonation and traffic injection mitigation can be mitigated
   through current secure communications best practices, including
   mutual authentication.  Preconfigured mitigation steps to take on the
   loss of keepalive traffic can partially mitigate signal blocking.
   But in general, it is impossible to comprehensively defend against an
   attacker that can selectively block any or all traffic.  Alternate
   communication paths that are (hopefully) not subject to blocking by
   the attacker in question is another potential mitigation.

   Additional details of DOTS security requirements can be found in

   Service disruption may be experienced if inadequate mitigation
   actions are applied.  These considerations are out of the scope of

5.  IANA Considerations

   This document has no IANA actions.

6.  Informative References

              Boucadair, M., Reddy, T., and W. Pan, "Multi-homing
              Deployment Considerations for Distributed-Denial-of-
              Service Open Threat Signaling (DOTS)", Work in Progress,
              Internet-Draft, draft-ietf-dots-multihoming-06, 25 May
              2021, <https://tools.ietf.org/html/draft-ietf-dots-

   [RFC8612]  Mortensen, A., Reddy, T., and R. Moskowitz, "DDoS Open
              Threat Signaling (DOTS) Requirements", RFC 8612,
              DOI 10.17487/RFC8612, May 2019,

   [RFC8782]  Reddy.K, T., Ed., Boucadair, M., Ed., Patil, P.,
              Mortensen, A., and N. Teague, "Distributed Denial-of-
              Service Open Threat Signaling (DOTS) Signal Channel
              Specification", RFC 8782, DOI 10.17487/RFC8782, May 2020,

   [RFC8783]  Boucadair, M., Ed. and T. Reddy.K, Ed., "Distributed
              Denial-of-Service Open Threat Signaling (DOTS) Data
              Channel Specification", RFC 8783, DOI 10.17487/RFC8783,
              May 2020, <https://www.rfc-editor.org/info/rfc8783>.


   The authors would like to thank, among others, Tirumaleswar Reddy.K,
   Andrew Mortensen, Mohamed Boucadair, Artyom Gavrichenkov, Jon
   Shallow, Yuuhei Hayashi, Elwyn Davies, the DOTS WG Chairs (at the
   time of writing) Roman Danyliw and Tobias Gondrom, as well as the
   Security AD Benjamin Kaduk for their valuable feedback.

   We also would like to thank Stephan Fouant, who was one of the
   initial coauthors of the documents.

Authors' Addresses

   Roland Dobbins
   Netscout, Inc.

   Email: roland.dobbins@netscout.com

   Daniel Migault
   8275 Trans Canada Route
   Saint Laurent, Quebec 4S 0B6

   Email: daniel.migault@ericsson.com

   Robert Moskowitz
   HTT Consulting
   Oak Park, MI 48237
   United States of America

   Email: rgm@labs.htt-consult.com

   Nik Teague
   Iron Mountain Data Centers
   United Kingdom

   Email: nteague@ironmountain.co.uk

   Liang Xia
   No. 101, Software Avenue, Yuhuatai District

   Email: Frank.xialiang@huawei.com

   Kaname Nishizuka
   NTT Communications
   GranPark 16F
   3-4-1 Shibaura, Minato-ku, Tokyo

   Email: kaname@nttv6.jp