DOTS                                                        A. Mortensen
Internet-Draft                                      Arbor Networks, Inc.
Intended status: Informational                              R. Moskowitz
Expires: April 21, 2016                                   HTT Consulting
                                                                T. Reddy
                                                     Cisco Systems, Inc.
                                                        October 19, 2015

                DDoS Open Threat Signaling Requirements


   This document defines the requirements for the DDoS Open Threat
   Signaling (DOTS) protocols coordinating attack response against
   Distributed Denial of Service (DDoS) attacks.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 21, 2016.

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   Copyright (c) 2015 IETF Trust and the persons identified as the
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  General Requirements  . . . . . . . . . . . . . . . . . .   6
     2.2.  Operational requirements  . . . . . . . . . . . . . . . .   7
     2.3.  Data channel requirements . . . . . . . . . . . . . . . .   9
     2.4.  Data model requirements . . . . . . . . . . . . . . . . .  10
   3.  Congestion Control Considerations . . . . . . . . . . . . . .  10
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   5.  Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  00 revision . . . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  Initial revision  . . . . . . . . . . . . . . . . . . . .  11
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

1.1.  Overview

   Distributed Denial of Service (DDoS) attacks continue to plague
   networks around the globe, from Tier-1 service providers on down to
   enterprises and small businesses.  Attack scale and frequency
   similarly have continued to increase, thanks to software
   vulnerabilities leading to reflection and amplification attacks.
   Once staggering attack traffic volume is now the norm, and the impact
   of larger-scale attacks attract the attention of international press

   The higher profile and greater impact of contemporary DDoS attacks
   has led to increased focus on coordinated attack response.  Many
   institutions and enterprises lack the resources or expertise to
   operate on-premise attack prevention solutions themselves, or simply
   find themselves constrained by local bandwidth limitations.  To
   address such gaps, security service providers have begun to offer on-
   demand traffic scrubbing services.  Each service offers its own
   interface for subscribers to request attack mitigation, tying
   subscribers to proprietary implementations while also limiting the
   subset of network elements capable of participating in the attack
   response.  As a result of incompatibility across services, attack

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   response may be fragmentary or otherwise incomplete, leaving key
   players in the attack path unable to assist in the defense.

   There are many ways to respond to an ongoing DDoS attack, some of
   them better than others, but the lack of a common method to
   coordinate a real-time response across layers and network domains
   inhibits the speed and effectiveness of DDoS attack mitigation.

   DOTS was formed to address this lack.  The DOTS protocols are
   therefore not concerned with the form of response, but rather with
   communicating the need for a response, supplementing the call for
   help with pertinent details about the detected attack.  To achieve
   this aim, the protocol must permit the DOTS client to request or
   withdraw a request for coordinated mitigation; to set the scope of
   mitigation, restricted to the client's network space; and to supply
   summarized attack information and additional hints the DOTS server
   elements can use to increase the accuracy and speed of the attack

   The protocol must also continue to operate even in extreme network
   conditions.  It must be resilient enough to ensure a high probability
   of signal delivery in spite of high packet loss rates.  As such,
   elements should be in regular, bidirectional contact to measure peer
   health, provide mitigation-related feedback, and allow for active
   mitigation adjustments.

   Lastly, the protocol must take care to ensure the confidentiality,
   integrity and authenticity of messages passed between peers to
   prevent the protocol from being repurposed to contribute to the very
   attacks it's meant to deflect.

   Drawing on the DOTS use cases [I-D.ietf-dots-use-cases] for
   reference, this document details the requirements for protocols
   achieving the DOTS goal of standards-based open threat signaling.

1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   The following terms are used to define relationships between
   elements, the data they exchange, and methods of communication among

   attack telemetry:  collected network traffic characteristics defining
      the nature of a DDoS attack.

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   mitigation:  A defensive response against a detected DDoS attack,
      performed by an entity in the network path between attack sources
      and the attack target, either through inline deployment or some
      form of traffic diversion.  The form mitigation takes is out of
      scope for this document.

   mitigator:  A network element capable of performing mitigation of a
      detected DDoS attack.

   DOTS client:  A DOTS-aware network element requesting attack response
      coordination with another DOTS-aware element, with the expectation
      that the remote element is capable of helping fend off the attack
      against the client.

   DOTS server:  A DOTS-aware network element handling and responding to
      messages from a DOTS client.  The DOTS server MAY enable
      mitigation on behalf of the DOTS client, if requested, by
      communicating the DOTS client's request to the mitigator and
      relaying any mitigator feedback to the client.  A DOTS server may
      also be a mitigator.

   DOTS relay:  A DOTS-aware network element positioned between a DOTS
      server and a DOTS client.  A DOTS relay receives messages from a
      DOTS client and relays them to a DOTS server, and similarly passes
      messages from the DOTS server to the DOTS client.

   DOTS agents:  A collective term for DOTS clients, servers and relays.

   signal channel:  A bidirectional, mutually authenticated
      communication layer between DOTS agents characterized by
      resilience even in conditions leading to severe packet loss, such
      as a volumetric DDoS attack causing network congestion.

   DOTS signal:  A concise authenticated status/control message
      transmitted between DOTS agents, used to indicate client's need
      for mitigation, as well as to convey the status of any requested

   heartbeat:  A keep-alive message transmitted between DOTS agents over
      the signal channel, used to measure peer health.  Heartbeat
      functionality is not required to be distinct from signal.

   client signal:  A message sent from a DOTS client to a DOTS server
      over the signal channel, possibly traversing a DOTS relay,
      indicating the DOTS client's need for mitigation, as well as the
      scope of any requested mitigation, optionally including detected
      attack telemetry to supplement server-initiated mitigation.

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   server signal:  A message sent from a DOTS server to a DOTS client
      over the signal channel.  Note that a server signal is not a
      response to client signal, but a DOTS server-initiated status
      message sent to the DOTS client, containing information about the
      status of any requested mitigation and its efficacy.

   data channel:  A secure communication layer between client and server
      used for infrequent bulk exchange of data not easily or
      appropriately communicated through the signal channel under attack

   blacklist:  a list of source addresses or prefixes from which traffic
      should be blocked.

   whitelist:  a list of source addresses or prefixes from which traffic
      should always be allowed, regardless of contradictory data gleaned
      in a detected attack.

2.  Requirements

   This section describes the required features and characteristics of
   the DOTS protocols.  The requirements are informed by the use cases
   described in [I-D.ietf-dots-use-cases].

   DOTS must at a minimum make it possible for a DOTS client to request
   a DOTS server's aid in mounting a coordinated defense against a
   detected attack, by signaling inter- or intra-domain using the DOTS
   protocol.  DOTS clients should similarly be able to withdraw aid
   requests arbitrarily.  Regular feedback between DOTS client and
   server supplement the defensive alliance by maintaining a common
   understanding of DOTS peer health and activity.  Bidirectional
   communication between DOTS client and server is therefore critical.

   Yet the DOTS protocol must also work with a set of competing
   operational goals.  On the one hand, the protocol must be resilient
   under extremely hostile network conditions, providing continued
   contact between DOTS agents even as attack traffic saturates the
   link.  Such resiliency may be developed several ways, but
   characteristics such as small message size, asynchronous, redundant
   message delivery and minimal connection overhead (when possible given
   local network policy) with a given network will tend to contribute to
   the robustness demanded by a viable DOTS protocol.

   On the other hand, DOTS must have adequate message confidentiality,
   integrity and authenticity to keep the protocol from becoming another
   vector for the very attacks it's meant to help fight off.  The DOTS
   client must be authenticated to the DOTS server, and vice versa, for
   DOTS to operate safely, meaning the DOTS agents must have a way to

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   negotiate and agree upon the terms of protocol security.  Attacks
   against the transport protocol should not offer a means of attack
   against the message confidentiality, integrity and authenticity.

   The DOTS server and client must also have some common method of
   defining the scope of any mitigation performed by the mitigator, as
   well as making adjustments to other commonly configurable features,
   such as listen ports, exchanging black- and white-lists, and so on.

   Finally, DOTS should provide sufficient extensibility to meet local,
   vendor or future needs in coordinated attack defense, although this
   consideration is necessarily superseded by the other operational

2.1.  General Requirements

   G-001  Interoperability: DOTS's objective is to develop a standard
      mechanism for signaling detected ongoing DDoS attacks.  That
      objective is unattainable without well-defined specifications for
      any protocols or data models emerging from DOTS.  All protocols,
      data models and interfaces MUST be detailed enough to ensure
      interoperable implementations.

   G-002  Extensibility: Any protocols or data models developed as part
      of DOTS MUST be designed to support future extensions.  Provided
      they do not undermine the interoperability and backward
      compatibility requirements, extensions are a critical part of
      keeping DOTS adaptable to changing operational and proprietary
      needs to keep pace with evolving DDoS attack methods.

   G-003  Resilience: The signaling protocol MUST be designed to
      maximize the probability of signal delivery even under the
      severely constrained network conditions imposed by the attack
      traffic.  The protocol SHOULD be resilient, that is, continue
      operating despite message loss and out-of-order or redundant
      signal delivery.

   G-004  Bidirectionality: To support peer health detection, to
      maintain an open signal channel, and to increase the probability
      of signal delivery during attack, the signal channel MUST be
      bidirectional, with client and server transmitting signals to each
      other at regular intervals, regardless of any client request for

   G-005  Sub-MTU Message Size: To avoid message fragmentation and the
      consequently decreased probability of message delivery, signaling
      protocol message size MUST be kept under signaling path Maximum
      Transmission Unit (MTU), including the byte overhead of any

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      encapsulation, transport headers, and transport- or message-level

   G-006  Message Integrity: DOTS protocols MUST take steps to protect
      the confidentiality, integrity and authenticity of messages sent
      between client and server.  While specific transport- and message-
      level security options are not specified, the protocols MUST
      follow current industry best practices for encryption and message

      In order for DOTS protocols to remain secure despite advancements
      in cryptanalysis, DOTS agents MUST be able to negotiate the terms
      and mechanisms of protocol security, subject to the
      interoperability and signal message size requirements above.

   G-007  Message Replay Protection: In order to prevent a passive
      attacker from capturing and replaying old messages, DOTS protocols
      MUST provide a method for replay detection, such as including a
      timestamp or sequence number in every heartbeat and signal sent
      between DOTS agents.

   G-008  Bulk Data Exchange: Infrequent bulk data exchange between DOTS
      client and server can also significantly augment attack response
      coordination, permitting such tasks as population of black- or
      white-listed source addresses; address group aliasing; exchange of
      incident reports; and other hinting or configuration supplementing
      attack response.

      As the resilience requirements for DOTS mandate small signal
      message size, a separate, secure data channel utilizing an
      established reliable protocol SHOULD be used for bulk data
      exchange.  The mechanism for bulk data exchange is not yet
      specified, but the nature of the data involved suggests use of a
      reliable, adaptable protocol with established and configurable
      conventions for authentication and authorization.

2.2.  Operational requirements

   OP-001  Use of Common Transports: DOTS MUST operate over common
      standardized transport protocols.  While the protocol resilience
      requirement strongly RECOMMENDS the use of connectionless
      protocols, in particular the User Datagram Protocol (UDP)
      [RFC0768], use of a standardized, connection-oriented protocol
      like the Transmission Control Protocol (TCP) [RFC0793] MAY be
      necessary due to network policy or middleware limitations.

   OP-002  Peer Mutual Authentication: The client and server MUST
      authenticate each other before a DOTS session is considered

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      active.  The method of authentication is not specified, but should
      follow current industry best practices with respect to any
      cryptographic mechanisms to authenticate the remote peer.

   OP-003  Session Health Monitoring: The client and server MUST
      regularly send heartbeats to each other after mutual
      authentication in order to keep the DOTS session open.  A session
      MUST be considered active until a client or server explicitly ends
      the session, or either DOTS agent fails to receive heartbeats from
      the other after a mutually negotiated timeout period has elapsed.

   OP-004  Mitigation Capability Opacity: DOTS is a threat signaling
      protocol.  The server and mitigator MUST NOT make any assumption
      about the attack detection, classification, or mitigation
      capabilities of the client.  While the server and mitigator MAY
      take hints from any attack telemetry included in client signals,
      the server and mitigator cannot depend on the client for
      authoritative attack classification.  Similarly, the mitigator
      cannot assume the client can or will mitigate attack traffic on
      its own.

      The client likewise MUST NOT make any assumptions about the
      capabilities of the server or mitigator with respect to detection,
      classification, and mitigation of DDoS attacks.  The form of any
      attack response undertaken by the mitigator is not in scope.

   OP-005  Mitigation Status: DOTS clients MUST be able to request or
      withdraw a request for mitigation from the DOTS server.  The DOTS
      server MUST acknowledge a DOTS client's request to withdraw from
      coordinated attack response in subsequent signals, and MUST cease
      mitigation activity as quickly as possible.  However, a DOTS
      client rapidly toggling active mitigation may result in
      undesirable side-effects for the network path, such as route or
      DNS flapping.  A DOTS server therefore MAY continue mitigating for
      a mutually negotiated period after receiving the DOTS client's
      request to stop.

      A server MAY refuse to engage in coordinated attack response with
      a client.  To make the status of a client's request clear, the
      server MUST indicate in server signals whether client-initiated
      mitigation is active.  When a client-initiated mitigation is
      active, and threat handling details such as mitigation scope and
      statistics are available to the server, the server SHOULD include
      those details in server signals sent to the client.  DOTS clients
      SHOULD take mitigation statistics into account when deciding
      whether to request the DOTS server cease mitigation.

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   OP-006  Mitigation Scope: DOTS clients MUST indicate the desired
      address space coverage of any mitigation, for example by using
      Classless Internet Domain Routing (CIDR) [RFC1518],[RFC1519]
      prefixes, [RFC2373] for IPv6 prefixes, the length/prefix
      convention established in the Border Gateway Protocol (BGP)
      [RFC4271], or by a prefix group alias agreed upon with the server
      through the data channel.  If there is additional information
      available narrowing the scope of any requested attack response,
      such as targeted port range, protocol, or service, clients SHOULD
      include that information in client signals.

      As an active attack evolves, clients MUST be able to adjust as
      necessary the scope of requested mitigation by refining the
      address space requiring intervention.

2.3.  Data channel requirements

   The data channel is intended to be used for bulk data exchanges
   between DOTS agents.  Unlike the signal channel, which must operate
   nominally even when confronted with despite signal degradation due to
   packet loss, the data channel is not expected to be constructed to
   deal with attack conditions.  As the primary function of the data
   channel is data exchange, a reliable transport is required in order
   for DOTS agents to detect data delivery success or failure.

   The data channel should be adaptable and extensible.  We anticipate
   the data channel will be used for such purposes as configuration or
   resource discovery.  For example, a DOTS client may submit to the
   DOTS server a collection of prefixes it wants to refer to by alias
   when requesting mitigation, to which the server would respond with a
   success status and the new prefix group alias, or an error status and
   message in the event the DOTS client's data channel request failed.
   The transactional nature of such data exchanges suggests a separate
   set of requirements for the data channel, while the potentially
   sensitive content sent between DOTS agents requires extra precautions
   to ensure data privacy and authenticity.

   DATA-001  Reliable transport: Transmissions over the data channel may
      be transactional, requiring reliable, in-order packet delivery.

   DATA-002  Data privacy and integrity: Transmissions over the data
      channel may contain sensitive information or instructions from the
      remote DOTS agent.  Theft or modification of data channel
      transmissions could lead to information leaks or malicious
      transactions on behalf of the sending agent.  (See Security
      Considerations below.)  Consequently data sent over the data
      channel MUST be encrypted and authenticated using current industry
      best practices.

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   DATA-003  Mutual authentication: DOTS agents MUST mutually
      authenticate each other before data may be exchanged over the data
      channel.  DOTS agents MAY take additional steps to authorize data
      exchange, as in the prefix group example above, before accepting
      data over the data channel.  The form of authentication and
      authorization is unspecified.

   DATA-004  Black- and whitelist management: DOTS servers SHOULD
      provide methods for DOTS clients to manage black- and white-lists
      of source addresses of traffic destined for addresses belonging to
      a client.

      For example, a DOTS client should be able to create a black- or
      whitelist entry; retrieve a list of current entries from either
      list; update the content of either list; and delete entries as

      How the DOTS server determines client ownership of address space
      is not in scope.

2.4.  Data model requirements


3.  Congestion Control Considerations

   The DOTS signal channel will not contribute measurably to link
   congestion, as the protocol's transmission rate will be negligible
   regardless of network conditions.  Bulk data transfers are performed
   over the data channel, which should use a reliable transport with
   built-in congestion control mechanisms, such as TCP.

4.  Security Considerations

   DOTS is at risk from three primary attacks: DOTS agent impersonation,
   traffic injection, and signaling blocking.  The DOTS protocol MUST be
   designed for minimal data transfer to address the blocking risk.
   Impersonation and traffic injection mitigation can be managed through
   current secure communications best practices.  DOTS is not subject to
   anything new in this area.  One consideration could be to minimize
   the security technologies in use at any one time.  The more needed,
   the greater the risk of failures coming from assumptions on one
   technology providing protection that it does not in the presence of
   another technology.

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5.  Change Log

5.1.  00 revision


5.2.  Initial revision

   2015-09-24 Andrew Mortensen

6.  References

6.1.  Normative References

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI
              10.17487/RFC0768, August 1980,

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
              793, DOI 10.17487/RFC0793, September 1981,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,

6.2.  Informative References

   [RFC1518]  Rekhter, Y. and T. Li, "An Architecture for IP Address
              Allocation with CIDR", RFC 1518, DOI 10.17487/RFC1518,
              September 1993, <>.

   [RFC1519]  Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless
              Inter-Domain Routing (CIDR): an Address Assignment and
              Aggregation Strategy", RFC 1519, DOI 10.17487/RFC1519,
              September 1993, <>.

   [RFC2373]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 2373, DOI 10.17487/RFC2373, July 1998,

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI
              10.17487/RFC4271, January 2006,

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Authors' Addresses

   Andrew Mortensen
   Arbor Networks, Inc.
   2727 S. State St
   Ann Arbor, MI  48104
   United States


   Robert Moskowitz
   HTT Consulting
   Oak Park, MI  42837
   United States


   Tirumaleswar Reddy
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103


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