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DOTS                                                        A. Mortensen
Internet-Draft                                            Arbor Networks
Intended status: Informational                              R. Moskowitz
Expires: June 8, 2018                                             Huawei
                                                                T. Reddy
                                                            McAfee, Inc.
                                                       December 05, 2017


Distributed Denial of Service (DDoS) Open Threat Signaling Requirements
                    draft-ietf-dots-requirements-08

Abstract

   This document defines the requirements for the Distributed Denial of
   Service (DDoS) Open Threat Signaling (DOTS) protocols coordinating
   attack response against 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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 8, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of




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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.  Context and Motivation  . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  General Requirements  . . . . . . . . . . . . . . . . . .   7
     2.2.  Signal Channel Requirements . . . . . . . . . . . . . . .   7
     2.3.  Data Channel Requirements . . . . . . . . . . . . . . . .  12
     2.4.  Security requirements . . . . . . . . . . . . . . . . . .  13
     2.5.  Data Model Requirements . . . . . . . . . . . . . . . . .  15
   3.  Congestion Control Considerations . . . . . . . . . . . . . .  16
     3.1.  Signal Channel  . . . . . . . . . . . . . . . . . . . . .  16
     3.2.  Data Channel  . . . . . . . . . . . . . . . . . . . . . .  16
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   5.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  17
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

1.1.  Context and Motivation

   Distributed Denial of Service (DDoS) attacks continue to plague
   network operators around the globe, from Tier-1 service providers on
   down to enterprises and small businesses.  Attack scale and frequency
   similarly have continued to increase, in part as a result of 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
   agencies.

   The 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-premises
   attack mitigation 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, which aim to separate the DDoS traffic from
   legitimate traffic and forward only the latter.  Today each such
   service offers a proprietary invocation interface for subscribers to
   request attack mitigation, tying subscribers to proprietary signaling



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   implementations while also limiting the subset of network elements
   capable of participating in the attack mitigation.  As a result of
   signaling interface incompatibility, attack responses may be
   fragmentary or otherwise incomplete, leaving key players in the
   attack path unable to assist in the defense.

   The lack of a common method to coordinate a real-time response among
   involved actors and network domains inhibits the speed and
   effectiveness of DDoS attack mitigation.  This document describes the
   required characteristics of protocols enabling requests for DDoS
   attack mitigation, reducing attack impact and leading to more
   efficient defensive strategies.

   DDoS Open Threat Signaling (DOTS) communicates the need for defensive
   action in anticipation of or in response to an attack, but does not
   dictate the form any defensive action takes.  DOTS supplements calls
   for help with pertinent details about the detected attack, allowing
   entities participating in DOTS to form ad hoc, adaptive alliances
   against DDoS attacks as described in the DOTS use cases
   [I-D.ietf-dots-use-cases].  The requirements in this document are
   derived from those use cases and [I-D.ietf-dots-architecture].

1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This document adopts the following terms:

   DDoS:  A distributed denial-of-service attack, in which traffic
      originating from multiple sources are directed at a target on a
      network.  DDoS attacks are intended to cause a negative impact on
      the availability of servers, services, applications, and/or other
      functionality of an attack target.  Denial-of-service
      considerations are discussed in detail in [RFC4732].

   DDoS attack target:  A network connected entity with a finite set of
      resources, such as network bandwidth, memory or CPU, that is the
      focus of a DDoS attack.  Potential targets include (but not
      limited to) network elements, network links, servers, and
      services.

   DDoS attack telemetry:  Collected measurements and behavioral
      characteristics defining the nature of a DDoS attack.






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   Countermeasure:  An action or set of actions taken to recognize and
      filter out DDoS attack traffic while passing legitimate traffic to
      the attack target.

   Mitigation:  A set of countermeasures enforced against traffic
      destined for the target or targets of a detected or reported DDoS
      attack, where countermeasure enforcement is managed by an entity
      in the network path between attack sources and the attack target.
      Mitigation methodology is out of scope for this document.

   Mitigator:  An entity, typically a network element, capable of
      performing mitigation of a detected or reported DDoS attack.  For
      the purposes of this document, this entity is a black box capable
      of mitigation, making no assumptions about availability or design
      of countermeasures, nor about the programmable interface(s)
      between this entity and other network elements.  The mitigator and
      invoked DOTS server are assumed to belong to the same
      administrative entity.

   DOTS client:  A DOTS-aware software module responsible for requesting
      attack response coordination with other DOTS-aware elements.

   DOTS server:  A DOTS-aware software module handling and responding to
      messages from DOTS clients.  The DOTS server enables mitigation on
      behalf of the DOTS client, if requested, by communicating the DOTS
      client's request to the mitigator and returning selected mitigator
      feedback to the requesting DOTS client.  A DOTS server may also be
      colocated with a mitigator.

   DOTS agent:  Any DOTS-aware software module capable of participating
      in a DOTS signal or data channel.  It can be a DOTS client, DOTS
      server, or, as a logical agent, a DOTS gateway.

   DOTS gateway:  A DOTS-aware software module resulting from the
      logical concatenation of a DOTS server and a DOTS client,
      analogous to a Session Initiation Protocol (SIP) [RFC3261] Back-
      to-Back User Agent (B2BUA) [RFC7092].  Client-side DOTS gateways
      are DOTS gateways that are in the DOTS client's domain, while
      server-side DOTS gateways denote DOTS gateways that are in the
      DOTS server's domain.  DOTS gateways are discussed in detail in
      [I-D.ietf-dots-architecture].

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





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   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
      mitigation.

   Heartbeat:  A message transmitted between DOTS agents over the signal
      channel, used as a keep-alive and to measure peer health.

   Data channel:  A secure communication layer between two DOTS agents
      used for infrequent bulk exchange of data not easily or
      appropriately communicated through the signal channel under attack
      conditions.

   Filter:  A specification of a matching network traffic flow or set of
      flows.  The filter will typically have a policy associated with
      it, e.g., rate-limiting or discarding matching traffic.

   Blacklist:  A filter list of addresses, prefixes, and/or other
      identifiers indicating sources from which traffic should be
      blocked, regardless of traffic content.

   Whitelist:  A list of addresses, prefixes, and/or other identifiers
      indicating sources from which traffic should always be allowed,
      regardless of contradictory data gleaned in a detected attack.

   Multi-homed DOTS client:  A DOTS client exchanging messages with
      multiple DOTS servers, each in a separate administrative domain.

2.  Requirements

   This section describes the required features and characteristics of
   the DOTS protocol.

   DOTS is an advisory protocol.  An active DDoS attack against the
   entity controlling the DOTS client need not be present before
   establishing a communication channel between DOTS agents.  Indeed,
   establishing a relationship with peer DOTS agents during normal
   network conditions provides the foundation for more rapid attack
   response against future attacks, as all interactions setting up DOTS,
   including any business or service level agreements, are already
   complete.  Peer DOTS agents are provisioned to a DOTS client using a
   variety of manual or dynamic methods.

   The DOTS protocol must at a minimum make it possible for a DOTS
   client to request a mitigator's aid mounting a defense, coordinated
   by a DOTS server, against a suspected attack, signaling within or
   between domains as requested by local operators.  DOTS clients should
   similarly be able to withdraw aid requests.  DOTS requires no



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   justification from DOTS clients for requests for help, nor do DOTS
   clients need to justify withdrawing help requests: the decision is
   local to the DOTS clients' domain.  Multi-homed DOTS clients must be
   able to select the appropriate DOTS server(s) to which a mitigation
   request is to be sent.  Further multi-homing considerations are out
   of scope.

   Regular feedback between DOTS clients and DOTS servers supplement the
   defensive alliance by maintaining a common understanding of the DOTS
   agents' health and activity.  Bidirectional communication between
   DOTS clients and DOTS servers is therefore critical.

   DOTS protocol implementations face competing operational goals when
   maintaining this bidirectional communication stream.  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) will tend to
   contribute to the robustness demanded by a viable DOTS protocol.
   Operators of peer DOTS-enabled domains may enable quality- or class-
   of-service traffic tagging to increase the probability of successful
   DOTS signal delivery, but DOTS does not require such policies be in
   place.  The DOTS solution indeed must be viable especially in their
   absence.

   On the other hand, DOTS must include protections ensuring message
   confidentiality, integrity and authenticity to keep the protocol from
   becoming another vector for the very attacks it's meant to help fight
   off.  DOTS clients must be able to authenticate DOTS servers, and
   vice versa, to avoid exposing new attack surfaces when deploying
   DOTS; specifically, to prevent DDoS mitigation in response to DOTS
   signaling from becoming a new form of attack.  In order to provide
   this level of protection, DOTS agents must have a way to 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 port numbers, exchanging black- and white-lists, and
   so on.

   Finally, DOTS should be sufficiently extensible to meet future needs
   in coordinated attack defense, although this consideration is
   necessarily superseded by the other operational requirements.



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2.1.  General Requirements

   GEN-001  Extensibility: Protocols and data models developed as part
      of DOTS MUST be extensible in order to keep DOTS adaptable to
      operational and proprietary DDoS defenses.  Future extensions MUST
      be backward compatible.  DOTS protocols MUST use a version number
      system to distinguish protocol revisions.  Implementations of
      older protocol versions SHOULD ignore information added to DOTS
      messages as part of newer protocol versions.

   GEN-002  Resilience and Robustness: The signaling protocol MUST be
      designed to maximize the probability of signal delivery even under
      the severely constrained network conditions imposed by particular
      attack traffic.  The protocol MUST be resilient, that is, continue
      operating despite message loss and out-of-order or redundant
      message delivery.  In support of signaling protocol robustness,
      DOTS signals SHOULD be conveyed over a transport not susceptible
      to Head of Line Blocking.

   GEN-003  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
      mitigation.  Unidirectional messages MUST be supported within the
      bidirectional signal channel to allow for unsolicited message
      delivery, enabling asynchronous notifications between agents.

   GEN-004  Bulk Data Exchange: Infrequent bulk data exchange between
      DOTS agents can also significantly augment attack response
      coordination, permitting such tasks as population of black- or
      white-listed source addresses; address or prefix group aliasing;
      exchange of incident reports; and other hinting or configuration
      supplementing attack response.

      As the resilience requirements for the DOTS signal channel mandate
      small signal message size, a separate, secure data channel
      utilizing a reliable transport protocol MUST be used for bulk data
      exchange.

2.2.  Signal Channel Requirements

   SIG-001  Use of Common Transport Protocols: DOTS MUST operate over
      common widely deployed and standardized transport protocols.
      While connectionless transport such as the User Datagram Protocol
      (UDP) [RFC0768] SHOULD be used for the signal channel, the
      Transmission Control Protocol (TCP) [RFC0793] MAY be used if




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      necessary due to network policy or middlebox capabilities or
      configurations.

   SIG-002  Sub-MTU Message Size: To avoid message fragmentation and the
      consequently decreased probability of message delivery over a
      congested link, signaling protocol message size MUST be kept under
      signaling Path Maximum Transmission Unit (PMTU), including the
      byte overhead of any encapsulation, transport headers, and
      transport- or message-level security.

      DOTS agents SHOULD attempt to learn the PMTU through mechanisms
      such as Path MTU Discovery [RFC1191] or Packetization Layer Path
      MTU Discovery [RFC4821].  If the PMTU cannot be discovered, DOTS
      agents SHOULD assume a PMTU of 1280 bytes.  If IPv4 support on
      legacy or otherwise unusual networks is a consideration and PMTU
      is unknown, DOTS implementations MAY rely on a PMTU of 576 bytes,
      as discussed in [RFC0791] and [RFC1122].

   SIG-003  Channel Health Monitoring: DOTS agents MUST support exchange
      of heartbeat messages over the signal channel to monitor channel
      health.  Peer DOTS agents SHOULD regularly send heartbeats to each
      other while a mitigation request is active.  The heartbeat
      interval during active mitigation is not specified, but SHOULD be
      frequent enough to maintain any on-path NAT bindings during
      mitigation.

      To support scenarios in which loss of heartbeat is used to trigger
      mitigation, and to keep the channel active, DOTS clients MAY
      solicit heartbeat exchanges after successful mutual
      authentication.  When DOTS agents are exchanging heartbeats and no
      mitigation request is active, either agent MAY request changes to
      the heartbeat rate.  For example, a DOTS server might want to
      reduce heartbeat frequency or cease heartbeat exchanges when an
      active DOTS client has not requested mitigation, in order to
      control load.

      Following mutual authentication, a signal channel MUST be
      considered active until a DOTS agent explicitly ends the session,
      or either DOTS agent fails to receive heartbeats from the other
      after a mutually agreed upon timeout period has elapsed.  Because
      heartbeat loss is much more likely during volumetric attack, DOTS
      agents SHOULD avoid signal channel termination when mitigation is
      active and heartbeats are not received by either DOTS agent for an
      extended period.  In such circumstances, DOTS clients MAY attempt
      to reestablish the signal channel.  DOTS servers SHOULD monitor
      the attack, using feedback from the mitigator and other available
      sources, and MAY use the absence of attack traffic and lack of
      client heartbeats as an indication the signal channel is defunct.



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   SIG-004  Channel Redirection: In order to increase DOTS operational
      flexibility and scalability, DOTS servers SHOULD be able to
      redirect DOTS clients to another DOTS server at any time.  DOTS
      clients MUST NOT assume the redirection target DOTS server shares
      security state with the redirecting DOTS server.  DOTS clients MAY
      attempt abbreviated security negotiation methods supported by the
      protocol, such as DTLS session resumption, but MUST be prepared to
      negotiate new security state with the redirection target DOTS
      server.

      Due to the increased likelihood of packet loss caused by link
      congestion during an attack, DOTS servers SHOULD NOT redirect
      while mitigation is enabled during an active attack against a
      target in the DOTS client's domain.

   SIG-005  Mitigation Requests and Status: Authorized DOTS clients MUST
      be able to request scoped mitigation from DOTS servers.  DOTS
      servers MUST send mitigation request status in response to DOTS
      clients requests for mitigation, and SHOULD accept scoped
      mitigation requests from authorized DOTS clients.  DOTS servers
      MAY reject authorized requests for mitigation, but MUST include a
      reason for the rejection in the status message sent to the client.

      Due to the higher likelihood of packet loss during a DDoS attack,
      DOTS servers SHOULD regularly send mitigation status to authorized
      DOTS clients which have requested and been granted mitigation,
      regardless of client requests for mitigation status.

      When DOTS client-requested mitigation is active, DOTS server
      status messages SHOULD include the following mitigation metrics:

      *  Total number of packets blocked by the mitigation

      *  Current number of packets per second blocked

      *  Total number of bytes blocked

      *  Current number of bytes per second blocked

      DOTS clients MAY take these metrics into account when determining
      whether to ask the DOTS server to cease mitigation.

      Once a DOTS client requests mitigation, the client MAY withdraw
      that request at any time, regardless of whether mitigation is
      currently active.  The DOTS server MUST immediately acknowledge a
      DOTS client's request to stop mitigation.





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      To protect against route or DNS flapping caused by a client
      rapidly toggling mitigation, and to dampen the effect of
      oscillating attacks, DOTS servers MAY allow mitigation to continue
      for a limited period after acknowledging a DOTS client's
      withdrawal of a mitigation request.  During this period, DOTS
      server status messages SHOULD indicate that mitigation is active
      but terminating.

      The initial active-but-terminating period is implementation-
      specific, but SHOULD be sufficiently long to absorb latency
      incurred by route propagation.  If the client requests mitigation
      again before the initial active-but-terminating period elapses,
      the DOTS server MAY exponentially increase the active-but-
      terminating period up to a maximum of 300 seconds (5 minutes).
      After the active-but-terminating period elapses, the DOTS server
      MUST treat the mitigation as terminated, as the DOTS client is no
      longer responsible for the mitigation.  For example, if there is a
      financial relationship between the DOTS client and server domains,
      the DOTS client ceases incurring cost at this point.

   SIG-006  Mitigation Lifetime: DOTS servers MUST support mitigation
      lifetimes, and MUST terminate a mitigation when the lifetime
      elapses.  DOTS servers also MUST support renewal of mitigation
      lifetimes in mitigation requests from DOTS clients, allowing
      clients to extend mitigation as necessary for the duration of an
      attack.

      DOTS servers MUST treat a mitigation terminated due to lifetime
      expiration exactly as if the DOTS client originating the
      mitigation had asked to end the mitigation, including the active-
      but-terminating period, as described above in SIG-005.

      DOTS clients SHOULD include a mitigation lifetime in all
      mitigation requests.  If a DOTS client does not include a
      mitigation lifetime in requests for help sent to the DOTS server,
      the DOTS server will use a reasonable default as defined by the
      protocol.

      DOTS servers SHOULD support indefinite mitigation lifetimes,
      enabling architectures in which the mitigator is always in the
      traffic path to the resources for which the DOTS client is
      requesting protection.  DOTS clients MUST be prepared to not be
      granted mitigations with indefinite lifetimes.  DOTS servers MAY
      refuse mitigations with indefinite lifetimes, for policy reasons.
      The reasons themselves are out of scope.  If the DOTS server does
      not grant a mitigation request with an indefinite mitigation
      lifetime, it MUST set the lifetime to a value that is configured




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      locally.  That value MUST be returned in a reply to the requesting
      DOTS client.

   SIG-007  Mitigation Scope: DOTS clients MUST indicate desired
      mitigation scope.  The scope type will vary depending on the
      resources requiring mitigation.  All DOTS agent implementations
      MUST support the following required scope types:

      *  IPv4 addresses in dotted quad format

      *  IPv4 prefixes in CIDR notation [RFC4632]

      *  IPv6 addresses [RFC4291][RFC5952]

      *  IPv6 prefixes [RFC4291][RFC5952]

      *  Domain names [RFC1035]

      The following mitigation scope types are OPTIONAL:

      *  Uniform Resource Identifiers [RFC3986]

      DOTS agents MUST support mitigation scope aliases, allowing DOTS
      clients and servers to refer to collections of protected resources
      by an opaque identifier created through the data channel, direct
      configuration, or other means.  Domain name and URI mitigation
      scopes may be thought of as a form of scope alias, in which the
      addresses to which the domain name or URI resolve represent the
      full scope of the mitigation.

      If there is additional information available narrowing the scope
      of any requested attack response, such as targeted port range,
      protocol, or service, DOTS clients SHOULD include that information
      in client signals.  DOTS clients MAY also include additional
      attack details.  Such supplemental information is OPTIONAL, and
      DOTS servers MAY ignore it when enabling countermeasures on the
      mitigator.

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

      The DOTS client may obtain the mitigation scope through direct
      provisioning or through implementation-specific methods of
      discovery.  DOTS clients MUST support at least one mechanism to
      obtain mitigiation scope.





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   SIG-008  Mitigation Efficacy: When a mitigation request by a DOTS
      client is active, DOTS clients SHOULD transmit a metric of
      perceived mitigation efficacy to the DOTS server.  DOTS servers
      MAY use the efficacy metric to adjust countermeasures activated on
      a mitigator on behalf of a DOTS client.

   SIG-009  Conflict Detection and Notification: Multiple DOTS clients
      controlled by a single administrative entity may send conflicting
      mitigation requests for pools of protected resources as a result
      of misconfiguration, operator error, or compromised DOTS clients.
      DOTS servers in the same administrative domain attempting to honor
      conflicting requests may flap network route or DNS information,
      degrading the networks attempting to participate in attack
      response with the DOTS clients.  DOTS servers in a single
      administrative domain SHALL detect such conflicting requests, and
      SHALL notify the DOTS clients in conflict.  The notification
      SHOULD indicate the nature and scope of the conflict, for example,
      the overlapping prefix range in a conflicting mitigation request.

   SIG-010:  Network Address Translator Traversal: DOTS clients may be
      deployed behind a Network Address Translator (NAT), and need to
      communicate with DOTS servers through the NAT.  DOTS protocols
      MUST therefore be capable of traversing NATs.

      If UDP is used as the transport for the DOTS signal channel, all
      considerations in "Middlebox Traversal Guidelines" in [RFC8085]
      apply to DOTS.  Regardless of transport, DOTS protocols MUST
      follow established best common practices (BCPs) for NAT traversal.

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 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 must be 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



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   sensitive content sent between DOTS agents requires extra precautions
   to ensure data privacy and authenticity.

   DATA-001  Reliable transport: Messages sent over the data channel
      MUST be delivered reliably, in order sent.

   DATA-002  Data privacy and integrity: Transmissions over the data
      channel are likely to contain operationally or privacy-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 Section 4 below).  Consequently data sent over
      the data channel MUST be encrypted and authenticated using current
      industry best practices.  DOTS servers MUST enable means to
      prevent leaking operationally or privacy-sensitive data.  Although
      administrative entities participating in DOTS may detail what data
      may be revealed to third-party DOTS agents, such considerations
      are not in scope for this document.

   DATA-003  Resource Configuration: To help meet the general and signal
      channel requirements in this document, DOTS server implementations
      MUST provide an interface to configure resource identifiers, as
      described in SIG-007.  DOTS server implementations MAY expose
      additional configurability.  Additional configurability is
      implementation-specific.

   DATA-004  Black- and whitelist management: DOTS servers MUST provide
      methods for DOTS clients to manage black- and white-lists of
      traffic destined for resources 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
      necessary.

      How the DOTS server authorizes DOTS client management of black-
      and white-list entries is implementation-specific.

2.4.  Security requirements

   DOTS must operate within a particularly strict security context, as
   an insufficiently protected signal or data channel may be subject to
   abuse, enabling or supplementing the very attacks DOTS purports to
   mitigate.

   SEC-001  Peer Mutual Authentication: DOTS agents MUST authenticate
      each other before a DOTS signal or data channel is considered
      valid.  The method of authentication is not specified, but should



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      follow current industry best practices with respect to any
      cryptographic mechanisms to authenticate the remote peer.

   SEC-002  Message Confidentiality, Integrity and Authenticity: 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 authentication.

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

      While the interfaces between downstream DOTS server and upstream
      DOTS client within a DOTS gateway are implementation-specific,
      those interfaces nevertheless MUST provide security equivalent to
      that of the signal channels bridged by gateways in the signaling
      path.  For example, when a DOTS gateway consisting of a DOTS
      server and DOTS client is running on the same logical device, they
      must be within the same process security boundary.

   SEC-003  Message Replay Protection: To prevent a passive attacker
      from capturing and replaying old messages, and thereby potentially
      disrupting or influencing the network policy of the receiving DOTS
      agent's domain, DOTS protocols MUST provide a method for replay
      detection and prevention.

      Within the signal channel, messages MUST be uniquely identified
      such that replayed or duplicated messages may be detected and
      discarded.  Unique mitigation requests MUST be processed at most
      once.

   SEC-004  Authorization: DOTS servers MUST authorize all messages from
      DOTS clients which pertain to mitigation, configuration,
      filtering, or status.

      DOTS servers MUST reject mitigation requests with scopes which the
      DOTS client is not authorized to manage.

      Likewise, DOTS servers MUST refuse to allow creation, modification
      or deletion of scope aliases and black-/white-lists when the DOTS
      client is unauthorized.

      The modes of authorization are implementation-specific.




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2.5.  Data Model Requirements

   The value of DOTS is in standardizing a mechanism to permit elements,
   networks or domains under threat of DDoS attack to request aid
   mitigating the effects of any such attack.  A well-structured DOTS
   data model is therefore critical to the development of a successful
   DOTS protocol.

   DM-001:  Structure: The data model structure for the DOTS protocol
      may be described by a single module, or be divided into related
      collections of hierarchical modules and sub-modules.  If the data
      model structure is split across modules, those distinct modules
      MUST allow references to describe the overall data model's
      structural dependencies.

   DM-002:  Versioning: To ensure interoperability between DOTS protocol
      implementations, data models MUST be versioned.  The version
      number of the initial data model SHALL be 1.  Each published
      change to the initial published DOTS data model SHALL increment
      the data model version by 1.

      How the protocol represents data model versions is not defined in
      this document.

   DM-003:  Mitigation Status Representation: The data model MUST
      provide the ability to represent a request for mitigation and the
      withdrawal of such a request.  The data model MUST also support a
      representation of currently requested mitigation status, including
      failures and their causes.

   DM-004:  Mitigation Scope Representation: The data model MUST support
      representation of a requested mitigation's scope.  As mitigation
      scope may be represented in several different ways, per SIG-007
      above, the data model MUST be capable of flexible representation
      of mitigation scope.

   DM-005:  Mitigation Lifetime Representation: The data model MUST
      support representation of a mitigation request's lifetime,
      including mitigations with no specified end time.

   DM-006:  Mitigation Efficacy Representation: The data model MUST
      support representation of a DOTS client's understanding of the
      efficacy of a mitigation enabled through a mitigation request.

   DM-007:  Acceptable Signal Loss Representation: The data model MUST
      be able to represent the DOTS agent's preference for acceptable
      signal loss when establishing a signal channel, as described in
      GEN-002.



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   DM-008:  Heartbeat Interval Representation: The data model MUST be
      able to represent the DOTS agent's preferred heartbeat interval,
      which the client may include when establishing the signal channel,
      as described in SIG-003.

   DM-009:  Relationship to Transport: The DOTS data model MUST NOT
      depend on the specifics of any transport to represent fields in
      the model.

3.  Congestion Control Considerations

3.1.  Signal Channel

   As part of a protocol expected to operate over links affected by DDoS
   attack traffic, the DOTS signal channel MUST NOT contribute
   significantly to link congestion.  To meet the signal channel
   requirements above, DOTS signal channel implementations SHOULD
   support connectionless transports.  However, some connectionless
   transports when deployed naively can be a source of network
   congestion, as discussed in [RFC5405].  Signal channel
   implementations using such connectionless transports, such as UDP,
   therefore MUST include a congestion control mechanism.

   Signal channel implementations using TCP may rely on built-in TCP
   congestion control support.

3.2.  Data Channel

   As specified in DATA-001, the data channel requires reliable, in-
   order message delivery.  Data channel implementations using TCP may
   rely on the TCP implementation's built-in congestion control
   mechanisms.

4.  Security Considerations

   DOTS is at risk from three primary attacks:

   o  DOTS agent impersonation

   o  Traffic injection

   o  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.  See Section 2.4 above for a detailed discussion.




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5.  Contributors

   Mohamed Boucadair
      Orange

      mohamed.boucadair@orange.com

   Flemming Andreasen
      Cisco Systems, Inc.

      fandreas@cisco.com

   Dave Dolson
      Sandvine

      ddolson@sandvine.com

6.  Acknowledgments

   Thanks to Roman Danyliw and Matt Richardson for careful reading and
   feedback.

7.  References

7.1.  Normative References

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/info/rfc768>.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <https://www.rfc-editor.org/info/rfc1122>.





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   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              DOI 10.17487/RFC1191, November 1990,
              <https://www.rfc-editor.org/info/rfc1191>.

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

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August
              2006, <https://www.rfc-editor.org/info/rfc4632>.

   [RFC4821]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
              Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
              <https://www.rfc-editor.org/info/rfc4821>.

   [RFC5405]  Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
              for Application Designers", RFC 5405,
              DOI 10.17487/RFC5405, November 2008,
              <https://www.rfc-editor.org/info/rfc5405>.

   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
              March 2017, <https://www.rfc-editor.org/info/rfc8085>.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952,
              DOI 10.17487/RFC5952, August 2010,
              <https://www.rfc-editor.org/info/rfc5952>.

7.2.  Informative References









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   [I-D.ietf-dots-architecture]
              Mortensen, A., Andreasen, F., Reddy, T.,
              christopher_gray3@cable.comcast.com, c., Compton, R., and
              N. Teague, "Distributed-Denial-of-Service Open Threat
              Signaling (DOTS) Architecture", draft-ietf-dots-
              architecture-05 (work in progress), October 2017.

   [I-D.ietf-dots-use-cases]
              Dobbins, R., Migault, D., Fouant, S., Moskowitz, R.,
              Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS
              Open Threat Signaling", draft-ietf-dots-use-cases-09 (work
              in progress), November 2017.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC7092]  Kaplan, H. and V. Pascual, "A Taxonomy of Session
              Initiation Protocol (SIP) Back-to-Back User Agents",
              RFC 7092, DOI 10.17487/RFC7092, December 2013,
              <https://www.rfc-editor.org/info/rfc7092>.

   [RFC4732]  Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
              Denial-of-Service Considerations", RFC 4732,
              DOI 10.17487/RFC4732, December 2006,
              <https://www.rfc-editor.org/info/rfc4732>.

Authors' Addresses

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

   Email: amortensen@arbor.net


   Robert Moskowitz
   Huawei
   Oak Park, MI  42837
   United States

   Email: rgm@htt-consult.com





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   Tirumaleswar Reddy
   McAfee, Inc.
   Embassy Golf Link Business Park
   Bangalore, Karnataka  560071
   India

   Email: TirumaleswarReddy_Konda@McAfee.com












































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