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rfc:rfc8612

Internet Engineering Task Force (IETF) A. Mortensen Request for Comments: 8612 Arbor Networks Category: Informational T. Reddy ISSN: 2070-1721 McAfee

                                                          R. Moskowitz
                                                                Huawei
                                                              May 2019
           DDoS Open Threat Signaling (DOTS) Requirements

Abstract

 This document defines the requirements for the Distributed Denial-of-
 Service (DDoS) Open Threat Signaling (DOTS) protocols enabling
 coordinated response to DDoS attacks.

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
 https://www.rfc-editor.org/info/rfc8612.

Copyright Notice

 Copyright (c) 2019 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Mortensen, et al. Informational [Page 1] RFC 8612 DOTS Requirements May 2019

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 . . . . . . . . . . . . . . .   8
   2.3.  Data Channel Requirements . . . . . . . . . . . . . . . .  13
   2.4.  Security Requirements . . . . . . . . . . . . . . . . . .  14
   2.5.  Data Model Requirements . . . . . . . . . . . . . . . . .  16
 3.  Congestion Control Considerations . . . . . . . . . . . . . .  17
   3.1.  Signal Channel  . . . . . . . . . . . . . . . . . . . . .  17
   3.2.  Data Channel  . . . . . . . . . . . . . . . . . . . . . .  17
 4.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
 6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
   6.1.  Normative References  . . . . . . . . . . . . . . . . . .  18
   6.2.  Informative References  . . . . . . . . . . . . . . . . .  20
 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  21
 Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  21
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1. Introduction

1.1. Context and Motivation

 Distributed Denial-of-Service (DDoS) attacks afflict networks
 connected to the Internet, plaguing network operators at service
 providers and enterprises around the world.  High-volume attacks
 saturating inbound links are now common as attack scale and frequency
 continue to increase.
 The prevalence and impact of these DDoS attacks has led to an
 increased focus on coordinated attack response.  However, many
 enterprises lack the resources or expertise to operate on-premise
 attack mitigation solutions themselves, or are constrained by local
 bandwidth limitations.  To address such gaps, service providers have
 begun to offer on-demand traffic scrubbing services, which are
 designed to separate the DDoS attack traffic from legitimate traffic
 and forward only the latter.
 Today, these services offer proprietary interfaces for subscribers to
 request attack mitigation.  Such proprietary interfaces tie a
 subscriber to a service and limit the abilities of network elements
 that would otherwise be capable of participating in attack
 mitigation.  As a result of signaling interface incompatibility,

Mortensen, et al. Informational [Page 2] RFC 8612 DOTS Requirements May 2019

 attack responses may be fragmented or otherwise incomplete, leaving
 operators in the attack path unable to assist in the defense.
 A standardized method to coordinate a real-time response among
 involved operators will increase the speed and effectiveness of DDoS
 attack mitigation and reduce the impact of these attacks.  This
 document describes the required characteristics of protocols that
 enable attack response coordination and mitigation of DDoS attacks.
 DDoS Open Threat Signaling (DOTS) communicates the need for defensive
 action in anticipation of or in response to an attack, but it does
 not dictate the implementation of these actions.  The DOTS use cases
 are discussed in [DOTS-USE], and the DOTS architecture is discussed
 in [DOTS-ARCH].

1.2. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.
 These capitalized words are used to signify the requirements for the
 DOTS protocols design.
 This document adopts the following terms:
 DDoS:  A distributed denial-of-service attack in which traffic
    originating from multiple sources is directed at a target on a
    network.  DDoS attacks are intended to cause a negative impact on
    the availability and/or functionality of an attack target.
    Denial-of-service considerations are discussed in detail in
    [RFC4732].
 DDoS attack target:  A network-connected entity that is the target of
    a DDoS attack.  Potential targets include (but are 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.
 Countermeasure:  An action or set of actions focused on recognizing
    and filtering out specific types of DDoS attack traffic while
    passing legitimate traffic to the attack target.  Distinct
    countermeasures can be layered to defend against attacks combining
    multiple DDoS attack types.

Mortensen, et al. Informational [Page 3] RFC 8612 DOTS Requirements May 2019

 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.  The
    means by which this entity performs these mitigations and how they
    are requested of it are out of scope for this document.  The
    mitigator and DOTS server receiving a mitigation request 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.
 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 the functionality of a DOTS server and a
    DOTS client into a single DOTS agent.  This functionality is
    analogous to a Session Initiation Protocol (SIP) [RFC3261] Back-
    to-Back User Agent (B2BUA) [RFC7092].  A DOTS gateway has a
    client-facing side, which behaves as a DOTS server for downstream
    clients, and a server-facing side, which performs the role of a
    DOTS client for upstream DOTS servers.  Client-domain DOTS
    gateways are DOTS gateways that are in the DOTS client's domain,
    while server-domain DOTS gateways denote DOTS gateways that are in
    the DOTS server's domain.  A DOTS gateway may terminate multiple
    discrete DOTS client connections and may aggregate these into one
    or more connections.  DOTS gateways are described further in
    [DOTS-ARCH].
 Signal channel:  A bidirectional, mutually authenticated
    communication channel between DOTS agents that is resilient even
    in conditions leading to severe packet loss such as a volumetric
    DDoS attack causing network congestion.

Mortensen, et al. Informational [Page 4] RFC 8612 DOTS Requirements May 2019

 DOTS signal:  A status/control message transmitted over the
    authenticated signal channel between DOTS agents, used to indicate
    the client's need for mitigation or 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 bidirectional, mutually authenticated communication
    channel between two DOTS agents used for infrequent but reliable
    bulk exchange of data not easily or appropriately communicated
    through the signal channel.  Reliable bulk data exchange may not
    function well or at all during attacks causing network congestion.
    The data channel is not expected to operate in such 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 [RFC4949].
 Drop-list:  A list of filters indicating sources from which traffic
    should be blocked regardless of traffic content.
 Accept-list:  A list of filters indicating sources from which traffic
    should always be allowed regardless of contradictory data gleaned
    in a detected attack.
 Multihomed DOTS client:  A DOTS client exchanging messages with
    multiple DOTS servers, each in a separate administrative domain.

2. Requirements

 The expected layout and interactions amongst DOTS entities is
 described in the DOTS Architecture [DOTS-ARCH].
 The goal of the DOTS requirements specification is to specify the
 requirements for DOTS signal channel and data channel protocols that
 have different application and transport-layer requirements.  This
 section describes the required features and characteristics of the
 DOTS protocols.
 The goal of DOTS protocols is to enable and manage mitigation on
 behalf of a network domain or resource that is or may become the
 focus of a DDoS attack.  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 a more rapid attack response against
 future attacks, as all interactions setting up DOTS, including any

Mortensen, et al. Informational [Page 5] RFC 8612 DOTS Requirements May 2019

 business or service-level agreements, are already complete.
 Reachability information of peer DOTS agents is provisioned to a DOTS
 client using a variety of manual or dynamic methods.  Once a
 relationship between DOTS agents is established, regular
 communication between DOTS clients and servers enables a common
 understanding of the DOTS agents' health and activity.
 The DOTS protocol must, at a minimum, make it possible for a DOTS
 client to request aid mounting a defense against a suspected attack.
 This defense could be coordinated by a DOTS server and include
 signaling within or between domains as requested by local operators.
 DOTS clients should similarly be able to withdraw aid requests.  DOTS
 requires no 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.  Multihomed DOTS
 clients must be able to select the appropriate DOTS server(s) to
 which a mitigation request is to be sent.  The method for selecting
 the appropriate DOTS server in a multihomed environment is out of
 scope for this document.
 DOTS protocol implementations face competing operational goals when
 maintaining this bidirectional communication stream.  On the one
 hand, DOTS must include measures to ensure message confidentiality,
 integrity, authenticity, and replay protection to keep the protocols
 from becoming additional vectors for the very attacks it is meant to
 help fight off.  On the other 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
 notifications, 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 either quality-of-
 service 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 and should be viable in their
 absence.
 The DOTS server and client must also have some standardized method of
 defining the scope of any mitigation, as well as managing other
 mitigation-related configurations.
 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.

Mortensen, et al. Informational [Page 6] RFC 8612 DOTS Requirements May 2019

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
    proprietary DDoS defenses.  Future extensions MUST be backward
    compatible.  Implementations of older protocol versions MUST
    ignore optional information added to DOTS messages as part of
    newer protocol versions.  Implementations of older protocol
    versions MUST reject DOTS messages carrying mandatory information
    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 caused by attack
    traffic.  Additional means to enhance the resilience of DOTS
    protocols, including when multiple DOTS servers are provisioned to
    the DOTS clients, SHOULD be considered.  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 transport and application protocols not susceptible to head-
    of-line blocking.  These requirements are at SHOULD strength to
    handle middle-boxes and firewall traversal.
 GEN-003  Bulk Data Exchange: Infrequent bulk data exchange between
    DOTS agents can also significantly augment attack response
    coordination, permitting such tasks as population of drop- or
    accept-listed source addresses, address or prefix group aliasing,
    exchange of incident reports, and other hinting or configuration
    supplementing attack responses.
    As the resilience requirements for the DOTS signal channel mandate
    a small signal message size, a separate, secure data channel
    utilizing a reliable transport protocol MUST be used for bulk data
    exchange.  However, reliable bulk data exchange may not be
    possible during attacks causing network congestion.
 GEN-004  Mitigation Hinting: DOTS clients may have access to attack
    details that can be used to inform mitigation techniques.  Example
    attack details might include locally collected fingerprints for an
    on-going attack, or anticipated or active attack focal points
    based on other threat intelligence.  DOTS clients MAY send
    mitigation hints derived from attack details to DOTS servers, with
    the full understanding that the DOTS server MAY ignore mitigation
    hints.  Mitigation hints MUST be transmitted across the signal
    channel, as the data channel may not be functional during an
    attack.  DOTS-server handling of mitigation hints is
    implementation-specific.

Mortensen, et al. Informational [Page 7] RFC 8612 DOTS Requirements May 2019

 GEN-005  Loop Handling: In certain scenarios, typically involving
    misconfiguration of DNS or routing policy, it may be possible for
    communication between DOTS agents to loop.  Signal and data
    channel implementations should be prepared to detect and terminate
    such loops to prevent service disruption.

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) [RFC768] SHOULD be used for the signal channel, the
    Transmission Control Protocol (TCP) [RFC793] MAY be used if
    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
    the signaling Path Maximum Transmission Unit (PMTU), including the
    byte overhead of any encapsulation, transport headers, and
    transport- or message-level security.  If the total message size
    exceeds the PMTU, the DOTS agent MUST split the message into
    separate messages; for example, the list of mitigation scope types
    could be split into multiple lists and each list conveyed in a new
    message.
    DOTS agents can attempt to learn PMTU using the procedures
    discussed in [IP-FRAG-FRAGILE].  If the PMTU cannot be discovered,
    DOTS agents MUST assume a PMTU of 1280 bytes, as IPv6 requires
    that every link in the Internet have an MTU of 1280 octets or
    greater as specified in [RFC8200].  If IPv4 support on legacy or
    otherwise unusual networks is a consideration and the PMTU is
    unknown, DOTS implementations MAY assume a PMTU of 576 bytes for
    IPv4 datagrams, as every IPv4 host must be capable of receiving a
    packet whose length is equal to 576 bytes as discussed in [RFC791]
    and [RFC1122].
 SIG-003  Bidirectionality: To support peer health detection, to
    maintain an active signal channel, and to increase the probability
    of signal delivery during an 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.  The bidirectional signal channel MUST support
    unidirectional messaging to enable notifications between DOTS
    agents.

Mortensen, et al. Informational [Page 8] RFC 8612 DOTS Requirements May 2019

 SIG-004  Channel Health Monitoring: DOTS agents MUST support exchange
    of heartbeat messages over the signal channel to monitor channel
    health.  These keep-alives serve to maintain any on-path NAT or
    Firewall bindings to avoid cryptographic handshake for new
    mitigation requests.  The heartbeat interval during active
    mitigation could be negotiable based on NAT/Firewall
    characteristics.  Absent information about the NAT/Firewall
    characteristics, DOTS agents need to ensure its on-path NAT or
    Firewall bindings do not expire, by using the keep-alive frequency
    discussed in Section 3.5 of [RFC8085].
    To support scenarios in which loss of heartbeat is used to trigger
    mitigation, and to keep the channel active, DOTS servers MUST
    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.
    When no attack traffic is present, the signal channel MUST be
    considered active until either DOTS agent fails to receive
    heartbeats from the other peer after a mutually agreed upon
    retransmission procedure has been exhausted.  Peer DOTS agents
    MUST regularly send heartbeats to each other while a mitigation
    request is active.  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.  The
    exception circumstances to terminating the signal channel session
    during active mitigation are discussed below:
  • To handle a possible DOTS server restart or crash, the DOTS

clients MAY attempt to establish a new signal channel session

       but MUST continue to send heartbeats on the current session so
       that the DOTS server knows the session is still alive.  If the
       new session is successfully established, the DOTS client can
       terminate the current session.
  • DOTS servers are assumed to have the ability to 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.

Mortensen, et al. Informational [Page 9] RFC 8612 DOTS Requirements May 2019

 SIG-005  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 are
    free to 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.  The redirection DOTS server and redirecting
    DOTS server MUST belong to the same administrative domain.
    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-006  Mitigation Requests and Status: Authorized DOTS clients MUST
    be able to request scoped mitigation from DOTS servers.  DOTS
    servers MUST send status to the DOTS clients about mitigation
    requests.  If a DOTS server rejects an authorized request for
    mitigation, the DOTS server MUST include a reason for the
    rejection in the status message sent to the client.
    DOTS servers MUST regularly send mitigation status updates to
    authorized DOTS clients that have requested and been granted
    mitigation.  If unreliable transport is used for the signal
    channel protocol, due to the higher likelihood of packet loss
    during a DDoS attack, DOTS servers need to send the mitigation
    status multiple times at regular intervals following the data
    transmission guidelines discussed in Section 3.1.3 of [RFC8085].
    When DOTS client-requested mitigation is active, DOTS server
    status messages MUST 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.

Mortensen, et al. Informational [Page 10] RFC 8612 DOTS Requirements May 2019

    A DOTS client MAY withdraw a mitigation 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.
    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.  DOTS clients MAY reverse the mitigation
    termination during this active-but-terminating period with a new
    mitigation request for the same scope.  The DOTS server MUST treat
    this request as a mitigation lifetime extension (see SIG-007).
    The initial active-but-terminating period is both implementation-
    and deployment-specific, but SHOULD be sufficiently long enough to
    absorb latency incurred by route propagation.  If a DOTS client
    refreshes the mitigation before the active-but-terminating period
    elapses, the DOTS server MAY 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.
 SIG-007  Mitigation Lifetime: DOTS servers MUST support mitigations
    for a negotiated time interval 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 MUST include a mitigation lifetime in all mitigation
    requests.
    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 for this document.  If the

Mortensen, et al. Informational [Page 11] RFC 8612 DOTS Requirements May 2019

    DOTS server does not grant a mitigation request with an indefinite
    mitigation lifetime, it MUST set the lifetime to a value that is
    configured locally.  That value MUST be returned in a reply to the
    requesting DOTS client.
 SIG-008  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 prefixes [RFC4632]
  • IPv6 prefixes [RFC4291] [RFC5952]
  • Domain names [RFC1035]
    The following mitigation scope type is OPTIONAL:
  • Uniform Resource Identifiers [RFC3986]
    DOTS servers MUST be able to resolve domain names and (when
    supported) URIs.  How name resolution is managed on the DOTS
    server is implementation-specific.
    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 mitigation requests.  DOTS clients MAY also include
    additional attack details.  DOTS servers MAY ignore such
    supplemental information when enabling countermeasures on the
    mitigator.
    As an active attack evolves, DOTS clients MUST be able to adjust
    as necessary the scope of requested mitigation by refining the
    scope of resources requiring mitigation.
    A 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 mitigation scope.

Mortensen, et al. Informational [Page 12] RFC 8612 DOTS Requirements May 2019

 SIG-009  Mitigation Efficacy: When a mitigation request is active,
    DOTS clients MUST be able to 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-010  Conflict Detection and Notification: Multiple DOTS clients
    controlled by a single administrative entity may send conflicting
    mitigation requests 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 MUST indicate the nature and scope
    of the conflict, for example, the overlapping prefix range in a
    conflicting mitigation request.
 SIG-011  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 established in BCP 127
    for NAT traversal [RFC4787] [RFC6888] [RFC7857].

2.3. Data Channel Requirements

 The data channel is intended to be used for bulk data exchanges
 between DOTS agents.  Unlike the signal channel, 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 provides a protocol for DOTS configuration and
 management.  For example, a DOTS client may submit to a 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.
 DATA-001  Reliable transport: Messages sent over the data channel
    MUST be delivered reliably in the order sent.

Mortensen, et al. Informational [Page 13] RFC 8612 DOTS Requirements May 2019

 DATA-003  Resource Configuration: To help meet the general and signal
    channel requirements in Sections 2.1 and 2.2, DOTS server
    implementations MUST provide an interface to configure resource
    identifiers, as described in SIG-008.  DOTS server implementations
    MAY expose additional configurability.  Additional configurability
    is implementation-specific.
 DATA-004  Policy Management: DOTS servers MUST provide methods for
    DOTS clients to manage drop- and accept-lists of traffic destined
    for resources belonging to a client.
    For example, a DOTS client should be able to create a drop- or
    accept-list entry, retrieve a list of current entries from either
    list, update the content of either list, and delete entries as
    necessary.
    How a DOTS server authorizes DOTS client management of drop- and
    accept-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 in this
    document but should follow current IETF best practices [RFC7525]
    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 IETF
    best practices [RFC7525] for encryption and message
    authentication.  Client-domain DOTS gateways are more trusted than
    DOTS clients, while server-domain DOTS gateways and DOTS servers
    share the same level of trust.  A security mechanism at the
    transport layer (TLS or DTLS) is thus adequate to provide security
    between peer DOTS agents.
    In order for DOTS protocols to remain secure despite advancements
    in cryptanalysis and traffic analysis, DOTS agents MUST support
    secure negotiation of the terms and mechanisms of protocol

Mortensen, et al. Informational [Page 14] RFC 8612 DOTS Requirements May 2019

    security, subject to the interoperability and signal message size
    requirements in Section 2.2.
    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, the
    two DOTS agents could be implemented within the same process
    security boundary.
 SEC-003  Data Privacy and Integrity: Transmissions over the DOTS
    protocols are likely to contain operationally or privacy-sensitive
    information or instructions from the remote DOTS agent.  Theft,
    modification, or replay of message transmissions could lead to
    information leaks or malicious transactions on behalf of the
    sending agent (see Section 4).  Consequently, data sent over the
    DOTS protocols MUST be encrypted using secure transports (TLS or
    DTLS).  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.
 SEC-004  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 can be detected and
    discarded.  Unique mitigation requests MUST be processed at most
    once.
 SEC-005  Authorization: DOTS servers MUST authorize all messages from
    DOTS clients that pertain to mitigation, configuration, filtering,
    or status.
    DOTS servers MUST reject mitigation requests with scopes that the
    DOTS client is not authorized to manage.
    Likewise, DOTS servers MUST refuse to allow creation,
    modification, or deletion of scope aliases and drop- or accept-
    lists when the DOTS client is unauthorized.
    The modes of authorization are implementation-specific.

Mortensen, et al. Informational [Page 15] RFC 8612 DOTS Requirements May 2019

2.5. Data Model Requirements

 A well-structured DOTS data model is critical to the development of
 successful DOTS protocols.
 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 submodules.  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.  How the protocols
    represent 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-008,
    the data model MUST include extensible 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.  Measurements of
    loss might include, but are not restricted to, number of
    consecutive missed heartbeat messages, retransmission count, or
    request timeouts.
 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.

Mortensen, et al. Informational [Page 16] RFC 8612 DOTS Requirements May 2019

 DM-009  Relationship to Transport: The DOTS data model MUST NOT make
    any assumptions about specific characteristics of any given
    transport into the data model, but instead represent the fields in
    the model explicitly.

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 [RFC8085].  Signal channel
 implementations using such connectionless transports, such as UDP,
 therefore MUST include a congestion control mechanism.
 Signal channel implementations using an IETF standard congestion-
 controlled transport protocol (like TCP) may rely on built-in
 transport 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 an IETF
 standard congestion-controlled transport protocol may rely on the
 transport implementation's built-in congestion control mechanisms.

4. Security Considerations

 This document informs future protocols under development and so does
 not have security considerations of its own.  However, operators
 should be aware of potential risks involved in deploying DOTS.  DOTS
 agent impersonation and signal blocking are discussed here.
 Additional DOTS security considerations may be found in [DOTS-ARCH]
 and DOTS protocol documents.
 Impersonation of either a DOTS server or a DOTS client could have
 catastrophic impact on operations in either domain.  If an attacker
 has the ability to impersonate a DOTS client, that attacker can
 affect policy on the network path to the DOTS client's domain up to
 and including instantiation of drop-lists blocking all inbound
 traffic to networks for which the DOTS client is authorized to
 request mitigation.

Mortensen, et al. Informational [Page 17] RFC 8612 DOTS Requirements May 2019

 Similarly, an impersonated DOTS server may be able to act as a sort
 of malicious DOTS gateway, intercepting requests from the downstream
 DOTS client and modifying them before transmission to the DOTS server
 to inflict the desired impact on traffic to or from the DOTS client's
 domain.  Among other things, this malicious DOTS gateway might
 receive and discard mitigation requests from the DOTS client,
 ensuring no requested mitigation is ever applied.
 To detect misuse, as detailed in Section 2.4, DOTS implementations
 require mutual authentication of DOTS agents in order to make agent
 impersonation more difficult.  However, impersonation may still be
 possible as a result of credential theft, implementation flaws, or
 DOTS agents being compromised.
 To detect compromised DOTS agents, DOTS operators should carefully
 monitor and audit DOTS agents to detect misbehavior and deter misuse
 while employing best current practices to secure network
 communications to reduce attack surface.
 Blocking communication between DOTS agents has the potential to
 disrupt the core function of DOTS, which is to request mitigation of
 active or expected DDoS attacks.  The DOTS signal channel is expected
 to operate over congested inbound links, and, as described in
 Section 2.2, the signal channel protocol must be designed for minimal
 data transfer to reduce the incidence of signal loss.

5. IANA Considerations

 This document has no IANA actions.

6. References

6.1. Normative References

 [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
            DOI 10.17487/RFC0768, August 1980,
            <https://www.rfc-editor.org/info/rfc768>.
 [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791,
            DOI 10.17487/RFC0791, September 1981,
            <https://www.rfc-editor.org/info/rfc791>.
 [RFC793]   Postel, J., "Transmission Control Protocol", STD 7,
            RFC 793, DOI 10.17487/RFC0793, September 1981,
            <https://www.rfc-editor.org/info/rfc793>.

Mortensen, et al. Informational [Page 18] RFC 8612 DOTS Requirements May 2019

 [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>.
 [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>.
 [RFC4787]  Audet, F., Ed. and C. Jennings, "Network Address
            Translation (NAT) Behavioral Requirements for Unicast
            UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
            2007, <https://www.rfc-editor.org/info/rfc4787>.
 [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>.
 [RFC6888]  Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
            A., and H. Ashida, "Common Requirements for Carrier-Grade
            NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
            April 2013, <https://www.rfc-editor.org/info/rfc6888>.
 [RFC7857]  Penno, R., Perreault, S., Boucadair, M., Ed., Sivakumar,
            S., and K. Naito, "Updates to Network Address Translation
            (NAT) Behavioral Requirements", BCP 127, RFC 7857,
            DOI 10.17487/RFC7857, April 2016,
            <https://www.rfc-editor.org/info/rfc7857>.

Mortensen, et al. Informational [Page 19] RFC 8612 DOTS Requirements May 2019

 [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>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.
 [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
            (IPv6) Specification", STD 86, RFC 8200,
            DOI 10.17487/RFC8200, July 2017,
            <https://www.rfc-editor.org/info/rfc8200>.

6.2. Informative References

 [DOTS-ARCH]
            Mortensen, A., Ed., Reddy, T., Ed., Andreasen, F., Teague,
            N., and R. Compton, "Distributed-Denial-of-Service Open
            Threat Signaling (DOTS) Architecture", Work in Progress,
            draft-ietf-dots-architecture-13, April 2019.
 [DOTS-USE]
            Dobbins, R., Migault, D., Fouant, S., Moskowitz, R.,
            Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS
            Open Threat Signaling", Work in Progress, draft-ietf-dots-
            use-cases-17, January 2019.
 [IP-FRAG-FRAGILE]
            Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
            and F. Gont, "IP Fragmentation Considered Fragile", Work
            in Progress, draft-ietf-intarea-frag-fragile-10, May 2019.
 [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>.

Mortensen, et al. Informational [Page 20] RFC 8612 DOTS Requirements May 2019

 [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
            FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
            <https://www.rfc-editor.org/info/rfc4949>.
 [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
            "Recommendations for Secure Use of Transport Layer
            Security (TLS) and Datagram Transport Layer Security
            (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
            2015, <https://www.rfc-editor.org/info/rfc7525>.

Acknowledgments

 Thanks to Roman Danyliw, Matt Richardson, Joe Touch, Scott Bradner,
 Robert Sparks, Brian Weis, Benjamin Kaduk, Eric Rescorla, Alvaro
 Retana, Suresh Krishnan, Ben Campbell, Mirja Kuehlewind, and Jon
 Shallow for their careful reading and feedback.

Contributors

 Mohamed Boucadair
    Orange
    mohamed.boucadair@orange.com
 Flemming Andreasen
    Cisco Systems, Inc.
    fandreas@cisco.com
 Dave Dolson
    Sandvine
    ddolson@sandvine.com

Mortensen, et al. Informational [Page 21] RFC 8612 DOTS Requirements May 2019

Authors' Addresses

 Andrew Mortensen
 Arbor Networks
 2727 S. State St.
 Ann Arbor, MI  48104
 United States of America
 Email: andrewmortensen@gmail.com
 Tirumaleswar Reddy
 McAfee
 Embassy Golf Link Business Park
 Bangalore, Karnataka  560071
 India
 Email: TirumaleswarReddy_Konda@McAfee.com
 Robert Moskowitz
 Huawei
 Oak Park, MI  42837
 United States of America
 Email: rgm@htt-consult.com

Mortensen, et al. Informational [Page 22]

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