DOTS                                                            T. Reddy
Internet-Draft                                                    McAfee
Intended status: Standards Track                            M. Boucadair
Expires: June 16, 2018                                            Orange
                                                                P. Patil
                                                                   Cisco
                                                            A. Mortensen
                                                    Arbor Networks, Inc.
                                                               N. Teague
                                                          Verisign, Inc.
                                                       December 13, 2017


   Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal
                                Channel
                   draft-ietf-dots-signal-channel-13

Abstract

   This document specifies the DOTS signal channel, a protocol for
   signaling the need for protection against Distributed Denial-of-
   Service (DDoS) attacks to a server capable of enabling network
   traffic mitigation on behalf of the requesting client.

   A companion document defines the DOTS data channel, a separate
   reliable communication layer for DOTS management and configuration
   purposes.

Editorial Note (To be removed by RFC Editor)

   Please update these statements with the RFC number to be assigned to
   this document:

   o  "This version of this YANG module is part of RFC XXXX;"

   o  "RFC XXXX: Distributed Denial-of-Service Open Threat Signaling
      (DOTS) Signal Channel";

   o  "| 3.00 | Alternate server | [RFCXXXX] |"

   o  reference: RFC XXXX

   o  This RFC

   Please update TBD statements with the port number to be assigned to
   DOTS Signal Channel Protocol.





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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 16, 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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Notational Conventions and Terminology  . . . . . . . . . . .   5
   3.  Design Overview . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  DOTS Signal Channel: Messages & Behaviors . . . . . . . . . .   8
     4.1.  DOTS Server(s) Discovery  . . . . . . . . . . . . . . . .   8
     4.2.  CoAP URIs . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.3.  Happy Eyeballs for DOTS Signal Channel  . . . . . . . . .   9
     4.4.  DOTS Mitigation Methods . . . . . . . . . . . . . . . . .  10
       4.4.1.  Request Mitigation  . . . . . . . . . . . . . . . . .  11
       4.4.2.  Retrieve Information Related to a Mitigation  . . . .  20
       4.4.3.  Efficacy Update from DOTS Clients . . . . . . . . . .  28
       4.4.4.  Withdraw a Mitigation . . . . . . . . . . . . . . . .  30
     4.5.  DOTS Signal Channel Session Configuration . . . . . . . .  32
       4.5.1.  Discover Configuration Parameters . . . . . . . . . .  33



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       4.5.2.  Convey DOTS Signal Channel Session Configuration  . .  35
       4.5.3.  Delete DOTS Signal Channel Session Configuration  . .  40
     4.6.  Redirected Signaling  . . . . . . . . . . . . . . . . . .  40
     4.7.  Heartbeat Mechanism . . . . . . . . . . . . . . . . . . .  42
   5.  DOTS Signal Channel YANG Module . . . . . . . . . . . . . . .  43
     5.1.  Tree Structure  . . . . . . . . . . . . . . . . . . . . .  43
     5.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  45
   6.  Mapping Parameters to CBOR  . . . . . . . . . . . . . . . . .  55
   7.  (D)TLS Protocol Profile and Performance Considerations  . . .  56
     7.1.  (D)TLS Protocol Profile . . . . . . . . . . . . . . . . .  56
     7.2.  (D)TLS 1.3 Considerations . . . . . . . . . . . . . . . .  58
     7.3.  MTU and Fragmentation . . . . . . . . . . . . . . . . . .  59
   8.  Mutual Authentication of DOTS Agents & Authorization of DOTS
       Clients . . . . . . . . . . . . . . . . . . . . . . . . . . .  60
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  61
     9.1.  DOTS Signal Channel UDP and TCP Port Number . . . . . . .  61
     9.2.  Well-Known 'dots' URI . . . . . . . . . . . . . . . . . .  61
     9.3.  CoAP Response Code  . . . . . . . . . . . . . . . . . . .  61
     9.4.  DOTS Signal Channel CBOR Mappings Registry  . . . . . . .  62
       9.4.1.  Registration Template . . . . . . . . . . . . . . . .  62
       9.4.2.  Initial Registry Contents . . . . . . . . . . . . . .  62
     9.5.  DOTS Signal Channel YANG Module . . . . . . . . . . . . .  68
   10. Implementation Status . . . . . . . . . . . . . . . . . . . .  68
     10.1.  nttdots  . . . . . . . . . . . . . . . . . . . . . . . .  69
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  69
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  70
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  70
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  71
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  71
     14.2.  Informative References . . . . . . . . . . . . . . . . .  73
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  76

1.  Introduction

   A distributed denial-of-service (DDoS) attack is an attempt to make
   machines or network resources unavailable to their intended users.
   In most cases, sufficient scale can be achieved by compromising
   enough end-hosts and using those infected hosts to perpetrate and
   amplify the attack.  The victim in this attack can be an application
   server, a host, a router, a firewall, or an entire network.

   Network applications have finite resources like CPU cycles, the
   number of processes or threads they can create and use, the maximum
   number of simultaneous connections it can handle, the limited
   resources of the control plane, etc.  When processing network
   traffic, such applications are supposed to use these resources to
   offer the intended task in the most efficient manner.  However, a
   DDoS attacker may be able to prevent an application from performing



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   its intended task by making the application exhaust its finite
   resources.

   TCP DDoS SYN-flood, for example, is a memory-exhausting attack while
   ACK-flood is a CPU-exhausting attack [RFC4987].  Attacks on the link
   are carried out by sending enough traffic so that the link becomes
   congested, thereby likely causing packet loss for legitimate traffic.
   Stateful firewalls can also be attacked by sending traffic that
   causes the firewall to maintain an excessive number of states that
   may jeopardize the firewall's operation overall, besides like
   performance impacts.  The firewall then runs out of memory, and can
   no longer instantiate the states required to process legitimate
   flows.  Other possible DDoS attacks are discussed in [RFC4732].

   In many cases, it may not be possible for network administrators to
   determine the cause(s) of an attack.  They may instead just realize
   that certain resources seem to be under attack.  This document
   defines a lightweight protocol that allows a DOTS client to request
   mitigation from one or more DOTS servers for protection against
   detected, suspected, or anticipated attacks.  This protocol enables
   cooperation between DOTS agents to permit a highly-automated network
   defense that is robust, reliable, and secure.

   An example of a network diagram that illustrates a deployment of DOTS
   agents is shown in Figure 1.  In this example, a DOTS server is
   operating on the access network.  A DOTS client is located on the LAN
   (Local Area Network), while a DOTS gateway is embedded in the CPE
   (Customer Premises Equipment).

   Network
   Resource        CPE router             Access network     __________
 +-----------+    +--------------+       +-------------+    /          \
 |           |____|              |_______|             |___ | Internet |
 |DOTS client|    | DOTS gateway |       | DOTS server |    |          |
 |           |    |              |       |             |    |          |
 +-----------+    +--------------+       +-------------+    \__________/

                   Figure 1: Sample DOTS Deployment (1)

   DOTS servers can also be reachable over the Internet, as depicted in
   Figure 2.










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   Network                                               DDoS mitigation
   Resource          CPE router           __________         service
  +-----------+    +-------------+       /          \    +-------------+
  |           |____|             |_______|          |___ |             |
  |DOTS client|    |DOTS gateway |       | Internet |    | DOTS server |
  |           |    |             |       |          |    |             |
  +-----------+    +-------------+       \__________/    +-------------+

                   Figure 2: Sample DOTS Deployment (2)

   In typical deployments, the DOTS client belongs to a different
   administrative domain than the DOTS server.  For example, the DOTS
   client is embedded in a firewall protecting services owned and
   operated by a domain, while the DOTS server is owned and operated by
   a different domain providing DDoS mitigation services.  The latter
   might or might not provide connectivity services to the network
   hosting the DOTS client.

   The DOTS server may (not) be co-located with the DOTS mitigator.  In
   typical deployments, the DOTS server belongs to the same
   administrative domain as the mitigator.  The DOTS client can
   communicate directly with a DOTS server or indirectly via a DOTS
   gateway.

   The document adheres to the DOTS architecture
   [I-D.ietf-dots-architecture].  The requirements for DOTS signal
   channel protocol are documented in [I-D.ietf-dots-requirements].
   This document satisfies all the use cases discussed in
   [I-D.ietf-dots-use-cases].

   This document focuses on the DOTS signal channel.  This is a
   companion document of the DOTS data channel specification
   [I-D.ietf-dots-data-channel] that defines a configuration and a bulk
   data exchange mechanism supporting the DOTS signal channel.

2.  Notational Conventions and 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
   [RFC2119].

   (D)TLS is used for statements that apply to both Transport Layer
   Security [RFC5246] and Datagram Transport Layer Security [RFC6347].
   Specific terms will be used for any statement that applies to either
   protocol alone.





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   The reader should be familiar with the terms defined in
   [I-D.ietf-dots-architecture].

   The meaning of the symbols in YANG tree diagrams is defined in
   [I-D.ietf-netmod-yang-tree-diagrams].

3.  Design Overview

   The DOTS signal channel is built on top of the Constrained
   Application Protocol (CoAP) [RFC7252], a lightweight protocol
   originally designed for constrained devices and networks.  The many
   features of CoAP (expectation of packet loss, support for
   asynchronous non-confirmable messaging, congestion control, small
   message overhead limiting the need for fragmentation, use of minimal
   resources, and support for (D)TLS) makes it a good candidate to build
   the DOTS signaling mechanism from.

   The DOTS signal channel is layered on existing standards (Figure 3).

                                  +--------------+
                                  |     DOTS     |
                                  +--------------+
                                  |     CoAP     |
                                  +--------------+
                                  | TLS  | DTLS  |
                                  +--------------+
                                  | TCP  |  UDP  |
                                  +--------------+
                                  |      IP      |
                                  +--------------+

     Figure 3: Abstract Layering of DOTS signal channel over CoAP over
                                  (D)TLS

   By default, a DOTS signal channel MUST run over port number TBD as
   defined in Section 9.1, for both UDP and TCP, unless the DOTS server
   has a mutual agreement with its DOTS clients to use a different port
   number.  DOTS clients may alternatively support means to dynamically
   discover the ports used by their DOTS servers.  In order to use a
   distinct port number (as opposed to TBD), DOTS clients and servers
   should support a configurable parameter to supply the port number to
   use.  The rationale for not using the default port number 5684
   ((D)TLS CoAP) is to allow for differentiated behaviors in
   environments where both a DOTS gateway and an IoT gateway (e.g.,
   Figure 3 of [RFC7452]) are present.

   The signal channel is initiated by the DOTS client (Section 4.4).
   Once the signal channel is established, the DOTS agents periodically



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   send heartbeats to keep the channel active (Section 4.7).  At any
   time, the DOTS client may send a mitigation request message to a DOTS
   server over the active channel.  While mitigation is active because
   of the higher likelihood of packet loss during a DDoS attack, the
   DOTS server periodically sends status messages to the client,
   including basic mitigation feedback details.  Mitigation remains
   active until the DOTS client explicitly terminates mitigation, or the
   mitigation lifetime expires.

   DOTS signaling can happen with DTLS [RFC6347] over UDP and TLS
   [RFC5246] over TCP.  Likewise, DOTS requests may be sent using IPv4
   or IPv6 transfer capabilities.  A Happy Eyeballs procedure for DOTS
   signal channel is specified in Section 4.3.

   Messages exchanged between DOTS agents are serialized using Concise
   Binary Object Representation (CBOR) [RFC7049], CBOR is a binary
   encoding scheme designed for small code and message size.  CBOR-
   encoded payloads are used to carry signal channel-specific payload
   messages which convey request parameters and response information
   such as errors.  In order to allow the use of the same data models,
   [RFC7951] specifies the JSON encoding of YANG-modeled data.  A
   similar effort for CBOR is defined in [I-D.ietf-core-yang-cbor].

   From that standpoint, this document specifies a YANG data model for
   representing mitigation scopes and DOTS signal channel session
   configuration data (Section 5).  Representing these data as CBOR data
   is assumed to follow the rules in [I-D.ietf-core-yang-cbor] or those
   in [RFC7951] combined with JSON/CBOR conversion rules in [RFC7049].

   In order to prevent fragmentation, DOTS agents must follow the
   recommendations documented in Section 4.6 of [RFC7252].  Refer to
   Section 7.3 for more details.

   DOTS agents MUST support GET, PUT, and DELETE CoAP methods.  The
   payload included in CoAP responses with 2.xx and 3.xx Response Codes
   MUST be of content type "application/cbor" (Section 5.5.1 of
   [RFC7252]).  CoAP responses with 4.xx and 5.xx error Response Codes
   MUST include a diagnostic payload (Section 5.5.2 of [RFC7252]).  The
   Diagnostic Payload may contain additional information to aid
   troubleshooting.

   In deployments where multiple DOTS clients are enabled in a network
   (owned and operated by the same entity), the DOTS server may detect
   conflicting mitigation requests from these clients.  This document
   does not aim to specify a comprehensive list of conditions under
   which a DOTS server will characterize two mitigation requests from
   distinct DOTS clients as conflicting, nor recommend a DOTS server
   behavior for processing conflicting mitigation requests.  Those



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   considerations are implementation- and deployment-specific.
   Nevertheless, the document specifies the mechanisms to notify DOTS
   clients when conflicts occur, including the conflict cause
   (Section 4.4).

   In deployments where one or more translators (e.g., NAT44, NAT64,
   NPTv6) are enabled between the client's network and the DOTS server,
   DOTS signal channel messages forwarded to a DOTS server must not
   include internal IP addresses/prefixes and/or port numbers; external
   addresses/ prefixes and/or port numbers as assigned by the translator
   must be used instead.  This document does not make any recommendation
   about possible translator discovery mechanisms.  The following are
   some (non-exhaustive) deployment examples that may be considered:

   o  Port Control Protocol (PCP) [RFC6887] or Session Traversal
      Utilities for NAT (STUN) [RFC5389] may be used to retrieve the
      external addresses/prefixes and/or port numbers.  Information
      retrieved by means of PCP will be used to feed the DOTS signal
      channel messages that will be sent to a DOTS server.

   o  A DOTS gateway may be co-located with the translator.  The DOTS
      gateway will need to update the DOTS messages, based upon the
      local translator's binding table.

4.  DOTS Signal Channel: Messages & Behaviors

4.1.  DOTS Server(s) Discovery

   This document assumes that DOTS clients are provisioned with the
   reachability information of their DOTS server(s) using a variety of
   means (e.g., local configuration, or dynamic means such as DHCP).
   These means are out of scope of this document.

   Likewise, it is out of scope of this document to specify the behavior
   of a DOTS client when it sends requests (e.g., contact all servers,
   select one server among the list) when multiple DOTS servers are
   provisioned.

4.2.  CoAP URIs

   The DOTS server MUST support the use of the path-prefix of "/.well-
   known/" as defined in [RFC5785] and the registered name of "dots".
   Each DOTS operation is indicated by a path-suffix that indicates the
   intended operation.  The operation path (Table 1) is appended to the
   path-prefix to form the URI used with a CoAP request to perform the
   desired DOTS operation.





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         +-----------------------+----------------+-------------+
         | Operation             | Operation path | Details     |
         +-----------------------+----------------+-------------+
         | Mitigation            | /v1/mitigate   | Section 4.4 |
         +-----------------------+----------------+-------------+
         | Session configuration | /v1/config     | Section 4.5 |
         +-----------------------+----------------+-------------+

             Table 1: Operations and their corresponding URIs

4.3.  Happy Eyeballs for DOTS Signal Channel

   DOTS signaling can operate with DTLS over UDP and TLS over TCP.  A
   DOTS client can use DNS to determine the IP address(es) of a DOTS
   server or a DOTS client may be provided with the list of the IP
   addresses of various DOTS servers.  The DOTS client MUST know a DOTS
   server's domain name; hard-coding the domain name of the DOTS server
   into software is NOT RECOMMENDED in case the domain name is not valid
   or needs to change for legal or other reasons.  The DOTS client
   performs A and/or AAAA record lookup of the domain name and the
   result will be a list of IP addresses, each of which can be used to
   contact the DOTS server using UDP and TCP.

   If an IPv4 path to reach a DOTS server is found, but the DOTS
   server's IPv6 path is not working, a dual-stack DOTS client can
   experience a significant connection delay compared to an IPv4-only
   DOTS client.  The other problem is that if a middlebox between the
   DOTS client and DOTS server is configured to block UDP traffic, the
   DOTS client will fail to establish a DTLS session with the DOTS
   server and , as a consequence, will have to fall back to TLS over
   TCP, thereby incurring significant connection delays.
   [I-D.ietf-dots-requirements] mentions that DOTS agents will have to
   support both connectionless and connection-oriented protocols.

   To overcome these connection setup problems, the DOTS client can
   attempt to connect to the DOTS server using both IPv6 and IPv4, and
   try both DTLS over UDP and TLS over TCP in a manner similar to the
   Happy Eyeballs mechanism [RFC6555].  These connection attempts are
   performed by the DOTS client when it initializes, and the DOTS client
   uses the results of the Happy Eyeballs procedure for sending its
   subsequent messages to the DOTS server.

   In order of preference (most preferred first), it is UDP over IPv6,
   UDP over IPv4, TCP over IPv6, and finally TCP over IPv4, which
   adheres to address preference order [RFC6724] and the DOTS
   preference, which privileges the use of UDP over TCP (to avoid TCP's
   head of line blocking).




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   DOTS client                                               DOTS server
      |                                                         |
      |--DTLS ClientHello, IPv6 ---->X                          |
      |--TCP SYN, IPv6-------------->X                          |
      |--DTLS ClientHello, IPv4 ---->X                          |
      |--TCP SYN, IPv4----------------------------------------->|
      |--DTLS ClientHello, IPv6 ---->X                          |
      |--TCP SYN, IPv6-------------->X                          |
      |<-TCP SYNACK---------------------------------------------|
      |--DTLS ClientHello, IPv4 ---->X                          |
      |--TCP ACK----------------------------------------------->|
      |<------------Establish TLS Session---------------------->|
      |----------------DOTS signal----------------------------->|
      |                                                         |

                       Figure 4: DOTS Happy Eyeballs

   In reference to Figure 4, the DOTS client sends two TCP SYNs and two
   DTLS ClientHello messages at the same time over IPv6 and IPv4.  In
   this example, it is assumed that the IPv6 path is broken and UDP is
   dropped by a middlebox but has little impact to the DOTS client
   because there is no long delay before using IPv4 and TCP.  The DOTS
   client repeats the mechanism to discover if DOTS signaling with DTLS
   over UDP becomes available from the DOTS server, so the DOTS client
   can migrate the DOTS signal channel from TCP to UDP.  But such
   probing SHOULD NOT be done more frequently than every 24 hours and
   MUST NOT be done more frequently than every 5 minutes.

4.4.  DOTS Mitigation Methods

   The following methods are used by a DOTS client to request, withdraw,
   or retrieve the status of mitigation requests:

   PUT:    DOTS clients use the PUT method to request mitigation from a
           DOTS server (Section 4.4.1).  During active mitigation, DOTS
           clients may use PUT requests to carry mitigation efficacy
           updates to the DOTS server (Section 4.4.3).

   GET:    DOTS clients may use the GET method to subscribe to DOTS
           server status messages, or to retrieve the list of its
           mitigations maintained by a DOTS server (Section 4.4.2).

   DELETE: DOTS clients use the DELETE method to withdraw a request for
           mitigation from a DOTS server (Section 4.4.4).

   Mitigation request and response messages are marked as Non-
   confirmable messages (Section 2.2 of [RFC7252]).




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   DOTS agents SHOULD follow the data transmission guidelines discussed
   in Section 3.1.3 of [RFC8085] and control transmission behavior by
   not sending more than one UDP datagram per RTT to the peer DOTS agent
   on average.

   Requests marked by the DOTS client as Non-confirmable messages are
   sent at regular intervals until a response is received from the DOTS
   server.  If the DOTS client cannot maintain an RTT estimate, it
   SHOULD NOT send more than one Non-confirmable request every 3
   seconds, and SHOULD use an even less aggressive rate whenever
   possible (case 2 in Section 3.1.3 of [RFC8085]).

4.4.1.  Request Mitigation

   When a DOTS client requires mitigation for some reason, the DOTS
   client uses the CoAP PUT method to send a mitigation request to its
   DOTS server(s) (Figure 5, illustrated in JSON diagnostic notation).
   If this DOTS client is entitled to solicit the DOTS service, the DOTS
   server can enable mitigation on behalf of the DOTS client by
   communicating the DOTS client's request to the mitigator and relaying
   selected mitigator feedback to the requesting DOTS client.






























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     Header: PUT (Code=0.03)
     Uri-Host: "host"
     Uri-Path: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "version"
     Uri-Path: "mitigate"
     Content-Type: "application/cbor"
     {
       "mitigation-scope": {
         "client-identifier": [
            "string"
         ],
         "scope": [
           {
             "mitigation-id": integer,
             "target-prefix": [
                "string"
              ],
             "target-port-range": [
                {
                  "lower-port": integer,
                  "upper-port": integer
                }
              ],
              "target-protocol": [
                integer
              ],
              "target-fqdn": [
                "string"
              ],
              "target-uri": [
                "string"
              ],
              "alias-name": [
                "string"
              ],
             "lifetime": integer
           }
         ]
       }
     }

             Figure 5: PUT to convey DOTS mitigation requests

   The parameters are described below:

   client-identifier:  The client identifier MAY be conveyed by the DOTS
      gateway to propagate the DOTS client identity from the gateway's



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      client-side to the gateway's server-side, and from the gateway's
      server-side to the DOTS server.  This allows the DOTS server to
      accept mitigation requests with scopes which the DOTS client is
      authorized to manage.

      The 'client-identifier' value MUST be assigned by the DOTS gateway
      in a manner that ensures that there is zero probability that the
      same value will be assigned to a different DOTS client.  The DOTS
      gateway MUST conceal potentially sensitive DOTS client identity
      information.  The client-identifier attribute SHOULD NOT be
      generated and included by the DOTS client.

      This is an optional attribute.

   mitigation-id:  Identifier for the mitigation request represented
      with an integer.  This identifier MUST be unique for each
      mitigation request bound to the DOTS client, i.e., the mitigation-
      id parameter value in the mitigation request needs to be unique
      relative to the mitigation-id parameter values of active
      mitigation requests conveyed from the DOTS client to the DOTS
      server.  This identifier MUST be generated by the DOTS client.
      This document does not make any assumption about how this
      identifier is generated.

      This is a mandatory attribute.

   target-prefix:  A list of prefixes identifying resources under
      attack.  Prefixes are represented using Classless Inter-Domain
      Routing (CIDR) notation [RFC4632].
      As a reminder, the prefix length must be less than or equal to 32
      (resp. 128) for IPv4 (resp.  IPv6).

      This is an optional attribute.

   target-port-range:  A list of port numbers bound to resources under
      attack.

      The port range is defined by two bounds, a lower port number
      (lower-port) and an upper port number (upper-port).  When only
      'lower-port' is present, it represents a single port number.  For
      TCP, UDP, Stream Control Transmission Protocol (SCTP) [RFC4960],
      or Datagram Congestion Control Protocol (DCCP) [RFC4340], the
      range of ports can be, for example, 1024-65535.

      This is an optional attribute.

   target-protocol:  A list of protocols involved in an attack.  Values
      are taken from the IANA protocol registry [proto_numbers].



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      The value 0 has a special meaning for 'all protocols'.

      This is an optional attribute.

   target-fqdn:   A list of Fully Qualified Domain Names (FQDNs)
      identifying resources under attack.  An FQDN is the full name of a
      resource, rather than just its hostname.  For example, "venera" is
      a hostname, and "venera.isi.edu" is an FQDN.

      This is an optional attribute.

   target-uri:   A list of Uniform Resource Identifiers (URIs) [RFC3986]
      identifying resources under attack.

      This is an optional attribute.

   alias-name:  A list of aliases of resources for which the mitigation
      is requested.  Aliases can be created using the DOTS data channel
      (Section 6.1 of [I-D.ietf-dots-data-channel]), direct
      configuration, or other means.  An alias is used in subsequent
      signal channel exchanges to refer more efficiently to the
      resources under attack.

      This is an optional attribute.

   lifetime:   Lifetime of the mitigation request in seconds.  The
      RECOMMENDED lifetime of a mitigation request is 3600 seconds (60
      minutes) -- this value was chosen to be long enough so that
      refreshing is not typically a burden on the DOTS client, while
      expiring the request where the client has unexpectedly quit in a
      timely manner.  DOTS clients MUST include this parameter in their
      mitigation requests.  Upon the expiry of this lifetime, and if the
      request is not refreshed, the mitigation request is removed.  The
      request can be refreshed by sending the same request again.

      A lifetime of 0 in a mitigation request is an invalid value.

      A lifetime of negative one (-1) indicates indefinite lifetime for
      the mitigation request.  The DOTS server MAY refuse indefinite
      lifetime, for policy reasons; the granted lifetime value is
      returned in the response.  DOTS clients MUST be prepared to not be
      granted mitigations with indefinite lifetimes.

      The DOTS server MUST always indicate the actual lifetime in the
      response and the remaining lifetime in status messages sent to the
      DOTS client.

      This is a mandatory attribute.



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   Because of the complexity to handle partial failure cases, this
   specification does not allow for including multiple mitigation
   requests in the same PUT request.  Concretely, a DOTS client MUST NOT
   include multiple 'scope' parameters in the same PUT request.

   The CBOR key values for the parameters are defined in Section 6.
   Section 9 defines how the CBOR key values can be allocated to
   standard bodies and vendors.

   FQDN 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.

   In the PUT request at least one of the attributes 'target-prefix' or
   'target-fqdn' or 'target-uri 'or 'alias-name' MUST be present.  If
   the attribute value is empty, then the attribute MUST NOT be present
   in the request.

   The relative order of two mitigation requests from a DOTS client is
   determined by comparing their respective 'mitigation-id' values.  If
   two mitigation requests have overlapping mitigation scopes, the
   mitigation request with the highest numeric 'mitigation-id' value
   will override the other mitigation request.  Two mitigation-ids from
   a DOTS client are overlapping if there is a common IP address, IP
   prefix, FQDN, URI, or alias-name.  To avoid maintaining a long list
   of overlapping mitigation requests from a DOTS client and avoid
   error-prone provisioning of mitigation requests from a DOTS client,
   the overlapped lower numeric 'mitigation-id' MUST be automatically
   deleted and no longer available at the DOTS server.

   The Uri-Path option carries a major and minor version nomenclature to
   manage versioning and DOTS signal channel in this specification uses
   v1 major version.

   Figure 6 shows a PUT request example to signal that ports 80, 8080,
   and 443 used by 2001:db8:6401::1 and 2001:db8:6401::2 servers are
   under attack (illustrated in JSON diagnostic notation).














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     Header: PUT (Code=0.03)
     Uri-Host: "www.example.com"
     Uri-Path: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "v1"
     Uri-Path: "mitigate"
     Content-Format: "application/cbor"
     {
       "mitigation-scope": {
         "client-identifier": [
            "dz6pHjaADkaFTbjr0JGBpw"
         ],
         "scope": [
           {
             "mitigation-id": 12332,
             "target-prefix": [
                "2001:db8:6401::1/128",
                "2001:db8:6401::2/128"
              ],
             "target-port-range": [
               {
                 "lower-port": 80
               },
               {
                 "lower-port": 443
               },
               {
                  "lower-port": 8080
               }
              ],
              "target-protocol": [
                6
              ]
           }
         ]
       }
     }

                       Figure 6: PUT for DOTS signal

   The corresponding CBOR encoding format is shown in Figure 7.










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A1                                      # map(1)
   01                                   # unsigned(1)
   A2                                   # map(2)
      18 20                             # unsigned(32)
      81                                # array(1)
      76                                # text(22)
         647A3670486A6141446B614654626A72304A47427077 # "dz6pHjaADkaFTbjr0JGBpw"
      02                                # unsigned(2)
      81                                # array(1)
         A4                             # map(4)
            03                          # unsigned(3)
            19 302C                     # unsigned(12332)
            04                          # unsigned(4)
            82                          # array(2)
               74                       # text(20)
                  323030313A6462383A363430313A3A312F313238 # "2001:db8:6401::1/128"
               74                       # text(20)
                  323030313A6462383A363430313A3A322F313238 # "2001:db8:6401::2/128"
            05                          # unsigned(5)
            83                          # array(3)
               A1                       # map(1)
                  06                    # unsigned(6)
                  18 50                 # unsigned(80)
               A1                       # map(1)
                  06                    # unsigned(6)
                  19 01BB               # unsigned(443)
               A1                       # map(1)
                  06                    # unsigned(6)
                  19 1F90               # unsigned(8080)
            08                          # unsigned(8)
            81                          # array(1)
               06                       # unsigned(6)

                   Figure 7: PUT for DOTS signal (CBOR)

   If the DOTS client is using the certificate provisioned by the
   Enrollment over Secure Transport (EST) server [RFC7030] in the DOTS
   gateway-domain to authenticate itself to the DOTS gateway, then the
   'client-identifier' value can be the output of a cryptographic hash
   algorithm whose input is the DER-encoded ASN.1 representation of the
   Subject Public Key Info (SPKI) of an X.509 certificate.

   In this version of the specification, the cryptographic hash
   algorithm used is SHA-256 [RFC6234].  The output of the cryptographic
   hash algorithm is truncated to 16 bytes; truncation is done by
   stripping off the final 16 bytes.  The truncated output is base64url
   encoded.  If the 'client-identifier' value is already present in the
   mitigation request received from the DOTS client, the DOTS gateway



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   MAY compute the 'client-identifier' value, as discussed above, and
   add the computed 'client-identifier' value to the end of the 'client-
   identifier' list.  The DOTS server MUST NOT use the 'client-
   identifier' for the DOTS client authentication process.

   In both DOTS signal and data channel sessions, the DOTS client MUST
   authenticate itself to the DOTS server (Section 8).  The DOTS server
   may use the algorithm presented in Section 7 of [RFC7589] to derive
   the DOTS client identity or username from the client certificate.
   The DOTS client identity allows the DOTS server to accept mitigation
   requests with scopes that the DOTS client is authorized to manage.
   The DOTS server couples the DOTS signal and data channel sessions
   using the DOTS client identity and the 'client-identifier' parameter
   value, so the DOTS server can validate whether the aliases conveyed
   in the mitigation request were indeed created by the same DOTS client
   using the DOTS data channel session.  If the aliases were not created
   by the DOTS client, the DOTS server returns 4.00 (Bad Request) in the
   response.

   The DOTS server couples the DOTS signal channel sessions using the
   DOTS client identity and the 'client-identifier' parameter value, and
   the DOTS server uses 'mitigation-id' parameter value to detect
   duplicate mitigation requests.  If the mitigation request contains
   the alias-name and other parameters identifying the target resources
   (such as, 'target-prefix', 'target-port-range', 'target-fqdn', or
   'target-uri'), then the DOTS server appends the parameter values in
   'alias-name' with the corresponding parameter values in 'target-
   prefix', 'target-port-range', 'target-fqdn', or 'target-uri'.

   The DOTS server indicates the result of processing the PUT request
   using CoAP response codes.  CoAP 2.xx codes are success.  CoAP 4.xx
   codes are some sort of invalid requests (client errors).  COAP 5.xx
   codes are returned if the DOTS server has erred or is currently
   unavailable to provide mitigation in response to the mitigation
   request from the DOTS client.

   Figure 8 shows an example of a PUT request that is successfully
   processed (i.e., CoAP 2.xx response codes).













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   {
     "mitigation-scope": {
        "client-identifier": [
            "string"
        ],
        "scope": [
           {
             "mitigation-id": 12332,
             "lifetime": 3600
           }
         ]
      }
   }

                       Figure 8: 2.xx response body

   If the request is missing one or more mandatory attributes, or
   includes multiple 'scope' parameters, or contains invalid or unknown
   parameters, the DOTS server replies with 4.00 (Bad Request).  DOTS
   agents can safely ignore Vendor-Specific parameters they don't
   understand.

   A DOTS server that receives a mitigation request with a lifetime set
   to '0' MUST reply with a 4.00 (Bad Request).

   If the DOTS server does not find the 'mitigation-id' parameter value
   conveyed in the PUT request in its configuration data, it MAY accept
   the mitigation request by sending back a 2.01 (Created) response to
   the DOTS client; the DOTS server will consequently try to mitigate
   the attack.

   If the DOTS server finds the 'mitigation-id' parameter value conveyed
   in the PUT request in its configuration data, it MAY update the
   mitigation request, and a 2.04 (Changed) response is returned to
   indicate a successful update of the mitigation request.

   If the request is conflicting with an existing mitigation request
   from a different DOTS client, and the DOTS server decides to maintain
   the conflicting mitigation request, the DOTS server returns 4.09
   (Conflict) [RFC8132] to the requesting DOTS client.  The response
   includes enough information for a DOTS client to recognize the source
   of the conflict (refer to 'conflict-information' specified in
   Section 4.4.2).

   For a mitigation request to continue beyond the initial negotiated
   lifetime, the DOTS client has to refresh the current mitigation
   request by sending a new PUT request.  This PUT request MUST use the
   same 'mitigation-id' value, and MUST repeat all the other parameters



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   as sent in the original mitigation request apart from a possible
   change to the lifetime parameter value.

   A DOTS gateway MUST update the 'client-identifier' list in the
   response to remove the 'client-identifier' value it had added in the
   corresponding request before forwarding the response to the DOTS
   client.

4.4.2.  Retrieve Information Related to a Mitigation

   A GET request is used by a DOTS client to retrieve information
   (including status) of DOTS mitigations from a DOTS server.

   The same considerations for manipulating 'client-identifier'
   parameter by a DOTS gateway specified in Section 4.4.1 MUST be
   followed for GET requests.

   If the DOTS server does not find the 'mitigation-id' parameter value
   conveyed in the GET request in its configuration data for the
   requesting DOTS client or the one identified by 'client-identifier',
   it MUST respond with a 4.04 (Not Found) error response code.
   Likewise, the same error MUST be returned as a response to a request
   to retrieve all mitigation records of a given DOTS client if the DOTS
   server does not find any mitigation record for that DOTS client or
   the one identified by 'client-identifier'.

   The 'c' (content) parameter and its permitted values defined in
   [I-D.ietf-core-comi] can be used to retrieve non-configuration data
   (attack mitigation status) or configuration data or both.  The DOTS
   server may support this optional filtering capability.  It can safely
   ignore it if not supported.

   The following examples illustrate how a DOTS client retrieves active
   mitigation requests from a DOTS server.  In particular:

   o  Figure 9 shows the example of a GET request to retrieve all DOTS
      mitigation requests signaled by a DOTS client.

   o  Figure 10 shows the example of a GET request to retrieve a
      specific DOTS mitigation request signaled by a DOTS client.  The
      configuration data to be reported in the response is formatted in
      the same order it was processed by the DOTS server.

   These two examples assume the default of "c=a"; that is, the DOTS
   client asks for all data to be reported by the DOTS server.






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     Header: GET (Code=0.01)
     Uri-Host: "host"
     Uri-Path: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "version"
     Uri-Path: "mitigate"
     Observe : 0
     {
       "mitigation-scope": {
         "client-identifier": [
            "dz6pHjaADkaFTbjr0JGBpw"
         ]
       }
     }

          Figure 9: GET to retrieve all DOTS mitigation requests

     Header: GET (Code=0.01)
     Uri-Host: "host"
     Uri-Path: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "version"
     Uri-Path: "mitigate"
     Observe : 0
     Content-Format: "application/cbor"
     {
       "mitigation-scope": {
         "client-identifier": [
            "dz6pHjaADkaFTbjr0JGBpw"
         ],
         "scope": [
           {
             "mitigation-id": 12332
           }
         ]
       }
     }

       Figure 10: GET to retrieve a specific DOTS mitigation request

   Figure 11 shows a response example of all active mitigation requests
   associated with the DOTS client on the DOTS server and the mitigation
   status of each mitigation request.








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   {
     "mitigation-scope": {
        "scope": [
           {
             "mitigation-id": 12332,
             "mitigation-start": 1507818434.00,
             "target-protocol": [
                 17
              ],
             "lifetime": 1800,
             "status": 2,
             "bytes-dropped": 134334555,
             "bps-dropped":  43344,
             "pkts-dropped": 333334444,
             "pps-dropped": 432432
            },
           {
             "mitigation-id": 12333,
             "mitigation-start": 1507818393.00,
             "target-protocol": [
                 6
              ],
             "lifetime": 1800,
             "status": 3,
             "bytes-dropped": 0,
             "bps-dropped":  0,
             "pkts-dropped": 0,
             "pps-dropped": 0
           }
        ]
     }
    }

                         Figure 11: Response body

   The mitigation status parameters are described below:

   mitigation-start:  Mitigation start time is expressed in seconds
      relative to 1970-01-01T00:00Z in UTC time (Section 2.4.1 of
      [RFC7049]).  The encoding is modified so that the leading tag 1
      (epoch-based date/time) MUST be omitted.

      This is a mandatory attribute.

   lifetime:  The remaining lifetime of the mitigation request, in
      seconds.

      This is a mandatory attribute.



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   status:  Status of attack mitigation.  The various possible values of
      'status' parameter are explained in Table 2.

      This is a mandatory attribute.

   conflict-information:  Indicates that a mitigation request is
      conflicting with another mitigation request(s) from other DOTS
      client(s).  This optional attribute has the following structure:

      conflict-status:  Indicates the status of a conflicting mitigation
         request.  The following values are defined:

         1:  DOTS server has detected conflicting mitigation requests
             from different DOTS clients.  This mitigation request is
             currently inactive until the conflicts are resolved.
             Another mitigation request is active.

         2:  DOTS server has detected conflicting mitigation requests
             from different DOTS clients.  This mitigation request is
             currently active.

         3:  DOTS server has detected conflicting mitigation requests
             from different DOTS clients.  All conflicting mitigation
             requests are inactive.

      conflict-cause:  Indicates the cause of the conflict.  The
         following values are defined:

         1:  Overlapping targets. 'conflict-scope' provides more details
             about the conflicting target clauses.

         2:  Conflicts with an existing white list.  This code is
             returned when the DDoS mitigation detects source addresses/
             prefixes in the white-listed ACLs are attacking the target.

      conflict-scope  Indicates the conflict scope.  It may include a
         list of IP addresses, a list of prefixes, a list of port
         numbers, a list of target protocols, a list of FQDNs, a list of
         URIs, a list of alias-names, or references to conflicting ACLs.

      retry-timer  Indicates, in seconds, the time after which the DOTS
         client may re-issue the same request.  The DOTS server returns
         'retry-timer' only to DOTS client(s) for which a mitigation
         request is deactivated.  Any retransmission of the same
         mitigation request before the expiry of this timer is likely to
         be rejected by the DOTS server for the same reasons.





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         The retry-timer SHOULD be equal to the lifetime of the active
         mitigation request resulting in the deactivation of the
         conflicting mitigation request.  The lifetime of the
         deactivated mitigation request will be updated to (retry-timer
         + 45 seconds), so the DOTS client can refresh the deactivated
         mitigation request after retry-timer seconds before expiry of
         lifetime and check if the conflict is resolved.

   bytes-dropped:  The total dropped byte count for the mitigation
      request since the attack mitigation is triggered.  The count wraps
      around when it reaches the maximum value of unsigned integer.

      This is an optional attribute.

   bps-dropped:  The average number of dropped bytes per second for the
      mitigation request since the attack mitigation is triggered.  This
      SHOULD be a five-minute average.

      This is an optional attribute.

   pkts-dropped:  The total number of dropped packet count for the
      mitigation request since the attack mitigation is triggered.

      This is an optional attribute.

   pps-dropped:  The average number of dropped packets per second for
      the mitigation request since the attack mitigation is triggered.
      This SHOULD be a five-minute average.

      This is an optional attribute.





















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   +-----------+-------------------------------------------------------+
   | Parameter | Description                                           |
   |     value |                                                       |
   +-----------+-------------------------------------------------------+
   |         1 | Attack mitigation is in progress (e.g., changing the  |
   |           | network path to re-route the inbound traffic to DOTS  |
   |           | mitigator).                                           |
   +-----------+-------------------------------------------------------+
   |         2 | Attack is successfully mitigated (e.g., traffic is    |
   |           | redirected to a DDOS mitigator and attack traffic is  |
   |           | dropped).                                             |
   +-----------+-------------------------------------------------------+
   |         3 | Attack has stopped and the DOTS client can withdraw   |
   |           | the mitigation request.                               |
   +-----------+-------------------------------------------------------+
   |         4 | Attack has exceeded the mitigation provider           |
   |           | capability.                                           |
   +-----------+-------------------------------------------------------+
   |         5 | DOTS client has withdrawn the mitigation request and  |
   |           | the mitigation is active but terminating.             |
   +-----------+-------------------------------------------------------+
   |         6 | Attack mitigation is now terminated.                  |
   +-----------+-------------------------------------------------------+
   |         7 | Attack mitigation is withdrawn.                       |
   +-----------+-------------------------------------------------------+
   |         8 | Attack mitigation is rejected.                        |
   +-----------+-------------------------------------------------------+

                   Table 2: Values of 'status' parameter

   The observe option defined in [RFC7641] extends the CoAP core
   protocol with a mechanism for a CoAP client to "observe" a resource
   on a CoAP server: The client retrieves a representation of the
   resource and requests this representation be updated by the server as
   long as the client is interested in the resource.  A DOTS client
   conveys the observe option set to '0' in the GET request to receive
   unsolicited notifications of attack mitigation status from the DOTS
   server.

   Unidirectional notifications within the bidirectional signal channel
   allows unsolicited message delivery, enabling asynchronous
   notifications between the agents.  Due to the higher likelihood of
   packet loss during a DDoS attack, DOTS server periodically sends
   attack mitigation status to the DOTS client and also notifies the
   DOTS client whenever the status of the attack mitigation changes.  If
   the DOTS server cannot maintain a RTT estimate, it SHOULD NOT send
   more than one unsolicited notification every 3 seconds, and SHOULD




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   use an even less aggressive rate whenever possible (case 2 in
   Section 3.1.3 of [RFC8085]).

   When conflicting requests are detected, the DOTS server enforces the
   corresponding policy (e.g., accept all requests, reject all requests,
   accept only one request but reject all the others, ...).  It is
   assumed that this policy is supplied by the DOTS server administrator
   or it is a default behavior of the DOTS server implementation.  Then,
   the DOTS server sends notification message(s) to the DOTS client(s)
   at the origin of the conflict.  A conflict notification message
   includes information about the conflict cause, scope, and the status
   of the mitigation request(s).  For example,

   o  A notification message with status code set to '8 (Attack
      mitigation is rejected)' and 'conflict-status' set to '1' is sent
      to a DOTS client to indicate that this mitigation request is
      rejected because a conflict is detected.

   o  A notification message with status code set to '7 (Attack
      mitigation is withdrawn)' and 'conflict-status' set to '1' is sent
      to a DOTS client to indicate that an active mitigation request is
      deactivated because a conflict is detected.

   o  A notification message with status code set to '1 (Attack
      mitigation is in progress)' and 'conflict-status' set to '2' is
      sent to a DOTS client to indicate that this mitigation request is
      in progress, but a conflict is detected.

   Upon receipt of a conflict notification message indicating that a
   mitigation request is deactivated because of a conflict, a DOTS
   client MUST NOT resend the same mitigation request before the expiry
   of 'retry-timer'.  It is also recommended that DOTS clients support
   means to alert administrators about mitigation conflicts.

   A DOTS client that is no longer interested in receiving notifications
   from the DOTS server can simply "forget" the observation.  When the
   DOTS server sends the next notification, the DOTS client will not
   recognize the token in the message and thus will return a Reset
   message.  This causes the DOTS server to remove the associated entry.
   Alternatively, the DOTS client can explicitly deregister itself by
   issuing a GET request that has the Token field set to the token of
   the observation to be cancelled and includes an Observe Option with
   the value set to '1' (deregister).

   Figure 12 shows an example of a DOTS client requesting a DOTS server
   to send notifications related to a given mitigation request.





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         DOTS Client                   DOTS Server
            |                               |
            |  GET /<mitigation-id number>  |
            |  Token: 0x4a                  |   Registration
            |  Observe: 0                   |
            +------------------------------>|
            |                               |
            |  2.05 Content                 |
            |  Token: 0x4a                  |   Notification of
            |  Observe: 12                  |   the current state
            |  status: "mitigation          |
            |          in progress"         |
            |<------------------------------+
            |  2.05 Content                 |
            |  Token: 0x4a                  |   Notification upon
            |  Observe: 44                  |    a state change
            |  status: "mitigation          |
            |          complete"            |
            |<------------------------------+
            |  2.05 Content                 |
            |  Token: 0x4a                  |   Notification upon
            |  Observe: 60                  |   a state change
            |  status: "attack stopped"     |
            |<------------------------------+
            |                               |

           Figure 12: Notifications of attack mitigation status

4.4.2.1.  Mitigation Status

   The DOTS client can send the GET request at frequent intervals
   without the Observe option to retrieve the configuration data of the
   mitigation request and non-configuration data (i.e., the attack
   status).  The frequency of polling the DOTS server to get the
   mitigation status should follow the transmission guidelines given in
   Section 3.1.3 of [RFC8085].  If the DOTS server has been able to
   mitigate the attack and the attack has stopped, the DOTS server
   indicates as such in the status, and the DOTS client recalls the
   mitigation request by issuing a DELETE request for the mitigation-id.

   A DOTS client SHOULD react to the status of the attack as per the
   information sent by the DOTS server rather than acknowledging by
   itself, using its own means, that the attack has been mitigated.
   This ensures that the DOTS client does not recall a mitigation
   request prematurely because it is possible that the DOTS client does
   not sense the DDOS attack on its resources but the DOTS server could
   be actively mitigating the attack and the attack is not completely
   averted.



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4.4.3.  Efficacy Update from DOTS Clients

   While DDoS mitigation is active, due to the likelihood of packet
   loss, a DOTS client MAY periodically transmit DOTS mitigation
   efficacy updates to the relevant DOTS server.  A PUT request is used
   to convey the mitigation efficacy update to the DOTS server.

   The PUT request MUST include all the parameters used in the PUT
   request to carry the DOTS signal (Section 4.4.1) unchanged apart from
   the lifetime parameter value.  If this is not the case, the DOTS
   server MUST reject the request with a 4.00 (Bad Request).

   The If-Match Option (Section 5.10.8.1 of [RFC7252]) with an empty
   value is used to make the PUT request conditional on the current
   existence of the mitigation request.  If UDP is used as transport,
   CoAP requests may arrive out-of-order.  For example, the DOTS client
   may send a PUT request to convey an efficacy update to the DOTS
   server followed by a DELETE request to withdraw the mitigation
   request, but the DELETE request arrives at the DOTS server before the
   PUT request.  To handle out-of-order delivery of requests, if an If-
   Match option is present in the PUT request and the 'mitigation-id' in
   the request matches a mitigation request from that DOTS client, then
   the request is processed.  If no match is found, the PUT request is
   silently ignored.

   An example of an efficacy update message, which includes an If-Match
   option with an empty value, is depicted in Figure 13.
























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      Header: PUT (Code=0.03)
      Uri-Host: "host"
      Uri-Path: ".well-known"
      Uri-Path: "dots"
      Uri-Path: "version"
      Uri-Path: "mitigate"
      Content-Format: "application/cbor"
      If-Match:
      {
       "mitigation-scope": {
         "client-identifier": [
            "string"
         ],
         "scope": [
           {
             "mitigation-id": integer,
             "target-prefix": [
                "string"
              ],
             "target-port-range": [
                {
                  "lower-port": integer,
                  "upper-port": integer
                }
              ],
              "target-protocol": [
                integer
              ],
              "target-fqdn": [
                "string"
              ],
              "target-uri": [
                "string"
              ],
              "alias-name": [
                "string"
              ],
             "lifetime": integer,
             "attack-status": integer
           }
         ]
       }
      }

                        Figure 13: Efficacy Update






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   The 'attack-status' parameter is a mandatory attribute when
   performing an efficacy update.  The various possible values contained
   in the 'attack-status' parameter are described in Table 3.

   +-----------+-------------------------------------------------------+
   | Parameter | Description                                           |
   |     value |                                                       |
   +-----------+-------------------------------------------------------+
   |         1 | The DOTS client determines that it is still under     |
   |           | attack.                                               |
   +-----------+-------------------------------------------------------+
   |         2 | The DOTS client determines that the attack is         |
   |           | successfully mitigated (e.g., attack traffic is not   |
   |           | seen).                                                |
   +-----------+-------------------------------------------------------+

               Table 3: Values of 'attack-status' parameter

   The DOTS server indicates the result of processing a PUT request
   using CoAP response codes.  The response code 2.04 (Changed) is
   returned if the DOTS server has accepted the mitigation efficacy
   update.  The error response code 5.03 (Service Unavailable) is
   returned if the DOTS server has erred or is incapable of performing
   the mitigation.

4.4.4.  Withdraw a Mitigation

   A DELETE request is used to withdraw a DOTS mitigation request from a
   DOTS server (Figure 14).

   The same considerations for manipulating 'client-identifier'
   parameter by a DOTS gateway, as specified in Section 4.4.1, MUST be
   followed for DELETE requests.


















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     Header: DELETE (Code=0.04)
     Uri-Host: "host"
     Uri-Path: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "version"
     Uri-Path: "mitigate"
     Content-Format: "application/cbor"
     {
       "mitigation-scope": {
         "client-identifier": [
            "string"
         ],
         "scope": [
           {
             "mitigation-id": integer
           }
         ]
       }
     }

                      Figure 14: Withdraw DOTS signal

   If the request does not include a 'mitigation-id' parameter, the DOTS
   server MUST reply with a 4.00 (Bad Request).

   Once the request is validated, the DOTS server immediately
   acknowledges a DOTS client's request to withdraw the DOTS signal
   using 2.02 (Deleted) response code with no response payload.  A 2.02
   (Deleted) Response Code is returned even if the 'mitigation-id'
   parameter value conveyed in the DELETE request does not exist in its
   configuration data before the request.

   If the DOTS server finds the 'mitigation-id' parameter value conveyed
   in the DELETE request in its configuration data for the DOTS client,
   then to protect against route or DNS flapping caused by a DOTS client
   rapidly removing a mitigation, and to dampen the effect of
   oscillating attacks, the DOTS server MAY allow mitigation to continue
   for a limited period after acknowledging a DOTS client's withdrawal
   of a mitigation request.  During this period, the DOTS server status
   messages SHOULD indicate that mitigation is active but terminating
   (Section 4.4.2).

   The initial active-but-terminating period SHOULD be sufficiently long
   to absorb latency incurred by route propagation.  The active-but-
   terminating period SHOULD be set by default to 120 seconds.  If the
   client requests mitigation again before the initial active-but-
   terminating period elapses, the DOTS server MAY exponentially




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   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 stops incurring cost at this point.

4.5.  DOTS Signal Channel Session Configuration

   The DOTS client can negotiate, configure, and retrieve the DOTS
   signal channel session behavior.  The DOTS signal channel can be
   used, for example, to configure the following:

   a.  Heartbeat interval (heartbeat-interval): DOTS agents regularly
       send heartbeats (CoAP Ping/Pong) to each other after mutual
       authentication is successfully completed in order to keep the
       DOTS signal channel open.  Heartbeat messages are exchanged
       between the DOTS agents every 'heartbeat-interval' seconds to
       detect the current status of the DOTS signal channel session.

   b.  Missing heartbeats allowed (missing-hb-allowed): This variable
       indicates the maximum number of consecutive heartbeat messages
       for which a DOTS agent did not receive a response before
       concluding that the session is disconnected or defunct.

   c.  Acceptable signal loss ratio: Maximum retransmissions,
       retransmission timeout value, and other message transmission
       parameters for the DOTS signal channel.

   Requests and responses are deemed reliable by marking them as
   Confirmable (CON) messages.  DOTS signal channel session
   configuration requests and responses are marked as Confirmable
   messages.  As explained in Section 2.1 of [RFC7252], a Confirmable
   message is retransmitted using a default timeout and exponential
   back-off between retransmissions, until the DOTS server sends an
   Acknowledgement message (ACK) with the same Message ID conveyed from
   the DOTS client.

   Message transmission parameters are defined in Section 4.8 of
   [RFC7252].  The DOTS server can either piggyback the response in the
   acknowledgement message or, if the DOTS server cannot respond
   immediately to a request carried in a Confirmable message, it simply
   responds with an Empty Acknowledgement message so that the DOTS
   client can stop retransmitting the request.  Empty Acknowledgement
   message is explained in Section 2.2 of [RFC7252].  When the response
   is ready, the server sends it in a new Confirmable message which in



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   turn needs to be acknowledged by the DOTS client (see Sections 5.2.1
   and 5.2.2 of [RFC7252]).  Requests and responses exchanged between
   DOTS agents during peacetime are marked as Confirmable messages.

      Implementation Note: A DOTS client that receives a response in a
      CON message may want to clean up the message state right after
      sending the ACK.  If that ACK is lost and the DOTS server
      retransmits the CON, the DOTS client may no longer have any state
      that would help it correlate this response, thereby unexpecting
      the retransmission message.  The DOTS client will send a Reset
      message so it does not receive any more retransmissions.  This
      behavior is normal and not an indication of an error (see
      Section 5.3.2 of [RFC7252] for more details).

4.5.1.  Discover Configuration Parameters

   A GET request is used to obtain acceptable (e.g., minimum and maximum
   values) and current configuration parameters on the DOTS server for
   DOTS signal channel session configuration.  Figure 15 shows how to
   obtain acceptable configuration parameters for the DOTS server.

     Header: GET (Code=0.01)
     Uri-Host: "host"
     Uri-Path: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "version"
     Uri-Path: "config"

                 Figure 15: GET to retrieve configuration

   The DOTS server in the 2.05 (Content) response conveys the current,
   minimum, and maximum attribute values acceptable by the DOTS server
   (Figure 16).


















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     Content-Format: "application/cbor"
      {
        "heartbeat-interval": {
                               "current-value": integer,
                               "min-value": integer,
                               "max-value": integer
                              },
        "missing-hb-allowed": {
                               "current-value": integer,
                               "min-value": integer,
                               "max-value": integer
                              },
        "max-retransmit":     {
                               "current-value": integer,
                               "min-value": integer,
                               "max-value": integer
                              },
        "ack-timeout":        {
                               "current-value": integer,
                               "min-value": integer,
                               "max-value": integer
                              },
        "ack-random-factor":  {
                               "current-value": number,
                               "min-value": number,
                               "max-value": number
                              },
        "trigger-mitigation": {
                               "current-value": boolean
                              },
        "config-interval": {
                               "current-value": integer,
                               "min-value": integer,
                               "max-value": integer
                              }
       }

                       Figure 16: GET response body

   Figure 17 shows an example of acceptable and current configuration
   parameters on a DOTS server for DOTS signal channel session
   configuration.









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     Content-Format: "application/cbor"
     {
       "heartbeat-interval": {
                               "current-value": 30,
                               "min-value": 15,
                               "max-value": 240
                              },
        "missing-hb-allowed": {
                               "current-value": 5,
                               "min-value": 3,
                               "max-value": 9
                              },
        "max-retransmit":     {
                               "current-value": 3,
                               "min-value": 2,
                               "max-value": 15
                              },
        "ack-timeout":        {
                               "current-value": 2,
                               "min-value": 1,
                               "max-value": 30
                              },
        "ack-random-factor": {
                               "current-value": 1.5,
                               "min-value": 1.1,
                               "max-value": 4.0
                              },
        "trigger-mitigation": {
                               "current-value": true
                              },
        "config-interval": {
                               "current-value": 1439,
                               "min-value": 0,
                               "max-value": 65535
                              }
     }

                  Figure 17: Configuration response body

4.5.2.  Convey DOTS Signal Channel Session Configuration

   A PUT request is used to convey the configuration parameters for the
   signal channel (e.g., heartbeat interval, maximum retransmissions).
   Message transmission parameters for CoAP are defined in Section 4.8
   of [RFC7252].  The RECOMMENDED values of transmission parameter
   values are ack-timeout (2 seconds), max-retransmit (3), ack-random-
   factor (1.5).  In addition to those parameters, the RECOMMENDED




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   specific DOTS transmission parameter values are heartbeat-interval
   (30 seconds) and missing-hb-allowed (5).

      Note: heartbeat-interval should be tweaked to also assist DOTS
      messages for NAT traversal (SIG-010 of
      [I-D.ietf-dots-requirements]).  According to [RFC8085], keepalive
      messages must not be sent more frequently than once every 15
      seconds and should use longer intervals when possible.
      Furthermore, [RFC4787] recommends NATs to use a state timeout of 2
      minutes or longer, but experience shows that sending packets every
      15 to 30 seconds is necessary to prevent the majority of
      middleboxes from losing state for UDP flows.  From that
      standpoint, this specification recommends a minimum heartbeat-
      interval of 15 seconds and a maximum heartbeat-interval of 240
      seconds.  The recommended value of 30 seconds is selected to
      anticipate the expiry of NAT state.

      A heartbeat-interval of 30 seconds may be seen as too chatty in
      some deployments.  For such deployments, DOTS agents may negotiate
      longer heartbeat-interval values to prevent any network overload
      with too frequent keepalives.

   When a confirmable "CoAP Ping" is sent, and if there is no response,
   the "CoAP Ping" is retransmitted max-retransmit number of times by
   the CoAP layer using an initial timeout set to a random duration
   between ack-timeout and (ack-timeout*ack-random-factor) and
   exponential back-off between retransmissions.  By choosing the
   recommended transmission parameters, the "CoAP Ping" will timeout
   after 45 seconds.  If the DOTS agent does not receive any response
   from the peer DOTS agent for 'missing-hb-allowed' number of
   consecutive "CoAP Ping" confirmable messages, it concludes that the
   DOTS signal channel session is disconnected.  A DOTS client MUST NOT
   transmit a "CoAP Ping" while waiting for the previous "CoAP Ping"
   response from the same DOTS server.

   If the DOTS agent wishes to change the default values of message
   transmission parameters, then it should follow the guidance given in
   Section 4.8.1 of [RFC7252].  The DOTS agents MUST use the negotiated
   values for message transmission parameters and default values for
   non-negotiated message transmission parameters.

   The signal channel session configuration is applicable to a single
   DOTS signal channel session between the DOTS agents.








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     Header: PUT (Code=0.03)
     Uri-Host: "host"
     Uri-Path: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "version"
     Uri-Path: "config"
     Content-Format: "application/cbor"
     {
      "signal-config": {
        "session-id": integer,
        "heartbeat-interval": integer,
        "missing-hb-allowed": integer,
        "max-retransmit": integer,
        "ack-timeout": integer,
        "ack-random-factor": number,
        "trigger-mitigation": boolean,
        "config-interval": integer
      }
     }

         Figure 18: PUT to convey the DOTS signal channel session
                            configuration data.

   The parameters in Figure 18 are described below:

   session-id:  Identifier for the DOTS signal channel session
      configuration data represented as an integer.  This identifier
      MUST be generated by the DOTS client.  This document does not make
      any assumption about how this identifier is generated.

      This is a mandatory attribute.

   heartbeat-interval:   Time interval in seconds between two
      consecutive heartbeat messages.

      '0' is used to disable the heartbeat mechanism.

      This is an optional attribute.

   missing-hb-allowed:   Maximum number of consecutive heartbeat
      messages for which the DOTS agent did not receive a response
      before concluding that the session is disconnected.

      This is an optional attribute.

   max-retransmit:   Maximum number of retransmissions for a message
      (referred to as MAX_RETRANSMIT parameter in CoAP).




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      This is an optional attribute.

   ack-timeout:   Timeout value in seconds used to calculate the initial
      retransmission timeout value (referred to as ACK_TIMEOUT parameter
      in CoAP).

      This is an optional attribute.

   ack-random-factor:   Random factor used to influence the timing of
      retransmissions (referred to as ACK_RANDOM_FACTOR parameter in
      CoAP).

      This is an optional attribute.

   trigger-mitigation:   If the parameter value is set to 'false', then
      DDoS mitigation is triggered only when the DOTS signal channel
      session is lost.  Automated mitigation on loss of signal is
      discussed in Section 3.3.3 of [I-D.ietf-dots-architecture].

      If the DOTS client ceases to respond to heartbeat messages, the
      DOTS server can detect that the DOTS session is lost.

      The default value of the parameter is 'true'.

      This is an optional attribute.

   config-interval:   This parameter is returned to indicate the time
      interval expressed in minutes, which a DOTS agent must wait for
      before re-contacting its peer in order to retrieve the signal
      channel configuration data.

      '0' is used to disable this refresh mechanism.

      If a non-null value of 'config-interval' is received by a DOTS
      agent, it has to issue a PUT request to refresh the configuration
      parameters for the signal channel before the expiry of 'config-
      interval'.

      This mechanism allows to update the configuration data if a change
      occurs at the DOTS server side.  For example, the new
      configuration may instruct a DOTS client to cease heartbeats or
      reduce heartbeat frequency.

      If this parameter is not returned, this is equivalent to receiving
      a 'config-interval' value set to '0'.

      If a DOTS server detects that a misbehaving DOTS client does not
      contact the DOTS server after the expiry of 'config-interval', in



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      order to retrieve the signal channel configuration data, it MAY
      terminate the (D)TLS session.  A (D)TLS session is terminated by
      the receipt of an authenticated message that closes the connection
      (e.g., a fatal alert (Section 7.2 of [RFC5246])).

      This is an optional attribute.

   At least one of the attributes 'heartbeat-interval', 'missing-hb-
   allowed', 'max-retransmit', 'ack-timeout', 'ack-random-factor', and
   'trigger-mitigation' MUST be present in the PUT request . The PUT
   request with a higher numeric 'session-id' value overrides the DOTS
   signal channel session configuration data installed by a PUT request
   with a lower numeric 'session-id' value.

   Figure 19 shows a PUT request example to convey the configuration
   parameters for the DOTS signal channel.

     Header: PUT (Code=0.03)
     Uri-Host: "www.example.com"
     Uri-Path: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "v1"
     Uri-Path: "config"
     Content-Format: "application/cbor"
     {
       "signal-config": {
        "session-id": 1234534333242,
        "heartbeat-interval": 91,
        "missing-hb-allowed": 3,
        "max-retransmit": 7,
        "ack-timeout": 5,
        "ack-random-factor": 1.5,
        "trigger-mitigation": false
       }
     }

           Figure 19: PUT to convey the configuration parameters

   The DOTS server indicates the result of processing the PUT request
   using CoAP response codes:

   o  If the DOTS server finds the 'session-id' parameter value conveyed
      in the PUT request in its configuration data and if the DOTS
      server has accepted the updated configuration parameters, then
      2.04 (Changed) code is returned in the response.

   o  If the DOTS server does not find the 'session-id' parameter value
      conveyed in the PUT request in its configuration data and if the



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      DOTS server has accepted the configuration parameters, then a
      response code 2.01 (Created) is returned in the response.

   o  If the request is missing one or more mandatory attributes or it
      contains one or more invalid or unknown parameters, then 4.00 (Bad
      Request) is returned in the response.

   o  Response code 4.22 (Unprocessable Entity) is returned in the
      response, if any of the 'heartbeat-interval', 'missing-hb-
      allowed', 'max-retransmit', 'target-protocol', 'ack-timeout', and
      'ack-random-factor' attribute values are not acceptable to the
      DOTS server.  Upon receipt of the 4.22 error response code, the
      DOTS client should request the maximum and minimum attribute
      values acceptable to the DOTS server (Section 4.5.1).

      The DOTS client may re-try and send the PUT request with updated
      attribute values acceptable to the DOTS server.

4.5.3.  Delete DOTS Signal Channel Session Configuration

   A DELETE request is used to delete the installed DOTS signal channel
   session configuration data (Figure 20).

     Header: DELETE (Code=0.04)
     Uri-Host: "host"
     Uri-Path: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "version"
     Uri-Path: "config"
     Content-Format: "application/cbor"

                      Figure 20: DELETE configuration

   The DOTS server resets the DOTS signal channel session configuration
   back to the default values and acknowledges a DOTS client's request
   to remove the DOTS signal channel session configuration using 2.02
   (Deleted) response code.

4.6.  Redirected Signaling

   Redirected DOTS signaling is discussed in detail in Section 3.2.2 of
   [I-D.ietf-dots-architecture].

   If a DOTS server wants to redirect a DOTS client to an alternative
   DOTS server for a signal session, then the response code 3.00
   (alternate server) will be returned in the response to the client.





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   The DOTS server can return the error response code 3.00 in response
   to a PUT request from the DOTS client or convey the error response
   code 3.00 in a unidirectional notification response from the DOTS
   server.

   The DOTS server in the error response conveys the alternate DOTS
   server's FQDN, and the alternate DOTS server's IP address(es) and
   time to live values in the CBOR body (Figure 21).

   {
       "alt-server": "string",
       "alt-server-record": [
         {
           "addr": "string",
           "ttl" : integer
         }
       ]
   }

                      Figure 21: Error response body

   The parameters are described below:

   alt-server:  FQDN of an alternate DOTS server.

   addr:  IP address of an alternate DOTS server.

   ttl:  Time to live (TTL) represented as an integer number of seconds.

   Figure 22 shows a 3.00 response example to convey the DOTS alternate
   server 'alt-server.example', its IP addresses 2001:db8:6401::1 and
   2001:db8:6401::2, and TTL values 3600 and 1800.

   {
       "alt-server": "alt-server.example",
       "alt-server-record": [
         {
           "ttl" :  3600,
           "addr": "2001:db8:6401::1"
         },
         {
           "ttl" :  1800,
           "addr": "2001:db8:6401::2"
         }
       ]
   }

                 Figure 22: Example of error response body



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   When the DOTS client receives 3.00 response, it considers the current
   request as failed, but SHOULD try re-sending the request to the
   alternate DOTS server.  During a DDOS attack, the DNS server may be
   the target of another DDoS attack, alternate DOTS server's IP
   addresses conveyed in the 3.00 response help the DOTS client skip DNS
   lookup of the alternate DOTS server.  The DOTS client can then try to
   establish a UDP or a TCP session with the alternate DOTS server.  The
   DOTS client SHOULD implement a DNS64 function to handle the scenario
   where an IPv6-only DOTS client communicates with an IPv4-only
   alternate DOTS server.

4.7.  Heartbeat Mechanism

   To provide an indication of signal health and distinguish an 'idle'
   signal channel from a 'disconnected' or 'defunct' session, the DOTS
   agent sends a heartbeat over the signal channel to maintain its half
   of the channel.  The DOTS agent similarly expects a heartbeat from
   its peer DOTS agent, and may consider a session terminated in the
   prolonged absence of a peer agent heartbeat.

   While the communication between the DOTS agents is quiescent, the
   DOTS client will probe the DOTS server to ensure it has maintained
   cryptographic state and vice versa.  Such probes can also keep
   firewall and/or NAT bindings alive.  This probing reduces the
   frequency of establishing a new handshake when a DOTS signal needs to
   be conveyed to the DOTS server.

   In case of a massive DDoS attack that saturates the incoming link(s)
   to the DOTS client, all traffic from the DOTS server to the DOTS
   client will likely be dropped, although the DOTS server receives
   heartbeat requests in addition to DOTS messages sent by the DOTS
   client.  In this scenario, the DOTS agents MUST behave differently to
   handle message transmission and DOTS session liveliness during link
   saturation:

   o  The DOTS client MUST NOT consider the DOTS session terminated even
      after a maximum 'missing-hb-allowed' threshold is reached.  The
      DOTS client SHOULD keep on using the current DOTS session to send
      heartbeat requests over it, so that the DOTS server knows the DOTS
      client has not disconnected the DOTS session.

      After the maximum 'missing-hb-allowed' threshold is reached, the
      DOTS client SHOULD try to resume the (D)TLS session.  The DOTS
      client SHOULD send mitigation requests over the current DOTS
      session, and in parallel, for example, try to resume the (D)TLS
      session or use 0-RTT mode in DTLS 1.3 to piggyback the mitigation
      request in the ClientHello message.




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      As soon as the link is no longer saturated, if traffic from the
      DOTS server reaches the DOTS client over the current DOTS session,
      the DOTS client can stop (D)TLS session resumption or if (D)TLS
      session resumption is successful then disconnect the current DOTS
      session.

   o  If the DOTS server does not receive any traffic from the peer DOTS
      client, then the DOTS server sends heartbeat requests to the DOTS
      client and after maximum 'missing-hb-allowed' threshold is
      reached, the DOTS server concludes the session is disconnected.

   In DOTS over UDP, heartbeat messages MUST be exchanged between the
   DOTS agents using the "CoAP Ping" mechanism defined in Section 4.2 of
   [RFC7252].  Concretely, the DOTS agent sends an Empty Confirmable
   message and the peer DOTS agent will respond by sending a Reset
   message.

   In DOTS over TCP, heartbeat messages MUST be exchanged between the
   DOTS agents using the Ping and Pong messages specified in Section 4.4
   of [I-D.ietf-core-coap-tcp-tls].  That is, the DOTS agent sends a
   Ping message and the peer DOTS agent would respond by sending a
   single Pong message.

5.  DOTS Signal Channel YANG Module

   This document defines a YANG [RFC7950] module for mitigation scope
   and DOTS signal channel session configuration data.

5.1.  Tree Structure

   This document defines the YANG module "ietf-dots-signal"
   (Section 5.2), which has the following tree structure.  A DOTS signal
   message can either be a mitigation or a configuration message.


















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module: ietf-dots-signal
    +--rw dots-signal
       +--rw (message-type)?
          +--:(mitigation-scope)
          |  +--rw client-identifier*    binary
          |  +--rw scope* [mitigation-id]
          |     +--rw mitigation-id           int32
          |     +--rw target-prefix*          inet:ip-prefix
          |     +--rw target-port-range* [lower-port upper-port]
          |     |  +--rw lower-port    inet:port-number
          |     |  +--rw upper-port    inet:port-number
          |     +--rw target-protocol*        uint8
          |     +--rw target-fqdn*            inet:domain-name
          |     +--rw target-uri*             inet:uri
          |     +--rw alias-name*             string
          |     +--rw lifetime?               int32
          |     +--rw mitigation-start?       int64
          |     +--ro status?                 enumeration
          |     +--ro conflict-information
          |     |  +--ro conflict-status?   enumeration
          |     |  +--ro conflict-cause?    enumeration
          |     |  +--ro retry-timer?       int32
          |     |  +--ro conflict-scope
          |     |     +--ro target-prefix*       inet:ip-prefix
          |     |     +--ro target-port-range* [lower-port upper-port]
          |     |     |  +--ro lower-port    inet:port-number
          |     |     |  +--ro upper-port    inet:port-number
          |     |     +--ro target-protocol*     uint8
          |     |     +--ro target-fqdn*         inet:domain-name
          |     |     +--ro target-uri*          inet:uri
          |     |     +--ro alias-name*          string
          |     |     +--ro acl-list* [acl-name acl-type]
          |     |        +--ro acl-name    -> /ietf-acl:access-lists/acl/acl-name
          |     |        +--ro acl-type    -> /ietf-acl:access-lists/acl/acl-type
          |     +--ro pkts-dropped?           yang:zero-based-counter64
          |     +--ro bps-dropped?            yang:zero-based-counter64
          |     +--ro bytes-dropped?          yang:zero-based-counter64
          |     +--ro pps-dropped?            yang:zero-based-counter64
          +--:(configuration)
             +--rw session-id            int32
             +--rw heartbeat-interval?   int16
             +--rw missing-hb-allowed?   int16
             +--rw max-retransmit?       int16
             +--rw ack-timeout?          int16
             +--rw ack-random-factor?    decimal64
             +--rw trigger-mitigation?   boolean
             +--rw config-interval?      int32




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5.2.  YANG Module

<CODE BEGINS> file "ietf-dots-signal@2017-12-12.yang"

module ietf-dots-signal {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-dots-signal";
  prefix "signal";

  import ietf-inet-types {prefix "inet";}
  import ietf-yang-types {prefix yang;}
  import ietf-access-control-list {prefix "ietf-acl";}

  organization "IETF DDoS Open Threat Signaling (DOTS) Working Group";

  contact
    "Konda, Tirumaleswar Reddy <TirumaleswarReddy_Konda@McAfee.com>
     Mohamed Boucadair <mohamed.boucadair@orange.com>
     Prashanth Patil <praspati@cisco.com>
     Andrew Mortensen <amortensen@arbor.net>
     Nik Teague <nteague@verisign.com>";

  description
    "This module contains YANG definition for the signaling
     messages exchanged between a DOTS client and a DOTS server.

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

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject
     to the license terms contained in, the Simplified BSD License
     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (http://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX; see
     the RFC itself for full legal notices.";

  revision 2017-12-12 {
    description
      "Initial revision.";
    reference
      "RFC XXXX: Distributed Denial-of-Service Open Threat
                 Signaling (DOTS) Signal Channel";
  }

  grouping target {



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    description
      "Specifies the scope of the mitigation request.";

    leaf-list target-prefix {
      type inet:ip-prefix;
      description
       "IPv4 or IPv6 prefix identifying the target.";
    }

    list target-port-range {
      key "lower-port upper-port";

      description
        "Port range. When only lower-port is
         present, it represents a single port.";

      leaf lower-port {
        type inet:port-number;
        mandatory true;
        description "Lower port number.";
      }

      leaf upper-port {
        type inet:port-number;
        must ". >= ../lower-port" {
           error-message
             "The upper port number must be greater than
              or equal to lower port number.";
        }
        description "Upper port number.";
      }
    }

    leaf-list target-protocol {
      type uint8;
      description
        "Identifies the target protocol number.

         The value '0' means 'all protocols'.

         Values are taken from the IANA protocol registry:
         https://www.iana.org/assignments/protocol-numbers/
         protocol-numbers.xhtml

         For example, 6 for TCP or 17 for UDP.";
    }

    leaf-list target-fqdn {



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      type inet:domain-name;
      description "FQDN identifying the target.";
    }

    leaf-list target-uri {
      type inet:uri;
      description "URI identifying the target.";
    }

    leaf-list alias-name {
      type string;
      description "alias name";
    }
  }

  grouping mitigation-scope {
    description
      "Specifies the scope of the mitigation request.";

    leaf-list client-identifier {
      type binary;
      description
        "The client identifier may be conveyed by
         the DOTS gateway to propagate the DOTS client
         identification information from the gateway's client-side to the
         gateway's server-side, and from the gateway's
         server-side to the DOTS server.

         It allows the destination DOTS server to accept
         mitigation requests with scopes which the DOTS
         client is authorized to manage.";
    }

    list scope {
      key mitigation-id;
      description
        "The scope of the request.";

      leaf mitigation-id {
        type int32;
        description
          "Mitigation request identifier.

           This identifier must be unique for each mitigation
           request bound to the DOTS client.";
      }

      uses target;



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      leaf lifetime {
        type int32;
        units "seconds";
        default 3600;
        description
          "Indicates the lifetime of the mitigation request.";
        reference
          "RFC XXXX: Distributed Denial-of-Service Open Threat
                     Signaling (DOTS) Signal Channel";
      }

      leaf mitigation-start {
        type int64;
        units "seconds";
        description
          "Mitigation start time is represented in seconds
           relative to 1970-01-01T00:00Z in UTC time.";
      }

      leaf status {
        type enumeration {
          enum "attack-mitigation-in-progress"  {
            value 1;
            description
              "Attack mitigation is in progress (e.g., changing
               the network path to re-route the inbound traffic
               to DOTS mitigator).";
          }

          enum "attack-successfully-mitigated" {
            value 2;
            description
              "Attack is successfully mitigated (e.g., traffic
               is redirected to a DDOS mitigator and attack
               traffic is dropped or blackholed).";
          }

          enum "attack-stopped" {
            value 3;
            description
              "Attack has stopped and the DOTS client can
               withdraw the mitigation request.";
          }

          enum "attack-exceeded-capability" {
            value 4;
            description
              "Attack has exceeded the mitigation provider



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               capability.";
          }

          enum "dots-client-withdrawn-mitigation" {
            value 5;
            description
              "DOTS client has withdrawn the mitigation
               request and the mitigation is active but
               terminating.";
          }

          enum "attack-mitigation-terminated" {
            value 6;
            description
              "Attack mitigation is now terminated.";
          }

          enum "attack-mitigation-withdrawn" {
            value 7;
            description
              "Attack mitigation is withdrawn.";
          }

          enum "attack-mitigation-rejected" {
            value 8;
            description
              "Attack mitigation is rejected.";
          }
        }
        config false;
        description
          "Indicates the status of a mitigation request.
           It must be included in responses only.";
        }

        container conflict-information {
          config false;
          description
            "Indicates that a conflict is detected.
             Must only be used for responses.";

          leaf conflict-status {
            type enumeration {
              enum "request-inactive-other-active"  {
                value 1;
                description
                  "DOTS Server has detected conflicting mitigation
                   requests from different DOTS clients.



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                   This mitigation request is currently inactive
                   until the conflicts are resolved. Another
                   mitigation request is active.";
              }

              enum "request-active" {
                value 2;
                description
                  "DOTS Server has detected conflicting mitigation
                   requests from different DOTS clients.
                   This mitigation request is currently active.";
               }

              enum "all-requests-inactive" {
                value 3;
                description
                  "DOTS Server has detected conflicting mitigation
                   requests from different DOTS clients.  All
                   conflicting mitigation requests are inactive.";
              }
            }
            description
              "Indicates the conflict status.
               It must be included in responses only.";
          }

          leaf conflict-cause {
             type enumeration {
               enum "overlapping-targets"  {
                 value 1;
                 description
                   "Overlapping targets. conflict-scope provides
                    more details about the exact conflict.";
               }

               enum "conflict-with-whitelist" {
                 value 2;
                 description
                   "Conflicts with an existing white list.

                    This code is returned when the DDoS mitigation
                    detects that some of the source addresses/prefixes
                    listed in the white list ACLs are actually
                    attacking the target.";
               }
            }
            description
              "Indicates the cause of the conflict.



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               It must be included in responses only.";
          }

          leaf retry-timer {
            type int32;
            units "seconds";
            description
              "The DOTS client must not re-send the
               same request before the expiry of this timer.
               It must be included in responses, only.";
          }

          container conflict-scope {
            description
              "Provides more information about the conflict scope.";

            uses target {
              when "../conflict-cause = 'overlapping-targets'";
            }

            list acl-list {
              when "../../conflict-cause = 'conflict-with-whitelist'";
              key "acl-name acl-type";
              description
                "List of conflicting ACLs";

              leaf acl-name {
                type leafref {
                  path "/ietf-acl:access-lists/ietf-acl:acl" +
                       "/ietf-acl:acl-name";
                }
                description
                  "Reference to the conflicting ACL name bound to
                   a DOTS client.";
              }

              leaf acl-type {
                type leafref {
                  path "/ietf-acl:access-lists/ietf-acl:acl" +
                       "/ietf-acl:acl-type";
                }
                description
                  "Reference to the conflicting ACL type bound to
                   a DOTS client.";
              }
            }
          }
        }



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        leaf pkts-dropped {
          type yang:zero-based-counter64;
          config false;
          description
            "Number of dropped packets";
        }

        leaf bps-dropped {
          type yang:zero-based-counter64;
          config false;
          description
            "The average number of dropped bytes per second for
             the mitigation request since the attack
             mitigation is triggered.";
        }

        leaf bytes-dropped {
          type yang:zero-based-counter64;
          units 'bytes';
          config false;
          description
            "Counter for dropped packets; in bytes.";
        }

        leaf pps-dropped {
          type yang:zero-based-counter64;
          config false;
          description
            "The average number of dropped packets per second
             for the mitigation request since the attack
             mitigation is triggered.";
      }
    }
  }

 grouping signal-config {
    description
      "DOTS signal channel session configuration.";

    leaf session-id {
      type int32;
      mandatory true;
      description
        "An identifier for the DOTS signal channel
         session configuration data.";
    }

    leaf heartbeat-interval {



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      type int16;
      units "seconds";
      default 30;
      description
        "DOTS agents regularly send heartbeats to each other
         after mutual authentication is successfully
         completed, in order to keep the DOTS signal channel
         open.

         '0' means that heartbeat mechanism is deactivated.";
      reference
        "RFC XXXX: Distributed Denial-of-Service Open Threat
                   Signaling (DOTS) Signal Channel";
    }

    leaf missing-hb-allowed {
      type int16;
      default 5;
      description
        "Maximum number of missing heartbeats allowed.";
      reference
        "RFC XXXX: Distributed Denial-of-Service Open Threat
                   Signaling (DOTS) Signal Channel";
    }

    leaf max-retransmit {
      type int16;
      default 3;
      description
        "Maximum number of retransmissions of a
         Confirmable message.";
      reference
        "RFC XXXX: Distributed Denial-of-Service Open Threat
                   Signaling (DOTS) Signal Channel";
    }

    leaf ack-timeout {
      type int16;
      units "seconds";
      default 2;
      description
        "Initial retransmission timeout value.";
      reference
        "Section 4.8 of RFC 7552.";
    }

    leaf ack-random-factor {
      type decimal64 {



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        fraction-digits 2;
      }
      default 1.5;
      description
        "Random factor used to influence the timing of
         retransmissions.";
      reference
        "Section 4.8 of RFC 7552.";
    }

    leaf trigger-mitigation {
      type boolean;
      default true;
      description
        "If false, then mitigation is triggered
         only when the DOTS server channel session is lost";
      reference
        "RFC XXXX: Distributed Denial-of-Service Open Threat
                   Signaling (DOTS) Signal Channel";
    }

    leaf config-interval {
      type int32;
      units "minutes";
      description
        "This parameter is returned by a DOTS server to
         a requesting DOTS client to indicate the time interval
         after which the DOTS client must contact the DOTS
         server in order to retrieve the signal channel
         configuration data.

         This mechanism allows the update of the configuration
         data if a change occurs.

         For example, the new configuration may instruct
         a DOTS client to cease heartbeats or reduce
         heartbeat frequency.

         '0' is used to disable this refresh mechanism.";
    }
  }

  container dots-signal {
    description
      "Main container for DOTS signal message.
       A DOTS signal message can be a mitigation message or
       a configuration message.";




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    choice message-type {
      description
        "Either a mitigation or a configuration message.";

      case mitigation-scope {
        description
          "Mitigation scope of a mitigation message.";
        uses mitigation-scope;
      }

      case configuration {
        description
          "Configuration message.";
        uses signal-config;
      }
    }
  }
}
<CODE ENDS>

6.  Mapping Parameters to CBOR

   All parameters in the payload of the DOTS signal channel MUST be
   mapped to CBOR types as shown in Table 4 and are assigned an integer
   key to save space.  The recipient of the payload MAY reject the
   information if it is not suitably mapped.

   /----------------------+----------------+--------------------------\
   | Parameter name       | CBOR key       | CBOR major type of value |
   +----------------------+----------------+--------------------------+
   | mitigation-scope     | 1              | 5 (map)                  |
   | scope                | 2              | 5 (map)                  |
   | mitigation-id        | 3              | 0 (unsigned)             |
   | acl-list             | 4              | 4                        |
   | target-port-range    | 5              | 4                        |
   | lower-port           | 6              | 0                        |
   | upper-port           | 7              | 0                        |
   | target-protocol      | 8              | 4                        |
   | target-fqdn          | 9              | 4                        |
   | target-uri           | 10             | 4                        |
   | alias-name           | 11             | 4                        |
   | lifetime             | 12             | 0                        |
   | attack-status        | 13             | 0                        |
   | signal-config        | 14             | 5                        |
   | heartbeat-interval   | 15             | 0                        |
   | max-retransmit       | 16             | 0                        |
   | ack-timeout          | 17             | 0                        |
   | ack-random-factor    | 18             | 7                        |



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   | min-value            | 19             | 0                        |
   | max-value            | 20             | 0                        |
   | status               | 21             | 0                        |
   | conflict-information | 22             | 5 (map)                  |
   | conflict-status      | 23             | 0                        |
   | conflict-cause       | 24             | 0                        |
   | retry-timer          | 25             | 0                        |
   | bytes-dropped        | 26             | 0                        |
   | bps-dropped          | 27             | 0                        |
   | pkts-dropped         | 28             | 0                        |
   | pps-dropped          | 29             | 0                        |
   | session-id           | 30             | 0                        |
   | trigger-mitigation   | 31             | 7 (simple types)         |
   | missing-hb-allowed   | 32             | 0                        |
   | current-value        | 33             | 0                        |
   | mitigation-start     | 34             | 7 (floating-point)       |
   | target-prefix        | 35             | 4 (array)                |
   | client-identifier    | 36             | 2 (byte string)          |
   | alt-server           | 37             | 2                        |
   | alt-server-record    | 38             | 4                        |
   | addr                 | 39             | 2                        |
   | ttl                  | 40             | 0                        |
   | conflict-scope       | 41             | 5 (map)                  |
   | acl-name             | 42             | 2                        |
   | acl-type             | 43             | 3                        |
   | config-interval      | 44             | 0                        |
   \----------------------+----------------+--------------------------/
        Table 4: CBOR mappings used in DOTS signal channel message

7.  (D)TLS Protocol Profile and Performance Considerations

7.1.  (D)TLS Protocol Profile

   This section defines the (D)TLS protocol profile of DOTS signal
   channel over (D)TLS and DOTS data channel over TLS.

   There are known attacks on (D)TLS, such as man-in-the-middle and
   protocol downgrade attacks.  These are general attacks on (D)TLS and,
   as such, they are not specific to DOTS over (D)TLS; please refer to
   the (D)TLS RFCs for discussion of these security issues.  DOTS agents
   MUST adhere to the (D)TLS implementation recommendations and security
   considerations of [RFC7525] except with respect to (D)TLS version.
   Since DOTS encryption that relies upon (D)TLS is virtually a green-
   field deployment, DOTS agents MUST implement only (D)TLS 1.2 or
   later.

   When a DOTS client is configured with a domain name of the DOTS
   server, and connects to its configured DOTS server, the server may



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   present it with a PKIX certificate.  In order to ensure proper
   authentication, a DOTS client MUST verify the entire certification
   path per [RFC5280].  The DOTS client additionally uses [RFC6125]
   validation techniques to compare the domain name with the certificate
   provided.

   A key challenge to deploying DOTS is the provisioning of DOTS
   clients, including the distribution of keying material to DOTS
   clients to enable the required mutual authentication of DOTS agents.
   EST defines a method of certificate enrollment by which domains
   operating DOTS servers may provide DOTS clients with all the
   necessary cryptographic keying material, including a private key and
   a certificate to authenticate themselves.  One deployment option is
   DOTS clients behave as EST clients for certificate enrollment from an
   EST server provisioned by the mitigation provider.  This document
   does not specify which EST mechanism the DOTS client uses to achieve
   initial enrollment.

   Implementations compliant with this profile MUST implement all of the
   following items:

   o  DTLS record replay detection (Section 3.3 of [RFC6347]) to protect
      against replay attacks.

   o  (D)TLS session resumption without server-side state [RFC5077] to
      resume session and convey the DOTS signal.

   o  Raw public keys [RFC7250] or PSK handshake [RFC4279] which reduces
      the size of the ServerHello, and can be used by DOTS agents that
      cannot obtain certificates.

   Implementations compliant with this profile SHOULD implement all of
   the following items to reduce the delay required to deliver a DOTS
   signal:

   o  TLS False Start [RFC7918] which reduces round-trips by allowing
      the TLS second flight of messages (ChangeCipherSpec) to also
      contain the DOTS signal.

   o  Cached Information Extension [RFC7924] which avoids transmitting
      the server's certificate and certificate chain if the client has
      cached that information from a previous TLS handshake.

   o  TCP Fast Open [RFC7413] can reduce the number of round-trips to
      convey DOTS signal.






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7.2.  (D)TLS 1.3 Considerations

   TLS 1.3 [I-D.ietf-tls-tls13] provides critical latency improvements
   for connection establishment over TLS 1.2.  The DTLS 1.3 protocol
   [I-D.ietf-tls-dtls13] is based upon the TLS 1.3 protocol and provides
   equivalent security guarantees.  (D)TLS 1.3 provides two basic
   handshake modes the DOTS signal channel can take advantage of:

   o  A full handshake mode in which a DOTS client can send a DOTS
      mitigation request message after one round trip.  This assumes no
      packet loss is expereienced,

   o  0-RTT mode in which the DOTS client can authenticate itself and
      send DOTS mitigation request messages in the first message, thus
      reducing handshake latency. 0-RTT only works if the DOTS client
      has previously communicated with that DOTS server, which is very
      likely with the DOTS signal channel.

      The DOTS client has to establish a (D)TLS session with the DOTS
      server during peacetime and share a PSK.

      During a DDoS attack, the DOTS client can use the (D)TLS session
      to convey the DOTS mitigation request message and, if there is no
      response from the server after multiple retries, the DOTS client
      can resume the (D)TLS session in 0-RTT mode using PSK.

      Section 8 of [I-D.ietf-tls-tls13] discusses some mechanisms to
      implement to limit the impact of replay attacks on 0-RTT data.  If
      TLS1.3 is used, DOTS servers must implement one of these
      mechanisms.

      A simplified TLS 1.3 handshake with 0-RTT DOTS mitigation request
      message exchange is shown in Figure 23.


















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          DOTS Client                                    DOTS Server

         ClientHello
         (Finished)
         (0-RTT DOTS signal message)
         (end_of_early_data)        -------->
                                                        ServerHello
                                               {EncryptedExtensions}
                                               {ServerConfiguration}
                                                       {Certificate}
                                                 {CertificateVerify}
                                                          {Finished}
                                   <--------   [DOTS signal message]
         {Finished}                -------->

         [DOTS signal message]     <------->   [DOTS signal message]

                  Figure 23: TLS 1.3 handshake with 0-RTT

7.3.  MTU and Fragmentation

   To avoid DOTS signal message fragmentation and the subsequent
   decreased probability of message delivery, DOTS agents MUST ensure
   that the DTLS record MUST fit within a single datagram.  If the path
   MTU is not known to the DOTS server, an IP MTU of 1280 bytes SHOULD
   be assumed.  The length of the URL MUST NOT exceed 256 bytes.  If UDP
   is used to convey the DOTS signal messages then the DOTS client must
   consider the amount of record expansion expected by the DTLS
   processing when calculating the size of CoAP message that fits within
   the path MTU.  Path MTU MUST be greater than or equal to [CoAP
   message size + DTLS overhead of 13 octets + authentication overhead
   of the negotiated DTLS cipher suite + block padding (Section 4.1.1.1
   of [RFC6347]).  If the request size exceeds the path MTU then the
   DOTS client MUST split the DOTS signal into separate messages, for
   example the list of addresses in the 'target-prefix' parameter could
   be split into multiple lists and each list conveyed in a new PUT
   request.

   Implementation Note: DOTS choice of message size parameters works
   well with IPv6 and with most of today's IPv4 paths.  However, with
   IPv4, it is harder to reliably ensure that there is no IP
   fragmentation.  If IPv4 path MTU is unknown, implementations may want
   to limit themselves to more conservative IPv4 datagram sizes such as
   576 bytes, as per [RFC0791].  IP packets whose size does not exceed
   576 bytes should never need to be fragmented: therefore, sending a
   maximum of 500 bytes of DOTS signal over a UDP datagram will
   generally avoid IP fragmentation.




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8.  Mutual Authentication of DOTS Agents & Authorization of DOTS Clients

   (D)TLS based upon client certificate can be used for mutual
   authentication between DOTS agents.  If a DOTS gateway is involved,
   DOTS clients and DOTS gateways MUST perform mutual authentication;
   only authorized DOTS clients are allowed to send DOTS signals to a
   DOTS gateway.  The DOTS gateway and the DOTS server MUST perform
   mutual authentication; a DOTS server only allows DOTS signals from an
   authorized DOTS gateway, thereby creating a two-link chain of
   transitive authentication between the DOTS client and the DOTS
   server.

 +-----------------------------------------------+
 |       example.com domain         +---------+  |
 |                                  | AAA     |  |
 | +---------------+                | Server  |  |
 | | Application   |                +------+--+  |
 | | server        +<-----------------+    ^     |
 | | (DOTS client) |                  |    |     |
 | +---------------+                  |    |     |
 |                                    V    V     |    example.net domain
 |                              +-----+----+--+  |     +---------------+
 | +--------------+             |             |  |     |               |
 | |   Guest      +<-----x----->+    DOTS     +<------>+    DOTS       |
 | | (DOTS client)|             |    Gateway  |  |     |    Server     |
 | +--------------+             |             |  |     |               |
 |                              +----+--------+  |     +---------------+
 |                                   ^           |
 |                                   |           |
 | +----------------+                |           |
 | | DDOS detector  |                |           |
 | | (DOTS client)  +<---------------+           |
 | +----------------+                            |
 +-----------------------------------------------+

   Figure 24: Example of Authentication and Authorization of DOTS Agents

   In the example depicted in Figure 24, the DOTS gateway and DOTS
   clients within the 'example.com' domain mutually authenticate with
   each other.  After the DOTS gateway validates the identity of a DOTS
   client, it communicates with the AAA server in the 'example.com'
   domain to determine if the DOTS client is authorized to request DDoS
   mitigation.  If the DOTS client is not authorized, a 4.01
   (Unauthorized) is returned in the response to the DOTS client.  In
   this example, the DOTS gateway only allows the application server and
   DDoS attack detector to request DDOS mitigation, but does not permit
   the user of type 'guest' to request DDoS mitigation.




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   Also, DOTS gateways and servers located in different domains MUST
   perform mutual authentication (e.g., using certificates).  A DOTS
   server will only allow a DOTS gateway with a certificate for a
   particular domain to request mitigation for that domain.  In
   reference to Figure 24, the DOTS server only allows the DOTS gateway
   to request mitigation for 'example.com' domain and not for other
   domains.

9.  IANA Considerations

   This specification registers a service port (Section 9.1), an URI
   suffix in the Well-Known URIs registry (Section 9.2), a CoAP response
   code (Section 9.3), a YANG module (Section 9.5).  It also creates a
   registry for mappings to CBOR (Section 9.4).

9.1.  DOTS Signal Channel UDP and TCP Port Number

   IANA is requested to assign the port number TBD to the DOTS signal
   channel protocol for both UDP and TCP from the "Service Name and
   Transport Protocol Port Number Registry" available at
   https://www.iana.org/assignments/service-names-port-numbers/service-
   names-port-numbers.xhtml.

   The assignment of port number 4646 is strongly suggested, as 4646 is
   the ASCII decimal value for ".." (DOTS).

9.2.  Well-Known 'dots' URI

   This document requests IANA to register the 'dots' well-known URI in
   the Well-Known URIs registry (https://www.iana.org/assignments/well-
   known-uris/well-known-uris.xhtml) as defined by [RFC5785].

   URI suffix: dots

   Change controller: IETF

   Specification document(s): This RFC

   Related information: None

9.3.  CoAP Response Code

   IANA is requested to add the following entry to the "CoAP Response
   Codes" sub-registry available at https://www.iana.org/assignments/
   core-parameters/core-parameters.xhtml#response-codes:






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                  +------+------------------+-----------+
                  | Code | Description      | Reference |
                  +------+------------------+-----------+
                  | 3.00 | Alternate server | [RFCXXXX] |
                  +------+------------------+-----------+

                        Table 4: CoAP Response Code

9.4.  DOTS Signal Channel CBOR Mappings Registry

   The document requests IANA to create a new registry, entitled "DOTS
   Signal Channel CBOR Mappings Registry".  The structure of this
   registry is provided in Section 9.4.1.

   The registry is initially populated with the values in Section 9.4.2.

   Values from that registry MUST be assigned via Expert Review
   [RFC8126].

9.4.1.  Registration Template

   Parameter name:
      Parameter name as used in the DOTS signal channel.

   CBOR Key Value:
      Key value for the parameter.  The key value MUST be an integer in
      the 1-65536 range.  The key values in the 32758-65536 range are
      assigned to Vendor-Specific parameters.

   CBOR Major Type:
      CBOR Major type and optional tag for the claim.

   Change Controller:
      For Standards Track RFCs, list the "IESG".  For others, give the
      name of the responsible party.  Other details (e.g., postal
      address, email address, home page URI) may also be included.

   Specification Document(s):
      Reference to the document or documents that specify the parameter,
      preferably including URIs that can be used to retrieve copies of
      the documents.  An indication of the relevant sections may also be
      included but is not required.

9.4.2.  Initial Registry Contents

   o  Parameter Name: mitigation-scope
   o  CBOR Key Value: 1
   o  CBOR Major Type: 5



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   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: scope
   o  CBOR Key Value: 2
   o  CBOR Major Type: 5
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: mitigation-id
   o  CBOR Key Value: 3
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: acl-type
   o  CBOR Key Value: 4
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: target-port-range
   o  CBOR Key Value: 5
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: lower-port
   o  CBOR Key Value: 6
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: upper-port
   o  CBOR Key Value: 7
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: target-protocol
   o  CBOR Key Value: 8
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: target-fqdn
   o  CBOR Key Value: 9
   o  CBOR Major Type: 4



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   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: target-uri
   o  CBOR Key Value: 10
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: alias-name
   o  CBOR Key Value: 11
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: lifetime
   o  CBOR Key Value: 12
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: attack-status
   o  CBOR Key Value: 13
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: signal-config
   o  CBOR Key Value: 14
   o  CBOR Major Type: 5
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: heartbeat-interval
   o  CBOR Key Value: 15
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: max-retransmit
   o  CBOR Key Value: 16
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: ack-timeout
   o  CBOR Key Value: 17
   o  CBOR Major Type: 0



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   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: ack-random-factor
   o  CBOR Key Value: 18
   o  CBOR Major Type: 7
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: min-value
   o  CBOR Key Value: 19
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: max-value
   o  CBOR Key Value: 20
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: status
   o  CBOR Key Value: 21
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: conflict-information
   o  CBOR Key Value: 22
   o  CBOR Major Type: 5
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: conflict-status
   o  CBOR Key Value: 23
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: conflict-cause
   o  CBOR Key Value: 24
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: retry-timer
   o  CBOR Key Value: 25
   o  CBOR Major Type: 0



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   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: bytes-dropped
   o  CBOR Key Value: 26
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: bps-dropped
   o  CBOR Key Value: 27
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: pkts-dropped
   o  CBOR Key Value: 28
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: pps-dropped
   o  CBOR Key Value: 29
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: session-id
   o  CBOR Key Value: 30
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: trigger-mitigation
   o  CBOR Key Value: 31
   o  CBOR Major Type: 7
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: missing-hb-allowed
   o  CBOR Key Value: 32
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: current-value
   o  CBOR Key Value: 33
   o  CBOR Major Type: 0



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   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: mitigation-start
   o  CBOR Key Value: 34
   o  CBOR Major Type: 7
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: target-prefix
   o  CBOR Key Value: 35
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: client-identifier
   o  CBOR Key Value: 36
   o  CBOR Major Type: 2
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: alt-server
   o  CBOR Key Value: 37
   o  CBOR Major Type: 2
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: alt-server-record
   o  CBOR Key Value: 38
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: addr
   o  CBOR Key Value: 39
   o  CBOR Major Type: 2
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: ttl
   o  CBOR Key Value: 40
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: conflict-scope
   o  CBOR Key Value: 41
   o  CBOR Major Type: 5



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   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: acl-name
   o  CBOR Key Value: 42
   o  CBOR Major Type: 2
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: acl-type
   o  CBOR Key Value: 43
   o  CBOR Major Type: 3
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: config-interval
   o  CBOR Key Value: 44
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

9.5.  DOTS Signal Channel YANG Module

   This document requests IANA to register the following URI in the
   "IETF XML Registry" [RFC3688]:

            URI: urn:ietf:params:xml:ns:yang:ietf-dots-signal
            Registrant Contact: The IESG.
            XML: N/A; the requested URI is an XML namespace.

   This document requests IANA to register the following YANG module in
   the "YANG Module Names" registry [RFC7950].

            name: ietf-signal
            namespace: urn:ietf:params:xml:ns:yang:ietf-dots-signal
            prefix: signal
            reference: RFC XXXX

10.  Implementation Status

   [Note to RFC Editor: Please remove this section and reference to
   [RFC7942] prior to publication.]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting this
   Internet-Draft, and is based upon a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision-making process when progressing



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   drafts to RFCs.  Please note that the listing of any individual
   implementation here does not imply endorsement by the IETF.
   Furthermore, no effort has been spent to verify the information
   presented here, and which was provided by individuals.  This is not
   intended as, and must not be construed to be, a catalog of available
   implementations or features.  Readers are advised to note that other
   implementations may exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

10.1.  nttdots

   Organization:   NTT Communication is developing a DOTS client and
      DOTS server software based on DOTS signal channel specified in
      this draft.  It will be open-sourced.
   Description:   Early implementation of DOTS protocol.  It is aimed to
      implement a full DOTS protocol specification in accordance with
      the nurturing DOTS protocol.
   Implementation:   https://github.com/nttdots/go-dots
   Level of maturity:   It is an early implementation of the DOTS
      protocol.  Messaging between DOTS clients and DOTS servers has
      been tested.  Level of maturity will increase in accordance with
      the nurturing DOTS protocol.
   Coverage:   Capability of DOTS client: sending DOTS messages to the
      DOTS server in CoAP over DTLS as dots-signal.  Capability of DOTS
      server: receiving dots-signal, validating received dots-signal,
      starting mitigation by handing over the dots-signal to DDOS
      mitigator.
   Licensing:   It will be open-sourced with BSD 3-clause license.
   Implementation experience:   It is implemented in Go-lang.  Core
      specification of signaling is mature to be implemented, however,
      finding good libraries(like DTLS, CoAP) is rather difficult.
   Contact:   Kaname Nishizuka <kaname@nttv6.jp>

11.  Security Considerations

   Authenticated encryption MUST be used for data confidentiality and
   message integrity.  The interaction between the DOTS agents requires
   Datagram Transport Layer Security (DTLS) and Transport Layer Security
   (TLS) with a cipher suite offering confidentiality protection and the
   guidance given in [RFC7525] MUST be followed to avoid attacks on
   (D)TLS.  The (D)TLS protocol profile for DOTS signal channel is
   specified in Section 7.



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   A single DOTS signal channel between DOTS agents can be used to
   exchange multiple DOTS signal messages.  To reduce DOTS client and
   DOTS server workload, DOTS clients SHOULD re-use the (D)TLS session.

   If TCP is used between DOTS agents, an attacker may be able to inject
   RST packets, bogus application segments, etc., regardless of whether
   TLS authentication is used.  Because the application data is TLS
   protected, this will not result in the application receiving bogus
   data, but it will constitute a DoS on the connection.  This attack
   can be countered by using TCP-AO [RFC5925].  If TCP-AO is used, then
   any bogus packets injected by an attacker will be rejected by the
   TCP-AO integrity check and therefore will never reach the TLS layer.

   In order to prevent leaking internal information outside a client-
   domain, DOTS gateways located in the client-domain SHOULD NOT reveal
   the identification information that pertains to internal DOTS clients
   (client-identifier) unless explicitly configured to do so.

   Special care should be taken in order to ensure that the activation
   of the proposed mechanism will not impact the stability of the
   network (including connectivity and services delivered over that
   network).

   Involved functional elements involved in the DDoS cooperation system
   must exchange instructions and notification over a secure and
   authenticated channel.  Adequate filters can apply to avoid that
   nodes outside a trusted domain can inject illegitimate requests.
   Attacks can be initiated from within the trusted domain if an entity
   has been corrupted.  Adequate means to monitor trusted nodes should
   also be enabled.

12.  Contributors

   The following individuals have contributed to this document:

   Mike Geller Cisco Systems, Inc. 3250 Florida 33309 USA Email:
   mgeller@cisco.com

   Robert Moskowitz HTT Consulting Oak Park, MI 42837 United States
   Email: rgm@htt-consult.com

   Dan Wing Email: dwing-ietf@fuggles.com

13.  Acknowledgements

   Thanks to Christian Jacquenet, Roland Dobbins, Roman D.  Danyliw,
   Michael Richardson, Ehud Doron, Kaname Nishizuka, Dave Dolson, Liang




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   Xia, Gilbert Clark, and Nesredien Suleiman for the discussion and
   comments.

   Special thanks to Jon Shallow for the careful reviews and inputs that
   enhanced this specification.

14.  References

14.1.  Normative References

   [I-D.ietf-core-coap-tcp-tls]
              Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
              Silverajan, B., and B. Raymor, "CoAP (Constrained
              Application Protocol) over TCP, TLS, and WebSockets",
              draft-ietf-core-coap-tcp-tls-10 (work in progress),
              October 2017.

   [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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC4279]  Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
              Ciphersuites for Transport Layer Security (TLS)",
              RFC 4279, DOI 10.17487/RFC4279, December 2005,
              <https://www.rfc-editor.org/info/rfc4279>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              DOI 10.17487/RFC5785, April 2010,
              <https://www.rfc-editor.org/info/rfc5785>.





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   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <https://www.rfc-editor.org/info/rfc6234>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC7250]  Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
              Weiler, S., and T. Kivinen, "Using Raw Public Keys in
              Transport Layer Security (TLS) and Datagram Transport
              Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
              June 2014, <https://www.rfc-editor.org/info/rfc7250>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [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>.

   [RFC7641]  Hartke, K., "Observing Resources in the Constrained
              Application Protocol (CoAP)", RFC 7641,
              DOI 10.17487/RFC7641, September 2015,
              <https://www.rfc-editor.org/info/rfc7641>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.






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   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8132]  van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
              FETCH Methods for the Constrained Application Protocol
              (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
              <https://www.rfc-editor.org/info/rfc8132>.

14.2.  Informative References

   [I-D.ietf-core-comi]
              Veillette, M., Stok, P., Pelov, A., and A. Bierman, "CoAP
              Management Interface", draft-ietf-core-comi-02 (work in
              progress), December 2017.

   [I-D.ietf-core-yang-cbor]
              Veillette, M., Pelov, A., Somaraju, A., Turner, R., and A.
              Minaburo, "CBOR Encoding of Data Modeled with YANG",
              draft-ietf-core-yang-cbor-05 (work in progress), August
              2017.

   [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-data-channel]
              Reddy, T., Boucadair, M., Nishizuka, K., Xia, L., Patil,
              P., Mortensen, A., and N. Teague, "Distributed Denial-of-
              Service Open Threat Signaling (DOTS) Data Channel", draft-
              ietf-dots-data-channel-10 (work in progress), December
              2017.

   [I-D.ietf-dots-requirements]
              Mortensen, A., Moskowitz, R., and T. Reddy, "Distributed
              Denial of Service (DDoS) Open Threat Signaling
              Requirements", draft-ietf-dots-requirements-08 (work in
              progress), December 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.



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   [I-D.ietf-netmod-yang-tree-diagrams]
              Bjorklund, M. and L. Berger, "YANG Tree Diagrams", draft-
              ietf-netmod-yang-tree-diagrams-02 (work in progress),
              October 2017.

   [I-D.ietf-tls-dtls13]
              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", draft-ietf-tls-dtls13-22 (work in progress),
              November 2017.

   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-22 (work in progress),
              November 2017.

   [proto_numbers]
              "IANA, "Protocol Numbers"", 2011,
              <http://www.iana.org/assignments/protocol-numbers>.

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

   [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>.

   [RFC4340]  Kohler, E., Handley, M., and S. Floyd, "Datagram
              Congestion Control Protocol (DCCP)", RFC 4340,
              DOI 10.17487/RFC4340, March 2006,
              <https://www.rfc-editor.org/info/rfc4340>.

   [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>.

   [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>.

   [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>.



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   [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              RFC 4960, DOI 10.17487/RFC4960, September 2007,
              <https://www.rfc-editor.org/info/rfc4960>.

   [RFC4987]  Eddy, W., "TCP SYN Flooding Attacks and Common
              Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007,
              <https://www.rfc-editor.org/info/rfc4987>.

   [RFC5077]  Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
              "Transport Layer Security (TLS) Session Resumption without
              Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
              January 2008, <https://www.rfc-editor.org/info/rfc5077>.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              DOI 10.17487/RFC5389, October 2008,
              <https://www.rfc-editor.org/info/rfc5389>.

   [RFC6555]  Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
              Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April
              2012, <https://www.rfc-editor.org/info/rfc6555>.

   [RFC6724]  Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
              <https://www.rfc-editor.org/info/rfc6724>.

   [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
              P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              DOI 10.17487/RFC6887, April 2013,
              <https://www.rfc-editor.org/info/rfc6887>.

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,
              <https://www.rfc-editor.org/info/rfc7030>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7413]  Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
              Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
              <https://www.rfc-editor.org/info/rfc7413>.







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   [RFC7452]  Tschofenig, H., Arkko, J., Thaler, D., and D. McPherson,
              "Architectural Considerations in Smart Object Networking",
              RFC 7452, DOI 10.17487/RFC7452, March 2015,
              <https://www.rfc-editor.org/info/rfc7452>.

   [RFC7589]  Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the
              NETCONF Protocol over Transport Layer Security (TLS) with
              Mutual X.509 Authentication", RFC 7589,
              DOI 10.17487/RFC7589, June 2015,
              <https://www.rfc-editor.org/info/rfc7589>.

   [RFC7918]  Langley, A., Modadugu, N., and B. Moeller, "Transport
              Layer Security (TLS) False Start", RFC 7918,
              DOI 10.17487/RFC7918, August 2016,
              <https://www.rfc-editor.org/info/rfc7918>.

   [RFC7924]  Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", RFC 7924,
              DOI 10.17487/RFC7924, July 2016,
              <https://www.rfc-editor.org/info/rfc7924>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.

   [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>.

Authors' Addresses

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

   Email: kondtir@gmail.com








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   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Prashanth Patil
   Cisco Systems, Inc.

   Email: praspati@cisco.com


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

   Email: amortensen@arbor.net


   Nik Teague
   Verisign, Inc.
   United States

   Email: nteague@verisign.com























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