draft-ietf-dots-signal-channel-03.txt

DOTS                                                            T. Reddy
Internet-Draft                                                    McAfee
Intended status: Standards Track                            M. Boucadair
Expires: February 17, 2018                                        Orange
                                                                P. Patil
                                                                   Cisco
                                                            A. Mortensen
                                                    Arbor Networks, Inc.
                                                               N. Teague
                                                          Verisign, Inc.
                                                         August 16, 2017


   Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal
                                Channel
                   draft-ietf-dots-signal-channel-03

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.

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 http://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 February 17, 2018.

Copyright Notice

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




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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  . . . . . . . . . . .   3
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Happy Eyeballs for DOTS Signal Channel  . . . . . . . . . . .   5
   5.  DOTS Signal Channel . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  DOTS Signal YANG Model  . . . . . . . . . . . . . . . . .   8
       5.2.1.  Mitigation Request Model structure  . . . . . . . . .   8
       5.2.2.  Mitigation Request Model  . . . . . . . . . . . . . .   8
       5.2.3.  Session Configuration Model structure . . . . . . . .  10
       5.2.4.  Session Configuration Model . . . . . . . . . . . . .  10
     5.3.  Mitigation Request  . . . . . . . . . . . . . . . . . . .  12
       5.3.1.  Requesting mitigation . . . . . . . . . . . . . . . .  12
       5.3.2.  Withdraw a DOTS Signal  . . . . . . . . . . . . . . .  17
       5.3.3.  Retrieving a DOTS Signal  . . . . . . . . . . . . . .  18
       5.3.4.  Efficacy Update from DOTS Client  . . . . . . . . . .  23
     5.4.  DOTS Signal Channel Session Configuration . . . . . . . .  25
       5.4.1.  Discover Acceptable Configuration Parameters  . . . .  26
       5.4.2.  Convey DOTS Signal Channel Session Configuration  . .  27
       5.4.3.  Delete DOTS Signal Channel Session Configuration  . .  30
       5.4.4.  Retrieving DOTS Signal Channel Session Configuration   30
     5.5.  Redirected Signaling  . . . . . . . . . . . . . . . . . .  31
     5.6.  Heartbeat Mechanism . . . . . . . . . . . . . . . . . . .  32
   6.  Mapping parameters to CBOR  . . . . . . . . . . . . . . . . .  33
   7.  (D)TLS Protocol Profile and Performance considerations  . . .  34
     7.1.  MTU and Fragmentation Issues  . . . . . . . . . . . . . .  34
   8.  (D)TLS 1.3 considerations . . . . . . . . . . . . . . . . . .  35
   9.  Mutual Authentication of DOTS Agents & Authorization of DOTS
       Clients . . . . . . . . . . . . . . . . . . . . . . . . . . .  36
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  38
     10.1.  CoAP Response Code . . . . . . . . . . . . . . . . . . .  38
     10.2.  DOTS signal channel CBOR Mappings Registry . . . . . . .  38
       10.2.1.  Registration Template  . . . . . . . . . . . . . . .  38
       10.2.2.  Initial Registry Contents  . . . . . . . . . . . . .  39
   11. Implementation Status . . . . . . . . . . . . . . . . . . . .  42
     11.1.  nttdots  . . . . . . . . . . . . . . . . . . . . . . . .  43



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   12. Security Considerations . . . . . . . . . . . . . . . . . . .  43
   13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  44
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  44
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  44
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  44
     15.2.  Informative References . . . . . . . . . . . . . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  48

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.

   In many cases, it may not be possible for an network administrators
   to determine the causes of an attack, but instead just realize that
   certain resources seem to be under attack.  This document defines a
   lightweight protocol permitting 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.

   The requirements for DOTS signal channel protocol are obtained from
   [I-D.ietf-dots-requirements].

   This document satisfies all the use cases discussed in
   [I-D.ietf-dots-use-cases] except the Third-party DOTS notifications
   use case in Section 3.2.3 of [I-D.ietf-dots-use-cases] which is an
   optional feature and not a core use case.  Third-party DOTS
   notifications are not part of the DOTS requirements document.
   Moreover, the DOTS architecture does not assess whether that use case
   may have an impact on the architecture itself and/or the DOTS trust
   model.

   This is a companion document to the DOTS data channel specification
   [I-D.ietf-dots-data-channel] that defines a configuration and 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].



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   (D)TLS: For brevity this term 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.

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

3.  Solution Overview

   Network applications have finite resources like CPU cycles, number of
   processes or threads they can create and use, maximum number of
   simultaneous connections it can handle, 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 fashion.  However, an attacker
   may be able to prevent an application from performing its intended
   task by causing the application to exhaust the finite supply of a
   specific resource.

   TCP DDoS SYN-flood, for example, is a memory-exhaustion attack on the
   victim and ACK-flood is a CPU exhaustion attack on the victim
   ([RFC4987]).  Attacks on the link are carried out by sending enough
   traffic such that the link becomes excessively congested, and
   legitimate traffic suffers high packet loss.  Stateful firewalls can
   also be attacked by sending traffic that causes the firewall to hold
   excessive state.  The firewall then runs out of memory, and can no
   longer instantiate the state required to pass legitimate flows.
   Other possible DDoS attacks are discussed in [RFC4732].

   In each of the cases described above, the possible arrangements
   between the DOTS client and DOTS server to mitigate the attack are
   discussed in [I-D.ietf-dots-use-cases].  An example of network
   diagram showing a deployment of these elements is shown in Figure 1.
   Architectural relationships between involved DOTS agents is explained
   in [I-D.ietf-dots-architecture].  In this example, the DOTS server is
   operating on the access network.

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

                   Figure 1: Sample DOTS Deployment (1)




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   The DOTS server can also be running on the Internet, as depicted in
   Figure 2.

   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 a firewall protecting services owned and operated by an
   domain, while the DOTS server is owned and operated by a different
   domain providing DDoS mitigation services.  That domain providing
   DDoS mitigation service might, or might not, also provide Internet
   access service to the website operator.

   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 the DOTS server or
   indirectly via a DOTS gateway.

   This document focuses on the DOTS signal channel.

4.  Happy Eyeballs for DOTS Signal Channel

   DOTS signaling can happen with DTLS [RFC6347] over UDP and TLS
   [RFC5246] 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 DOTS server IP addresses.  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, the DOTS



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   client will fail to establish a DTLS session with the DOTS server and
   will, then, have to fall back to TLS over TCP incurring significant
   connection delays.  [I-D.ietf-dots-requirements] discusses that DOTS
   client and server will have to support both connectionless and
   connection-oriented protocols.

   To overcome these connection setup problems, the DOTS client can try
   connecting to the DOTS server using both IPv6 and IPv4, and try both
   DTLS over UDP and TLS over TCP in a fashion similar to the Happy
   Eyeballs mechanism [RFC6555].  These connection attempts are
   performed by the DOTS client when its initializes, and the client
   uses that information for its subsequent alert 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
   that UDP be used over TCP (to avoid TCP's head of line blocking).

   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 3: Happy Eyeballs

   In reference to Figure 3, 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 middle box 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.







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5.  DOTS Signal Channel

5.1.  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.  CoAP's
   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 make it a good foundation on which to build the DOTS signaling
   mechanism.

   The DOTS signal channel is layered on existing standards (Figure 4).

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

     Figure 4: Abstract Layering of DOTS signal channel over CoAP over
                                  (D)TLS

   The signal channel is initiated by the DOTS client.  Once the signal
   channel is established, the DOTS agents periodically send heartbeats
   to keep the channel active.  At any time, the DOTS client may send a
   mitigation request message to the DOTS server over the active
   channel.  While mitigation is active, 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.

   Messages exchanged between DOTS client and server are serialized
   using Concise Binary Object Representation (CBOR) [RFC7049], CBOR is
   a binary encoding designed for small code and message size.  CBOR
   encoded payloads are used to convey signal channel specific payload
   messages that convey request parameters and response information such
   as errors.  This specification uses the encoding rules defined in
   [I-D.ietf-core-yang-cbor] for representing mitigation scope and DOTS
   signal channel session configuration data defined using YANG
   (Section 5.2) as CBOR data.



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5.2.  DOTS Signal YANG Model

   This document defines a YANG [RFC6020] data model for mitigation
   scope and DOTS signal channel session configuration data.

5.2.1.  Mitigation Request Model structure

   This document defines the YANG module "ietf-dots-signal", which has
   the following structure:

   module: ietf-dots-signal
       +--rw mitigation-scope
          +--rw scope* [mitigation-id]
             +--rw mitigation-id         int32
             +--rw target-ip*            inet:ip-address
             +--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 fqdn*                 inet:domain-name
             +--rw uri*                  inet:uri
             +--rw alias*                string
             +--rw lifetime?             int32

5.2.2.  Mitigation Request Model

<CODE BEGINS> file "ietf-dots-signal@2017-08-03.yang"

module ietf-dots-signal {
      namespace "urn:ietf:params:xml:ns:yang:ietf-dots-signal";
      prefix "signal";
      import ietf-inet-types {
          prefix "inet";
      }
     organization "McAfee, Inc.";
     contact "Konda, Tirumaleswar Reddy <TirumaleswarReddy_Konda@McAfee.com>";

     description
       "This module contains YANG definition for DOTS
       signal sent by the DOTS client to the DOTS server.";

     revision 2017-08-03 {
       reference
       "https://tools.ietf.org/html/draft-reddy-dots-signal-channel";
     }

     container mitigation-scope {



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          description
             "Top level container for a mitigation request.";

          list scope {
             key mitigation-id;
             description "Identifier for the mitigation request.";
             leaf mitigation-id {
                type int32;
                description "Mitigation request identifier.";
              }
              leaf-list target-ip {
                  type inet:ip-address;
                  description
                     "IPv4 or IPv6 address identifyting the target.";
              }

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



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              leaf-list fqdn {
                   type inet:domain-name;
                   description "FQDN";
              }

              leaf-list uri {
                  type inet:uri;
                  description "URI";
              }

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

              leaf lifetime {
                  type int32;
                  description
                    "Indicates the lifetime of the mitigation request.";
              }
          }
     }
  }
<CODE ENDS>

5.2.3.  Session Configuration Model structure

   This document defines the YANG module "ietf-dots-signal-config",
   which has the following structure:

   module: ietf-dots-signal-config
       +--rw signal-config
          +--rw session-id?           int32
          +--rw heartbeat-timeout?    int16
          +--rw max-retransmit?       int16
          +--rw ack-timeout?          int16
          +--rw ack-random-factor?    decimal64
          +--rw trigger-mitigation?   boolean

5.2.4.  Session Configuration Model

<CODE BEGINS> file "ietf-dots-signal-config@2016-11-28.yang"

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

     organization "McAfee, Inc.";



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     contact "Konda, Tirumaleswar Reddy <TirumaleswarReddy_Konda@McAfee.com>";

     description
       "This module contains YANG definition for DOTS
       signal channel session configuration.";

     revision 2016-11-28 {
       reference
       "https://tools.ietf.org/html/draft-reddy-dots-signal-channel";
     }

     container signal-config {
          description "Top level container for DOTS signal channel session
                       configuration.";

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

          leaf heartbeat-timeout {
              type int16;
              description
                 "DOTS agents regularly send heartbeats to each other
                  after mutual authentication in order to keep
                  the DOTS signal channel open.";
          }

          leaf max-retransmit {
              type int16;
              description
                  "Maximum retransmissions of a Confirmable message.";
          }

          leaf ack-timeout {
              type int16;
              description
                 "Initial retransmission timeout value.";
          }

          leaf ack-random-factor {
              type decimal64 {
              fraction-digits 2;
              }
              description
                   "Random factor used to influence the timing of
                    retransmissions";



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         }
         leaf trigger-mitigation {
             type boolean;
             default true;
             description
                 "If false, then mitigation is triggered
                  only when the DOTS server channel session is lost";
         }
      }
}

<CODE ENDS>

5.3.  Mitigation Request

   The following methods are used to request or withdraw mitigation
   requests:

   PUT:  DOTS clients use the PUT method to request mitigation
      (Section 5.3.1).  During active mitigation, DOTS clients may use
      PUT requests to convey mitigation efficacy updates to the DOTS
      server (Section 5.3.4).

   DELETE:  DOTS clients use the DELETE method to withdraw a request for
      mitigation from the DOTS server (Section 5.3.2).

   GET:  DOTS clients may use the GET method to subscribe to DOTS server
      status messages, or to retrieve the list of existing mitigations
      (Section 5.3.3).

   Mitigation request and response messages are marked as Non-
   confirmable messages.  DOTS agents should follow the data
   transmission guidelines discussed in Section 3.1.3 of [RFC8085] and
   control transmission behavior by not sending on average more than one
   UDP datagram per RTT to the peer DOTS agent.  Requests marked by the
   DOTS client as Non-confirmable messages are sent at regular intervals
   until a response is received from the DOTS server and if the DOTS
   client cannot maintain a RTT estimate then it SHOULD NOT send more
   than one Non-confirmable request every 3 seconds, and SHOULD use an
   even less aggressive rate when possible (case 2 in Section 3.1.3 of
   [RFC8085]).

5.3.1.  Requesting mitigation

   When a DOTS client requires mitigation for any reason, the DOTS
   client uses CoAP PUT method to send a mitigation request to the DOTS
   server (Figure 5, illustrated in JSON diagnostic notation).  The DOTS
   server can enable mitigation on behalf of the DOTS client by



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   communicating the DOTS client's request to the mitigator and relaying
   selected mitigator feedback to the requesting DOTS client.

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

                   Figure 5: PUT to convey DOTS signals

   The parameters are described below.




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   mitigation-id:  Identifier for the mitigation request represented
      using 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-ip:  A list of IP addresses under attack.  This is an optional
      attribute.

   target-prefix:  A list of prefixes under attack.  Prefixes are
      represented using CIDR notation [RFC4632].  This is an optional
      attribute.

   target-port-range:  A list of ports under attack.  The port range,
      lower-port for lower port number and upper-port for upper port
      number.  When only lower-port is present, it represents a single
      port.  For TCP, UDP, SCTP, or DCCP: the range of ports (e.g.,
      1024-65535).  This is an optional attribute.

   target-protocol:  A list of protocols under attack.  Values are taken
      from the IANA protocol registry [proto_numbers].  The value 0 has
      a special meaning for 'all protocols'.  This is an optional
      attribute.

   fqdn:   A list of Fully Qualified Domain Names.  Fully Qualified
      Domain Name (FQDN) is the full name of a system, rather than just
      its hostname.  For example, "venera" is a hostname, and
      "venera.isi.edu" is an FQDN.  This is an optional attribute.

   uri:   A list of Uniform Resource Identifiers (URI).  This is an
      optional attribute.

   alias:  A list of aliases.  Aliases can be created using the DOTS
      data channel (Section 3.1.1 in [I-D.ietf-dots-data-channel]) or
      direct configuration, or other means and then 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.  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.  The default lifetime of the
      mitigation request is 3600 seconds (60 minutes) -- this value was
      chosen to be long enough so that refreshing is not typically a



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      burden on the DOTS client, while expiring the request where the
      client has unexpectedly quit in a timely manner.  A lifetime of
      negative one (-1) indicates indefinite lifetime for the mitigation
      request.  The server MUST always indicate the actual lifetime in
      the response and the remaining lifetime in status messages sent to
      the client.  This is an optional attribute in the request.

   The CBOR key values for the parameters are defined in Section 6.  The
   IANA Considerations section defines how the CBOR key values can be
   allocated to standards 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-ip or target-prefix or fqdn or uri or alias MUST be
   present.  DOTS agents can safely ignore Vendor-Specific parameters
   they don't understand.  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 higher numeric
   mitigation-id value will override the mitigation request with a lower
   numeric mitigation-id value.  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.

   In both DOTS signal and data channel sessions, the DOTS client MUST
   authenticate itself to the DOTS server (Section 9).  The DOTS server
   can use the algorithm discussed in Section 7 of [RFC7589] to derive
   the DOTS client identity or username from the client certificate.
   The DOTS server couples the DOTS signal and data channel sessions
   using the DOTS client identity, 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 then 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 DOTS server uses mitigation-id parameter value to
   detect duplicate mitigation requests.  If the mitigation request
   contains both alias and other parameters identifying the target
   resource (such as, target-ip, target-prefix, target-port-range, fqdn,
   or uri) then the DOTS server appends the parameter values in alias
   with the corresponding parameter values in target-ip, target-prefix,
   target-port-range, fqdn, or uri.

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

   Header: PUT (Code=0.03)



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   Uri-Host: "www.example.com"
   Uri-Path: "v1"
   Uri-Path: "dots-signal"
   Uri-Path: "signal"
   Content-Format: "application/cbor"
   {
     "mitigation-scope": {
       "scope": [
         {
           "mitigation-id": 12332,
           "target-ip": [
              "2001:db8:6401::1",
              "2001:db8:6401::2"
            ],
           "target-port-range": [
             {
               "lower-port": 80
             },
             {
               "lower-port": 443
             },
             {
                "lower-port": 8080
             }
            ],
            "target-protocol": [
              6
            ]
         }
       ]
     }
   }

 The CBOR encoding format is shown below:

 a1                                      # map(1)
    01                                   # unsigned(1)
    a1                                   # map(1)
       02                                # unsigned(2)
       81                                # array(1)
          a4                             # map(4)
             03                          # unsigned(3)
             19 302c                     # unsigned(12332)
             04                          # unsigned(4)
             82                          # array(2)
                70                       # text(16)
                   323030313A6462383A363430313A3A31 # "2001:db8:6401::1"
                70                       # text(16)



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                   323030313A6462383A363430313A3A32 # "2001:db8:6401::2"
             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 6: PUT for DOTS signal

   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.  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.  If the DOTS server does not find the mitigation-id
   parameter value conveyed in the PUT request in its configuration data
   then the server MAY accept the mitigation request, and a 2.01
   (Created) response is returned to the DOTS client, and the DOTS
   server will try to mitigate the attack.  If the DOTS server finds the
   mitigation-id parameter value conveyed in the PUT request in its
   configuration data then the server 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 missing one or
   more mandatory attributes, then 4.00 (Bad Request) will be returned
   in the response or if the request contains invalid or unknown
   parameters then 4.02 (Invalid query) will be returned in the
   response.  For responses indicating a client or server error, the
   payload explains the error situation of the result of the requested
   action (Section 5.5 in [RFC7252]).

5.3.2.  Withdraw a DOTS Signal

   A DELETE request is used to withdraw a DOTS signal from a DOTS server
   (Figure 7).






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     Header: DELETE (Code=0.04)
     Uri-Host: "host"
     Uri-Path: "version"
     Uri-Path: "dots-signal"
     Uri-Path: "signal"
     Content-Format: "application/cbor"
     {
       "mitigation-scope": {
         "scope": [
           {
             "mitigation-id": integer
           }
         ]
       }
     }

                      Figure 7: Withdraw DOTS signal

   The DOTS server immediately acknowledges a DOTS client's request to
   withdraw the DOTS signal using 2.02 (Deleted) response code.  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, then to protect against route or DNS flapping
   caused by a client rapidly toggling mitigation, and to dampen the
   effect of oscillating attacks, DOTS servers MAY allow mitigation to
   continue for a limited period after acknowledging a DOTS client's
   withdrawal of a mitigation request.  During this period, DOTS server
   status messages SHOULD indicate that mitigation is active but
   terminating.  The active-but-terminating period is initially 30
   seconds.  If the client requests mitigation again before that 30
   second window elapses, the DOTS server MAY exponentially increase the
   active- but-terminating period up to a maximum of 240 seconds (4
   minutes).  After the active-but-terminating period elapses, the DOTS
   server MUST treat the mitigation as terminated, as the DOTS client is
   no longer responsible for the mitigation.  For example, if there is a
   financial relationship between the DOTS client and server domains,
   the DOTS client ceases incurring cost at this point.

5.3.3.  Retrieving a DOTS Signal

   A GET request is used to retrieve information and status of a DOTS
   signal from a DOTS server (Figure 8).  If the DOTS server does not
   find the mitigation-id parameter value conveyed in the GET request in
   its configuration data, then it responds with a 4.04 (Not Found)
   error response code.  The 'c' (content) parameter and its permitted




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   values defined in [I-D.ietf-core-comi] can be used to retrieve non-
   configuration data or configuration data or both.

   1) To retrieve all DOTS signals signaled by the DOTS client.

     Header: GET (Code=0.01)
     Uri-Host: "host"
     Uri-Path: "version"
     Uri-Path: "dots-signal"
     Uri-Path: "signal"
     Observe : 0

   2) To retrieve a specific DOTS signal signaled by the DOTS client.
      The configuration data in the response will be formatted in the
      same order it was processed at the DOTS server.

     Header: GET (Code=0.01)
     Uri-Host: "host"
     Uri-Path: "version"
     Uri-Path: "dots-signal"
     Uri-Path: "signal"
     Observe : 0
     Content-Format: "application/cbor"
     {
       "mitigation-scope": {
         "scope": [
           {
             "mitigation-id": integer
           }
         ]
       }
     }

                    Figure 8: GET to retrieve the rules

   Figure 9 shows a response example of all the 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,
             "target-protocol": [
                 17
              ],
             "lifetime":1800,
             "status":2,
             "bytes-dropped": 134334555,
             "bps-dropped":  43344,
             "pkts-dropped": 333334444,
             "pps-dropped": 432432
           }
         ]
       },
       {
         "scope": [
           {
             "mitigation-id": 12333,
             "target-protocol": [
                 6
              ],
             "lifetime":1800,
             "status":3
             "bytes-dropped": 0,
             "bps-dropped":  0,
             "pkts-dropped": 0,
             "pps-dropped": 0
           }
         ]
       }
     ]
   }

                          Figure 9: Response body

   The mitigation status parameters are described below.

   bytes-dropped:  The total dropped byte count for the mitigation
      request.  This is a optional attribute.

   bps-dropped:  The average dropped bytes per second for the mitigation
      request.  This is a optional attribute.





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   pkts-dropped:  The total dropped packet count for the mitigation
      request.  This is a optional attribute.

   pps-dropped:  The average dropped packets per second for the
      mitigation request.  This is a optional attribute.

   status:  Status of attack mitigation.  The 'status' parameter is a
      mandatory attribute.

   The various possible values of 'status' parameter are explained
   below:

/--------------------+---------------------------------------------------\
| Parameter value     | Description                                      |
|--------------------+---------------------------------------------------|
| 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.     |
|                    |                                                   |
\--------------------+---------------------------------------------------/


   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.  A DOTS client that is no longer
   interested in receiving notifications from the DOTS server can simply
   "forget" the observation.  When the DOTS server then sends the next
   notification, the DOTS client will not recognize the token in the



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   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 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).

                       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 10: Notifications of attack mitigation status

5.3.3.1.  Mitigation Status

   A DOTS client retrieves the information about a DOTS signal at
   frequent intervals to determine the status of an attack.  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.

   A DOTS client should react to the status of the attack from the DOTS
   server and not the fact that it has recognized, using its own means,
   that the attack has been mitigated.  This ensures that the DOTS
   client does not recall a mitigation request in a premature fashion
   because it is possible that the DOTS client does not sense the DDOS




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   attack on its resources but the DOTS server could be actively
   mitigating the attack and the attack is not completely averted.

5.3.4.  Efficacy Update from DOTS Client

   While DDoS mitigation is active, a DOTS client MAY frequently
   transmit DOTS mitigation efficacy updates to the relevant DOTS
   server.  An PUT request (Figure 11) 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 convey the DOTS signal
   (Section 5.3.1).  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 efficacy update to the
   DOTS server followed by a DELETE request to withdraw the mitigation
   request, but 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 the DOTS client then the
   request is processed, and if no match is found then the PUT request
   is silently ignored.





























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      Header: PUT (Code=0.03)
      Uri-Host: "host"
      Uri-Path: "version"
      Uri-Path: "dots-signal"
      Uri-Path: "signal"
      Content-Format: "application/cbor"
      {
       "mitigation-scope": {
         "scope": [
           {
             "mitigation-id": integer,
             "target-ip": [
                "string"
              ],
             "target-port-range": [
                {
                  "lower-port": integer,
                  "upper-port": integer
                }
              ],
              "target-protocol": [
                integer
              ],
              "fqdn": [
                "string"
              ],
              "uri": [
                "string"
              ],
              "alias": [
                "string"
              ],
             "lifetime": integer,
             "attack-status": integer
           }
         ]
       }
      }

                        Figure 11: Efficacy Update

   The 'attack-status' parameter is a mandatory attribute.  The various
   possible values contained in the 'attack-status' parameter are
   explained below:







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


   The DOTS server indicates the result of processing the PUT request
   using CoAP response codes.  The response code 2.04 (Changed) will be
   returned in the response if the DOTS server has accepted the
   mitigation efficacy update.  The 5.xx response codes are returned if
   the DOTS server has erred or is incapable of performing the
   mitigation.

5.4.  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 timeout: DOTS agents regularly send heartbeats (Ping/
       Pong) to each other after mutual authentication in order to keep
       the DOTS signal channel open, heartbeat timeout is the time to
       wait for a Pong in milliseconds.

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

   Reliability is provided to requests and responses by marking them as
   Confirmable (CON) messages.  DOTS signal channel session
   configuration requests and responses are marked as Confirmable (CON)
   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].  Reliability is provided to the responses
   by marking them as Confirmable (CON) messages.  The DOTS server can
   either piggyback the response in the acknowledgement message or if
   the DOTS server is not able to 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



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   explained in Section 2.2 of [RFC7252].  When the response is ready,
   the server sends it in a new Confirmable message which then in turn
   needs to be acknowledged by the DOTS client (see Sections 5.2.1 and
   Sections 5.2.2 in [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 to which to
   correlate this response, making the retransmission an unexpected
   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 in [RFC7252] for more
   details).

5.4.1.  Discover Acceptable Configuration Parameters

   A GET request is used to obtain acceptable configuration parameters
   on the DOTS server for DOTS signal channel session configuration.
   Figure 12 shows how to obtain acceptable configuration parameters for
   the server.

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

                 Figure 12: GET to retrieve configuration

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

    Content-Format: "application/cbor"
     {
       "heartbeat-timeout": {"MinValue": integer, "MaxValue" : integer},
       "max-retransmit": {"MinValue": integer, "MaxValue" : integer},
       "ack-timeout": {"MinValue": integer, "MaxValue" : integer},
       "ack-random-factor": {"MinValue": number, "MaxValue" : number}
      }

                       Figure 13: GET response body







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5.4.2.  Convey DOTS Signal Channel Session Configuration

   A PUT request is used to convey the configuration parameters for the
   signaling channel (e.g., heartbeat timeout, maximum retransmissions
   etc).  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 (7),
   ack-random-factor (1.5) and heartbeat-timeout (371 seconds).  The
   heartbeat-timeout value is equal to the MAX_TRANSMIT_WAIT counter
   (Section 4.8.2 in [RFC7252]) whose value is derived from transmission
   parameters.  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
   signaling channel session configuration is applicable to a single
   DOTS signal channel session between the DOTS agents.

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

         Figure 14: PUT to convey the DOTS signal channel session
                            configuration data.

   The parameters 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.






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   heartbeat-timeout:   Heartbeat timeout is the time to wait for a
      response in milliseconds to check the DOTS peer health.  This is
      an optional attribute.

   max-retransmit:   Maximum number of retransmissions for a message
      (referred to as MAX_RETRANSMIT parameter in CoAP).  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 mtigation 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, then the
      DOTS server can detect that the DOTS session is lost.  The default
      value of the parameter is 'true'.  This is an optional attribute.

   In the PUT request at least one of the attributes heartbeat-timeout,
   max-retransmit, ack-timeout, ack-random-factor, and trigger-
   mitigation MUST be present.  The PUT request with higher numeric
   session-id value over-rides the DOTS signal channel session
   configuration data installed by a PUT request with a lower numeric
   session-id value.

   Figure 15 shows a PUT request example to convey the configuration
   parameters for the DOTS signal channel.


















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     Header: PUT (Code=0.03)
     Uri-Host: "www.example.com"
     Uri-Path: "v1"
     Uri-Path: "dots-signal"
     Uri-Path: "config"
     Content-Format: "application/cbor"
     {
       "signal-config": {
        "session-id": 1234534333242,
        "heartbeat-timeout": 30,
        "max-retransmit": 7,
        "ack-timeout": 5,
        "ack-random-factor": 1.5,
        "trigger-mitigation": false
       }
     }

           Figure 15: PUT to convey the configuration parameters

   The DOTS server indicates the result of processing the PUT request
   using CoAP response codes.  The CoAP response will include the CBOR
   body received in the request.  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 the a 2.04 (Changed) response will be returned in the
   response.  If the DOTS server does not find the session-id parameter
   value conveyed in the PUT request in its configuration data and if
   the DOTS server has accepted the configuration parameters then a
   response code 2.01 (Created) will be returned in the response.  If
   the request is missing one or more mandatory attributes then 4.00
   (Bad Request) will be returned in the response or if the request
   contains invalid or unknown parameters then 4.02 (Invalid query) will
   be returned in the response.  Response code 4.22 (Unprocessable
   Entity) will be returned in the response if any of the heartbeat-
   timeout, max-retransmit, target-protocol, ack-timeout and ack-random-
   factor attribute values is not acceptable to the DOTS server.  The
   DOTS server in the error response conveys the minimum and maximum
   attribute values acceptable by the DOTS server.  The DOTS client can
   re-try and send the PUT request with updated attribute values
   acceptable to the DOTS server.











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     Content-Format: "application/cbor"
     {
        "heartbeat-timeout": {"MinValue": 15, "MaxValue" : 60},
        "max-retransmit": {"MinValue": 3, "MaxValue" : 15},
        "ack-timeout": {"MinValue": 1, "MaxValue" : 30},
        "ack-random-factor": {"MinValue": 1.0, "MaxValue" : 4.0}
     }

                      Figure 16: Error response body

5.4.3.  Delete DOTS Signal Channel Session Configuration

   A DELETE request is used to delete the installed DOTS signal channel
   session configuration data (Figure 17).

     Header: DELETE (Code=0.04)
     Uri-Host: "host"
     Uri-Path: "version"
     Uri-Path: "dots-signal"
     Uri-Path: "config"
     Content-Format: "application/cbor"
     {
       "signal-config": {
        "session-id": integer
       }
     }

                      Figure 17: DELETE configuration

   If the DOTS server does not find the session-id parameter value
   conveyed in the DELETE request in its configuration data, then it
   responds with a 4.04 (Not Found) error response code.  The DOTS
   server successfully acknowledges a DOTS client's request to remove
   the DOTS signal channel session configuration using 2.02 (Deleted)
   response code.

5.4.4.  Retrieving DOTS Signal Channel Session Configuration

   A GET request is used to retrieve the installed DOTS signal channel
   session configuration data from a DOTS server.  Figure 18 shows how
   to retrieve the DOTS signal channel session configuration data.










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     Header: GET (Code=0.01)
     Uri-Host: "host"
     Uri-Path: "version"
     Uri-Path: "dots-signal"
     Uri-Path: "config"
     Content-Format: "application/cbor"
     {
       "signal-config": {
        "session-id": integer
       }
     }

                 Figure 18: GET to retrieve configuration

5.5.  Redirected Signaling

   Redirected Signaling is discussed in detail in Section 3.2.2 of
   [I-D.ietf-dots-architecture].  If the DOTS server wants to redirect
   the DOTS client to an alternative DOTS server for a signaling session
   then the response code 3.00 (alternate server) will be returned in
   the response to the client.  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 FQDN, and the alternate DOTS server IP addresses and time to
   live values in the CBOR body.

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

                      Figure 19: 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.



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   Figure 20 shows a 3.00 response example to convey the DOTS alternate
   server www.example-alt.com, its IP addresses 2001:db8:6401::1 and
   2001:db8:6401::2, and TTL values 3600 and 1800.

   {

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

                 Figure 20: Example of error response body

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

5.6.  Heartbeat Mechanism

   To provide a metric 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
   agent, and may consider a session terminated in the extended 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 alive firewall and/or NAT bindings.  This
   probing reduces the frequency of establishing a new handshake when a
   DOTS signal needs to be conveyed to the DOTS server.  In DOTS over
   UDP, heartbeat messages can be exchanged between the DOTS agents
   using the "COAP ping" mechanism (Section 4.2 in [RFC7252]).  The DOTS
   agent sends an Empty Confirmable message and the peer DOTS agent will
   respond by sending an Reset message.  In DOTS over TCP, heartbeat



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   messages can be exchanged between the DOTS agents using the Ping and
   Pong messages (Section 4.4 in [I-D.ietf-core-coap-tcp-tls]).  The
   DOTS agent sends a Ping message and the peer DOTS agent would respond
   by sending a single Pong message.

6.  Mapping parameters to CBOR

   All parameters in DOTS signal channel are mapped to CBOR types as
   follows and are given an integer key value to save space.

/--------------------+------------------------+--------------------------\
| Parameter name     | CBOR key               | CBOR major type of value |
|--------------------+------------------------+--------------------------|
| mitigation-scope   | 1                      | 5 (map)                  |
| scope              | 2                      | 5 (map)                  |
| mitigation-id      | 3                      | 0 (unsigned)             |
| target-ip          | 4                      | 4 (array)                |
| target-port-range  | 5                      | 4                        |
| lower-port         | 6                      | 0                        |
| upper-port         | 7                      | 0                        |
| target-protocol    | 8                      | 4                        |
| fqdn               | 9                      | 4                        |
| uri                | 10                     | 4                        |
| alias              | 11                     | 4                        |
| lifetime           | 12                     | 0                        |
| attack-status      | 13                     | 0                        |
| signal-config      | 14                     | 5                        |
| heartbeat-timeout  | 15                     | 0                        |
| max-retransmit     | 16                     | 0                        |
| ack-timeout        | 17                     | 0                        |
| ack-random-factor  | 18                     | 7                        |
| MinValue           | 19                     | 0                        |
| MaxValue           | 20                     | 0                        |
| status             | 21                     | 0                        |
| bytes-dropped      | 22                     | 0                        |
| bps-dropped        | 23                     | 0                        |
| pkts-dropped       | 24                     | 0                        |
| pps-dropped        | 25                     | 0                        |
| session-id         | 26                     | 0                        |
| trigger-mitigation | 27                     | 7 (simple types)         |
\--------------------+------------------------+--------------------------/

       Figure 21: CBOR mappings used in DOTS signal channel message








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7.  (D)TLS Protocol Profile and Performance considerations

   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 machine-in-the-middle and
   protocol downgrade.  These are general attacks on (D)TLS and 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 encryption of
   DOTS using (D)TLS is virtually a green-field deployment DOTS agents
   MUST implement only (D)TLS 1.2 or later.

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

   o  DOTS agents MUST support DTLS record replay detection (Section 3.3
      in [RFC6347]) to protect against replay attacks.

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

   o  Raw public keys [RFC7250] which reduce the size of the
      ServerHello, and can be used by servers that cannot obtain
      certificates (e.g., DOTS gateways on private networks).

   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.

7.1.  MTU and Fragmentation Issues

   To avoid DOTS signal message fragmentation and the consequently
   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



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   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-ip' 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 absolutely ensure that there is no IP
   fragmentation.  If IPv4 support on unusual networks is a
   consideration and 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 up to 576 bytes should never need
   to be fragmented, thus sending a maximum of 500 bytes of DOTS signal
   over a UDP datagram will generally avoid IP fragmentation.

8.  (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.rescorla-tls-dtls13] is based on the TLS 1.3 protocol and
   provides equivalent security guarantees.  (D)TLS 1.3 provides two
   basic handshake modes of interest to DOTS signal channel:

   o  Absent packet loss, a full handshake in which the DOTS client is
      able to send the DOTS signal message after one round trip and the
      DOTS server immediately after receiving the first DOTS signal
      message from the client.

   o  0-RTT mode in which the DOTS client can authenticate itself and
      send DOTS signal message on its first flight, 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 SHOULD
      establish a (D)TLS session with the DOTS server during peacetime
      and share a PSK.  During DDOS attack, the DOTS client can use the
      (D)TLS session to convey the DOTS signal message and if there is
      no response from the server after multiple re-tries then the DOTS
      client can resume the (D)TLS session in 0-RTT mode using PSK.  A
      simplified TLS 1.3 handshake with 0-RTT DOTS signal message
      exchange is shown in Figure 22.



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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 22: TLS 1.3 handshake with 0-RTT

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

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






















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

   Figure 23: Example of Authentication and Authorization of DOTS Agents

   In the example depicted in Figure 23, 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 detector to request DDOS mitigation, but does not permit the
   user of type 'guest' to request DDOS mitigation.

   Also, DOTS gateway and DOTS server MUST perform mutual authentication
   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 23, the DOTS server only allows
   the DOTS gateway to request mitigation for 'example.com' domain and
   not for other domains.








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10.  IANA Considerations

   This specification registers new CoAP response code, new parameters
   for DOTS signal channel and establishes registries for mappings to
   CBOR.

10.1.  CoAP Response Code

   The following entry is added to the "CoAP Response Codes" sub-
   registry:

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

                       Figure 24: CoAP Response Code

   [Note to RFC Editor: Please replace XXXX with the RFC number of this
   specification.]

10.2.  DOTS signal channel CBOR Mappings Registry

   A new registry will be requested from IANA, entitled "DOTS signal
   channel CBOR Mappings Registry".  The registry is to be created as
   Expert Review Required.

10.2.1.  Registration Template

   Parameter name:
      Parameter names (e.g., "target_ip") in the DOTS signal channel.

   CBOR Key Value:
      Key value for the parameter.  The key value MUST be an integer in
      the range of 1 to 65536.  The key values in the range of 32768 to
      65536 are assigned for 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):




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      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.

10.2.2.  Initial Registry Contents

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



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   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: "FQDN"
   o  CBOR Key Value: 9
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

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




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   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
   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: MinValue
   o  CBOR Key Value: 19
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name: MaxValue
   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: bytes-dropped
   o  CBOR Key Value: 22
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

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




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

   o  Parameter Name: pps-dropped
   o  CBOR Key Value: 25
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

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

   o  Parameter Name: trigger-mitigation
   o  CBOR Key Value: 27
   o  CBOR Major Type: 7
   o  Change Controller: IESG
   o  Specification Document(s): this document

11.  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 of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing 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 that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   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".



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11.1.  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 spec in accordance with maturing of
      DOTS protocol itself.
   Implementation:   To be open-sourced.
   Level of maturity:   It is a early implementation of DOTS protocol.
      Messaging between DOTS clients and DOTS servers has been tested.
      Level of maturity will increase in accordance with maturing of
      DOTS protocol itself.
   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>

12.  Security Considerations

   Authenticated encryption MUST be used for data confidentiality and
   message integrity.  (D)TLS based on client certificate MUST be used
   for mutual authentication.  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.

   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 client 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.





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   Special care should be taken in order to ensure that the activation
   of the proposed mechanism won't have an impact on the stability of
   the network (including connectivity and services delivered over that
   network).

   Involved functional elements in the cooperation system must establish
   exchange instructions and notification over a secure and
   authenticated channel.  Adequate filters can be enforced to avoid
   that nodes outside a trusted domain can inject request such as
   deleting filtering rules.  Nevertheless, 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.

13.  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

14.  Acknowledgements

   Thanks to Christian Jacquenet, Roland Dobbins, Andrew Mortensen,
   Roman D.  Danyliw, Michael Richardson, Ehud Doron, Kaname Nishizuka,
   Dave Dolson, Liang Xia, Jon Shallow and Gilbert Clark for the
   discussion and comments.

15.  References

15.1.  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-09 (work in progress), May
              2017.

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




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

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

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <http://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, <http://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,
              <http://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, <http://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,
              <http://www.rfc-editor.org/info/rfc7641>.

15.2.  Informative References

   [I-D.ietf-core-comi]
              Veillette, M., Stok, P., Pelov, A., and A. Bierman, "CoAP
              Management Interface", draft-ietf-core-comi-01 (work in
              progress), July 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.




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   [I-D.ietf-dots-architecture]
              Mortensen, A., Andreasen, F., Reddy, T.,
              christopher_gray3@cable.comcast.com, c., Compton, R., and
              N. Teague, "Distributed-Denial-of-Service Open Threat
              Signaling (DOTS) Architecture", draft-ietf-dots-
              architecture-04 (work in progress), July 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-02 (work in progress), June 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-06 (work in
              progress), July 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-07 (work
              in progress), July 2017.

   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-21 (work in progress),
              July 2017.

   [I-D.rescorla-tls-dtls13]
              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", draft-rescorla-tls-dtls13-01 (work in progress),
              March 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,
              <http://www.rfc-editor.org/info/rfc791>.

   [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, <http://www.rfc-editor.org/info/rfc4632>.



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

   [RFC4987]  Eddy, W., "TCP SYN Flooding Attacks and Common
              Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007,
              <http://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, <http://www.rfc-editor.org/info/rfc5077>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <http://www.rfc-editor.org/info/rfc6020>.

   [RFC6555]  Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
              Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April
              2012, <http://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,
              <http://www.rfc-editor.org/info/rfc6724>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <http://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,
              <http://www.rfc-editor.org/info/rfc7413>.

   [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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc7918>.





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   [RFC7924]  Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", RFC 7924,
              DOI 10.17487/RFC7924, July 2016,
              <http://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,
              <http://www.rfc-editor.org/info/rfc7942>.

   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
              March 2017, <http://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


   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





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   Nik Teague
   Verisign, Inc.
   United States

   Email: nteague@verisign.com














































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