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DOTS                                                            T. Reddy
Internet-Draft                                                    McAfee
Intended status: Standards Track                            M. Boucadair
Expires: May 31, 2018                                             Orange
                                                                P. Patil
                                                                   Cisco
                                                            A. Mortensen
                                                    Arbor Networks, Inc.
                                                               N. Teague
                                                          Verisign, Inc.
                                                       November 27, 2017


   Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal
                                Channel
                   draft-ietf-dots-signal-channel-09

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.

Editorial Note (To be removed by RFC Editor)

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

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

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

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

   o  reference: RFC XXXX

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute



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   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on May 31, 2018.

Copyright Notice

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

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Notational Conventions and Terminology  . . . . . . . . . . .   5
   3.  Design Overview . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  DOTS Signal Channel: Messages & Behaviors . . . . . . . . . .   7
     4.1.  DOTS Server(s) Discovery  . . . . . . . . . . . . . . . .   7
     4.2.  CoAP URIs . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.3.  Happy Eyeballs for DOTS Signal Channel  . . . . . . . . .   8
     4.4.  DOTS Mitigation Methods . . . . . . . . . . . . . . . . .   9
       4.4.1.  Request Mitigation  . . . . . . . . . . . . . . . . .  10
       4.4.2.  Withdraw a Mitigation . . . . . . . . . . . . . . . .  18
       4.4.3.  Retrieve Information Related to a Mitigation  . . . .  19
       4.4.4.  Efficacy Update from DOTS Clients . . . . . . . . . .  25
     4.5.  DOTS Signal Channel Session Configuration . . . . . . . .  27
       4.5.1.  Discover Configuration Parameters . . . . . . . . . .  28
       4.5.2.  Convey DOTS Signal Channel Session Configuration  . .  30
       4.5.3.  Delete DOTS Signal Channel Session Configuration  . .  34
     4.6.  Redirected Signaling  . . . . . . . . . . . . . . . . . .  35
     4.7.  Heartbeat Mechanism . . . . . . . . . . . . . . . . . . .  36
   5.  DOTS Signal Channel YANG Modules  . . . . . . . . . . . . . .  37
     5.1.  Mitigation Request YANG Module Tree Structure . . . . . .  37
     5.2.  Mitigation Request YANG Module  . . . . . . . . . . . . .  38



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     5.3.  Session Configuration YANG Module Tree Structure  . . . .  41
     5.4.  Session Configuration YANG Module . . . . . . . . . . . .  41
   6.  Mapping Parameters to CBOR  . . . . . . . . . . . . . . . . .  44
   7.  (D)TLS Protocol Profile and Performance Considerations  . . .  45
     7.1.  (D)TLS Protocol Profile . . . . . . . . . . . . . . . . .  46
     7.2.  MTU and Fragmentation . . . . . . . . . . . . . . . . . .  47
   8.  (D)TLS 1.3 Considerations . . . . . . . . . . . . . . . . . .  48
   9.  Mutual Authentication of DOTS Agents & Authorization of DOTS
       Clients . . . . . . . . . . . . . . . . . . . . . . . . . . .  49
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  50
     10.1.  DOTS Signal Channel UDP and TCP Port Number  . . . . . .  50
     10.2.  Well-Known 'dots' URI  . . . . . . . . . . . . . . . . .  50
     10.3.  CoAP Response Code . . . . . . . . . . . . . . . . . . .  50
     10.4.  DOTS Signal Channel CBOR Mappings Registry . . . . . . .  51
       10.4.1.  Registration Template  . . . . . . . . . . . . . . .  51
       10.4.2.  Initial Registry Contents  . . . . . . . . . . . . .  51
     10.5.  YANG Modules . . . . . . . . . . . . . . . . . . . . . .  56
   11. Implementation Status . . . . . . . . . . . . . . . . . . . .  56
     11.1.  nttdots  . . . . . . . . . . . . . . . . . . . . . . . .  57
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  57
   13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  58
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  58
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  59
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  59
     15.2.  Informative References . . . . . . . . . . . . . . . . .  60
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  63

1.  Introduction

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

   Network applications have finite resources like CPU cycles, 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, a DDoS
   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



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   [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 many cases, it may not be possible for 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.

   An example of network diagram showing a deployment of DOTS agents is
   shown in Figure 1.  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)

   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



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   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.

   The document adheres to the DOTS architecture
   [I-D.ietf-dots-architecture].  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].

   This document focuses on the DOTS signal channel.  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].

   (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].

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

3.  Design Overview

   The DOTS signal channel is built on top of the Constrained
   Application Protocol (CoAP) [RFC7252], a lightweight protocol
   originally designed for constrained devices and networks.  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




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   (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 3).

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

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

   By default, DOTS signal channel MUST run over port number TBD as
   defined in Section 10.1, for both UDP and TCP, unless the DOTS server
   has mutual agreement with its DOTS clients to use a port other than
   TBD for DOTS signal channel, or DOTS clients supports means to
   dynamically discover the ports used by their DOTS servers.  In order
   to use a distinct port number (vs.  TBD), DOTS clients and servers
   should support a configurable parameter to supply the port number to
   use.

   The signal channel is initiated by the DOTS client (Section 4.4).
   Once the signal channel is established, the DOTS agents periodically
   send heartbeats to keep the channel active (Section 4.7).  At any
   time, the DOTS client may send a mitigation request message to a DOTS
   server over the active channel.  While mitigation is active, due to
   the higher likelihood of packet loss during a DDoS attack, the DOTS
   server periodically sends status messages to the client, including
   basic mitigation feedback details.  Mitigation remains active until
   the DOTS client explicitly terminates mitigation, or the mitigation
   lifetime expires.

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

   Messages exchanged between DOTS clients and servers are serialized
   using Concise Binary Object Representation (CBOR) [RFC7049], CBOR is
   a binary encoding designed for small code and message size.  CBOR



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   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) as CBOR data.

   In order to prevent fragmentation, DOTS agents must follow the
   recommendations in Section 4.6 of [RFC7252].  Refer to Section 7.2
   for more details.

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

4.  DOTS Signal Channel: Messages & Behaviors

4.1.  DOTS Server(s) Discovery

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

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

4.2.  CoAP URIs

   The DOTS server MUST support the use of the path-prefix of "/.well-
   known/" as defined in [RFC5785] and the registered name of "dots".
   Each DOTS operation is indicated by a path-suffix that indicates the
   intended operation.












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

             Table 1: Operations and their corresponding URIs

4.3.  Happy Eyeballs for DOTS Signal Channel

   DOTS signaling can happen with DTLS over UDP and TLS over TCP.  A
   DOTS client can use DNS to determine the IP address(es) of a DOTS
   server or a DOTS client may be provided with the list of 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
   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).







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

                       Figure 4: DOTS Happy Eyeballs

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

4.4.  DOTS Mitigation Methods

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

   PUT:  DOTS clients use the PUT method to request mitigation from a
      DOTS server (Section 4.4.1).  During active mitigation, DOTS
      clients may use PUT requests to convey mitigation efficacy updates
      to the DOTS server (Section 4.4.4).

   DELETE:  DOTS clients use the DELETE method to withdraw a request for
      mitigation from the DOTS server (Section 4.4.2).

   GET:  DOTS clients may use the GET method to subscribe to DOTS server
      status messages, or to retrieve the list of existing mitigations
      (Section 4.4.3).

   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



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   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.  If the DOTS client cannot maintain an RTT estimate, it
   SHOULD NOT send more than one Non-confirmable request every 3
   seconds, and SHOULD use an even less aggressive rate when possible
   (case 2 in Section 3.1.3 of [RFC8085]).

4.4.1.  Request 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(s) (Figure 5, illustrated in JSON diagnostic notation).  If
   this DOTS client is entitled to solicit the DOTS service, the DOTS
   server can enable mitigation on behalf of the DOTS client by
   communicating the DOTS client's request to the mitigator and relaying
   selected mitigator feedback to the requesting DOTS client.
































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

                   Figure 5: PUT to convey DOTS signals

   The parameters are described below:



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   client-identifier:  The client identifier MAY be conveyed by the DOTS
      gateway to propagate the DOTS client identity from the gateway's
      client-side to the gateway's server-side, and from the gateway's
      server-side to the DOTS server.  This allows the final DOTS server
      to accept mitigation requests with scopes which the DOTS client is
      authorized to manage.

      The 'client-identifier' value MUST be assigned by the DOTS gateway
      in a manner that ensures that there is no probability that the
      same value will be assigned to a different DOTS client.  The DOTS
      gateway MUST obscure potentially sensitive DOTS client identity
      information.  The client-identifier attribute SHOULD NOT to be
      generated and included by the DOTS client.

      This is an optional attribute.

   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, Stream Control Transmission Protocol (SCTP)
      [RFC4960], or Datagram Congestion Control Protocol (DCCP)
      [RFC4340]: 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



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      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-name:  A list of aliases.  Aliases can be created using the
      DOTS data channel (Section 3.1.1 of [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.  The
      RECOMMENDED lifetime of a mitigation request is 3600 seconds (60
      minutes) -- this value was chosen to be long enough so that
      refreshing is not typically a burden on the DOTS client, while
      expiring the request where the client has unexpectedly quit in a
      timely manner.

      A lifetime of negative one (-1) indicates indefinite lifetime for
      the mitigation request.  A lifetime of 0 in the request is an
      invalid value.

      DOTS clients MUST include this parameter in their mitigation
      requests.  Upon the expiry of this lifetime, and if the request is
      not refreshed, the mitigation request is removed.  The request can
      be refreshed by sending the same request again.  The server MAY
      refuse indefinite lifetime, for policy reasons; the granted
      lifetime value is returned in the response.  DOTS clients MUST be
      prepared to not be granted mitigations with indefinite lifetimes.
      The server MUST always indicate the actual lifetime in the
      response and the remaining lifetime in status messages sent to the
      client.  This is a mandatory attribute.

   The CBOR key values for the parameters are defined in Section 6.
   Section 10 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-name' MUST be present.
   If the attribute value is empty, then the attribute MUST NOT be
   present in the request.  DOTS agents can safely ignore Vendor-
   Specific parameters they don't understand.




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   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.  Two mitigation-ids from a DOTS client are overlapping if
   there is a common IP address, IP prefix, FQDN, URI, or alias-name.
   To avoid maintaining a long list of overlapping mitigation requests
   from a DOTS client and avoid error-prone provisioning of mitigation
   requests from a DOTS client, the overlapped lower numeric
   'mitigation-id' MUST be automatically deleted and no longer available
   at the DOTS server.

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

   If the DOTS client is using the certificate provisioned by the
   Enrollment over Secure Transport (EST) server [RFC7030] in the DOTS
   gateway-domain to authenticate itself to the DOTS gateway, then the
   'client-identifier' value can be the output of a cryptographic hash
   algorithm whose input is the DER-encoded ASN.1 representation of the
   Subject Public Key Info (SPKI) of an X.509 certificate.  In this
   version of the specification, the cryptographic hash algorithm used
   is SHA-256 [RFC6234].  The output of the cryptographic hash algorithm
   is truncated to 16 bytes; truncation is done by stripping off the
   final 16 bytes.  The truncated output is base64url encoded.  If the
   'client-identifier' value is already present in the mitigation
   request received from the DOTS client, the DOTS gateway MAY compute
   the 'client-identifier' value, as discussed above, and add the
   computed 'client-identifier' value to the end of the 'client-
   identifier' list.  The DOTS server MUST NOT use the 'client-
   identifier' for the DOTS client authentication process.

   In both DOTS signal and data channel sessions, the DOTS client MUST
   authenticate itself to the DOTS server (Section 9).  The DOTS server
   may use the algorithm in Section 7 of [RFC7589] to derive the DOTS
   client identity or username from the client certificate.  The DOTS
   client identity allows the DOTS server to accept mitigation requests
   with scopes which the DOTS client is authorized to manage.  The DOTS
   server couples the DOTS signal and data channel sessions using the
   DOTS client identity and the 'client-identifier' parameter value, so
   the DOTS server can validate whether the aliases conveyed in the
   mitigation request were indeed created by the same DOTS client using
   the DOTS data channel session.  If the aliases were not created by
   the DOTS client, the DOTS server returns 4.00 (Bad Request) in the
   response.




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   The DOTS server couples the DOTS signal channel sessions using the
   DOTS client identity and the 'client-identifier' parameter value, and
   the DOTS server uses 'mitigation-id' parameter value to detect
   duplicate mitigation requests.  If the mitigation request contains
   both alias-name and other parameters identifying the target resources
   (such as, 'target-ip', 'target-prefix', 'target-port-range', 'fqdn',
   or 'uri'), then the DOTS server appends the parameter values in
   'alias-name' 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)
  Uri-Host: "www.example.com"
  Uri-Path: ".well-known"
  Uri-Path: "dots"
  Uri-Path: "v1"
  Uri-Path: "mitigate"
  Content-Format: "application/cbor"
  {
    "mitigation-scope": {
      "client-identifier": [
         "dz6pHjaADkaFTbjr0JGBpw"
      ],
      "scope": [
        {
          "mitigation-id": 12332,
          "target-ip": [
             "2001:db8:6401::1",
             "2001:db8:6401::2"
           ],
          "target-port-range": [
            {
              "lower-port": 80
            },
            {
              "lower-port": 443
            },
            {
               "lower-port": 8080
            }
           ],
           "target-protocol": [
             6
           ]
        }



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      ]
    }
  }

The CBOR encoding format is shown below:

A1                                      # map(1)
   01                                   # unsigned(1)
   A2                                   # map(2)
      18 20                             # unsigned(32)
      81                                # array(1)
      76                                # text(22)
         647A3670486A6141446B614654626A72304A47427077 # "dz6pHjaADkaFTbjr0JGBpw"
      02                                # unsigned(2)
      81                                # array(1)
         A4                             # map(4)
            03                          # unsigned(3)
            19 302C                     # unsigned(12332)
            04                          # unsigned(4)
            82                          # array(2)
               70                       # text(16)
                  323030313A6462383A363430313A3A31 # "2001:db8:6401::1"
               70                       # text(16)
                  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 (client errors).  COAP 5.xx
   codes are returned if the DOTS server has erred or is currently
   unavailable to provide mitigation in response to the mitigation
   request from the DOTS client.



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   Figure 7 shows an example of a PUT request that is successfully
   processed (i.e., CoAP 2.xx response codes).

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

                       Figure 7: 2.xx response body

   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 by sending back a 2.01
   (Created) response to the DOTS client; the DOTS server will
   consequently try to mitigate the attack.

   If the DOTS server finds the 'mitigation-id' parameter value conveyed
   in the PUT request in its configuration data, 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) is
   returned in the response.

   For a mitigation request to continue beyond the initial negotiated
   lifetime, the DOTS client need to refresh the current mitigation
   request by sending a new PUT request.  The PUT request MUST use the
   same 'mitigation-id' value, and MUST repeat all the other parameters
   as sent in the original mitigation request apart from a possible
   change to the lifetime parameter value.

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





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4.4.2.  Withdraw a Mitigation

   A DELETE request is used to withdraw a DOTS mitigation request from a
   DOTS server (Figure 8).

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

                      Figure 8: Withdraw DOTS signal

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

   If the DOTS server finds the 'mitigation-id' parameter value conveyed
   in the DELETE request in its configuration data, 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, the DOTS server status messages SHOULD indicate
   that mitigation is active but terminating.  The initial active-but-
   terminating period SHOULD be sufficiently long to absorb latency
   incurred by route propagation.  The active-but-terminating period
   SHOULD be set by default to 120 seconds.  If the client requests
   mitigation again before the initial active-but-terminating period
   elapses, the DOTS server MAY exponentially increase the active-but-
   terminating period up to a maximum of 300 seconds (5 minutes).  After
   the active-but-terminating period elapses, the DOTS server MUST treat



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   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.

4.4.3.  Retrieve Information Related to a Mitigation

   A GET request is used to retrieve information (including status) of a
   DOTS mitigation from a DOTS server (Figure 9).  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 values defined in [I-D.ietf-core-comi] can be used to
   retrieve non-configuration data (attack mitigation status) or
   configuration data or both.  The DOTS server SHOULD support this
   optional filtering capability but can safely ignore it if not
   supported.

   The examples depicted in Figure 9 assume the default of "c=a".
































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

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

   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: ".well-known"
     Uri-Path: "dots"
     Uri-Path: "version"
     Uri-Path: "mitigate"
     Observe : 0
     Content-Format: "application/cbor"
     {
       "mitigation-scope": {
         "client-identifier": [
            "string"
         ],
         "scope": [
           {
             "mitigation-id": integer
           }
         ]
       }
     }

                    Figure 9: GET to retrieve the rules

   Figure 10 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,
             "mitigation-start": 1507818434.00,
             "target-protocol": [
                 17
              ],
             "lifetime":1800,
             "status":2,
             "bytes-dropped": 134334555,
             "bps-dropped":  43344,
             "pkts-dropped": 333334444,
             "pps-dropped": 432432
            },
           {
             "mitigation-id": 12333,
             "mitigation-start": 1507818393.00,
             "target-protocol": [
                 6
              ],
             "lifetime":1800,
             "status":3
             "bytes-dropped": 0,
             "bps-dropped":  0,
             "pkts-dropped": 0,
             "pps-dropped": 0
           }
        ]
     }
    }

                         Figure 10: Response body

   The mitigation status parameters are described below.

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

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

   bytes-dropped:  The total dropped byte count for the mitigation
      request since the attack mitigation is triggered.  The count wraps




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      around when it reaches the maximum value of unsigned integer.
      This is an optional attribute.

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

   pkts-dropped:  The total dropped packet count for the mitigation
      request since the attack mitigation is triggered.  This is an
      optional attribute.

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

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

   The various possible values of 'status' parameter are explained in
   Table 2.

   +-----------+-------------------------------------------------------+
   | Parameter | Description                                           |
   |     value |                                                       |
   +-----------+-------------------------------------------------------+
   |         1 | Attack mitigation is in progress (e.g., changing the  |
   |           | network path to re-route the inbound traffic to DOTS  |
   |           | mitigator).                                           |
   +-----------+-------------------------------------------------------+
   |         2 | Attack is successfully mitigated (e.g., traffic is    |
   |           | redirected to a DDOS mitigator and attack traffic is  |
   |           | dropped).                                             |
   +-----------+-------------------------------------------------------+
   |         3 | Attack has stopped and the DOTS client an 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.             |
   +-----------+-------------------------------------------------------+

                   Table 2: Values of 'status' parameter

   The observe option defined in [RFC7641] extends the CoAP core
   protocol with a mechanism for a CoAP client to "observe" a resource
   on a CoAP server: the client retrieves a representation of the



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   resource and requests this representation be updated by the server as
   long as the client is interested in the resource.  A DOTS client
   conveys the observe option set to '0' in the GET request to receive
   unsolicited notifications of attack mitigation status from the DOTS
   server.  Unidirectional notifications within the bidirectional signal
   channel allows unsolicited message delivery, enabling asynchronous
   notifications between the agents.  Due to the higher likelihood of
   packet loss during a DDoS attack, DOTS server periodically sends
   attack mitigation status to the DOTS client and also notifies the
   DOTS client whenever the status of the attack mitigation changes.  If
   the DOTS server cannot maintain a RTT estimate, it SHOULD NOT send
   more than one unsolicited notification every 3 seconds, and SHOULD
   use an even less aggressive rate when possible (case 2 in
   Section 3.1.3 of [RFC8085]).

   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 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).

   Figure 11 shows an example of a DOTS client requesting a DOTS server
   to send notifications related a given mitigation request.
























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

           Figure 11: Notifications of attack mitigation status

4.4.3.1.  Mitigation Status

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

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




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4.4.4.  Efficacy Update from DOTS Clients

   While DDoS mitigation is active, due to the likelihood of packet
   loss, a DOTS client MAY periodically transmit DOTS mitigation
   efficacy updates to the relevant DOTS server.  A PUT request
   (Figure 12) 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 4.4.1) unchanged apart
   from the lifetime parameter value.  If this is not the case, the DOTS
   server MUST reject the request with a 4.02 error response code.

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


























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

                        Figure 12: Efficacy Update

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



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

               Table 3: Values of 'attack-status' parameter

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

4.5.  DOTS Signal Channel Session Configuration

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

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

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

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

   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



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   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
   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
   5.2.2 of [RFC7252]).  Requests and responses exchanged between DOTS
   agents during peacetime are marked as Confirmable messages.

   Implementation Note: A DOTS client that receives a response in a CON
   message may want to clean up the message state right after sending
   the ACK.  If that ACK is lost and the DOTS server retransmits the
   CON, the DOTS client may no longer have any state 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 of [RFC7252] for more
   details).

4.5.1.  Discover Configuration Parameters

   A GET request is used to obtain acceptable and current configuration
   parameters on the DOTS server for DOTS signal channel session
   configuration.  Figure 13 shows how to obtain acceptable
   configuration parameters for the DOTS server.

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

                 Figure 13: GET to retrieve configuration

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







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     Content-Format: "application/cbor"
      {
        "heartbeat-interval": {
                               "CurrentValue": integer,
                               "MinValue": integer,
                               "MaxValue" : integer,
                              },
        "missing-hb-allowed": {
                               "CurrentValue": integer,
                               "MinValue": integer,
                               "MaxValue" : integer,
                              },
        "max-retransmit":     {
                               "CurrentValue": integer,
                               "MinValue": integer,
                               "MaxValue" : integer,
                              },
        "ack-timeout":        {
                               "CurrentValue": integer,
                               "MinValue": integer,
                               "MaxValue" : integer,
                              },
        "ack-random-factor":  {
                               "CurrentValue": number,
                               "MinValue": number,
                               "MaxValue" : number,
                              },
        "trigger-mitigation": {
                               "CurrentValue": boolean,
                              }
       }

                       Figure 14: GET response body

   Figure 15 shows an example of acceptable and current configuration
   parameters on the DOTS server for DOTS signal channel session
   configuration.














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     Content-Format: "application/cbor"
     {
       "heartbeat-interval": {
                               "CurrentValue": 30,
                               "MinValue": 15,
                               "MaxValue" : 240,
                              },
        "missing-hb-allowed": {
                               "CurrentValue": 5,
                               "MinValue": 3,
                               "MaxValue" : 9,
                              },
        "max-retransmit":     {
                               "CurrentValue": 3,
                               "MinValue": 2,
                               "MaxValue" : 15,
                              },
        "ack-timeout":        {
                               "CurrentValue": 2,
                               "MinValue": 1,
                               "MaxValue" : 30,
                              },
        "ack-random-factor": {
                               "CurrentValue": 1.5,
                               "MinValue": 1.1,
                               "MaxValue" : 4.0,
                              },
        "trigger-mitigation": {
                               "CurrentValue": true,
                              }
     }

                  Figure 15: Configuration response body

4.5.2.  Convey DOTS Signal Channel Session Configuration

   A PUT request is used to convey the configuration parameters for the
   signal channel (e.g., heartbeat interval, maximum retransmissions).
   Message transmission parameters for CoAP are defined in Section 4.8
   of [RFC7252].  The RECOMMENDED values of transmission parameter
   values are ack_timeout (2 seconds), max-retransmit (3), ack-random-
   factor (1.5).  In addition to those parameters, the RECOMMENDED
   specific DOTS transmission parameter values are heartbeat-interval
   (30 seconds) and missing-hb-allowed (5).

      Note: heartbeat-interval should be tweaked to also assist DOTS
      messages for NAT traversal (SIG-010 of
      [I-D.ietf-dots-requirements]).  According to [RFC8085], keepalive



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      messages must not be sent more frequently than once every 15
      seconds and should use longer intervals when possible.
      Furthermore, [RFC4787] recommends NATs to use a state timeout of 2
      minutes or longer, but experience shows that sending packets every
      15 to 30 seconds is necessary to prevent the majority of
      middleboxes from losing state for UDP flows.  From that
      standpoint, this specification recommends a minimum heartbeat-
      interval of 15 seconds and a maximum heartbeat-interval of 240
      seconds.  The recommended value of 30 seconds is selected to
      anticipate the expiry of NAT state.

      A heartbeat-interval of 30 second may be seen as too chatty in
      some deployments.  For such deployments, DOTS agents may negotiate
      longer heartbeat-interval values to avoid overloading the network
      with too frequent keepalives.

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

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

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














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

         Figure 16: 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.

   heartbeat-interval:   Time interval in seconds between two
      consecutive heartbeat messages.  This is an optional attribute.

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

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






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

   trigger-mitigation:   If the parameter value is set to 'false', then
      DDoS mitigation is triggered only when the DOTS signal channel
      session is lost.  Automated mitigation on loss of signal is
      discussed in Section 3.3.3 of [I-D.ietf-dots-architecture].  If
      the DOTS client ceases to respond to heartbeat messages, 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-interval,
   missing-hb-allowed, 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 17 shows a PUT request example to convey the configuration
   parameters for the DOTS signal channel.

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

           Figure 17: PUT to convey the configuration parameters

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

   o  If the DOTS server finds the 'session-id' parameter value conveyed
      in the PUT request in its configuration data and if the DOTS



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      server has accepted the updated configuration parameters, then
      2.04 (Changed) code is returned in the response.

   o  If the DOTS server does not find the 'session-id' parameter value
      conveyed in the PUT request in its configuration data and if the
      DOTS server has accepted the configuration parameters, then a
      response code 2.01 (Created) is returned in the response.

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

   o  If the request contains one or more invalid or unknown parameters,
      then 4.02 (Invalid query) code is returned in the response.

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

4.5.3.  Delete DOTS Signal Channel Session Configuration

   A DELETE request is used to delete the installed DOTS signal channel
   session configuration data (Figure 18).

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

                      Figure 18: DELETE configuration

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








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4.6.  Redirected Signaling

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

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

   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.











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   {

       "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.

4.7.  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
   DOTS 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 case of a volumetric DDoS attack saturating the incoming link to
   the DOTS client, all traffic from the DOTS server to the DOTS client
   will likely be dropped, although the DOTS server receives heartbeat
   requests and DOTS messages from the DOTS client.  In this scenario,




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   the DOTS agents MUST behave differently to handle message
   transmission and DOTS session liveliness during link saturation:

   o  The DOTS client MUST NOT consider the DOTS session terminated even
      after maximum "missing-hb-allowed" threshold is reached.  The DOTS
      client SHOULD continue to use the current DOTS session, and send
      heartbeat requests over the current DOTS session, so the DOTS
      server knows the DOTS client has not disconnected the DOTS
      session.  After the maximum "missing-hb-allowed" threshold is
      reached, the DOTS client SHOULD try (D)TLS session resumption.
      The DOTS client SHOULD send mitigation requests over the current
      DOTS session, and in parallel, try (D)TLS session resumption or
      0-RTT mode in DTLS 1.3 to piggyback the mitigation request in the
      ClientHello message.  Once the link is no longer statured, if
      traffic from the DOTS server reaches the DOTS client over the
      current DOTS session, the DOTS client can stop (D)TLS session
      resumption or if (D)TLS session resumption is successful then
      disconnect the current DOTS session.

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

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

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

5.  DOTS Signal Channel YANG Modules

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

5.1.  Mitigation Request YANG Module Tree Structure

   This document defines the YANG module "ietf-dots-signal"
   (Section 5.2), which has the following tree structure:






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   module: ietf-dots-signal
       +--rw mitigation-scope
          +--rw client-identifier*   binary
          +--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-name*          string
             +--rw lifetime?            int32

5.2.  Mitigation Request YANG Module

<CODE BEGINS> file "ietf-dots-signal@2017-11-27.yang"

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

      import ietf-inet-types {
          prefix "inet";
      }

    organization "IETF DOTS Working Group";

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

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

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

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Simplified BSD License



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        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

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

     revision 2017-11-27 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: A Distributed Denial-of-Service Open Threat
                    Signaling (DOTS) Signal Channel";
     }

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

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

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

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

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

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

              leaf-list target-ip {



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                  type inet:ip-address;
                  description
                    "IPv4 or IPv6 address identifying the target.";
              }

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

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

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

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

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

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

                     The value '0' means 'all protocols'.

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

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



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

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

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

              leaf lifetime {
                  type int32;
                  units "seconds";
                  default 3600;
                  description
                    "Indicates the lifetime of the mitigation request.";
              }
          }
     }
  }
<CODE ENDS>

5.3.  Session Configuration YANG Module Tree Structure

   This document defines the YANG module "ietf-dots-signal-config"
   (Section 5.4), which has the following structure:

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

5.4.  Session Configuration YANG Module

   <CODE BEGINS> file "ietf-dots-signal-config@2017-11-27.yang"

   module ietf-dots-signal-config {
        yang-version 1.1;



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

       organization "IETF DOTS Working Group";

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

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

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

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

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

        revision 2017-11-27 {
          description
            "Initial revision.";
          reference
            "RFC XXXX: A Distributed Denial-of-Service Open Threat
                       Signaling (DOTS) Signal Channel";
        }

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

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




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             leaf heartbeat-interval {
                 type int16;
                 units "seconds";
                 default 30;
                 description
                   "DOTS agents regularly send heartbeats to each other
                    after mutual authentication in order to keep
                    the DOTS signal channel open.";
             }

             leaf missing-hb-allowed {
                 type int16;
                 default 5;
                 description
                   "Maximum number of missing heartbeats allowed.";
             }

             leaf max-retransmit {
                 type int16;
                 default 3;
                 description
                   "Maximum number of retransmissions of a
                    Confirmable message.";
             }

             leaf ack-timeout {
                 type int16;
                 units "seconds";
                 default 2;
                 description
                    "Initial retransmission timeout value.";
             }

             leaf ack-random-factor {
                 type decimal64 {
                   fraction-digits 2;
                 }
                default 1.5;
                description
                  "Random factor used to influence the timing of
                   retransmissions.";
            }
            leaf trigger-mitigation {
                type boolean;
                default true;
                description
                  "If false, then mitigation is triggered
                   only when the DOTS server channel session is lost";



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            }
         }
   }
   <CODE ENDS>

6.  Mapping Parameters to CBOR

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








































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 /--------------------+---------------------+--------------------------\
 | 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-name         | 11                  | 4                        |
 | lifetime           | 12                  | 0                        |
 | attack-status      | 13                  | 0                        |
 | signal-config      | 14                  | 5                        |
 | heartbeat-interval | 15                  | 0                        |
 | max-retransmit     | 16                  | 0                        |
 | ack-timeout        | 17                  | 0                        |
 | ack-random-factor  | 18                  | 7                        |
 | 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)         |
 | missing-hb-allowed | 28                  | 0                        |
 | CurrentValue       | 29                  | 0                        |
 | mitigation-start   | 30                  | 7 (floating-point)       |
 | target-prefix      | 31                  | 4 (array)                |
 | client-identifier  | 32                  | 2 (byte string)          |
 | alt-server         | 33                  | 2                        |
 | alt-server-record  | 34                  | 4                        |
 | addr               | 35                  | 2                        |
 | ttl                | 36                  | 0                        |
 \--------------------+---------------------+--------------------------/
      Table 4: CBOR mappings used in DOTS signal channel message

7.  (D)TLS Protocol Profile and Performance Considerations








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7.1.  (D)TLS Protocol Profile

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

   There are known attacks on (D)TLS, such as 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.

   When a DOTS client is configured with a domain name of the DOTS
   server, and connects to its configured DOTS server, the server may
   present it with a PKIX certificate.  In order to ensure proper
   authentication, DOTS client MUST verify the entire certification path
   per [RFC5280].  The DOTS client additionaly uses [RFC6125] validation
   techniques to compare the domain name to the certificate provided.

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

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

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

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

   o  Raw public keys [RFC7250] or PSK handshake [RFC4279] which reduce
      the size of the ServerHello, and can be used by DOTS agents that
      cannot obtain certificates (e.g., DOTS clients and DOTS gateways
      on private networks).





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   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.

7.2.  MTU and Fragmentation

   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
   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.








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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 21.

          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 21: TLS 1.3 handshake with 0-RTT







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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.

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

   Figure 22: Example of Authentication and Authorization of DOTS Agents

   In the example depicted in Figure 22, 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.





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   Also, DOTS gateway and DOTS server located in different domains MUST
   perform mutual authentication (e.g., using certificates).  A DOTS
   server will only allow a DOTS gateway with a certificate for a
   particular domain to request mitigation for that domain.  In
   reference to Figure 22, the DOTS server only allows the DOTS gateway
   to request mitigation for 'example.com' domain and not for other
   domains.

10.  IANA Considerations

   This specification registers a default port, new URI suffix in the
   Well-Known URIs registry, new CoAP response code, new parameters for
   DOTS signal channel and establishes registries for mappings to CBOR.

10.1.  DOTS Signal Channel UDP and TCP Port Number

   IANA has assigned the port number TBD to the DOTS signal channel
   protocol, for both UDP and TCP.

10.2.  Well-Known 'dots' URI

   This memo registers the 'dots' well-known URI in the Well-Known URIs
   registry as defined by [RFC5785].

   URI suffix: dots

   Change controller: IETF

   Specification document(s): This RFC

   Related information: None

10.3.  CoAP Response Code

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

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

                        Table 4: CoAP Response Code







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10.4.  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.

10.4.1.  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):
      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.

10.4.2.  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



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   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

   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-name
   o  CBOR Key Value: 11
   o  CBOR Major Type: 4
   o  Change Controller: IESG



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   o  Specification Document(s): this document

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

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

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

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

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

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



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   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

   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



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   o  Specification Document(s): this document

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

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

   o  Parameter Name:mitigation-start
   o  CBOR Key Value: 30
   o  CBOR Major Type: 7
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name:target-prefix
   o  CBOR Key Value: 31
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name:client-identifier
   o  CBOR Key Value: 32
   o  CBOR Major Type: 2
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name:alt-server
   o  CBOR Key Value: 33
   o  CBOR Major Type: 2
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name:alt-server-record
   o  CBOR Key Value: 34
   o  CBOR Major Type: 4
   o  Change Controller: IESG
   o  Specification Document(s): this document

   o  Parameter Name:addr
   o  CBOR Key Value: 35
   o  CBOR Major Type: 2
   o  Change Controller: IESG



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   o  Specification Document(s): this document

   o  Parameter Name:ttl
   o  CBOR Key Value: 36
   o  CBOR Major Type: 0
   o  Change Controller: IESG
   o  Specification Document(s): this document

10.5.  YANG Modules

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

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

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

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

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

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

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



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   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".

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:   https://github.com/nttdots/go-dots
   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.



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

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

   Special care should be taken in order to ensure that the activation
   of the proposed mechanism 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, Roman D.  Danyliw,
   Michael Richardson, Ehud Doron, Kaname Nishizuka, Dave Dolson, Liang
   Xia, Jon Shallow, and Gilbert Clark for the discussion and comments.







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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-10 (work in progress),
              October 2017.

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

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

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

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

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

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

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







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

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

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

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

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

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

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

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

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.



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

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

   [I-D.ietf-dots-data-channel]
              Reddy, T., Boucadair, M., Nishizuka, K., Xia, L., Patil,
              P., Mortensen, A., and N. Teague, "Distributed Denial-of-
              Service Open Threat Signaling (DOTS) Data Channel", draft-
              ietf-dots-data-channel-08 (work in progress), November
              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-07 (work in
              progress), October 2017.

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

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

   [I-D.ietf-tls-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.




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

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

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

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

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

   [RFC4787]  Audet, F., Ed. and C. Jennings, "Network Address
              Translation (NAT) Behavioral Requirements for Unicast
              UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
              2007, <https://www.rfc-editor.org/info/rfc4787>.

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

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

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

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







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

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

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

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

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

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

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

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

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

Authors' Addresses







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   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


   Nik Teague
   Verisign, Inc.
   United States

   Email: nteague@verisign.com














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