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Versions: (draft-reddy-dots-transport) 00 01 02 03 04 05 06 07 08 09 10 draft-ietf-dots-signal-channel

DOTS                                                            T. Reddy
Internet-Draft                                                     Cisco
Intended status: Standards Track                            M. Boucadair
Expires: February 19, 2017                                        Orange
                                                                 D. Wing
                                                                P. Patil
                                                                   Cisco
                                                         August 18, 2016


   Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal
                                Channel
                   draft-reddy-dots-signal-channel-00

Abstract

   This document specifies a mechanism that a DOTS client can use to
   signal that a network is under a Distributed Denial-of-Service (DDoS)
   attack to an upstream DOTS server so that appropriate mitigation
   actions are undertaken (including, blackhole, drop, rate-limit, or
   add to watch list) on the suspect traffic.  The document specifies
   the DOTS signal channel including Happy Eyeballs considerations.  The
   specification of the DOTS data channel is elaborated in a companion
   document.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on February 19, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Notational Conventions and Terminology  . . . . . . . . . . .   3
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Happy Eyeballs for DOTS Signal Channel  . . . . . . . . . . .   5
   5.  DOTS Signal Channel . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Mitigation Service Requests . . . . . . . . . . . . . . .   7
       5.2.1.  Convey DOTS Signals . . . . . . . . . . . . . . . . .   8
       5.2.2.  Withdraw a DOTS Signal  . . . . . . . . . . . . . . .  11
       5.2.3.  Retrieving a DOTS Signal  . . . . . . . . . . . . . .  12
       5.2.4.  Efficacy Update from DOTS Client  . . . . . . . . . .  16
   6.  (D)TLS Protocol Profile and Performance considerations  . . .  16
   7.  Mutual Authentication of DOTS Agents & Authorization of DOTS
       Clients . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  20
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  20
     12.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

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

   In many cases, it may not be possible for an enterprise network
   administrators to determine the causes of an attack, but instead just
   realize that certain resources seem to be under attack.  This
   document, which adheres to the DOTS architecture



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   [I-D.ietf-dots-architecture], proposes that, in such cases, the DOTS
   client just inform its DOTS server(s) that the enterprise is under a
   potential attack and that the mitigator monitor traffic to the
   enterprise to mitigate any possible attacks.  This cooperation
   between DOTS agents contributes to ensure a highly automated network
   that is also robust, reliable and secure.

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

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

   This is a companion document to the DOTS data channel specification
   [I-D.reddy-dots-data-channel].

2.  Notational Conventions and Terminology

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

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

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

3.  Solution Overview

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




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

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

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

                                 Figure 1

   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

   In typical deployments, the DOTS client belongs to a different
   administrative domain than the DOTS server.  For example, the DOTS
   client is a web server serving content owned and operated by an
   domain, while the DOTS server is owned and operated by a different
   domain providing DDoS mitigation services.  That domain providing
   DDoS mitigation service might, or might not, also provide Internet
   access service to the website operator.



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   The DOTS server may (not) be co-located with the DOTS mitigator.  In
   typical deployments, the DOTS server belongs to the same
   administrative domain as the mitigator.

   The DOTS client can communicate directly with the DOTS server or
   indirectly via a DOTS gateway.

   This document focuses on the DOTS signal channel.

4.  Happy Eyeballs for DOTS Signal Channel

   DOTS signaling can happen with DTLS [RFC6347] over UDP and TLS
   [RFC5246] over TCP.  A DOTS client can use DNS to determine the IP
   address(es) of a DOTS server or a DOTS client may be provided with
   the list of DOTS server IP addresses.  The DOTS client MUST know a
   DOTS server's domain name; hard-coding the domain name of the DOTS
   server into software is NOT RECOMMENDED in case the domain name is
   not valid or needs to change for legal or other reasons.  The DOTS
   client performs A and/or AAAA record lookup of the domain name and
   the result will be a list of IP addresses, each of which can be used
   to contact the DOTS server using UDP and TCP.

   If an IPv4 path to reach a DOTS server is found, but the DOTS
   server's IPv6 path is not working, a dual-stack DOTS client can
   experience a significant connection delay compared to an IPv4-only
   DOTS client.  The other problem is that if a middlebox between the
   DOTS client and DOTS server is configured to block UDP, the DOTS
   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 3: Happy Eyeballs

   In reference to Figure 3, the DOTS client sends two TCP SYNs and two
   DTLS ClientHello messages at the same time over IPv6 and IPv4.  In
   this example, it is assumed that the IPv6 path is broken and UDP is
   dropped by a middle box but has little impact to the DOTS client
   because there is no long delay before using IPv4 and TCP.  The IPv6
   path and UDP over IPv6 and IPv4 is retried until the DOTS client
   gives up.

5.  DOTS Signal Channel

5.1.  Overview

   Constrained Application Protocol (CoAP) [RFC7252] is used for DOTS
   signal channel (Figure 4).  COAP was designed according to the REST
   architecture, and thus exhibits functionality similar to that of
   HTTP, it is quite straightforward to map from CoAP to HTTP and from
   HTTP to CoAP.  CoAP has been defined to make use of both DTLS over
   UDP and TLS over TCP.  The advantages of COAP are: (1) Like HTTP,
   CoAP is based on the successful REST model, (2) CoAP is designed to
   use minimal resources, (3) CoAP integrates with JSON, CBOR or any
   other data format, (4) asynchronous message exchanges, etc.













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

     Figure 4: Abstract Layering of DOTS signal channel over CoAP over
                                  (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.

   JSON [RFC7159] payloads are used to convey signal channel specific
   payload messages that convey request parameters and response
   information such as errors.

   TBD: Do we want to use CBOR [RFC7049] instead of JSON?

5.2.  Mitigation Service Requests

   The following APIs define the means to convey a DOTS signal from a
   DOTS client to a DOTS server:

   POST requests:  are used to convey the DOTS signal from a DOTS client
      to a DOTS server over the signal channel, possibly traversing a
      DOTS gateway, indicating the DOTS client's need for mitigation, as
      well as the scope of any requested mitigation (Section 5.2.1).
      DOTS gateway act as a CoAP-to-CoAP Proxy (explained in [RFC7252]).

   DELETE requests:  are used by the DOTS client to withdraw the request
      for mitigation from the DOTS server (Section 5.2.2).

   GET requests:  are used by the DOTS client to retrieve the DOTS
      signal(s) it had conveyed to the DOTS server (Section 5.2.3).

   PUT requests:  are used by the DOTS client to convey mitigation
      efficacy updates to the DOTS server (Section 5.2.4).

   Reliability is provided to the POST, DELETE, GET, and PUT requests by
   marking them as Confirmable (CON) messages.  As explained in
   Section 2.1 of [RFC7252], a Confirmable message is retransmitted



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   using a default timeout and exponential back-off between
   retransmissions, until the DOTS server sends an Acknowledgement
   message (ACK) with the same Message ID conveyed from the DOTS client.
   Message transmission parameters are defined in Section 4.8 of
   [RFC7252].  Reliability is provided to the responses by marking them
   as Confirmable (CON) messages.  The DOTS server can either piggback
   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 Sections 5.2.2 in [RFC7252]).

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

5.2.1.  Convey DOTS Signals

   When suffering an attack and desiring DoS/DDoS mitigation, a DOTS
   signal is sent by the DOTS client to the DOTS server.  A POST request
   is used to convey a DOTS signal to the DOTS server (Figure 5).  The
   DOTS server can enable mitigation on behalf of the DOTS client by
   communicating the DOTS client's request to the mitigator and relaying
   any mitigator feedback to the requesting DOTS client.


















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     Header: POST (Code=0.02)
     Uri-Host: "host"
     Uri-Path: ".well-known"
     Uri-Path: "DOTS-signal"
     Uri-Path: "version"
     Content-Type: "application/json"
     {
        "policy-id": "integer",
        "target-ip": "string",
        "target-port": "string",
        "target-protocol": "string",
        "alias": "string"
        "lifetime": "number"
      }


                   Figure 5: POST to convey DOTS signals

   The header fields are described below.

   policy-id:  Identifier of the policy represented using an integer.
      This identifier MUST be unique for each policy bound to the DOTS
      client, i.e. ,the policy-id needs to be unique relative to the
      active policies with 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 or prefixes under attack.  IP
      addresses and prefixes are separated by commas.  Prefixes are
      represented using CIDR notation [RFC4632].  This is an optional
      attribute.

   target-port:  A list of ports under attack.  Ports are separated by
      commas and port number range (using "-").  For TCP, UDP, SCTP, or
      DCCP: the range of ports (e.g., 1024-65535).  This is an optional
      attribute.

   target-protocol:  A list of protocols under attack.  Valid protocol
      values include tcp, udp, sctp, and dccp.  Protocol values are
      separated by commas.  This is an optional attribute.

   alias:  Name of the alias (see Section 3.1.1 in [I-D.reddy-dots-data-
      channel).  This is an optional attribute.

   lifetime:   Lifetime of the mitigation request policy in seconds.
      Upon the expiry of this lifetime, and if the request is not
      refreshed, the mitigation request is removed.  The request can be



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      refreshed by sending the same request again.  The default lifetime
      of the policy is 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 policy where the client has
      unexpectedly quit in a timely manner.  A lifetime of zero
      indicates indefinite lifetime for the mitigation request.  The
      server MUST always indicate the actual lifetime in the response.
      This is an optional attribute in the request.

   The relative order of two rules is determined by comparing their
   respective policy identifiers.  The rule with lower numeric policy
   identifier value has higher precedence (and thus will match before)
   than the rule with higher numeric policy identifier value.

   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 and 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' field could be split into multiple lists and each list conveyed
   in a new POST 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.

   Figure 6 shows a POST request to signal that ports 80, 8080, and 443
   on the servers 2002:db8:6401::1 and 2002:db8:6401::2 are being
   attacked.













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     Header: POST (Code=0.02)
     Uri-Host: "www.example.com"
     Uri-Path: ".well-known"
     Uri-Path: "v1"
     Uri-Path: "DOTS-signal"
     Content-Type: "application/json"
     {
       "policy-id":123321333242,
       "target-ip":[
           "2002:db8:6401::1",
           "2002:db8:6401::2"
       ],
       "target-port":[
           "80",
           "8080",
           "443"
       ],
       "target-protocol":"tcp"
     }

                      Figure 6: POST for DOTS signal

   The DOTS server indicates the result of processing the POST request
   using CoAP response codes.  CoAP 2xx codes are success, CoAP 4xx
   codes are some sort of invalid requests and 5xx codes are returned if
   the DOTS server has erred or is incapable of performing the
   mitigation.  Response code 2.01 (Created) will be returned in the
   response if the DOTS server has accepted the mitigation request and
   will try to mitigate the attack.  If the request is missing one or
   more mandatory attributes, then 4.00 (Bad Request) will be returned
   in the response or if the request contains invalid or unknown
   parameters then 4.02 (Invalid query) will be returned in the
   response.  The CoAP response will include the JSON body received in
   the request.

5.2.2.  Withdraw a DOTS Signal

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












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     Header: DELETE (Code=0.04)
     Uri-Host: "host"
     Uri-Path: ".well-known"
     Uri-Path: "version"
     Uri-Path: "DOTS-signal"
     Content-Type: "application/json"
     {
        "policy-id": "number"
     }

                      Figure 7: Withdraw DOTS signal

   If the DOTS server does not find the policy number conveyed in the
   DELETE request in its policy state data, then it responds with a 4.04
   (Not Found) error response code.  The DOTS server successfully
   acknowledges a DOTS client's request to withdraw the DOTS signal
   using 2.02 (Deleted) response code, and ceases mitigation activity as
   quickly as possible.

5.2.3.  Retrieving a DOTS Signal

   A GET request is used to retrieve information and status of a DOTS
   signal from a DOTS server (Figure 8).  If the DOTS server does not
   find the policy number conveyed in the GET request in its policy
   state data, then it responds with a 4.04 (Not Found) error response
   code.

























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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: "version"
     Uri-Path: "DOTS-signal"
     Uri-Path: "list"
     Observe : 0

   2) To retrieve a specific DOTS signal signaled by the DOTS client.
      The policy information 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: "version"
     Uri-Path: "DOTS-signal"
     Uri-Path: "policy-id value"
     Observe : 0


                    Figure 8: GET to retrieve the rules

   Figure 9 shows the response of all the active policies on the DOTS
   server.
























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   {
     "policy-data":[
       {
         "policy-id":123321333242,
         "target-protocol":"tcp",
         "lifetime":3600,
         "status":"mitigation in progress"
       },
       {
         "policy-id":123321333244,
         "target-protocol":"udp",
         "lifetime":1800,
         "status":"mitigation complete"
       },
       {
         "policy-id":123321333245,
         "target-protocol":"tcp",
         "lifetime":1800,
         "status":"attack stopped"
       }
     ]
   }

                          Figure 9: Response body

   The various possible values of status field are explained below:

   mitigation in progress:  Attack mitigation is in progress (e.g.,
      changing the network path to re-route the inbound traffic to DOTS
      mitigator).

   mitigation complete:  Attack is successfully mitigated (e.g., attack
      traffic is dropped).

   attack stopped:  Attack has stopped and the DOTS client can withdraw
      the mitigation request.

   The observe option defined in [RFC7641] extends the CoAP core
   protocol with a mechanism for a CoAP client to "observe" a resource
   on a CoAP server: the client retrieves a representation of the
   resource and requests this representation be updated by the server as
   long as the client is interested in the resource.  A DOTS client
   conveys the observe option set to 0 in the GET request to receive
   unsolicited notifications of attack mitigation status from the DOTS
   server.  Unidirectional notifications within the bidirectional signal
   channel allows unsolicited message delivery, enabling asynchronous
   notifications between the agents.  A DOTS client that is no longer
   interested in receiving notifications from the DOTS server can simply



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   "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.

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

           Figure 10: Notifications of attack mitigation status

5.2.3.1.  Mitigation Status

   A DOTS client retrieves the information about a DOTS signal at
   frequent intervals to determine the status of an attack.  If the DOTS
   server has been able to mitigate the attack and the attack has
   stopped, the DOTS server indicates as such in the status, and the
   DOTS client recalls the mitigation request.

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

   While DDoS mitigation is active, a DOTS client MAY frequently
   transmit DOTS mitigation efficacy updates to the relevant DOTS
   server.  An PUT request (Figure 11) is used to convey the mitigation
   efficacy update to the DOTS server.  The PUT request MUST include all
   the header fields used in the POST request to convey the DOTS signal
   (Section 5.2.1).  If the DOTS server does not find the policy number
   conveyed in the PUT request in its policy state data, it responds
   with a 4.04 (Not Found) error response code.

      Header: PUT (Code=0.03)
      Uri-Host: "host"
      Uri-Path: ".well-known"
      Uri-Path: "version"
      Uri-Path: "DOTS-signal"
      Uri-Path: "policy-id value"
      Content-Type: "application/json"
      {
        "target-ip": "string",
        "target-port": "string",
        "target-protocol": "string",
        "lifetime": "number",
        "attack-status": "string"
       }

                        Figure 11: Efficacy Update

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

   in-progress:  DOTS client determines that it is still under attack.

   terminated:  Attack is successfully mitigated (e.g., attack traffic
      is dropped).

6.  (D)TLS Protocol Profile and Performance considerations

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

   There are known attacks on (D)TLS, such as machine-in-the-middle and
   protocol downgrade.  These are general attacks on (D)TLS and not
   specific to DOTS over (D)TLS; please refer to the (D)TLS RFCs for
   discussion of these security issues.  DOTS agents MUST adhere to the
   (D)TLS implementation recommendations and security considerations of
   [RFC7525] except with respect to (D)TLS version.  Since encryption of



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   DOTS using (D)TLS is virtually a green-field deployment DOTS agents
   MUST implement only (D)TLS 1.2 or later.

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

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

   o  While the communication to the DOTS server is quiescent, the DOTS
      client MAY probe the server to ensure it has maintained
      cryptographic state.  Such probes can also keep alive firewall or
      NAT bindings.  This probing reduces the frequency of needing a new
      handshake when a DOTS signal needs to be conveyed to the DOTS
      server.

      *  A (D)TLS heartbeat [RFC6520] verifies the DOTS server still has
         DTLS state by returning a DTLS message.  If the server has lost
         state, it returns a DTLS Alert.  Upon receipt of an
         unauthenticated DTLS Alert, the DTLS client validates the Alert
         is within the replay window (Section 4.1.2.6 of [RFC6347]).  It
         is difficult for the DTLS client to validate the DTLS Alert was
         generated by the DTLS server in response to a request or was
         generated by an on- or off-path attacker.  Thus, upon receipt
         of an in-window DTLS Alert, the client SHOULD continue re-
         transmitting the DTLS packet (in the event the Alert was
         spoofed), and at the same time it SHOULD initiate DTLS session
         resumption.

      *  TLS runs over TCP, so a simple probe is a 0-length TCP packet
         (a "window probe").  This verifies the TCP connection is still
         working, which is also sufficient to prove the server has
         retained TLS state, because if the server loses TLS state it
         abandons the TCP connection.  If the server has lost state, a
         TCP RST is returned immediately.

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

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

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




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   o  Cached Information Extension [I-D.ietf-tls-cached-info] 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.  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) |<-----------------+    |     |
 |   +---------------+                  +    |     |                example.net domain
 |                                      V    V     |
 |                               +-------------+   |              +---------------+
 |  +--------------+             |             |   |              |               |
 |  |   Guest      +<-----x----->+             +<---------------->+    DOTS       |
 |  | (DOTS client)|             |   DOTS      |   |              |    Server     |
 |  +--------------+             |   Gateway   |   |              |               |
 |                               +----+--------+   |              +---------------+
 |                                    ^            |
 |                                    |            |
 |   +----------------+               |            |
 |   | DDOS detector  |               |            |
 |   | (DOTS client)  +<--------------+            |
 |   +----------------+                            |
 |                                                 |
 +-------------------------------------------------+

   Figure 12: Example of Authentication and Authorization of DOTS Agents

   In the example depicted in Figure 12, 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



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   client, it communicates with the AAA server in the 'example.com'
   domain to determine if the DOTS client is authorized to request DDOS
   mitigation.  If the DOTS client is not authorized, a 4.01
   (Unauthorized) is returned in the response to the DOTS client.  In
   this example, the DOTS gateway only allows the application server and
   DDOS detector to request DDOS mitigation, but does not permit the
   user of type 'guest' to request DDOS mitigation.

   Also, DOTS gateway and DOTS server MUST perform mutual authentication
   using certificates.  A DOTS server will only allow a DOTS gateway
   with a certificate for a particular domain to request mitigation for
   that domain.  In reference to Figure 12, the DOTS server only allows
   the DOTS gateway to request mitigation for 'example.com' domain and
   not for other domains.

8.  IANA Considerations

   TODO

   [TBD: DOTS WG will probably have to do something similar to
   https://tools.ietf.org/html/rfc7519#section-10, create JSON DOTS
   claim registry and register the JSON attributes defined in this
   specification].

9.  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.

   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.

   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).




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   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.

10.  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

11.  Acknowledgements

   Thanks to Christian Jacquenet, Roland Dobbins, Andrew Mortensen,
   Roman D.  Danyliw, and Gilbert Clark for the discussion and comments.

12.  References

12.1.  Normative References

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

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

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

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







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

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

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

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

12.2.  Informative References

   [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-00 (work in progress), July 2016.

   [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-02 (work in
              progress), July 2016.

   [I-D.ietf-dots-use-cases]
              Dobbins, R., Fouant, S., Migault, D., Moskowitz, R.,
              Teague, N., and L. Xia, "Use cases for DDoS Open Threat
              Signaling", draft-ietf-dots-use-cases-01 (work in
              progress), March 2016.

   [I-D.ietf-tls-cached-info]
              Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", draft-ietf-tls-
              cached-info-23 (work in progress), May 2016.




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   [I-D.ietf-tls-falsestart]
              Langley, A., Modadugu, N., and B. Moeller, "Transport
              Layer Security (TLS) False Start", draft-ietf-tls-
              falsestart-02 (work in progress), May 2016.

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

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

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

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

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

   [RFC6520]  Seggelmann, R., Tuexen, M., and M. Williams, "Transport
              Layer Security (TLS) and Datagram Transport Layer Security
              (DTLS) Heartbeat Extension", RFC 6520,
              DOI 10.17487/RFC6520, February 2012,
              <http://www.rfc-editor.org/info/rfc6520>.

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

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

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <http://www.rfc-editor.org/info/rfc7159>.





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

Authors' Addresses

   Tirumaleswar Reddy
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: tireddy@cisco.com


   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Dan Wing
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, California  95134
   USA

   Email: dwing@cisco.com


   Prashanth Patil
   Cisco Systems, Inc.

   Email: praspati@cisco.com














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