DOTS                                                            T. Reddy
Internet-Draft                                                   D. Wing
Intended status: Standards Track                                P. Patil
Expires: December 23, 2016                                     M. Geller
                                                                   Cisco
                                                            M. Boucadair
                                                                  Orange
                                                            R. Moskowitz
                                                          HTT Consulting
                                                           June 21, 2016


                      Co-operative DDoS Mitigation
                     draft-reddy-dots-transport-04

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
   both DOTS signal and data channels.  Happy Eyeballs considerations
   for the DOTS signal channel are also elaborated.

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 December 23, 2016.

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  . . . . . . . . . . . . . . . . . . .   3
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Happy Eyeballs for DOTS Signal Channel  . . . . . . . . . . .   6
   5.  DOTS Signal Channel . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  Mitigation Service Requests . . . . . . . . . . . . . . .   8
       5.2.1.  Convey DOTS Signals . . . . . . . . . . . . . . . . .   9
       5.2.2.  Withdraw a DOTS Signal  . . . . . . . . . . . . . . .  11
       5.2.3.  Retrieving a DOTS Signal  . . . . . . . . . . . . . .  12
       5.2.4.  Efficacy Update from DOTS Client  . . . . . . . . . .  15
   6.  DOTS Data Channel . . . . . . . . . . . . . . . . . . . . . .  15
     6.1.  Filtering Rules . . . . . . . . . . . . . . . . . . . . .  16
       6.1.1.  Install Filtering Rules . . . . . . . . . . . . . . .  16
       6.1.2.  Remove Filtering Rules  . . . . . . . . . . . . . . .  18
       6.1.3.  Retrieving Installed Filtering Rules  . . . . . . . .  18
   7.  (D)TLS Protocol Profile and Performance considerations  . . .  19
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     11.2.  Informative References . . . . . . . . . . . . . . . . .  22
   Appendix A.  BGP  . . . . . . . . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

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 client, a router, a firewall, or an entire network, etc.





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   In a lot of cases, it may not be possible for an enterprise to
   determine the cause for an attack, but instead just realize that
   certain resources seem to be under attack.  The document proposes
   that, in such cases, the DOTS client just inform the DOTS server that
   the enterprise is under a potential attack and that the Mitigator
   monitor traffic to the enterprise to mitigate any possible attack.
   This document also describes a means for an enterprise, which act as
   DOTS clients, to dynamically inform its DOTS server of the IP
   addresses or prefixes that are causing DDoS.  A Mitigator can use
   this information to discard flows from such IP addresses reaching the
   customer network.

   The proposed mechanism can also be used between applications from
   various vendors that are deployed within the same network, some of
   them are responsible for monitoring and detecting attacks while
   others are responsible for enforcing policies on appropriate network
   elements.  This cooperations contributes to a ensure a highly
   automated network that is also robust, reliable and secure.  The
   advantage of this mechanism is that the DOTS server can provide
   protection to the DOTS client from bandwidth-saturating DDoS traffic.

   How a Mitigator determines which network elements should be modified
   to install appropriate filtering rules is out of scope.  A variety of
   mechanisms and protocols (including NETCONF) may be considered to
   exchange information through a communication interface between the
   server and these underlying elements; the selection of appropriate
   mechanisms and protocols to be invoked for that interfaces is
   deployment-specific.

   Terminology and protocol requirements for co-operative DDoS
   mitigation are obtained from [I-D.ietf-dots-requirements].

2.  Notational Conventions

   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].

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 an
   application uses these resources to offer its intended task in the
   most efficient fashion.  However, an attacker may be able to prevent
   the 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, some of the possible
   arrangements to mitigate the attack are:

   o  If a DOTS client determines it is under an attack, the DOTS client
      can notify the DOTS server using the DOTS signal that it is under
      a potential attack and request that the DOTS server take
      precautionary measures to mitigate the attack.  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.

   o  If a DOTS client determines it is under an attack, the DOTS client
      can notify its servicing router (DOTS gateway) using the DOTS
      signal that it is under a potential attack and request that the
      DOTS gateway take precautionary measures to mitigate the attack.
      The DOTS gateway propagates the DOTS signal to a DOTS server.

      The DOTS server can enable mitigation on behalf of the DOTS
      gateway by communicating the DOTS gateway's request to the
      mitigator and relaying any mitigator feedback to the DOTS gateway
      which in turn propagates the feedback to the requesting DOTS
      client.

      The DOTS client must authenticate itself to the DOTS gateway,
      which in turn authenticates itself to a DOTS server, creating a
      two-link chain of transitive authentication between the DOTS
      client and the DOTS server.

   o  If a network resource detects a potential DDoS attack from a set
      of IP addresses, the network resource (DOTS client) informs its
      servicing router (DOTS gateway) of all suspect IP addresses that
      need to be blocked or black-listed for further investigation.

      The DOTS client could also specify a list of protocols and ports
      in the black-list rule.  That DOTS gateway in-turn propagates the
      black-listed IP addresses to the DOTS server and the DOTS server
      blocks traffic from these IP addresses to the DOTS client thus
      reducing the effectiveness of the attack.



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      The DOTS client periodically queries the DOTS server to check the
      counters mitigating the attack.  If the DOTS client receives a
      response that the counters have not incremented then it can
      instruct the black-list rules to be removed.  If a blacklisted
      IPv4 address is shared by multiple subscribers, then the side
      effect of applying the black-list rule will be that traffic from
      non-attackers will also be blocked by the access network
      [RFC6269].

   An example of network diagram showing a deployment of these elements
   is shown in Figure 1.  In this example, the DOTS server 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.

   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.




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

4.  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 [RFC6347] with the DOTS
   server and will, then, have to fall back to TLS over TCP [RFC5246]
   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.  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

   JSON [RFC7159] payloads is 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 [RFC 7049] 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
   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.




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   TBD: Do we want any of the above requests to be Non-confirmable ?

5.2.1.  Convey DOTS Signals

   A POST request is used to convey a DOTS signal to the DOTS server
   (Figure 5).

  POST {scheme}://{host}:{port}/.well-known/{version}/{URI suffix for DOTS signal}
  Accept: application/json
  Content-Format: application/json
  {
     "policy-id": "number",
     "target-ip": "string",
     "target-port": "string",
     "target-protocol": "string",
     "lifetime": "number"
   }

                   Figure 5: POST to convey DOTS signals

   The header fields are described below.

   policy-id:  Identifier of the policy represented using a number.
      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.  This is
      an optional attribute.

   target-port:  A list of ports under attack.  This is an optional
      attribute.

   target-protocol:  A list of protocols under attack.  Valid protocol
      values include tcp, udp, sctp, and dccp.  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
      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



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      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.

   If the DOTS server is not able to respond immediately to a POST
   request carried in a Confirmable message, it simply responds with an
   Empty Acknowledgement message so that the DOTS client can stop
   retransmitting the request.  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]).

   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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     POST coaps://www.example.com/.well-known/v1/DOTS signal
     Accept: application/json
     Content-Format: 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 request 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).

  DELETE {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}
  Accept: application/json
  Content-Format: 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



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   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.

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

GET {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}/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.

GET {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}/<policy-id number>
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-prtoocol":"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.




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                       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.

  PUT {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}/<policy-id number>
  Accept: application/json
  Content-Format: 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.  DOTS Data Channel

   The data channel is intended to be used for bulk data exchanges and
   requires a reliable transport, CoAP over TLS over TCP is used for
   data channel.

   JSON payloads is used to convey both filtering rules as well as data
   channel specific payload messages that convey request parameters and
   response information such as errors.  All data channel URIs defined
   in this document, and in subsequent documents, MUST NOT have a URI
   containing "/DOTS signal".

   One of the possible arrangements for DOTS client to signal filtering
   rules to a DOTS server via the DOTS gateway is discussed below:




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   The DOTS conveys the black-list rules to the DOTS gateway.  The DOTS
   gateway validates if the DOTS client is authorized to signal the
   black-list rules and if the client is authorized propagates the rules
   to the DOTS server.  Likewise, the DOTS server validates if the DOTS
   gateway is authorized to signal the black-list rules.  To create or
   purge filters, the DOTS client sends CoAP requests to the DOTS
   gateway.  The DOTS gateway acts as a proxy, validates the rules and
   proxies the requests containing the black-listed IP addresses to a
   DOTS server.  When the DOTS gateway receives the associated CoAP
   response from the DOTS server, it propagates the response back to the
   DOTS client.  If an attack is detected by the DOTS gateway then it
   can act as a DOTS client and signal the black-list rules to the DOTS
   server.  The DOTS gateway plays the role of both client and server.

6.1.  Filtering Rules

   The following APIs define means for a DOTS client to configure
   filtering rules on a DOTS server.

6.1.1.  Install Filtering Rules

   An POST request is used to push filtering rules to a DOTS server
   (Figure 12).

  POST {scheme}://{host}:{port}/.well-known/{version}/{URI suffix for filtering}
  Accept: application/json
  Content-Format: application/json
  {
     "policy-id": "number",
     "traffic-protocol": "string",
     "source-protocol-port": "string",
     "destination-protocol-port": "string",
     "destination-ip": "string",
     "source-ip": "string",
     "lifetime": "number",
     "traffic-rate" : "number"
   }

                Figure 12: POST to install filtering rules

   The header fields are described below:

   policy-id:  Identifier of the policy represented using a number.
      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 client.  This document does not make any




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      assumption about how this identifier is generated.  This is an
      mandatory attribute.

   traffic-protocol:   Valid protocol values include tcp, udp, sctp, and
      dccp.  This is an mandatory attribute.

   source-protocol-port:   The source port number, port number range
      (using "-").  For TCP, UDP, SCTP, or DCCP: the source range of
      ports (e.g., 1024-65535).  This is an optional attribute.

   destination-protocol-port:   The destination port number, port number
      range (using "-").  For TCP, UDP, SCTP, or DCCP: the destination
      range of ports (e.g., 443-443).  This information is useful to
      avoid disturbing a group of customers when address sharing is in
      use [RFC6269].  This is an optional attribute.

   destination-ip:   The destination IP address, IP addresses separated
      by commas, or prefixes using "/" notation.  This is an optional
      attribute.

   source-ip:   The source IP addresses, IP addresses separated by
      commas, or prefixes using "/" notation.  This is an optional
      attribute.

   lifetime:   Lifetime of the rule in seconds.  Upon the expiry of this
      lifetime, and if the request is not refreshed, this particular
      rule is removed.  The rule can be refreshed by sending the same
      message again.  The default lifetime of the rule 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 rule
      where the client has unexpectedly quit in a timely manner.  A
      lifetime of zero indicates indefinite lifetime for the rule.  The
      server MUST always indicate the actual lifetime in the response.
      This is an optional attribute in the request.

   traffic-rate:   This is the allowed traffic rate in bytes per second
      indicated in IEEE floating point [IEEE.754.1985] format.  The
      value 0 indicates all traffic for the particular flow to be
      discarded.  This is a mandatory attribute.

   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.

   Figure 13 shows a POST request to block traffic from attacker IPv6
   prefix 2001:db8:abcd:3f01::/64 to network resource using IPv6 address
   2002:db8:6401::1 to operate a server on TCP port 443.



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     POST coaps://www.example.com/.well-known/v1/filter
     Accept: application/json
     Content-Format: application/json
      {
        "policy-id": 123321333242,
        "traffic-protocol": "tcp",
        "source-protocol-port": "0-65535",
        "destination-protocol-port": "443",
        "destination-ip": "2001:db8:abcd:3f01::/64",
        "source-ip": "2002:db8:6401::1",
        "lifetime": 1800,
        "traffic-rate": 0
      }

                Figure 13: POST to Install Black-list Rules

6.1.2.  Remove Filtering Rules

   A DELETE request is used to delete filtering rules from a DOTS server
   (Figure 14).

  DELETE {scheme}://{host}:{port}/.well-known/{URI suffix for filtering}
  Accept: application/json
  Content-Format: application/json
   {
     "policy-id": "number"
   }

                   Figure 14: DELETE to remove the rules

6.1.3.  Retrieving Installed Filtering Rules

   A GET request is used to retrieve filtering rules from a DOTS server.

   Figure 15 shows an example to retrieve all the black-lists rules
   programmed by the DOTS client while Figure 16 shows an example to
   retrieve specific black-list rules programmed by the DOTS client.

   GET {scheme}://{host}:{port}/.well-known/{URI suffix for filtering}

                 Figure 15: GET to retrieve the rules (1)










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   GET {scheme}://{host}:{port}/.well-known/{URI suffix for filtering}
   Accept: application/json
   Content-Format: application/json
   {
      "policy-id": "number"
   }

                 Figure 16: GET to retrieve the rules (2)

   TODO: show response

7.  (D)TLS Protocol Profile and Performance considerations

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

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

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

   o  DOTS 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 want to 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



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         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.

   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.

8.  IANA Considerations

   TODO

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 ciphersuite 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, 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



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   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).

   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.  Acknowledgements

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

11.  References

11.1.  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>.

11.2.  Informative References

   [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-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.

   [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.

   [IEEE.754.1985]
              Institute of Electrical and Electronics Engineers,
              "Standard for Binary Floating-Point Arithmetic", August
              1985.

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



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

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

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

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
              <http://www.rfc-editor.org/info/rfc5575>.

   [RFC6269]  Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
              P. Roberts, "Issues with IP Address Sharing", RFC 6269,
              DOI 10.17487/RFC6269, June 2011,
              <http://www.rfc-editor.org/info/rfc6269>.

   [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>.

   [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>.





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Appendix A.  BGP

   BGP defines a mechanism as described in [RFC5575] that can be used to
   automate inter-domain coordination of traffic filtering, such as what
   is required in order to mitigate DDoS attacks.  However, support for
   BGP in an access network does not guarantee that traffic filtering
   will always be honored.  Since a DOTS client will not receive an
   acknowledgment for the filtering request, the DOTS client should
   monitor and apply similar rules in its own network in cases where the
   DOTS server is unable to enforce the filtering rules.  In addition,
   enforcement of filtering rules of BGP on Internet routers are usually
   governed by the maximum number of data elements the routers can hold
   as well as the number of events they are able to process in a given
   unit of time.

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


   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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   Mike Geller
   Cisco Systems, Inc.
   3250
   Florida  33309
   USA

   Email: mgeller@cisco.com


   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Robert Moskowitz
   HTT Consulting
   Oak Park, MI  42837
   United States

   Email: rgm@htt-consult.com




























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