Co-operative DDoS Mitigation
draft-reddy-dots-transport-02

DOTS                                                            T. Reddy
Internet-Draft                                                   D. Wing
Intended status: Standards Track                                P. Patil
Expires: August 12, 2016                                       M. Geller
                                                                   Cisco
                                                            M. Boucadair
                                                          France Telecom
                                                            R. Moskowitz
                                                          HTT Consulting
                                                        February 9, 2016

                      Co-operative DDoS Mitigation
                     draft-reddy-dots-transport-02

Abstract

   This document discusses mechanisms that a DOTS client can use, when
   it detects a potential Distributed Denial-of-Service (DDoS) attack,
   to signal that the DOTS client is under an attack or request an
   upstream DOTS server to perform inbound filtering in its ingress
   routers for traffic that the DOTS client wishes to drop.  The DOTS
   server can then undertake appropriate actions (including, blackhole,
   drop, rate-limit, or add to watch list) on the suspect traffic to the
   DOTS client, thus reducing the effectiveness of the attack.

Status of This Memo

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   This Internet-Draft will expire on August 12, 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   3
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Happy Eyeballs  . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Protocol for Signal Channel: HTTP REST  . . . . . . . . . . .   7
     5.1.  Mitigation service request  . . . . . . . . . . . . . . .   7
       5.1.1.  Convey DOTS signal  . . . . . . . . . . . . . . . . .   7
       5.1.2.  Recall DOTS signal  . . . . . . . . . . . . . . . . .   9
       5.1.3.  Retrieving DOTS signal  . . . . . . . . . . . . . . .   9
     5.2.  REST  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
       5.2.1.  Filtering Rules . . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Appendix A.  BGP  . . . . . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

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.
   The reader may refer, for example, to [REPORT] that reports the
   following:

   o  Very large DDoS attacks above the 100 Gbps threshold are
      experienced.

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   o  DDoS attacks against customers remain the number one operational
      threat for service providers, with DDoS attacks against
      infrastructures being the top concern for 2014.

   o  Over 60% of service providers are seeing increased demand for DDoS
      detection and mitigation services from their customers (2014),
      with just over one-third seeing the same demand as in 2013.

   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 DOTS server
   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 DOTS server 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 the proposed mechanism is that the DOTS server can
   provide protection to the DOTS client from bandwidth-saturating DDoS
   traffic.

   How a DOTS server 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].

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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.

   TCP DDoS SYN-flood is a memory-exhaustion attack on the victim and
   ACK-flood is a CPU exhaustion attack on the victim.  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, 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 relay) of
   all suspect IP addresses that need to be blocked or black-listed for
   further investigation.  DOTS client could also specify protocols and
   ports in the black-list rule.  That DOTS relay 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.  The DOTS client
   periodically queries the DOTS server to check the counters mitigating
   the attack.  If the DOTS client receives 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.

   If a DOTS client cannot determine the IP address(s) that are causing
   the attack, but is under an attack nonetheless, the DOTS client can
   just notify the DOTS server that it is under a potential attack and
   request that the DOTS server take precautionary measures to mitigate
   the attack.

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4.  Happy Eyeballs

   If a DOTS server IPv4 path is working, but the DOTS server's IPv6
   path is not working, a dual-stack DOTS client can experience
   significant connection delay compared to an IPv4-only DOTS client.
   The other problem is that if a middle box between the DOTS client and
   server is configured to block UDP, DOTS client will fail to establish
   DTLS session [RFC6347] with the DOTS server and will have to fall
   back to TLS over TCP [RFC5246] incurring significant connection
   delay.  [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 MUST try
   connecting to the DOTS server using both IPv6 and IPv4, and MUST 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 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).

   TBD: How does the DOTS client discover the DOTS server (use DNS-SD) ?

   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 1: Happy Eyeballs

   In the diagram above, the DOTS client sends two TCP SYNs and two DTLS
   ClientHello messages at the same time over IPv6 and IPv4.  In the
   diagram, 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

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   delay before using IPv4 and TCP.  The IPv6 path and UDP over IPv6 and
   IPv4 is retried until the DOTS client gives up.

   DOTS client and server can also use the following techniques to
   reduce delay to convey DOTS signal:

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

   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 server.

      *  A DTLS heartbeat [RFC6520] verifies the 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 un-
         authenicated 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.

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5.  Protocol for Signal Channel: HTTP REST

   A DOTS client can use RESTful APIs discussed in this section to
   signal/inform a DOTS server of an attack or any desired IP filtering
   rules.

5.1.  Mitigation service request

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

5.1.1.  Convey DOTS signal

   An HTTP POST request will be used to convey DOTS signal to the DOTS
   server.

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

                   Figure 2: POST to convey DOTS signal

   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 and used as an opaque value by the server.
      This document does not make any assumption about how this
      identifier is generated.  This is an mandatory attribute.

   target-ip:  A list of 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.

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   Note: administrative-related clauses may be included as part of the
   request (such a contract Identifier or a customer identifier).  Those
   clauses are out of scope of this document.

   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.

   The following example shows POST request to signal that a Web-Service
   is under attack.

     POST https://www.example.com/.well-known/v1/DOTS signal
     Accept: application/json
     Content-type: application/json
      {
        "policy-id": 123321333242,
        "target-ip": {"2002:db8:6401::1", "2002:db8:6401::1"},
        "target-port": {"80", "8080", "443"},
        "target-protocol": "tcp",
      }

                       Figure 3: POST to signal SOS

   The DOTS server indicates the result of processing the POST request
   using HTTP response codes.  HTTP 2xx codes are success whereas HTTP
   4xx codes are some sort of invalid request.  If the request is

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   missing one or more mandatory attributes then 400 (Bad Request) will
   be returned in the response or if the request contains invalid or
   unknown parameters then 400 (Invalid query) will be returned in the
   response.  The HTTP response will include the JSON body received in
   the request.

5.1.2.  Recall DOTS signal

   An HTTP DELETE request will be used to delete an DOTS signal signaled
   to the DOTS server.  If the DOTS server does not find the policy
   number conveyed in the DELETE request in its policy state data then
   it responds with 404 HTTP error response code.

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

                           Figure 4: Recall SOS

5.1.3.  Retrieving DOTS signal

   An HTTP GET request will be used to retrieve an DOTS signal signaled
   to the DOTS server.  If the DOTS server does not find the policy
   number conveyed in the GET request in its policy state data then it
   responds with 404 HTTP error response code.

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

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

  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}
  Accept: application/json
  Content-type: application/json
   {
     "policy-id": number
   }

                    Figure 5: GET to retrieve the rules

   The following example shows the response of all the active policies
   on the DOTS server.

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      {
        "policy-data": [
            { "policy-id": 123321333242, "target-protocol": "tcp"},
            { "policy-id": 123321333244, "target-protocol": "udp"},
        ]
      }

                          Figure 6: Response body

5.2.  REST

   A DOTS client could use HTTPS to provision and manage filters on the
   DOTS server.  The DOTS client authenticates itself to the DOTS relay,
   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.  The DOTS relay validates if the DOTS client is
   authorized to signal the black-list rules.  Likewise, the DOTS server
   validates if the DOTS relay is authorized to signal the black-list
   rules.  To create or purge filters, the DOTS client sends HTTP
   requests to the DOTS relay.  The DOTS relay acts as an HTTP proxy,
   validates the rules and proxies the HTTP requests containing the
   black-listed IP addresses to the DOTS server.  When the DOTS relay
   receives the associated HTTP response from the HTTP server, it
   propagates the response back to the DOTS client.

   If an attack is detected by the DOTS relay then it can act as a HTTP
   client and signal the black-list rules to the DOTS server.  Thus the
   DOTS relay plays the role of both HTTP client and HTTP proxy.

     Network
     Resource        CPE router        Access network
   (DOTS client)    (DOTS relay)       (DOTS server)       __________
   +-----------+    +----------+       +-------------+    /          \
   |           |____|          |_______|             |___ | Internet |
   |HTTP Client|    |HTTP Proxy|       | HTTP Server |    |          |
   |           |    |          |       |             |    |          |
   +-----------+    +----------+       +-------------+    \__________/

                                 Figure 7

   JSON [RFC7159] payloads can be used to convey both filtering rules as
   well as protocol-specific payload messages that convey request
   parameters and response information such as errors.

   The figure above explains the protocol with a DOTS relay.  The
   protocol is equally applicable to scenarios where a DOTS client
   directly talks to the DOTS server.

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5.2.1.  Filtering Rules

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

5.2.1.1.  Install filtering rules

   An HTTP POST request will be used to push filtering rules to the DOTS
   server.

  POST {scheme}://{host}:{port}/.well-known/{version}/{URI suffix for filtering}
  Accept: application/json
  Content-type: 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 8: 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 and used as an opaque value by the server.
      This document does not make any 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:   For TCP or UDP or SCTP or DCCP: the source
      range of ports (e.g., 1024-65535).  This is an optional attribute.

   destination-protocol-port:   For TCP or UDP or 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.

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   destination-ip:   The destination IP addresses or prefixes.  This is
      an optional attribute.

   source-ip:   The source IP addresses or prefixes.  This is an
      optional attribute.

   lifetime:   Lifetime of the policy in seconds.  Indicates the
      validity of a rule.  Upon the expiry of this lifetime, and if the
      request is not reiterated, the rule will be withdrawn at the
      upstream network.  The request can be reiterated by sending the
      same message again.  The server always indicates the actual
      lifetime in the response.  A null value is not allowed.  This is
      an mandatory attribute.

   traffic-rate:   This field carries the rate information in IEEE
      floating point [IEEE.754.1985] format, units being bytes per
      second.  A traffic-rate of '0' should result on all traffic for
      the particular flow to be discarded.  This is an 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.

   Note: administrative-related clauses may be included as part of the
   request (such a contract Identifier or a customer identifier).  Those
   clauses are out of scope of this document.

   The following example shows 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 provide HTTPS web service.

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

                Figure 9: POST to install black-list rules

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5.2.1.2.  Remove filtering rules

   An HTTP DELETE request will be used to delete filtering rules
   programmed on the DOTS server.

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

                   Figure 10: DELETE to remove the rules

5.2.1.3.  Retrieving installed filtering rules

   An HTTP GET request will be used to retrieve filtering rules
   programmed on the DOTS server.

  1) To retrieve all the black-lists rules programmed by the DOTS client.

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

  2) To retrieve specific black-list rules programmed by the DOTS cient.

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

                   Figure 11: GET to retrieve the rules

6.  IANA Considerations

   TODO

7.  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.

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   If TCP is used between DOTS agents, attacker will 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).

   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.

8.  Acknowledgements

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

9.  References

9.1.  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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   [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>.

9.2.  Informative References

   [I-D.ietf-dots-requirements]
              Mortensen, A., Moskowitz, R., and T. Reddy, "DDoS Open
              Threat Signaling Requirements", draft-ietf-dots-
              requirements-00 (work in progress), October 2015.

   [I-D.ietf-tls-cached-info]
              Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", draft-ietf-tls-
              cached-info-22 (work in progress), January 2016.

   [I-D.ietf-tls-falsestart]
              Langley, A., Modadugu, N., and B. Moeller, "Transport
              Layer Security (TLS) False Start", draft-ietf-tls-
              falsestart-01 (work in progress), November 2015.

   [REPORT]   "Worldwide Infrastructure Security Report", 2014,
              <http://pages.arbornetworks.com/rs/arbor/images/
              WISR2014.pdf>.

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

   [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>.

   [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>.

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   [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>.

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

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   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

   Mike Geller
   Cisco Systems, Inc.
   3250
   Florida  33309
   USA

   Email: mgeller@cisco.com

   Mohamed Boucadair
   France Telecom
   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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