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Versions: 00 01 02                                                      
DOTS                                                         J. Francois
INTERNET-DRAFT                                                     Inria
Intended Status: Standard Track                               A. Lahmadi
Expires: May 4, 2017                      University of Lorraine - LORIA
                                                            Marco Davids
                                                               SIDN Labs
                                                     Giovane C. M. Moura
                                                               SIDN Labs
                                                        October 31, 2016

                       IPv6 DOTS Signal Option


   This document specifies an optional fall-back opportunistic method
   that employs the IPv6 Hop-by-Hop options extension header type. It
   allows a DOTS client to send a signaling message over a congested
   network due to a DDoS attack by ''tagging'' bypassing outgoing IPv6
   packets to reach a DOTS server or gateway.

Status of this Memo

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

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

   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."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

Copyright and License Notice

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

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

Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.3  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  4
   2. Opportunistic DOTS signal option  . . . . . . . . . . . . . . .  4
     2.1 Hop-by-Hop option encoding . . . . . . . . . . . . . . . . .  5
     2.2 DOTS signal Option attributes  . . . . . . . . . . . . . . .  6
     2.3 Example  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   3 Option Processing  . . . . . . . . . . . . . . . . . . . . . . .  8
     3.2 Opportunistic DOTS signal initialization by a DOTS client  .  8
     3.2 Processing by a non DOTS opportunistic-capable router  . . .  9
     3.3 Processing by a DOTS opportunistic-capable router  . . . . . 10
     3.4 Processing by a DOTS opportunistic-capable gateway . . . . . 10
     3.5 Processing by a DOTS opportunistic-capable server  . . . . . 10
   4 Deployment considerations  . . . . . . . . . . . . . . . . . . . 10
   5  Impact on existing IP layer implementations . . . . . . . . . . 11
   6  Security Considerations . . . . . . . . . . . . . . . . . . . . 12
   7  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 12
   7  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     7.1  Normative References  . . . . . . . . . . . . . . . . . . . 13
     7.2  Informative References  . . . . . . . . . . . . . . . . . . 13
   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

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1  Introduction

1.1 Overview

   A distributed denial-of-service (DDoS) attack aims at rendering
   machines or network resources unavailable. These attacks have grown
   in frequency, intensity and target diversity [I-D.draft-ietf-dots-
   requirements]. Moreover, several protocols have been utilized to
   amplify the intensity of the attacks [kuhrer2014exit],  peaking at
   several hundred gigabits per second.

   The DOTS aims at defining a common and open protocol to signal DDoS
   attacks to facilitate a coordinated response to these attacks. This
   document specifies a signalling mechanism that instead of designing a
   new application-layer protocol, it utilizes the IPv6 Hop-by-Hop
   header [RFC2460]. This header has the advantage to be fully inspected
   by all network devices and it is the first header in IPv6 extension
   headers [RFC7045].

   The new option containing the attributes of the signalling message is
   included in an opportunistic way in available IPv6 packets leaving a
   network element until the message reaches a DOTS server. It thus
   constitutes an additional signalling channel but MUST NOT replace the
   original signalling channel used between DOTS client and servers as
   the one defined in [I-D.draft-reddy-dots-signal-channel]. The DOTS
   client will thus embed the signalling attributes into outgoing IPv6
   packets not necessarily going to the DOTS server. Intermediate
   routers receiving such a packet will examine it and embed the same
   information into other IPv6 packets. domain in this opportunistic way
   to increase the probability that such a packet will be finally
   forwarded to a DOTS gateway or Server, but also in controlled way to
   avoid that the mechanism is exploited for a malicious purposes.

   Only the Hop-by-Hop options header allows such behavior and using
   Destination options header is not enough to make the DOTS signal
   going through the network in an opportunistic way. Each network
   element recognizing this new option will select the best fitted IPv6
   packets to deliver the signal to the DOTS server or gateway. For this
   reason the Hop-by-Hop header option is essential to make such
   behavior compared to other existing IPv6 extension headers [RFC6564].

1.2 Motivation

   The traffic generated by a DDoS can be characterized according to
   various parameters, such as the layer (IP/ICMP or application),
   maximum and instant throughput, among others. Regardless its nature,
   we assume that for most cases, a DOTS client will be able to signal
   back one or few messages, during the attack, to the DOTS phase.

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   We have the same behavior in other DDoS attacks. For instance, on
   November 30th and December 1st, 2015, the Root DNS system was hit by
   an application layer (DNS) attack [rootops-ddos]. Each one of the 13
   root server letters (A--M) was hit by attacks peaking at 5 million
   queries per second. By utilizing the RIPE Atlas DNSMON
   infrastructure, we can see that during the DDoS attacks, most of the
   root server letters remained reachable and able to respond to the DNS
   request sent by the probes employed by the DNSMON [ripe-dnsmon-ddos].
   Few letters, however, had a packet loss rate of more than 99%. The
   DNSMON probes, however, experience mostly delays in their DNS
   requests instead.

   Our signalling mechanism operates in an opportunistic way it is
   designed for DDoS as the ones on the Root DNS system.

1.3  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   The terms DOTS client, DOTS server, DOTS gateway, DOTS agents, signal
   channel, DOTS signal and DOTS signal refers to the terminology
   introduced in [I-D.draft-ietf-dots-requirements].

   The following terms are introduced:

      Opportunistic DOTS signal:
         an IPv6 packet containing the signalling attributes of an
         attack within the Hop-by-Hop extension header. The purpose is
         the same as the DOTS signal. It is used to request help for
         mitigating the attack.

      DOTS opportunistic-capable router:
         a router  with the capacity to decode the opportunistic DOTS
         signal and re-embed such an information in other IPv6 packets.

      All DOTS opportunistic-capable agents are defined as the DOTS
      agents supporting the opportunistic DOTS signal processing.

2. Opportunistic DOTS signal option

      The goal is to provide an efficient mechanism where nodes in a
      IPv6 network facing a DDoS attack can deliver a DOTS signal
      message sent by a DOTS client to the DOTS server. The specified
      mechanism does not generate transport packets to carry the DOST
      signal message but it only relies on existing IPv6 packets in the

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      network to include inside them a hop-by-hop extension header which
      contains an encoded DOTS signal message. The solution defines a
      new IPv6 Hop-by-Hop header option with the semantic that the
      network node SHOULD include the option content within one or
      multiple outgoing IPv6 packets available in that network node.

2.1 Hop-by-Hop option encoding

      According to [RFC2460], options encoded into the IPv6  Hop-by-Hop
      header are formatted as Type-Length-Values (TLVs). The option for
      opportunistic DOTS signal is thus defined as follows:

   0               7              15              22              31
   |  Option type  |Option Data Len|    DOTS Signal Attribute[1]   |
   | DOTS Signal Attribute[2] |  ...  | DOTS Signal Attribute[n]   |

   The first byte defines the Hop-by-Hop Option type number allocated to
   the DOTS opportunistic signalling. This number is not yet fixed but
   the first three bits MUST be set to 0. The first two zero bits
   indicate that routers which cannot handle the DOTS signal option will
   continue to process other options. The third 0 bit means that the
   option processing will not change the packet's final destination

   The second byte contains the length of the option content. The
   content of the DOTS Signal option is a variable-length field that
   contains one or more type-length-values (TLV) encoded DOTS signal
   attributes, and has the following format:

   0               7              15
   |   Attr Type   | Attr Data Len | Attr Data ...   |

   The Attr Type is 8-bit identifier of a DOTS signal attribute.

   The Attr Data Len is 8-bit unsigned integer which is the length of
   Attr Data in bytes.

   The Attr Data is variable-length field that contains the data of the

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   Since using TLVs in Hop-by-Hop options is known to be a factor of
   attacks [I-D.draft-krishnan-ipv6-hopbyhop], DOTS attributes are
   encoded with fixed length when possible. Another issue is the   size
   of IPv6 datagram is constrained by the path MTU (Maximum
   Transmission Unit) to avoid fragmentation. There are several options
    to overcome this issue. It is RECOMMENDED that  DOTS opportunistic
   signal NOT embedded is such a requirement is not satisfied.

2.2 DOTS signal Option attributes

   The first attribute embedded into the opportunistic DOTS signal is a
   TTL (Time-to-Live) field which indicates the maximum number of
   retransmission of the signal into another IPv6 packets until it MUST
   be discarded. Remaining attributes are similar to the header fields
   described in [I-D.draft-reddy-dots-signal-channel] (section 5.1.1)
   used to convey a DOTS signal through a HTTP POST.

   The sequence of attributes to be inserted within the header MUST
   start with fixed-length attributes which are defined in the following

   TTL: Time-to-Live. This is a mandatory attribute encoded in one byte.

   Flags: one byte is reserved for flags.
      The first bit indicates the type of the IP address of the host: 0
      for IPv4, 1 for IPv6. The second bit indicate if the
      protocol to use is TCP (1) or UDP (0). The third bit indicates if
      the message is signed The remaining bit are
      not used yet.

   host: the IP address of the DOTS server where the signal option
      SHOULD be delivered. Depending on the flags, this field is
   encoded in 4 or 16 bytes.

   port: the listening port of the DOTS server.
      It is encoded in 2 bytes.

   The remaining attributes MUST be TLV encoded, and they are defined
   in the following order:

   policy-id: defined in [I-D.draft-reddy-dots-signal-channel].

   target-ip: defined in [I-D.draft-reddy-dots-signal-channel].
      However, each address or prefix is encoded in its own TLV
      element. The distinction between IPv4 and IPv6 is done
      over the length of the value.

   target-port: defined in [I-D.draft-reddy-dots-signal-channel].

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      However, each target port is encoded in its own TLV element.

   target-protocol: defined in [I-D.draft-reddy-dots-signal-channel].
      However each target protocol is encoded in its own TLV element.

   lifetime (lt): lifetime of the mitigation request defined in

   The encoded attributes MUST be included in the option header in the
   order defined above.

   The following table provides the value of types that are used by the
   TLV encoded attributes.

      | Attribute type | value  |
      |policy-id       |0       |
      |target-ip       |1       |
      |target-port     |2       |
      |target-protocol |3       |
      |lifetime        |4       |

2.3 Example

   Following is an example of an encoded Hop-by-Hop Option header to
   signal that a web service is under attack.

   0               7              15              22              31
   |  Next header  | Hdr Ext Len=6 |    TTL=128    | Flags=IPv4,TCP|
   |                         host=                        |
   |            port=443           | A. type=policy| Att Data Len=2|
   |              143              |  Attr. type=ip| Att Data Len=4|
   |                                           |
   | Attr. type=ip |Att Data Len=16|                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   +                                                               +

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   |                                                               |
   +                                                               +
   |                        2001:db8:6401::1                       |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |Attr. type=port| Att Data Len=2|
   |              8080             |Attr. type=port| Att Data Len=2|
   |              443              |Attr.type=proto| Att Data Len=2|
   |              TCP              | Attr. type=lt | Att Data Len=2|
   |              600              |       1       | Opt Data Len=0|

   In the previous example, the message is not signed and terminates
   with padding. If it is the case, then the signature MUST BE added at
   the end such that the integrity and authenticity can be checked by
   the DOTS server or gateway. The TTL attributes MUST be excluded from
   the signature calculation (see section 6).

3 Option Processing

3.2 Opportunistic DOTS signal initialization by a DOTS client

   When a DOTS client needs to inform the DOTS server that it is under
   attack, it firstly makes a connection attempt and applies the
   mechanisms described in [I-D.draft-reddy-dots-signal-channel].

   In addition, it MAY activates an opportunistic mechanism to include
   the Hop-by-Hop header option specified in this document in one or
   multiple available IPv6 packets leaving the node. Because the DOTS
   client location is independent of the signalling, it can be
   positioned in a part of the network where there is no passing-by
   traffic which can serve for opportunistic signalling. DOTS client MAY
   also create and emit IPv6 datagrams without payload but with the
   signal encoded in the Hop-by-Hop option header.

   Otherwise, the selection of packets has to be configured  a priori.
   The configuration is composed of a sequence of rules defined in a
   hierarchical order such that they are triggered in a sequential

   The selection of packets has to be configured  a priori. The
   configuration is composed of a sequence of rules defined in a
   hierarchical order such that they are triggered in a sequential

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   Each rule is defined by:
      o a set of filters over the IPv6 packet headers. Only packets
      matching those filters are selected for opportunistic signalling.
      For instance, only packets heading to a given subnetwork or to
      specific address close to a DOTS server can be selected to
      increase the chance to reach the latter.

      o a ratio to select only a proportion of packets matching the
      filters in order to limit the induced overhead of the
      opportunistic signalling.

      o a timeout until the rule is active and selected IPv6 packets
      embed the DOTS opportunistic signal.

   The objective is to apply each ordered rule after another according
   to their timeouts. The first rule is triggered immediately after the
   opportunistic signalling is activated.

   In all cases (embedding information into an existing packet or
   creating an new packet with no payload), the client MUST avoid

   Although the definition of rules MUST be configured by the user. It
   is RECOMMENDED to order them inversely related to the number of
   packets that would be selected. This can be approximated regarding
   the definition of filters. The core idea is to benefit from the first
   instants of the attack before losing connectivity by using a maximum
   number of outgoing packets to include the DOTS signalling option. It
   is thus RECOMMENDED to define the first as matching all IPv6 packets
   with a ratio equals one to rapidly disseminate the information but
   with a short timeout to limit the implied overhead.

   Here is the an example of rules:
      1: all outgoing IPv6 packets with a 10 second timeout
      2: all outgoing IPv6 packets with a ratio of 10% and a 1 minute
      3: all outgoing multicast IPv6 packets with a ratio of 10% and a 1
      minute timeout
      4: all outgoing anycast IPv6 packets with a ratio of 10% and a 5
      minute timeout
      5: all outgoing IPv6 packets heading to the DOTS server with a
      ratio of 100% and a one hour timeout

3.2 Processing by a non DOTS opportunistic-capable router

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   When receiving an opportunistic DOTS signal encoded in a IPv6 packet,
   a non DOT opportunistic capable router simply skips the Hop-by-Hop
   option and continue the normal processing of the IPv6 packet because
   the option type MUST start with three zero bits.

3.3 Processing by a DOTS opportunistic-capable router

   A DOTS opportunistic-capable router MUST store DOTS signalling
   information whose it is aware of. If a router processes an IPv6 DOTS
   opportunistic signal and supports this option, it first checks if it
   has already stored the associated information. In that case, the
   router simply skips the option and continues the normal processing
   otherwise it stores the encoded information in order to embed it
   again in other IPv6 packets similarly to the DOTS client. Hence, a
   set of rules are also defined in advance and are triggered upon the
   reception of a new opportunistic DOTS signal. Once all rule have been
   applied, signalling information MUST be discarded by the router. When
   embedding the information into other IPv6 packets, the router MUST
   decrease the TTL by one since opportunistic signalling does not
   prevent loops in the dissemination of signalling.

3.4 Processing by a DOTS opportunistic-capable gateway

   If a DOTS gateway has DOTS capabilities, it will apply the same
   strategy as a DOTS client by making attempts of direct connections to
   the DOST server and in addition it inserts the Hop-by-Hop header DOTS
   signalling option in leaving IPv6 packets using the strategy
   specified above.

3.5 Processing by a DOTS opportunistic-capable server

   When the IP layer of the host where the DOTS server is running
   receives an IPv6 packet carrying a Hop-by-Hop DOTS signal option
   header it MUST extracts the content of the option and provides the
   attributes data to the server program.

4 Deployment considerations

   This mechanism will be potentially used by networks with IPv6 capable
   elements and requires that of IPv6 traffic exist in the network
   during the attack. The existing IPv6 traffic to be used could be of
   any type from management or user levels. It is also important to
   emphasize that while our mechanism utilizes an IPv6 header field, it
   can also be used to signal IPv4 attacks as well - given that the
   network devices are dual stacked.

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   IPv6 extension headers are often rate-limited or dropped entirely
   [HBH-HEADER]. To be able to use the mechanism specified in this
   document, network operators need to avoid discarding packets or
   ignoring the processing of the hop-by-hop option on their deployed
   network elements. However, instead of dropping or ignoring packets
   with hop-by-hop option carrying DOTS signal, they need to assign
   these packets to slow forwarding path, and be processed by the
   router's CPU. This behavior will not affect the performance of the
   network devices since the network is already facing a DDoS attack and
   fast forwarding paths are saturated by the attacker traffic.

   If the DOTS server, gateway and the client are located in the same
   administrative domain, marking the IPv6 packets with the proposed
   hop-by-hop header option could be done in a straight forward way,
   while considering that an agreement exists inside the domain to avoid
   dropping or rate limiting of IPv6 extension headers as described
   above. The proposed mechanism becomes less practical and difficult to
   deploy when the DOST server is running on the Internet. In such
   scenario, the mechanism could be used in the intra-domain part to
   deliver the hop-by-hop option carrying the DOTS signal until it
   reaches a DOTS gateway located in the same domain as the client, then
   the gateway will apply mechanisms provided by the DOTS transport
   protocol [I-D.draft-reddy-dots-signal-channel] to inform the server
   running on Internet about the attack. This deployment scenario
   requires that at least one DOTS gateway is deployed in the same
   domain than the DOTS client.

5  Impact on existing IP layer implementations

   For this option to be applicable within an IP system, it requires
   modifications to existing IP layer implementation. At DOTS capable
   nodes (client, gateway and server), it requires a service interface
   used by upper-layer protocols and application programs to ask the IP
   layer to insert and listen to the Hop-by-Hop header option in IPv6
   packets with the content and strategies described in Section 3. A
   DOTS client invokes the service interface to insert the option, A
   DOTS gateway invokes the service interface for listening and
   inserting the option, and finally a DOTS server only invokes the
   service interface to listen to the DOTS signalling option.

   Intermediate nodes (routers or middle boxes) IP layer needs to be
   extended to perform processing of the new Hop-by-Hop header option as
   described in Section 3. They mainly parse the first host attribute of
   the option and make a selection of a leaving IPv6 packet where the
   option will be inserted.

   Every node inserting the new proposed Hop-by-Hop option SHOULD only
   select IPv6 packets with enough left space to avoid fragmentation.

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6  Security Considerations

   Any IPv6 header option could be used by an attacker to create an
   attack on the routers and intermediate boxes that process packets
   containing the option. The proposed IPv6 option in this document MAY
   be abused by an attacker to create a covert channel at the IP layer
   where data is hidden inside the content of the option [RFC6564].
   However, this attack is not specific to the proposed option and it is
   a known issue of IPv6 header extensions and options. The option MAY
   also be used by an attacker to forge or modify opportunistic DOTS
   signal leading to trigger additional processing on intermediate nodes
   and DOTS servers.

   However the proposed option should be only initiated by a DOTS client
   and information embedded in new IPv6 messages by opportunistic DOTS
   capable routers. Defining proper policies to filter all messages with
   this option set and originated from other nodes would limit security
   issues since these DOTS opportunistic-capable agents SHOULD be

   In addition, the message MAY be signed using techniques to enforce
   authenticity and integrity over the opportunistic DOTS signal
   channel. The signalling message specification includes a flag to
   indicate if the message is signed by the choice of the signature
   algorithm is let to the users. This signature has to be computed by
   the DOTS opportunistic-capable client and checked by the DOTS
   opportunistic-capable gateway or router. Hence, intermediate routers
   MUST NOT modify the message and its signature except the TTL, which
   so has not be considered during the signature computation.

   Assuming a compromised router, the attacker could nevertheless replay
   the message or increase the TTL but thanks to the unique policy-id
   all intermediate-DOTS capable router will drop such messages and thus
   limiting their forwarding in the network.

   Besides, an attacker can also listen  opportunistic DOTS signals to
   monitor the impact of its own attack. These considerations are not
   specific to the proposed option and supposes that the attacker is
   able to compromise intermediate routers.

7  IANA Considerations

   This draft defines a new IPv6 [RFC2460] hop-by-hop option. This
   requires an IANA RFC3692-style update of:
   and ultimately the assignment of a new hop-by-hop option according to
   the guidelines described in [RFC5237].

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7  References

7.1  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-

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

   [RFC6564]  Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
              M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
              RFC 6564, DOI 10.17487/RFC6564, April 2012,

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045, DOI
              10.17487/RFC7045, December 2013, <http://www.rfc-

7.2  Informative References

      A. Mortensen., R. Moskowitz., and T. Reddy., "DDoS Open Threat
      Signaling Requirements", draft-ietf-dots-requirements-00 (work in
      progress), October 2015.
      Kuhrer, Marc and Hupperich, Thomas and Rossow, Christian and Holz,
      Thorsten. Exit from Hell? Reducing the Impact of Amplification
      DDoS Attacks. In: 23rd USENIX Security Symposium (USENIX Security
      T. Reddy., D. Wing., P. Patil., M. Geller., M. Boucadair.,and R.
      Moskowitz., "Co-operative DDoS Mitigation", draft-reddy-dots-
      transport-03 (work in progress), March 2016.
      rootops.: Events of 2015-11-30. Online: http://root-
      RIPE NCC DNS Monitoring Service (DNSMON). Online:
      Baker, F., "IPv6 Hop-by-Hop Options Extension Header",Work in
      Progress, draft-ietf-6man-hbh-header-handling-03,March 2016.

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      This work is partly funded by FLAMINGO, a Network of Excellence
      project (ICT-318488) supported by the European Commission under
      its Seventh Framework Programme.

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Authors' Addresses

   Jerome Francois
   615 rue du Jardin Botanique
   54600 Villers-les-Nancy

   Phone: +33 3 83 59 30 66
   EMail: jerome.francois@inria.fr

   Abdelkader Lahmadi
   University of Lorraine - LORIA
   615 rue du Jardin Botanique
   54600 Villers-les-Nancy

   Phone: +33 3 83 59 30 00
   Email: Abdelkader.Lahmadi@loria.fr

   Marco Davids
   SIDN Labs
   Meander 501
   6825 MD Arnhem
   The Netherlands

   Email: marco.davids@sidn.nl

   Giovane C. M. Moura
   SIDN Labs
   Meander 501
   6825 MD Arnhem
   The Netherlands

   Email: giovane.moura@sidn.nl

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