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DOTS                                                         J. Francois
Internet-Draft                                                     Inria
Intended status: Standards Track                              A. Lahmadi
Expires: November 4, 2017                 University of Lorraine - LORIA
                                                               M. Davids
                                                                G. Moura
                                                               SIDN Labs
                                                             May 3, 2017


                        IPv6 DOTS Signal Option
               draft-francois-dots-ipv6-signal-option-02

Abstract

   DOTS client signal using original signal communication channel can
   expect service degradation and even service disruption as any other
   service over Internet but in more severe conditions because the
   signal may have to be transmitted over congested paths due to the
   denial-of-service attack.

   This document specifies a fall-back asynchronous mechanism using an
   intermediate agent to store DOTS signal information during a limited
   period of time.  This mechanism allows a DOTS server to request a
   signal information stored by a DOTS client when no heartbeat is
   received from the DOTS client.  This intermediate agent called DOTS
   Signal Repository have to be connected to the DOTS client and server
   independently.  The repository must be located and/or reached through
   one or multiple network paths, preferably as most as possible
   disjoint from regular signal channel, in order to increase its
   reachability.  The document introduces a set of support protocols to
   build the asynchronous communication between the DOTS cient, server
   and the repository.

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."



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   This Internet-Draft will expire on November 4, 2017.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (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.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Asynchronous DOTS signaling . . . . . . . . . . . . . . . . .   4
     2.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Architecture  . . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Asynchronous process  . . . . . . . . . . . . . . . . . .   5
     2.4.  Protocol requirements . . . . . . . . . . . . . . . . . .   6
   3.  DOTS Signal Repository  . . . . . . . . . . . . . . . . . . .   7
   4.  Protocol  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Between DSR and DOTS server . . . . . . . . . . . . . . .   7
     4.2.  Between DSR and DOTS client . . . . . . . . . . . . . . .   7
       4.2.1.  Opportunistic DOTS signaling  . . . . . . . . . . . .   8
         4.2.1.1.  Hop-by-Hop option encoding  . . . . . . . . . . .   9
         4.2.1.2.  DOTS signal Option attributes . . . . . . . . . .  10
         4.2.1.3.  Example . . . . . . . . . . . . . . . . . . . . .  11
         4.2.1.4.  Option Processing . . . . . . . . . . . . . . . .  12
         4.2.1.5.  Deployment considerations . . . . . . . . . . . .  14
         4.2.1.6.  Impact on existing IP layer implementations . . .  15
       4.2.2.  IPv6 SRH  . . . . . . . . . . . . . . . . . . . . . .  15
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Appendix A.  Additional Stuff . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19




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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.ietf-dots-requirements].  Moreover, several protocols have been
   utilized to amplify the intensity of the attacks [kuhrer2014exit],
   peaking at several hundred gigabits per second.

   DDoS Open Threat Signaling (DOTS) aims at defining a common and open
   protocol to signal DDoS attacks to facilitate a coordinated response
   to these attacks.  This document specifies an asynchronous signaling
   method that MAY be used between a DOTS client and server instead of
   relying on purely synchronous communication as specified in
   [I-D.ietf-dots-signal-channel].  Indeed initial signaling should be
   done in real-time through connections between DOTS clients and severs
   such that a client can forward signal information as soon as the
   attack is detected.  However, the signaling messages may have to be
   forwarded through paths impacted by the attack itself, i.e. highly
   congested.  Asynchronous signaling in this document is an additional
   mechanism which MAY propagate signal information in a less reactive
   manner due to the use of an asynchronous communication channel but
   through alternative paths in the network.  It increases the
   reachability of the DOTS server which will then in charge of
   requesting the mitigation.

   The proposed mechanism constitutes an additional signaling channel
   but MUST NOT replace the original signaling channel used between DOTS
   client and servers as the one defined in
   [I-D.ietf-dots-signal-channel].

   To perform asynchronous communication, this document introduces DOTS
   Signals Repository (DSR) which represents datastores where DOTS
   clients can send signal information.  This information is then stored
   and the DOTS server can request it.  In addition to provide a general
   process for achieving asynchronous signaling, this document
   introduces also a set of protocols which can support it.

1.2.  Terminology

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

   The terms DOTS client, DOTS server, DOTS gateway, DOTS agents refers
   to the terminology introduced in [I-D.ietf-dots-architecture].



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   The following terms are introduced:

   o  DSR (DOTS signal repository): intermediate agent able to store
      signal from clients during a limited period of time and which can
      be requested by DOTS servers.

   o  Opportunistic DOTS signal: an IPv6 packet containing the signaling
      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.

   o  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.

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

2.  Asynchronous DOTS signaling

2.1.  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.

   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.

   As regular signaling from the DOTS client to the DOTS server or the
   DOTS gateway might be affected by the attack traffic, it is important
   to maximize the delivering success of the signals by using
   alternative packets and/or paths to deliver it.  As a result, it
   forces to have intermediate agents, DSRs, able to catch DOTS signals
   delivered through those auxiliary mechanisms.  However, those agents
   MUST not always forward DOTS signal to the server in order to limit
   the induced overhead.  Only if the regular signal is not received by



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   the server, retrieving the signal from the DSRs is required, which
   has thus initiated by the DOTS server itself.

2.2.  Architecture

   DSR (DOTS Signal Repository) are additional REQUIRED datastores.
   They are integrated in the DOTS architecture
   [I-D.ietf-dots-architecture]as highlighted in Figure 1. (1) refers to
   the regular signaling. (2) and (3) refers to the proposed auxiliary
   mechanism.  As shown in this figure, DSRs act as synchronizing agent
   where the DOTS client drops signal information (2) (attack details).
   On the contrary, the server will retrieve this information (3).

   +-----------+            +-------------+
   | Mitigator | ~~~~~~~~~~ | DOTS Server |~~~~+
   +-----------+            +-------------+    |(3)
                                   ^           v
                                   |   +----------------+
                                (1)|   |   DOTS Signal  |
                                   |   |   Repository   |
                                   |   +----------------+
                                   |           ^
   +---------------+        +-------------+    |(2)
   | Attack Target | ~~~~~~ | DOTS Client |~~~~+
   +---------------+        +-------------+

                     Figure 1: Asynchronous signaling

2.3.  Asynchronous process

   This section describes the process of asynchronous DOTS signal
   processing.  In Figure Figure 1, there are two main communication
   channels which are not synchronized:

   o  Between DOTS client and DSR: the client sends DOTS signal
      information when a condition is satisfied.  The condition MUST be
      configured by the user but SHOULD be linked to information
      provided by Attack target.  For instance, when an attack is
      detected, the client connects to DOTS server and in parallel sends
      signal to one or more DSRs.











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   o  Between DOTS server and DSR: the server will retrieve signal
      information when a specific condition occurs.  Such a condition is
      linked with the probable occurrence of an attack.  The server can
      infer this condition when the client is not responsive anymore.
      In [I-D.ietf-dots-signal-channel], an heartbeat mechanism is
      defined.  Hence, when no heartbeat is received from the client,
      the server MUST try to get signal information by the asynchronous
      communication channel.

   Each communication channel can implement its own protocol.  They are
   NOT REQUIRED to be the same.

   We have to note that the client condition to provide signals to the
   DSR can be weaker than regular synchronous signaling between DOTS
   client and server.  Indeed, a client can signal to the DSR some
   suspect activities for which no mitigation is required yet.  However,
   when the supposed attack is stronger provoking client disruption, the
   latter is not able to provide any type of signaling anymore and the
   server can thus retrieve information on prior stored signals.

2.4.  Protocol requirements

   DOTS signaling requirements are documented in
   [I-D.ietf-dots-requirements].

   GEN-003 (Bidirectionality) requires that signal channel MUST enable
   asynchronous communications between DOTS agent by allowing
   unsolicited messages.  Asynchronous signaling described in the
   current document allows DOTS client to provide signals, which can be
   retrieved later by DOTS server(s).

   Because of this mechanism, there are requirements which are not
   supported: OP-002 (Session Health Monitoring), OP-003 (Session
   Redirection).  Therefore, the fall-back asynchronous DOTS signaling
   is an additionnal mechanism and MUST NOT replace regular signaling as
   described in [I-D.ietf-dots-signal-channel].

   It is particularly designed to fulfill GEN-002 (Resilience and
   Robustness) by increasing the signal delivery success even under the
   severely constrained network conditions imposed by particular attack
   traffic.

   In addition, the fall-back asynchronous DOTS signal MUST specify a
   TTL (Time-to-Live) used by DSRs to store received signal in a limited
   period of time.  It is different from mitigation lifetime but MUST be
   lower or equals.





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3.  DOTS Signal Repository

   DSRs have to be deployed and distributed in order to enhance its
   reachability by the DOTS client.  It is NOT REQUIRED that all DOTS
   agents use the same set of DSRs and a DOTS client and server SHOULD
   define their own set regarding their particular context, e.g. the
   network topology.  The Data channel [I-D.ietf-dots-data-channel]
   between client and server MUST be used to configure it.  As an
   example in the case of the inter-domain scenario, the DOTS server can
   inform the DOTS client to use DSRs scattered in multiple domains.

   There is no restriction on the environment where DSRs can be
   deployed.  Two types of DSRs are mainly considered:

   o  Routers: they have low capacity to process and store received
      signals but they are well distributed by nature in the network.

   o  Servers or stations: they provide higher computational power and
      storage but are less distributed

   Selection of protocols to use for asynchronous signaling MUST take
   into account those specificities.

4.  Protocol

4.1.  Between DSR and DOTS server

   To retrieve signals, the DOTS server MUST request the DSRs.  Standard
   protocols can be used.  Requests from the DOTS server MUST specify a
   client identifier and the DSRs returns all stored signal related to
   this client.  The protocol MUST provide integrity and authenticity
   and SHOULD guarantee confidentiality.  To limit entailed overhead
   lightweight protocol SHOULD be used.  COAP [RFC7252] over DTLS
   [RFC6347] is RECOMMENDED when DSRs are servers.  In the case of
   routers acting as DSR, network management protocol such as SNMP
   [RFC1157] or NETCONF [RFC6241] SHOULD be leveraged.

4.2.  Between DSR and DOTS client

   The signal sent by the DOTS client to the DSR is more prone to be
   affected by attack traffic due to its proximity to the attack victim.
   Similar protocol as between DSR and DOTS server can be used but it is
   RECOMMENDED to convey the signal over multiple paths to increase the
   reachability sucess







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   This document introduces two mechanisms to deliver the signal from
   the DOTS client to the DSR: IPv6 opportunistic signaling using Hop-
   by-Hop Option header; source routing using IPv6 Segment Routing
   Header (SRH).

4.2.1.  Opportunistic DOTS signaling

   This section specifies a signalling mechanism that instead of
   designing a new application-layer protocol, it utilizes the IPv6 Hop-
   by-Hop header [RFC2460].  This header SHOULD be processed by
   intermediate devices and it MUST be the first header in IPv6
   extension headers [RFC7045].

   In such a particular scenario, DSRs are intermediate routers capable
   of processing the option.  DOTS server MAY also receive IPV6 packets
   with the Hop-by-Hop option and could thus process it directly.  It is
   till considered as asynchronous since the server MAY NOT receive the
   initial packet emitted by the client but a copy of the signal in
   another packet (done by an intermediate DSR/router).  Otherwise, it
   MUST connect to the DSR (section Section 4.1)

   The new option containing the attributes of the signalling message is
   included in an opportunistic way in available IPv6 packets leaving a
   network element.  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 DSRs.  For this reason the
   Hop-by-Hop header option is essential to make such behavior compared
   to other existing IPv6 extension headers [RFC6564].

   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 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



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   the option content within one or multiple outgoing IPv6 packets
   available in that network node.

4.2.1.1.  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 described in Figure 2

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

                   Figure 2: Hop-by-Hop option encoding

   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
   [RFC2460].

   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 format described in Figure 3.

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

                   Figure 3: Hop-by-Hop option encoding

   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
   attribute.






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   Since using TLVs in Hop-by-Hop options is known to be a factor of
   attacks [I-D.krishnan-ipv6-hopbyhop], DOTS attributes are encoded
   with fixed length when possible.

4.2.1.2.  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.ietf-dots-signal-channel]  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
   order:

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

   o  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.

   o  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.

   o  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:

   o  policy-id: defined in [I-D.ietf-dots-signal-channel].

   o  target-ip: defined in [I-D.ietf-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.

   o  target-port: defined in [I-D.ietf-dots-signal-channel].
      However, each target port is encoded in its own TLV element.

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



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   o  lifetime (lt): lifetime of the mitigation request defined in
      [I-D.ietf-dots-signal-channel]

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

   Table 1 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     |
                        +-----------------+-------+

                   Table 1: TLV encoded attributes types

4.2.1.3.  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=192.0.2.1                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            port=443           | A. type=policy| Att Data Len=2|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              143              |  Attr. type=ip| Att Data Len=4|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           192.0.2.20                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Attr. type=ip |Att Data Len=16|                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   +                                                               +
   |                                                               |
   +                                                               +
   |                        2001:db8:6401::1                       |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |Attr. type=port| Att Data Len=2|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   |              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|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 4: Example of Hop-by-Hop DOTS signal encoding

   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.

4.2.1.4.  Option Processing

4.2.1.4.1.  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.ietf-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
   positionned 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
   manner.

   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
   manner.

   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.



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      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 exsiting packet or
   creating an new pakket with no payload), the client MUST avoid
   fragmentation.

   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
       timeout

   3.  all outgoing multicast IPv6 packets with a ratio of 10% and a 1
       minute timeout

   4.  all outgoing IPv6 packets heading to the DOTS server with a ratio
       of 100% and a one hour timeout

4.2.1.4.2.  Processing by a non DOTS opportunistic-capable router

   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.



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4.2.1.4.3.  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.

4.2.1.4.4.  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.

4.2.1.4.5.  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.

4.2.1.5.  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.

   IPv6 extension headers are often rate-limited or dropped entirely.
   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



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   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.ietf-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.

4.2.1.6.  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.  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.
   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.

4.2.2.  IPv6 SRH

   DOTS signalling may be carried using IPv6 source routing header.
   Details will be provided in a later version of this document.

5.  Security Considerations





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   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 trustworhy.

   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.

6.  IANA Considerations

   This draft defines a new IPv6 hop-by-hop option[RFC2460].This
   requires an IANA RFC3692-style update of:http://www.iana.org/
   assignments/ipv6-parameters/ipv6-parameters.xhtml and ultimately the
   assignment of a new hop-by-hop option according to the guidelines
   described in [RFC5237].

7.  Acknowledgements




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   This work is partly funded by FLAMINGO, a Network of Excellence
   Seventh Framework Programme.

8.  References

8.1.  Normative References

   [I-D.ietf-dots-architecture]
              Mortensen, A., Andreasen, F., Reddy, T.,
              christopher_gray3@cable.comcast.com, c., Compton, R., and
              N. Teague, "Distributed-Denial-of-Service Open Threat
              Signaling (DOTS) Architecture", draft-ietf-dots-
              architecture-01 (work in progress), October 2016.

   [I-D.ietf-dots-data-channel]
              Reddy, T., Boucadair, M., Nishizuka, K., Xia, L., Patil,
              P., Mortensen, A., and N. Teague, "Distributed Denial-of-
              Service Open Threat Signaling (DOTS) Data Channel", draft-
              ietf-dots-data-channel-00 (work in progress), April 2017.

   [I-D.ietf-dots-requirements]
              Mortensen, A., Moskowitz, R., and T. Reddy, "Distributed
              Denial of Service (DDoS) Open Threat Signaling
              Requirements", draft-ietf-dots-requirements-04 (work in
              progress), March 2017.

   [I-D.ietf-dots-signal-channel]
              Reddy, T., Boucadair, M., Patil, P., Mortensen, A., and N.
              Teague, "Distributed Denial-of-Service Open Threat
              Signaling (DOTS) Signal Channel", draft-ietf-dots-signal-
              channel-01 (work in progress), April 2017.

   [I-D.krishnan-ipv6-hopbyhop]
              Krishnan, S., "The case against Hop-by-Hop options",
              draft-krishnan-ipv6-hopbyhop-05 (work in progress),
              October 2010.

8.2.  Informative References

   [RFC1157]  Case, J., Fedor, M., Schoffstall, M., and J. Davin,
              "Simple Network Management Protocol (SNMP)", RFC 1157, DOI
              10.17487/RFC1157, May 1990,
              <http://www.rfc-editor.org/info/rfc1157>.

   [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>.



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   [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>.

   [RFC5237]  Arkko, J. and S. Bradner, "IANA Allocation Guidelines for
              the Protocol Field", BCP 37, RFC 5237, DOI 10.17487/
              RFC5237, February 2008,
              <http://www.rfc-editor.org/info/rfc5237>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

   [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>.

   [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,
              <http://www.rfc-editor.org/info/rfc6564>.

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045, DOI 10.17487/
              RFC7045, December 2013,
              <http://www.rfc-editor.org/info/rfc7045>.

   [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>.

   [kuhrer2014exit]
              M. Kuhrer, T. Hupperich, C. Rossow, T. Holz, "Exit from
              Hell? Reducing the Impact of Amplification DDoS Attacks",
              USENIX Security Symposium 23rd, 2014.

   [ripe-dnsmon-ddos]
              RIPE, "NCC DNS Monitoring Service (DNSMON)", <https://
              atlas.ripe.net/dnsmon/>.

   [rootops-ddos]
              rootops., "Events of 2015-11-30", 2015,
              <http://root-servers.org/news/events-of-20151130.txt>.

Appendix A.  Additional Stuff




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   This becomes an Appendix.

Authors' Addresses

   Jerome Francois
   Inria
   615 rue du jardin botanique
   Villers-les-Nancy  54600
   FR

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


   Abdelkader Lahmadi
   University of Lorraine - LORIA
   615 rue du jardin botanique
   Villers-les-Nancy  54600
   FR

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


   Marco Davids
   SIDN Labs
   Meander 501
   Arnhem  6825 MD
   NL

   Email: marco.davids@sidn.nl


   Giovane Moura
   SIDN Labs
   Meander 501
   Arnhem  6825 MD
   NL

   Email: marco.davids@sidn.nl











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