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Versions: (draft-boucadair-dots-dhcp) 00 01 02 03 04 05

Network Working Group                                       M. Boucadair
Internet-Draft                                                    Orange
Intended status: Standards Track                                T. Reddy
Expires: December 29, 2017                                        McAfee
                                                                P. Patil
                                                                   Cisco
                                                           June 27, 2017


   Distributed-Denial-of-Service Open Threat Signaling (DOTS) Server
                               Discovery
                draft-boucadair-dots-server-discovery-00

Abstract

   It may not be possible for a network to determine the cause for an
   attack, but instead just realize that some resources seem to be under
   attack.  To fill that gap, Distributed-Denial-of-Service Open Threat
   Signaling (DOTS) allows a network to inform a server that it is under
   a potential attack so that appropriate mitigation actions are
   undertaken.

   This document specifies mechanisms to configure nodes with DOTS
   servers.

Status of This Memo

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

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

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

   This Internet-Draft will expire on December 29, 2017.

Copyright Notice

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





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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Why Multiple Discovery Mechanisms?  . . . . . . . . . . . . .   4
   5.  How to Build the List of DOTS Servers?  . . . . . . . . . . .   7
   6.  DHCP Options for DOTS . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Design Rationale  . . . . . . . . . . . . . . . . . . . .   7
     6.2.  DHCPv6 DOTS Option  . . . . . . . . . . . . . . . . . . .   8
       6.2.1.  Format  . . . . . . . . . . . . . . . . . . . . . . .   8
       6.2.2.  DHCPv6 Client Behavior  . . . . . . . . . . . . . . .   9
     6.3.  DHCPv4 DOTS Option  . . . . . . . . . . . . . . . . . . .   9
       6.3.1.  Format  . . . . . . . . . . . . . . . . . . . . . . .   9
       6.3.2.  DHCPv4 Client Behavior  . . . . . . . . . . . . . . .   9
   7.  Discovery using Service Resolution  . . . . . . . . . . . . .  10
     7.1.  Retrieving Domain Name  . . . . . . . . . . . . . . . . .  10
       7.1.1.  DHCP  . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.2.  Resolution  . . . . . . . . . . . . . . . . . . . . . . .  11
   8.  DNS-SD/mDNS . . . . . . . . . . . . . . . . . . . . . . . . .  14
   9.  Anycast . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  14
     10.1.  DHCP . . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.2.  Service Resolution . . . . . . . . . . . . . . . . . . .  14
     10.3.  Anycast  . . . . . . . . . . . . . . . . . . . . . . . .  14
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     11.1.  DHCPv6 Option  . . . . . . . . . . . . . . . . . . . . .  15
     11.2.  DHCPv4 Option  . . . . . . . . . . . . . . . . . . . . .  15
     11.3.  Application Service & Application Protocol Tags  . . . .  15
       11.3.1.  DOTS Application Service Tag Registration  . . . . .  15
       11.3.2.  signal.udp Application Protocol Tag Registration . .  15
       11.3.3.  signal.tcp Application Protocol Tag Registration . .  16
       11.3.4.  data.tcp Application Protocol Tag Registration . . .  16
     11.4.  IPv4 Anycast . . . . . . . . . . . . . . . . . . . . . .  16
     11.5.  IPv6 Anycast . . . . . . . . . . . . . . . . . . . . . .  16
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  17



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     13.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   In many deployments, it may not be possible for a network to
   determine the cause for a distributed Denial-of-Service (DoS) attack
   [RFC4732], but instead just realize that some resources seem to be
   under attack.  To fill that gap, the IETF is specifying an
   architecture, called DDoS Open Threat Signaling (DOTS)
   [I-D.ietf-dots-architecture], in which a DOTS client can inform a
   DOTS server that the network is under a potential attack and that
   appropriate mitigation actions are required.  Indeed, because the
   lack of a common method to coordinate a real-time response among
   involved actors and network domains inhibits the effectiveness of
   DDoS attack mitigation, DOTS protocol is meant to carry requests for
   DDoS attack mitigation, thereby reducing the impact of an attack and
   leading to more efficient defensive actions.
   [I-D.ietf-dots-use-cases] identifies a set of scenarios for DOTS;
   almost all these scenarios involve a CPE.

   The basic high-level DOTS architecture is illustrated in Figure 1
   ([I-D.ietf-dots-architecture]):

          +-----------+            +-------------+
          | Mitigator | ~~~~~~~~~~ | DOTS Server |
          +-----------+            +-------------+
                                          |
                                          |
                                          |
          +---------------+        +-------------+
          | Attack Target | ~~~~~~ | DOTS Client |
          +---------------+        +-------------+

                     Figure 1: Basic DOTS Architecture

   [I-D.ietf-dots-architecture] specifies that the DOTS client may be
   provided with a list of DOTS servers; each associated with one or
   more IP addresses.  These addresses may or may not be of the same
   address family.  The DOTS client establishes one or more signaling
   sessions by connecting to the provided DOTS server addresses.  The
   logic for connecting to one or multiple IP addresses is out of scope
   of this document.

   This document specifies methods for DOTS clients to discover their
   DOTS server(s).  The rationale for specifying multiple discovery
   mechanisms is discussed in Section 4.




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   Considerations for the selection of DOTS server(s) by multi-homed
   DOTS client is out of scope; the reader should refer to
   [I-D.boucadair-dots-multihoming] for more details.

2.  Requirements Language

   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 RFC 2119 [RFC2119].

3.  Terminology

   This document makes use of the following terms:

   o  DDoS: A distributed Denial-of-Service attack, in which traffic
      originating from multiple sources are directed at a target on a
      network.  DDoS attacks are intended to cause a negative impact on
      the availability of servers, services, applications, and/or other
      functionality of an attack target.
   o  DHCP refers to both DHCPv4 [RFC2131] and DHCPv6 [RFC3315].
   o  DHCP client denotes a node that initiates requests to obtain
      configuration parameters from one or more DHCP servers.
   o  DHCP server refers to a node that responds to requests from DHCP
      clients.
   o  DOTS client: A DOTS-aware software module responsible for
      requesting attack response coordination with other DOTS-aware
      elements.
   o  DOTS server: A DOTS-aware software module handling and responding
      to messages from DOTS clients.  The DOTS server should enable
      mitigation on behalf of the DOTS client, if requested, by
      communicating the DOTS client's request to the mitigator and
      returning selected mitigator feedback to the requesting DOTS
      client.  A DOTS server may also be a mitigator.
   o  DOTS gateway: A DOTS-aware software module that is logically
      equivalent to a DOTS client back-to-back with a DOTS server.

   The reader should be familiar with other terms defined in
   [I-D.ietf-dots-architecture] and [RFC3958].

4.  Why Multiple Discovery Mechanisms?

   It is tempting to specify one single discovery mechanism for DOTS.
   Nevertheless, the analysis of the various use cases sketched in
   [I-D.ietf-dots-use-cases] reveals that it is unlikely that one single
   discovery method can be suitable for all the sample deployments
   (Table 1).  Concretely:





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   o  Almost all the use cases do involve a CPE device.  Multiple CPEs,
      connected to distinct network providers may even be considered.
      It is intuitive to leverage on existing mechanisms such as DHCP to
      provision the CPE acting as a DOTS client with the DOTS server(s).
      Further, the use of a dedicated DHCP option is used as an explicit
      signal to activate the DOTS service.

   o  The upstream network provider is not the DDoS mitigation provider
      for some of these use cases.  The use of anycast is not
      appropriate for this use case, in particular.  It is safe to
      assume that for such deployments, the DOTS server(s) domain name
      is provided during the service subscription (i.e., configuration
      file).

   o  Multiple DOTS clients may be enabled within a network (e.g.,
      enterprise network).  Automatic means to discover DOTS servers in
      a deterministic manner are interesting from an operational
      standpoint.

   o  Some of the use cases may involve a DOTS gateway that is
      responsible for forking requests received from internal DOTS
      clients to upstream DOTS servers or for selecting the appropriate
      DOTS server.  Particularly, the use of anycast may simplify the
      operations within the enterprise network to discover a DOTS
      gateway, if the enterprise network is single-homed.

   o  Some of the use cases may allow DOTS clients to have direct
      communications with upstream DOTS servers; that is no DOTS gateway
      is involved.  Leveraging on existing features that do not require
      specific feature on the node embedding the DOTS client may ease
      DOTS deployment.  Typically, the use of Straightforward-Naming
      Authority Pointer (S-NAPTR) lookups [RFC3958] together with
      existing DHCP options is an interesting technique to achieve DOTS
      server discovery.

   o  Resolving a DOTS server domain name provisioned to a DOTS client
      into IP address(es) require the use of the appropriate DNS
      resolvers; otherwise, resolving those names will fail.  The use of
      protocols such as DHCP does allow to associate provisioned DOTS
      server domain names with a list of DNS servers to be used for name
      resolution.










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   +-----------------------------+----------+--------------------------+
   |                    Use Case | Requires | The Network Provider is  |
   |                             |  a CPE   | also the DDoS Mitigation |
   |                             |          |         Provider         |
   +-----------------------------+----------+--------------------------+
   | Enterprise with an upstream |   Yes    |           Yes            |
   |       transit provider DDoS |          |                          |
   |          mitigation Service |          |                          |
   +-----------------------------+----------+--------------------------+
   |     Enterprise with a Cloud |   Yes    |            No            |
   |    DDoS Mitigation Provider |          |                          |
   +-----------------------------+----------+--------------------------+
   |      Homenet DDoS Detection |   Yes    |           Yes            |
   |       Collaboration for ISP |          |                          |
   |          network management |          |                          |
   +-----------------------------+----------+--------------------------+
   |          DDoS Orchestration |    No    |           N/A            |
   +-----------------------------+----------+--------------------------+

                    Table 1: Summary of DOTS Use Cases

   Consequently:

   o  This document specifies DHCP options that can be used to configure
      nodes, embedding a DOTS client, with DOTS servers' names
      (Section 6).  These names will be resolved into one or a list of
      IP addresses.  The use of DHCP for DOTS provisioning is justified
      because many of the target use cases identified in
      [I-D.ietf-dots-use-cases] involve CPEs; these devices widely
      support DHCP.  Also, the use of DHCP to provision a name that will
      be resolved into one or many IP address(es) of the appropriate
      DOTS server(s) to contact, does not suffer from the complications
      encountered if a anycast address is used (see Section 3.2.4.1 of
      [I-D.ietf-dots-architecture]).  Further, the use of DHCP ensures a
      deterministic behavior since DHCP can also be used to provision a
      list of DNS servers that can be used to resolve DOTS server domain
      names.

   o  Also, the document specifies how S-NAPTR can be used for dynamic
      DOTS server discovery (Section 7).

   o  Last, the document reserves IP anycast addresses for DOTS usage
      (Section 9).

   A common logic to build the DOTS servers list is elaborated in
   Section 5.





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5.  How to Build the List of DOTS Servers?

   In order to encourage consistent DOTS behaviors while allowing for
   automated DOTS server discovery, the following procedure MUST be
   followed by a DOTS client to built a DOTS server(s) list to contact:

   1.  if the DOTS client is explicitly configured with DOTS servers
       (e.g., local configuration file, DHCP), that list of DOTS servers
       is used, else

   2.  if DOTS service name(s) are configured, those names are used to
       retrieve the corresponding DOTS servers list, else

   3.  the DOTS client uses the DOTS anycast addresses (IPv4/IPv6) to
       contact it DOTS server(s).

   The above procedure MUST also be followed by a DOTS gateway.

   Details specific to each aforementioned step are elaborated in
   Sections 6,7, and 9.

6.  DHCP Options for DOTS

6.1.  Design Rationale

   As reported in Section 1.7.2 of [RFC6125], "few certification
   authorities issue server certificates based on IP addresses, but
   preliminary evidence indicates that such certificates are a very
   small percentage (less than 1%) of issued certificates".  In order to
   allow for PKIX-based authentication between a DOTS client and server,
   this document specifies the DHCP option as a name.  One or multiple
   IP addresses may be returned as a result of name resolution.

   Defining the option to include a list of IP addresses would avoid a
   dependency on an underlying name resolution, but that design requires
   to also supply a name for PKIX-based authentication purposes.

   Because aliasing is to be avoided (Section 7 of [RFC7227]), this
   document specifies one single option that conveys a DOTS server's
   name.

   This specification assumes that the same name is used to contact the
   DOTS server for both signal and data channels needs.  The selection
   of the transport protocols to be used and the companion service port
   numbers are assumed to be by default determined by the DOTS client as
   specified in [I-D.ietf-dots-signal-channel] and
   [I-D.ietf-dots-data-channel].  The provisioned DOTS name is passed to




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   the DOTS client that in its turn pass it to an underlying resolution
   library (e.g., DNS).

      DISCUSSION NOTE: Consider whether the DOTS client proceeds with
      S-NAPTR lookups.

6.2.  DHCPv6 DOTS Option

6.2.1.  Format

   The DHCPv6 DOTS option is used to configure a name of the DOTS
   server.  The format of this option is shown in Figure 2.

       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     OPTION_V6_DOTS            |         Option-length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                      dots-server-name (FQDN)                  |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                       Figure 2: DHCPv6 DOTS option

   The fields of the option shown in Figure 2 are as follows:

   o  Option-code: OPTION_V6_DOTS (TBA, see Section 11.1)
   o  Option-length: Length of the dots-server-name field in octets.
   o  dots-server-name: A fully qualified domain name of the DOTS
      server.  This field is formatted as specified in Section 8 of
      [RFC3315].

   An example of the dots-server-name encoding is shown in Figure 3.
   This example conveys the FQDN "dots.example.com.".

        +------+------+------+------+------+------+------+------+------+
        | 0x04 |   d  |   o  |   t  |  s   | 0x07 |   e  |   x  |   a  |
        +------+------+------+------+------+------+------+------+------+
        |   m  |   p  |   l  |   e  | 0x03 |   c  |   o  |   m  | 0x00 |
        +------+------+------+------+------+------+------+------+------+

           Figure 3: An example of the dots-server-name encoding








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6.2.2.  DHCPv6 Client Behavior

   DHCP clients MAY request option OPTION_V6_DOTS, as defined in
   [RFC3315], Sections 17.1.1, 18.1.1, 18.1.3, 18.1.4, 18.1.5, and 22.7.
   As a convenience to the reader, it is mentioned here that the DHCP
   client includes the requested option codes in the Option Request
   Option.

   If the DHCP client receives more than one OPTION_V6_DOTS option, it
   MUST use only the first instance of that option.

   If the OPTION_V6_DOTS option contains more than one name, as
   distinguished by the presence of multiple root labels, the DHCP
   client MUST use only the first name.  Once the name is validated
   (Section 8 of [RFC3315]), the name is passed to a name resolution
   library.

6.3.  DHCPv4 DOTS Option

6.3.1.  Format

   The DHCPv4 DOTS option is used to configure a name of the DOTS
   server.  The format of this option is illustrated in Figure 4.

            Code  Length   DOTS server name
           +-----+-----+-----+-----+-----+-----+-----+--
           | TBA |  n  |  s1 |  s2 |  s3 |  s4 | s5  |  ...
           +-----+-----+-----+-----+-----+-----+-----+--

     The values s1, s2, s3, etc. represent the domain name labels in the
     domain name encoding.


                       Figure 4: DHCPv4 DOTS option

   The fields of the option shown in Figure 4 are as follows:

   o  Code: OPTION_V4_DOTS (TBA, see Section 11.2);
   o  Length: Includes the length of the "DOTS server name" field in
      octets; the maximum length is 255 octets.
   o  DOTS server name: The domain name of the DOTS server.  This field
      is formatted as specified in Section 8 of [RFC3315].

6.3.2.  DHCPv4 Client Behavior

   To discover a DOTS server, the DHCPv4 client MUST include
   OPTION_V4_DOTS in a Parameter Request List Option [RFC2132].




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   If the DHCP client receives more than one OPTION_V4_DOTS option, it
   MUST use only the first instance of that option.

   If the OPTION_V4_DOTS option contains more than one name, as
   distinguished by the presence of multiple root labels, the DHCP
   client MUST use only the first FQDN.  Once the name is validated
   (Section 8 of [RFC3315]), the name is passed to a name resolution
   library.

7.  Discovery using Service Resolution

   This mechanism is performed in two steps:

   1.  A DNS domain name is retrieved for each combination of interface
       and address family.

   2.  Retrieved DNS domain names are then used for S-NAPTR lookups.
       Further DNS lookups may be necessary to determine DOTS server IP
       address(es).

7.1.  Retrieving Domain Name

   A DOTS client has to determine the domain in which it is located.
   The following section describes the means to obtain the domain name
   from DHCP.  Other means of retrieving domain names may be used, which
   are outside the scope of this document, e.g., local configuration.

   Implementations MAY allow the user to specify a default name that is
   used, if no specific name has been configured.

7.1.1.  DHCP

   DHCP can be used to determine the domain name related to an
   interface's point of network attachment.  Network operators may
   provide the domain name to be used for service discovery within an
   access network using DHCP.  Sections 3.2 and 3.3 of [RFC5986] define
   DHCP IPv4 and IPv6 access network domain name options,
   OPTION_V4_ACCESS_DOMAIN and OPTION_V6_ACCESS_DOMAIN respectively, to
   identify a domain name that is suitable for service discovery within
   the access network.

   For IPv4, the discovery procedure MUST request the access network
   domain name option in a Parameter Request List option, as described
   in [RFC2131].  [RFC2132] defines the DHCP IPv4 domain name option;
   while this option is less suitable, a client MAY request for it if
   the access network domain name defined in [RFC5986] is not available.





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   For IPv6, the discovery procedure MUST request for the access network
   domain name option in an Options Request Option (ORO) within an
   Information-request message, as described in [RFC3315].

   If neither option can be retrieved the procedure fails for this
   interface.  If a result can be retrieved it will be used as an input
   for S-NAPTR resolution.

7.2.  Resolution

   Once the DOTS client has retrieved domain names, an S-NAPTR lookup
   with 'DOTS' application service and the desired protocol tag is made
   to obtain information necessary to connect to the authoritative DOTS
   server within the given domain.  S-NAPTR lookup lets the DOTS server
   administrators provision the preferred DOTS transport protocol
   between the client and the server and allows the DOTS client to
   discover this preference.

   This specification defines "DOTS" as an application service tag
   (Section 11.3.1) and "signal.udp" (Section 11.3.2), "signal.tcp"
   (Section 11.3.3), and "data.tcp" (Section 11.3.4) as application
   protocol tags.





























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   (Proposal-1)
   In the example below, for domain 'example.net', the resolution
   algorithm will result in IP address(es), port, tag and protocol tuples as
   follows:

   example.net.
   IN NAPTR 100 10 "" DOTS:signal.udp "" signal.example.net.
   IN NAPTR 200 10 "" DOTS:signal.tcp "" signal.example.net.
   IN NAPTR 300 10 "" DOTS:data.tcp "" data.example.net.

   signal.example.net.
   IN NAPTR 100 10 S DOTS:signal.udp "" _dots._signal._udp.example.net.
   IN NAPTR 200 10 S DOTS:signal.tcp "" _dots._signal._tcp.example.net.

   data.example.net.
   IN NAPTR 100 10 S DOTS:data.tcp "" _dots._data._tcp.example.net.

   _dots._signal._udp.example.net.
   IN SRV   0 0 5000 a.example.net.

   _dots._signal._tcp.example.net.
   IN SRV   0 0 5001 a.example.net.

   _dots._data._tcp.example.net.
   IN SRV   0 0 5002 a.example.net.

   a.example.net.
   IN AAAA  2001:db8::1

                 +-------+----------+-------------+------+--------+
                 | Order | Protocol | IP address  | Port |   Tag  |
                 +-------+----------+-------------+------+--------+
                 | 1     | UDP      | 2001:db8::1 | 5000 | Signal |
                 | 2     | TCP      | 2001:db8::1 | 5001 | Signal |
                 | 3     | TCP      | 2001:db8::1 | 5002 | Data   |
                 +-------+----------+-------------+------+--------+















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   (Proposal-2)
   In the example below, for domain 'example.net', the resolution
   algorithm will result in IP address(es), port, tag and protocol tuples as
   follows:

   example.net.
   IN NAPTR 100 10 "" DOTS-SIGNAL:dots.udp "" signal.example.net.
   IN NAPTR 200 10 "" DOTS-SIGNAL:dots.tcp "" signal.example.net.
   IN NAPTR 300 10 "" DOTS-DATA:dots.tcp "" data.example.net.

   signal.example.net.
   IN NAPTR 100 10 S DOTS:signal.udp "" _dots._signal._udp.example.net.
   IN NAPTR 200 10 S DOTS:signal.tcp "" _dots._signal._tcp.example.net.

   data.example.net.
   IN NAPTR 100 10 S DOTS:data.tcp "" _dots._data._tcp.example.net.

   _dots._signal._udp.example.net.
   IN SRV   0 0 5000 a.example.net.

   _dots._signal._tcp.example.net.
   IN SRV   0 0 5001 a.example.net.

   _dots._data._tcp.example.net.
   IN SRV   0 0 5003 a.example.net.

   a.example.net.
   IN AAAA  2001:db8::1

                 +-------+----------+-------------+------+--------+
                 | Order | Protocol | IP address  | Port |   Tag  |
                 +-------+----------+-------------+------+--------+
                 | 1     | UDP      | 2001:db8::1 | 5000 | Signal |
                 | 2     | TCP      | 2001:db8::1 | 5001 | Signal |
                 | 3     | TCP      | 2001:db8::1 | 5003 | Data   |
                 +-------+----------+-------------+------+--------+

   If no DOTS-specific S-NAPTR records can be retrieved, the discovery
   procedure fails for this domain name (and the corresponding interface
   and IP protocol version).  If more domain names are known, the
   discovery procedure MAY perform the corresponding S-NAPTR lookups
   immediately.  However, before retrying a lookup that has failed, a
   DOTS client MUST wait a time period that is appropriate for the
   encountered error (e.g., NXDOMAIN, timeout, etc.).







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8.  DNS-SD/mDNS

   To be completed (if needed).

9.  Anycast

   IP anycast can also be used for DOTS service discovery.  A packet
   sent to an anycast address is delivered to the 'topologically
   nearest' network interface with the anycast address.

   When a DOTS client requires DOTS services, it attempts to establish a
   signaling session with the assigned anycast address(es) defined in
   Sections 11.4 and 11.5.  A DOTS server, that receives a DOTS request
   with an anycast address, SHOULD redirect the DOTS client to the
   appropriate DOTS unicast server(s) using the mechanism described in
   Section 5.5 of [I-D.ietf-dots-signal-channel], unless it is
   configured otherwise.  Indeed, a DOTS server SHOULD be configurable
   to maintain all DOTS communications using anycast.  DOTS redirect is
   not made mandatory because the use of anycast is not problematic for
   some deployment scenarios such as an enterprise network deploying one
   single DOTS gateway connected to one single network provider.

   [I-D.boucadair-dots-multihoming] identifies a set of deployment
   schemes in which the use of anycast is not recommended.

10.  Security Considerations

   DOTS-related security considerations are discussed in Section 4 of
   [I-D.ietf-dots-architecture].

10.1.  DHCP

   The security considerations in [RFC2131] and [RFC3315] are to be
   considered.

10.2.  Service Resolution

   The primary attack against the methods described in Section 7 is one
   that would lead to impersonation of a DOTS server.  An attacker could
   attempt to compromise the S-NAPTR resolution.  The use of mutual
   authentication makes it difficult to redirect a DOTS client to an
   illegitimate DOTS server.

10.3.  Anycast

   Anycast-related security considerations are discussed in [RFC4786]
   and [RFC7094].




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11.  IANA Considerations

11.1.  DHCPv6 Option

   IANA is requested to assign the following new DHCPv6 Option Code in
   the registry maintained in http://www.iana.org/assignments/
   dhcpv6-parameters:

                              Option Name Value
                           -------------- -----
                           OPTION_V6_DOTS TBA

11.2.  DHCPv4 Option

   IANA is requested to assign the following new DHCPv4 Option Code in
   the registry maintained in http://www.iana.org/assignments/bootp-
   dhcp-parameters/:

      Option Name Value Data length               Meaning
   -------------- ----- ------------------------- ----------------------
   OPTION_V4_DOTS TBA   Variable; the maximum     Includes the name of
                        length is 255 octets.     the DOTS server.

11.3.  Application Service & Application Protocol Tags

   This document requests IANA to make the following allocations from
   the registry available at: https://www.iana.org/assignments/s-naptr-
   parameters/s-naptr-parameters.xhtml.

11.3.1.  DOTS Application Service Tag Registration

   o  Application Protocol Tag: DOTS

   o  Intended Usage: See Section 7.2

   o  Security Considerations: See Section 10

   o  Contact Information: <one of the authors>

11.3.2.  signal.udp Application Protocol Tag Registration

   o  Application Protocol Tag: signal.udp

   o  Intended Usage: See Section 7.2

   o  Security Considerations: See Section 10

   o  Contact Information: <one of the authors>



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11.3.3.  signal.tcp Application Protocol Tag Registration

   o  Application Protocol Tag: signal.tcp

   o  Intended Usage: See Section 7.2

   o  Security Considerations: See Section 10

   o  Contact Information: <one of the authors>

11.3.4.  data.tcp Application Protocol Tag Registration

   o  Application Protocol Tag: data.tcp

   o  Intended Usage: See Section 7.2

   o  Security Considerations: See Section 10

   o  Contact Information: <one of the authors>

11.4.  IPv4 Anycast

   IANA has assigned a single IPv4 address from the 192.0.0.0/24 prefix
   and registered it in the "IANA IPv4 Special-Purpose Address Registry"
   [RFC6890].

    +----------------------+-------------------------------------------+
    | Attribute            | Value                                     |
    +----------------------+-------------------------------------------+
    | Address Block        | TBA                                       |
    | Name                 | Distributed-Denial-of-Service Open Threat |
    |                      | Signaling (DOTS) Anycast                  |
    | RFC                  | <this document>                           |
    | Allocation Date      | <date of approval of this document>       |
    | Termination Date     | N/A                                       |
    | Source               | True                                      |
    | Destination          | True                                      |
    | Forwardable          | True                                      |
    | Global               | True                                      |
    | Reserved-by-Protocol | False                                     |
    +----------------------+-------------------------------------------+

11.5.  IPv6 Anycast

   IANA has assigned a single IPv6 address from the 2001:0000::/23
   prefix and registered it in the "IANA IPv6 Special-Purpose Address
   Registry" [RFC6890].




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    +----------------------+-------------------------------------------+
    | Attribute            | Value                                     |
    +----------------------+-------------------------------------------+
    | Address Block        | TBA                                       |
    | Name                 | Distributed-Denial-of-Service Open Threat |
    |                      | Signaling (DOTS) Anycast                  |
    | RFC                  | <this document>                           |
    | Allocation Date      | <date of approval of this document>       |
    | Termination Date     | N/A                                       |
    | Source               | True                                      |
    | Destination          | True                                      |
    | Forwardable          | True                                      |
    | Global               | True                                      |
    | Reserved-by-Protocol | False                                     |
    +----------------------+-------------------------------------------+

12.  Acknowledgements

   To be completed.

13.  References

13.1.  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-03 (work in progress), June 2017.

   [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>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <http://www.rfc-editor.org/info/rfc2131>.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
              <http://www.rfc-editor.org/info/rfc2132>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.



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   [RFC3958]  Daigle, L. and A. Newton, "Domain-Based Application
              Service Location Using SRV RRs and the Dynamic Delegation
              Discovery Service (DDDS)", RFC 3958, DOI 10.17487/RFC3958,
              January 2005, <http://www.rfc-editor.org/info/rfc3958>.

   [RFC5986]  Thomson, M. and J. Winterbottom, "Discovering the Local
              Location Information Server (LIS)", RFC 5986,
              DOI 10.17487/RFC5986, September 2010,
              <http://www.rfc-editor.org/info/rfc5986>.

   [RFC6890]  Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
              "Special-Purpose IP Address Registries", BCP 153,
              RFC 6890, DOI 10.17487/RFC6890, April 2013,
              <http://www.rfc-editor.org/info/rfc6890>.

13.2.  Informative References

   [I-D.boucadair-dots-multihoming]
              Boucadair, M. and T. Reddy, "Multi-homing Considerations
              for Distributed-Denial-of-Service Open Threat Signaling
              (DOTS)", draft-boucadair-dots-multihoming-00 (work in
              progress), June 2017.

   [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-02 (work in progress), June 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-02 (work in progress), June 2017.

   [I-D.ietf-dots-use-cases]
              Dobbins, R., Fouant, S., Migault, D., Moskowitz, R.,
              Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS
              Open Threat Signaling (DDoS) Open Threat Signaling",
              draft-ietf-dots-use-cases-05 (work in progress), May 2017.

   [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>.






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   [RFC4786]  Abley, J. and K. Lindqvist, "Operation of Anycast
              Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
              December 2006, <http://www.rfc-editor.org/info/rfc4786>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <http://www.rfc-editor.org/info/rfc6125>.

   [RFC7094]  McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
              "Architectural Considerations of IP Anycast", RFC 7094,
              DOI 10.17487/RFC7094, January 2014,
              <http://www.rfc-editor.org/info/rfc7094>.

   [RFC7227]  Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
              S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
              BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
              <http://www.rfc-editor.org/info/rfc7227>.

Authors' Addresses

   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Tirumaleswar Reddy
   McAfee, Inc.
   Embassy Golf Link Business Park
   Bangalore, Karnataka  560071
   India

   Email: TirumaleswarReddy_Konda@McAfee.com


   Prashanth Patil
   Cisco Systems, Inc.

   Email: praspati@cisco.com







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