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Versions: (draft-boucadair-dots-server-discovery) 00 01 02 03 04 05 06

DOTS                                                        M. Boucadair
Internet-Draft                                                    Orange
Intended status: Standards Track                                T. Reddy
Expires: May 21, 2020                                             McAfee
                                                       November 18, 2019


    Distributed-Denial-of-Service Open Threat Signaling (DOTS) Agent
                               Discovery
                  draft-ietf-dots-server-discovery-06

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 DOTS server that it is
   under a potential attack so that appropriate mitigation actions are
   undertaken.

   This document specifies mechanisms to configure DOTS clients with
   their DOTS servers.  The discovery procedure also covers the DOTS
   Signal Channel Call Home.

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 https://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 May 21, 2020.

Copyright Notice

   Copyright (c) 2019 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



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   (https://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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Why Multiple Discovery Mechanisms?  . . . . . . . . . . . . .   5
   4.  Unified DOTS Discovery Procedure  . . . . . . . . . . . . . .   6
   5.  DHCP Options for DOTS Agent Discovery . . . . . . . . . . . .   8
     5.1.  DHCPv6 DOTS Options . . . . . . . . . . . . . . . . . . .   9
       5.1.1.  Format of DOTS Reference Identifier Option  . . . . .   9
       5.1.2.  Format of DOTS Address Option . . . . . . . . . . . .  10
       5.1.3.  DHCPv6 Client Behavior  . . . . . . . . . . . . . . .  10
     5.2.  DHCPv4 DOTS Options . . . . . . . . . . . . . . . . . . .  11
       5.2.1.  Format of DOTS Reference Identifier Option  . . . . .  11
       5.2.2.  Format of DOTS Address Option . . . . . . . . . . . .  12
       5.2.3.  DHCPv4 Client Behavior  . . . . . . . . . . . . . . .  13
   6.  Discovery using Service Resolution  . . . . . . . . . . . . .  13
   7.  DNS Service Discovery . . . . . . . . . . . . . . . . . . . .  16
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
     8.1.  DHCP  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
     8.2.  Service Resolution  . . . . . . . . . . . . . . . . . . .  17
     8.3.  DNS Service Discovery . . . . . . . . . . . . . . . . . .  17
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
     9.1.  DHCPv6 Options  . . . . . . . . . . . . . . . . . . . . .  18
     9.2.  DHCPv4 Options  . . . . . . . . . . . . . . . . . . . . .  18
     9.3.  Application Service & Application Protocol Tags . . . . .  18
       9.3.1.  DOTS Application Service Tag Registration . . . . . .  18
       9.3.2.  DOTS Call Home Application Service Tag Registration .  19
       9.3.3.  signal.udp Application Protocol Tag Registration  . .  19
       9.3.4.  signal.tcp Application Protocol Tag Registration  . .  19
       9.3.5.  data.tcp Application Protocol Tag Registration  . . .  19
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  19
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  20
     12.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23







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1.  Introduction

   DDoS Open Threat Signaling (DOTS) [I-D.ietf-dots-architecture]
   specifies an 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 signal channel protocol
   [I-D.ietf-dots-signal-channel] is meant to carry requests for DDoS
   attack mitigation, thereby reducing the impact of an attack and
   leading to more efficient defensive actions in various deployment
   scenarios such as those discussed in [I-D.ietf-dots-use-cases].
   Moreover, DOTS clients can instruct a DOTS server to install
   filtering rules by means of the DOTS data channel protocol
   [I-D.ietf-dots-data-channel].

   The basic high-level DOTS architecture is illustrated in Figure 1:

                     +-----------+            +-------------+
                     | 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 DOTS
   sessions by connecting to the provided DOTS server addresses.

   This document specifies methods for DOTS clients to discover their
   DOTS server(s).  The rationale for specifying multiple discovery
   mechanisms is discussed in Section 3.

   The discovery methods can also be used by a DOTS server to locate a
   DOTS client in the context of DOTS Signal Channel Call Home
   [I-D.ietf-dots-signal-call-home].  The basic high-level DOTS Call
   Home architecture is illustrated in Figure 2:






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                 +---------------+        +-------------+
                 | Alert/DMS/    | ~~~~~~ |  Call Home  |
                 | Peer DMS/...  |        | DOTS client |
                 +---------------+        +------+------+
                                                 |
                                                 |
                                                 |
                 +---------------+        +------+------+
                 |    Attack     | ~~~~~~ |  Call Home  |
                 |   Source(s)   |        | DOTS server |
                 +---------------+        +-------------+

   Figure 2: Basic DOTS Signal Channel Call Home Functional Architecture

   A DOTS agent may be used to establish base DOTS channels, DOTS Call
   Home, or both.  This specification accommodates all these deployment
   cases.

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

   This document assumes that security credentials to authenticate DOTS
   server(s) are provisioned to a DOTS client using a variety of means
   such as (but not limited to) those discussed in [RFC8572] or
   [I-D.ietf-anima-bootstrapping-keyinfra].  DOTS clients use those
   credentials for authentication purposes following the rules
   documented in [I-D.ietf-dots-signal-channel].

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The reader should be familiar with the terms defined in
   [I-D.ietf-dots-architecture], [RFC3958], and
   [I-D.ietf-dots-signal-call-home].

   DHCP refers to both DHCPv4 [RFC2131] and DHCPv6 [RFC8415].

   "Peer DOTS agent" refers to the peer DOTS server (base DOTS
   operation) or to a peer Call Home DOTS client (for DOTS Signal
   Channel Call Home).





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3.  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.
   Concretely:

   o  Many use cases discussed in [I-D.ietf-dots-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 discovery using service resolution or
      DHCP to provision the CPE acting as a DOTS client with the DOTS
      server(s).

   o  Resolving a DOTS server domain name offered by an upstream transit
      provider 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.  Furthermore,
      DHCP allows to directly provision IP addresses avoiding therefore
      the need for extra lookup delays.

   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] allows the DOTS
      server administrators to provision the preferred DOTS transport
      protocol between the DOTS client and the DOTS server and allows
      the DOTS client to discover this preference.

   o  The upstream network provider is not the DDoS mitigation provider
      for some of these use cases.  It is safe to assume that for such
      deployments, the DOTS server(s) domain name is provided during the
      service subscription (i.e., manual/local configuration).

   o  Multiple DOTS clients may be enabled within a network (e.g.,
      enterprise network).  Dynamic 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 selecting the appropriate DOTS server(s) to relay
      requests received from DOTS clients.




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   Consequently, this document describes a unified discovery logic
   (Section 4) which involves the following mechanisms:

   o  Dynamic discovery using DHCP (Section 5).

   o  A resolution mechanism based on straightforward Naming Authority
      Pointer (S-NAPTR) resource records in the Domain Name System (DNS)
      (Section 6).

   o  DNS Service Discovery (Section 7).

4.  Unified DOTS Discovery Procedure

   A key point in the deployment of DOTS is the ability of network
   operators to be able to configure DOTS clients with the correct DOTS
   server(s) information consistently.  To accomplish this, operators
   will need a consistent set of ways in which DOTS clients can discover
   this information, and a consistent priority among these options.  If
   some devices prefer manual configuration over dynamic discovery,
   while others prefer dynamic discovery over manual configuration, the
   result will be a process of "whack-a-mole", where the operator must
   find devices that are using the wrong DOTS server(s), determine how
   to ensure the devices are configured properly, and then reconfigure
   the device through the preferred method.

   All DOTS clients MUST support at least one of the three mechanisms
   below to determine a DOTS server list.  All DOTS clients SHOULD
   implement all three, or as many as are practical for any specific
   device (e.g., a CPE will support the first two mechanisms, a host
   within a LAN will support the last two mechanisms, or an application
   server will support a local configuration.  More samples are
   discussed in Section 3), of these ways to discover DOTS servers, in
   order to facilitate the deployment of DOTS in large scale
   environments:

   1.  Explicit configuration:

       *  Local/Manual configuration: A DOTS client, will learn the DOTS
          server(s) by means of local or manual DOTS configuration
          (i.e., DOTS servers configured at the system level).
          Configuration discovered from a DOTS client application is
          considered as local configuration.

          An implementation may give the user an opportunity (e.g., by
          means of configuration file options or menu items) to specify
          DOTS server(s) for each address family.  These may be
          specified either as IP addresses or the DNS name of a DOTS
          server.  When only DOTS server's IP addresses are configured,



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          a reference identifier must also be configured for
          authentication purposes.

       *  Automatic configuration (e.g., DHCP, an automation system):
          The DOTS client attempts to discover DOTS server(s) names and/
          or addresses from DHCP, as described in Section 5.

   2.  Service Resolution : The DOTS client attempts to discover DOTS
       server name(s) using service resolution, as specified in
       Section 6.

   3.  DNS SD: DNS Service Discovery.  The DOTS client attempts to
       discover DOTS server name(s) using DNS service discovery, as
       specified in Section 7.

   Some of these mechanisms imply the use of DNS to resolve the IP
   address(es) of the DOTS server, while others imply an IP address of
   the relevant DOTS server is obtained directly.  Implementation
   options may vary on a per device basis, as some devices may not have
   DNS capabilities and/or proper configuration.

   DOTS clients will prefer information received from the discovery
   methods in the order listed.

   On hosts with more than one interface or address family (IPv4/v6),
   the DOTS server discovery procedure has to be performed for each
   combination of interface and address family.  A DOTS client may
   choose to perform the discovery procedure only for a desired
   interface/address combination if the client does not wish to discover
   a DOTS server for all combinations of interface and address family.

   This procedure is also followed by a Call Home DOTS server to
   discover its Call Home DOTS client in the context of
   [I-D.ietf-dots-signal-call-home].

   The discovery method is reiterated by a DOTS agent upon the following
   events:

   o  Expiry of a lease associated with a discovered DOTS agent.

   o  Expiry of a peer DOTS agent's certificate currently in use.

   o  Attachment to a new network.








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5.  DHCP Options for DOTS Agent Discovery

   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 while accommodating for the current best practices for
   issuing certificates, this document allows for configuring names to
   DOTS clients.  These names can be used for two purposes: to retrieve
   the list of IP addresses of a DOTS server or to be presented as a
   reference identifier for authentication purposes.

   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.

   The list of the IP addresses returned by DHCP servers is typically
   used to fed the DOTS server selection procedure or to provide DOTS
   agents with primary and backup IP addresses of their peer DOTS
   agents.

   The design assumes that the same peer DOTS agent is used for
   establishing both signal and data channels.  For more customized
   configurations (e.g., transport-specific configuration, distinct DOTS
   servers for the signal and the data channels), an operator can supply
   only a DOTS reference identifier that will be then passed to the
   procedure described in Section 6.

   The design allows to terminate the base DOTS channels and DOTS Call
   Home on the same or distinct peer DOTS agents.  If distinct peer DOTS
   agents are deployed, the DHCP option can return, for example, a list
   of IP addresses to a requesting DOTS agent.  This list includes the
   IP address to be used for the base DOTS channels and the IP address
   for the DOTS Call Home.  The DOTS client (or Call Home DOTS server)
   will then use the address selection specified in Section 4.3 of
   [I-D.ietf-dots-signal-channel] to identify the IP address of the peer
   DOTS server (or Call Home DOTS client).  For example:

      Let's consider that the DOTS server is reachable at
      2001:db8:122:300::1 while the Call Home DOTS client is reachable
      at 2001:db8:122:300::2.  The DHCP server will then return one DOTS
      reference identifier and a list that includes both
      2001:db8:122:300::1 and 2001:db8:122:300::2 to a requesting DHCP
      client.  That list is passed to the DOTS client (or Call Home DOTS



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      server) which will try to establish connections to the addresses
      of that list and destination port number 4646 (or 4647).  As a
      result, the DOTS client (or Call Home DOTS server) will select
      2001:db8:122:300::1 (or 2001:db8:122:300::2) as a DOTS server (or
      Call Home DOTS client).

5.1.  DHCPv6 DOTS Options

5.1.1.  Format of DOTS Reference Identifier Option

   The DHCPv6 DOTS Reference Identifier option is used to configure a
   name of the DOTS server (or the name of the Call Home DOTS client).
   The format of this option is shown in Figure 3.

       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_RI         |         Option-length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                      dots-agent-name (FQDN)                   |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


             Figure 3: DHCPv6 DOTS Reference Identifier Option

   The fields of the option shown in Figure 3 are as follows:

   o  Option-code: OPTION_V6_DOTS_RI (TBA1, see Section 9.1)
   o  Option-length: Length of the dots-agent-name field in octets.
   o  dots-agent-name: A fully qualified domain name of the peer DOTS
      agent.  This field is formatted as specified in Section 10 of
      [RFC8415].

   An example of the dots-agent-name encoding is shown in Figure 4.
   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 4: An example of the dots-agent-name Encoding







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5.1.2.  Format of DOTS Address Option

   The DHCPv6 DOTS Address option can be used to configure a list of
   IPv6 addresses of a DOTS server (or a Call Home DOTS client).  The
   format of this option is shown in Figure 5.  As a reminder, this
   format follows the guidelines for creating new DHCPv6 options
   (Section 5.1 of [RFC7227]).

       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_ADDRESS       |         Option-length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                    DOTS ipv6-address                          |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                    DOTS ipv6-address                          |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 5: DHCPv6 DOTS Address Option

   The fields of the option shown in Figure 5 are as follows:

   o  Option-code: OPTION_V6_DOTS_ADDRESS (TBA2, see Section 9.1)
   o  Option-length: Length of the 'DOTS ipv6-address(es)' field in
      octets.  MUST be a multiple of 16.
   o  DOTS ipv6-address: Includes one or more IPv6 addresses [RFC4291]
      of the peer DOTS agent to be used by a DOTS agent for establishing
      a DOTS session.

      Note, IPv4-mapped IPv6 addresses (Section 2.5.5.2 of [RFC4291])
      are allowed to be included in this option.

5.1.3.  DHCPv6 Client Behavior

   DHCP clients MAY request options OPTION_V6_DOTS_RI and
   OPTION_V6_DOTS_ADDRESS, as defined in [RFC8415], Sections 18.2.1,
   18.2.2, 18.2.4, 18.2.5, 18.2.6, and 21.7.  As a convenience to the
   reader, it is mentioned here that the DHCP client includes the
   requested option codes in the Option Request Option.




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   If the DHCP client receives more than one instance of
   OPTION_V6_DOTS_RI (or OPTION_V6_DOTS_ADDRESS) option, it MUST use
   only the first instance of that option.

   If the DHCP client receives both OPTION_V6_DOTS_RI and
   OPTION_V6_DOTS_ADDRESS, the content of OPTION_V6_DOTS_RI is used as
   reference identifier for authentication purposes (e.g., PKIX
   [RFC6125]), while the addresses included in OPTION_V6_DOTS_ADDRESS
   are used to reach the peer DOTS agent.  In other words, the name
   conveyed in OPTION_V6_DOTS_RI MUST NOT be passed to underlying
   resolution library in the presence of OPTION_V6_DOTS_ADDRESS in a
   response.

   If the DHCP client receives OPTION_V6_DOTS_RI only, but
   OPTION_V6_DOTS_RI 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 [RFC8415]), the name is passed to a name resolution
   library.  Moreover, that name is also used as a reference identifier
   for authentication purposes.

   If the DHCP client receives OPTION_V6_DOTS_ADDRESS only, the
   address(es) included in OPTION_V6_DOTS_ADDRESS are used to reach the
   peer DOTS agent.  In addition, these addresses can be used as
   identifiers for authentication.

   The DHCP client MUST silently discard multicast and host loopback
   addresses [RFC6890] conveyed in OPTION_V6_DOTS_ADDRESS.

5.2.  DHCPv4 DOTS Options

5.2.1.  Format of DOTS Reference Identifier Option

   The DHCPv4 DOTS Reference Identifier option is used to configure a
   name of the peer DOTS agent.  The format of this option is
   illustrated in Figure 6.

            Code  Length   Peer DOTS agent name
           +-----+-----+-----+-----+-----+-----+-----+--
           |TBA3 |  n  |  s1 |  s2 |  s3 |  s4 | s5  |  ...
           +-----+-----+-----+-----+-----+-----+-----+--

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


             Figure 6: DHCPv4 DOTS Reference Identifier Option




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   The fields of the option shown in Figure 6 are as follows:

   o  Code: OPTION_V4_DOTS_RI (TBA3, see Section 9.2).
   o  Length: Includes the length of the "Peer DOTS agent name" field in
      octets; the maximum length is 255 octets.
   o  Peer DOTS agent name: The domain name of the peer DOTS agent.
      This field is formatted as specified in Section 10 of [RFC8415].

5.2.2.  Format of DOTS Address Option

   The DHCPv4 DOTS Address option can be used to configure a list of
   IPv4 addresses of a peer DOTS agent.  The format of this option is
   illustrated in Figure 7.

          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |  Code=TBA4    |     Length    |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |                               |
         +       DOTS IPv4 Address       |
         |                               |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  ---
         |                               |   |
         +       DOTS IPv4 Address       |   |
         |                               | optional
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
         .             ...               .   |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  ---


                   Figure 7: DHCPv4 DOTS Address Option

   The fields of the option shown in Figure 7 are as follows:

   o  Code: OPTION_V4_DOTS_ADDRESS (TBA4, see Section 9.2).
   o  Length: is set to 4*N, where N is the number of IPv4 addresses
      included in the option.
   o  DOTS IPv4 Address(es): Contains one or more IPv4 addresses of the
      peer DOTS agent to be used by a DOTS agent.

   OPTION_V4_DOTS_ADDRESS is a concatenation-requiring option.  As such,
   the mechanism specified in [RFC3396] MUST be used if
   OPTION_V4_DOTS_ADDRESS exceeds the maximum DHCPv4 option size of 255
   octets.







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5.2.3.  DHCPv4 Client Behavior

   To discover a peer DOTS agent, the DHCPv4 client MUST include both
   OPTION_V4_DOTS_RI and OPTION_V4_DOTS_ADDRESS in a Parameter Request
   List Option [RFC2132].

   If the DHCP client receives more than one instance of
   OPTION_V4_DOTS_RI (or OPTION_V4_DOTS_ADDRESS) option, it MUST use
   only the first instance of that option.

   If the DHCP client receives both OPTION_V4_DOTS_RI and
   OPTION_V4_DOTS_ADDRESS, the content of OPTION_V6_DOTS_RI is used as
   reference identifier for authentication purposes, while the addresses
   included in OPTION_V4_DOTS_ADDRESS are used to reach the peer DOTS
   agent.  In other words, the name conveyed in OPTION_V4_DOTS_RI MUST
   NOT be passed to underlying resolution library in the presence of
   OPTION_V4_DOTS_ADDRESS in a response.

   If the DHCP client receives OPTION_V4_DOTS_RI only, but
   OPTION_V4_DOTS_RI 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 10 of [RFC8415]), the name is passed to a name resolution
   library.  Moreover, that name is also used as a reference identifier
   for authentication purposes.

   If the DHCP client receives OPTION_V4_DOTS_ADDRESS only, the
   address(es) included in OPTION_V4_DOTS_ADDRESS are used to reach the
   peer DOTS server.  In addition, these addresses can be used as
   identifiers for authentication.

   The DHCP client MUST silently discard multicast and host loopback
   addresses conveyed in OPTION_V4_DOTS_ADDRESS.

6.  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.  A DOTS agent has to determine the domain in
       which it is located relying on dynamic means such as DHCP
       (Section 5) . Implementations may allow the user to specify a
       default name that is used, if no specific name has been
       configured.

   2.  Retrieved DNS domain names are then used for S-NAPTR lookups
       [RFC3958].  Further DNS lookups may be necessary to determine the
       peer DOTS agent IP address(es).



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   Once the DOTS agent has retrieved its DNS domain or discovered the
   peer DOTS agent name that needs to be resolved (e.g., Section 5), an
   S-NAPTR lookup with 'DOTS' application service and the desired
   protocol tag is made to obtain information necessary to connect to
   the authoritative peer DOTS agent within the given domain.

   This specification defines "DOTS" and "DOTS-CALL-HOME" as application
   service tags (Sections 9.3.1 and 9.3.2).  It also defines
   "signal.udp" (Section 9.3.3), "signal.tcp" (Section 9.3.4), and
   "data.tcp" (Section 9.3.5) as application protocol tags.  An example
   is provided in Figure 8.








































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

    Figure 8: Sample Example of Discovery of DOTS Servers using Service
                                Resolution

   An example is provided in Figure 9 for the Call Home case.











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    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-CALL-HOME:signal.udp "" signal.example.net.
    IN NAPTR 200 10 "" DOTS-CALL-HOME:signal.tcp "" signal.example.net.

    signal.example.net.
    IN NAPTR 100 10 "s" DOTS-CALL-HOME:signal.udp ""
               _dots-call-home._signal._udp.example.net.
    IN NAPTR 200 10 "s" DOTS-CALL-HOME:signal.tcp ""
               _dots-call-home._signal._tcp.example.net.

    _dots-call-home._signal._udp.example.net.
    IN SRV   0 0 6000 b.example.net.

    _dots-call-home._signal._tcp.example.net.
    IN SRV   0 0 6001 b.example.net.

    b.example.net.
    IN AAAA  2001:db8::2

             +-------+----------+-------------+------+--------+
             | Order | Protocol | IP address  | Port |   Tag  |
             +-------+----------+-------------+------+--------+
             | 1     | UDP      | 2001:db8::2 | 6000 | Signal |
             | 2     | TCP      | 2001:db8::2 | 6001 | Signal |
             +-------+----------+-------------+------+--------+

   Figure 9: Sample Example of Discovery of DOTS Call Home Client using
                            Service Resolution

   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.).

7.  DNS Service Discovery

   DNS-based Service Discovery (DNS-SD) [RFC6763] provides generic
   solutions for discovering services.  DNS-SD defines a set of naming
   rules for certain DNS record types that they use for advertising and
   discovering services.




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   Section 4.1 of [RFC6763] specifies that a service instance name in
   DNS-SD has the following structure:

   <Instance> . <Service> . <Domain>

   The <Domain> portion specifies the DNS sub-domain where the service
   instance is registered.  It may be "local.", indicating the mDNS
   local domain, or it may be a conventional domain name such as
   "example.com.".

   The <Service> portion of the DOTS service instance name MUST be
   "_dots._signal._udp" or "_dots._signal._tcp" or "_dots._data._tcp" or
   "_dots-call-home._signal._udp" or "_dots-call-home._signal._tcp".

8.  Security Considerations

   DOTS-related security considerations are discussed in Section 4 of
   [I-D.ietf-dots-architecture].  As a reminder, DOTS agents must
   authenticate each other using (D)TLS before a DOTS session is
   considered valid according to the [I-D.ietf-dots-signal-channel].

8.1.  DHCP

   The security considerations in [RFC2131] and [RFC8415] are to be
   considered.

8.2.  Service Resolution

   The primary attack against the methods described in Section 6 is one
   that would lead to impersonation of a peer DOTS agent.  An attacker
   could attempt to compromise the S-NAPTR resolution.  The use of
   mutual authentication makes it difficult to redirect a DOTS client
   (or a Call Home DOTS server) to an illegitimate DOTS server (or a
   Call Home DOTS client).

8.3.  DNS Service Discovery

   Since DNS-SD is a specification for how to name and use records in
   the existing DNS system, it has no specific additional security
   requirements over and above those that already apply to DNS queries
   and DNS updates.  For DNS queries, DNS Security Extensions (DNSSEC)
   [RFC4033] SHOULD be used where the authenticity of information is
   important.  For DNS updates, secure updates [RFC2136][RFC3007] SHOULD
   generally be used to control which clients have permission to update
   DNS records.






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9.  IANA Considerations

   IANA is requested to allocate the SRV service name of "_dots._signal"
   for DOTS signal channel over UDP or TCP, and the service name of
   "_dots._data" for DOTS data channel over TCP.

9.1.  DHCPv6 Options

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

   Value   Description              Client ORO    Singleton Option
   TBD1    OPTION_V6_DOTS_RI        Yes           Yes
   TBD2    OPTION_V6_DOTS_ADDRESS   Yes           Yes

9.2.  DHCPv4 Options

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

              Option Name Value Data length       Meaning
   ---------------------- ----- ----------------- ----------------------
        OPTION_V4_DOTS_RI TBA3  Variable; the     Includes the name of
                                maximum length is the peer DOTS agent.
                                255 octets.
   OPTION_V4_DOTS_ADDRESS TBA4  Variable          Includes one or more
                                                  IP addresses of peer
                                                  DOTS agent(s).

9.3.  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.

9.3.1.  DOTS Application Service Tag Registration

   o  Application Protocol Tag: DOTS

   o  Intended Usage: See Section 6

   o  Security Considerations: See Section 8

   o  Contact Information: <one of the authors>





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9.3.2.  DOTS Call Home Application Service Tag Registration

   o  Application Protocol Tag: DOTS-CALL-HOME

   o  Intended Usage: See Section 6

   o  Security Considerations: See Section 8

   o  Contact Information: <one of the authors>

9.3.3.  signal.udp Application Protocol Tag Registration

   o  Application Protocol Tag: signal.udp

   o  Intended Usage: See Section 6

   o  Security Considerations: See Section 8

   o  Contact Information: <one of the authors>

9.3.4.  signal.tcp Application Protocol Tag Registration

   o  Application Protocol Tag: signal.tcp

   o  Intended Usage: See Section 6

   o  Security Considerations: See Section 8

   o  Contact Information: <one of the authors>

9.3.5.  data.tcp Application Protocol Tag Registration

   o  Application Protocol Tag: data.tcp

   o  Intended Usage: See Section 6

   o  Security Considerations: See Section 8

   o  Contact Information: <one of the authors>

10.  Contributors

      Prashanth Patil
      Cisco Systems, Inc.

      Email: praspati@cisco.com





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11.  Acknowledgements

   Thanks to Brian Carpenter for the review of the BRSKI text.

   Many thanks to Russ White for the review, comments, and text
   contribution.

   Thanks for Dan Wing, Pei Wei, Valery Smyslov, and Jon Shallow for the
   review and comments.

   Thanks to Bernie Volz for the review of the DHCP section.

12.  References

12.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://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,
              <https://www.rfc-editor.org/info/rfc2132>.

   [RFC3396]  Lemon, T. and S. Cheshire, "Encoding Long Options in the
              Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396,
              DOI 10.17487/RFC3396, November 2002,
              <https://www.rfc-editor.org/info/rfc3396>.

   [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, <https://www.rfc-editor.org/info/rfc3958>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
              <https://www.rfc-editor.org/info/rfc6763>.





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   [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,
              <https://www.rfc-editor.org/info/rfc6890>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8415]  Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
              RFC 8415, DOI 10.17487/RFC8415, November 2018,
              <https://www.rfc-editor.org/info/rfc8415>.

12.2.  Informative References

   [I-D.ietf-anima-bootstrapping-keyinfra]
              Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-29 (work in progress), October 2019.

   [I-D.ietf-dots-architecture]
              Mortensen, A., K, R., Andreasen, F., Teague, N., and R.
              Compton, "Distributed-Denial-of-Service Open Threat
              Signaling (DOTS) Architecture", draft-ietf-dots-
              architecture-14 (work in progress), May 2019.

   [I-D.ietf-dots-data-channel]
              Boucadair, M. and R. K, "Distributed Denial-of-Service
              Open Threat Signaling (DOTS) Data Channel Specification",
              draft-ietf-dots-data-channel-31 (work in progress), July
              2019.

   [I-D.ietf-dots-multihoming]
              Boucadair, M., K, R., and W. Pan, "Multi-homing Deployment
              Considerations for Distributed-Denial-of-Service Open
              Threat Signaling (DOTS)", draft-ietf-dots-multihoming-02
              (work in progress), July 2019.

   [I-D.ietf-dots-signal-call-home]
              K, R., Boucadair, M., and J. Shallow, "Distributed Denial-
              of-Service Open Threat Signaling (DOTS) Signal Channel
              Call Home", draft-ietf-dots-signal-call-home-06 (work in
              progress), September 2019.





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   [I-D.ietf-dots-signal-channel]
              K, R., Boucadair, M., Patil, P., Mortensen, A., and N.
              Teague, "Distributed Denial-of-Service Open Threat
              Signaling (DOTS) Signal Channel Specification", draft-
              ietf-dots-signal-channel-38 (work in progress), October
              2019.

   [I-D.ietf-dots-use-cases]
              Dobbins, R., Migault, D., Moskowitz, R., Teague, N., Xia,
              L., and K. Nishizuka, "Use cases for DDoS Open Threat
              Signaling", draft-ietf-dots-use-cases-20 (work in
              progress), September 2019.

   [RFC2136]  Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, DOI 10.17487/RFC2136, April 1997,
              <https://www.rfc-editor.org/info/rfc2136>.

   [RFC3007]  Wellington, B., "Secure Domain Name System (DNS) Dynamic
              Update", RFC 3007, DOI 10.17487/RFC3007, November 2000,
              <https://www.rfc-editor.org/info/rfc3007>.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <https://www.rfc-editor.org/info/rfc4033>.

   [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, <https://www.rfc-editor.org/info/rfc6125>.

   [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,
              <https://www.rfc-editor.org/info/rfc7227>.

   [RFC8572]  Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
              Touch Provisioning (SZTP)", RFC 8572,
              DOI 10.17487/RFC8572, April 2019,
              <https://www.rfc-editor.org/info/rfc8572>.








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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


































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