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ADD                                                         M. Boucadair
Internet-Draft                                                    Orange
Intended status: Standards Track                                T. Reddy
Expires: February 17, 2021                                        McAfee
                                                                 D. Wing
                                                                  Citrix
                                                                 N. Cook
                                                            Open-Xchange
                                                         August 16, 2020


Encrypted DNS Discovery and Deployment Considerations for Home Networks
                         draft-btw-add-home-08

Abstract

   This document discusses encrypted DNS (e.g., DoH, DoT, DoQ)
   deployment considerations for home networks.  It particularly
   sketches the required steps to use of encrypted DNS capabilities
   provided by local networks.

   The document specifies new DHCP and Router Advertisement Options to
   convey a DNS Authentication Domain Name.

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 February 17, 2021.

Copyright Notice

   Copyright (c) 2020 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.  Sample Deployment Scenarios . . . . . . . . . . . . . . . . .   5
     3.1.  Managed CPEs  . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Unmanaged CPEs  . . . . . . . . . . . . . . . . . . . . .   6
   4.  DNS Reference Identifier Option . . . . . . . . . . . . . . .   8
     4.1.  DHCPv6 Reference Identifier Option  . . . . . . . . . . .   8
     4.2.  DHCP DNS Reference Identifier Option  . . . . . . . . . .  10
     4.3.  RA DNS Reference Identifier Option  . . . . . . . . . . .  12
   5.  Locating Encrypted DNS Servers  . . . . . . . . . . . . . . .  13
   6.  DoH URI Templates . . . . . . . . . . . . . . . . . . . . . .  14
   7.  Make Use of Discovered Encrypted DNS Server . . . . . . . . .  15
     7.1.  Encrypted DNS Auto-Upgrade  . . . . . . . . . . . . . . .  15
     7.2.  DNS Server Identity Assertion . . . . . . . . . . . . . .  15
     7.3.  Other Deployment Options  . . . . . . . . . . . . . . . .  16
   8.  Hosting Encrypted DNS Forwarder in the CPE  . . . . . . . . .  16
     8.1.  Managed CPEs  . . . . . . . . . . . . . . . . . . . . . .  16
       8.1.1.  ACME  . . . . . . . . . . . . . . . . . . . . . . . .  16
       8.1.2.  Auto-Upgrade Based on Domains and their Subdomains  .  17
     8.2.  Unmanaged CPEs  . . . . . . . . . . . . . . . . . . . . .  18
   9.  Legacy CPEs . . . . . . . . . . . . . . . . . . . . . . . . .  19
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  19
     10.1.  Spoofing Attacks . . . . . . . . . . . . . . . . . . . .  19
     10.2.  Deletion Attacks . . . . . . . . . . . . . . . . . . . .  21
     10.3.  Passive Attacks  . . . . . . . . . . . . . . . . . . . .  21
     10.4.  Security Capabilities of CPEs  . . . . . . . . . . . . .  21
     10.5.  Wireless Security - Authentication Attacks . . . . . . .  21
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     11.1.  DHCPv6 Option  . . . . . . . . . . . . . . . . . . . . .  22
     11.2.  DHCP Option  . . . . . . . . . . . . . . . . . . . . . .  22
     11.3.  RA Option  . . . . . . . . . . . . . . . . . . . . . . .  23
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  23
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     13.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Appendix A.  Customized Port Numbers and IP Addresses . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28




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1.  Introduction

   Internet Service Providers (ISPs) traditionally provide DNS resolvers
   to their customers.  Typically, ISPs deploy the following mechanisms
   to advertise a list of DNS Recursive DNS server(s) to their
   customers:

   o  Protocol Configuration Options in cellular networks [TS.24008].
   o  DHCP [RFC2132] (Domain Name Server Option) or DHCPv6
      [RFC8415][RFC3646] (OPTION_DNS_SERVERS).
   o  IPv6 Router Advertisement [RFC4861][RFC8106] (Type 25 (Recursive
      DNS Server Option)).

   The communication between a customer's device (possibly via Customer
   Premises Equipment (CPE)) and an ISP-supplied DNS resolver takes
   place by using cleartext DNS messages (Do53)
   [I-D.ietf-dnsop-terminology-ter].  Some examples are depicted in
   Figure 1.  In the case of cellular networks, the cellular network
   will provide connectivity directly to a host (e.g., smartphone,
   tablet) or via a CPE.  Do53 mechanisms used within the Local Area
   Network (LAN) are similar in both fixed and cellular CPE-based
   broadband service offerings.

           (a) Fixed Networks
                      ,--,--,--.             ,--,--,--.
                   ,-'   +--+  `-.       ,-'   ISP    `-.
                  ( LAN  |H |    CPE----(                 )
                   `-.   +--+   ,-'       `-.          ,-'
                      `--'|-'--'             `--'--'--'
                          |                     |
                          |<=======Do53========>|

           (b) Cellular Networks
                           |<===========Do53=========>|
                      ,--,-|,--.                      |
                   ,-'   +--+   `-.               ,--,--,--.
                  ( LAN  |H |     CPE------------+          \
                   `-.   +--+   ,-'            ,'   ISP     `-.
                      `--'--'--'              (                )
                                         +-----+-.          ,-'
                         +--+            |        `--'--'--'
                         |H +------------+
                         +--+
           Legend:
            * H: refers to a host.

                    Figure 1: Sample Legacy Deployments




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   This document focuses on the support of encrypted DNS such as DNS-
   over-HTTPS (DoH) [RFC8484], DNS-over-TLS (DoT) [RFC7858], or DNS-
   over-QUIC (DoQ) [I-D.ietf-dprive-dnsoquic] in local networks.  In
   particular, the document describes how a local encrypted DNS server
   can be discovered and used by connected hosts.  This document
   specifies options that allow DNS clients to discover local encrypted
   DNS servers.  Section 4 describes DHCP, DHCPv6, and RA options to
   convey the DNS Authentication Domain Name (ADN) [RFC8310].

   Some ISPs rely upon external resolvers (e.g., outsourced service or
   public resolvers); these ISPs provide their customers with the IP
   addresses of these resolvers.  These addresses are typically
   configured on CPEs using the same mechanisms listed above.  Likewise,
   users can modify the default DNS configuration of their CPEs (e.g.,
   supplied by their ISP) to configure their favorite DNS servers.  This
   document permits such deployments.

   Both managed and unmanaged CPEs are discussed in the document
   (Section 3).  Also, considerations related to hosting a DNS forwarder
   in the CPE are described (Section 8).

   Hosts and/or CPEs may be connected to multiple networks; each
   providing their own DNS configuration using the discovery mechanisms
   specified in this document.  Nevertheless, it is out of the scope of
   this specification to discuss DNS selection of multi-interface
   devices.  The reader may refer to [RFC6731] for a discussion of
   issues and an example of DNS server selection for multi-interfaced
   devices.

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.

   This document makes use of the terms defined in [RFC8499] and
   [I-D.ietf-dnsop-terminology-ter].

   Do53 refers to unencrypted DNS.

   'DoH/DoT' refers to DNS-over-HTTPS and/or DNS-over-TLS.








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3.  Sample Deployment Scenarios

3.1.  Managed CPEs

   ISPs have developed an expertise in managing service-specific
   configuration information (e.g., CPE WAN Management Protocol
   [TR-069]).  For example, these tools may be used to provision the ADN
   to managed CPEs if an encrypted DNS is supported by a local network
   similar to what is depicted in Figure 2.

   For example, DoH-capable (or DoT) clients establish the DoH (or DoT)
   session with the discovered DoH (or DoT) server.

   The DNS client discovers whether the DNS server in the local network
   supports DoH/DoT/DoQ by using a dedicated field in the discovery
   message: Encrypted DNS Types (Section 4).

           (a) Fixed Networks

                      ,--,--,--.             ,--,--,--.
                   ,-'   +--+  `-.       ,-'   ISP    `-.
                  ( LAN  |H |    CPE----(    DNS Server  )
                   `-.   +--+   ,-'       `-.         ,-'
                      `--'|-'--'             `--'--'--'
                          |                     |
                          |<===Encrypted DNS===>|

           (b) Cellular Networks

                           |<=====Encrypted DNS======>|
                      ,--,-|,--.                      |
                   ,-'   +--+   `-.               ,--,--,--.
                  ( LAN  |H |     CPE------------+          \
                   `-.   +--+   ,-'            ,'   ISP     `-.
                      `--'--'--'              (    DNS Server  )
                                         +-----+-.          ,-'
                          +--+           |        `--'--'--'
                          |H +-----------+
                          +--+

                    Figure 2: Encrypted DNS in the WAN

   Figure 2 shows the scenario where the CPE relays the list of
   encrypted DNS servers it learns for the network by using mechanisms
   like DHCP or a specific Router Advertisement message.  In such
   context, direct encrypted DNS sessions will be established between a
   host serviced by a CPE and an ISP-supplied encrypted DNS server (see
   the example depicted in Figure 3 for a DoH/DoT-capable host).



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                         ,--,--,--.             ,--,--,--.
                      ,-'          `-.       ,-'   ISP    `-.
              Host---(      LAN      CPE----(    DNS Server  )
                |     `-.          ,-'       `-.          ,-'
                |        `--'--'--'             `--'--'--'
                |                                   |
                |<=========Encrypted DNS===========>|

                  Figure 3: Direct Encrypted DNS Sessions

   Figure 4 shows a deployment where the CPE embeds a caching DNS
   forwarder.  The CPE advertises itself as the default DNS server to
   the hosts it serves.  The CPE relies upon DHCP or RA to advertise
   itself to internal hosts as the default DoT/DoH/Do53 server.  When
   receiving a DNS request it cannot handle locally, the CPE forwards
   the request to an upstream DoH/DoT/Do53 resolver.  Such deployment is
   required for IPv4 service continuity purposes (e.g.,
   [I-D.ietf-v6ops-rfc7084-bis]) or for supporting advanced services
   within the home (e.g., malware filtering, parental control,
   Manufacturer Usage Description (MUD) [RFC8520] to only allow intended
   communications to and from an IoT device).  When the CPE behaves as a
   DNS forwarder, DNS communications can be decomposed into two legs:

   o  The leg between an internal host and the CPE.

   o  The leg between the CPE and an upstream DNS resolver.

   An ISP that offers encrypted DNS to its customers may enable
   encrypted DNS in both legs as shown in Figure 4.  Additional
   considerations related to this deployment are discussed in Section 8.

                         ,--,--,--.             ,--,--,--.
                      ,-'          `-.       ,-'   ISP    `-.
              Host---(      LAN      CPE----(    DNS Server  )
                |     `-.          ,-'|      `-.          ,-'
                |        `--'--'--'   |         `--'--'--'
                |                     |             |
                |<=====Encrypted=====>|<=Encrypted=>|
                          DNS                DNS

                 Figure 4: Proxied Encrypted DNS Sessions

3.2.  Unmanaged CPEs

   Customers may decide to deploy unmanaged CPEs (assuming the CPE is
   compliant with the network access technical specification that is
   usually published by ISPs).  Upon attachment to the network, an
   unmanaged CPE receives from the network its service configuration



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   (including the DNS information) by means of, e.g., DHCP.  That DNS
   information is shared within the LAN following the same mechanisms as
   those discussed in Section 3.1.  A host can thus, for example,
   establish DoH/DoT session with a DoH/DoT server similar to what is
   depicted in Figure 3.

   Customers may also decide to deploy internal home routers (called
   hereafter, Internal CPEs) for a variety of reasons that are not
   detailed here.  Absent any explicit configuration on the internal CPE
   to override the DNS configuration it receives from the ISP-supplied
   CPE, an Internal CPE relays the DNS information it receives via DHCP/
   RA from the ISP-supplied CPE to connected hosts.  Encrypted DNS
   sessions can be established by a host with the DNS servers of the ISP
   (see Figure 5).

                    ,--,--,--.                    ,--,--,--.
                 ,-'          Internal         ,-'    ISP   `-.
          Host--(    Network#A   CPE----CPE---(    DNS Server   )
           |     `-.          ,-'              `-.          ,-'
           |        `--'--'--'                    `--'--'--'
           |                                          |
           |<==============Encrypted DNS=============>|

     Figure 5: Direct Encrypted DNS Sessions with the ISP DNS Resolver
                              (Internal CPE)

   Similar to managed CPEs, a user may modify the default DNS
   configuration of an unmanaged CPE to use his/her favorite DNS servers
   instead.  Encrypted DNS sessions can be established directly between
   a host and a 3rd Party DNS server (see Figure 6).

                 ,--,--,--.                  ,--,
               ,'         Internal        ,-'    '-     3rd Party
        Host--(  Network#A  CPE----CPE---(   ISP   )--- DNS Server
         |     `.         ,-'             `-.    -'         |
         |       `-'--'--'                   `--'           |
         |                                                  |
         |<=================Encrypted DNS==================>|

      Figure 6: Direct Encrypted DNS Sessions with a Third Party DNS
                                 Resolver

   Section 8.2 discusses considerations related to hosting a forwarder
   in the Internal CPE.







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4.  DNS Reference Identifier Option

   This section describes how a DNS client can discover the ADN of local
   encrypted DNS server(s) using DHCP (Sections 4.1 and 4.2) and
   Neighbor Discovery protocol (Section 4.3).

   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 DNS client
   and an encrypted DNS server while accommodating the current best
   practices for issuing certificates, this document allows for
   configuring an authentication domain name to be presented as a
   reference identifier for DNS authentication purposes.

   The DNS client establishes an encrypted DNS session with the
   discovered DNS IP address(es) (Section 5) and uses the mechanism
   discussed in Section 8 of [RFC8310] to authenticate the DNS server
   certificate using the authentication domain name conveyed in the DNS
   Reference Identifier.  This assumes that default port numbers are
   used to establish an encrypted DNS session (e.g., 853 for DoT, 443
   for DoH).  A discussion on the use of customized port numbers is
   included in Appendix A.

   If the DNS Reference Identifier is discovered by a host using both RA
   and DHCP, the rules discussed in Section 5.3.1 of [RFC8106] MUST be
   followed.

4.1.  DHCPv6 Reference Identifier Option

   The DHCPv6 Reference Identifier option is used to configure an
   authentication domain name of the encrypted DNS server.  The format
   of this option is shown in Figure 7.














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       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_DNS_RI          |         Option-length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Encr DNS Types|                                               |
      +---------------+                                               |
      |                                                               |
      ~                 Authentication Domain Name                    ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 7: DHCPv6 DNS Reference Identifier Option

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

   o  Option-code: OPTION_V6_DNS_RI (TBA1, see Section 11.1)
   o  Option-length: Length of the enclosed data in octets.
   o  Encr DNS Types (Encrypted DNS Types): Indicates the type(s) of the
      encrypted DNS server conveyed in this attribute.  The format of
      this 8-bit field is shown in Figure 8.

                             +-+-+-+-+-+-+-+-+
                             |U|U|U|U|U|Q|H|T|
                             +-+-+-+-+-+-+-+-+

                       Figure 8: Encrypted DNS Types

         T: If set, this bit indicates that the server supports DoT
         [RFC7858].
         H: If set, this bit indicates that the server supports DoH
         [RFC8484].
         Q: If set, this bit indicates that the server supports DoQ
         [I-D.ietf-dprive-dnsoquic].
         U: Unassigned bits.  These bits MUST be unset by the sender.
         Associating a meaning with an unassigned bit can be done via
         Standards Action [RFC8126].

      In a request, these bits are assigned to indicate the requested
      encrypted DNS server type(s) by the client.  In a response, these
      bits are set as a function of the encrypted DNS supported by the
      server and the requested encrypted DNS server type(s).

      To keep the packet small, if more than one encrypted DNS type
      (e.g., both DoH and DoT) are to be returned to a requesting client
      and the same ADN is used for these types, the corresponding bits
      MUST be set in the 'Encrypted DNS Types' field of the same option
      instance in a response.  For example, if the client requested DoH




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      and DoTand the server supports both, then both T and H bits must
      be set.
   o  Authentication Domain Name: A fully qualified domain name of the
      encrypted DNS server.  This field is formatted as specified in
      Section 10 of [RFC8415].

   An example of the Authentication Domain Name encoding is shown in
   Figure 9.  This example conveys the FQDN "doh1.example.com.".

        +------+------+------+------+------+------+------+------+------+
        | 0x04 |   d  |   o  |   h  |  1   | 0x07 |   e  |   x  |   a  |
        +------+------+------+------+------+------+------+------+------+
        |   m  |   p  |   l  |   e  | 0x03 |   c  |   o  |   m  | 0x00 |
        +------+------+------+------+------+------+------+------+------+

      Figure 9: An example of the authentication-domain-name Encoding

   Multiple instances of OPTION_V6_DNS_RI may be returned to a DHCPv6
   client; each pointing to a distinct encrypted DNS server type.

   To discover an encrypted DNS server, the DHCPv6 client including
   OPTION_V6_DNS_RI in an Option Request Option (ORO), as in Sections
   18.2.1, 18.2.2, 18.2.4, 18.2.5, 18.2.6, and 21.7 of [RFC8415].  The
   DHCPv6 client sets the Encrypted DNS Types field to the requested
   encrypted DNS server type(s).

   If the DHCPv6 client requested more than one encrypted DNS server
   type, the DHCP client MUST be prepared to receive multiple DHCP
   OPTION_V6_DNS_RI options; each option is to be treated as a separate
   encrypted DNS server.

4.2.  DHCP DNS Reference Identifier Option

   The DHCP DNS Reference Identifier option is used to configure an
   authentication domain name of the encrypted DNS server.  The format
   of this option is illustrated in Figure 10.















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            0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |     TBA2      |     Length    |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           | Encr DNS Types|               |
           +-+-+-+-+-+-+-+-+               |
           |                               |
           ~  Authentication Domain Name   ~
           |                               |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  with:

            Authentication Domain Name
           +-----+-----+-----+-----+-----+--
           |  s1 |  s2 |  s3 |  s4 | s5  |  ...
           +-----+-----+-----+-----+-----+--

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


              Figure 10: DHCP DNS Reference Identifier Option

   The fields of the option shown in Figure 10 are as follows:

   o  Code: OPTION_V4_DNS_RI (TBA2, see Section 11.2).
   o  Length: Length of the enclosed data in octets.
   o  Encr DNS Types (Encrypted DNS Types): Indicates the type(s) of the
      encrypted DNS server conveyed in this attribute.  The format of
      this field is shown in Figure 8.
   o  Authentication Domain Name: The domain name of the DoH/DoT server.
      This field is formatted as specified in Section 10 of [RFC8415].

   OPTION_V4_DNS_RI is a concatenation-requiring option.  As such, the
   mechanism specified in [RFC3396] MUST be used if OPTION_V4_DNS_RI
   exceeds the maximum DHCP option size of 255 octets.

   To discover an encrypted DNS server, the DHCP client requests the
   Encrypted DNS Reference Identifier by including OPTION_V4_DNS_RI in a
   Parameter Request List option [RFC2132].  The DHCP client sets the
   Encrypted DNS Types field to the requested encrypted DNS server.

   If the DHCP client requested more than one encrypted DNS server type,
   the DHCP client MUST be prepared to receive multiple DHCP
   OPTION_V4_DNS_RI options; each option is to be treated as a separate
   encrypted DNS server.




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4.3.  RA DNS Reference Identifier Option

   The IPv6 Router Advertisement (RA) DNS Reference Identifier option is
   used to configure an authentication domain name of the DoH/DoT
   server.  The format of this option is illustrated in Figure 11.

        0                   1                   2                   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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |     Length    | Encr DNS Types|   Unassigned  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Lifetime                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       :                  Authentication Domain Name                   :
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 11: RA DNS Reference Identifier Option

   The fields of the option shown in Figure 11 are as follows:

   o  Type: 8-bit identifier of the DNS Reference Identifier Option as
      assigned by IANA (TBA3, see Section 11.3).
   o  Length: 8-bit unsigned integer.  The length of the option
      (including the Type and Length fields) is in units of 8 octets.
   o  Encr DNS Types (Encrypted DNS Types): Indicates the type(s) of the
      encrypted DNS server conveyed in this attribute.  The format of
      this field is shown in Figure 8.
   o  Unassigned: This field is unused.  It MUST be initialized to zero
      by the sender and MUST be ignored by the receiver.
   o  Lifetime: 32-bit unsigned integer.  The maximum time in seconds
      (relative to the time the packet is received) over which the
      authentication domain name MAY be used as a DNS Reference
      Identifier.

      The value of Lifetime SHOULD by default be at least 3 *
      MaxRtrAdvInterval, where MaxRtrAdvInterval is the maximum RA
      interval as defined in [RFC4861].

      A value of all one bits (0xffffffff) represents infinity.

      A value of zero means that the DNS Reference Identifier MUST no
      longer be used.
   o  Authentication Domain Name: The domain name of the encrypted DNS
      server.  This field is formatted as specified in Section 10 of
      [RFC8415].




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      This field MUST be padded with zeros so that its size is a
      multiple of 8 octets.

5.  Locating Encrypted DNS Servers

   From an IP reachability standpoint, encrypted DNS servers SHOULD be
   located by their address literals rather than passing the discovered
   names (ADN) to a resolution library.  This avoids adding a dependency
   on another server to resolve the ADN.

   In the various scenarios sketched in Section 3, encrypted DNS servers
   may terminate on the same IP address or distinct IP addresses.
   Terminating encrypted DNS servers on the same or distinct IP
   addresses is deployment-specific.

   In order to optimize the size of discovery messages when all servers
   terminate on the same IP address, a CPE or a host relies upon the
   discovery mechanisms specified in [RFC2132][RFC3646][RFC8106] to
   retrieve a list of IP addresses to reach their DNS servers.

   In deployments where encrypted DNS servers are not co-located, a list
   of servers that is composed of encrypted DNS servers can be returned
   using in [RFC2132][RFC3646][RFC8106].  For example, a host that is
   also DoH-capable (and/or DoT-capable), will try to establish a DoH
   (and/or DoT) session to that list.  DoT and/or DoH are supported if
   the client succeeds to establish a session.

   Let's consider that the DoH server is reachable at
   2001:db8:122:300::2 while the Do53 server is reachable at
   2001:db8:122:300::1.  The DHCP server will then return a list that
   includes both 2001:db8:122:300::1 and 2001:db8:122:300::2 to a
   requesting DNS client.  That list is passed to the DNS client.  The
   DNS clients will try connecting to the DNS servers using both IP
   addresses and the standard ports for DoH and Do53 protocols in a
   fashion similar to the Happy Eyeballs mechanism defined in [RFC8305].
   The DoH client selects the IP address 2001:db8:122:300::2 with which
   the TLS session is established, whereas the legacy Do53 client
   selects the IP address 2001:db8:122:300::1 with which cleartext DNS
   messages are exchanged over UDP or TCP.












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                         Legacy Do53
                           client
                               |<===RA======|
                               | {RI,@1,@2} |             |
                               |            |             |
                               |========Do53 Query=======>|
                               |            |           --,--,-
                              ,+-,--,--.    |        ,/  S1 (@1)\.
                           ,-'          `-. |     ,-'    ISP     `-.
                 DoH/DoT --(      LAN      CPE----(                 )
            capable client  `-.          ,-'|      `-.   S2 (@2)  ,-'
                     |        `--'--'--'    |         `--'--'--'
                     |<=========RA==========|             |
                     |      {RI,@1,@2}      |             |
                     |                                    |
                     |<===============DoT/DoH============>|

        Legend:
          * S1: Do53 server
          * S2: DoH/DoT server
          * @1: IP address of S1
          * @1: IP address of S2
          * RI: DNS Reference Identifier

   The DHCP server may return a customized DNS configuration ([RFC7969])
   as a function of the requested DHCP options.  For example, if the
   DHCP client does not include a DNS Reference Identifier option in its
   request, the DHCP server will return the IP address of the Do53
   server (2001:db8:122:300::1).  If a DNS Reference Identifier option
   is present in the request, the DHCP server returns the IP address(es)
   of the DoH server (2001:db8:122:300::2) (or 2001:db8:122:300::2 and
   2001:db8:122:300::1 in this order).

   An alternate design where a list of IP addresses is also included in
   the same option conveying ADN is discussed in Appendix A.

6.  DoH URI Templates

   DoH servers may support more than one URI Template [RFC8484].  Also,
   if the resolver hosts several DoH services (e.g., no-filtering,
   blocking adult content, blocking malware), these services can be
   discovered as templates.  The following discusses a mechanism for a
   DoH client to retrieve the list of supported templates by a DoH
   server.

   Upon discovery of a DoH resolver (Section 4), the DoH client contacts
   that DoH resolver to retrieve the list of supported DoH services
   using the well-known URI defined in



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   [I-D.btw-add-rfc8484-clarification].  DoH clients re-iterates that
   request regularly to retrieve an updated list of supported DoH
   services.  Note that a "push" mode can be considered using the
   mechanism defined in [I-D.ietf-dnssd-push].

   How a DoH client makes use of the configured DoH services is out of
   scope of this document.

7.  Make Use of Discovered Encrypted DNS Server

   Even if the use of a discovered encrypted DNS server is beyond the
   discovery process and falls under encrypted server selection, the
   following subsections discuss conditions under which discovered
   encrypted DNS server can be used.

7.1.  Encrypted DNS Auto-Upgrade

   Additional considerations are discussed below for the use of DoH and
   DoT servers provided by local networks:

   o  If the DNS server's IP address discovered by using DHCP/RA is pre-
      configured in the OS or Browser as a verified resolver (e.g., part
      of an auto-upgrade program such as [Auto-upgrade]), the DNS client
      auto-upgrades to use the pre-configured encrypted DNS server tied
      to the discovered DNS server IP address.  In such a case the DNS
      client will perform additional checks out of band, such as
      confirming that the Do53 IP address and the encrypted DNS server
      are owned and operated by the same organisation.

   o  Similarly, if the ADN conveyed in DHCP/RA (Section 4) is pre-
      configured in the OS or browser as a verified resolver, the DNS
      client auto-upgrades to establish an encrypted a DoH/DoT/DoQ
      session with the ADN.

      In such case, the DNS client matches the domain name in the DNS
      Reference Identifier DHCP/RA option with the 'DNS-ID' identifier
      type within subjectAltName entry in the server certificate
      conveyed in the TLS handshake.

7.2.  DNS Server Identity Assertion

   If the discovered encrypted DNS server information is not pre-
   configured in the OS or the browser, the DNS client needs evidence
   about the encrypted server to assess its trustworthiness and a way to
   appraise such evidence.  The DNS client can validate the Policy
   Assertion Token signature (Section 7 of
   [I-D.reddy-add-server-policy-selection]) to cryptographically assert




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   the DNS server identity to identify it is connecting to an encrypted
   DNS server hosted by a specific organization (e.g., ISP).

7.3.  Other Deployment Options

   Some deployment options to securely configure hosts are discussed
   below.  These options are provided for the sake of completeness.

   o  If Device Provisioning Protocol (DPP) [DPP] is used, the
      configurator can securely configure devices in the home network
      with the local DoT/DoH server using DPP.  If the DoT/DoH servers
      use raw public keys [RFC7250], the Subject Public Key Info (SPKI)
      pin set [RFC7250] of raw public keys may be encoded in a QR code.
      The configurator (e.g., mobile device) can scan the QR code and
      provision SPKI pin set in OS/Browser.  The configurator can in-
      turn securely configure devices (e.g., thermostat) in the home
      network with the SPKI pin set using DPP.

   o  If a CPE is co-located with security services within the home
      network, the CPE can use WPA-PSK but with unique pre-shared keys
      for different endpoints to deal with security issues.  In such
      networks, [I-D.reddy-add-iot-byod-bootstrap] may be used to
      securely bootstrap endpoint devices with the authentication domain
      name and DNS server certificate of the local network's DoH/DoT
      server.

      The OS would not know if the WPA pre-shared-key is the same for
      all clients or a unique pre-shared key is assigned to the host.
      Hence, the user has to indicate to the system that a unique pre-
      shared key is assigned to trigger the bootstrapping procedure.

      If the device joins a home network using a single shared password
      among all the attached devices, a compromised device can host a
      fake access point, and the device cannot be securely bootstrapped
      with the home network's DoH/DoT server.

8.  Hosting Encrypted DNS Forwarder in the CPE

8.1.  Managed CPEs

   The following mechanisms can be used to host a DoH/DoT forwarder in a
   managed CPE (Section 3.1).

8.1.1.  ACME

   The ISP can assign a unique FQDN (e.g., cpe1.example.com) and a
   domain-validated public certificate to the encrypted DNS forwarder
   hosted on the CPE.  Automatic Certificate Management Environment



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   (ACME) [RFC8555] can be used by the ISP to automate certificate
   management functions such as domain validation procedure, certificate
   issuance and certificate revocation.

   The managed CPE should support a configuration parameter to instruct
   the CPE whether it has to relay the encrypted DNS server received
   from the ISP's network or has to announce itself as a forwarder
   within the local network.  The default behavior of the CPE is to
   supply the encrypted DNS server received from the ISP's network.

8.1.2.  Auto-Upgrade Based on Domains and their Subdomains

   If the ADN conveyed in DHCP/RA (Section 4) is pre-configured in
   popular OSes or browsers as a verified resolver and the auto-upgrade
   (Section 7.1) is allowed for both the pre-configured ADN and its sub-
   domains, the DoH/DoT client will learn the local encrypted DNS
   forwarder using DHCP/RA and auto-upgrade because the left-most label
   of the pre-configured ADN would match the subjectAltName value in the
   server certificate.  Concretely, the CPE can communicate the ADN of
   the local DoH forwarder (Section 8.1.1) to internal hosts using DHCP/
   RA (Section 4).

   Let's suppose that "example.net" is pre-configured as a verified
   resolved in the browser or OS.  If the DoH/DoT client discovers a
   local forwarder "cpe1-internal.example.net", the encrypted DNS client
   will auto-upgrade because the pre-configured ADN would match
   subjectAltName value "cpe1-internal.example.net" of type dNSName.  As
   shown in Figure 12, the auto-upgrade to a rogue server advertising
   "rs.example.org" will fail.






















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                            Rogue Server
                |              |
                X<==DHCP=======|
                | {ADN=        |
                |  rs.example.org, @rs}
                |              |                  --,--,-
                |        ,+-,--+--.             ,/  ISP   \.
                |     ,-'          `-.       ,-'            `-.
            DoH/DoT --(      LAN      CPE----( S (@1)          )
       capable client  `-.          ,-'|      `-.           ,-'
                |        `--'--'--'    |         `--'--'--'
                |<========DHCP========>|
                |{ADN=                 |
                |  cpe1-internal.example.net, @i}
                |
                |<========DoH=========>|
                |                      |
   Legend:
     * S: DoH/DoT server
     * @1: IP address of S
     * @i: internal IP address of the CPE
     * @rs: IP address of a rogue server

   Figure 12: A Simplified Example of Auto-upgrade based on Sub-domains

8.2.  Unmanaged CPEs

   The approach specified in Section 8.1 does not apply for hosting a
   DNS forwarder in an unmanaged CPE.

   The unmanaged CPE administrator (referred to as administrator) can
   host a DoH/DoT forwarder on the unmanaged CPE.  This assumes the
   following:

   o  The encrypted DNS server certificate is managed by the entity in-
      charge of hosting the encrypted DNS forwarder.

      Alternatively, a security service provider can assign a unique
      FQDN to the CPE.  The encrypted DNS forwarder will act like a
      private encrypted DNS server only be accessible from within the
      home network.

   o  The encrypted DNS forwarder will either be configured to use the
      ISP's or a 3rd party encrypted DNS server.

   o  The unmanaged CPE will advertise the encrypted DNS forwarder ADN
      using DHCP/RA to internal hosts.




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   Figure 13 illustrates an example of an unmanaged CPE hosting a
   forwarder which connects to a 3rd party encrypted DNS server.  In
   this example, the DNS information received from the managed CPE (and
   therefore from the ISP) is ignored by the Internal CPE hosting the
   forwarder.

              ,--,--,--.                         ,--,
            ,'         Internal   Managed     ,-'    '-     3rd Party
     Host--(  Network#A  CPE--------CPE------(   ISP   )--- DNS Server
      |     `.         ,-'|          |        `-.    -'       |
      |       `-'--'--'   |          |<==DHCP==>|`--'         |
      |                   |<==DHCP==>|          |             |
      |<======DHCP=======>|          |                        |
      |     {RI, @i}      |                                   |
      |<==Encrypted DNS==>|<==========Encrypted DNS==========>|

     Legend:
       * @i: IP address of the DNS forwarder hosted in the Internal
             CPE.

         Figure 13: Example of an Internal CPE Hosting a Forwarder

9.  Legacy CPEs

   Hosts serviced by legacy CPEs that can't be upgraded to support the
   options defined in Section 4 won't be able to learn the encrypted DNS
   server hosted by the ISP, in particular.  If the ADN is not
   discovered using DHCP/RA, such hosts will have to fallback to use the
   special-use domain name defined in [I-D.pp-add-resinfo] to discover
   the encrypted DNS server and to retrieve the list of supported DoH
   services using the RESINFO RRtype [I-D.pp-add-resinfo].

   The DHCP/RA option to discover ADN takes precedence over special-use
   domain name since the special-use domain name is suseptible to both
   internal and external attacks whereas DHCP/RA is only vulnerable to
   internal attacks.

10.  Security Considerations

10.1.  Spoofing Attacks

   Because DHCP/RA messages are not encrypted or protected against
   modification in any way, their content can be spoofed or modified by
   active attackers (e.g., compromised devices within the home network).
   An active attacker (Section 3.3 of [RFC3552]) can spoof the DHCP/RA
   response to provide the attacker's DoH/DoT/DoQ server.  Note that
   such an attacker can launch other attacks as discussed in Section 22
   of [RFC8415].  The attacker can get a domain name, domain-validated



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   public certificate from a CA, host a DoH/DoT/DoQ server and claim the
   best DNS privacy preservation policy.  Also, an attacker can use a
   public IP address, get an 'IP address'-validated public certificate
   from a CA, host a DoH/DoT/DoQ server and claim the best DNS privacy
   preservation policy.

   The possible mitigations for this attack are listed below:

   o  Encrypted DNS server pre-configured in the OS or browser.  If the
      local DoH/DoT server offers malware and phishing filtering
      service, an attacker can spoof the DHCP/RA response to provide an
      non-filtering DNS server pre-configured in the OS or browser,
      which the attacker can leverage to deliver malware or mislead the
      user to access phishing sites.  If the discovered encrypted DNS
      server does not meet the filtering requirements of the user, the
      DNS client can take appropriate actions.  For example, the action
      by the DNS client can be not use the locally-discovered DoH/DoT
      server if it does not offer malware and phishing filtering service
      (e.g., [I-D.reddy-add-server-policy-selection]).

   o  Cryptographically assert the DNS server identity to identify the
      DNS client is connecting to an encrypted DNS server hosted by a
      specific organization [I-D.reddy-add-server-policy-selection].

   o  The client can use STUN Binding request/response transaction to
      discover its public IP address, as described in [RFC8489].  The IP
      address ownership validation of the public IP address can be used
      by the client to identify the organization that registers
      ownership of the public IP address (using the freely available
      tools on the Internet).  If the DNS server is not hosted by the
      same organization, the endpoint can detect DHCP/RA response is
      spoofed.  In order to prevent an attacker from modifying the STUN
      messages in transit, the STUN client and server MUST use the
      message-integrity mechanism discussed in Section 9 of [RFC8489] or
      use STUN over DTLS or use STUN over TLS.

   DoT/DoH sessions with rogue servers spoofing the IP address of a DNS
   server will fail because the DNS client will fail to authenticate
   that rogue server based upon PKIX authentication [RFC6125] based upon
   the authentication domain name in the Reference Identifier Option.
   DNS clients that ignore authentication failures and accept spoofed
   certificates will be subject to attacks (e.g., redirect to malicious
   servers, intercept sensitive data).








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10.2.  Deletion Attacks

   If the DHCP responses or RAs are dropped by the attacker, the client
   can fallback to use a pre-configured encrypted DNS server.  However,
   the use of policies to select servers is out of scope of this
   document.

   Note that deletion attack is not specific to DHCP/RA.

10.3.  Passive Attacks

   A passive attacker (Section 3.2 of [RFC3552]) can identify a host is
   using DHCP/RA to discover an encrypted DNS server and can infer that
   host is capable of using DoH/DoT/DoQ to encrypt DNS messages.
   However, a passive attacker cannot spoof or modify DHCP/RA messages.

10.4.  Security Capabilities of CPEs

   TCP connections received from outside the home network MUST be
   discarded by the encrypted DNS forwarder in the CPE.  This behavior
   adheres to REQ#8 in [RFC6092]; it MUST apply for both IPv4 and IPv6.

   Various home routers also offer levels of security.  Attacks of
   spoofed or modified DHCP responses and RA messages by attackers
   within the home network may be mitigated by making use of the
   following mechanisms:

   o  DHCPv6-Shield described in [RFC7610], the CPEs discards DHCP
      response messages received from any local endpoint.

   o  RA-Guard described in [RFC7113], the CPE discards RAs messages
      received from any local endpoint.

   o  Source Address Validation Improvement (SAVI) solution for DHCP
      described in [RFC7513], the CPE filters packets with forged source
      IP addresses.

10.5.  Wireless Security - Authentication Attacks

   Wireless LAN (WLAN) as frequently deployed in home networks is
   vulnerable to various attacks (e.g., [Evil-Twin], [Krack],
   [Dragonblood]).  Because of these attacks, only cryptographically
   authenticated communications are trusted on WLANs.  This means
   information provided by such networks via DHCP, DHCPv6, or RA (e.g.,
   NTP server, DNS server, default domain) are untrusted because DHCP
   and RA are not authenticated.





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   With the current deployments (2020), the pre-shared-key is the same
   for all clients that connect to the same WLAN.  This results in the
   key being shared to attackers resulting in security breach.  Man-in-
   the-middle attacks are possible within home networks because WLAN
   authentication lacks peer entity authentication.

   This leads to the need for provisioning unique credentials for
   different clients.  Endpoints can be provisioned with unique
   credentials (username and password, typically) provided by the home
   network administraor to mutually authenticate to the home WLAN Access
   Point (e.g., 802.1x Wireless User Authentication on OpenWRT [dot1x],
   EAP-pwd [RFC8146]).  Not all of endpoint devices (e.g., IoT devices)
   support 802.1x supplicant and need an alternate mechanism to connect
   to the home network.  To address this limitation, unique pre-shared
   keys can be created for each such device and WPA-PSK is used (e.g.,
   [PSK]).

11.  IANA Considerations

11.1.  DHCPv6 Option

   IANA is requested to assign the following new DHCPv6 Option Code in
   the registry maintained in: https://www.iana.org/assignments/dhcpv6-
   parameters/dhcpv6-parameters.xhtml#dhcpv6-parameters-2.

   +-------+------------------+---------+-------------+----------------+
   | Value | Description      | Client  | Singleton   | Reference      |
   |       |                  | ORO     | Option      |                |
   +-------+------------------+---------+-------------+----------------+
   | TBA1  | OPTION_V6_DNS_RI | Yes     | Yes         | [ThisDocument] |
   +-------+------------------+---------+-------------+----------------+

11.2.  DHCP Option

   IANA is requested to assign the following new DHCP Option Code in the
   registry maintained in: https://www.iana.org/assignments/bootp-dhcp-
   parameters/bootp-dhcp-parameters.xhtml#options.

   +------+------------------+-------+----------------+----------------+
   | Tag  | Name             | Data  | Meaning        | Reference      |
   |      |                  | Length|                |                |
   +------+------------------+-------+----------------+----------------+
   | TBA2 | OPTION_V4_DNS_RI | N     | DoT/DoH server | [ThisDocument] |
   |      |                  |       | authentication |                |
   |      |                  |       | domain name    |                |
   +------+------------------+-------+----------------+----------------+





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11.3.  RA Option

   IANA is requested to assign the following new IPv6 Neighbor Discovery
   Option type in the "IPv6 Neighbor Discovery Option Formats" sub-
   registry under the "Internet Control Message Protocol version 6
   (ICMPv6) Parameters" registry maintained in
   http://www.iana.org/assignments/icmpv6-parameters/
   icmpv6-parameters.xhtml#icmpv6-parameters-5.

        +------+---------------------------------+----------------+
        | Type | Description                     | Reference      |
        +------+---------------------------------+----------------+
        | TBA3 | DNS Reference Identifier Option | [ThisDocument] |
        +------+---------------------------------+----------------+

12.  Acknowledgements

   Many thanks to Christian Jacquenet for the review.

   Thanks to Tommy Jensen, Stephen Farrell, Martin Thomson, Vittorio
   Bertola, Stephane Bortzmeyer, Ben Schwartz and Iain Sharp for the
   comments.

   Thanks to Mark Nottingham for the feedback on HTTP redirection.

13.  References

13.1.  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>.

   [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>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.




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   [RFC8106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 8106, DOI 10.17487/RFC8106, March 2017,
              <https://www.rfc-editor.org/info/rfc8106>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [RFC8310]  Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
              for DNS over TLS and DNS over DTLS", RFC 8310,
              DOI 10.17487/RFC8310, March 2018,
              <https://www.rfc-editor.org/info/rfc8310>.

   [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>.

13.2.  Informative References

   [Auto-upgrade]
              The Unicode Consortium, "DoH providers: criteria, process
              for Chrome", <docs.google.com/document/
              d/128i2YTV2C7T6Gr3I-81zlQ-_Lprnsp24qzy_20Z1Psw/edit>.

   [dot1x]    Cisco, "Basic 802.1x Wireless User Authentication",
              <https://openwrt.org/docs/guide-user/network/wifi/
              wireless.security.8021x>.

   [DPP]      The Wi-Fi Alliance, "Device Provisioning Protocol
              Specification", <https://www.wi-fi.org/file/device-
              provisioning-protocol-specification>.

   [Dragonblood]
              The Unicode Consortium, "Dragonblood: Analyzing the
              Dragonfly Handshake of WPA3 and EAP-pwd",
              <https://papers.mathyvanhoef.com/dragonblood.pdf>.







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   [Evil-Twin]
              The Unicode Consortium, "Evil twin (wireless networks)",
              <https://en.wikipedia.org/wiki/
              Evil_twin_(wireless_networks)>.

   [I-D.btw-add-rfc8484-clarification]
              Boucadair, M., Cook, N., Reddy.K, T., and D. Wing,
              "Supporting Redirection for DNS Queries over HTTPS (DoH)",
              draft-btw-add-rfc8484-clarification-02 (work in progress),
              July 2020.

   [I-D.ietf-dnsop-terminology-ter]
              Hoffman, P., "Terminology for DNS Transports and
              Location", draft-ietf-dnsop-terminology-ter-02 (work in
              progress), August 2020.

   [I-D.ietf-dnssd-push]
              Pusateri, T. and S. Cheshire, "DNS Push Notifications",
              draft-ietf-dnssd-push-25 (work in progress), October 2019.

   [I-D.ietf-dprive-dnsoquic]
              Huitema, C., Mankin, A., and S. Dickinson, "Specification
              of DNS over Dedicated QUIC Connections", draft-ietf-
              dprive-dnsoquic-00 (work in progress), April 2020.

   [I-D.ietf-v6ops-rfc7084-bis]
              Palet, J., "Basic Requirements for IPv6 Customer Edge
              Routers", draft-ietf-v6ops-rfc7084-bis-04 (work in
              progress), June 2017.

   [I-D.pp-add-resinfo]
              Sood, P. and P. Hoffman, "DNS Resolver Information Self-
              publication", draft-pp-add-resinfo-02 (work in progress),
              June 2020.

   [I-D.reddy-add-iot-byod-bootstrap]
              Reddy.K, T., Wing, D., Richardson, M., and M. Boucadair,
              "A Bootstrapping Procedure to Discover and Authenticate
              DNS-over-TLS and DNS-over-HTTPS Servers for IoT and BYOD
              Devices", draft-reddy-add-iot-byod-bootstrap-01 (work in
              progress), July 2020.

   [I-D.reddy-add-server-policy-selection]
              Reddy.K, T., Wing, D., Richardson, M., and M. Boucadair,
              "DNS Server Selection: DNS Server Information with
              Assertion Token", draft-reddy-add-server-policy-
              selection-04 (work in progress), July 2020.




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   [Krack]    The Unicode Consortium, "Key Reinstallation Attacks",
              2017, <https://www.krackattacks.com/>.

   [PSK]      Cisco, "Identity PSK Feature Deployment Guide",
              <https://www.cisco.com/c/en/us/td/docs/wireless/
              controller/technotes/8-5/
              b_Identity_PSK_Feature_Deployment_Guide.html>.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              DOI 10.17487/RFC3552, July 2003,
              <https://www.rfc-editor.org/info/rfc3552>.

   [RFC3646]  Droms, R., Ed., "DNS Configuration options for Dynamic
              Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              DOI 10.17487/RFC3646, December 2003,
              <https://www.rfc-editor.org/info/rfc3646>.

   [RFC6092]  Woodyatt, J., Ed., "Recommended Simple Security
              Capabilities in Customer Premises Equipment (CPE) for
              Providing Residential IPv6 Internet Service", RFC 6092,
              DOI 10.17487/RFC6092, January 2011,
              <https://www.rfc-editor.org/info/rfc6092>.

   [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>.

   [RFC6731]  Savolainen, T., Kato, J., and T. Lemon, "Improved
              Recursive DNS Server Selection for Multi-Interfaced
              Nodes", RFC 6731, DOI 10.17487/RFC6731, December 2012,
              <https://www.rfc-editor.org/info/rfc6731>.

   [RFC7113]  Gont, F., "Implementation Advice for IPv6 Router
              Advertisement Guard (RA-Guard)", RFC 7113,
              DOI 10.17487/RFC7113, February 2014,
              <https://www.rfc-editor.org/info/rfc7113>.

   [RFC7250]  Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
              Weiler, S., and T. Kivinen, "Using Raw Public Keys in
              Transport Layer Security (TLS) and Datagram Transport
              Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
              June 2014, <https://www.rfc-editor.org/info/rfc7250>.





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   [RFC7513]  Bi, J., Wu, J., Yao, G., and F. Baker, "Source Address
              Validation Improvement (SAVI) Solution for DHCP",
              RFC 7513, DOI 10.17487/RFC7513, May 2015,
              <https://www.rfc-editor.org/info/rfc7513>.

   [RFC7610]  Gont, F., Liu, W., and G. Van de Velde, "DHCPv6-Shield:
              Protecting against Rogue DHCPv6 Servers", BCP 199,
              RFC 7610, DOI 10.17487/RFC7610, August 2015,
              <https://www.rfc-editor.org/info/rfc7610>.

   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/info/rfc7858>.

   [RFC7969]  Lemon, T. and T. Mrugalski, "Customizing DHCP
              Configuration on the Basis of Network Topology", RFC 7969,
              DOI 10.17487/RFC7969, October 2016,
              <https://www.rfc-editor.org/info/rfc7969>.

   [RFC8146]  Harkins, D., "Adding Support for Salted Password Databases
              to EAP-pwd", RFC 8146, DOI 10.17487/RFC8146, April 2017,
              <https://www.rfc-editor.org/info/rfc8146>.

   [RFC8305]  Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
              Better Connectivity Using Concurrency", RFC 8305,
              DOI 10.17487/RFC8305, December 2017,
              <https://www.rfc-editor.org/info/rfc8305>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.

   [RFC8489]  Petit-Huguenin, M., Salgueiro, G., Rosenberg, J., Wing,
              D., Mahy, R., and P. Matthews, "Session Traversal
              Utilities for NAT (STUN)", RFC 8489, DOI 10.17487/RFC8489,
              February 2020, <https://www.rfc-editor.org/info/rfc8489>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.

   [RFC8520]  Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
              Description Specification", RFC 8520,
              DOI 10.17487/RFC8520, March 2019,
              <https://www.rfc-editor.org/info/rfc8520>.





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   [RFC8555]  Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
              Kasten, "Automatic Certificate Management Environment
              (ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
              <https://www.rfc-editor.org/info/rfc8555>.

   [TR-069]   The Broadband Forum, "CPE WAN Management Protocol",
              December 2018, <https://www.broadband-
              forum.org/technical/download/TR-069.pdf>.

   [TS.24008]
              3GPP, "Mobile radio interface Layer 3 specification; Core
              network protocols; Stage 3 (Release 16)", December 2019,
              <http://www.3gpp.org/DynaReport/24008.htm>.

Appendix A.  Customized Port Numbers and IP Addresses

   DoT and DoQ may make use of customized port numbers instead of
   default ones.  Also, if many encrypted DNS types are supported by a
   network but terminate in distinct IP addresses, it is tempting to
   simplify the probing at the client side by returning both a port
   number and a list of IP addresses in the option that conveys the ADN.
   An example of such option is shown in Figure 14.  This design will
   exacerbate the size of discovery messages.

   More input is required from the WG.

       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_DNS_RI          |         Option-length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Enc DNS Type | Num addresses |          Port Number          |
      +---------------+---------------+-------------------------------+
      |                                                               |
      ~                         IPv6 Addresses                        ~
      |                                                               |
      +---------------------------------------------------------------+
      |                                                               |
      ~                  DNS Authentication Domain Name               ~
      |                                                               |
      +---------------------------------------------------------------+

                                 Figure 14

Authors' Addresses







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   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


   Dan Wing
   Citrix Systems, Inc.
   USA

   Email: dwing-ietf@fuggles.com


   Neil Cook
   Open-Xchange
   UK

   Email: neil.cook@noware.co.uk






















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