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Discovery of Encrypted DNS Resolvers: Deployment Considerations
draft-boucadair-add-deployment-considerations-01

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Mohamed Boucadair , Tirumaleswar Reddy.K , Dan Wing , Neil Cook , Tommy Jensen
Last updated 2022-09-20 (Latest revision 2022-09-07)
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draft-boucadair-add-deployment-considerations-01
Network Working Group                                  M. Boucadair, Ed.
Internet-Draft                                                    Orange
Intended status: Informational                             T. Reddy, Ed.
Expires: 11 March 2023                                             Nokia
                                                                 D. Wing
                                                                  Citrix
                                                                 N. Cook
                                                            Open-Xchange
                                                               T. Jensen
                                                               Microsoft
                                                        7 September 2022

    Discovery of Encrypted DNS Resolvers: Deployment Considerations
            draft-boucadair-add-deployment-considerations-01

Abstract

   The document discusses some deployment considerations of the various
   options to discover encrypted DNS resolvers (e.g., DNS-over-HTTPS,
   DNS-over-TLS, or DNS-over-QUIC).  Particularly, this document is
   meant to exemplify how Discovery of Network-designated Resolvers
   (DNR) and Discovery of Designated Resolvers (DDR) can be used in
   typical deployment contexts.  Also, the document includes
   considerations related to hosting a DNS forwarder in local networks.

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 11 March 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Sample Target Deployment Scenarios  . . . . . . . . . . . . .   4
     3.1.  Managed CPEs  . . . . . . . . . . . . . . . . . . . . . .   6
       3.1.1.  Direct DNS  . . . . . . . . . . . . . . . . . . . . .   6
       3.1.2.  Proxied DNS . . . . . . . . . . . . . . . . . . . . .   8
     3.2.  Unmanaged CPEs  . . . . . . . . . . . . . . . . . . . . .  10
       3.2.1.  ISP-facing Unmanaged CPEs . . . . . . . . . . . . . .  10
       3.2.2.  Internal Unmanaged CPEs . . . . . . . . . . . . . . .  10
   4.  Hosting Encrypted DNS Forwarder in Local Networks . . . . . .  11
     4.1.  Managed CPEs  . . . . . . . . . . . . . . . . . . . . . .  11
       4.1.1.  DNS Forwarders  . . . . . . . . . . . . . . . . . . .  11
       4.1.2.  ACME  . . . . . . . . . . . . . . . . . . . . . . . .  11
     4.2.  Unmanaged CPEs  . . . . . . . . . . . . . . . . . . . . .  12
   5.  Legacy CPEs . . . . . . . . . . . . . . . . . . . . . . . . .  14
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   Discovery of Network-designated Resolvers (DNR) [I-D.ietf-add-dnr]
   specifies how a local encrypted DNS resolver can be discovered by
   connected hosts by means of DHCP [RFC2132], DHCPv6 [RFC8415], and
   IPv6 Router Advertisement (RA) [RFC4861] options.  These options are
   designed to convey the following information: the DNS Authentication
   Domain Name (ADN), a list of IP addresses, and a set of service
   parameters.  The ADN is used as a reference identifier for
   authentication purposes, while the list of IP addresses designate
   where to locate the resolver without relying upon an external
   resolver.  The service parameters provide additional information to
   characterize a DNS resolver (e.g., supported encrypted DNS,
   customized DNS port number, or URI Template for DNS-over-HTTPS

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   (DoH)).  Such an information is used by a DNS client for DNS resolver
   selection and session establishment.

   This document discusses some deployment considerations for the
   discovery of encrypted DNS resolvers such as DoH [RFC8484], DNS-over-
   TLS (DoT) [RFC7858], or DNS-over-QUIC (DoQ) [RFC9250] in local
   networks.

   Sample target deployment scenarios are discussed in Section 3; both
   managed and unmanaged Customer Premises Equipment (CPEs) are covered.
   It is out of the scope of this document to provide an exhaustive
   inventory of deployments where Encrypted DNS options can be used.

   Considerations related to hosting a DNS forwarder in a local network
   are described in Section 4.  In contexts where CPEs can't be upgraded
   to support DNR, Discovery of Designated Resolvers (DDR)
   [I-D.ietf-add-ddr] can be used.  See Section 5 for more details.

   Techniques, such as the one defined in
   [I-D.boucadair-opsawg-add-encrypted-dns], can be enabled together
   with [I-D.ietf-add-dnr] to feed the Encrypted DNS options.  However,
   the document does not make any assumption about the internal behavior
   at the network side to feed the Encrypted DNS options that are
   supplied to requesting hosts; only the external observed behavior is
   detailed in the following sections.

   Policies to guide the activation and selection of encrypted DNS can
   be configured by users using implementation specific means (e.g., CPE
   management interface).

2.  Terminology

   This document makes use of the terms defined in [RFC8499].

   The following additional terms are used:

   DHCP:  refers to both DHCPv4 and DHCPv6.

   Do53:  refers to unencrypted DNS.

   DNR:  refers to the Discovery of Network-designated Resolvers
      procedure defined in [I-D.ietf-add-dnr].

   DDR:  refers to the Discovery of Designated Resolvers procedure
      defined in [I-D.ietf-add-ddr].

   Encrypted DNS:  refers to a scheme where DNS exchanges are

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      transported over an encrypted channel.  Examples of encrypted DNS
      are DoT, DoH, or DoQ.

   Encrypted DNS options:  refers to the options defined in
      [I-D.ietf-add-dnr].

   Managed CPE:  refers to a CPE that is managed by an Internet Service
      Provider (ISP).

   Unmanaged CPE:  refers to a CPE that is not managed by an ISP.

3.  Sample Target Deployment Scenarios

   ISPs usually provide DNS resolvers to their customers.  To that aim,
   ISPs deploy the following mechanisms to advertise a list of DNS
   Recursive DNS server(s) to their customers:

   *  Protocol Configuration Options in cellular networks [TS.24008].

   *  DHCPv4 [RFC2132] (Domain Name Server Option) or DHCPv6
      [RFC8415][RFC3646] (OPTION_DNS_SERVERS).

   *  IPv6 Router Advertisement [RFC4861][RFC8106] (Type 25 (Recursive
      DNS Server Option)).

   The communication between a customer's device (possibly via a CPE)
   and an ISP-supplied DNS resolver takes place by using cleartext DNS
   messages (Do53).  Some examples are depicted in cases (a) and (c) of
   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.

   Some ISPs rely upon external resolvers (e.g., outsourced service or
   public resolvers); these ISPs provide their customers with the IP
   addresses of these external DNS resolvers.  An example is depicted in
   cases (b) and (d) of Figure 1.

   The IP addresses of the DNS resolver can also be configured on CPEs
   using dedicated management tools.  As such, 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.

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     (a) Fixed networks with a local DNS resolver

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

     (b) Fixed networks with a 3rd party DNS resolver

                                      ,--,--,--.
         +-+      LAN     +---+    ,-'           `-.      3rd Party
         |H+--------------+CPE+---+      ISP        )--- DNS Resolver
         +-+              +---+    `-.          ,-'         |
          |                           `--'--'--'            |
          |                                                 |
          |<========================Do53===================>|
          |                                                 |

     (c) Cellular networks with a local DNS resolver

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

     (d) Cellular networks with a 3rd party DNS resolver

          |                                               |
          |<==================Do53=======================>|
          |                                               |
          |                           ,--,--,-.           |
         +-+      LAN     +---+    ,-'         .          |
         |H+--------------+CPE+---+             \         |

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         +-+              +---+  ,'     ISP     `-.    3rd Party
                                 (                )--- DNS Resolver
                            +-----+-.          ,-'        |
         +-+                |        `--'--'--'           |
         |H+----------------+                             |
         +-+                                              |
          |                                               |
          |<==================Do53=======================>|
          |                                               |

     Legend:
      * H: refers to a host.

                    Figure 1: Sample Legacy Deployments

3.1.  Managed CPEs

   This section focuses on CPEs that are managed by ISPs.

3.1.1.  Direct DNS

   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 DNS
   server's ADN and additional service parameters to managed CPEs if an
   encrypted DNS is supported by a network similar to what is depicted
   in Figure 2.

   For example, DoH-capable DNS clients establish the DoH session with
   the discovered DoH server.

   The DNS client discovers whether the network-designated DNS resolver
   supports a given encrypted DNS scheme (e.g., DoT or DoH) by using the
   "alpn" service parameter (Section 3.1.5 of [I-D.ietf-add-dnr]).

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             (a) Fixed Networks

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

             (b) Cellular Networks

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

                     Figure 2: Encrypted DNS in the WAN

   Figure 2 shows the scenario where the CPE relays the list of
   encrypted DNS resolvers it learns from the network by using, e.g.,
   DNR.  Direct encrypted DNS sessions will be established between a
   host serviced by a CPE and an ISP-supplied encrypted DNS resolver.
   Figure 3 shows the example of exchanges that occur for an encrypted
   DNS capable host.  The DNR exchanges that occur at the CPE WAN may be
   terminated by a centralized DHCP server or a router that is located
   at the edge of the ISP's network.

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

                  Figure 3: Direct Encrypted DNS Sessions

3.1.2.  Proxied DNS

   Figure 4 shows various deployments where the CPE embeds a caching DNS
   forwarder.  Cases (b) and (d) involves a host (called legacy host)
   that does not support DNR.

 (a)

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

 (b)
                       ,--,--,--.             ,--,--,--.
           Legacy   ,-'          `-.       ,-'   ISP    `-.
            Host---(      LAN      CPE----(    DNS Resolver)
              |     `-.          ,-'|      `-.          ,-'
              |        `--'--'--'   |       | `--'--'--'
              |                     |<=DNR=>|     |
              |<====DHCP/RA(Do53)==>|       |     |
              |                     |             |
              |<=======Do53========>|<=Encrypted=>|
              |                     |     DNS     |

 (c)

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                   ,--,--,--.             ,--,--,--.
                ,-'          `-.       ,-'   ISP    `-.      3rd Party
        Host---(      LAN      CPE----(                )--- DNS Resolver
          |     `-.          ,-'|      `-.          ,-'        |
          |        `--'--'--'   |       | `--'--'--'           |
          |                     |<=DNR=>|                      |
          |<========DNR========>|       |                      |
          |                     |                              |
          |<=====Encrypted=====>|<=========Encrypted DNS======>|
          |         DNS         |                              |

 (d)

                   ,--,--,--.             ,--,--,--.
       Legacy   ,-'          `-.       ,-'   ISP    `-.      3rd Party
        Host---(      LAN      CPE----(                )--- DNS Resolver
          |     `-.          ,-'|      `-.          ,-'        |
          |        `--'--'--'   |       | `--'--'--'           |
          |                     |<=DNR=>|                      |
          |<====DHCP/RA(Do53)==>|       |                      |
          |                     |                              |
          |<========Do53=======>|<=========Encrypted DNS======>|
          |                     |                              |

                Figure 4: Proxied Encrypted DNS Sessions

   For all the cases shown in Figure 4, the CPE advertises itself as the
   default DNS server to the hosts it serves in the LAN.  The CPE relies
   upon DHCP or RA to advertise itself to internal hosts as the default
   encrypted DNS (cases (a) and (c)) or Do53 resolver (cases (b) and
   (d)).  When receiving a DNS request it cannot handle locally, the CPE
   forwards the request to an upstream encrypted DNS.  The upstream
   encrypted DNS can be hosted by the ISP (cases (a) and (b)) or
   provided by a third party (cases (c) and (d)).

   Such a forwarder deployment is required for IPv4 service continuity
   purposes (e.g., Section 5.4.1 of [I-D.ietf-v6ops-rfc7084-bis]) or for
   supporting advanced services within a local network (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:

   *  The leg between an internal host and the CPE.

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

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

3.2.  Unmanaged CPEs

3.2.1.  ISP-facing 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
   (including the network-designated 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 then
   establish encrypted DNS sessions with encrypted DNS resolvers similar
   to what is depicted in Figure 3 or Figure 4.

3.2.2.  Internal Unmanaged CPEs

   Customers may also decide to deploy internal 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 resolvers that are supplied by the
   ISP (see Figure 5).

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

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

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

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

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

   Section 4.2 discusses considerations related to hosting a forwarder
   in the Internal CPE.

4.  Hosting Encrypted DNS Forwarder in Local Networks

   This section discusses some deployment considerations to host an
   encrypted DNS forwarder within a local network.

4.1.  Managed CPEs

   The section discusses mechanisms that can be used to host an
   encrypted DNS forwarder in a managed CPE (Section 3.1).

4.1.1.  DNS Forwarders

   The managed CPE should support a configuration parameter to instruct
   the CPE whether it has to relay the encrypted DNS resolver 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 resolver received from the ISP's network.

4.1.2.  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.

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

4.2.  Unmanaged CPEs

   The approach specified in Section 4.1 does not apply for hosting a
   DNS forwarder in an unmanaged CPE.

   The unmanaged CPE administrator can host an encrypted DNS forwarder
   on the unmanaged CPE.  This assumes the following:

   *  The encrypted DNS resolver 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 resolver only be accessible from within the
      local network.

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

   *  The unmanaged CPE will advertise the encrypted DNS forwarder ADN
      using DHCP/RA to internal hosts as per [I-D.ietf-add-dnr].

   Figure 7 illustrates an example of an unmanaged CPE hosting a
   forwarder which connects to a 3rd party encrypted DNS resolver.  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.  The internal CPE may support a mechanism (e.g.,
   [I-D.ietf-add-split-horizon-authority]) to resolve split-horizon
   domains (e.g., provider's private name discussed in Section 2 of
   [RFC6731]).

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

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

          Figure 7: Example of an Internal CPE Hosting a Forwarder

   An unmanaged CPE can be used to host an encrypted DNS forwarder even
   if the managed CPE does not support DNR.  In the example depicted in
   Figure 8, the ISP uses DHCP to provision Do53 resolvers to managed
   CPEs, while DNR is enabled between the internal CPE and the hosts it
   services.  The internal CPE ignores the DNS configuration that it
   receives from the managed CPE.

              ,--,--,--.                         ,--,
            ,'         Internal   Managed     ,-'    '-     3rd Party
     Host--(  Network#A  CPE--------CPE------(   ISP   )--- DNS Server
      |     `.         ,-'|          |        `-.    -'       |
      |       `-'--'--'   |          |<==DHCP==>|`--'         |
      |                   X<==DHCP==>|   Do53   |             |
      |<=======DNR=======>|   Do53   |                        |
      |    {ADN, @i}      |                                   |
      |<==Encrypted DNS==>|<==========Encrypted DNS==========>|
      |                   |                                   |

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

        Figure 8: Example of an Internal CPE Hosting a Forwarder (2)

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5.  Legacy CPEs

   Hosts serviced by legacy CPEs that can't be upgraded to support the
   options defined in Sections 4, 5, and 6 of [I-D.ietf-add-dnr] won't
   be able to learn the encrypted DNS resolver hosted by the ISP, in
   particular.  If the ADN is not discovered using DHCP/RA, such hosts
   will have to fallback to use discovery using the resolver IP address
   as defined in Section 4 of [I-D.ietf-add-ddr] to discover the
   designated resolvers.

   The guidance in Sections 4.1 and 4.2 of [I-D.ietf-add-ddr] related to
   the designated resolver verification has to be followed in such a
   case.

6.  Security Considerations

   DNR-related security considerations are discussed in Section 7 of
   [I-D.ietf-add-dnr].  Likewise, DDR-related security considerations
   are discussed in Section 7 of [I-D.ietf-add-ddr].

7.  IANA Considerations

   This document does not require any IANA action.

8.  Acknowledgements

   This text was initially part of [I-D.ietf-add-dnr].

9.  References

9.1.  Normative References

   [I-D.ietf-add-ddr]
              Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
              Jensen, "Discovery of Designated Resolvers", Work in
              Progress, Internet-Draft, draft-ietf-add-ddr-10, 5 August
              2022, <https://www.ietf.org/archive/id/draft-ietf-add-ddr-
              10.txt>.

   [I-D.ietf-add-dnr]
              Boucadair, M., Reddy, T., Wing, D., Cook, N., and T.
              Jensen, "DHCP and Router Advertisement Options for the
              Discovery of Network-designated Resolvers (DNR)", Work in
              Progress, Internet-Draft, draft-ietf-add-dnr-13, 13 August
              2022, <https://www.ietf.org/archive/id/draft-ietf-add-dnr-
              13.txt>.

9.2.  Informative References

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   [I-D.boucadair-opsawg-add-encrypted-dns]
              Boucadair, M. and T. Reddy, "RADIUS Extensions for
              Encrypted DNS", Work in Progress, Internet-Draft, draft-
              boucadair-opsawg-add-encrypted-dns-06, 5 September 2022,
              <https://www.ietf.org/archive/id/draft-boucadair-opsawg-
              add-encrypted-dns-06.txt>.

   [I-D.ietf-add-split-horizon-authority]
              Reddy, T., Wing, D., Smith, K., and B. Schwartz,
              "Establishing Local DNS Authority in Split-Horizon
              Environments", Work in Progress, Internet-Draft, draft-
              ietf-add-split-horizon-authority-01, 22 August 2022,
              <https://www.ietf.org/archive/id/draft-ietf-add-split-
              horizon-authority-01.txt>.

   [I-D.ietf-v6ops-rfc7084-bis]
              Martinez, J. P., "Basic Requirements for IPv6 Customer
              Edge Routers", Work in Progress, Internet-Draft, draft-
              ietf-v6ops-rfc7084-bis-04, 12 June 2017,
              <https://www.ietf.org/archive/id/draft-ietf-v6ops-rfc7084-
              bis-04.txt>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

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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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [RFC9250]  Huitema, C., Dickinson, S., and A. Mankin, "DNS over
              Dedicated QUIC Connections", RFC 9250,
              DOI 10.17487/RFC9250, May 2022,
              <https://www.rfc-editor.org/info/rfc9250>.

   [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>.

Authors' Addresses

   Mohamed Boucadair (editor)
   Orange
   35000 Rennes
   France

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   Email: mohamed.boucadair@orange.com

   Tirumaleswar Reddy (editor)
   Nokia
   India
   Email: kondtir@gmail.com

   Dan Wing
   Citrix Systems, Inc.
   United States of America
   Email: dwing-ietf@fuggles.com

   Neil Cook
   Open-Xchange
   United Kingdom
   Email: neil.cook@noware.co.uk

   Tommy Jensen
   Microsoft
   United States of America
   Email: tojens@microsoft.com

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