path: root/doc/rfc/rfc9526.txt

Internet Engineering Task Force (IETF)                        D. Migault
Request for Comments: 9526                                      Ericsson
Category: Experimental                                          R. Weber
ISSN: 2070-1721                                                  Nominum
                                                           M. Richardson
                                                Sandelman Software Works
                                                               R. Hunter
                                                    Globis Consulting BV
                                                            January 2024


      Simple Provisioning of Public Names for Residential Networks

Abstract

   Home network owners may have devices or services hosted on their home
   network that they wish to access from the Internet (i.e., from a
   network outside of the home network).  Home networks are increasingly
   numbered using IPv6 addresses, which in principle makes this access
   simpler, but accessing home networks from the Internet requires the
   names and IP addresses of these devices and services to be made
   available in the public DNS.

   This document describes how a Home Naming Authority (NHA) instructs
   the outsourced infrastructure to publish these pieces of information
   in the public DNS.  The names and IP addresses of the home network
   are set in the Public Homenet Zone by the Homenet Naming Authority
   (HNA), which in turn instructs an outsourced infrastructure to
   publish the zone on behalf of the home network owner.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are candidates for any level of
   Internet Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9526.

Copyright Notice

   Copyright (c) 2024 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
   (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.  Terminology
   3.  Selecting Names and Addresses to Publish
   4.  Envisioned Deployment Scenarios
     4.1.  CPE Vendor
     4.2.  Agnostic CPE
   5.  Architecture Description
     5.1.  Architecture Overview
     5.2.  Distribution Manager (DM) Communication Channels
   6.  Control Channel
     6.1.  Building the Public Homenet Zone
     6.2.  Building the DNSSEC Chain of Trust
     6.3.  Setting Up the Synchronization Channel
     6.4.  Deleting the Delegation
     6.5.  Message Exchange Description
       6.5.1.  Retrieving Information for the Public Homenet Zone
       6.5.2.  Providing Information for the DNSSEC Chain of Trust
       6.5.3.  Providing Information for the Synchronization Channel
       6.5.4.  Initiating Deletion of the Delegation
     6.6.  Securing the Control Channel
   7.  Synchronization Channel
     7.1.  Securing the Synchronization Channel
   8.  DM Distribution Channel
   9.  HNA Security Policies
   10. Public Homenet Reverse Zone
   11. DNSSEC-Compliant Homenet Architecture
   12. Renumbering
   13. Privacy Considerations
   14. Security Considerations
     14.1.  Registered Homenet Domain
     14.2.  HNA DM Channels
     14.3.  Names Are Less Secure than IP Addresses
     14.4.  Names Are Less Volatile than IP Addresses
     14.5.  Deployment Considerations
     14.6.  Operational Considerations
   15. IANA Considerations
   16. References
     16.1.  Normative References
     16.2.  Informative References
   Appendix A.  HNA Channel Configurations
     A.1.  Public Homenet Zone
   Appendix B.  Information Model for Outsourced Information
   Appendix C.  Example: A Manufacturer-Provisioned HNA Product Flow
   Acknowledgments
   Contributors
   Authors' Addresses

1.  Introduction

   Home network owners may have devices or services hosted on their home
   network that they wish to access from the Internet (i.e., from a
   network outside of the home network).  The use of IPv6 addresses in
   the home makes, in principle, the actual network access simpler,
   while on the other hand, the addresses are much harder to remember
   and are subject to regular renumbering.  To make this situation
   simpler for typical home owners to manage, there needs to be an easy
   way for the names and IP addresses of these devices and services to
   be published in the public DNS.

   As depicted in Figure 1, the names and IP address of the home network
   are made available in the Public Homenet Zone by the Homenet Naming
   Authority (HNA), which in turn instructs the DNS Outsourcing
   Infrastructure (DOI) to publish the zone on behalf of the HNA.  This
   document describes how an HNA can instruct a DOI to publish a Public
   Homenet Zone on its behalf.

   This document introduces the Synchronization Channel and the Control
   Channel between the HNA and the Distribution Manager (DM), which is
   the main interface to the DOI.

   The Synchronization Channel (see Section 7) is used to synchronize
   the Public Homenet Zone.

                                        Internet
         .---------------------.           .-------------------.
         |      Home Network   | Control   |        DOI        |
         |.-------------------.| Channel   |.-----------------.|
         ||         HNA       |<----------->|  Distribution   ||
         ||.-----------------.||           ||  Manager        ||
         |||  Public Homenet |||           ||                 ||
         |||       Zone      ||<----------->|                 ||
         ||| myhome.example  ||| Synchron- |'-----------------'|
         ||'-----------------'|| ization   |         |         |
         |'-------------------'| Channel   |         V         |
         |                     |           |.-----------------.|
         |                     |           ||  Public Homenet ||
         '---------------------'           ||       Zone      ||
                                           || myhome.example  ||
                                           |'-----------------'|
                                           '---^--^--^--^--^---'
                                               |  |  |  |  |
                                          (served on the Internet)

       Figure 1: High-Level Architecture Overview of Outsourcing the
                            Public Homenet Zone

   The Synchronization Channel is a zone transfer, with the HNA
   configured as a primary server and the Distribution Manager
   configured as a secondary server.  Some operators refer to this kind
   of configuration as a "hidden primary", but that term is not used in
   this document as it is not precisely defined anywhere, but it has
   many slightly different meanings to many.

   The Control Channel (see Section 6) is used to set up the
   Synchronization Channel.  This channel is in the form of a dynamic
   DNS update process, authenticated by TLS.

   For example, to build the Public Homenet Zone, the HNA needs the
   authoritative servers (and associated IP addresses) of the DOI's
   servers (the visible primaries) that are actually serving the zone.
   Similarly, the DOI needs to know the IP address of the (hidden)
   primary (HNA) as well as potentially the hash of the Key Signing Key
   (KSK) in the DS RRset to secure the DNSSEC delegation with the parent
   zone.

   The remainder of the document is as follows.

   Section 2 defines the terminology.  Section 3 presents the general
   problem of publishing names and IP addresses.  Section 4 briefly
   describes some potential envisioned deployment scenarios.  And
   Section 5 provides an architectural view of the HNA, DM, and DOI as
   well as their different communication channels (Control Channel,
   Synchronization Channel, and DM Distribution Channel) described in
   Sections 6, 7, and 8, respectively.

   Then, Sections 6 and 7 deal with the two channels that interface to
   the home.  Section 8 provides a set of requirements and expectations
   on how the distribution system works.  This section is non-normative
   and not subject to standardization but reflects how many scalable DNS
   distribution systems operate.

   Sections 9 and 11 respectively detail HNA security policies as well
   as DNSSEC compliance within the home network.

   Section 12 discusses how renumbering should be handled.

   Finally, Sections 13 and 14 respectively discuss privacy and security
   considerations when outsourcing the Public Homenet Zone.

   The appendices discuss the following aspects: management (see
   Section 10), provisioning (see Section 10), configurations (see
   Appendix B), and deployment (see Section 4 and Appendix C).

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.

   Customer Premises Equipment (CPE):  A router providing connectivity
      to the home network.

   Homenet Zone:  The DNS zone for use within the boundaries of the home
      network: "home.arpa" (see [RFC8375]).  This zone is not considered
      public and is out of scope for this document.

   Registered Homenet Domain:  The domain name that is associated with
      the home network.  A given home network may have multiple
      Registered Homenet Domains.

   Public Homenet Zone:  Contains the names in the home network that are
      expected to be publicly resolvable on the Internet.  A home
      network can have multiple Public Homenet Zones.

   Homenet Naming Authority (HNA):  A function responsible for managing
      the Public Homenet Zone.  This includes populating the Public
      Homenet Zone, signing the zone for DNSSEC, as well as managing the
      distribution of that Homenet Zone to the DOI.

   DNS Outsourcing Infrastructure (DOI):  The infrastructure responsible
      for receiving the Public Homenet Zone and publishing it on the
      Internet.  It is mainly composed of a Distribution Manager and
      Public Authoritative Servers.

   Public Authoritative Servers:  The authoritative name servers for the
      Public Homenet Zone.  Name resolution requests for the Registered
      Homenet Domain are sent to these servers.  Some DNS operators
      refer to these as public secondaries, and higher resiliency
      networks are often implemented in an anycast fashion.

   Homenet Authoritative Servers:  The authoritative name servers for
      the Homenet Zone within the Homenet network itself.  These are
      sometimes called "hidden primary servers".

   Distribution Manager (DM):  The server (or set of servers) that the
      HNA synchronizes the Public Homenet Zone to and that then
      distributes the relevant information to the Public Authoritative
      Servers.  This server has been historically known as the
      Distribution Master.

   Public Homenet Reverse Zone:  The reverse zone file associated with
      the Public Homenet Zone.

   Reverse Public Authoritative Servers:  These are equivalent to Public
      Authoritative Servers, specifically for reverse resolution.

   Reverse Distribution Manager:  This is equivalent to the Distribution
      Manager, specifically for reverse resolution.

   DNS Resolver:  A resolver that performs a DNS resolution on the
      Internet for the Public Homenet Zone.  The resolution is performed
      by requesting the Public Authoritative Servers.  While the
      resolver does not necessarily perform DNSSEC resolutions, it is
      RECOMMENDED that DNSSEC is enabled.

      Note that when "DNS Resolver" is used in this document, it refers
      to "DNS or DNSSEC Resolver".

   Homenet DNS Resolver:  A resolver that performs a DNS or DNSSEC
      resolution on the home network for the Public Homenet Zone.  The
      resolution is performed by requesting the Homenet Authoritative
      Servers.

3.  Selecting Names and Addresses to Publish

   While this document does not create any normative mechanism to select
   the names to publish, it does anticipate that the home network
   administrator (a human being) will be presented with a list of
   current names and addresses either directly on the HNA or via another
   device such as a smartphone.

   The administrator will mark which devices and services (by name) are
   to be published.  The HNA will then collect the IP address(es)
   associated with that device or service and put the name into the
   Public Homenet Zone.  The address of the device or service can be
   collected from a number of places: Multicast DNS (mDNS) [RFC6762],
   DHCP [RFC8415], Universal Plug and Play (UPnP), the Port Control
   Protocol (PCP) [RFC6887], or manual configuration.

   A device or service SHOULD have Global Unicast Addresses (GUAs) (IPv6
   [RFC3587] or IPv4) but MAY also have IPv6 Unique Local Addresses
   (ULAs) [RFC4193], IPv6 Link-Local Addresses (LLAs) [RFC4291]
   [RFC7404], IPv4 LLAs [RFC3927], and private IPv4 addresses [RFC1918].

   Of these, the LLAs are almost never useful for the Public Zone and
   should be omitted.

   The IPv6 ULA and private IPv4 addresses may be useful to publish, if
   the home network environment features a VPN that would allow the home
   owner to reach the network.  [RFC1918] addresses in public zones are
   generally filtered out by many DNS servers as they are considered
   rebind attacks [REBIND].

   In general, one expects the GUA to be the default address to be
   published.  A direct advantage of enabling local communication is to
   enable communications even in case of Internet disruption.  Since
   communications are established with names that remain a global
   identifier, the communication can be protected (at the very least
   with integrity protection) by TLS the same way it is protected on the
   global Internet -- by using certificates.

4.  Envisioned Deployment Scenarios

   A number of deployment scenarios have been envisioned; this section
   aims at providing a brief description.  The use cases are not
   limitations, and this section is not normative.

   The main difference between the various deployments concerns the
   provisioning of the HNA -- that is, how it is configured to outsource
   the Public Homenet Zone to the DOI -- as well as how the Public
   Homenet Zone is being provisioned before being outsourced.  In both
   cases, these configuration aspects are out of the scope of this
   document.

   Provisioning the configuration related to the DOI is expected to be
   automated as much as possible and require interaction with the end
   user as little as possible.  Zero configuration can only be achieved
   under some circumstances, and [RFC9527] provides one such example
   under the assumption that the ISP provides the DOI.  Section 4.1
   describes another variant where the Customer Premises Equipment (CPE)
   is provided preconfigured with the DOI.  Section 4.2 describes how an
   agnostic CPE may be configured by the home network administrator.  Of
   course even in this case, the configuration can leverage mechanisms
   to prevent the end user from manually entering all information.

   On the other hand, provisioning the Public Homenet Zone needs to
   combine the ability to closely reflect what the end user wishes to
   publish on the Internet while easing such interaction.  The HNA may
   implement such interactions using web-based GUIs or specific mobile
   applications.

   With the CPE configured with the DOI, the HNA contacts the DOI to
   build a template for the Public Homenet Zone and then provisions the
   Public Homenet Zone.  Once the Public Homenet Zone is built, the HNA
   starts synchronizing it with the DOI on the Synchronization Channel.

4.1.  CPE Vendor

   A specific vendor that has specific relations with a registrar or a
   registry may sell a CPE that is provisioned with a domain name.  Such
   a domain name is probably not human friendly and may consist of some
   kind of serial number associated with the device being sold.

   One possible scenario is that the vendor provisions the HNA with a
   private key with an associated certificate used for the mutual TLS
   authentication.  Note that these keys are not expected to be used for
   DNSSEC signing.

   Instead, these keys are solely used by the HNA for the authentication
   to the DM.  Normally, the keys are necessary and sufficient to
   proceed to the authentication.

   When the home network owner plugs in the CPE at home, the relation
   between the HNA and DM is expected to work out of the box.

4.2.  Agnostic CPE

   A CPE that is not preconfigured may also use the protocol defined in
   this document, but some configuration steps will be needed.

   1.  The owner of the home network buys a domain name from a registrar
       and, as such, creates an account on that registrar.

   2.  The registrar may provide the outsourcing infrastructure, or the
       home network may need to create a specific account on the
       outsourcing infrastructure.

   *  If the DOI is the DNS Registrar, it has by design a proof of
      ownership of the domain name by the Homenet owner.  In this case,
      it is expected that the DOI provides the necessary parameters to
      the home network owner to configure the HNA.  One potential
      mechanism to provide the parameters would be to provide the user
      with a JSON object that they can copy and paste into the CPE, such
      as described in Appendix B.  But what matters to the
      infrastructure is that the HNA is able to authenticate itself to
      the DOI.

   *  If the DOI is not the DNS Registrar, then the proof of ownership
      needs to be established using some other protocol.  Automatic
      Certificate Management Environment (ACME) [RFC8555] is one
      protocol that would allow an owner of an existing domain name to
      prove their ownership (but it requires that they have DNS already
      set up!).  There are other ways to establish proof such as
      providing a DOI-generated TXT record, or web site contents, as
      championed by entities like Google's Sitemaster and Postmaster
      protocols.  [DOMAIN-VALIDATION] describes a few ways ownership or
      control of a domain can be achieved.

5.  Architecture Description

   This section provides an overview of the architecture for outsourcing
   the authoritative naming service from the HNA to the DOI.  As a
   consequence, this prevents HNA from handling the DNS traffic from the
   Internet that is associated with the resolution of the Homenet Zone.

   The device-assigned zone or user-configurable zone that is used as
   the domain to publicly serve hostnames in the home network is called
   the Public Homenet Zone.  In this document, "myhome.example" is used
   as the example for an end-user-owned domain configured as a Public
   Homenet Zone.

   More specifically, DNS resolution for the Public Homenet Zone (here
   "myhome.example") from Internet DNSSEC resolvers is handled by the
   DOI as opposed to the HNA.  The DOI benefits from a cloud
   infrastructure while the HNA is dimensioned for a home network and,
   as such, is likely unable to support any load.  In the case where the
   HNA is a CPE, outsourcing to the DOI reduces the attack surface of
   the home network to DDoS, for example.  Of course, the DOI needs to
   be informed dynamically about the content of myhome.example.  The
   description of such a synchronization mechanism is the purpose of
   this document.

   Note that Appendix B shows the necessary parameters to configure the
   HNA.

5.1.  Architecture Overview

  .----------------------------.         .-----------------------------.
  |        Home Network        |         |          Internet           |
  | .-----------------------.  | Control |  .-----------------------.  |
  | |          HNA          |  | Channel |  |          DOI          |  |
  | |   (hidden primary)    |<------------->|   (hidden secondary)  |  |
  | |                       |  | DNSUPD  |  |  Distribution Manager |  |
  | | .-------------------. |  |         |  |                       |  |
  | | |  Public Homenet   | |  |         |  |  .-------------------.|  |
  | | |       Zone        |<------------------>|Public Homenet Zone||  |
  | | | myhome.example    | |  |Synchron-|  |  | myhome.example    ||  |
  | | '-------------------' |  |ization  |  |  '-------------------'|  |
  | '-----------------------'  |Channel  |  |             |         |  |
  |             ^              |  AXFR   |  |             |         |  |
  |             |              |         |  |             v         |  |
  | .-----------------------.  |         |  |.---------------------.|  |
  | | Homenet Authoritative |  |         |  || Public Authoritative||  |
  | |        Server         |  |         |  || (secondary) Servers ||  |
  | | + myhome.example      |  |         |  || + myhome.example    ||  |
  | | + home.arpa           |  |         |  || + x.y.z.ip6.arpa    ||  |
  | | + x.y.z.ip6.arpa      |  |         |  ||                     ||  |
  | '-----------------------'  |         |  ||                     ||  |
  |        |       ^           |         |  |'---------------------'|  |
  |        |       |           |         |  |  ^            |       |  |
  |        |       |           |         |  '--|------------|-------'  |
  |        v       |           |         |     |            v          |
  |  .----------------------.  |         | .------------------------.  |
  |  | Homenet DNS Resolver |  |         | |   Internet Resolvers   |  |
  |  '----------------------'  |         | '------------------------'  |
  |                            |         |                             |
  '----------------------------'         |                             |
                                         '-----------------------------'

                  Figure 2: Homenet Naming Architecture

   Figure 2 illustrates the architecture where the HNA outsources the
   publication of the Public Homenet Zone to the DOI.  The DOI will
   serve every DNS request of the Public Homenet Zone coming from
   outside the home network.  When the request is coming from within the
   home network, the resolution is expected to be handled by the Homenet
   DNS Resolver as further detailed below.

   In this example, the Public Homenet Zone is identified by the
   Registered Homenet Domain name "myhome.example".  This diagram also
   shows a reverse IPv6 map being hosted.

   ".local" and ".home.arpa" are explicitly not considered Public
   Homenet Zones; therefore, they are represented as a Homenet Zone in
   Figure 2.  They are resolved locally but are not published because
   they are considered local content.

   It is RECOMMENDED that the HNA implements DNSSEC, in which case the
   HNA MUST sign the Public Homenet Zone with DNSSEC.

   The HNA handles all operations and keying material required for
   DNSSEC, so there is no provision made in this architecture for
   transferring private DNSSEC-related keying material between the HNA
   and the DM.

   Once the Public Homenet Zone has been built, the HNA communicates and
   synchronizes it with the DOI using a primary/secondary setting as
   depicted in Figure 2.  The HNA acts as a stealth server (see
   [RFC8499]) while the DM behaves as a hidden secondary.  It is
   responsible for distributing the Public Homenet Zone to the multiple
   Public Authoritative Server instances that DOI is responsible for.
   The DM has three communication channels:

   *  DM Control Channel (Section 6) to configure the HNA and the DOI.
      This includes necessary parameters to configure the primary/
      secondary relation as well as some information provided by the DOI
      that needs to be included by the HNA in the Public Homenet Zone.

   *  DM Synchronization Channel (Section 7) to synchronize the Public
      Homenet Zone on the HNA and on the DM with the appropriately
      configured primary/secondary.  This is a zone transfer over
      mutually authenticated TLS.

   *  One or more Distribution Channels (Section 8) that distribute the
      Public Homenet Zone from the DM to the Public Authoritative
      Servers serving the Public Homenet Zone on the Internet.

   There might be multiple DMs and multiple servers per the DM.  This
   document assumes a single DM server for simplicity, but there is no
   reason why each channel needs to be implemented on the same server or
   use the same code base.

   It is important to note that while the HNA is configured as an
   authoritative server, it is not expected to answer DNS requests from
   the _public_ Internet for the Public Homenet Zone.  More
   specifically, the addresses associated with the HNA SHOULD NOT be
   mentioned in the NS records of the Public Homenet Zone, unless
   additional security provisions necessary to protect the HNA from
   external attack have been taken.

   The DOI is also responsible for ensuring the DS record has been
   updated in the parent zone.

   Resolution is performed by DNS Resolvers.  When the resolution is
   performed outside the home network, the DNS Resolver resolves the DS
   record on the Global DNS and the name associated with the Public
   Homenet Zone (myhome.example) on the Public Authoritative Servers.

   In order to provide resilience to the Public Homenet Zone in case of
   WAN connectivity disruption, the Homenet DNS Resolver MUST be able to
   perform the resolution on the Homenet Authoritative Servers.  Note
   that the use of the Homenet DNS Resolver enhances privacy since the
   user on the home network would no longer be leaking interactions with
   internal services to an external DNS provider and to an on-path
   observer.  These servers are not expected to be mentioned in the
   Public Homenet Zone nor to be accessible from the Internet.  As such,
   their information as well as the corresponding signed DS record MAY
   be provided by the HNA to the Homenet DNS Resolvers, e.g., by using
   the Home Networking Control Protocol (HNCP) [RFC7788] or by
   configuring a trust anchor [DRO-RECS].  Such configuration is outside
   the scope of this document.  Since the scope of the Homenet
   Authoritative Servers is limited to the home network, these servers
   are expected to serve the Homenet Zone as represented in Figure 2.

5.2.  Distribution Manager (DM) Communication Channels

   This section details the DM channels: the Control Channel,
   Synchronization Channel, and Distribution Channel.

   The Control Channel and the Synchronization Channel are the
   interfaces used between the HNA and the DOI.  The entity within the
   DOI responsible for handling these communications is the DM.
   Communications between the HNA and the DM MUST be protected and
   mutually authenticated.  The different protocols that can be used for
   security are discussed in more depth in Section 6.6.

   The information exchanged between the HNA and the DM uses DNS
   messages protected by DNS over TLS (DoT) [RFC7858].  This is
   configured identically to that described in [RFC9103], Section 9.3.3.

   It is worth noting that both the DM and HNA need to agree on a common
   configuration in order to set up the Synchronization Channel and
   build and serve a coherent Public Homenet Zone.  As previously noted,
   the visible NS records of the Public Homenet Zone (built by the HNA)
   remain pointing at the IP address of the DOI's Public Authoritative
   Servers.  Unless the HNA is able to support the traffic load, the HNA
   SHOULD NOT appear as a visible NS record of the Public Homenet Zone.
   In addition, and depending on the configuration of the DOI, the DM
   also needs to update the parent zone's NS, DS, and associated A or
   AAAA glue records.  Refer to Section 6.2 for more details.

   This specification assumes:

   *  The DM serves both the Control Channel and Synchronization Channel
      on a single IP address, on a single port, and by using a single
      transport protocol.

   *  By default, the HNA uses a single IP address for both the Control
      and Synchronization channels; however, the HNA MAY use distinct IP
      addresses for the Control Channel and the Synchronization Channel
      -- see Sections 7 and 6.3 for more details.

   The Distribution Channel is internal to the DOI and, as such, is not
   normatively defined by this specification.

6.  Control Channel

   The DM Control Channel is used by the HNA and the DOI to exchange
   information related to the configuration of the delegation, which
   includes information to build the Public Homenet Zone (Section 6.1),
   to build the DNSSEC chain of trust (Section 6.2), and to set the
   Synchronization Channel (Section 6.3).

   Some information is carried from the DOI to the HNA, as described in
   the next section.  The HNA updates the DOI with the IP address on
   which the zone is to be transferred using the Synchronization
   Channel.  The HNA is always initiating the exchange in both
   directions.

   As such, the HNA has a prior knowledge of the DM identity (via an
   X.509 certificate), the IP address and port number to use, and the
   protocol to establish a secure session.  The DM acquires knowledge of
   the identity of the HNA (X.509 certificate) as well as the Registered
   Homenet Domain.  For more detail on how this can be achieved, please
   see Appendix A.1.

6.1.  Building the Public Homenet Zone

   The HNA builds the Public Homenet Zone based on a template that is
   returned by the DM to the HNA.  Section 6.5 explains how this
   leverages the Authoritative Transfer (AXFR) mechanism.

   In order to build its zone completely, the HNA needs the names (and
   possibly IP addresses) of the Public Authoritative Name Servers.
   These are used to populate the NS records for the zone.  All the
   content of the zone MUST be created by the HNA because the zone is
   DNSSEC signed.

   In addition, the HNA needs to know what to put into the MNAME of the
   SOA, and only the DOI knows what to put there.  The DM MUST also
   provide useful operational parameters such as other fields of the SOA
   (SERIAL, RNAME, REFRESH, RETRY, EXPIRE, and MINIMUM); however, the
   HNA is free to override these values based upon local configuration.
   For instance, an HNA might want to change these values if it thinks
   that a renumbering event is approaching.

   Because the information associated with the DM is necessary for the
   HNA to proceed, this information exchange is mandatory.

   The HNA then performs a DNS Update operation to the DOI, updating the
   DOI with an NS, a DS, and A and AAAA records.  These indicate where
   its Synchronization Channel is.  The DOI does not publish this NS
   record but uses it to perform zone transfers.

6.2.  Building the DNSSEC Chain of Trust

   The HNA MUST provide the hash of the KSK via the DS RRset so that the
   DOI can provide this value to the parent zone.  A common deployment
   use case is that the DOI is the registrar of the Registered Homenet
   Domain; therefore, its relationship with the registry of the parent
   zone enables it to update the parent zone.  When such relation
   exists, the HNA should be able to request the DOI to update the DS
   RRset in the parent zone.  A direct update is especially necessary to
   initialize the chain of trust.

   Though the HNA may also directly update the values of the DS via the
   Control Channel at a later time, it is RECOMMENDED to use other
   mechanisms such as CDS and CDNSKEY [RFC7344] for transparent updates
   during key rollovers.

   As some deployments may not provide a DOI that will be able to update
   the DS in the parent zone, this information exchange is OPTIONAL.

   By accepting the DS RR, the DM commits to advertise the DS to the
   parent zone.  On the other hand, if the DM does not have the capacity
   to advertise the DS to the parent zone, it indicates this by refusing
   the update to the DS RR.

6.3.  Setting Up the Synchronization Channel

   The HNA works as a hidden primary authoritative DNS server while the
   DM works like a secondary one.  As a result, the HNA needs to provide
   the IP address that the DM should use to reach the HNA.

   If the HNA detects that it has been renumbered, then it MUST use the
   Control Channel to update the DOI with the new IPv6 address it has
   been assigned.

   The Synchronization Channel will be set between the new IPv6 (and
   IPv4) address and the IP address of the DM.  By default, the IP
   address used by the HNA in the Control Channel is considered by the
   DM, and the explicit specification of the IP by the HNA is only
   OPTIONAL.  The transport channel (including the port number) is the
   same as the one used between the HNA and the DM for the Control
   Channel.

6.4.  Deleting the Delegation

   The purpose of the previous sections is to exchange information in
   order to set a delegation.  The HNA MUST also be able to delete a
   delegation with a specific DM.

   Section 6.5.4 explains how a DNS Update operation on the Control
   Channel is used.

   Upon receiving the instruction to delete the delegation, the DM MUST
   stop serving the Public Homenet Zone.

   The decision to delete an inactive HNA by the DM is part of the
   commercial agreement between the DOI and HNA.

6.5.  Message Exchange Description

   Multiple ways were considered on how the control information could be
   exchanged between the HNA and the DM.

   This specification defines a mechanism that reuses the DNS zone
   transfer format.  Note that while information is provided using DNS
   exchanges, the exchanged information is not expected to be set in any
   zone file; instead, this information is used as commands between the
   HNA and the DM.  This was found to be simpler on the home router
   side, as the HNA already has to have code to deal with all the DNS
   encodings/decodings.  Inventing a new way to encode the DNS
   information in, for instance, JSON seemed to add complexity for no
   return on investment.

   The Control Channel is not expected to be a long-term session.  After
   a predefined timer (similar to those used for TCP), the Control
   Channel is expected to be terminated by closing the transport
   channel.  The Control Channel MAY be reopened at any later time.

   The use of TLS session tickets (see [RFC8446], Section 4.6.1) is
   RECOMMENDED.

   The authentication of the channel MUST be based on certificates for
   both the DM and each HNA.  The DM may also create the initial
   configuration for the delegation zone in the parent zone during the
   provisioning process.

6.5.1.  Retrieving Information for the Public Homenet Zone

   The information provided by the DM to the HNA is retrieved by the HNA
   with an AXFR exchange [RFC1034].  AXFR enables the response to
   contain any type of RRsets.

   To retrieve the necessary information to build the Public Homenet
   Zone, the HNA MUST send a DNS request of type AXFR associated with
   the Registered Homenet Domain.

   The zone that is returned by the DM is used by the HNA as a template
   to build its own zone.

   The zone template MUST contain an RRset of type SOA, one or multiple
   RRsets of type NS, and zero or more RRsets of type A or AAAA (if the
   NS is in-domain [RFC8499]).  The zone template will include Time-To-
   Live (TTL) values for each RR, and the HNA SHOULD take these as
   suggested maximum values, but it MAY use lower values for operational
   reasons, such as for impending renumbering events.

   *  The SOA RR indicates the value of the MNAME of the Public Homenet
      Zone to the HNA.

   *  The NAME of the SOA RR MUST be the Registered Homenet Domain.

   *  The MNAME value of the SOA RDATA is the value provided by the DOI
      to the HNA.

   *  Other RDATA values (RNAME, REFRESH, RETRY, EXPIRE, and MINIMUM)
      are provided by the DOI as suggestions.

   The NS RRsets carry the Public Authoritative Servers of the DOI.
   Their associated NAME MUST be the Registered Homenet Domain.

   In addition to the considerations above about default TTL, the HNA
   SHOULD take care to not pick a TTL larger than the parent NS, based
   upon the resolver's guidelines in [NS-REVALIDATION] and [DRO-RECS].
   The RRsets of Type A and AAAA MUST have their NAME matching the
   NSDNAME of one of the NS RRsets.

   Upon receiving the response, the HNA MUST validate the format and
   properties of the SOA, NS, and A or AAAA RRsets.  If an error occurs,
   the HNA MUST stop proceeding and MUST log an error.  Otherwise, the
   HNA builds the Public Homenet Zone by setting the MNAME value of the
   SOA as indicated by the SOA provided by the AXFR response.  The HNA
   MUST NOT exceed the values of NAME, REFRESH, RETRY, EXPIRE, and
   MINIMUM of the SOA provided by the AXFR response.  The HNA MUST
   insert the NS and corresponding A or AAAA RRsets in its Public
   Homenet Zone.  The HNA MUST ignore other RRsets.

   If an error message is returned by the DM, the HNA MUST proceed as a
   regular DNS resolution.  Error messages SHOULD be logged for further
   analysis.  If the resolution does not succeed, the outsourcing
   operation is aborted and the HNA MUST close the Control Channel.

6.5.2.  Providing Information for the DNSSEC Chain of Trust

   To provide the DS RRset to initialize the DNSSEC chain of trust, the
   HNA MAY send a DNS update [RFC3007] message.

   The DNS update message is composed of a Header section, a Zone
   section, a Prerequisite section, an Update section, and an additional
   section.  The Zone section MUST set the ZNAME to the parent zone of
   the Registered Homenet Domain, which is where the DS records should
   be inserted.  As described in [RFC2136], ZTYPE is set to SOA and
   ZCLASS is set to the zone's class.  The Prerequisite section MUST be
   empty.  The Update section is a DS RRset with its NAME set to the
   Registered Homenet Domain, and the associated RDATA corresponds to
   the value of the DS.  The Additional Data section MUST be empty.

   Though the Prerequisite section MAY be ignored by the DM, this value
   is fixed to remain coherent with a standard DNS update.

   Upon receiving the DNS update request, the DM reads the DS RRset in
   the Update section.  The DM checks that ZNAME corresponds to the
   parent zone.  The DM MUST ignore the Prerequisite and Additional Data
   sections, if present.  The DM MAY update the TTL value before
   updating the DS RRset in the parent zone.  Upon a successful update,
   the DM should return a NOERROR response as a commitment to update the
   parent zone with the provided DS.  An error indicates that the DM
   does not update the DS, and the HNA needs to act accordingly;
   otherwise, another method should be used by the HNA.

   The regular DNS error message MUST be returned to the HNA when an
   error occurs.  In particular, a FORMERR is returned when a format
   error is found, including when unexpected RRsets are added or when
   RRsets are missing.  A SERVFAIL error is returned when an internal
   error is encountered.  A NOTZONE error is returned when the Update
   and Zone sections are not coherent, and a NOTAUTH error is returned
   when the DM is not authoritative for the Zone section.  A REFUSED
   error is returned when the DM refuses the configuration or performing
   the requested action.

6.5.3.  Providing Information for the Synchronization Channel

   The default IP address used by the HNA for the Synchronization
   Channel is the IP address of the Control Channel.  To provide a
   different IP address, the HNA MAY send a DNS UPDATE message.

   Similar to what is described in Section 6.5.2, the HNA MAY specify
   the IP address using a DNS update message.  The Zone section sets its
   ZNAME to the parent zone of the Registered Homenet Domain, ZTYPE to
   SOA, and ZCLASS to the zone's type.  Prerequisite is empty.  The
   Update section is an RRset of type NS.  The Additional Data section
   contains the RRsets of type A or AAAA that designate the IP addresses
   associated with the primary (or the HNA).

   The reason to provide these IP addresses is to keep them unpublished
   and prevent them from being resolved.  It is RECOMMENDED that the IP
   address of the HNA be randomly chosen to prevent it from being easily
   discovered as well.

   Upon receiving the DNS update request, the DM reads the IP addresses
   and checks that the ZNAME corresponds to the parent zone.  The DM
   MUST ignore a non-empty Prerequisite section.  The DM configures the
   secondary with the IP addresses and returns a NOERROR response to
   indicate it is committed to serve as a secondary.

   Similar to what is described in Section 6.5.2, DNS errors are used,
   and an error indicates the DM is not configured as a secondary.

6.5.4.  Initiating Deletion of the Delegation

   To initiate the deletion of the delegation, the HNA sends a DNS
   UPDATE Delete message.

   The Zone section sets its ZNAME to the Registered Homenet Domain, the
   ZTYPE to SOA, and the ZCLASS to the zone's type.  The Prerequisite
   section is empty.  The Update section is an RRset of type NS with the
   NAME set to the Registered Domain Name.  As indicated by [RFC2136],
   Section 2.5.2, the delete instruction is initiated by setting TTL to
   0, CLASS to ANY, and RDLENGTH to 0, and RDATA MUST be empty.  The
   Additional Data section is empty.

   Upon receiving the DNS update request, the DM checks the request and
   removes the delegation.  The DM returns a NOERROR response to
   indicate the delegation has been deleted.  Similar to what is
   described in Section 6.5.2, DNS errors are used, and an error
   indicates that the delegation has not been deleted.

6.6.  Securing the Control Channel

   TLS [RFC8446] MUST be used to secure the transactions between the DM
   and the HNA, and the DM and HNA MUST be mutually authenticated.  The
   DNS exchanges are performed using DNS over TLS [RFC7858].

   The HNA may be provisioned by the manufacturer or during some user-
   initiated onboarding process, for example, with a browser, by signing
   up to a service provider, and with a resulting OAuth 2.0 token to be
   provided to the HNA.  Such a process may result in a passing of a
   settings from a registrar into the HNA through an http API interface.
   (This is not in scope for this document.)

   When the HNA connects to the DM's Control Channel, TLS will be used,
   and the connection will be mutually authenticated.  The DM will
   authenticate the HNA's certificate based upon having participated in
   some provisioning process that is not standardized by this document.
   The results of the provisioning process is a series of settings
   described in Appendix A.1.

   The HNA will validate the DM's Control Channel certificate by
   performing a DNS-ID check on the name as described in [RFC9525].

   In the future, other specifications may consider protecting DNS
   messages with other transport layers such as DNS over DTLS [RFC8094],
   DNS over HTTPS (DoH) [RFC8484], or DNS over QUIC [RFC9250].

7.  Synchronization Channel

   The DM Synchronization Channel is used for communication between the
   HNA and the DM for synchronizing the Public Homenet Zone.  Note that
   the Control Channel and the Synchronization Channel are different
   channels by construction even though they may use the same IP
   address.  Suppose the HNA and the DM are using a single IP address
   designated by XX, and YYYYY and ZZZZZ are the various ports involved
   in the communications.

   The Control Channel is between

   *  the HNA working as a client using port number YYYYY (an ephemeral
      also commonly designated as a high range port) and

   *  a service provided by the DM at port 853, when using DoT.

   On the other hand, the Synchronization Channel is between

   *  the DM working as a client using port ZZZZZ (another ephemeral
      port) and

   *  a service provided by the HNA at port 853.

   As a result, even though the same pair of IP addresses may be
   involved, the Control Channel and the Synchronization Channel are
   always distinct channels.

   Uploading and dynamically updating the zone file on the DM can be
   seen as zone provisioning between the HNA (hidden primary server) and
   the DM (secondary server).  This is handled using the normal zone
   transfer mechanism involving the AXFR and Incremental Zone Transfer
   (IXFR).

   Part of the process to update the zone involves the owner of the zone
   (the hidden primary server, the HNA) sending a DNS Notify to the
   secondaries.  In this situation, the only destination that is known
   by the HNA is the DM's Control Channel, so DNS Notifies are sent over
   the Control Channel, secured by a mutually authenticated TLS.

   Please note that DNS Notifies are not critical to normal operation,
   as the DM will be checking the zone regularly based upon SOA record
   comments.  DNS Notifies do speed things up as they cause the DM to
   use the Synchronization Channel to immediately do an SOA query to
   detect any updates.  If there are any changes, then the DM
   immediately transfers the zone updates.

   This specification standardizes the use of a primary/secondary
   mechanism [RFC1996] rather than an extended series of DNS update
   messages.  The primary/secondary mechanism was selected as it scales
   better and avoids DoS attacks.  Because this AXFR runs over a TCP
   channel secured by a mutually authenticated TLS, the DNS update is
   more complicated.

   Note that this document provides no standard way to distribute a DNS
   primary between multiple devices.  As a result, if multiple devices
   are candidates for hosting the hidden primary server, some specific
   mechanisms should be designed so the home network only selects a
   single HNA for the hidden primary server.  Selection mechanisms based
   on HNCP [RFC7788] are good candidates for future work.

7.1.  Securing the Synchronization Channel

   The Synchronization Channel uses mutually authenticated TLS, as
   described by [RFC9103].

   There is a TLS client certificate used by the DM to authenticate
   itself.  The DM uses the same certificate that was configured into
   the HNA for authenticating the Control Channel, but as a client
   certificate rather than a server certificate.

   [RFC9103] makes no requirements or recommendations on any extended
   key usage flags for zone transfers, and this document adopts the view
   that none should be required.  Note that once an update to [RFC9103]
   is published, this document's normative reference to [RFC9103] will
   be considered updated as well.

   For the TLS server certificate, the HNA uses the same certificate
   that it uses to authenticate itself to the DM for the Control
   Channel.

   The HNA MAY use this certificate as the authorization for the zone
   transfer, or the HNA MAY have been configured with an Access Control
   List (ACL) that will determine if the zone transfer can proceed.
   This is a local configuration option as it is premature to determine
   which will be operationally simpler.

   When the HNA expects to do zone transfer authorization by certificate
   only, the HNA MAY still apply an ACL on inbound connection requests
   to avoid load.  In this case, the HNA MUST regularly check (via a DNS
   resolution) the validity of the address(es) of the DM in the filter.

8.  DM Distribution Channel

   The DM Distribution Channel is used for communication between the DM
   and the Public Authoritative Servers.  The architecture and
   communication used for the DM Distribution Channels are outside the
   scope of this document, but there are many existing solutions
   available, e.g., rsync, DNS AXFR, REST, and DB copy.

9.  HNA Security Policies

   The HNA, as the hidden primary server, processes only limited message
   exchanges on its Internet-facing interface.  This should be enforced
   using security policies to allow only a subset of DNS requests to be
   received by HNA.

   The hidden primary server on the HNA differs from the regular
   authoritative server for the home network due to the following:

   Interface Binding:  The hidden primary server will almost certainly
      listen on the WAN Interface, whereas a regular Homenet
      Authoritative Server will listen on the internal home network
      interface.

   Limited Exchanges:  The purpose of the hidden primary server is to
      synchronize with the DM, not to serve any zones to end users or
      the public Internet.  This results in a limited number of possible
      exchanges (AXFR/IXFR) with a small number of IP addresses, and an
      implementation MUST enable filtering policies: it should only
      respond to queries that are required to do zone transfers.  That
      list includes SOA queries and AXFR/IXFR queries.

10.  Public Homenet Reverse Zone

   The Public Homenet Reverse Zone works similarly to the Public Homenet
   Zone.  The main difference is that the ISP that provides the IPv6
   connectivity is likely to also be the owner of the corresponding IPv6
   reverse zone who administrates the Reverse Public Authoritative
   Servers.  The configuration and the setting of the Synchronization
   Channel and Control Channel can largely be automated using DHCPv6
   messages that are a part of the IPv6 prefix delegation process.

   The Public Homenet Zone is associated with a Registered Homenet
   Domain, and the ownership of that domain requires a specific
   registration from the end user as well as the HNA being provisioned
   with some authentication credentials.  Such steps are mandatory
   unless the DOI has some other means to authenticate the HNA.  Such
   situation may occur, for example, when the ISP provides the Homenet
   Domain as well as the DOI.

   In this case, the HNA may be authenticated by the physical link
   layer, in which case the authentication of the HNA may be performed
   without additional provisioning of the HNA.  While this may not be so
   common for the Public Homenet Zone, this situation is expected to be
   quite common for the Reverse Homenet Zone as the ISP owns the IP
   address or IP prefix.

   More specifically, a common case is that the upstream ISP provides
   the IPv6 prefix to the Homenet with an identity association for a
   prefix delegation (IA_PD) option [RFC8415] and manages the DOI of the
   associated reverse zone.

   This leaves a place for setting up the relation between the HNA and
   DOI automatically as described in [RFC9527].

   In the case of the reverse zone, the DOI authenticates the source of
   the updates by IPv6 ACLs, and the ISP knows exactly what addresses
   have been delegated.  Therefore, the HNA SHOULD always originate
   Synchronization Channel updates from an IP address within the zone
   that is being updated.  Exceptionally, the Synchronization Channel
   might be from a different zone delegated to the HNA (if there were
   multiple zones or renumbering events were in progress).

   For example, if the ISP has assigned 2001:db8:f00d:1234::/64 to the
   WAN interface (by DHCPv6 or PPP with Router Advertisement (RA)), then
   the HNA should originate Synchronization Channel updates from, for
   example, 2001:db8:f00d:1234::2.

   If an ISP has delegated 2001:db8:aeae::/56 to the HNA via DHCPv6-PD,
   then the HNA should originate Synchronization Channel updates to an
   IP address within that subnet, such as 2001:db8:aeae:1::2.

   With this relation automatically configured, the synchronization
   between the Home network and the DOI happens in a similar way to the
   synchronization of the Public Homenet Zone described earlier in this
   document.

   Note that for home networks connected to multiple ISPs, each ISP
   provides only the DOI of the reverse zones associated with the
   delegated prefix.  It is also likely that the DNS exchanges will need
   to be performed on dedicated interfaces to be accepted by the ISP.
   More specifically, the reverse zone update associated with prefix 1
   cannot be performed by the HNA using an IP address that belongs to
   prefix 2.  Such constraints do not raise major concerns for hot
   standby or load-sharing configuration.

   With IPv6, the reverse domain space for IP addresses associated with
   a subnet such as ::/64 is so large that the reverse zone may be
   confronted with scalability issues.  How the reverse zone is
   generated is out of scope of this document.  [RFC8501] provides
   guidance on how to address scalability issues.

11.  DNSSEC-Compliant Homenet Architecture

   Section 3.7.3 of [RFC7368] recommends that DNSSEC be deployed on both
   the authoritative server and the resolver.

   The resolver side is out of scope of this document, and only the
   authoritative part of the server is considered.  Other documents such
   as [RFC5011] deal with the continuous update of trust anchors
   required for operation of a DNSSEC Resolver.

   The Public Homenet Zone and the Public Reverse Zone MUST be DNSSEC
   signed by the HNA.

   Secure delegation is achieved only if the DS RRset is properly set in
   the parent zone.  Secure delegation can be performed by the HNA or
   the DOIs, and the choice highly depends on which entity is authorized
   to perform such updates.  Typically, the DS RRset is updated manually
   through a registrar interface and can be maintained with mechanisms
   such as CDS [RFC7344].

   When the operator of the DOI is also the registrar for the domain,
   then it is a trivial matter for the DOI to initialize the relevant DS
   records in the parent zone.  In other cases, some other
   initialization will be required, and that will be specific to the
   infrastructure involved.  It is beyond the scope of this document.

   There may be some situations where the HNA is unable to arrange for
   secure delegation of the zones, but the HNA MUST still sign the
   zones.

12.  Renumbering

   During a renumbering of the home network, the HNA IP address may be
   changed and the Public Homenet Zone will be updated by the HNA with
   new AAAA records.

   The HNA will then advertise to the DM via a NOTIFY on the Control
   Channel.  The DM will need to note the new originating IP for the
   connection, and it will need to update its internal database of
   Synchronization Channels.  A new zone transfer will occur with the
   new records for the resources that the HNA wishes to publish.

   The remainder of the section provides recommendations regarding the
   provisioning of the Public Homenet Zone, especially the IP addresses.

   Renumbering has been extensively described in [RFC4192] and analyzed
   in [RFC7010], and the reader is expected to be familiar with them
   before reading this section.  In the make-before-break renumbering
   scenario, the new prefix is advertised, and the network is configured
   to prepare the transition to the new prefix.  During a period of
   time, the two prefixes (old and new) coexist before the old prefix is
   completely removed.  New resource records containing the new prefix
   SHOULD be published, while the old resource records with the old
   prefixes SHOULD be withdrawn.  If the HNA anticipates that the period
   of overlap will be long (perhaps due to the knowledge of router and
   DHCPv6 lifetimes), it MAY publish the old prefixes with a
   significantly lower TTL.

   In break-before-make renumbering scenarios, including flash
   renumbering scenarios [RFC8978], the old prefix becomes unusable
   before the new prefix is known or advertised.  As explained in
   [RFC8978], some flash renumberings occur due to power cycling of the
   HNA, where ISPs do not properly remember what prefixes have been
   assigned to which user.

   An HNA that boots up MUST immediately use the Control Channel to
   update the location for the Synchronization Channel.  This is a
   reasonable thing to do on every boot, as the HNA has no idea how long
   it has been offline or if the (DNSSEC) zone has perhaps expired
   during the time the HNA was powered off.

   The HNA will have a list of names that should be published, but it
   might not yet have IP addresses for those devices.  This could be
   because at the time of power on, the other devices were not yet
   online.  If the HNA is sure that the prefix has not changed, then it
   should use the previously known addresses, with a very low TTL.

   Although the new and old IP addresses may be stored in the Public
   Homenet Zone, it is RECOMMENDED that only the newly reachable IP
   addresses be published.

   Regarding the Public Homenet Reverse Zone, the new Public Homenet
   Reverse Zone has to be populated as soon as possible, and the old
   Public Homenet Reverse Zone will be deleted by the owner of the zone
   (and the owner of the old prefix, which is usually the ISP) once the
   prefix is no longer assigned to the HNA.  The ISP MUST ensure that
   the DNS cache has expired before reassigning the prefix to a new home
   network.  This may be enforced by controlling the TTL values.

   To avoid reachability disruption, IP connectivity information
   provided by the DNS MUST be coherent with the IP in use.  In our
   case, this means the old IP address MUST NOT be provided via the DNS
   when it is not reachable anymore.

   In the make-before-break scenario, it is possible to make the
   transition seamless.  Let T be the TTL associated with an RRset of
   the Public Homenet Zone; Time_NEW be the time the new IP address
   replaces the old IP address in the Homenet Zone; and
   Time_OLD_UNREACHABLE be the time the old IP will not be reachable
   anymore.

   In the case of the make-before-break scenario, seamless reachability
   is provided as long as Time_OLD_UNREACHABLE - T_NEW > (2 * T).  If
   this is not satisfied, then devices associated with the old IP
   address in the home network may become unreachable for 2 * T -
   (Time_OLD_UNREACHABLE - Time_NEW).

   In the case of a break-before-make scenario, Time_OLD_UNREACHABLE =
   Time_NEW, and the device may become unreachable up to 2 * T.  Of
   course, if Time_NEW >= Time_OLD_UNREACHABLE, then the outage is not
   seamless.

13.  Privacy Considerations

   Outsourcing the DNS Authoritative service from the HNA to a third
   party raises a few privacy-related concerns.

   The Public Homenet Zone lists the names of services hosted in the
   home network.  Combined with blocking of AXFR queries, the use of
   NSEC3 [RFC5155] (vs. NSEC [RFC4034]) prevents an attacker from being
   able to walk the zone to discover all the names.  However, recent
   work [GPUNSEC3] [ZONEENUM] has shown that the protection provided by
   NSEC3 against dictionary attacks should be considered cautiously, and
   [RFC9276] provides guidelines to configure NSEC3 properly.  In
   addition, the attacker may be able to walk the reverse DNS zone or
   use other reconnaissance techniques to learn this information as
   described in [RFC7707].

   The zone may be also exposed during the synchronization between the
   primary and the secondary.  The casual risk of this occurring is low,
   and the use of [RFC9103] significantly reduces this.  Even if DNS
   zone transfer over TLS [RFC9103] is used by the DOI, it may still
   leak the existence of the zone through Notifies.  The protocol
   described in this document does not increase that risk, as all
   Notifies use the encrypted Control Channel.

   In general, a home network owner is expected to publish only names
   for which there is some need to reference them externally.
   Publication of the name does not imply that the service is
   necessarily reachable from any or all parts of the Internet.
   [RFC7084] mandates that the outgoing-only policy [RFC6092] be
   available, and in many cases, it is configured by default.  A well-
   designed user interface would combine a policy for making a service
   public by a name with a policy on who may access it.

   In many cases, and for privacy reasons, the home network owner has
   wanted to publish names only for services that they will be able to
   access.  The access control may consist of an IP source address
   range, or access may be restricted via some VPN functionality.  The
   main advantages of publishing the names are that the service may be
   accessed by the same name both within and outside the home, and the
   DNS resolution can be handled similarly both within and outside the
   home.  This considerably eases the ability to use VPNs where the VPN
   can be chosen according to the IP address of the service.  Typically,
   a user may configure its device to reach its Homenet devices via a
   VPN while the remaining traffic is accessed directly.

   Enterprise networks have generally adopted another strategy
   designated as split-horizon-DNS.  While such strategy might appear as
   providing more privacy at first sight, its implementation remains
   challenging and the privacy advantages need to be considered
   carefully.  In split-horizon-DNS, names are designated with internal
   names that can only be resolved within the corporate network.  When
   such strategy is applied to the homenet, VPNs need to be configured
   with naming resolution policies and routing policies.  Such an
   approach might be reasonable with a single VPN, but maintaining a
   coherent DNS space and IP space among various VPNs comes with serious
   complexities.  Firstly, if multiple homenets are using the same
   domain name -- like home.arpa -- it becomes difficult to determine on
   which network the resolution should be performed.  As a result,
   homenets should at least be differentiated by a domain name.
   Secondly, the use of split-horizon-DNS requires each VPN to be
   associated with a resolver and specific resolutions to be performed
   by the dedicated resolver.  Such policies can easily raise some
   conflicts (with significant privacy issues) while remaining hard to
   be implemented.

   In addition to the Public Homenet Zone, pervasive DNS monitoring can
   also monitor the traffic associated with the Public Homenet Zone.
   This traffic may provide an indication of the services an end user
   accesses, plus how and when they use these services.  Although,
   caching may obfuscate this information inside the home network, it is
   likely that this information will not be cached outside the home
   network.

14.  Security Considerations

   The HNA never answers DNS requests from the Internet.  These requests
   are instead served by the DOI.

   While this limits the level of exposure of the HNA, the HNA still has
   some exposure to attacks from the Internet.  This section analyses
   the attack surface associated with these communications, the data
   published by the DOI, as well as operational considerations.

14.1.  Registered Homenet Domain

   The DOI MUST NOT serve any Public Homenet Zone when it is not
   confident that the HNA owns the Registered Homenet Domain.  Proof of
   ownership is outside the scope of this document, and it is assumed
   that such a phase has preceded the outsourcing of the zone.

14.2.  HNA DM Channels

   The channels between HNA and DM are mutually authenticated and
   encrypted with TLS [RFC8446], and its associated security
   considerations apply.

   To ensure that the multiple TLS sessions are continuously
   authenticating the same entity, TLS may take advantage of second-
   factor authentication as described in [RFC8672] for the TLS server
   certificate for the Control Channel.  The HNA should also cache the
   TLS server certificate used by the DM, in order to authenticate the
   DM during the setup of the Synchronization Channel.  (Alternatively,
   the HNA is configured with an ACL from which Synchronization Channel
   connections will originate.)

   The Control Channel and Synchronization Channel follow the guidelines
   in [RFC7858] and [RFC9103], respectively.

   The DNS protocol is subject to reflection attacks; however, these
   attacks are largely applicable when DNS is carried over UDP.  The
   interfaces between the HNA and DM are using TLS over TCP, which
   prevents such reflection attacks.  Note that Public Authoritative
   servers hosted by the DOI are subject to such attacks, but that is
   out of scope of this document.

   Note that in the case of the Reverse Homenet Zone, the data is less
   subject to attacks than in the Public Homenet Zone.  In addition, the
   DM and Reverse Distribution Manager (RDM) may be provided by the ISP
   -- as described in [RFC9527], in which case DM and RDM might be less
   exposed to attacks -- as communications within a network.

14.3.  Names Are Less Secure than IP Addresses

   This document describes how an end user can make their services and
   devices from their home network reachable on the Internet by using
   names rather than IP addresses.  This exposes the home network to
   attackers because names are expected to include less entropy than IP
   addresses.  IPv4 addresses are 4-bytes long leading to 2^32
   possibilities.  With IPv6 addresses, the Interface Identifier is
   64-bits long leading to up to 2^64 possibilities for a given
   subnetwork.  This is not to mention that the subnet prefix is also
   64-bits long, thus providing up to 2^64 possibilities.  On the other
   hand, names used for either the home network domain or the devices
   present less entropy (livebox, router, printer, nicolas, jennifer,
   ...) and thus potentially expose the devices to dictionary attacks.

14.4.  Names Are Less Volatile than IP Addresses

   IP addresses may be used to locate a device, a host, or a service.
   However, home networks are not expected to be assigned a time-
   invariant prefix by ISPs.  In addition, IPv6 enables temporary
   addresses that makes them even more volatile [RFC8981].  As a result,
   observing IP addresses only provides some ephemeral information about
   who is accessing the service.  On the other hand, names are not
   expected to be as volatile as IP addresses.  As a result, logging
   names over time may be more valuable than logging IP addresses,
   especially to profile an end user's characteristics.

   PTR provides a way to bind an IP address to a name.  In that sense,
   responding to PTR DNS queries may affect the end user's privacy.  For
   that reason, PTR DNS queries MAY be configured to return with
   NXDOMAIN instead.

14.5.  Deployment Considerations

   The HNA is expected to sign the DNSSEC zone and, as such, hold the
   private KSK and Zone Signing Key (ZSK).

   In this case, there is no strong justification to use a separate KSK
   and ZSK.  If an attacker can get access to one of them, it is likely
   that they will access both of them.  If the HNA is run in a home
   router with a secure element (SE) or trusted platform module (TPM),
   storing the private keys in the secure element would be a useful
   precaution.  The DNSSEC keys are generally needed on an hourly to
   weekly basis, but not more often.

   While there is some risk that the DNSSEC keys might be disclosed by
   malicious parties, the bigger risk is that they will simply be lost
   if the home router is factory reset or just thrown out / replaced
   with a newer model.

   Generating new DNSSEC keys is relatively easy; they can be deployed
   using the Control Channel to the DM.  The key that is used to
   authenticate that connection is the critical key that needs
   protection and should ideally be backed up to offline storage (such
   as a USB key).

14.6.  Operational Considerations

   Homenet technologies make it easier to expose devices and services to
   the Internet.  This imposes broader operational considerations for
   the operator and the Internet as follows:

   *  The home network operator must carefully assess whether a device
      or service previously fielded only on a home network is robust
      enough to be exposed to the Internet.

   *  The home network operator will need to increase the diligence to
      regularly managing these exposed devices due to their increased
      risk posture of being exposed to the Internet.

   *  Depending on the operational practices of the home network
      operators, there is an increased risk to the Internet through the
      possible introduction of additional Internet-exposed systems that
      are poorly managed and likely to be compromised.

15.  IANA Considerations

   This document has no IANA actions.

16.  References

16.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
              J., and E. Lear, "Address Allocation for Private
              Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
              February 1996, <https://www.rfc-editor.org/info/rfc1918>.

   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
              August 1996, <https://www.rfc-editor.org/info/rfc1996>.

   [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>.

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

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <https://www.rfc-editor.org/info/rfc4034>.

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
              <https://www.rfc-editor.org/info/rfc5155>.

   [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
              DNSSEC Delegation Trust Maintenance", RFC 7344,
              DOI 10.17487/RFC7344, September 2014,
              <https://www.rfc-editor.org/info/rfc7344>.

   [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>.

   [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>.

   [RFC8375]  Pfister, P. and T. Lemon, "Special-Use Domain
              'home.arpa.'", RFC 8375, DOI 10.17487/RFC8375, May 2018,
              <https://www.rfc-editor.org/info/rfc8375>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [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>.

   [RFC9103]  Toorop, W., Dickinson, S., Sahib, S., Aras, P., and A.
              Mankin, "DNS Zone Transfer over TLS", RFC 9103,
              DOI 10.17487/RFC9103, August 2021,
              <https://www.rfc-editor.org/info/rfc9103>.

   [RFC9525]  Saint-Andre, P. and R. Salz, "Service Identity in TLS",
              RFC 9525, DOI 10.17487/RFC9525, November 2023,
              <https://www.rfc-editor.org/info/rfc9525>.

16.2.  Informative References

   [DOMAIN-VALIDATION]
              Sahib, S., Huque, S., Wouters, P., and E. Nygren, "Domain
              Control Validation using DNS", Work in Progress, Internet-
              Draft, draft-ietf-dnsop-domain-verification-techniques-03,
              17 October 2023, <https://datatracker.ietf.org/doc/html/
              draft-ietf-dnsop-domain-verification-techniques-03>.

   [DRO-RECS] Migault, D., Lewis, E., and D. York, "Recommendations for
              DNSSEC Resolvers Operators", Work in Progress, Internet-
              Draft, draft-ietf-dnsop-dnssec-validator-requirements-07,
              13 November 2023, <https://datatracker.ietf.org/doc/html/
              draft-ietf-dnsop-dnssec-validator-requirements-07>.

   [GPUNSEC3] Wander, M., Schwittmann, L., Boelmann, C., and T. Weis,
              "GPU-Based NSEC3 Hash Breaking", DOI 10.1109/NCA.2014.27,
              August 2014, <https://doi.org/10.1109/NCA.2014.27>.

   [HOMEROUTER-PROVISION]
              Richardson, M., "Provisioning Initial Device Identifiers
              into Home Routers", Work in Progress, Internet-Draft,
              draft-richardson-homerouter-provisioning-02, 14 November
              2021, <https://datatracker.ietf.org/doc/html/draft-
              richardson-homerouter-provisioning-02>.

   [NS-REVALIDATION]
              Huque, S., Vixie, P., and R. Dolmans, "Delegation
              Revalidation by DNS Resolvers", Work in Progress,
              Internet-Draft, draft-ietf-dnsop-ns-revalidation-04, 13
              March 2023, <https://datatracker.ietf.org/doc/html/draft-
              ietf-dnsop-ns-revalidation-04>.

   [REBIND]   Wikipedia, "DNS rebinding", September 2023,
              <https://en.wikipedia.org/w/
              index.php?title=DNS_rebinding&oldid=1173433859>.

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

   [RFC3587]  Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global
              Unicast Address Format", RFC 3587, DOI 10.17487/RFC3587,
              August 2003, <https://www.rfc-editor.org/info/rfc3587>.

   [RFC3927]  Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
              Configuration of IPv4 Link-Local Addresses", RFC 3927,
              DOI 10.17487/RFC3927, May 2005,
              <https://www.rfc-editor.org/info/rfc3927>.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              DOI 10.17487/RFC4192, September 2005,
              <https://www.rfc-editor.org/info/rfc4192>.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
              <https://www.rfc-editor.org/info/rfc4193>.

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

   [RFC5011]  StJohns, M., "Automated Updates of DNS Security (DNSSEC)
              Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
              September 2007, <https://www.rfc-editor.org/info/rfc5011>.

   [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>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/info/rfc6749>.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013,
              <https://www.rfc-editor.org/info/rfc6762>.

   [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
              P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              DOI 10.17487/RFC6887, April 2013,
              <https://www.rfc-editor.org/info/rfc6887>.

   [RFC7010]  Liu, B., Jiang, S., Carpenter, B., Venaas, S., and W.
              George, "IPv6 Site Renumbering Gap Analysis", RFC 7010,
              DOI 10.17487/RFC7010, September 2013,
              <https://www.rfc-editor.org/info/rfc7010>.

   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              DOI 10.17487/RFC7084, November 2013,
              <https://www.rfc-editor.org/info/rfc7084>.

   [RFC7368]  Chown, T., Ed., Arkko, J., Brandt, A., Troan, O., and J.
              Weil, "IPv6 Home Networking Architecture Principles",
              RFC 7368, DOI 10.17487/RFC7368, October 2014,
              <https://www.rfc-editor.org/info/rfc7368>.

   [RFC7404]  Behringer, M. and E. Vyncke, "Using Only Link-Local
              Addressing inside an IPv6 Network", RFC 7404,
              DOI 10.17487/RFC7404, November 2014,
              <https://www.rfc-editor.org/info/rfc7404>.

   [RFC7707]  Gont, F. and T. Chown, "Network Reconnaissance in IPv6
              Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
              <https://www.rfc-editor.org/info/rfc7707>.

   [RFC7788]  Stenberg, M., Barth, S., and P. Pfister, "Home Networking
              Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April
              2016, <https://www.rfc-editor.org/info/rfc7788>.

   [RFC8094]  Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
              Transport Layer Security (DTLS)", RFC 8094,
              DOI 10.17487/RFC8094, February 2017,
              <https://www.rfc-editor.org/info/rfc8094>.

   [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>.

   [RFC8501]  Howard, L., "Reverse DNS in IPv6 for Internet Service
              Providers", RFC 8501, DOI 10.17487/RFC8501, November 2018,
              <https://www.rfc-editor.org/info/rfc8501>.

   [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>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.

   [RFC8672]  Sheffer, Y. and D. Migault, "TLS Server Identity Pinning
              with Tickets", RFC 8672, DOI 10.17487/RFC8672, October
              2019, <https://www.rfc-editor.org/info/rfc8672>.

   [RFC8978]  Gont, F., Žorž, J., and R. Patterson, "Reaction of IPv6
              Stateless Address Autoconfiguration (SLAAC) to Flash-
              Renumbering Events", RFC 8978, DOI 10.17487/RFC8978, March
              2021, <https://www.rfc-editor.org/info/rfc8978>.

   [RFC8981]  Gont, F., Krishnan, S., Narten, T., and R. Draves,
              "Temporary Address Extensions for Stateless Address
              Autoconfiguration in IPv6", RFC 8981,
              DOI 10.17487/RFC8981, February 2021,
              <https://www.rfc-editor.org/info/rfc8981>.

   [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>.

   [RFC9276]  Hardaker, W. and V. Dukhovni, "Guidance for NSEC3
              Parameter Settings", BCP 236, RFC 9276,
              DOI 10.17487/RFC9276, August 2022,
              <https://www.rfc-editor.org/info/rfc9276>.

   [RFC9527]  Migault, D., Weber, R., and T. Mrugalski, "DHCPv6 Options
              for the Homenet Naming Authority", RFC 9527,
              DOI 10.17487/RFC9527, January 2024,
              <https://www.rfc-editor.org/info/rfc9527>.

   [ZONEENUM] Wang, Z., Xiao, L., and R. Wang, "An efficient DNSSEC zone
              enumeration algorithm", DOI 10.2495/MIIT130591, April
              2014, <https://doi.org/10.2495/MIIT130591>.

Appendix A.  HNA Channel Configurations

A.1.  Public Homenet Zone

   This document does not deal with how the HNA is provisioned with a
   trusted relationship to the Distribution Manager for the forward
   zone.

   This section details what needs to be provisioned into the HNA and
   serves as a requirements statement for mechanisms.

   The HNA needs to be provisioned with:

   *  the Registered Domain (e.g., myhome.example);

   *  the contact information for the DM, including the DNS name (the
      fully qualified domain name (FQDN)), possibly the IP literal, and
      a certificate (or anchor) to be used to authenticate the service;

   *  the DM transport protocol and port (the default is DNS over TLS,
      on port 853); and

   *  the HNA credentials used by the DM for its authentication.

   The HNA will need to select an IP address for communication for the
   Synchronization Channel.  This is typically the WAN address of the
   CPE, but it could be an IPv6 LAN address in the case of a home with
   multiple ISPs (and multiple border routers).  This is detailed in
   Section 6.5.3 when the NS and A or AAAA RRsets are communicated.

   The above parameters MUST be provisioned for ISP-specific reverse
   zones.  One example of how to do this can be found in [RFC9527].
   ISP-specific forward zones MAY also be provisioned using [RFC9527],
   but zones that are not related to a specific ISP zone (such as with a
   DNS provider) must be provisioned through other means.

   Similarly, if the HNA is provided by a registrar, the HNA may be
   handed preconfigured to the end user.

   In the absence of specific pre-established relations, these pieces of
   information may be entered manually by the end user.  In order to
   ease the configuration from the end user, the following scheme may be
   implemented.

   The HNA may present the end user with a web interface that provides
   the end user the ability to indicate the Registered Homenet Domain or
   the registrar with, for example, a preselected list.  Once the
   registrar has been selected, the HNA redirects the end user to that
   registrar in order to receive an access token.  The access token will
   enable the HNA to retrieve the DM parameters associated with the
   Registered Domain.  These parameters will include the credentials
   used by the HNA to establish the Control and Synchronization
   Channels.

   Such architecture limits the necessary steps to configure the HNA
   from the end user.

Appendix B.  Information Model for Outsourced Information

   This section specifies an optional format for the set of parameters
   required by the HNA to configure the naming architecture of this
   document.

   In cases where a home router has not been provisioned by the
   manufacturer (when forward zones are provided by the manufacturer) or
   by the ISP (when the ISP provides this service), then a home user/
   owner will need to configure these settings via an administrative
   interface.

   By defining a standard format (in JSON) for this configuration
   information, the user/owner may be able to copy and paste a
   configuration blob from the service provider into the administrative
   interface of the HNA.

   This format may also provide the basis for a future OAuth 2.0
   [RFC6749] flow that could do the set up automatically.

   The HNA needs to be configured with the following parameters as
   described by the Concise Data Definition Language (CDDL) [RFC8610].
   These parameters are necessary to establish a secure channel between
   the HNA and the DM as well as to specify the DNS zone that is in the
   scope of the communication.

   hna-configuration = {
     "registered_domain" : tstr,
     "dm"                : tstr,
     ? "dm_transport" : "DoT"
     ? "dm_port"        : uint,
     ? "dm_acl"         : hna-acl / [ +hna-acl ]
     ? "hna_auth_method": hna-auth-method
     ? "hna_certificate": tstr
   }

   hna-acl          = tstr
   hna-auth-method  /= "certificate"

   For example:

   {
     "registered_domain" : "n8d234f.r.example.net",
     "dm"                : "2001:db8:1234:111:222::2",
     "dm_transport"      : "DoT",
     "dm_port"           : 4433,
     "dm_acl"            : "2001:db8:1f15:62e::/64"
                      or [ "2001:db8:1f15:62e::/64", ... ]
     "hna_auth_method"   : "certificate",
     "hna_certificate"   : "-----BEGIN CERTIFICATE-----\nMIIDTjCCFGy..",
   }

   Registered Homenet Domain (registered_domain):  The Domain Name of
      the zone.  Multiple Registered Homenet Domains may be provided.
      This will generate the creation of multiple Public Homenet Zones.
      This parameter is mandatory.

   Distribution Manager notification address (dm):  The associated FQDNs
      or IP addresses of the DM to which DNS Notifies should be sent.
      This parameter is mandatory.  IP addresses are optional, and the
      FQDN is sufficient and preferred.  If there are concerns about the
      security of the name to IP translation, then DNSSEC should be
      employed.

   As the session between the HNA and the DM is authenticated with TLS,
   the use of names is easier.

   As certificates are more commonly emitted for FQDN than for IP
   addresses, it is preferred to use names and authenticate the name of
   the DM during the TLS session establishment.

   Supported Transport (dm_transport):  The transport that carries the
      DNS exchanges between the HNA and the DM.  The typical value is
      "DoT", but it may be extended in the future with "DoH" or "DoQ",
      for example.  This parameter is optional, and the HNA uses DoT by
      default.

   Distribution Manager Port (dm_port):  Indicates the port used by the
      DM.  This parameter is optional, and the default value is provided
      by the Supported Transport.  In the future, an additional
      transport may not have a default port, in which case either a
      default port needs to be defined or this parameter becomes
      mandatory.

   Note that HNA does not define ports for the Synchronization Channel.
   In any case, this is not expected to be a part of the configuration
   but is instead negotiated through the Configuration Channel.
   Currently, the Configuration Channel does not provide this and limits
   its agility to a dedicated IP address.  If such agility is needed in
   the future, additional exchanges will need to be defined.

   Authentication Method ("hna_auth_method"):  How the HNA authenticates
      itself to the DM within the TLS connection(s).  The authentication
      method can typically be "certificate", "psk", or "none".  This
      parameter is optional, and the Authentication Method is
      "certificate" by default.

   Authentication data ("hna_certificate", "hna_key"):  The certificate
      chain used to authenticate the HNA.  This parameter is optional,
      and when not specified, a self-signed certificate is used.

   Distribution Manager AXFR permission netmask (dm_acl):  The subnet
      from which the CPE should accept SOA queries and AXFR requests.  A
      subnet is used in the case where the DOI consists of a number of
      different systems.  An array of addresses is permitted.  This
      parameter is optional, and if unspecified, the CPE uses the IP
      addresses provided by the dm parameter either directly when the dm
      indicates the IP address(es) returned by the DNS or DNSSEC
      resolution when dm indicates an FQDN.

   For forward zones, the relationship between the HNA and the forward
   zone provider may be the result of a number of transactions:

   1.  The forward zone outsourcing may be provided by the maker of the
       Homenet router.  In this case, the identity and authorization
       could be built in the device at the manufacturer provisioning
       time.  The device would need to be provisioned with a device-
       unique credential, and it is likely that the Registered Homenet
       Domain would be derived from a public attribute of the device,
       such as a serial number (see Appendix C or [HOMEROUTER-PROVISION]
       for more details).

   2.  The forward zone outsourcing may be provided by the ISP.  In this
       case, the use of [RFC9527] to provide the credentials is
       appropriate.

   3.  The forward zone may be outsourced to a third party, such as a
       domain registrar.  In this case, the use of the JSON-serialized
       YANG data model described in this section is appropriate, as it
       can easily be copy and pasted by the user or downloaded as part
       of a web transaction.

   For reverse zones, the relationship is always with the upstream ISP
   (although there may be more than one), so [RFC9527] always applies.

   The following is an abridged example of a set of data that represents
   the needed configuration parameters for outsourcing.

Appendix C.  Example: A Manufacturer-Provisioned HNA Product Flow

   This scenario is one where a Homenet router device manufacturer
   decides to offer DNS hosting as a value add.

   [HOMEROUTER-PROVISION] describes a process for a home router
   credential provisioning system.  The outline of it is that near the
   end of the manufacturing process, as part of the firmware loading,
   the manufacturer provisions a private key and certificate into the
   device.

   In addition to having an asymmetric credential known to the
   manufacturer, the device also has been provisioned with an agreed-
   upon name.  In the example in the above document, the name
   "n8d234f.r.example.net" has already been allocated and confirmed with
   the manufacturer.

   The HNA can use the above domain for itself.  It is not very pretty
   or personal, but if the owner would like to have a better name, they
   can arrange it.

   The configuration would look like the following:

   {
     "dm" : "2001:db8:1234:111:222::2",
     "dm_acl"    : "2001:db8:1234:111:222::/64",
     "dm_ctrl"   : "manufacturer.example.net",
     "dm_port"   : "4433",
     "ns_list"   : [ "ns1.publicdns.example", "ns2.publicdns.example"],
     "zone"      : "n8d234f.r.example.net",
     "auth_method" : "certificate",
     "hna_certificate":"-----BEGIN CERTIFICATE-----\nMIIDTjCCFGy....",
   }

   The dm_ctrl and dm_port values would be built into the firmware.

Acknowledgments

   The authors wish to thank Philippe Lemordant for his contributions to
   the earlier draft versions of this document; Ole Troan for pointing
   out issues with the IPv6-routed home concept and placing the scope of
   this document in a wider picture; Mark Townsley for encouragement and
   injecting a healthy debate on the merits of the idea; Ulrik de Bie
   for providing alternative solutions; Paul Mockapetris, Christian
   Jacquenet, Francis Dupont, and Ludovic Eschard for their remarks on
   HNA and low power devices; Olafur Gudmundsson for clarifying DNSSEC
   capabilities of small devices; Simon Kelley for its feedback as
   dnsmasq implementer; Andrew Sullivan, Mark Andrew, Ted Lemon, Mikael
   Abrahamson, Stephen Farrell, and Ray Bellis for their feedback on
   handling different views as well as clarifying the impact of
   outsourcing the zone-signing operation outside the HNA; and Mark
   Andrew and Peter Koch for clarifying the renumbering.

   The authors would like to thank Kiran Makhijani for her in-depth
   review that contributed to shaping the final version of this
   document.

   The authors would also like to thank our Area Director Éric Vyncke
   for his constant support and pushing the document through the IESG
   process and the many reviewers from various directorates including
   Anthony Somerset, Geoff Huston, Tim Chown, Tim Wicinski, Matt Brown,
   Darrel Miller, and Christer Holmberg.

Contributors

   The coauthors would like to thank Chris Griffiths and Wouter Cloetens
   for providing significant contributions to the earlier draft versions
   of this document.

Authors' Addresses

   Daniel Migault
   Ericsson
   8275 Trans Canada Route
   Saint Laurent QC 4S 0B6
   Canada
   Email: daniel.migault@ericsson.com


   Ralf Weber
   Nominum
   2000 Seaport Blvd.
   Redwood City, CA 94063
   United States of America
   Email: ralf.weber@nominum.com


   Michael Richardson
   Sandelman Software Works
   470 Dawson Avenue
   Ottawa ON K1Z 5V7
   Canada
   Email: mcr+ietf@sandelman.ca


   Ray Hunter
   Globis Consulting BV
   Weegschaalstraat 3
   5632CW Eindhoven
   Netherlands
   Email: v6ops@globis.net