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Versions: (draft-tldm-simple-homenet-naming) 00 01

Network Working Group                                           T. Lemon
Internet-Draft                                       Nibbhaya Consulting
Intended status: Informational                                D. Migault
Expires: September 6, 2018                                      Ericsson
                                                             S. Cheshire
                                                              Apple Inc.
                                                           March 5, 2018


        Simple Homenet Naming and Service Discovery Architecture
                  draft-ietf-homenet-simple-naming-01

Abstract

   This document describes how names are published and resolved on
   homenets, and how hosts are configured to use these names to discover
   services on homenets.  It presents the complete architecture, and
   describes a simple subset of that architecture that can be used in
   low-cost homenet routers.

Status of This Memo

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

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

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

   This Internet-Draft will expire on September 6, 2018.

Copyright Notice

   Copyright (c) 2018 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



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Managed LAN versus Homenet  . . . . . . . . . . . . . . .   4
     2.2.  Homenet-specific considerations . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Name  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Authority . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Resolution  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Publication . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  DNS Service Discovery Registration Protocol . . . . . . .   7
     7.2.  Configuring Service Discovery . . . . . . . . . . . . . .   7
   8.  Host Configurtion . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Globally Unique Name  . . . . . . . . . . . . . . . . . . . .  10
   10. DNSSEC Validation . . . . . . . . . . . . . . . . . . . . . .  10
   11. Support for Multiple Provisioning Domains . . . . . . . . . .  11
   12. Using the Local Namespace While Away From Home  . . . . . . .  11
   13. Management Considerations . . . . . . . . . . . . . . . . . .  11
   14. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  12
   15. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   16. IANA considerations . . . . . . . . . . . . . . . . . . . . .  12
   17. Normative References  . . . . . . . . . . . . . . . . . . . .  12
   Appendix A.  Existing solutions . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   This document is a homenet architecture document.  The term 'homenet'
   refers to a set of technologies that allow home network users to have
   a local-area network (LAN) with more than one physical link and,
   optionally, more than one internet service provider.  Home network
   users are assumed not to be knowledgable in network operations, so
   homenets automatically configure themselves, providing connectivity
   and service discovery within the home with no operator intervention.
   This document describes the aspect of homenet automatic configuration
   that has to do with service discovery and name resolution.

   The homenet naming architecture consists of two parts: the simple
   naming architecture, and the advanced naming architecture.  The
   advanced architecture provides approximate parity of features with a
   managed network, including the ability to publish services on the
   internet.  The simple architecture provides a minimal set of features
   required to enable seamless service discovery on a multi-link home



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   network, but does not attempt to provide feature parity with a
   managed LAN.

   This document begins by presenting a motivational list of
   requirements and considerations, which should give the reader a clear
   idea of the scope of the problem being solved.  It then explains how
   each requirement is addressed, and provides references for relevant
   standards documents describing the details of the implementation.
   Some requirements are not satisfied by the simple architecture; these
   are discussed in this document, but explained in more detail in the
   Advanced Homenet Naming Architecture document, which is to follow.

2.  Requirements

   Name service on a local area network (LAN) requires the following:

   o  Name: a forward domain under which information about local
      services will be published

   o  Authority: a name server that is authoritative for at least a
      forward and one or two reverse domains that are applicable to that
      network

   o  Resolution: a full-service caching DNS resolver

   o  Publication: a mechanism that

      *  allows services on the LAN to publish information about the
         services they provide

      *  allows services to publish information on how to reach them

      *  manages the lifetime of such information, so that it persists
         long enough to prevent spoofing, but protects end users from
         seeing stale information

   o  Host configuration: one or more automatic mechanisms (e.g.  DHCP
      or RA) that provide:

      *  caching resolver information to hosts on the LAN

      *  information about how services on the LAN can publish
         information

   o  Trust: some basis for trusting the information that is provided by
      the service discovery system





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2.1.  Managed LAN versus Homenet

   On a managed LAN, many of these services can be provided by
   operators.  When a new printer is added to the network, it can be
   added to the service discovery system (the authoritative server)
   manually.  When a printer is taken out of service, it can be removed.
   In this scenario, the role of "publisher" is filled by the network
   operator.

   In many managed LANs, establishment of trust for service discovery is
   simply on the basis of a belief that the local resolver will give a
   correct answer.  Once the service has been discovered and chosen,
   there may be some security (e.g., TLS) that protects the connection
   to the service, but the trust model is often just "you're connected
   to a network you trust, so you can trust the printer that you
   discovered on this network."

   A homenet does not have an operator, so functions that would normally
   be performed by the operator have to happen automatically.  This has
   implications for trust establishment--since there is no operator
   controlling what services are published locally, some other mechanism
   is required for basic trust establishment.  Additionally, whereas in
   a managed LAN with multiple links to the Internet, the network
   operator can configure the network so that multihoming is handled
   seamlessly, in a homenet, multihoming must be handled using multiple
   provisioning domains [RFC7556].

2.2.  Homenet-specific considerations

   A naming architecture for homenets therefore adds the following
   considerations:

   o  All of the operations mentioned here must reliably function
      automatically, without any user intervention or debugging.

   o  Because user intervention cannot be required, naming conflicts
      must be resolved automatically, and, to the extent possible,
      transparently.

   o  Devices that provide services must be able to publish those
      services on the homenet, and those services must be available from
      any part of the homenet, not just the link to which the device is
      attached.

   o  Homenets must address the problem of multiple provisioning
      domains, in the sense that the DNS may give a different answer
      depending on whether caching resolvers at one ISP or another are
      queried.



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   An additional requirement from the Homenet Architecture [9] is that
   hosts are not required to implement any homenet-specific capabilities
   in order to discover and access services on the homenet.  This
   architecture may define optional homenet-specific features, but hosts
   that do not implement these features must work on homenets.

3.  Terminology

   This document uses the following terms and abbreviations:

   HNR  Homenet Router

   SHNR  Homenet Router implementing simple homenet naming architecture

   AHNR  Homenet Router implementing advanced homenet naming
      architecture

   ISP  Internet Service Provider

4.  Name

   In order for names to be published on a homenet, it is necessary that
   there be a set of domain names under which such names are published.
   These domain names, together, are referred to as the "local domains."
   By default, homenets use the reserved domain 'home.arpa.' for
   publishing names for forward lookups.  So a host called 'example'
   that published its name on the homenet would publish its records on
   the domain name 'example.home.arpa.'.  Because 'home.arpa.' is used
   by all homenets, it has no global meaning, and names published under
   the domain 'home.arpa' cannot be used outside of the homenet on which
   they are published.

   Homenet routers that implement advanced homenet naming may also be
   configured with a global domain.  How such a domain is configured is
   out of scope for this document, and is described in the Advanced
   Homenet Naming Architecture document [advanced].

   In addition to the name, which defaults to 'home.arpa.', names are
   needed for reverse lookups.  These names are dependent on the IP
   addressing used on the homenet.  If the homenet is addressed with
   IPv4, a reverse domain corresponding to the IPv4 subnet [1] section
   5.2.1 should be constructed.  For example, if the homenet is
   allocating local IP addresses out of net 10 [3], a domain, '10.in-
   addr.arpa' would be required.  Like 'home.arpa.', '10.in-addr.arpa'
   is a locally-served zone, and has no validity outside of the homenet.

   If the homenet is addressed with IPv6, it is expected to have a
   unique local address prefix; subsets of this prefix will be



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   advertised on every link on the homenet.  Every service on the
   homenet that supports IPv6 is expected to be reachable at an address
   that is configured using the ULA prefix.  Therefore there is no need
   for any IPv6 reverse zone to be populated other than the ULA zone.
   So for example if the homenet's ULA prefix is fd00:2001:db8::/48,
   then the reverse domain name for the homenet would end in
   '8.b.d.0.1.0.0.2.0.0.d.f.ip6.arpa'.

5.  Authority

   The authority role is provided by a name server that is authoritative
   for each of the local domains.  SHNRs provide authoritative service
   for the homenet using DNSSD Discovery Broker [17].  SHNRs also
   provide Discovery Relay service [12].  On a homenet that has only
   SHNRs, each SHNR individually provides authoritative service for the
   whole homenet by using Discovery relays to discover services off the
   local link.

   The Discovery Proxy model relies on each link having its own name.
   However, homenets do not actually have a way to name local links that
   will make any sense to the end user.  Consequently, this mechanism
   will not work without some tweaks.  In order to address this,
   homenets will use Discovery Brokers [17].  The discovery broker will
   be configured so that a single query for a particular service will be
   successful in providing the information required to access that
   service, regardless of the link it is on.

   Artificial link names will be generated using HNCP.  These should
   only be visible to the user in graphical user interfaces in the event
   that the same name is claimed by a service on two links.  Services
   that are expected to be accessed by users who type in names should
   use [13] if it is available.

   It is possible that local services may offer services available on IP
   addresses in public as well as ULA prefixes.  Homenet hybrid proxies
   MUST filter out global IP addresses, providing only ULA addresses,
   similar to the process described in section 5.5.2 of [11].

   This filtering applies to queries within the homenet; it is
   appropriate for non-ULA addresses to be used for offering services,
   because in some cases end users may want such services to be
   reachable outside of the homenet.  Configuring this is however out of
   scope for this document.








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6.  Resolution

   Name resolution is provided by a local DNS cache or proxy on the
   homenet, henceforth the "local resolver."  All host queries are sent
   to this local resolver.  The local resolver may either act as a full-
   service caching resolver, or as a DNS proxy.  Its responsibility with
   respect to queries on the homenet is to notice queries for names for
   which the local authoritative server is authoritative.  Queries for
   such names are handled through the local authoritative server.
   Queries for all other names are resolved either by forwarding them to
   an ISP-provided full service resolver, or by providing the full
   service resolver function locally.

7.  Publication

7.1.  DNS Service Discovery Registration Protocol

   The DNSSD Service Registration protocol [13] requires that DNS
   updates be validated on the basis that they are received on the local
   link.  To ensure that such registrations are actually received on
   local links in the homenet, updates are sent to the local relay proxy
   ([12]) (XXX how?).

   The relay proxy encapsulates the update and sends it to whatever
   Discovery Proxy is listening on the link; the Discovery proxy then
   either consumes the update directly, or forwards it to the
   authoritative resolver for the local service discovery zone.  If the
   registration protocol is not supported on the homenet, the Discovery
   Proxy rejects the update with a ??? RCODE.

   Homenets are not required to support Service Registration.  Service
   registration requires a stateful authoritative DNS server; this may
   be beyond the capability of the minimal Homenet router.  However,
   more capable Homenet routers should provide this capability.  In
   order to make this work, minimal Homenet routers MUST implement the
   split hybrid proxy [12].  This enables a Homenet with one or more
   Homenet routers that provide a stateful registration cache to allow
   those routers to take over service, using Discovery Relays to service
   links that are connected using Homenet routers with more limited
   functionality.

7.2.  Configuring Service Discovery

   Clients discovering services using DNS-SD [7] follow a two-step
   process.  The first step is for the client device to determine in
   which domain(s) to attempt to discover services.  The second step is
   for the client device to then seek desired service(s) in those
   domain(s).  For an example of the second step, given the desired



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   service type "IPP Printing", and the domains "local" and
   "meeting.ietf.org", the client device forms the queries
   "_ipp._tcp.local.  PTR ?" (resolved using Multicast DNS) and
   "_ipp._tcp.meeting.ietf.org PTR. ?" (resolved using Unicast DNS) and
   then presents the combined list of results to the user.

   The first step, determining in which domain(s) to attempt to discover
   services, is performed in a variety of ways, as described in
   Section 11 of the DNS-Based Service Discovery specification [7].

   The domain "local" is generally always in the set of domains in which
   the client devices attempt to discover services, and other domains
   for service discovery may be configured manually by the user.

   The device also learns additional domains automatically from its
   network environment.  For this automatic configuration discovery,
   special DNS queries are formulated.  To learn additional domain(s) in
   which to attempt to discover services, the query string
   "lb._dns_sd._udp" is prepended onto three different kinds of
   "bootstrap domain" to form DNS queries that allow the device to learn
   the configuration information.

   One of these bootstrap domains is the fixed string "local".  The
   device issues the query "lb._dns_sd._udp.local.  PTR ?" (resolved
   using Multicast DNS), and if any answers are received, then they are
   added to the set of domains in which the client devices attempt to
   discover services.

   Another kind of these bootstrap domains is name-based, derived from
   the DHCPv4 "domain name" option (code 15) [4] (for IPv4) or the DNS
   Search List (DNSSL) Router Advertisement option [10] (for IPv6).  If
   a domain in the DNSSL is "example.com", then the device issues the
   query "lb._dns_sd._udp.example.com.  PTR ?" (resolved using Unicast
   DNS), and if any answers are received, then they are likewise added
   to the set of domains in which the client devices attempt to discover
   services.

   Finally, the third kind of bootstrap domain is address-based, derived
   from the device's IP address(es) themselves.  If the device has IP
   address 192.168.1.100/24, then the device issues the query
   "lb._dns_sd._udp.0.1.168.192.in-addr.arpa.  PTR ?" (resolved using
   Unicast DNS), and if any answers are received, then they are also
   added to the set of domains in which the client devices attempt to
   discover services.

   Since there is an HNR on every link of a homenet, automatic
   configuration could be performed by having HNRs answer the
   "lb._dns_sd._udp.local.  PTR ?" (Multicast DNS) queries.  However,



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   because multicast is slow and unreliable on many modern network
   technologies like Wi-Fi, we prefer to avoid using it.  Instead we
   require that a homenet be configured to answer the name-based
   bootstrap queries.  By default the domain in the DNSSL communicated
   to the client devices will be "home.arpa", and the homenet will be
   configured to correctly answer queries such as
   "lb._dns_sd._udp.example.com.  PTR ?", though client devices must not
   assume that the name will always be "home.arpa".  A client could be
   configured with any valid DNSSL, and should construct the appropriate
   bootstrap queries derived from the name(s) in their configured DNS
   Search List.

   HNRs will answer domain enumeration queries against every IPv4
   address prefix advertised on a homenet link, and every IPv6 address
   prefix advertised on a homenet link, including prefixes derived from
   the homenet's ULA(s).  Whenever the "<domain>" sequence appears in
   this section, it references each of the domains mentioned in this
   paragraph.

   Homenets advertise the availability of several browsing zones in the
   "b._dns_sd._udp.<domain>" subdomain.  By default, the 'home.arpa'
   domain is advertised.  Similarly, 'home.arpa' is advertised as the
   default browsing and service registration domain under
   "db._dns_sd._udp.<domain>", "r._dns_sd._udp.<domain>",
   "dr._dns_sd._udp.<domain>" and "lb._dns_sd._udp.<domain>".

   In order for this discovery process to work, the homenet must provide
   authoritative answers for each of the domains that might be queried.
   To do this, it provides authoritative name service for the 'ip6.arpa'
   and 'in-addr.arpa' subdomains corresponding to each of the prefixes
   advertised on the homenet.  For example, consider a homenet with the
   192.168.1.0/24, 2001:db8:1234:5600::/56 and fc01:2345:6789:1000::/56
   prefixes.  This homenet will have to provide a name server that
   claims to be authoritative for 1.168.192.in-addr.arpa,
   6.5.4.3.2.1.8.b.d.0.1.0.0.2.ip6.arpa and
   0.0.9.8.7.6.5.4.3.2.1.0.c.f.ip6.arpa.

   An IPv6-only homenet would not have an authoritative server for a
   subdomain of in-addr.arpa.  These public authoritative zones are
   required for the public prefixes even if the prefixes are not
   delegated.  However, they need not be accessible outside of the
   homenet.

   It is out of the scope of this document to specify ISP behavior, but
   we note that ISPs have the option of securely delegating the zone, or
   providing an unsigned delegation, or providing no delegation.  Any
   delegation tree that does not include an unsigned delegation at or




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   above the zone cut for the ip6.arpa reverse zone for the assigned
   prefix will fail to validate.

   Ideally, an ISP should provide a secure delegation using a zone-
   signing key provided by the homenet.  However, that too is out of
   scope for this document.  Therefore, an ISP that wishes to support
   users of the simple homenet naming architecture will have to provide
   an unsigned delegation.  We do not wish, however, to discourage
   provisioning of signed delegations when that is possible.

8.  Host Configurtion

   Hosts on the homenet receive a set of resolver IP addresses using
   either DHCP or RA.  IPv4-only hosts will receive IPv4 addresses of
   resolvers, if available, over DHCP.  IPv6-only hosts will receive
   resolver IPv6 addresses using either stateful (if available) or
   stateless DHCPv6, or through the Recursive DNS Server Option ([10],
   Section 5.1) in router advertisements.

   All Homenet routers provide resolver information using both stateless
   DHCPv6 and RA; support for stateful DHCPv6 and DHCPv4 is optional,
   however if either service is offered, resolver addresses will be
   provided using that mechanism as well.

9.  Globally Unique Name

   Automatic configuration of a globally unique name for the homenet is
   out of scope for this document.  However, homenet servers MUST allow
   the user to configure a globally unique name in place of the default
   name, 'home.arpa.'  By default, even if configured with a global
   name, homenet routers MUST NOT answer queries from outside of the
   homenet for subdomains of that name.

10.  DNSSEC Validation

   DNSSEC Validation for the 'home.arpa' zone and for the locally-served
   'ip6.arpa and 'in-adr.arpa' domains is not possible without a trust
   anchor.  Establishment of a trust anchor for such validation is out
   of scope for this document.

   Homenets that have been configured with a globally unique domain MUST
   support DNSSEC signing of local names, and must provide a way to
   generate a KSK that can be used in the secure delegation of the
   globally unique domain assigned to the homenet.







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11.  Support for Multiple Provisioning Domains

   Homenets must support the Multiple Provisioning Domain Architecture
   [9].  Hosts connected to the homenet may or may not support multiple
   provisioning domains.  For hosts that do not support multiple
   provisioning domains, the homenet provides one or more resolvers that
   will answer queries for any provisioning domain.  Such hosts may
   receive answers to queries that either do not work as well if the
   host chooses a source address from a different provisioning domain,
   or does not work at all.  However, the default source address
   selection policy, longest-match [CITE], will result in the correct
   source address being chosen as long as the destination address has a
   close match to the prefix assigned by the ISP.

   Hosts that support multiple provisioning domains will be provisioned
   with one or more resolvers per provisioning domain.  Such hosts can
   use the IP address of the resolver to determine which provisioning
   domain is applicable for a particular answer.

   Each ISP has its own provisioning domain.  Because ISPs connections
   cannot be assumed to be persistent, the homenet has its own separate
   provisioning domain.

   Configuration from the IPv4 DHCP server are treated as being part of
   the homenet provisioning domain.  The case where a homenet advertises
   IPv4 addresses from one or more public prefixes is out of scope for
   this document.  Such a configuration is NOT RECOMMENDED for homenets.

   Configuration for IPv6 provisioning domains is done using the
   Multiple Provisioning Domain RA option [CITE].

12.  Using the Local Namespace While Away From Home

   This architecture does not provide a way for service discovery to be
   performed on the homenet by devices that are not directly connected
   to a link that is part of the homenet.

13.  Management Considerations

   This architecture is intended to be self-healing, and should not
   require management.  That said, a great deal of debugging and
   management can be done simply using the DNS Service Discovery
   protocol.








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14.  Privacy Considerations

   Privacy is somewhat protected in the sense that names published on
   the homenet are only visible to devices connected to the homenet.
   This may be insufficient privacy in some cases.

   The privacy of host information on the homenet is left to hosts.
   Various mechanisms are available to hosts to ensure that tracking
   does not occur if it is not desired.  However, devices that need to
   have special permission to manage the homenet will inevitably reveal
   something about themselves when doing so.  It may be possible to use
   something like HTTP token binding [15] to mitigate this risk.

15.  Security Considerations

   There are some clear issues with the security model described in this
   document, which will be documented in a future version of this
   section.  A full analysis of the avenues of attack for the security
   model presented here have not yet been done, and must be done before
   the document is published.

16.  IANA considerations

   No new actions are required by IANA for this document.

   Note however that this document is relying on the allocation of
   'home.arpa' described in Special Use Top Level Domain '.home.arpa'
   [16].  This document therefore can't proceed until that allocation is
   done.  [RFC EDITOR PLEASE REMOVE THIS PARAGRAPH PRIOR TO
   PUBLICATION].

17.  Normative References

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

   [2]        Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [3]        Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              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>.






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

   [5]        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>.

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

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

   [8]        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>.

   [9]        Anipko, D., Ed., "Multiple Provisioning Domain
              Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
              <https://www.rfc-editor.org/info/rfc7556>.

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

   [11]       Cheshire, S., "Discovery Proxy for Multicast DNS-Based
              Service Discovery", draft-ietf-dnssd-hybrid-07 (work in
              progress), September 2017.

   [12]       Cheshire, S. and T. Lemon, "Multicast DNS Discovery
              Relay", draft-sctl-dnssd-mdns-relay-02 (work in progress),
              November 2017.

   [13]       Cheshire, S. and T. Lemon, "Service Registration Protocol
              for DNS-Based Service Discovery", draft-sctl-service-
              registration-00 (work in progress), July 2017.

   [14]       Korhonen, J., Krishnan, S., and S. Gundavelli, "Support
              for multiple provisioning domains in IPv6 Neighbor
              Discovery Protocol", draft-ietf-mif-mpvd-ndp-support-03
              (work in progress), February 2016.




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   [15]       Popov, A., Nystrom, M., Balfanz, D., Langley, A., Harper,
              N., and J. Hodges, "Token Binding over HTTP", draft-ietf-
              tokbind-https-12 (work in progress), January 2018.

   [16]       Pfister, P. and T. Lemon, "Special Use Domain
              'home.arpa.'", draft-ietf-homenet-dot-14 (work in
              progress), September 2017.

   [17]       Cheshire, S. and T. Lemon, "Service Discovery Broker",
              draft-sctl-discovery-broker-00 (work in progress), July
              2017.

Appendix A.  Existing solutions

   Previous attempts to automate naming and service discovery in the
   context of a home network are able to function with varying degrees
   of success depending on the topology of the home network.
   Unfortunately, these solutions do not fully address the requirements
   of homenets.

   For example, Multicast DNS [6] can provide naming and service
   discovery [7], but only within a single multicast domain.

   The Domain Name System provides a hierarchical namespace [1], a
   mechanism for querying name servers to resolve names [2], a mechanism
   for updating namespaces by adding and removing names [5], and a
   mechanism for discovering services [7].  Unfortunately, DNS provides
   no mechanism for automatically provisioning new namespaces, and
   secure updates to namespaces require that the host submitting the
   update have a public or symmetric key that is known to the network
   and authorized for updates.  In an unmanaged network, the publication
   of and authorization of these keys is an unsolved problem.

   Some managed networks get around this problem by having the DHCP
   server do DNS updates.  However, this doesn't really work, because
   DHCP doesn't provide a mechanism for updating service discovery
   records: it only supports publishing A and AAAA records.

   This partially solves the trust problem: DHCP can validate that a
   device is at least connected to a network link that is actually part
   of the managed network.  This prevents an off-network attacker from
   registering a name, but provides no mechanism for actually validating
   the identity of the host registering the name.  For example, it would
   be easy for an attacker on the network to steal a registered name.

   Hybrid Multicast DNS [11] proposes a mechanism for extending
   multicast DNS beyond a single multicast domain.  However, in order to
   use this as a solution, some shortcomings need to be considered.



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   Most obviously, it requires that every multicast domain have a
   separate name.  This then requires that the homenet generate names
   for every multicast domain.  These names would then be revealed to
   the end user.  But since they would be generated automatically and
   arbitrarily, they would likely cause confusion rather than clarity,
   and in degenerate cases requires that the end user have a mental
   model of the topology of the network in order to guess on which link
   a given service may appear.

   At present, the approach we intend to take with respect to
   disambiguation is that this will not be solved at a protocol level
   for devices that do not implement the registration protocol.

Authors' Addresses

   Ted Lemon
   Nibbhaya Consulting
   P.O. Box 958
   Brattleboro, Vermont  05301
   United States of America

   Email: mellon@fugue.com


   Daniel Migault
   Ericsson
   8400 boulevard Decarie
   Montreal, QC H4P 2N2
   Canada

   Email: daniel.migault@ericsson.com


   Stuart Cheshire
   Apple Inc.
   1 Infinite Loop
   Cupertino, California  95014
   USA

   Phone: +1 408 974 3207
   Email: cheshire@apple.com










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