Service Discovery Broker

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Last updated 2017-07-03
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Internet Engineering Task Force                              S. Cheshire
Internet-Draft                                                Apple Inc.
Intended status: Informational                                  T. Lemon
Expires: January 3, 2018                                   Nominum, Inc.
                                                            July 2, 2017

                        Service Discovery Broker


   DNS-Based Service Discovery allows clients to discover available
   services using unicast DNS queries.  In simple configurations these
   unicast DNS queries go directly to the appropriate authoritative
   server(s).  In large networks that have complicated topology, or
   many client devices, or both, it can be advantageous to have an
   intermediary between the clients and authoritative servers.  This
   intermediary, called a Discovery Broker, serves several purposes.
   A Discovery Broker can reduce load on both the servers and the
   clients, and gives the option of presenting clients with service
   discovery organized around logical, rather than physical, topology.

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1.  Introduction

   DNS-Based Service Discovery (DNS-SD) [RFC6763] is a component of Zero
   Configuration Networking [RFC6760] [ZC] [Roadmap].

   DNS-SD operates on a single network link (broadcast domain) using
   Multicast DNS [RFC6762].  DNS-SD can span multiple links using
   unicast DNS.

   In the DNS-SD specification [RFC6763] section 11, "Discovery of
   Browsing and Registration Domains (Domain Enumeration)", describes
   how client devices are automatically configured with the appropriate
   unicast DNS domains in which to perform their service discovery
   queries.  When used in conjunction with a Discovery Proxy [DisProx]
   this allows clients to discover services on remote links, even when
   the devices providing those services support only the basic Multicast
   DNS form of DNS-Based Service Discovery.  A Discovery Broker is a
   companion technology that operates in conjunction with existing
   authoritative DNS servers (such as a Discovery Proxy [DisProx]) and
   existing clients performing service discovery using unicast DNS

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2.  Problem Statement

   The following description of how a Discovery Broker works is
   illustrated using the example of a long rectangular office building.
   The building is large enough to have hundreds or even thousands of
   employees working there, the network is large enough that it would be
   impractical to operate it as a single link (a single broadcast
   domain, with a single IPv4 subnet or IPv6 network prefix).

   Suppose, for this example, that the network is divided into twelve
   separate links, connected by routers.  Each link has its own IPv6
   network prefix.  The division of the network into twelve sections of
   roughly equal size is somewhat arbitrary, and does not necessarily
   follow any physical boundaries in the building that are readily
   apparent to its inhabitants.  Two people in adjacent offices on the
   same corridor may have Ethernet ports connected to different links.
   Indeed, two devices in the same office, connected to the company
   network using secure Wi-Fi, may inadvertently associate with
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