DISCOVER: Supporting Multicast DNS Queries
RFC 6804

Document Type RFC - Historic (November 2012; No errata)
Author Bill Manning 
Last updated 2015-10-14
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Independent Submission                                        B. Manning
Request for Comments: 6804                                 November 2012
Category: Historic
ISSN: 2070-1721

               DISCOVER: Supporting Multicast DNS Queries


   This document describes the DISCOVER opcode, an experimental
   extension to the Domain Name System (DNS) to use multicast queries
   for resource discovery.  This opcode was tested in experiments run
   during 1995 and 1996 for the Topology Based Domain Search (TBDS)
   project.  This project is no longer active and there are no current
   plans to restart it.  TBDS was the first known use of multicast
   transport for DNS.  A client multicasts a DNS query using the
   DISCOVER opcode and processes the multiple responses that may result.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for the historical record.

   This document defines a Historic Document for the Internet community.
   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2012 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
   ( 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.

Manning                         Historic                        [Page 1]
RFC 6804                        DISCOVER                   November 2012

1.  Introduction

   The TBDS project developed extensions to existing network services to
   enable software for clients and servers of an application to become
   more resilient to changes in topology by dynamically sensing changes
   and switching between client/server and peer-peer methods for both
   end-system-to-server and server-to-server communications.

   The first existing network service to be investigated was the Domain
   Name Systems (DNS), which is used to map symbolic Internet names to
   numeric Internet addresses.  Based upon a hierarchical tree
   structure, the DNS relies upon uninterrupted connectivity of nodes to
   a special set of static, manually configured root servers.  To
   improve the robustness and availability of the DNS service, TBDS
   developed and defined enhancements that enable nodes to map names to
   numbers without the need for uninterrupted connectivity to the
   Internet root servers.  These techniques were automated, allowing
   transition between connected and unconnected operations to be done
   without direct human intervention.

   These enhancements to the DNS server code are based on the open
   source BIND to support reception and processing of multicast packets.

   Proof-of-concept modifications to BIND 8.1.2 were made to show that
   multicast awareness could be added to BIND.  An analysis was made of
   the existing DNS code deployment and the schedule of new feature
   deployment so that we could synchronize TBDS with a more appropriate
   code base.  Testing identified a race condition due to overloading
   the semantics of the DNS opcode that was used to communicate to

   This race condition was explored within the IETF regarding use of
   existing DNS opcodes.  Discussion within the team and with others in
   the IETF led to the idea that we needed a new opcode that would not
   overload the semantics of existing opcodes.  The original DNS design
   specification presumes that few clients exist that would share common
   DNS data.  To correct this problem, a new opcode was designed to
   disambiguate TBDS requests from normal nameserver requests.

   In the standard Domain Name System (DNS) [1] [2], queries are always
   unicast using the QUERY opcode.  The TBDS research project [5],
   funded under DARPA grant F30602-99-1-0523, explored the use of
   multicast DNS [1] [2] queries for resource discovery by autonomous,
   mobile nodes in disconnected networks.  The operations model is
   covered in the TBDS documentation.  Multicast queries may return
   multiple replies, while the standard DNS QUERY operation (see
   Sections 3.7, 4.3, and 5 of RFC 1034 [1]; and Section 4.1.1 of RFC
   1035 [2]) expects a single reply.  Instead of extending the QUERY

Manning                         Historic                        [Page 2]
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