Multicast DNS
RFC 6762

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Internet Engineering Task Force (IETF)                       S. Cheshire
Request for Comments: 6762                                   M. Krochmal
Category: Standards Track                                     Apple Inc.
ISSN: 2070-1721                                            February 2013

                             Multicast DNS

Abstract

   As networked devices become smaller, more portable, and more
   ubiquitous, the ability to operate with less configured
   infrastructure is increasingly important.  In particular, the ability
   to look up DNS resource record data types (including, but not limited
   to, host names) in the absence of a conventional managed DNS server
   is useful.

   Multicast DNS (mDNS) provides the ability to perform DNS-like
   operations on the local link in the absence of any conventional
   Unicast DNS server.  In addition, Multicast DNS designates a portion
   of the DNS namespace to be free for local use, without the need to
   pay any annual fee, and without the need to set up delegations or
   otherwise configure a conventional DNS server to answer for those
   names.

   The primary benefits of Multicast DNS names are that (i) they require
   little or no administration or configuration to set them up, (ii)
   they work when no infrastructure is present, and (iii) they work
   during infrastructure failures.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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
   http://www.rfc-editor.org/info/rfc6762.

Cheshire & Krochmal          Standards Track                    [Page 1]
RFC 6762                      Multicast DNS                February 2013

Copyright Notice

   Copyright (c) 2013 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
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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Cheshire & Krochmal          Standards Track                    [Page 2]
RFC 6762                      Multicast DNS                February 2013

Table of Contents

   1. Introduction ....................................................4
   2. Conventions and Terminology Used in This Document ...............4
   3. Multicast DNS Names .............................................5
   4. Reverse Address Mapping .........................................7
   5. Querying ........................................................8
   6. Responding .....................................................13
   7. Traffic Reduction ..............................................22
   8. Probing and Announcing on Startup ..............................25
   9. Conflict Resolution ............................................31
   10. Resource Record TTL Values and Cache Coherency ................33
   11. Source Address Check ..........................................38
   12. Special Characteristics of Multicast DNS Domains ..............40
   13. Enabling and Disabling Multicast DNS ..........................41
   14. Considerations for Multiple Interfaces ........................42
   15. Considerations for Multiple Responders on the Same Machine ....43
   16. Multicast DNS Character Set ...................................45
   17. Multicast DNS Message Size ....................................46
   18. Multicast DNS Message Format ..................................47