Selecting Labels for Use with Conventional DNS and Other Resolution Systems in DNS-Based Service Discovery
RFC 8222

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Internet Engineering Task Force (IETF)                       A. Sullivan
Request for Comments: 8222                                        Oracle
Category: Informational                                   September 2017
ISSN: 2070-1721

           Selecting Labels for Use with Conventional DNS and
        Other Resolution Systems in DNS-Based Service Discovery

Abstract

   Despite its name, DNS-Based Service Discovery (DNS-SD) can use naming
   systems other than DNS when looking for services.  Moreover, when it
   uses DNS, DNS-SD uses the full capability of DNS, rather than using a
   subset of available octets.  This is of particular relevance where
   some environments use DNS labels that conform to Internationalized
   Domain Names for Applications (IDNA), and other environments use
   labels containing Unicode characters (such as containing octets
   corresponding to characters encoded as UTF-8).  In order for DNS-SD
   to be used effectively in environments where multiple different name
   systems and conventions for their operation are in use, it is
   important to attend to differences in the underlying technology and
   operational environment.  This memo presents an outline of the
   requirements for the selection of labels for conventional DNS and
   other resolution systems when they are expected to interoperate in
   this manner.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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 a candidate 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/rfc8222.

Sullivan                      Informational                     [Page 1]
RFC 8222                 DNS-SD Label Selection           September 2017

Copyright Notice

   Copyright (c) 2017 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 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
     1.1.  Conventions and Terms Used in This Document . . . . . . .   3
   2.  Why There Could Be a Problem at All . . . . . . . . . . . . .   4
   3.  Requirements for a Profile for Label Interoperation . . . . .   5
   4.  DNS-SD Portions . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  The <Instance> Portion of the Service Instance Name . . .   6
     4.2.  The <Service> Portion of the Service
           Instance Name . . . . . . . . . . . . . . . . . . . . . .   7
     4.3.  The <Domain> Portion of the Service Instance Name . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   9
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   DNS-Based Service Discovery (DNS-SD, [RFC6763]) specifies a mechanism
   for discovering services using queries to DNS ([RFC1034] and
   [RFC1035]) and to any other system that uses domain names, such as
   Multicast DNS (mDNS, [RFC6762]).  Many applications that use DNS
   follow "Internet hostname" syntax [RFC952] for labels -- the
   so-called LDH (letters, digits, and hyphen) rule.  That convention is
   the reason behind the development of Internationalized Domain Names
   for Applications (IDNA2008, [RFC5890], [RFC5891], [RFC5892],
   [RFC5893], [RFC5894], and [RFC5895]).  It is worth noting that the
   LDH rule is a convention, and not a rule of the DNS; this is made
   entirely plain by Section 11 of [RFC2181], and discussed further in
   Section 3 of [RFC6055].  Nevertheless, there is a widespread belief
   that in many circumstances domain names cannot be used in the DNS
   unless they follow the LDH rule.

Sullivan                      Informational                     [Page 2]
RFC 8222                 DNS-SD Label Selection           September 2017