Selecting Labels for Use with Conventional DNS and Other Resolution Systems in DNS-Based Service Discovery
RFC 8222
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.
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RFC 8222 DNS-SD Label Selection September 2017
Copyright Notice
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document authors. All rights reserved.
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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.
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