One document matched: draft-ietf-dnssd-mdns-dns-interop-01.xml
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<rfc
category="info"
ipr="trust200902"
docName="draft-ietf-dnssd-mdns-dns-interop-01"
>
<front>
<title abbrev="mDNS and DNS Interop">On Interoperation of Labels Between mDNS and DNS</title>
<!-- add 'role="editor"' below for the editors if appropriate -->
<author
fullname="Andrew Sullivan"
initials="A. J."
surname="Sullivan">
<!-- abbrev not needed but can be used for the header
if the full organization name is too long -->
<organization abbrev="Dyn">Dyn</organization>
<address>
<postal>
<street>150 Dow St.</street>
<city>Manchester</city>
<region>NH</region>
<code>03101</code>
<country>U.S.A.</country>
</postal>
<email>asullivan@dyn.com</email>
</address>
</author>
<date /> <!-- month="May" is no longer necessary
note also, day="30" is optional -->
<!-- <area>Internet</area> -->
<!-- WG name at the upperleft corner of the doc,
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<workgroup>DNSSD</workgroup>
<abstract>
<t>Despite its name, DNS-Based Service Discovery can use naming
systems other than the Domain Name System when looking for
services. Moreover, when it uses the DNS, DNS-Based Service
Discovery uses the full capability of DNS, rather than using a
subset of available octets. 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 selection of labels for conventional DNS and other resolution
systems when they are expected to interoperate in this manner.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>DNS-Based Service Discovery (DNS-SD, <xref target="RFC6763" />)
specifies a mechanism for discovering services using queries to
the Domain Name System (DNS, <xref target="RFC1034" />, <xref
target="RFC1035" />); and to any other system that uses domain
names, such as Multicast DNS (mDNS, <xref target="RFC6762" />).
Conventional use of the DNS generally follows the host name rules
<xref target="RFC0952" /> for labels -- the so-called LDH rule.
That convention is the reason behind the development of
Internationalized Domain Names for Applications (IDNA2008, <xref
target="RFC5890" />, <xref target="RFC5891" />, <xref
target="RFC5892" />, <xref target="RFC5893" />, <xref
target="RFC5894" />, <xref target="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 <xref target="RFC2181" />,
section 11. Nevertheless, there is a widespread belief that in
many circumstances domain names cannot be used in the DNS unless
they cleave to the LDH rule.</t>
<t>At the same time, mDNS requires that labels be encoded in UTF-8,
and permits a range of characters in labels that are not permitted
by IDNA2008 or the LDH rule. For example, mDNS encourages the use of
spaces and punctuation in mDNS names (see <xref target="RFC6763" />,
section 4.1.3). It does not restrict which Unicode code points may
be used in those labels, so long as the code points are UTF-8 in
Net-Unicode <xref target="RFC5198" /> format.</t>
<t>Users of applications are, of course, frequently unconcerned
with (not to say oblivious to) the name-resolution system(s) in
service at any given moment, and are inclined simply to use the
same domain names in different contexts. As a result, the same
domain name might be tried using different name resolution
technologies. If DNS-SD is to be used in an environment where
multiple resolution systems (such as mDNS and DNS) are to be
queried for services, then some parts of the domain names to be
queried will need to be compatible with the rules and conventions
for all the relevant technologies.</t>
<t>One approach to interoperability under these circumstances is
to use a single operational convention (a "profile") for domain
names under the different naming systems. This memo assumes such
a use profile, and attempts to outline what is necessary to make
it work without specifying any particular technology. It does
assume, however, that the global DNS is eventually likely to be
implicated. Given the general tendency of all resolution
eventually to fall through to the DNS, that assumption does not
seem controversial.</t>
<t>It is worth noting that users of DNS-SD do not use the service
discovery names in the same way that users of other domain names
might. Domain names often might as easily be entered as direct
user input as by any other method. But the service discovery
context generally assumes users are picking a service from a list.
As a result, the sorts of application considerations that are
appropriate to the general-purpose DNS name, and that resulted in
the A-label/U-label split (see below) in IDNA2008, are not
entirely the right approach for DNS-SD.</t>
<section title="Conventions and terms used in this document">
<t>Wherever appropriate, this memo uses the terminology defined
in Section 2 of <xref target="RFC5890" />. In particular, the
reader is assumed to be familiar with the terms "U-label", "LDH
label", and "A-label" from that document. Similarly, the reader
is assumed to be familiar with the U+NNNN notation for Unicode
code points used in <xref target="RFC5890" /> and other documents
dealing with Unicode code points. In the interests of brevity
and consistency, the definitions are not repeated here.</t>
<t>Sometimes this memo refers to names in the DNS as though the
LDH rule and IDNA2008 are strict requirements. They are not.
DNS labels are, in principle, just collections of octets, and
therefore in principle the LDH rule is not a constraint. In
practice, applications sometimes intercept labels that do not
conform to the LDH rule and apply IDNA and other
transformations.</t>
<t>The DNS, perhaps unfortunately, has produced its own jargon.
Unfamiliar DNS-related terms in this memo should be found in
<xref target="I-D.ietf-dnsop-dns-terminology" />.</t>
<t>The term "owner name" (common to the DNS vernacular; see
above) is used here to apply not just to the domain names to be
looked up in the DNS, but to any name that might be looked up
either in the DNS or using other technologies. It therefore
includes names that might not actually exist anywhere. In
addition, what follows depends on the idea that not every domain
name may be looked up in the DNS. For instance, names ending in
"local." (in the presentation format) are not ordinarily looked
up in the DNS, but instead by querying mDNS.</t>
<t>DNS-SD specifies three portions of the owner name for a
DNS-SD resource record. These are the <Instance> portion,
the <Service> portion, and the <Domain>. The owner
name made of these three parts is called the Service Instance
Name. It is worth observing that a portion may be more than one
label long. See <xref target="RFC6763" />, section 4.1.
Further discussion of the parts is found in <xref
target="sec-dnssd-portions" />.</t>
<t>Throughout this memo, mDNS is used liberally as the
alternative resolution mechanism to DNS. This is for
convenience rather than rigour: any alternative name resolution
to DNS could present the same friction with the prevailing
operational conventions of the global DNS. It so happens that
mDNS is the overwhelmingly successful alternative as of this
writing, so it is used in order to make the issues plainer to
the reader. Other alternative resolution mechanisms may in
general be read wherever mDNS appears in the text, except where
details of the mDNS specification appear.</t>
</section>
</section>
<section title="Why there could be a problem at all"
anchor="sec-problem-at-all">
<t>One might reasonably wonder why there is a problem to be solved
at all. After all, DNS labels permit any octet whatsoever, and
anything that can be useful with DNS-SD cannot use any names that
are outside the protocol strictures of the DNS.</t>
<t>The reason for the trouble is twofold. First, and least
troublesome, is the possibility of resolvers that are attempting
to offer IDNA service system-wide. Given the design of IDNA2008,
it is reasonable to suppose that on some systems high-level name
resolution libraries will perform the U-label/A-label
transformation automatically, saving applications from these
details. If this were the main problem, however, it would
presumably be self-correcting; for the right answer would be,
"Don't use those libraries for DNS-SD," and DNS-SD would not work
reliably in cases where such libraries were in use. This would be
unfortunate; but given that DNS-SD in Internet contexts is as of
this writing not in ubiquitous use, it should not represent a
fatal issue.</t>
<t>The greater problem is that the "infrastructure" types of DNS
service -- the root zone, the top-level domains, and so on -- have
embraced IDNA and refuse registration of raw UTF-8 into their
zones. As of this writing there is (perhaps unfortunately) no
reliable way to discover where these sorts of DNS services end.
Nevertheless, some client programs (notably web browsers) have
adopted a number of different policies about how domain names will
be looked up and presented to users given the policies of the
relevant DNS zone operators. None of these policies permit raw
UTF-8. Since it is anticipated that DNS-SD when used with the DNS
will be inside domain names beneath those kinds of
"infrastructure" domains, the implications of IDNA2008 must be a
consideration.</t>
<t>For further exploration of issues relating to encoding of
domain names generally, the reader should consult <xref
target="RFC6055" />.</t>
</section>
<section title="Requirements for a profile for label interoperation"
anchor="sec-label-interop">
<t>Any interoperability between DNS (including prevailing
operational conventions and other resolution technologies will
require interoperability across the portions of a DNS-SD Service
Instance Name that are implicated in regular DNS lookups. Only
some portions are implicated. In any case, if a given portion is
implicated, the profile will need to apply to all labels in that
portion.</t>
<t>In addition, because DNS-SD Service Instance Names can be used
in a domain name slot, care must be taken by DNS-SD-aware
resolvers to handle the different portions as outlined here, so
that DNS-SD portions that do not use IDNA2008 will not be treated
as U-labels and will not accidentally undergo IDNA processing.</t>
<t>Because the profile will need to apply to names that might need
to interoperate with names in the public DNS, and because other
resolution mechanisms (such as mDNS) could permit labels that IDNA
does not, the profile might reduce the labels that could be used
with those other resolution mechanisms. One consequence of this
is that some recommendations from <xref target="RFC6763" /> will
not really be possible to implement using names subject to the
profile. In particular, <xref target="RFC6763" />, section 4.1.3
recommends that labels always be stored and communicated as UTF-8,
even in the DNS. Because of the way the public DNS is currently
operated (see <xref target="sec-problem-at-all" />), the advice to
store and transmit labels as UTF-8 in the DNS is likely either to
encounter problems or result in unnecessary traffic to the public
DNS (or both). In particular, the <Domain> part of a
Service Instance Name is unlikely to be found in its UTF-8 form in
the public DNS tree for zones that are using IDNA2008. By
contrast, for example, mDNS normally uses UTF-8.</t>
<t>U-labels cannot contain upper case letters. That restriction
extends to ASCII-range upper case letters that work fine in
LDH-labels. It may be confusing that the character "A" works in
the DNS when none of the characters in the label has a diacritic,
but does not work when there is such a diacritic in the label.
Labels in mDNS names (or other resolution technologies) may
contain upper case characters, so the profile will need either to
restrict the use of upper case or come up with a reliable and
predictable (to users) convention for case folding even in the
presence of diacritics.</t>
</section>
<section title="DNS-SD portions" anchor="sec-dnssd-portions">
<t>Service Instance Names are made up of three portions.</t>
<section title="The <Instance> Portion of the Service
Instance Name" anchor="sec-prof-instance">
<t><xref target="RFC6763" /> is clear that the <Instance>
portion of the Service Instance Name is intended for
presentation to users, and therefore virtually any character is
permitted in it. There are two ways that a profile might address
this portion.</t>
<t>The first way would be to treat this portion as likely to be
intercepted by system-wide IDNA-aware resolvers, or likely
subject to strict IDNA conformance requirements for publication
in the relevant zone. In this case, the portion would need to
be made subject to the profile, thereby curtailing what
characters may appear in this portion. This approach permits
DNS-SD to use any standard system resolver but presents
inconsistencies with the DNS-SD specification and with DNS-SD
that is exclusively mDNS-based. Therefore, this strategy is
rejected.</t>
<t>Instead, DNS-SD implementations can intercept the
<Instance> portion of a Service Instance Name and ensure
that those labels are never handed to IDNA-aware resolvers that
might attempt to convert these labels into A-labels. Under this
approach, the DNS-SD <Instance> portion works as it always
does, but at the cost of using special resolution code built into
the DNS-SD system. A practical consequence of this is that zone
operators need to be prepared not to apply the LDH rule to all
labels, and may need to make special concessions to ensure that
the <Instance> portion can contain spaces, upper and
lower case, and any UTF-8 code point; or else to prepare a user
interface to handle the exceptions that would otherwise be
generated. Automatic conversion to A-labels is not acceptable.</t>
</section>
<section title="The <Service> Portion of the Service
Instance Name" anchor="sec-prof-service">
<t>DNS-SD includes a <Service> component in the Service
Instance Name. This component is not really user-facing data, but
is instead control data embedded in the Service Instance Name.
This component includes so-called "underscore labels", which are
labels prepended with U+005F (_). The underscore label convention
was established by DNS SRV (<xref target="RFC2782" />) for
identifying metadata inside DNS names. A system-wide resolver (or
DNS middlebox) that cannot handle underscore labels will not work
with DNS-SD at all, so it is safe to suppose that such resolvers
will not attempt to do special processing on these
labels. Therefore, the <Service> portion of the Service
Instance Name will not be subject to the profile. By the same
token, it should be noted that underscore labels are never
subject to IDNA processing (they're formally incompatible), and
therefore concerns about IDNA are irrelevant for these labels.</t>
</section>
<section title="The <Domain> Portion of the
Service Instance Name" anchor="sec-prof-domain">
<t>The <Domain> portion of the Service Instance Name forms
an integral part of the owner name submitted for DNS resolution.
A system-wide resolver that is IDNA2008-aware is likely to
interpret labels with UTF-8 in the owner name as candidates for
IDNA2008 processing. More important, operators of
internationalized domain names will frequently publish such names
in the DNS as A-labels; certainly, the top-most labels will always
be A-labels. Therefore, these labels will need to be subject to
the profile. DNS-SD implementations ought to identify the
<Domain> portion of the Service Instance Name and treat it
subject to IDNA2008 in case the domain is to be queried from the
global DNS. In the event that the <Domain> portion of the
Service Instance Name fails to resolve, it is acceptable to
substitute labels with plain UTF-8, starting at the lowest label
in the DNS tree and working toward the root. This approach
differs from the rule for resolution published in <xref
target="RFC6763" />, because it privileges IDNA2008-compatible
labels over UTF-8 labels.
</t>
<t>One might argue against this restriction on either of two
grounds:
<list style="numbers">
<t>It is possible the names may be in the DNS in UTF-8, and RFC
6763 already specifies a fallback strategy of progressively
attempting first the UTF-8 label lookup (it might not be a
U-label) and then if possible the A-label lookup.</t>
<t>Zone administrators that wish to support DNS-SD can publish a
UTF-8 version of the zone along side the A-label version of the
zone.</t>
</list>
The first of these is rejected because it represents a potentially
significant increase in DNS lookup traffic for no value. It is
possible for a DNS-SD application to identify the <Domain>
portion of the Service Instance Name. The standard way to publish
IDNs on the Internet uses IDNA. Therefore, additional lookups
should not be encouraged. When <xref target="RFC6763" /> was
published, the bulk of IDNs were lower in the tree. Now that
there are internationalized labels in the root zone, it is
desirable to minimize queries to the Internet infrastructure if
they are sure to be answered in the negative.</t>
<t>The second reason depends on the idea that it is possible to
maintain two names in sync with one another. This is not strictly
speaking true, although in this case the domain operator could
simply create a DNAME record <xref target="RFC6672" /> from the
UTF-8 name to the IDNA2008 zone. This still, however, relies on
being able to reach the (UTF-8) name in question, and it is
unlikely that the UTF-8 version of the zone will be delegated from
anywhere. Moreover, in many organizations the support for DNS-SD
and the support for domain name delegations are not performed by
the same department, and depending on a co-ordination between the
two will make the system more fragile, or slower, or both.</t>
</section>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>The author gratefully acknowledges the insights of Stuart
Cheshire, Kerry Lynn, and Dave Thaler. Kerry Lynn deserves special
gratitude for his energy and persistence in pressing unanswered
questions.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This memo makes no requests of IANA.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>This memo presents some requirements for future development, but
does not specify anything. Therefore, it has no implications for security.</t>
</section>
</middle>
<back>
<!--references split to informative and normative-->
<!--
<references title="Normative References"> -->
<!-- BEGIN INCLUDED references file draft-sullivan-dnssd-mdns-dns-interop-01.xml-normative -->
<!-- END INCLUDED references file draft-sullivan-dnssd-mdns-dns-interop-01.xml-normative -->
<!--</references>
-->
<references title="Informative References">
<!-- BEGIN INCLUDED references file draft-sullivan-dnssd-mdns-dns-interop-01.xml-informative -->
<reference anchor='RFC0952'>
<front>
<title>DoD Internet host table specification</title>
<author initials='K.' surname='Harrenstien' fullname='K. Harrenstien'>
<organization>SRI International</organization></author>
<author initials='M.' surname='Stahl' fullname='M. Stahl'>
<organization>SRI International</organization></author>
<author initials='E.' surname='Feinler' fullname='E. Feinler'>
<organization>SRI International</organization></author>
<date year='1985' day='1' month='October' /></front>
<seriesInfo name='RFC' value='952' />
<format type='TXT' octets='12388' target='http://www.rfc-editor.org/rfc/rfc952.txt' />
</reference>
<reference anchor='RFC1034'>
<front>
<title abbrev='Domain Concepts and Facilities'>Domain names - concepts and facilities</title>
<author initials='P.' surname='Mockapetris' fullname='P. Mockapetris'>
<organization>Information Sciences Institute (ISI)</organization></author>
<date year='1987' day='1' month='November' /></front>
<seriesInfo name='STD' value='13' />
<seriesInfo name='RFC' value='1034' />
<format type='TXT' octets='129180' target='http://www.rfc-editor.org/rfc/rfc1034.txt' />
</reference>
<reference anchor='RFC1035'>
<front>
<title abbrev='Domain Implementation and Specification'>Domain names - implementation and specification</title>
<author initials='P.' surname='Mockapetris' fullname='P. Mockapetris'>
<organization>USC/ISI</organization>
<address>
<postal>
<street>4676 Admiralty Way</street>
<city>Marina del Rey</city>
<region>CA</region>
<code>90291</code>
<country>US</country></postal>
<phone>+1 213 822 1511</phone></address></author>
<date year='1987' day='1' month='November' /></front>
<seriesInfo name='STD' value='13' />
<seriesInfo name='RFC' value='1035' />
<format type='TXT' octets='125626' target='http://www.rfc-editor.org/rfc/rfc1035.txt' />
</reference>
<reference anchor='RFC2181'>
<front>
<title abbrev='DNS Clarifications'>Clarifications to the DNS Specification</title>
<author initials='R.' surname='Elz' fullname='Robert Elz'>
<organization>Computer Science</organization>
<address>
<postal>
<street>Parkville</street>
<street>Victoria</street>
<street>3052</street>
<street>Australia.</street></postal>
<email>kre@munnari.OZ.AU</email>
<uri>e</uri></address></author>
<author initials='R.' surname='Bush' fullname='Randy Bush'>
<organization>RGnet, Inc.</organization>
<address>
<postal>
<street>5147 Crystal Springs Drive</street>
<street>Bainbridge Island</street>
<street>Washington</street>
<street>98110</street>
<street>United States.</street>
<country>NE</country></postal>
<email>randy@psg.com</email></address></author>
<date year='1997' month='July' />
<area>Applications</area>
<keyword>DNS</keyword>
<keyword>domain name system</keyword></front>
<seriesInfo name='RFC' value='2181' />
<format type='TXT' octets='36989' target='http://www.rfc-editor.org/rfc/rfc2181.txt' />
<format type='XML' octets='38931' target='http://xml.resource.org/public/rfc/xml/rfc2181.xml' />
</reference>
<reference anchor='RFC2782'>
<front>
<title abbrev='DNS SRV RR'>A DNS RR for specifying the location of services (DNS SRV)</title>
<author initials='A.' surname='Gulbrandsen' fullname='Arnt Gulbrandsen'>
<organization>Troll Tech</organization>
<address>
<postal>
<street>Waldemar Thranes gate 98B</street>
<city>Oslo</city>
<region />
<code>N-0175</code>
<country>NO</country></postal>
<phone>+47 22 806390</phone>
<facsimile>+47 22 806380</facsimile>
<email>arnt@troll.no</email></address></author>
<author initials='P.' surname='Vixie' fullname='Paul Vixie'>
<organization>Internet Software Consortium</organization>
<address>
<postal>
<street>950 Charter Street</street>
<city>Redwood City</city>
<region>CA</region>
<code>94063</code>
<country>US</country></postal>
<phone>+1 650 779 7001</phone></address></author>
<author initials='L.' surname='Esibov' fullname='Levon Esibov'>
<organization>Microsoft Corporation</organization>
<address>
<postal>
<street>One Microsoft Way</street>
<city>Redmond</city>
<region>WA</region>
<code>98052</code>
<country>US</country></postal>
<email>levone@microsoft.com</email></address></author>
<date year='2000' month='February' />
<abstract>
<t>This document describes a DNS RR which specifies the location of the
server(s) for a specific protocol and domain.</t></abstract></front>
<seriesInfo name='RFC' value='2782' />
<format type='TXT' octets='24013' target='http://www.rfc-editor.org/rfc/rfc2782.txt' />
</reference>
<reference anchor='RFC5198'>
<front>
<title>Unicode Format for Network Interchange</title>
<author initials='J.' surname='Klensin' fullname='J. Klensin'>
<organization /></author>
<author initials='M.' surname='Padlipsky' fullname='M. Padlipsky'>
<organization /></author>
<date year='2008' month='March' />
<abstract>
<t>The Internet today is in need of a standardized form for the transmission of internationalized "text" information, paralleling the specifications for the use of ASCII that date from the early days of the ARPANET. This document specifies that format, using UTF-8 with normalization and specific line-ending sequences. [STANDARDS-TRACK]</t></abstract></front>
<seriesInfo name='RFC' value='5198' />
<format type='TXT' octets='45708' target='http://www.rfc-editor.org/rfc/rfc5198.txt' />
</reference>
<reference anchor='RFC5890'>
<front>
<title>Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework</title>
<author initials='J.' surname='Klensin' fullname='J. Klensin'>
<organization /></author>
<date year='2010' month='August' />
<abstract>
<t>This document is one of a collection that, together, describe the protocol and usage context for a revision of Internationalized Domain Names for Applications (IDNA), superseding the earlier version. It describes the document collection and provides definitions and other material that are common to the set. [STANDARDS-TRACK]</t></abstract></front>
<seriesInfo name='RFC' value='5890' />
<format type='TXT' octets='54245' target='http://www.rfc-editor.org/rfc/rfc5890.txt' />
</reference>
<reference anchor='RFC5891'>
<front>
<title>Internationalized Domain Names in Applications (IDNA): Protocol</title>
<author initials='J.' surname='Klensin' fullname='J. Klensin'>
<organization /></author>
<date year='2010' month='August' />
<abstract>
<t>This document is the revised protocol definition for Internationalized Domain Names (IDNs). The rationale for changes, the relationship to the older specification, and important terminology are provided in other documents. This document specifies the protocol mechanism, called Internationalized Domain Names in Applications (IDNA), for registering and looking up IDNs in a way that does not require changes to the DNS itself. IDNA is only meant for processing domain names, not free text. [STANDARDS-TRACK]</t></abstract></front>
<seriesInfo name='RFC' value='5891' />
<format type='TXT' octets='38105' target='http://www.rfc-editor.org/rfc/rfc5891.txt' />
</reference>
<reference anchor='RFC5892'>
<front>
<title>The Unicode Code Points and Internationalized Domain Names for Applications (IDNA)</title>
<author initials='P.' surname='Faltstrom' fullname='P. Faltstrom'>
<organization /></author>
<date year='2010' month='August' />
<abstract>
<t>This document specifies rules for deciding whether a code point, considered in isolation or in context, is a candidate for inclusion in an Internationalized Domain Name (IDN).</t><t> It is part of the specification of Internationalizing Domain Names in Applications 2008 (IDNA2008). [STANDARDS-TRACK]</t></abstract></front>
<seriesInfo name='RFC' value='5892' />
<format type='TXT' octets='187370' target='http://www.rfc-editor.org/rfc/rfc5892.txt' />
</reference>
<reference anchor='RFC5893'>
<front>
<title>Right-to-Left Scripts for Internationalized Domain Names for Applications (IDNA)</title>
<author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
<organization /></author>
<author initials='C.' surname='Karp' fullname='C. Karp'>
<organization /></author>
<date year='2010' month='August' />
<abstract>
<t>The use of right-to-left scripts in Internationalized Domain Names (IDNs) has presented several challenges. This memo provides a new Bidi rule for Internationalized Domain Names for Applications (IDNA) labels, based on the encountered problems with some scripts and some shortcomings in the 2003 IDNA Bidi criterion. [STANDARDS-TRACK]</t></abstract></front>
<seriesInfo name='RFC' value='5893' />
<format type='TXT' octets='38870' target='http://www.rfc-editor.org/rfc/rfc5893.txt' />
</reference>
<reference anchor='RFC5894'>
<front>
<title>Internationalized Domain Names for Applications (IDNA): Background, Explanation, and Rationale</title>
<author initials='J.' surname='Klensin' fullname='J. Klensin'>
<organization /></author>
<date year='2010' month='August' />
<abstract>
<t>Several years have passed since the original protocol for Internationalized Domain Names (IDNs) was completed and deployed. During that time, a number of issues have arisen, including the need to update the system to deal with newer versions of Unicode. Some of these issues require tuning of the existing protocols and the tables on which they depend. This document provides an overview of a revised system and provides explanatory material for its components. This document is not an Internet Standards Track specification; it is published for informational purposes.</t></abstract></front>
<seriesInfo name='RFC' value='5894' />
<format type='TXT' octets='115174' target='http://www.rfc-editor.org/rfc/rfc5894.txt' />
</reference>
<reference anchor='RFC5895'>
<front>
<title>Mapping Characters for Internationalized Domain Names in Applications (IDNA) 2008</title>
<author initials='P.' surname='Resnick' fullname='P. Resnick'>
<organization /></author>
<author initials='P.' surname='Hoffman' fullname='P. Hoffman'>
<organization /></author>
<date year='2010' month='September' />
<abstract>
<t>In the original version of the Internationalized Domain Names in Applications (IDNA) protocol, any Unicode code points taken from user input were mapped into a set of Unicode code points that "made sense", and then encoded and passed to the domain name system (DNS). The IDNA2008 protocol (described in RFCs 5890, 5891, 5892, and 5893) presumes that the input to the protocol comes from a set of "permitted" code points, which it then encodes and passes to the DNS, but does not specify what to do with the result of user input. This document describes the actions that can be taken by an implementation between receiving user input and passing permitted code points to the new IDNA protocol. This document is not an Internet Standards Track specification; it is published for informational purposes.</t></abstract></front>
<seriesInfo name='RFC' value='5895' />
<format type='TXT' octets='16556' target='http://www.rfc-editor.org/rfc/rfc5895.txt' />
</reference>
<reference anchor='RFC6055'>
<front>
<title>IAB Thoughts on Encodings for Internationalized Domain Names</title>
<author initials='D.' surname='Thaler' fullname='D. Thaler'>
<organization /></author>
<author initials='J.' surname='Klensin' fullname='J. Klensin'>
<organization /></author>
<author initials='S.' surname='Cheshire' fullname='S. Cheshire'>
<organization /></author>
<date year='2011' month='February' />
<abstract>
<t>This document explores issues with Internationalized Domain Names (IDNs) that result from the use of various encoding schemes such as UTF-8 and the ASCII-Compatible Encoding produced by the Punycode algorithm. It focuses on the importance of agreeing on a single encoding and how complicated the state of affairs ends up being as a result of using different encodings today.</t></abstract></front>
<seriesInfo name='RFC' value='6055' />
<format type='TXT' octets='58799' target='http://www.rfc-editor.org/rfc/rfc6055.txt' />
</reference>
<reference anchor='RFC6672'>
<front>
<title>DNAME Redirection in the DNS</title>
<author initials='S.' surname='Rose' fullname='S. Rose'>
<organization /></author>
<author initials='W.' surname='Wijngaards' fullname='W. Wijngaards'>
<organization /></author>
<date year='2012' month='June' />
<abstract>
<t>The DNAME record provides redirection for a subtree of the domain name tree in the DNS. That is, all names that end with a particular suffix are redirected to another part of the DNS. This document obsoletes the original specification in RFC 2672 as well as updates the document on representing IPv6 addresses in DNS (RFC 3363). [STANDARDS-TRACK]</t></abstract></front>
<seriesInfo name='RFC' value='6672' />
<format type='TXT' octets='45704' target='http://www.rfc-editor.org/rfc/rfc6672.txt' />
</reference>
<reference anchor='RFC6762'>
<front>
<title>Multicast DNS</title>
<author initials='S.' surname='Cheshire' fullname='S. Cheshire'>
<organization /></author>
<author initials='M.' surname='Krochmal' fullname='M. Krochmal'>
<organization /></author>
<date year='2013' month='February' />
<abstract>
<t>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.</t><t> 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.</t><t> 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.</t></abstract></front>
<seriesInfo name='RFC' value='6762' />
<format type='TXT' octets='184992' target='http://www.rfc-editor.org/rfc/rfc6762.txt' />
</reference>
<reference anchor='RFC6763'>
<front>
<title>DNS-Based Service Discovery</title>
<author initials='S.' surname='Cheshire' fullname='S. Cheshire'>
<organization /></author>
<author initials='M.' surname='Krochmal' fullname='M. Krochmal'>
<organization /></author>
<date year='2013' month='February' />
<abstract>
<t>This document specifies how DNS resource records are named and structured to facilitate service discovery. Given a type of service that a client is looking for, and a domain in which the client is looking for that service, this mechanism allows clients to discover a list of named instances of that desired service, using standard DNS queries. This mechanism is referred to as DNS-based Service Discovery, or DNS-SD.</t></abstract></front>
<seriesInfo name='RFC' value='6763' />
<format type='TXT' octets='125192' target='http://www.rfc-editor.org/rfc/rfc6763.txt' />
</reference>
<reference anchor='I-D.ietf-dnsop-dns-terminology'>
<front>
<title>DNS Terminology</title>
<author initials='P' surname='Hoffman' fullname='Paul Hoffman'>
<organization />
</author>
<author initials='A' surname='Sullivan' fullname='Andrew Sullivan'>
<organization />
</author>
<author initials='K' surname='Fujiwara' fullname='Kazunori Fujiwara'>
<organization />
</author>
<date month='June' day='22' year='2015' />
<abstract><t>The DNS is defined in literally dozens of different RFCs. The terminology used in by implementers and developers of DNS protocols, and by operators of DNS systems, has sometimes changed in the decades since the DNS was first defined. This document gives current definitions for many of the terms used in the DNS in a single document.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-dnsop-dns-terminology-03' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-dnsop-dns-terminology-03.txt' />
</reference>
<!-- END INCLUDED references file draft-sullivan-dnssd-mdns-dns-interop-01.xml-informative -->
</references>
<section title="Change History" anchor="sec_change_hist">
<section title="draft-ietf-dnssd-mdns-dns-interop-01">
<t>Alter text to make clear that the main issue is the way the
public DNS is currently administered, not system resolvers. I
suppose this should have been clear before, but I didn't do that.
Many thanks to Kerry Lynn for penetrating questions that
illuminated what I'd left out.</t>
</section>
<section title="draft-ietf-dnssd-mdns-dns-interop-00">
<t>1st WG version</t>
<t>Add text to make clear that fallback from A-label lookup to
UTF-8 label lookup ok, per WG comments at IETF 91</t>
</section>
<section title="draft-sullivan-dnssd-mdns-dns-interop-01">
<t>
<list style="symbols">
<t>Decided which portions would be affected</t>
<t>Explained the difference in user interfaces between DNS-SD
and usual DNS operation</t>
<t>Provided background on why the Domain portion should be
treated differently</t>
</list>
</t>
</section>
<section title="draft-sullivan-dnssd-mdns-dns-interop-00">
<t>Initial version.</t>
</section>
</section>
</back>
</rfc>
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