wdiff rfc8324.alt-original rfc8324.txt

Network Working Group
1;95;0c.
Independent Submission J. Klensin

Intended status: Informational
Expires: June 24,
Request for Comments: 8324 February 2018
Category: Informational
ISSN: 2070-1721

DNS Privacy, Authorization, Special Uses, Encoding, Characters,
Matching, and Root Structure: Time for Another Look?
draft-klensin-dns-function-considerations-05

Abstract

The basic design of the Domain Name System was completed almost 30
years ago. The last half of that period has been characterized by
significant changes in requirements and expectations, some of which
either require changes to how the DNS is used or that can be accommodated
only poorly or not at all. This document asks the question of
whether it is time to either redesign and replace the DNS to match
contemporary requirements and expectations (rather than continuing to
try to design and implement incremental patches that are not fully
satisfactory) or to draw some clear lines about functionality that is
not really needed or that should be performed in some other way.

Status of This Memo

This Internet-Draft document is submitted in full conformance with not an Internet Standards Track specification; it is
published for informational purposes.

This is a contribution to the
provisions RFC Series, independently of BCP 78 any other
RFC stream. The RFC Editor has chosen to publish this document at
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see Section 2 of RFC 7841.

Information about the current Internet-
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This Internet-Draft will expire on June 24, 2018.
https://www.rfc-editor.org/info/rfc8324.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 4
2. Background and Hypothesis . . . . . . . . . . . . . . . . . . 4 5
3. Warts and Tensions With The with the Current DNS . . . . . . . . . . . 5 6
3.1. Multi-type Queries . . . . . . . . . . . . . . . . . . . 5 6
3.2. Matching Part I: Case Sensitivity in Labels and Other
Anomalies . . . . . . . . . . . . . . . . . . . . . . . . 6 7
3.3. Matching Part II: Non-ASCII ("internationalized") ("Internationalized") Domain
Name Labels . . . . . . . . . . . . . . . . . . . . . . . 6 7
3.4. Matching Part III: Label Synonyms, Equivalent Names, and
Variants . . . . . . . . . . . . . . . . . . . . . . . . 7 8
3.5. Query Privacy . . . . . . . . . . . . . . . . . . . . . . 9 10
3.6. Alternate Name Spaces Namespaces for Public Use in the DNS Framework:
The CLASS Problem . . . . . . . . . . . . . . 9 . . . . . . 10
3.7. Loose Synchronization . . . . . . . . . . . . . . . . . . 9 10
3.8. Private Name Spaces Namespaces and Special Names . . . . . . . . . . 10 11
3.9. Alternate Query or Response Encodings . . . . . . . . . . 11 12
3.10. Distribution and Management of Root Servers . . . . . . . 11 12
3.11. Identifiers Versus versus Brands and Other Convenience Names . . 12 13
3.12. A Single Hierarchy with a Centrally-controlled Centrally Controlled Root . . . 13 14
3.13. Newer Application Protocols, New Requirements, and DNS
Evolution . . . . . . . . . . . . . . . . . . . . . . . . 13 14
3.13.1. The Extensions . . . . . . . . . . . . . . . . . . . 14 15
3.13.2. Extensions and Deployment Pressures -- The TXT
RRTYPE . . . . . . . . . . . . . . . . . . . . . . . 14 15
3.13.3. Periods and Zone Cut Issues . . . . . . . . . . . . 15 16
3.14. Scaling of Reputation and Other Ancillary Information . . 16 17
3.15. Tensions among transport, scaling Transport, Scaling, and content Content . . . . . . 17 18
4. The Inverse Lookup Requirement . . . . . . . . . . . . . . . 18 19
5. Internet Scale, Function Support, and Incremental Deployment 19 20
6. Searching and the DNS - -- An Historical Note . . . . . . . . . 19
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9.
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
10.
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
10.1. 22
8.1. Normative References . . . . . . . . . . . . . . . . . . 21
10.2. 22
8.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 27
A.1. Changes from version -00 (2017-06-02) to -01 . . . . . . 28
A.2. Changes from version -01 (2017-06-06) to -02 22
Acknowledgements . . . . . . 28
A.3. Changes from version -02 (2017-06-19) to -03 . . . . . . 28
A.4. Changes from version -03 (2017-06-26) to -04 . . . . . . 28
A.5. Changes from version -04 (2017-10-05) to -05 . . . . . . 29
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 29

1. Introduction

This document explores contemporary expectations of the Internet's
domain system (DNS) and compares them to the assumptions and
properties of the DNS design, including both those documented in the
RFC Series, an important early paper by the principal author of the
original RFCs [Mockapetris-1988], and a certain amount of oral
tradition. It is primarily intended to ask the question of whether
the differences are causing enough stresses on the system, stresses
that cannot be resolved satisfactorily by further patching, that the
Internet community should be considering designing a new system, one
that is better adapted to current needs and expectations, and
developing a deployment and transition strategy for it. For those
(perhaps the majority of us) for whom actually replacing the DNS is
too radical to be realistic, the document may be useful in two other
ways. It may provide a foundation for discussing what functions the
DNS should not be expected to support and how those functions can be
supported in other ways, perhaps via an intermediate system that then
calls on the DNS or by using some other type of database technology
for some set of functions while leaving the basic DNS functions
intact. Or it may provide a basis for "better just get used to that
and the way it works" discussions to replace fantasies about what the
DNS might do in some alternate reality.

There is a key design or philosophical question associated with the
analysis in this document that the document does not address. It is
whether changes to perceived requirements to DNS functionality as
described here are, in most respects, evolutionary or whether many of
them are instances of trying to utilize the DNS for new requirements
because it exists and is already deployed independent of whether the
DNS is really appropriate or not. The latter might be an instance of
a problem often described in the IETF as "when all you have is a
hammer, everything looks like a nail".

Other recent work, including a short article by Vint Cerf [Cerf2017],
has discussed an overlapping set of considerations from a different
perspective, reinforcing the view that it may be time to ask
fundamental questions about the evolution and future of the DNS.

While this document does not assume deep technical or operational
knowledge of the DNS, it does assume some knowledge and at least
general familiarity with the concepts of RFC 1034 [RFC1034] and RFC
1035 [RFC1035] and the terminology discussed in RFC 7719 [RFC7719]
and elsewhere. Although some of the comments it contains might be
taken as hints or examples of different ways to think about the
design issues, it makes no attempt to explore, much less offer a
tutorial on, alternate naming systems or database technologies.

It is perhaps worth noting that, while the perspective is different
and more than a dozen years have passed, many of the issues discussed
in this document were analyzed and described (most of them with more
extensive explanations) in a 2005 US National Research Council report
[NRC-Signposts].

Readers should note that several references are to obsolete
documents. That was done because they are intended to show the
documents and dates that introduced particular features or concepts.
When current versions are intended, they are referenced.

2. Background and Hypothesis

The domain name system Domain Name System (DNS) [RFC1034] was designed starting in the
early 1980s [RFC0799] [RFC0881] [RFC0882] [RFC0883] with the main
goal of replacing the flat, centrally-administered, centrally administered, host table system
[RFC0810] [RFC0952] [RFC0953] with a hierarchical, administratively- administratively
distributed, system. The DNS design included some features that,
after initial implementation and deployment, were judged to be
unworkable and either replaced (e.g., the mail destination (MD) and
mail forwarder (MF) approach [RFC0882] that were replaced by the MX
approach [RFC0974]), abandoned (e.g., the mechanism for using email
local parts as labels described in RFC 1034 1034, Section 3.3), or
deprecated (e.g., the WKS RR TYPE [RFC1123]). Newer ideas and
requirements have identified a number of other features, some of
which were less developed than others. Of course the original
designers could not anticipate everything that has come to be
expected of the DNS in the last 30 years.

In recent years, demand for new and extended services and uses of the
DNS have, in turn, led to proposals for DNS extensions or changes of
various sorts. Some have been adopted, including a model for
negotiating extended functionality [RFC2671], [RFC2671] (commonly known as
EDNS(0)) and to support IPv6 [RFC3596], others were found to be
impracticable, and still others continue to be under consideration.
Some examples of the latter two categories are discussed below. A
few features of the original DNS specification, such as the CLASS
property and label types, have also been suggested to be so badly
specified that they should be deprecated [Sullivan-Class].

Unlike earlier changes such as the IDNA Internationalized Domain Names for
Applications (IDNA) mechanisms for better incorporating non-ASCII
labels without modifying the DNS structure itself [RFC3490]
[RFC5890], some recent proposals require or strongly suggest changes
to APIs, formats, or interfaces by programs that need to retrieve
information from the DNS or interpret that information. Differences
between the DNS architecture and the requirements that imply those
proposals suggest that it may be time to stop patching the DNS or
trying to extend it in small increments, but to consider small increments. Instead, we should be
considering moving some current or proposed functionality elsewhere
or development of developing a new system that better meets today's needs and a
transition strategy to it.

The next section of this document discusses a number of issues with
the current DNS design that could appropriately be addressed by a
different and newer design model. In at least some cases, changing
the model and protocols could bring significant benefits to the
Internet and/or its administration.

This document is not a proposal for a new protocol. It is intended
to stimulate thought about how far we want to try to push the
existing DNS, to examine whether expectations of it are already
exceeding its plausible capabilities, and to start discussion of a
redesign or alternatives to one if the time for that decision has
come.

3. Warts and Tensions With The with the Current DNS

As suggested above, there are many signs that the DNS is incapable of
meeting contemporary expectations of how it should work and
functionality it should support. Some of those expectations are
unrealistic under any imaginable circumstances; others are impossible
(or merely problematic) in the current DNS structure but could be
accommodated in a redesign. These are examples, rather than a
comprehensive list, and do not appear in any particular order.

3.1. Multi-type Queries

The DNS does not gracefully support multi-type queries.The queries. The current
case where this problem rears its head involves attempts at solutions
that return both TYPE A (IPv4) and type AAA (IPv6) addresses
collectively. The problem was originally seen with "QTYPE=MAILA"
[RFC0882] for the original MA and MD RRTYPEs, an experience that
strongly suggests that some very careful thinking about cache effects
(and possibly additional DNS changes) would be needed. Other
solutions might seem equally or more plausible. What they, including
"two types of addresses", probably have in common is that they
illustrate stresses on the system and that changing the DNS to deal
with those stresses, stresses is not straightforward or likely to be problem-
free.

3.2. Matching Part I: Case Sensitivity in Labels and Other Anomalies

The DNS specifications assume that labels are octet strings and
octets with the high bit zero have seven-bit ASCII codes in the
remaining bits. They require that, when a domain name used in a
query is matched to one stored in the database, those ASCII
characters be interpreted in a case-independent way, i.e., upper upper- and
lower case
lower-case letters are treated as equivalent (digits and symbols are
not affected) [RFC4343]. For non-ASCII octets, i.e., octets in
labels with the first bit turned on, there are no assumptions about
the character coding used, much less any rules about character case
equivalence -- strings must be compared by matching bits in sequence.
Even though the current model for handling non-ASCII (i.e.,
"internationalized") domain name labels (IDNs) [RFC5890] (and see (see
Section 3.3 below) encodes information so the DNS is not directly
affected, the notion that some characters in labels are handled in a
case-insensitive way and that others are case-sensitive case sensitive (or that
upper case must be prohibited entirely as IDNA does) has caused a
good deal of confusion and resentment. Those concerns and complaints
about inconsistent behavior and mishandling (or suboptimal handling)
of case relationships for some languages have not been mitigated by
repeated explanations that the relationships between "decorated"
lower-case characters and their upper-case equivalents are often
sensitive to language and locality and therefore not deterministic
with information available to DNS servers.

3.3. Matching Part II: Non-ASCII ("internationalized") ("Internationalized") Domain Name
Labels

Quite independent of the case-sensitivity problem, one of the
fundamental properties of Unicode [Unicode] is that some abstract
characters can be represented in multiple ways, such as by a single,
precomposed, code point or by a base code point followed by one or
more code points that specify combining characters. While Unicode
Normalization can be used to eliminate many (but not all) of those
distinctions for comparison (matching) purposes, it is best applied
during matching rather than by changing one string into another. The
first version of IDNA ("IDNA2003") made the choice to change strings
during processing for either storage or retrieval [RFC3490]
[RFC3491]; the second ("IDNA2008") required that all strings be
normalized and that upper case upper-case characters are not allowed at all
[RFC5891]. Neither is optimal, if only because, independent of where
they are changed if they are changed at all, transforming the strings
themselves implies that the input string in an application may not be
the same as the string used in processing and perhaps later display.

It would almost certainly be preferable, and more consistent with
Unicode recommendations, to use normalization (and perhaps other
techniques if they are appropriate) at matching time rather than
altering the strings at all, even if there were still only a single
matching algorithm, i.e., normalization were added to the existing
ASCII-only case folding. However, even Unicode's discussion of
normalization [Unicode-UAX15] indicates that there are special,
language-dependent, cases (the most commonly-cited commonly cited example is the
dotless "i" (U+0131)). Not only does the DNS lack any information
about languages that could be used in a mapping algorithm, but, as
long as there is a requirement that there be only one mapping
algorithm for the entire system, that information could not be used
even if it were available. One could imagine a successor system that
would use information stored at nodes in the hierarchy to specify
different matching rules for subsidiary nodes (or equivalent
arrangements for non-hierarchical systems). It is not clear whether
that would be a good idea, but it certainly is not possible with the
DNS as we know it.

3.4. Matching Part III: Label Synonyms, Equivalent Names, and Variants

As the initial phases of work on IDNs started to conclude, it became
obvious that the nature and evolution of human language and writing
systems required treating some names as "the same as" others. The
first important example of this involved the relatively recent effort
to simplify the Chinese writing system, thereby creating a
distinction between "Simplified" and "Traditional" Chinese even
though the meaning of the characters remained the same in almost all
cases (in so-called ideographic character sets, characters have
meaning rather than exclusively representing sounds). A joint effort
among the relevant country code top level domain (TLD) Country Code Top-Level Domain (ccTLD) registries
and some other interested parties produced a set of recommendations
for dealing with the issues with that script [RFC3743] and introduced
the concept of "variant" characters and domain names.

However, when names are seen as having meanings, rather than merely
being mnemonics, especially when they represent brands or the
equivalent, or when spelling for a particular written language is not
completely standardized, demands to treat different strings as exact
equivalents are obvious and inevitable. As a trivial English-
language example, it is widely understood that "colour" and "color"
represent the same word, so does that imply that, if they are used as
DNS labels in domain names all of whose other labels are identical,
the two domain names should be treated as identical? Examples for
other languages or writing systems, especially ones in which some or
all markings that distinguish characters or words by sound or tone or
that change the pronunciation of words are optional, are often more
numerous and more problematic than national spelling differences in
English, but they are harder to explain to those unfamiliar with
those other languages or writing systems (and hard to illustrate in
ASCII-only Internet-Drafts and RFCs). Although approximations are
possible, the DNS cannot handle that requirement: not only do its
aliasing mechanisms (CNAME, DNAME, and various proposals for newer
and different types of aliasing [DNS-Aliases] [DNS-BNAME], [DNS-BNAME]) not
provide a strong enough binding, but the ability to use those aliases
from a subtree controlled by one administrative entity to that of
another one implies that there is little or no possibility of the
owner (in either the DNS sense or the registrar-registrant one) of a
particular name to control the synonyms for it. Some of that issue
can be dealt with at the application level, e.g., by redirects in web
protocols, but taking that approach, which is the essential
characteristic of "if both names belong to the same owner, everything
is ok" OK" approaches, results in names being handled in inconsistent
ways in different protocols.

A different way of looking at part of this issue (and, to some
degree, of the one discussed above in Section 3.3) is that these
perceived equivalences and desired transformations are context-
dependent, but the DNS resolution process is not [RFC6912].

Similar problems arise as people notice that some characters are
easily mistaken for others and that might be an opportunity for user
confusion and attacks. Commonly-cited Commonly cited examples include the Latin and
Cyrillic script "a" characters, which are identical [CACM-Homograph],
the characters in many scripts that look like open circles or
vertical or horizontal lines, and even the Latin script letter "l"
and the European digit "1", but examples abound in other scripts and
combinations of scripts as well. The most common proposed solution
within the DNS context has been to treat these cases, as well as
those involving orthographic variations, as "variants" (but variants
different from the system for Chinese characters mentioned above) and
either ban all but one (or a few) of the possible labels from the DNS
(possibly on a first come come, first served basis) or by ensuring ensure that any
collection of such strings that are delegated as assigned to the same
ownership (see above). Neither solution is completely satisfactory:
if all but one string is excluded, users who guess at a different
form, perhaps in trying to transcribe characters from written or
printed form, don't find what they are looking for and, as pointed
out above, "same ownership" is sufficient only with carefully- carefully
designed and administered applications protocol support support, and
sometimes not then.

Some of these issues are discussed at more length in an ICANN report
[ICANN-VIP].

3.5. Query Privacy

There has been growing concern in recent years that DNS queries occur
in clear text cleartext on the public Internet and that, if those queries can be
intercepted, they can expose a good deal of information about
interests and contacts that could compromise individual privacy.
While a number of proposals, including query name minimization
[RFC7816] and running DNS over an encrypted tunnel [RFC7858], have
been made to mitigate that problem, they all appear to share the
common properties of security patches rather than designed-in
security or privacy mechanisms. While experience may prove otherwise
once (and if) they are widely deployed, it does not appear that any
of them are as satisfactory as a system with query privacy designed
in might be. More general tutorials on this issue have appeared
recently [Huston2017a].

3.6. Alternate Name Spaces Namespaces for Public Use in the DNS Framework: The
CLASS Problem

The DNS standards include specification of a CLASS value to "identify value, which
"identifies a protocol family or instance of a protocol" [RFC (RFC 1034,
Section 3.6 3.6, and elsewhere]. elsewhere). While CLASS was used effectively in the
early days of the DNS to manage different protocol families within
the same administrative environment, recent attempts to use it to
either partition the DNS namespace in other ways such as for
non-ASCII names (partially to address the issues in Section Sections 3.2 Section and
3.3) or to use DNS mechanisms for entirely different namespaces have
exposed fundamental problems with the mechanism [Sullivan-Class].
Perhaps the most fundamental of those problems is disagreement about
whether multiple CLASSes were intended to exist within a given zone
(with records within RRSETs) or whether different CLASSes implied
different zones. Different implementations make different
assumptions [Faltstrom-2004] [Vixie-20170704]. These problems have
led to recommendations that it be dropped entirely [Sullivan-Class],
but discussions on the IETF list and in WGs in mid-2017 made it clear
that there is no clear consensus on that matter.

3.7. Loose Synchronization

The DNS model of master and slave servers, with the latter initiating
updates based on expiration interval values, and local caches with
updates based on TTL values, depends heavily on an approach that has
come to be called "loose synchronization", i.e., that there can be no
expectation that all of the servers that might reasonably answer a
query will have exactly the same data unless those data have been
unchanged for a rather long period. Put differently, if some or all
of the records associated with a particular node in the DNS
(informally, a fully-qualified fully qualified domain name (FQDN)) change, one cannot
expect those changes to be propagated immediately.

That model has worked rather well since the DNS was first deployed,
protecting the system from requirements for mechanisms that are
typical where a simultaneous update of multiple systems is needed.
Such mechanisms include elaborate locking, complex update procedures
and handshaking, or journaling. As has often been pointed out with
the Internet, implementation and operational complexity are often the
enemy of stability, security, and robustness. Loose synchronization
has helped keep the DNS as simple and robust as possible.

A number of recent ideas about using the DNS to store data for which
important changes occur very rapidly are, however, largely
incompatible with loose synchronization. Efforts to use very short
(or zero) refresh times (in SOA records for slave updates from
masters) and TTLs (for caches) to simulate nearly-simultaneous nearly simultaneous
updating may work up to a point but appear to impose very heavy loads
on servers and distribution mechanisms that were not designed to
accommodate that style of working. Similar observations can be made
about attempts to use the NOTIFY extension [RFC1996] or dynamic,
"server-push", updating rather than the traditional DNS mechanisms.
While the NOTIFY and push mechanisms normally provide refresh times
and update mechanisms faster than those specified in RFC RFCs 1034 and
1035, they imply that a "master" server must know the identities of
(and have good connectivity to all of) its slaves. That defeats at
least some of the advantages associated with stealth slaves,
particularly those associated with reduction of query traffic across
the Internet. Those mechanisms do nothing for cache updates: unless
servers keep track of the source of every query for names associated
with a specific zone and then somehow notify the query source
systems, the only alternative to having information that might be
obsolete stored in caches is to use very short or zero TTLs so the
cached data time out almost immediately after being stored (or are
not stored at all), requiring a new query to an authoritative server
each time a resolver attempts to look up a name.

3.8. Private Name Spaces Namespaces and Special Names

Almost since the DNS was first deployed, there have been situations
in which it is desirable to use DNS-like names, and often DNS
resolution mechanisms or modifications of them, with name spaces namespaces for
which globally-available globally available and consistent resolution using the public
DNS is either unfeasible or undesirable (and for which the use of
CLASS is not an appropriate mechanism). The need to isolate names
and addresses on LANs from the public Internet, typically via "split
horizon" approaches, is one example of this requirement although
often not recognized as such. Another example that has generated a
good deal of controversy involves "special names" -- labels or
pseudo-labels, often in TLD positions, that signal that the full name
should not be subject to normal DNS resolution or other processing
[RFC6761] [RFC8244].

Independent of troublesome policy questions about who should allocate
such names and the procedures to be used, they almost inherently
require either a syntax convention to identify them (there actually
was such a convention, but it was abandoned many years ago and there
is no plausible way to re-institute reinstitute it) or tables of such names that
are known to, and kept updated on, every resolver on the Internet, at
least if spurious queries to the root servers are to be avoided.

If the DNS were to be redesigned and replaced, we could recognize
this requirement as part of the design and handle it much better than
it is possible to handle it today.

3.9. Alternate Query or Response Encodings

The DNS specifies formats for queries and data responses, based on
the state of the art and best practices at the time it was designed.
Recent work has suggested that there would be significant advantages
to supporting at least a description of the DNS messages in one or
more alternate formats, such as JSON [Hoffman-DNS-JSON]
[Hoffman-SimpleDNS-JSON]. While that work has been carefully done to
avoid requiring changes to the DNS, much of the argument for having
such a JSON-based description format could easily be turned into an
argument that, if the DNS were being revised, that format might be
preferable as a more direct alternative to having DNS queries and
responses in the original form.

3.10. Distribution and Management of Root Servers

The DNS model requires a collection of root servers that hold, at
minimum, information about top-level domains. Over the years, that
requirement has evolved from a technically fairly minor function,
normally carried out as a service to the broader Internet community
and its users and systems, to a subject that is intensely
controversial with regard to control of those servers, including how
they should be distributed and where they should be located. While a
number of mechanisms, most recently including making the information
more local [RFC7706], have been proposed and one (anycast [RFC7094])
is in very active use to mitigate some of the real and perceived
problems, it seems obvious that a DNS successor, designed for today's
global Internet and perceived requirements, could handle these
problems in a technically more appropriate and less controversial
way. Some additional discussion of the issues involved appears in a
recent paper [Huston2017b].

3.11. Identifiers Versus versus Brands and Other Convenience Names

A key design element of the original network object naming systems
for the ARPANET, largely inherited by the DNS, was that the names,
while expected to be mnemonic, were identifiers and their being
highly distinguishable and not prone to ambiguity was important.
That led to restrictive rules about what could appear in a name.
Those restrictions originated with the host table and even earlier
[RFC0236] [RFC0247] and came to the DNS (largely via SMTP) as the
"preferred syntax" [RFC 1034 (RFC 1034, Section 3.5] 3.5) or what we now often call
the letter-digit-hyphen (LDH) rule. Similar rules to make
identifiers easier to use, less prone to ambiguity, or less likely to
interfere with syntax occur frequently in more formal languages. For
example, almost every programming language has restrictions on what
can appear in an identifier identifier, and Unicode provides general
recommendations about identifier composition [Unicode-USA31]. Both
are quite restrictive as compared to the number of characters and
total number of strings that can be written using that character
coding system.

That model, which originally prohibited labels starting with digits
in order to avoid any possible confusion with IP addresses, began to
break down in 1987 or 1988 when a company named 3Com wanted to use
its corporate name as a label within the COM TLD TLD, and the rule was
relaxed [RFC1123].

In the last decade or two, the perspective that company names should
be supported if possible has expanded and done so largely without its
limits, if any, being explicitly understood or acknowledged. In the
current form, the DNS is really (and primarily) a system for
expressing thoughts and concepts. Those include free expression of
ideas in as close to natural language as possible as well as
representation of product names and brands. That view requires
letter-like characters that might not be reasonable in identifiers
along with a variety of symbols and punctuation. It may also require
indicators of preferred type styles to provide information in a form
that exactly matches personal or legal preferences. At least it if
carried to an extreme, that perspective would argue for standardizing
word and sentence separators, for removing the limit of 63 octet octets per
label
limit and probably the limit of 255 octets on the total length of a
domain name, and perhaps even eliminating the hierarchy or allowing
separators for labels in presentation form (now fixed at "." for the
DNS) to be different according to context. It suggests that, at
least, the original design was defective in not prioritizing those
uses over the more restrictive approach associated with prioritizing
unique and unambiguous identifiers.

So we have two, two or, depending on how one counts, three very different
use cases. The historical one is support for unique identifiers.
The other is expression of ideas and, if one considers them separate,
presentation of brand and product names. Because they inherently
involve different constraints, priorities, and success criteria,
these perspectives are, at best, only loosely compatible.

We cannot simultaneously optimize both the identifier perspective and
either or both of the others in the same system. At best, there are
some complex trade-offs involved. Even then, it is not clear that
the same DNS (or other system) can accommodate all of them. Until we
come to terms with that, the differences manifest themselves with
friction among communities, most often with tension between "we want
to do (or use or sell) these types of labels" and "not good for the
operational Internet or the DNS".

3.12. A Single Hierarchy with a Centrally-controlled Centrally Controlled Root

A good many Internet policy discussions in the last two decades have
revolved around such questions of how many top level top-level domains there
should be, what they should be, who should control them and how, how
(or if) their individual operations and policy decisions should be
accountable to others, and what processes should be used (and by what
entities or organizational structures) to make those decisions.
Several people have pointed out that, if we were designing a next-
generation DNS using today's technology, it should be possible to
remove the technical requirement for a central authority over the
root (some people have suggested that blockchain approaches would be
helpful for this purpose; others believe they just would not scale
adequately, at least at acceptable cost, but that other options are
possible). Whether elimination of a single, centrally-controlled, centrally controlled,
root would be desirable or not is fairly obviously a question of
perspective and priorities.

3.13. Newer Application Protocols, New Requirements, and DNS Evolution

New work done in other areas has led to demands for new DNS features,
many of them involving data values that require recursively
referencing the DNS. Early record types that did that were
accompanied by restrictions that reduced the risk of looping
references or other difficulties. For example, while the MX RRTYPE
has a fully-qualified fully qualified domain name as its data, SMTP imposes "primary
name" restrictions that prevent the name used from being, e.g., a
CNAME. While loops with CNAMEs are possible, RFC 1034, Section 3.6, 3.6 of RFC 1034
includes a discussion about ways to avoid problems and how they
should be handled. Some newer protocols and conventions can cause
more stress. There are separate issues with additions and with how
the DNS has been extended to try to deal with them.

3.13.1. The Extensions

Some examples of DNS extensions for new protocol demands that
illustrate, or have led to, increased stress include:

NAPTR

NAPTR: Requires far more complex data in the DNS for ENUM (e.g.,
VoIP,
Voice over IP (VoIP), specifically SIP) support, including URI
information and hence recursive or repeated lookups, than any of
the RRTYPEs originally supported. The RRSET associated with these
records can become quite large because the separator between the
various records is part of the RDATA, and not the {owner, class,
type} triple (a problem slightly related to the problem with
overloading of TXT RTYPE RRTYPE discussed in Section 3.13.2).
[[CREF1: I'm told this issue was brought up by IAB in RFCXXXX ???,
but have not yet tracked down the reference -JcK]] This
problem, and similar ones for some of the cases below. may suggest
that any future design is in need of a different TYPE model such
as systematic arrangements for subtypes or some explicit hierarchy
in the TYPEs.

URI

URI: Has a URI as its data, typically also requiring recursive or
repeated lookups.

Service location (SRV) and credential information (including SPF and
DKIM) Sender
Policy Framework (SPF) and DomainKeys Identified Mail (DKIM)):
Require structured data and, especially for the latter two,
significantly more data, data than most original RRTYPEs.

URI/URL

URI/URL: The early design decision for the World Wide Web that its
mechanism for identifying digital web content (now known as
Uniform Resource Identifiers [RFC3986]) did so by using domain
names and hence the network location of the information or other
material. That, in turn, has required systems intended to improve
web performance by locating and retrieving a "nearest copy"
(rather than the single copy designated by the URL) to intercept
DNS queries and respond with values that are not precisely those
stored for the designated domain name in the DNS or to otherwise
access information in a way not supported by the DNS itself.

3.13.2. Extensions and Deployment Pressures -- The TXT RRTYPE

Unfortunately (but unsurprisingly), and despite IETF efforts to make
things easier [RFC6895], DNS support libraries have often been slow
to add full support for new RRTYPEs. This has impeded deployment of
applications that depend on those types and that must ask (query)
explicitly for them. Both to get faster deployment and, at least
until recently, to avoid burdensome IETF approval procedures, many
application designers have chosen to push protocol-critical
information into records with TXT RRTYPE, a record type that was
originally intended to include only information equivalent to
comments.

This causes two problems. First, TXT records used this way tend to
get long and complex, which is a problem in itself if one is trying
to minimize TCP connections. Second, applications that are
attempting to obtain data cannot merely ask for the relevant QTYPE, QTYPE;
they must obtain all of the records with QTYPE TXT and parse them to
determine which ones are of interest. That would be easier if there
was some standard for how to do that parsing parsing, but, at least in part
because the clear preference in the DNS design is for distinct
RRTYPEs for different kinds of information, there is no such standard
(there
standard. (There was a proposal in 1993 to structure the TXT DATA in
a way that would have addressed the issue [RFC1464] [RFC1464], but it
apparently never went
anywhere). anywhere.)

On the other hand, this issue is somewhat different from most of the
others described in this document because (as the IETF has
recommended several times) the problem is easily solved within the
current DNS design by allocating and supporting new RRTYPEs when
needed rather than using TXT as a workaround (that does not mean that
other solutions are impossible, either with the current DNS or with
some other design). The problem then lies in the implementations
and/or mechanisms that deter or impede rapid deployment of support
for new RRTYPEs.

3.13.3. Periods and Zone Cut Issues

One of the DNS characteristics that is poorly understood by non-
experts
non-experts is that the period (".", U+002E) character can be used in
three
four different ways:

o As a label separator in the presentation form that also designates
a "zone break" (delegation boundary). For example,
foo.bar.example.com indicates the owner, "foo", of records in the
"bar.example.com" zone.

o As a label separator in the presentation form that does not
designate a zone break. For example, foo.bar.example.com
indicates the owner, "foo.bar", of records in the "example.com"
zone.

o As a character within a label, including as a substitute for an
at-sign ("@") when an email address appears in an SOA record or in
a label that denotes such an address (see Section 2 above). The
ability to embed periods in labels in this way has also led to
attacks in which, e.g., a domain name consisting of the labels
"example" followed by "com" is deliberately confused with the
single label "example.com" with an embedded period.

o At the end of a fully qualified domain name to designate the root
zone, e.g., "example.com." (RFC 1034, Section 3.1).

In general, these cases cannot be distinguished by looking at them.
The third is problematic for non-DNS reasons, e.g.,
"john.doe.example.net" is ambiguous as to whether it should can be interpreted as either a simple FQDN, FQDN or
as a notation for john.doe@example.net,
for john@doe.example.net, and so on. john.doe@example.net, or even
(at least in principle) john.doe.example@net.

The distinction between the FQDN interpretation and the first two cases email-
like one was probably not important as the DNS was originally
intended to be used. However, as soon as RRTYPEs (other than NS
records that define the zone cut) are used that are sensitive to the
boundaries between zones, the distinctions become important to people
other than the relevant zone administrators. DNSSEC [RFC4033]
involves one such set of relationships. It increases the importance
of questions about what should go in a parent zone and what should go
in child zones and how much difference it makes if NS records in a
parent zone for a child zone are consistent with the records and data
in the child zone. This also causes application issues and may raise
questions about relationships between registrars and one or more
registries or, if they are separate, DNS operators.

3.14. Scaling of Reputation and Other Ancillary Information

The original design for DNS administration, reflected in RFC 1591
[RFC1591] and elsewhere, assumed that all domains would exhibit a
very high level of responsibility toward and for the community and
that level of responsibility would be enforced if necessary.

More recent decisions, many of them associated with commercialization
of the DNS, have eroded those very strong assumptions of registry
responsibility and accountability to the point that many consider
decisions about delegation of names, identification of registrants,
and relationships among names to be matters of of "registrant beware"
and even "user and applications beware". While some recent protocols
and proposals at least partially reflect that original model of a
high level of responsibility (see, e.g., IDNA [RFC5890] and the
discussion in a more
recent Internet-Draft discussion [Klensin-5891bis]), other decisions and actions
tend to shift responsibility to the registrant or try to avoid
accountability entirely. One possible approach to the problems,
especially security problems, that are enabled by those new trends
and the associated environment is to establish reputation systems
associated with clearly-defined clearly defined administrative boundaries and with
warnings to users, even if those reputation systems are managed by
parties not directly associated with the DNS.

The IETF DBOUND WG [IETF-DBOUND] addressed ways to establish and
document boundaries more precise than simple dependencies on TLDs TLDs,
but it was not successful in producing a standard.

A TLD reputation-based approach was adopted by some web browsers
after IDNs and a growing number of gTLDs Generic Top-Level Domains (gTLDs)
were introduced; that approach was based on a simple list and does
not scale to the current size of the DNS or even the DNS root.

3.15. Tensions among transport, scaling Transport, Scaling, and content Content

The original design for the DNS envisaged a simple query and response
protocol where both the command and the response could be readily
mapped into a single IP packet. The Hosts Requirement host requirements specification
[RFC1123] required all DNS applications to accept a UDP query or
response over UDP with up to 512 octets of DNS payload. TCP was seen
as a fallback when the response was greater than this 512 octet 512-octet
limit, and this fallback to use TCP as the transport protocol was
considered to be the exception rather than the rule.

Over the intervening years years, we have seen the rise of a common
assumption of an Internet-wide Maximum Transmission Unit (MTU) size
of 1,500 octets, accompanied with an assumption that UDP
fragmentation is generally viable. This underpins the adoption of
the Extended Extension Mechanisms for DNS
Options (EDNS(0)) [RFC6891] to to, among other
things, specify a UDP buffer size larger than 512 octets and a
suggestion within that specification to use 4,096 as a suitable
compromise as a for the UDP payload size. This has proved to be
fortuitous for the DNSSEC security extensions where the addition of
DNSSEC security credentials in DNS responses [RFC4034] can lead to
the use of large DNS responses. However, this exposes some tensions
over the handling of fragmentation in IP, where UDP fragments have
been observed to be filtered by various firewalls. Additionally for
IPv6, there are the factors of filtering of the ICMPv6 Packet Too Big
diagnostic messages, messages and discarding of the IPv6 packets that contain
extension headers [RFC7872]. More generally, fragmented UDP packets
appear to have a lower level of reliability than unfragmented TCP
packets.

Behind this observation about relative reliability of delivery is the
tension between the lightweight load of UDP and the downside of
elevated probability of discarding of packet fragments as compared to
TCP, which offers increased levels of assurance of content delivery,
but with the associated imposition of TCP session state and the
downside of reduced DNS scalability and increased operational cost.

4. The Inverse Lookup Requirement

The requirement for an inverse lookup capability, i.e., the ability
to find a domain name given an address and, in principle, to find the
owner of a record by any of its data elements, was recognized in RFC
882. The feature was identified as optional but carried forward into
RFC
RFCs 1034 and 1035 but was explicitly deprecated by RFC 1034 for
address to host name
address-to-hostname lookup (although RFC 1035 uses exactly that type
of lookup in an example). Despite the discussion of inverted forms
of the database in RFC 1035, inverse lookup has rarely, if ever, been
implemented, at least in its general form. The fundamental
difficulties with inverse lookup in either the form described in RFC
882 form or the "in-addr.arpa" approach mentioned below are consistent
with the problems described in fundamental papers on database
management [Codd1970] but were not described in RFC 1035 or related
contemporary IETF documents.

It is interesting to speculate on how many of the current
requirements to treat aliases as an integrated set of synonyms (e.g.,
for variant handling) would have been addressed if inverse lookups
could reliably produce the owners of CNAME records.

At the same time, it was obviously important to have some mechanism
for address to name address-to-name resolution. It was provided by PTR RRTYPE
entries in the IN-ADDR.ARPA zone, with delegations on octet
boundaries. However, that approach required that information be
maintained in parallel, in separate zones, for the name-> address name-to-address
and
address-> name address-to-name mappings. That synchronization requirement for
two copies of essentially the same data was another popular topic in
the database management literature a decade or more before the DNS
and, predictably, led to many inconsistencies and other failures.

The introduction of CIDR Classless Inter-Domain Routing (CIDR) [RFC1518]
and Provider Dependent Provider-Dependent addresses made the situation even more
difficult, because it was no longer possible to delegate the
administration of reverse mapping records for small networks to the
actual operators of those networks. ISPs and other aggregators often
had no incentive to maintain reverse mapping records consistent with
network operator assignment of domain names. A proposal to use
binary labels to work around that issue [RFC2673] was abandoned
somewhat over three years later [RFC6891].

Independent of how much or little harm the absence of a general
inverse lookup facility has caused and how effective the IN-ADDR.ARPA
"in-addr.arpa" approach has been, inverse lookup remains a facility
that was anticipated and known to be useful in the original DNS
design but that has never been fully realized.

5. Internet Scale, Function Support, and Incremental Deployment

In addition to the stresses caused by the new functions, including
those described in Section 3.13, incremental deployment of systems
that utilize them means that some functions will work in some
environments and not others. This has been especially problematic
with complex, multi-record, capabilities like DNSSEC that provide or
require special validation mechanisms and with some EDNS0 mechanisms EDNS(0)
extensions [RFC6891] that require that both the client and server to
accept particular extensions. When DNS functionality is required in
embedded devices, deployment of new features across the entire
Internet in a reasonable period of time is nearly impossible.

If one were redesigning the DNS, one could imagine ways to address
these issues that would make them slightly more tractable tractable, and, of
course, the features that are known to be necessary today could
become part of the baseline, "mandatory to implement", specification.

6. Searching and the DNS - -- An Historical Note

Some of the issues identified above might reasonably be addressed,
not by changing the DNS itself but by changing our model of what it
is about and how it is used. Specifically, one key assumption when
the DNS (and the host table system before it) was designed was that
it was a naming system for network resources, not, e.g., digital
content. As such, exact matching was important, it was reasonable to
have labels treated as mnemonics that did not necessarily have
linguistic or semantic meaning except to those using them, and so on.
A return to that model, presumably by having user-facing applications
call on an intermediate layer to disambiguate user-friendly names and
map them to DNS names (or network object locators more generally) generally),
would significantly reduce stress on the DNS and would also allow
dealing with types of matching and similar or synonymous strings that
cannot be handled algorithmically no matter how much DNS matching
rules were altered.

In some respects, search engines based on free-text analysis and
linkages among information have come to serve many of the functions
of such an intermediate layer. Many studies and sources have pointed
out that few users actually understand, much less care about, the
distinction between a DNS name and a search term. Recent versions of
some web browsers have both recognized the failure of that
distinction and reinforced it by eliminating the separation between
"URL" and "search bar".

It is worth noting that, while that "search" approach, or some other
approach that abstracted and separated several of the issues
identified in Section 3 from the DNS protocol and database
themselves, it does not address all of them. At least some elements
of several of those issues, such as the synchronization ones
described in Section 3.7 and the transport ones described in
Section 3.15, are inherent in the DNS design design, and, if we are not
going to replace the DNS, we had best get used to them.

In the early part of the last decade, the IETF engaged in some
preliminary exploration of the intermediate layer intermediate-layer approach in the
context of IDNs and what were then called "Internet keywords"
[DNS-search]. It may be time to examine While that approach again and to
do so more deeply in exploratory effort met several times
informally, it never became an organized IETF activity, largely
because of the context choice of developments since what became the IDNA approach but also in
part by signs that the "Internet keywords" efforts were beginning to
fall apart.

It may be time of
that earlier work and the degree to which reexamine intermediate-layer approaches. If so,
the effort should examine use of an intermediate
layer those approaches by appropriate
user-facing applications that might be used to address some of the
issues identified above.

8. IANA Considerations

[[CREF2: RFC Editor: Please remove The Internet and the DNS have changed
considerably since the 2000-2003 period. Several of those changes
are discussed elsewhere in this section before publication.]]

This memo includes no requests document; others, including
repurposing of the DNAME RRTYPE from support for transitions
[RFC2672] to or actions a general-purpose mechanism for aliases of subtrees
[RFC6672] and the addition of over a thousand new TLDs
[IANA-TLD-registry], are not but nonetheless are part of the context
for IANA.

9. intermediate-layer work that did not exist in 2003.

7. Security Considerations

A wide range of security issues related to both securing the DNS and
also to abilities to use namespaces for nefarious purposes have
arisen. Issues of securing the DNS would obviously be essential to a
replacement of the DNS. Issues of preventing nefarious use of the
namespace (e.g. use of the name that appears or disappears as a
signal to bots) would appear to be harder to solve within the naming
system.

[[CREF3: References needed ]]

10.

8. References

10.1.

8.1. Normative References

[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.

[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.

10.2.

8.2. Informative References

[CACM-Homograph]
Gabrilovich, E. and A. Gontmakher, "The Homograph Attack",
Communications of the ACM 45(2):128, ACM, Volume 45, Issue 2, pp. 128,
DOI 10.1145/503124.503156, February 2002,
<http://www.cs.technion.ac.il/~gabr/papers/
homograph_full.pdf>.

[Cerf2017] Cerf, V., "Desirable Properties of Internet Identifiers",
IEEE Internet Computing November/December 2017, Computing, Volume 21, Issue 6, pp. 2-3, 63-64,
DOI 1089-7801/17, 10.1109/MIC.2017.4180839, November/December 2017.

[Codd1970] Codd, E., "A Relational Model of Data for Large Shared
Data Banks", Commun. ACM Communications of the ACM, Volume 13, Issue
6, pp. 377-387, DOI 10.1145/362384.362685, June 1970, <http://doi.acm.org/10.1145/362384.362685>.
<https://dl.acm.org/citation.cfm?id=362685>.

[DNS-Aliases]
Woolf, S., Lee, X., and J. Yao, "Problem Statement: DNS
Resolution of Aliased Names", Work in Progress,
draft-ietf-dnsext-aliasing-requirements-01, March 2011,
<https://datatracker.ietf.org/doc/
draft-ietf-dnsext-aliasing-requirements/>. 2011.

[DNS-BNAME]
Yao, J., Lee, X., and P. Vixie, "Bundled DNS Name
Redirection", Work in Progress, draft-yao-dnsext-bname-06,
May 2016, <https://datatracker.ietf.org/doc/
draft-yao-dnsext-bname/>. 2016.

[DNS-search]
IETF, "Internet Resource Name Search Service", Service (IRNSS)",
2003, <https://datatracker.ietf.org/wg/irnss/about/>.

While it met several times informally and as one or more
BOFs, this effort never really got off the ground. That
was due in part to the IETF decision to go forward with
the IDNA approach and in part by signs that the "keyword"
efforts were beginning to fall apart.

[Faltstrom-2004]
Faltstrom, P. and R. Austein, "Design Choices When
Expanding DNS", Work in Progress,
draft-ymbk-dns-choices-00, May 2004, <draft-ymbk-dns-choices-00>. 2004.

[Hoffman-DNS-JSON]
Hoffman, P., "Representing DNS Messages in JSON", May
2017, <https://datatracker.ietf.org/doc/
draft-hoffman-dns-in-json/>. Work in
Progress, draft-hoffman-dns-in-json-13, October 2017.

[Hoffman-SimpleDNS-JSON]
Hoffman, P., "Simple DNS Queries and Responses in JSON",
June 2017, <https://datatracker.ietf.org/doc/
draft-hoffman-simplednsjsonn/>.
Work in Progress, draft-hoffman-simplednsjson-01, November
2017.

[Huston2017a]
Huston, G. and J. Silva Dama, "DNS Privacy", The Internet
Protocol Journal Vol Journal, Vol. 20, No No. 1, March 2017,
<http://ipj.dreamhosters.com/wp-
content/uploads/issues/2017/ipj20-1.pdf>.
<http://ipj.dreamhosters.com/wp-content/uploads/
issues/2017/ipj20-1.pdf>.

[Huston2017b]
Huston, G., "The Root of the Domain Name System", The
Internet Protocol Journal Journal, Vol. 20, No. 2, pp. 15-25, June
2017,
<http://ipj.dreamhosters.com/wp-content/uploads/2017/08/
ipj20-2.pdf>. <http://ipj.dreamhosters.com/wp-content/uploads/
2017/08/ipj20-2.pdf>.

[IANA-TLD-registry]
Internet Assigned Numbers Authority (IANA), "Root Zone
Database", <https://www.iana.org/domains/root/db>.

[ICANN-VIP]
ICANN, "IDN Variant Issues Project: Final Integrated
Issues Report Published and Proposed Project Plan for Next
Steps is Now Open for Public Comment", February 2012,
<https://www.icann.org/news/announcement-2012-02-20-en>.

[IETF-DBOUND]
IETF, "Domain Boundaries (dbound)", 2017,
<https://datatracker.ietf.org/wg/dbound/about/>.

[Klensin-5891bis]
Klensin, J., J. and A. Freytag, "Internationalized Domain
Names in Applications (IDNA): Registry Restrictions and
Recommendations", March 2017,
<https://datatracker.ietf.org/doc/
draft-klensin-idna-rfc5891bis/>. Work in Progress,
draft-klensin-idna-rfc5891bis-01, September 2017.

[Mockapetris-1988]
Mockapetris, P. and K. Dunlap, "Development of the Domain
Name System", SIGCOMM '88 Symposium Symposium, pp. 123-133,
DOI 10.1145/52324.52338, ISO
available from ISI Reprint Series Series, ISI/RS-88-219
(ftp://ftp.isi.edu/isi-pubs/rs-88-219.pdf),
<ftp://ftp.isi.edu/isi-pubs/rs-88-219.pdf>,
DOI 10.1145/52324.52338, August 1988,
<http://dl.acm.org/citation.cfm?id=52338&dl=ACM&coll=DL&CF
ID=963850156&CFTOKEN=83791048>.
<http://dl.acm.org/citation.cfm?id=52338>.

[NRC-Signposts]
National Research Council, "Signposts Signposts in Cyberspace: The
Domain Name System and Internet Navigation"", Navigation,
ISBN 0-309-54979-5, 2005,
<https://www.nap.edu/catalog/11258/signposts-in-
cyberspace-the-domain-name-system-and-internet-
navigation>. <https://www.nap.edu/
catalog/11258/signposts-in-cyberspace-the-domain-name-
system-and-internet-navigation>.

[RFC0236] Postel, J., "Standard host names", RFC 236,
DOI 10.17487/RFC0236, September 1971,
<https://www.rfc-editor.org/info/rfc236>.

[RFC0247] Karp, P., "Proffered set of standard host names", RFC 247,
DOI 10.17487/RFC0247, October 1971,
<https://www.rfc-editor.org/info/rfc247>.

[RFC0799] Mills, D., "Internet name domains", RFC 799,
DOI 10.17487/RFC0799, September 1981,
<https://www.rfc-editor.org/info/rfc799>.

[RFC0810] Feinler, E., Harrenstien, K., Su, Z., and V. White, "DoD
Internet host table specification", RFC 810,
DOI 10.17487/RFC0810, March 1982,
<https://www.rfc-editor.org/info/rfc810>.

[RFC0881] Postel, J., "Domain names plan and schedule", RFC 881,
DOI 10.17487/RFC0881, November 1983,
<https://www.rfc-editor.org/info/rfc881>.

[RFC0882] Mockapetris, P., "Domain names: Concepts and facilities",
RFC 882, DOI 10.17487/RFC0882, November 1983,
<https://www.rfc-editor.org/info/rfc882>.

[RFC0883] Mockapetris, P., "Domain names: Implementation
specification", RFC 883, DOI 10.17487/RFC0883, November
1983, <https://www.rfc-editor.org/info/rfc883>.

[RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
host table specification", RFC 952, DOI 10.17487/RFC0952,
October 1985, <https://www.rfc-editor.org/info/rfc952>.

[RFC0953] Harrenstien, K., Stahl, M., and E. Feinler, "Hostname
Server", RFC 953, DOI 10.17487/RFC0953, October 1985,
<https://www.rfc-editor.org/info/rfc953>.

[RFC0974] Partridge, C., "Mail routing and the domain system",
STD 10, RFC 974, DOI 10.17487/RFC0974, January 1986,
<https://www.rfc-editor.org/info/rfc974>.

[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<https://www.rfc-editor.org/info/rfc1123>.

[RFC1464] Rosenbaum, R., "Using the Domain Name System To Store
Arbitrary String Attributes", RFC 1464,
DOI 10.17487/RFC1464, May 1993,
<https://www.rfc-editor.org/info/rfc1464>.

[RFC1518] Rekhter, Y. and T. Li, "An Architecture for IP Address
Allocation with CIDR", RFC 1518, DOI 10.17487/RFC1518,
September 1993, <https://www.rfc-editor.org/info/rfc1518>.

[RFC1591] Postel, J., "Domain Name System Structure and Delegation",
RFC 1591, DOI 10.17487/RFC1591, March 1994,
<https://www.rfc-editor.org/info/rfc1591>.

[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
August 1996, <https://www.rfc-editor.org/info/rfc1996>.

[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, DOI 10.17487/RFC2671, August 1999,
<https://www.rfc-editor.org/info/rfc2671>.

[RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection",
RFC 2672, DOI 10.17487/RFC2672, August 1999,
<https://www.rfc-editor.org/info/rfc2672>.

[RFC2673] Crawford, M., "Binary Labels in the Domain Name System",
RFC 2673, DOI 10.17487/RFC2673, August 1999,
<https://www.rfc-editor.org/info/rfc2673>.

[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, DOI 10.17487/RFC3490, March 2003,
<https://www.rfc-editor.org/info/rfc3490>.

[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)",
RFC 3491, DOI 10.17487/RFC3491, March 2003,
<https://www.rfc-editor.org/info/rfc3491>.

[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", STD 88,
RFC 3596, DOI 10.17487/RFC3596, October 2003,
<https://www.rfc-editor.org/info/rfc3596>.

[RFC3743] Konishi, K., Huang, K., Qian, H., and Y. Ko, "Joint
Engineering Team (JET) Guidelines for Internationalized
Domain Names (IDN) Registration and Administration for
Chinese, Japanese, and Korean", RFC 3743,
DOI 10.17487/RFC3743, April 2004,
<https://www.rfc-editor.org/info/rfc3743>.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.

[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.

[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005,
<https://www.rfc-editor.org/info/rfc4034>.

[RFC4343] Eastlake 3rd, D., "Domain Name System (DNS) Case
Insensitivity Clarification", RFC 4343,
DOI 10.17487/RFC4343, January 2006,
<https://www.rfc-editor.org/info/rfc4343>.

[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/info/rfc5890>.

[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891,
DOI 10.17487/RFC5891, August 2010,
<https://www.rfc-editor.org/info/rfc5891>.

[RFC6672] Rose, S. and W. Wijngaards, "DNAME Redirection in the
DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,
<https://www.rfc-editor.org/info/rfc6672>.

[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>.

[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013,
<https://www.rfc-editor.org/info/rfc6891>.

[RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
April 2013, <https://www.rfc-editor.org/info/rfc6895>.

[RFC6912] Sullivan, A., Thaler, D., Klensin, J., and O. Kolkman,
"Principles for Unicode Code Point Inclusion in Labels in
the DNS", RFC 6912, DOI 10.17487/RFC6912, April 2013,
<https://www.rfc-editor.org/info/rfc6912>.

[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
"Architectural Considerations of IP Anycast", RFC 7094,
DOI 10.17487/RFC7094, January 2014,
<https://www.rfc-editor.org/info/rfc7094>.

[RFC7706] Kumari, W. and P. Hoffman, "Decreasing Access Time to Root
Servers by Running One on Loopback", RFC 7706,
DOI 10.17487/RFC7706, November 2015,
<https://www.rfc-editor.org/info/rfc7706>.

[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, <https://www.rfc-editor.org/info/rfc7719>.

[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<https://www.rfc-editor.org/info/rfc7816>.

[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.

[RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/info/rfc7872>.

[RFC8244] Lemon, T., Droms, R., and W. Kumari, "Special-Use Domain
Names Problem Statement", RFC 8244, DOI 10.17487/RFC8244,
October 2017, <https://www.rfc-editor.org/info/rfc8244>.

[Sullivan-Class]
Sullivan, A., "The DNS Is Not Classy: DNS Classes
Considered Useless", Work in Progress,
draft-sullivan-dns-class-useless-03, July 2016,
<https://datatracker.ietf.org/doc/
draft-sullivan-dns-class-useless/>. 2016.

[Unicode] The Unicode Consortium, "The The Unicode Standard, Version
9.0.0,",
9.0.0, (Mountain View, CA: The Unicode Consortium,
2016. ISBN 978-1-936213-13-9, 2016, 978-1-936213-13-9),
<http://www.unicode.org/versions/Unicode9.0.0/>.

[Unicode-UAX15]
Davis, M. and K. Whistler, "Unicode Standard Annex #15:
Unicode Normalization Forms", February 2016,
<http://unicode.org/reports/tr15/>.

[Unicode-USA31]
Davis, M., "Unicode Standard Annex #31: Unicode Identifier
and Pattern Syntax", May 2016,
<http://unicode.org/reports/tr31/>.

[Vixie-20170704]
Vixie, P., "Re: "Subject: Re: new DNS classes (email communication>", classes", message to
the IETF Mailing Lists IETF-discuss and dnsop, Jule dnsop mailing list, 4 July 2017,
<https://www.ietf.org/mail-archive/web/ietf/current/
msg103486.html>.

Acknowledgements

Many of the concerns and ideas described in this document reflect
conversations over a period of many years, some rooted in DNS
"keyword" and "search" discussions that paralleled the development of
Internationalized Domain Names (IDNs).
IDNs. Conversations with, or writings of, Rob Austein, Christine
Borgman, Carolina Carvalho, Vint Cerf, Lyman Chapin, Nazli Choucri,
Patrik Faltstrom, Geoff Huston, Xiaodong Lee, Karen Liu, Gervase
Markham, Yaqub Mueller, Andrew Sullivan, Paul Twomey, Nico Williams,
Suzanne Woolf, Jiankang Yao, other participants in the circa 2003
"DNS Search" effort and in the ICANN SSAC Working Party on IDNs, and
some others whose names were sadly forgotten, were particularly
important to either the content of this document or the motivation
for writing it even though they may not agree with the conclusions I
have reached and bear no responsibility for them.

Many of the subsections of Section 3 were extracted from comments
first made in conjunctions conjunction with recent email discussions. Comments
from Suzanne Woolf about an early earlier draft version were particularly
important as was material developed with suggestions from Patrik
Faltstrom, especially Section 3.13. Feedback and suggestions from
several of the above and from Stephane Bortzmeyer, Tony Finch, Bob
Harold, Warren Kumari, Craig Partridge, and George Sadowsky were
extremely helpful for improving the clarity and accuracy of parts of
the document, especially so for a broader audience. Craig Partridge
also contributed much of the material about queries for multiple
types. Geoff Huston made several useful comments and contributed
most of Section 3.15 3.15, and Bill Manning pointed out some broader
requirements about integrity of information and DNS management and
operations.

Special thanks are due to Karen Moore of the RFC Production Center
for her efforts, patience, and persistence in preparing this document
for publication, a process that raised far more issues that required
careful discussion than usual.

Author's Address

John C C. Klensin
1770 Massachusetts Ave, Ste 322
Cambridge, MA 02140
USA
United States of America

Phone: +1 617 245 1457
Email: john-ietf@jck.com