Internet DRAFT - draft-klensin-dns-role

draft-klensin-dns-role



Jsnuary 14, 2003
Expires July 2003


                  Role of the Domain Name System
                 draft-klensin-dns-role-05.txt

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups.  Note that
other groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet-Drafts as reference
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

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http://www.ietf.org/shadow.html.

This document represents an overview of an evolving technology area
and is not intended to evolve into a standard of any kind.

This draft (-05) is posted at the request of the RFC Editor as part of
the publication process.  It supercedes revision -04, for which a
Protocol Action was issued by the IESG on 16 December 2002.

Copyright Notice

Copyright (c) The Internet Society (2000, 2001, 2002).  All Rights
Reserved. 



Abstract

This document reviews the original function and purpose of the domain
name system (DNS).  It contrasts that history with some of the purposes
for which the DNS has recently been applied and some of the newer
demands being placed upon it or suggested for it.  A framework for an
alternative to placing these additional stresses on the DNS is then
outlined.  This document and that framework are not a proposed solution,
only a strong suggestion that the time has come to begin thinking more
broadly about the problems we are encountering and possible approaches
to solving them.

Table of Contents

0. Abstract
1. Introduction and History
1.1 Context for DNS Development
1.2 Review of the DNS and Its Role as Designed
1.3 The Web and User-visible Domain Names
1.4 Internet Applications Protocols and Their Evolution
2. Signs of DNS Overloading
3. Searching, Directories, and the DNS
3.1 Overview 
3.2 Some Details and Comments
4. Internationalization
4.1 ASCII Isn't Just Because of English
4.2 The "ASCII Encoding" Approaches
4.3 "Stringprep" and Its Complexities
4.4 The Unicode Stability Problem
4.5. Audiences, End Users, and the User Interface Problem
4.6 Business Cards and Other Natural Uses of Natural Languages
4.7 ASCII Encodings and the Roman Keyboard Assumption
4.8 Intra-DNS Approaches for "Multilingual Names"
5. Search-based Systems: The Key Controversies
6. Security Considerations
7. References
7.1 Normative References
7.2 Explanatory and Informative References
8. Acknowledgements
9. Author's Address


1. Introduction and History

The DNS was designed as a replacement for the older "host table" system.
Both were intended to provide names for network resources at a more
abstract level than network (IP) addresses (see, e.g., [RFC625],
[RFC811], [RFC819], [RFC830], [RFC882]}.  In recent years, the DNS has
become a database of convenience for the Internet, with many proposals
to add new features.  Only some of these proposals have been successful.
Often the main (or only) motivation for using the DNS is because it
exists and is widely deployed, not because its existing structure,
facilities, and content are appropriate for the particular application
of data involved.  This document reviews the history of the DNS,
including examination of some of those newer applications.  It then
argues that the overloading process is often inappropriate.  Instead, it
suggests that the DNS should be supplemented by systems better matched
to the intended applications and outlines a framework and rationale for
one such system.

Several of the comments that follow are somewhat revisionist.  Good
design and engineering often requires a level of intuition by the
designers about things that will be necessary in the future; the
reasons for some of these design decisions are not made explicit at
the time because no one is able to articulate them.  The discussion
below reconstructs some of the decisions about the Internet's primary
namespace (the "Class=IN" DNS) in the light of subsequent development
and experience.  In addition, the historical reasons for particular

decisions about the Internet were often severely underdocumented
contemporaneously and, not surprisingly, different participants have
different recollections about what happened and what was considered
important.  Consequently, the quasi-historical story below is just one
story.  There may be (indeed, almost certainly are) other stories
about how the DNS evolved to its present state, but those variants do
not invalidate the inferences and conclusions.

This document presumes a general understanding of the terminology of
RFC 1034 [RFC1034] or of any good DNS tutorial (see, e.g., [Albitz]).

1.1  Context for DNS Development

During the entire post-startup-period life of the ARPANET and nearly the
first decade or so of operation of the Internet, the list of host names
and their mapping to and from addresses was maintained in a
frequently-updated "host table" [RFC625, RFC811, RFC952].  The names
themselves were restricted to a subset of ASCII chosen to avoid
ambiguities in printed form, to permit interoperation with systems using
other character codings (notably EBCDIC), and to avoid the "national
use" code positions of ISO 646 [IS646].  These restrictions later became
collectively known as the "LDH" rules for "letter-digit- hyphen", the
permitted characters.  The table was just a list with a common format
that was eventually agreed upon; sites were expected to frequently
obtain copies of, and install, new versions.  The host tables themselves
were introduced to

o Eliminate the requirement for people to remember host numbers
(addresses).  Despite apparent experience to the contrary in the
conventional telephone system, numeric numbering systems, including the
numeric host number strategy, did not (and do not) work well for more
than a (large) handful of hosts.

o Provide stability when addresses changed.  Since addresses --to some
degree in the ARPANET and more importantly in the contemporary
Internet-- are a function of network topology and routing, they often
had to be changed when connectivity or topology changed.  The names
could be kept stable even as addresses changed.

o Provide the capability to have multiple addresses associated with a
given host to reflect different types of connectivity and topology.  Use
of names, rather than explicit addresses, avoided the requirement that
would otherwise exist for users and other hosts to track these multiple
host numbers and addresses and the topological considerations for
selecting one over others. 

After several years of using the host table approach, the community
concluded that model did not scale adequately and that it would not
adequately support new service variations.  A number of discussions and
meetings were held which drew several ideas and incomplete proposals
together.  The DNS was the result of that effort.  It continued to
evolve during the design and initial implementation period, with a
number of documents recording the changes (see [RFC819], [RFC830], and
[RFC1034]).


The goals for the DNS included

o Preservation of the capabilities of the host table arrangements
(especially unique, unambiguous, host names),

o Provision for addition of additional services (e.g., the special
record types for electronic mail routing which quickly followed
introduction of the DNS), and

o Creation of a robust, hierarchical, distributed, name lookup system to
accomplish the other goals.  

The DNS design also permitted distribution of name administration,
rather than requiring that each host be entered into a single, central,
table by a central administration.

1.2 Review of the DNS and Its Role as Designed

The DNS was designed to identify network resources.  Although there was
speculation about including, e.g., personal names and email addresses,
it was not designed primarily to identify people, brands, etc.  At the
same time, the system was designed with the flexibility to accomodate
new data types and structures, both through the addition of new record
types to the initial "INternet" class, and, potentially, through the
introduction of new classes.  Since the appropriate identifiers and
content of those future extensions could not be anticipated, the design
provided that these fields could contain any (binary) information, not
just the restricted text forms of the host table.

However, the DNS, as it is actually used, is intimately tied to the
applications and application protocols that utilize it, often at a
fairly low level.

In particular, despite the ability of the protocols and data structures
themselves to accomodate any binary representation, DNS names as used
were historically not even unrestricted ASCII, but a very restricted
subset of it, a subset that derives from the original host table naming
rules.  Selection of that subset was driven in part by human factors
considerations, including a desire to eliminate possible ambiguities in
an international context.  Hence character codes that had international
variations in interpretation were excluded, the underscore character and
case distinctions were eliminated as being confusing (in the
underscore's case, with the hyphen character) when written or read by
people, and so on.  These considerations appear to be very similar to
those that resulted in similarly restricted character sets being used as
protocol elements in many ITU and ISO protocols (cf. [X29]).

Another assumption was that there would be a high ratio of physical
hosts to second level domains and, more generally, that the system would
be deeply hierarchical, with most systems (and names) at the third level
or below and a very large percentage of the total names representing
physical hosts.  There are domains that follow this model: many
university and corporate domains use fairly deep hierarchies, as do a
few country-oriented top level domains ("ccTLDs"). Historically, the
"US." domain has been an excellent example of the deeply hierarchical

approach.  However, by 1998, comparison of several efforts to survey the
DNS showed a count of SOA records that approached (and may have passed)
the number of distinct hosts.  Looked at differently, we appear to be
moving toward a situation in which the number of delegated domains on
the Internet is approaching or exceeding the number of hosts. This
presumably results from synomyms or aliases that map a great many names
onto a smaller number of hosts.  While experience up to this time has
shown that the DNS is robust enough --given contemporary machines as
servers and current bandwidth norms-- to be able to continue to operate
reasonably well when those historical assumptions are not met (e.g.,
with a flat, structure under ".COM" containing well over ten million
delegated subdomains [COMSIZE]), it is still useful to remember that the
system could have been designed to work optimally with a flat structure
(and very large zones) rather than a deeply hierarchical one, and was
not.

Similarly, despite some early speculation about entering people's names
and email addresses into the DNS directly (e.g., see [RFC1034]),
electronic mail addresses in the Internet have preserved the original,
pre-DNS, "user (or mailbox) at location" conceptual format rather than a
flatter or strictly dot-separated one.  Location, in that instance, is a
reference to a host. The sole exception, at least in the "IN" class, has
been one field of the SOA record.


Both the DNS architecture itself and the two-level (host name and
mailbox name) provisions for email and similar functions (e.g., see
the finger protocol [FINGER]), also anticipated a relatively high
ratio of users to actual hosts.  Despite the observation in RFC 1034
that the DNS was expected to grow to be proportional to the number of
users (section 2.3), it has never been clear that the DNS was
seriously designed for, or could, scale to the order of magnitude of
number of users (or, more recently, products or document objects),
rather than that of physical hosts.

Just as was the case for the host table before it, the DNS provided
critical uniqueness for names, and universal accessibility to them,
as part of overall "single internet" and "end to end" models (cf
[RFC2826]).  However, there are many signs that, as new uses evolved
and original assumptions were abused (if not violated outright), the
system was being stretched to, or beyond, its practical limits.

The original design effort that led to the DNS included examination of
the directory technologies available at the time.  The design group
concluded that the DNS design, with its simplifying assumptions and
restricted capabilities, would be feasible to deploy and make
adequately robust, which the more comprehensive directory approaches
were not.  At the same time, some of the participants feared that the
limitations might cause future problems; this document essentially
takes the position that they were probably correct.  On the other
hand, directory technology and implementations have evolved
significantly in the ensuing years: it may be time to revisit the
assumptions, either in the context of the two- (or more) level
mechanism contemplated by the rest of this document or, even more
radically, as a path toward a DNS replacement.



1.3 The Web and User-visible Domain Names

>From the standpoint of the integrity of the domain name system --and
scaling of the Internet, including optimal accessibility to content--
the web design decision to use "A record" domain names directly in URLs,
rather than some system of indirection, has proven to be a serious
mistake in several respects.  Convenience of typing, and the desire to
make domain names out of easily-remembered product names, has led to a
flattening of the DNS, with many people now perceiving that second-level
names under COM (or in some countries, second- or third-level names
under the relevant ccTLD) are all that is meaningful.  This perception
has been reinforced by some domain name registrars [REGISTRAR] who have
been anxious to "sell" additional names.  And, of course, the perception
that one needed a second-level (or even top-level) domain per product,
rather than having names associated with a (usually organizational)
collection of network resources, has led to a rapid acceleration in the
number of names being registered.  That acceleration has, in turn,
clearly benefited registrars charging on a per-name basis,
"cybersquatters", and others in the business of "selling" names, but it
has not obviously benefited the Internet as a whole.

This emphasis on second-level domain names has also created a problem
for the trademark community.  Since the Internet is international, and
names are being populated in a flat and unqualified space,
similarly-named entities are in conflict even if there would ordinarily
be no chance of confusing them in the marketplace.  The problem appears
to be unsolvable except by a choice between draconian measures.  These
might include significant changes to the legislation and conventions
that govern disputes over "names" and "marks".  Or they might result in
a situation in which the "rights" to a name are typically not settled
using the subtle and traditional product (or industry) type and
geopolitical scope rules of the trademark system.  Instead they have
depended largely on political or economic power, e.g., the organization
with the greatest resources to invest in defending (or attacking) names
will ultimately win out.  The latter raises not only important issues of
equity, but also the risk of backlash as the numerous small players are
forced to relinquish names they find attractive and to adopt
less-desirable naming conventions.

Independent of these sociopolitical problems, content distribution
issues have made it clear that it should be possible for an
organization to have copies of data it wishes to make available
distributed around the network, with a user who asks for the
information by name getting the topologically-closest copy.  This is
not possible with simple, as-designed, use of the DNS: DNS names
identify target resources or, in the case of email "MX" records, a
preferentially-ordered list of resources "closest" to a target (not
to the source/user).  Several technologies (and, in some cases,
corresponding business models) have arisen to work around these
problems, including intercepting and altering DNS requests so as to
point to other locations.

Additional implications are still being discovered and evaluated.

Approaches that involve interception of DNS queries and rewriting of DNS
names (or otherwise altering the resolution process based on the
topological location of the user) seem, however, to risk disrupting
end-to-end applications in the general case and raise many of the issues
discussed by the IAB in [IAB-OPES].  These problems occur even if the
rewriting machinery is accompanied by additional workarounds for
particular applications.  For example, security associations and
applications that need to identify "the same host" often run into
problems if DNS names or other references are changed in the network
without participation of the applications that are trying to invoke the
associated services.


1.4 Internet Applications Protocols and Their Evolution

At the applications level, few of the protocols in active, widespread,
use on the Internet reflect either contemporary knowledge in computer
science or human factors or experience accumulated through deployment
and use.  Instead, protocols tend to be deployed at a
just-past-prototype level, typically including the types of expedient
compromises typical with prototypes.  If they prove useful, the nature
of the network permits very rapid dissemination (i.e., they fill a
vacuum, even if a vacuum that no one previously knew existed).  But,
once the vacuum is filled, the installed base provides its own
inertia: unless the design is so seriously faulty as to prevent
effective use (or there is a widely-perceived sense of impending
disaster unless the protocol is replaced), future developments must
maintain backward compatibility and workarounds for problematic
characteristics rather than benefiting from redesign in the light of
experience.  Applications that are "almost good enough" prevent
development and deployment of high-quality replacements.  

The DNS is both an illustration of, and an exception to, parts of this
pessimistic interpretation. It was a second-generation development, with
the host table system being seen as at the end of its useful life.
There was a serious attempt made to reflect the computing state of the
art at the time.  However, deployment was much slower than expected (and
very painful for many sites) and some fixed (although relaxed several
times) deadlines from a central network administration were necessary
for deployment to occur at all.  Replacing it now, in order to add
functionality, while it continues to perform its core functions at least
reasonable well, would presumably be extremely difficult.

There are many, perhaps obvious, examples of this.  Despite many known
deficiencies and weaknesses of definition, the "finger" and "whois"
[WHOIS] protocols have not been replaced (despite many efforts to
update or replace the latter [WHOIS-UPDATE]).  The Telnet protocol and
its many options drove out the SUPDUP [RFC734] one, which was arguably
much better designed for a diverse collection of network hosts.  A
number of efforts to replace the email or file transfer protocols with
models which their advocates considered much better have failed.  And,
more recently and below the applications level, there is some reason
to believe that this resistance to change has been one of the factors
impeding IPv6 deployment.



2. Signs of DNS Overloading

Parts of the historical discussion above identify areas in which the DNS
has become overloaded (semantically if not in the mechanical ability to
resolve names).  Despite this overloading, it appears that DNS
performance and reliability are still within an acceptable range: there
is little evidence of serious performance degradation.  Recent proposals
and mechanisms to better respond to overloading and scaling issues have
all focused on patching or working around limitations that develop when
the DNS is utilized for out-of-design functions, rather than on dramatic
rethinking of either DNS design or those uses. The number of these
issues that have arisen at much the same time may argue for just that
type of rethinking, and not just for adding complexity and attempting to
incrementally alter the design (see, for example, the discussion of
simplicity in section 2 of [RFC3439]).

For example:

o While technical approaches such as larger and higher-powered
servers and more bandwidth, and legal/political mechanisms such as
dispute resolution policies, have arguably kept the problems from
becoming critical, the DNS has not proven adequately responsive to
business and individual needs to describe or identify things (such as
product names and names of individuals) other than strict network
resources.

o While stacks have been modified to better handle multiple addresses
on a physical interface and some protocols have been extended to
include DNS names for determining context, the DNS does not deal
especially well with many names associated with a given host (needed
for, e.g. web hosting facilities with multiple domains on a server).

o Efforts to add names deriving from languages or character sets
based on other than simple ASCII and English-like names (see below),
or even to utilize complex company or product names without the use
of hierarchy, have created apparent requirements for names (labels)
that are over 63 octets long.  This requirement will undoubtedly
increase over time; while there are workarounds to accomodate longer
names, they impose their own restrictions and cause their own
problems.

o Increasing commercialization of the Internet, and visibility of domain
names that are assumed to match names of companies or products, has
turned the DNS and DNS names into a trademark battleground.  The
traditional trademark system in (at least) most countries makes careful
distinctions about fields of applicability.  When the space is
flattened, without differentation by either geography or industry
sector, not only are there likely conflicts between "Joe's Pizza" (of
Boston) and "Joe's Pizza" (of San Francisco) but between both and "Joe's
Auto Repair" (of Los Angeles).  All three would like to control
"Joes.com" (and would prefer, if it were permitted by DNS naming rules,
to spell it as "Joe's.com" and have both resolve the same way) and may

claim trademark rights to do so, even though conflict or confusion would
not occur with traditional trademark principles.

o Many organizations wish to have different web sites under the same
URL and domain name.  Sometimes this is to create local variations
--the Widget Company might want to present different material to a UK
user relative to a US one-- and sometimes it is to provide higher
performance by supplying information from the server topologically
closest to the user.  If the name resolution mechanism is expected to
provide this functionality, there are three possible models (which
might be combined):

	- supply information about multiple sites (or locations or
	references).  Those sites would, in turn, provide information
	associated with the name and sufficient site-specific attributes to
	permit the application to make a sensible choice of destination, or 

	- accept client-site attributes and utilize them in the search
	process, or

	- return different answers based on the location or identity of the
	requestor.

While there are some tricks that can provide partial simulations of
these types of function, DNS responses cannot be reliably conditioned in
this way.

These, and similar, issues of performance or content choices can, of
course, be thought of as not involving the DNS at all.  For example,
the commonly-cited alternate approach of coupling these issues to HTTP
content negotiation (cf. [RFC2295]), requires that an HTTP connection
first be opened to some "common" or "primary" host so that preferences
can be negotiated and then the client redirected or sent alternate
data.  At least from the standpoint of improving performance by
accessing a "closer" location, both initially and thereafter, this
approach sacrifices the desired result before the client initiates any
action.  It could even be argued that some of the characteristics of
common content negotiation approaches are workarounds for the
non-optimal use of the DNS in web URLs.

o Many existing and proposed systems for "finding things on the
Internet" require a true search capability in which near matches can
be reported to the user (or to some user agent with an apppropriate
rule-set) and to which queries may be ambiguous or fuzzy.  The DNS, by
contrast, can accomodate only one set of (quite rigid) matching rules.
Proposals to permit different rules in different localities (e.g.,
matching rules that are TLD- or zone-specific) help to identify the
problem.  But they cannot be applied directly to the DNS without
either abandoning the desired level of flexibility or isolating
different parts of the Internet from each other (or both).  Fuzzy or
ambiguous searches are desirable for resolution of names that might
have spelling variations and for names that can be resolved into
different sets of glyphs depending on context.  Especially when
internationalization is considered, variant name problems go beyond
simple differences in representation of a character or ordering of a

string.  Instead, avoiding user astonishment and confusion requires
consideration of relationships such as languages that can be written
with different alphabets, Kanji-Hiragana relationships, Simplified and
Traditional Chinese, etc.  See [Seng] for a discussion and suggestions
for addressing a subset of these issues in the context of characters
based on Chinese ones.  But that document essentially illustrates the
difficulty of providing the type of flexible matching that would be
anticipated by users; instead, it tries to protect against the worst
types of confusion (and opportunities for fraud).

o The historical DNS, and applications that make assumptions about how
it works, impose significant risk (or forces technical kludges and
consequent odd restrictions), when one considers adding mechanisms for
use with various multi-character-set and multilingual
"internationalization" systems.  See the IAB's discussion of some of
these issues [RFC2825] for more information.

o In order to provide proper functionality to the Internet, the DNS
must have a single unique root (the IAB provides more discussion of
this issue [RFC2826]).  There are many desires for local treatment of
names or character sets that cannot be accomodated without either
multiple roots (e.g., a separate root for multilingual names, proposed
at various times by MINC [MINC] and others), or mechanisms that would
have similar effects in terms of Internet fragmentation and isolation.

o For some purposes, it is desirable to be able to search not only an
index entry (labels or fully-qualified names in the DNS case), but their
values or targets (DNS data).  One might, for example, want to locate
all of the host (and virtual host) names which cause mail to be directed
to a given server via MX records.  The DNS does not support this
capability (see the discussion in [IQUERY]) and it can be simulated only
by extracting all of the relevant records (perhaps by zone transfer if
the source permits doing so -- which is becoming less frequently
available) and then searching a file built from those records.

o Finally, as additional types of personal or identifying information
are added to the DNS, issues arise with protection of that
information.  There are increasing calls to make different information
available based on the credentials and authorization of the source of
the inquiry.  As with information keyed to site locations or proximity
(as discussed above), the DNS protocols make providing these
differentiated services quite difficult if not impossible.

In each of these cases, it is, or might be, possible to devise ways
to trick the DNS system into supporting mechanisms that were not
designed into it.  Several ingenious solutions have been proposed in
many of these areas already, and some have been deployed into the
marketplace with some success.  But the price of each of these changes
is added complexity and, with it, added risk of unexpected and
destabilizing problems.

Several of the above problems are addressed well by a good directory
system (supported by the LDAP protocol or some protocol more precisely
suited to these specific applications) or searching environment (such
as common web search engines) although not by the DNS.  Given the

difficulty of deploying new applications discussed above, an important
question is whether the tricks and kludges are bad enough, or will
become bad enough as usage grows, that new solutions are needed and
can be deployed.



3. Searching, Directories, and the DNS

3.1 Overview 

The constraints of the DNS and the discussion above suggest the
introduction of an intermediate protocol mechanism, referred to below
as a "search layer" or "searchable system".  The terms "directory" and
"directory system" are used interchangeably with "searchable system"
in this document, although the latter is far more precise.  Search
layer proposals would use a two (or more) -stage lookup, not unlike
several of the proposals for internationalized names in the DNS (see
section 4), but all operations but the final one would involve
searching other systems, rather than looking up identifiers in the DNS
itself.  As explained below, this would permit relaxation of several
constraints, leading to a more capable and comprehensive overall
system.

Ultimately, many of the issues with domain names arise as the result
of efforts to use the DNS as a directory.  While, at the time this
document was written, sufficient pressure or demand had not occurred
to justify a change, it was already quite clear that, as a directory
system, the DNS is a good deal less than ideal.  This document
suggests that there actually is a requirement for a directory system,
and that the right solution to a searchable system requirement is a
searchable system, not a series of DNS patches, kludges, or
workarounds.

The following points illustrate particular aspects of this conclusion.

o A directory system would not require imposition of particular
length limits on names.

o A directory system could permit explicit association of attributes,
e.g., language and country, with a name, without having to utilize
trick encodings to incorporate that information in DNS labels (or
creating artificial hierarchy for doing so).

o There is considerable experience (albeit not much of it very
successful) in doing fuzzy and "sonex" (similar-sounding) matching in
directory systems.  Moreover, it is plausible to think about different
matching rules for different areas and sets of names so that these can
be adapted to local cultural requirements.  Specifically, it might be
possible to have a single form of a name in a directory, but to have
great flexibility about what queries matched that name (and even have
different variations in different areas).  Of course, the more
flexibility that a system provides, the greater the possibility of
real or imagined trademark conflicts.  But the opportunity would exist
to design a directory structure that dealt with those issues in an

intelligent way, while DNS constraints almost certainly make a general
and equitable DNS-only solution impossible.

o If a directory system is used to translate to DNS names, and then
DNS names are looked up in the normal fashion, it may be possible to
relax several of the constraints that have been traditional (and
perhaps necessary) with the DNS.  For example, reverse-mapping of
addresses to directory names may not be a requirement even if mapping
of addresses to DNS names continues to be, since the DNS name(s) would
(continue to) uniquely identify the host.

o Solutions to multilingual transcription problems that are common in
"normal life" (e.g., two-sided business cards to be sure that
recipients trying to contact a person can access romanized spellings
and numbers if the original language is not comprehensible to them)
can be easily handled in a directory system by inserting both sets of
entries.

o A directory system could be designed that would return, not a
single name, but a set of names paired with network-locational
information or other context-establishing attributes.  This type of
information might be of considerable use in resolving the "nearest
(or best) server for a particular named resource" problems that are a
significant concern for organizations hosting web and other sites
that are accessed from a wide range of locations and subnets.

o Names bound to countries and languages might help to manage
trademark realities, while, as discussed in section 1.3 above, use of
the DNS in trademark-significant contexts tends to require worldwide
"flattening" of the trademark system. 

Many of these issues are a consequence of another property of the DNS:
names must be unique across the Internet.  The need to have a system
of unique identifiers is fairly obvious (see [RFC2826]).  However, if
that requirement were to be eliminated in a search or directory system
that was visible to users instead of the DNS, many difficult problems
-- of both an engineering and a policy nature -- would be likely to
vanish.


3.2 Some Details and Comments

Almost any internationalization proposal for names that are in, or map
into, the DNS will require changing DNS resolver API calls
("gethostbyname" or equivalent), or adding some pre-resolution
preparation mechanism, in almost all Internet applications -- whether
to cause the API to take a different character set (no matter how it
is then mapped into the bits used in the DNS or another system), to
accept or return more arguments with qualifying or identifying
information, or otherwise.  Once applications must be opened to make
such changes, it is a relatively small matter to switch from calling
into the DNS to calling a directory service and then the DNS (in many
situations, both actions could be accomplished in a single API call).


A directory approach can be consistent both with "flat" models and
multi-attribute ones.  The DNS requires strict hierarchies, limiting its
ability to differentiate among names by their properties.  By contrast,
modern directories can utilize independently-searched attributes and
other structured schema to provide flexibilities not present in a
strictly hierarchical system.

There is a strong historical argument for a single directory structure
(implying a need for mechanisms for registration, delegation, etc.).
But a single structure is not a strict requirement, especially if
in-depth case analysis and design work leads to the conclusion that
reverse-mapping to directory names is not a requirement (see section 4).
If a single structure is not needed, then, unlike the DNS, there would
be no requirement for a global organization to authorize or delegate
operation of portions of the structure.

The "no single structure" concept could be taken further by moving away
from simple "names" in favor of, e.g., faceted systems in which most of
the facets use restricted vocabularies. (These terms are fairly standard
in the information retrieval and classification system literature, see,
e.g., [IS5127].)  Such systems could be designed to avoid the need for
procedures to ensure uniqueness across, or even within, providers and
databases of the faceted entities being searched for.  (Cf. [DNS-Search]
for further discussion.)

While the discussion above includes very general comments about
attributes, it appears that only a very small number of attributes would
be needed.  The list would almost certainly include country and language
for internationalization purposes.  It might require "charset" if we
cannot agree on a character set and encoding, although there are strong
arguments for simply using ISO 10646 (also known as Unicode or "UCS"
(for Universal Character Set) [UNICODE, IS10646] coding in interchange.
Trademark issues might motivate "commercial" and "non-commercial" (or
other) attributes if they would be helpful in bypassing trademark
problems.  And applications to resource location, such as those
contemplated for Uniform Resource Identifiers (URIs) [RFC2396, RFC3305]
or the Service Location Protocol [RFC2608], might argue for a few other
attributes (as outlined above).


4.  Internationalization

Much of the thinking underlying this document was driven by
considerations of internationalizing the DNS or, more specifically,
providing access to the functions of the DNS from languages and naming
systems that cannot be accurately expressed in the traditional DNS
subset of ASCII.  Much of the relevant work was done in the IETF's
"Internationalized Access to Domain Names" Working Group (IDN-WG),
although this document also draws on extensive parallel discussions in
other forums.  This section contains an evaluation of what was learned
as an "internationalized DNS" or "multilingual DNS" was explored and
suggests future steps based on that evaluation.

When the IDN-WG was initiated, it was obvious to several of the
participants that its first important task was an undocumented one: to

increase the understanding of the complexities of the problem
sufficiently that naive solutions could be rejected and people could
go to work on the harder problems.  The IDN-WG clearly accomplished
that task. The beliefs that the problems were simple, and in the
corresponding simplistic approaches and their promises of quick and
painless deployment, effectively disappeared as the WG's efforts
matured.

Some of the lessons learned from increased understanding and the
dissipation of naive beliefs should be taken as cautions by the wider
community: the problems are not simple. Specifically, extracting small
elements for solution rather than looking at whole systems, may result
in obscuring the problems but not solving any problem that is worth the
trouble.

4.1 ASCII Isn't Just Because of English

The hostname rules chosen in the mid-70s weren't just "ASCII because
English uses ASCII", although that was a starting point.  We have
discovered that almost every other script (and even ASCII if we permit
the rest of the characters specified in the ISO 646 International
Reference Version) is more complex than hostname-restricted-ASCII
[ASCII] (the "LDH" form, see section 1.1).  And ASCII isn't sufficient
to completely represent English -- there are several words in the
language that are correctly spelled only with characters or diacritical
marks that do not appear in ASCII.  With a broader selection of scripts,
in some examples, case mapping works from one case to the other but is
not reversible.  In others, there are conventions about alternate ways
to represent characters (in the language, not [only] in character
coding) that work most of the time, but not always.  And there are
issues in coding, with Unicode/10646 providing
different ways to represent the same character ("character", rather than
"glyph", is used deliberately here).  And, in still others, there are
questions as to whether two glyphs "match", which may be a
distance-function question, not one with a binary answer.  The IETF
approach to these problems is to require pre-matching canonicalization
(see the "stringprep" discussion below).

The IETF has resisted the temptations to either try to specify an
entirely new coded character set, or to pick and choose Unicode/10646
characters on a per-character basis rather than by using well-defined
blocks.  While it may appear that a character set designed to meet
Internet-specific needs would be very attractive, the IETF has never had
the expertise, resources, and representation from critically-important
communities to actually take on that job.  Perhaps more important, a new
effort might have chosen to make some of the many complex tradeoffs
differently than the Unicode committee did, producing a code with
somewhat different characteristics.  But there is no evidence that doing
so would produce a code with fewer problems and side-effects.  It is
much more likely that making tradeoffs differently would simply result
in a different set of problems, which would be equally or more
difficult.


4.2.  The "ASCII Encoding" Approaches

While the DNS can handle arbitrary binary strings without known internal
problems (see [RFC2181]), some restrictions are imposed by the
requirement that text be interpreted in a case-independent way
([RFC1034], [RFC1035]).  More important, most internet applications
assume the hostname-restricted "LDH" syntax specified in the host table
RFCs and as "prudent" in RFC 1035.  If those assumptions are not met,
many conforming implementations of those applications may exhibit
behavior that would surprise implementors and users.  To avoid these
potential problems, IETF internationalization work has focused on
"ASCII-Compatible Encodings" (ACE).  These encodings preserve the LDH
conventions in the DNS itself.  Implementations of applications that
have not been upgraded utilize the encoded forms, while newer ones can
be written to recognize the special codings and map them into non-ASCII
characters. These approaches are, however, not problem-free even if
human interface issues are ignored.  Among other issues, they rely on
what is ultimately a heuristic to determine whether a DNS label is to be
considered as an internationlized name (i.e., encoded Unicode) or
interpreted as an actual LDH name in its own right.  And, while all
determinations of whether a particular query matches a stored object are
traditionally made by DNS servers, the ACE systems, when combined with
the complexities of international scripts and names, require that much
of the matching work be separated into a separate, client-side,
canonicalization or "preparation" process before the DNS matching
mechanisms are invoked [STRINGPREP].

4.3.  "Stringprep" and Its Complexities

As outlined above, the model for avoiding problems associated with
putting non-ASCII names in the DNS and elsewhere evolved into the
principle that strings are to be placed into the DNS only after being
passed through a string preparation function that eliminates or
rejects spurious character codes, maps some characters onto others,
performs some sequence canonicalization, and generally creates forms
that can be accurately compared.  The impact of this process on
hostname-restricted ASCII (i.e., "LDH") strings is trivial and
essentially adds only overhead.  For other scripts, the impact is, of
necessity, quite significant.

Although the general notion underlying stringprep is simple, the many
details are quite subtle and the associated tradeoffs are complex. A
design team worked on it for months, with considerable effort placed
into clarifying and fine-tuning the protocol and tables.  Despite
general agreement that the IETF would avoid getting into the business
of defining character sets, character codings, and the associated
conventions, the group several times considered and rejected special
treatment of code positions to more nearly match the distinctions made
by Unicode with user perceptions about similarities and differences
between characters.  But there were intense temptations (and
pressures) to incorporate language-specific or country-specific rules.
Those temptations, even when resisted, were indicative of parts of the
ongoing controversy or of the basic unsuitability of the DNS for fully
internationalized names that are visible, comprehensible, and
predictable for end users.


There have also been controversies about how far one should go in
these processes of preparation and transformation and, ultimately,
about the validity of various analogies.  For example, each of the
following operations has been claimed to be similar to case-mapping in
ASCII: 

o stripping of vowels in Arabic or Hebrew

o matching of "look-alike" characters such as upper-case Alpha in Greek
and upper-case A in Roman-based alphabets

o matching of Traditional and Simplified Chinese characters that
represent the same words,

o matching of Serbo-Croatian words whether written in Roman-derived or
Cyrillic characters

A decision to support any of these operations would have implications
for other scripts or languages and would increase the overall
complexity of the process.  For example, unless language-specific
information is somehow available, performing matching between
Traditional and Simplified Chinese has impacts on Japanese and Korean
uses of the same "traditional" characters: e.g., it would not be
appropriate to map Kanji into Simplified Chinese.

Even were the IDN-WG's other work to have been abandoned completely or
if it were to fail in the marketplace, the stringprep and nameprep work
will continue to be extremely useful, both in identifying issues and
problem code points and in providing a reasonable set of basic rules.
Where problems remain, they are arguably not with nameprep, but with the
DNS-imposed requirement that its results, as with all other parts of the
matching and comparison process, yield a binary "match or no match"
answer, rather than, e.g., a value on a similarity scale that can be
evaluated by the user or by user-driven heuristic functions.


4.4 The Unicode Stability Problem

ISO 10646 basically defines only code points, and not rules for using or
comparing the characters.  This is part of a long-standing tradition
with the work of what is now ISO/IEC JTC1/SC2: they have performed code
point assignments and have typically treated the ways in which
characters are used as beyond their scope.  Consequently, they have not
dealt effectively with the broader range of internationalization issues.
By constrast, the Unicode Technical Committee (UTC) has defined, in
annexes and technical reports (see, e.g., [UTR15]), some additional
rules for canonicalization and comparision.  Many of those rules and
conventions have been factored into the "stringprep" and "nameprep"
work, but it is not straightforward to make or define them in a fashion
that is sufficiently precise and permanent to be relied on by the DNS.

Perhaps more important, the discussions leading to nameprep also
identified several areas in which the UTC definitions are inadequate, at
least without additional information, to make matching precise and

unambiguous.  In some of these cases, the Unicode Standard permits
several alternate approaches, none of which are an exact and obvious
match to DNS needs.  That has left these sensitive choices up to IETF,
which lacks sufficient in-depth expertise, much less any mechanism for
deciding to optimize one language at the expense of another.

For example, it is tempting to define some rules on the basis of
membership in particular scripts, or for punctuation characters, but
there is no precise definition of what characters belong to which script
or which ones are, or are not, punctuation.  The existence of these
areas of vagueness raises two issues: whether trying to do precise
matching at the character set level is actually possible (addressed
below) and whether driving toward more precision could create issues
that cause instability in the implementation and resolution models for
the DNS.

The Unicode definition also evolves.  Version 3.2 appeared shortly after
work on this document was initiated.  It added some characters and
functionality and included a few minor incompatible code point changes.
IETF has secured an agreement about constraints on future changes, but
it remains to be seen how that agreement will work out in practice.  The
prognosis actually appears poor at this stage, since UTC chose to ballot
a recent possible change which should have been prohibited by the
agreement (the outcome of the ballot is not relevant, only that the
ballot was issued rather than having the result be a foregone
conclusion).  However, some members of the community consider some of
the changes between Unicode 3.0 and 3.1 and between 3.1 and 3.2, as well
as this recent ballot, to be evidence of instability and that these
instabilities are better handled in a system that can be more flexible
about handling of characters, scripts, and ancillary information than
the DNS.

In addition, because the systems implications of internationalization
are considered out of scope in SC2, ISO/IEC JTC1 has assigned some of
those issues to its SC22/WG20 (the Internationalization working group
within the subcommittee that deals with programming languages, systems,
and environments).  WG20 has historically dealt with
internationalization issues thoughtfully and in depth, but its status
has several times been in doubt in recent years.  However, assignment of
these matters to WG20 increases the risk of eventual ISO
internationalization standards that specify different behavior than the
UTC specifications.

4.5. Audiences, End Users, and the User Interface Problem

Part of what has "caused" the DNS internationalization problem, as
well as the DNS trademark problem and several others, is that we have
stopped thinking about "identifiers for objects" -- which normal
people are not expected to see -- and started thinking about "names"
-- strings that are expected not only to be readable, but to have
linguistically-sensible and culturally-dependent meaning to
non-specialist users.

Within the IETF, the IDN-WG, and sometimes other groups, avoided
addressing the implications of that transition by taking "outside our

scope -- someone else's problem" approaches or by suggesting that
people will just become accustomed to whatever conventions are
adopted.  The realities of user and vendor behavior suggest that these
approaches will not serve the Internet community well in the long
term:

o If we want to make it a problem in a different part of the user
interface structure, we need to figure out where it goes in order to
have proof of concept of our solution.  Unlike vendors whose sole
[business] model is the selling or registering of names, the IETF must
produce solutions that actually work, in the applications context as
seen by the end user. 

o The principle that "they will get used to our conventions and adapt"
is fine if we are writing rules for programming languages or an API.
But the conventions under discussion are not part of a semi-
mathematical system, they are deeply ingrained in culture.  No matter
how often an English-speaking American is told that the Internet
requires that the correct spelling of "colour" be used, he or she isn't
going to be convinced. Getting a French-speaker in Lyon to use exactly
the same lexical conventions as a French-speaker in Quebec in order to
accomodate the decisions of the IETF or of a registrar or registry is
just not likely.  "Montreal" is either a misspelling or an anglicization
of a similar word with an acute accent mark over the "e" (i.e., using
the Unicode character U+00E9 or one of its equivalents). But global
agreement on a rule that will determine whether the two forms should
match --and that won't astonish end users and speakers of one language
or the other-- is as unlikely as agreement on whether "misspelling" or
"anglicization" is the greater travesty.

More generally, it is not clear that the outcome of any conceivable
nameprep-like process is going to be good enough for practical,
user-level, use.  In the use of human languages by humans, there are
many cases in which things that do not match are nonetheless
interpreted as matching.  The Norwegian/Danish character that appears
in U+00F8 (visually, a lower case 'o' overstruck with a forward slash)
and the German character that appears in U+00F6 (visually, a lower
case 'o' with diaeresis (or umlaut)) are clearly different and no
matching program should yield an "equal" comparison.  But they are
more similar to each other than either of them is to, e.g., "e".
Humans are able to mentally make the correction in context, and do so
easily, and they can be surprised if computers cannot do so.  Worse, there
is a Swedish character whose appearance is identical to the German
o-umlaut, and which shares code point U+00F6, but that, if the
languages are known and the sounds of the letters or meanings of words
including the character are considered, actually should match the
Norwegian/Danish use of U+00F8.

This text uses examples in Roman scripts because it is being written in
English and those examples are relatively easy to render.  But one of
the important lessons of the discussions about domain name
internationalization in recent years is that problems similar to those
described above exist in almost every language and script.  Each one has
its idiosyncracies, and each set of idiosyncracies is tied to common
usage and cultural issues that are very familiar in the relevant group,

and often deeply held as cultural values.  As long as a schoolchild in
the US can get a bad grade on a spelling test for using a perfectly
valid British spelling, or one in France or Germany can get a poor grade
for leaving off a diacritical mark, there are issues with the relevant
language.  Similarly, if children in Egypt or Israel are taught that it
is acceptable to write a word with or without vowels or stress marks,
but that, if those marks are included, they must be the correct ones, or
a user in Korea is potentially offended or astonished by out-of-order
sequences of Jamo, systems based on character-at-a-time processing and
simplistic matching, with no contextual information, are not going to
satisfy user needs.  

Users are demanding solutions that deal with language and culture.
Systems of identifier symbol-strings that serve specialists or
computers are, at best, a solution to a rather different (and, at the
time this document was written, somewhat ill-defined), problem.  The
recent efforts have made it ever more clear that, if we ignore the
distinction between the user requirements and narrowly-defined
identifiers, we are solving an insufficient problem.  And, conversely,
the approaches that have been proposed to approximate solutions to the
user requirement may be far more complex than simple identifiers
require.


4.6 Business Cards and Other Natural Uses of Natural Languages

Over the last few centuries, local conventions have been established
in various parts of the world for dealing with multilingual
situations.  It may be helpful to examine some of these.  For example,
if one visits a country where the language is different from ones own,
business cards are often printed on two sides, one side in each
language.  The conventions are not completely consistent and the
technique assumes that recipients will be tolerant. Translations of
names or places are attempted in some situations and transliterations
in others.  Since it is widely understood that exact translations or
transliterations are often not possible, people typically smile at
errors, appreciate the effort, and move on.  

The DNS situation differs from these practices in at least two ways.
Since a global solution is required, the business card would need a
number of sides approximating the number of languages in the world,
which is probably impossible without violating laws of physics.  More
important, the opportunities for tolerance don't exist: the DNS
requires a exact match or the lookup fails.


4.7 ASCII Encodings and the Roman Keyboard Assumption
 
Part of the argument for ACE-based solutions is that they provide an
escape for multilingual environments when applications have not been
upgraded.  When an older application encounters an ACE-based name, the
assumption is that the (admittedly ugly) ASCII-coded string will be
displayed and can be typed in.  This argument is reasonable from the
standpoint of mixtures of Latin-based alphabets, but may not be
relevant if user-level systems and devices are involved that do not

support the entry of Roman-based characters or which cannot
conveniently render such characters.  Such systems are few in the
world today, but the number can reasonably be expected to rise as the
Internet is increasingly used by populations whose primary concern is
with local issues, local information, and local languages.  It is, for
example, fairly easy to imagine populations who use Arabic or Thai
scripts and who do not have routine access to scripts or input devices
based on Roman-derived alphabets.


4.8 Intra-DNS Approaches for "Multilingual Names"

It appears, from the cases above and others, that none of the
intra-DNS-based solutions for "multilingual names" are workable.  They
rest on too many assumptions that do not appear to be feasible -- that
people will adapt deeply-entrenched language habits to conventions
laid down to make the lives of computers easy; that we can make
"freeze it now, no need for changes in these areas" decisions about
Unicode and nameprep; that ACE will smooth over applications problems,
even in environments without the ability to key or render Roman-based
glyphs (or where user experience is such that such glyphs cannot
easily be distinguished from each other); that the Unicode Consortium
will never decide to repair an error in a way that creates a risk of
DNS incompatibility; that we can either deploy EDNS [RFC2671] or that
long names are not really important; that Japanese and Chinese
computer users (and others) will either give up their local or IS
2022-based character coding solutions (for which addition of a large
fraction of a million new code points to Unicode is almost certainly a
necessary, but probably not sufficient, condition) or build leakproof
and completely accurate boundary conversion mechanisms; that out of
band or contextual information will always be sufficient for the "map
glyph onto script" problem; and so on.  In each case, it is likely
that about 80% or 90% of cases will work satisfactorily, but it is
unlikely that such partial solutions will be good enough.  For
example, suppose someone can spell her name 90% correctly, or a
company name is matched correctly 80% of the time but the other 20% of
attempts identify a competitor: are either likely to be considered
adequate?


5. Search-based Systems: The Key Controversies

For many years, a common response to requirements to locate people or
resources on the Internet has been to invoke the term "directory".
While an in-depth analysis of the reasons would require a separate
document, the history of failure of these invocations has given
"directory" efforts a bad reputation.  The effort proposed here is
different from those predecessors for several reasons, perhaps the
most important of which is that it focuses on a fairly-well-understood
set of problems and needs, rather than on finding uses for a
particular technology.

As suggested in some of the text above, it is an open question as to
whether the needs of the community would be best served by a single
(even if functionally, and perhaps administratively, distributed)

directory with universal applicability, a single directory that
supports locally-tailored search (and, most important, matching)
functions, or multiple, locally-determined, directories.  Each has its
attractions.  Any but the first would essentially prevent
reverse-mapping (determination of the user-visible name of the host or
resource from target information such as an address or DNS name).  But
reverse mapping has become less useful over the years --at least to
users-- as more and more names have been associated with many host
addresses and as CIDR [CIDR] has proven problematic for mapping smaller
address blocks to meaningful names.  

Locally-tailored searchs and mappings would permit national variations
on interpretation of which strings matched which other ones, an
arrangement that is especially important when different localities
apply different rules to, e.g., matching of characters with and
without diacriticals.  But, of course, this implies that a URL may
evaluate properly or not depending on either settings on a client
machine or the network connectivity of the user.  That is not, in
general, a desirable situation, since it implies that users could not,
in the general case, share URLs (or other host references) and that a
particular user might not be able to carry references from one host or
location to another.

And, of course, completely separate directories would permit
translation and transliteration functions to be embedded in the
directory, giving much of the Internet a different appearance
depending on which directory was chosen.  The attractions of this are
obvious, but, unless things were very carefully designed to preserve
uniqueness and precise identities at the right points (which may or
may not be possible), such a system would have many of the
difficulties associated with multiple DNS roots.

Finally, a system of separate directories and databases, if coupled
with removal of the DNS-imposed requirement for unique names, would
largely eliminate the need for a single worldwide authority to manage
the top of the naming hierarchy.
 

6.  Security Considerations

The set of proposals implied by this document suggests an interesting
set of security issues (i.e., nothing important is ever easy).  A
directory system used for locating network resources would presumably
need to be as carefully protected against unauthorized changes as the
DNS itself.  There also might be new opportunities for problems in an
arrangement involving two or more (sub)layers, especially if such a
system were designed without central authority or uniqueness of names.
It is uncertain how much greater those risks would be as compared to a
DNS lookup sequence that involved looking up one name, getting back
information, and then doing additional lookups potentially in different
subtrees.  That multistage lookup will often be the case with, e.g.,
NAPTR records [RFC 2915] unless additional restrictions are imposed.
But additional steps, systems, and databases almost certainly involve
some additional risks of compromise.



7.  References

7.1. Normative References

None

7.2. Explanatory and Informative References

[Albitz] Any of the editions of Albitz, P. and C. Liu, DNS and
BIND, O'Reilly and Associates, 1992, 1997, 1998, 2001.

[ASCII] American National Standards Institute (formerly United States
of America Standards Institute), X3.4, 1968, "USA Code for Information
Interchange". ANSI X3.4-1968 has been replaced by newer versions with
slight modifications, but the 1968 version remains definitive for the
Internet.  Some time after ASCII was first forumulated as a standard,
ISO adopted international standard 646, which uses ASCII as a base.
IS 646 actually contained two code tables: an "International Reference
Version" (often referenced as ISO 646-IRV) which was essentially
identical to the ASCII of the time, and a "Basic Version" (ISO
646-BV), which designates a number of character positions for national
use.   

[CIDR] See Fuller, V., T. Li, J. Yu, K. Varadhan "Classless
Inter-Domain Routing (CIDR): an Address Assignment and Aggregation
Strategy" , RFC 1519, September 1993 and Eidnes, H., G. de Groot, P.
Vixie, "Classless IN-ADDR.ARPA delegation", RFC 2317, March 1998.

[COM-SIZE] Size information supplied by Verisign Global Registry
Services (the zone administrator, or "registry operator", for COM, see
[REGISTRAR], below) to ICANN, third quarter 2002.

[DNS-Search] Klensin, J., "A Search-based access model for the DNS",
work in progress (draft-klensin-dns-search-05.txt)

[FINGER] Zimmerman, D., RFC 1288 "The Finger User Information Protocol". 
December 1991.  The original version of this protocol was outlined in
Harrenstien, K., RFC 742 "NAME/FINGER Protocol, Dec-30-1977.

[IAB-OPES] Floyd, S, and L. Daigle, Eds, IAB, RFC 3238 "IAB
Architectural and Policy Considerations for Open Pluggable Edge
Services", January 2002.

[IQUERY] Lawrence, D., "Obsoleting IQUERY", work in progress
(draft-ietf-dnsext-obsolete-iquery-04.txt).

[IS646] ISO/IEC 646:1991 Information technology -- ISO 7-bit coded
character set for information interchange 

[IS10646] ISO/IEC 10646-1:2000 Information technology -- Universal
Multiple-Octet Coded Character Set (UCS) -- Part 1: Architecture and
Basic Multilingual Plane and ISO/IEC 10646-2:2001 Information
technology -- Universal Multiple-Octet Coded Character Set (UCS) --
Part 2: Supplementary Planes 


[MINC] The Multilingual Internet Names Consortium,
http://www.minc.org/ has been an early advocate for the importance of
expansion of DNS names to accomodate non-ASCII characters.  Some of
their specific proposals, while helping people to understand the
problems better, were not compatible with the design of the DNS.

[NAPTR] Mealling, M. and R. Daniel, "The Naming Authority Pointer
(NAPTR) DNS Resource Record", RFC 2915, September 2000.

[REGISTRAR] In an early stage of the process that created the Internet
Corporation for Assigned Names and Numbers (ICANN), a "Green Paper"
was released by the US Government.   That paper introduced new
terminology and some concepts not needed by traditional DNS
operations.  The term "registry" was applied to the actual operator
and database holder of a domain (typically at the top level, since the
Green Paper was little concerned with anything else), while
organizations that marketed names and made them available to
"registrants" were known as "registrars".  In the classic DNS model,
the function of "zone administrator" encompassed both registry and
registrar roles, although that model did not anticipate a commercial
market in names.

[RFC625] Kudlick, M.D., E.J.  Feinler, "On-line hostnames service", RFC
625, March 1974.

[RFC734] Crispin, M.R.,  "SUPDUP Protocol", RFC 734, October 1977.

[RFC811] Harrenstien, K., V. White, E.J.  Feinler, "Hostnames Server"
RFC 811, March 1982.

[RFC819] Su, Z. and J. Postel, "Domain naming convention for Internet
user applications", RFC 819, August 1982.

[RFC830] Su, Z., "Distributed system for Internet name service", RFC
830, October 1982..

[RFC882] Mockapetris, P.V., "Domain names: Concepts and facilities", RFC
882, November 1983.  (This document was superceded by RFC1034, cited
below.)

[RFC883] Mockapetris, P.V., "Domain names: Implementation
specification", RFC 883, November 1983.  (This document was superceded
by RFC1035, cited below.)

[RFC952] Harrenstien, K, M.K. Stahl, E.J. Feinler, "DoD Internet host
table specification", RFC 952, October 1985.

[RFC1034] Mockapetris, P.V., "Domain names, Concepts and facilities",
RFC 1034, November 1987.

[RFC1035] Mockapetris, P.V., "Domain names - implementation and
specification", RFC 1035, November 1987.


[RFC1591] Postel, J., "Domain Name System Structure and Delegation", RFC
1591, March 1994.

[RFC2181] Elz, R., R.  Bush, "Clarifications to the DNS Specification",
RFC 2181, July 1997.

[RFC2295] Holtman, K. and A. Mutz, "Transparent Content Negotiation in
HTTP", RFC 2295, March 1998

[RFC2396] Berners-Lee, T., R. Fielding, L. Masinter, "Uniform Resource
Identifiers (URI): Generic Syntax", RFC 2396, August 1998.

[RFC2608] Guttman, E., C. Perkins, J.  Veizades, M. Day, "Service
Location Protocol, Version 2", RFC 2608, June 1999.

[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
August 1999.

[RFC2825] IAB, L. Daigle, ed., "A Tangled Web: Issues of I18N, Domain
Names, and the Other Internet protocols", RFC 2825, May 2000.

[RFC2826] IAB, "IAB Technical Comment on the Unique DNS Root", RFC 2826,
May 2000.

[RFC2972] Popp, N., M.  Mealling, L. Masinter, K. Sollins, "Context and
Goals for Common Name Resolution", RFC 2972, October 2000.

[RFC3305] Mealling, M., R.  Denenberg, Eds., "Report from the Joint
W3C/IETF URI Planning Interest Group: Uniform Resource Identifiers
(URIs), URLs, and Uniform Resource Names (URNs): Clarifications and
Recommendations", RFC 3305, August 2002.

[RFC3439] Bush, R., T. Griffin, D. Meyer, "Some Internet Architectural
Guidelines and Philosophy", RFC 3439, December 2002.

[Seng] Seng, J., et al., Eds., "Internationalized Domain Names:
Registration and Administration Guideline for Chinese, Japanese, and
Korean", work in progress (draft-jseng-idn-admin-01.txt, coming soon)

[STRINGPREP] The canonicalization processes described are profiles on
a set of tables and processing steps known collectively as
"stringprep" and described in Hoffman, P. and M. Blanchet,
"Preparation of Internationalized Strings ('stringprep')", work in
progress (draft-hoffman-stringprep-06.txt).  The particular profile
used for placing internationalized strings in the DNS is called
"nameprep", described in Hoffman, P. and M. Blanchet, "Nameprep: A
Stringprep Profile for Internationalized Domain Names", work in
progress (draft-ietf-idn-nameprep-11.txt).

[TELNET] See Postel, J. and J.K. Reynolds, RFC 854 "Telnet Protocol
Specification" and RFC 855 "Telnet Option Specifications",
May-01-1983, and many RFCs describing specific options.


[UNICODE] The Unicode Consortium, The Unicode Standard, Version 3.0,
Addison-Wesley: Reading, MA, 2000.   Update to version 3.1, 2001.
Update to version 3.2, 2002.

[UTR15] Davis, M. and M. Duerst, "Unicode Standard Annex #15: Unicode
Normalization Forms", Unicode Consortium, March 2002.  An integral part
of The Unicode Standard, Version 3.1.1.  Available at
(http://www.unicode.org/reports/tr15/tr15-21.html).

[WHOIS] Harrenstien, K, M.K. Stahl, E.J. Feinler, RFC 0954
"NICNAME/WHOIS", Oct-01-1985.

[WHOIS-UPDATE] See, for example, Gargano, J. and K. Weiss, RFC 1834
"Whois and Network Information Lookup Service, Whois++", August 1995;
Weider, C., J. Fullton, S. Spero, RFC 1913 "Architecture of the
Whois++ Index Service", February 1996; Williamson, S., M. Kosters, D.
Blacka, J. Singh, K. Zeilstra. RFC 2167 "Referral Whois (RWhois)
Protocol V1.5", June 1997; and Daigle, L. and P. Faltstrom, RFC 2957
"The application/whoispp-query Content-Type" and RFC 2958 "The
application/whoispp-response Content-type", October 2000.

[X29] International Telecommuncations Union, "Recommendation X.29:
Procedures for the exchange of control information and user data
between a Packet Assembly/Disassembly (PAD) facility and a packet mode
DTE or another PAD", December 1997.


8. Acknowledgements

Many people have contributed to versions of this document or the
thinking that went into it.  The author would particularly like to
thank Harald Alvestrand, Rob Austein, Bob Braden, Matt Crawford,
Leslie Daigle, Patrik Faltstrom, Eric A. Hall, Ted Hardie, and Paul
Hoffman for making specific suggestions and/or challenging the
assumptions and presentation of earlier versions and suggesting ways
to improve them.


9. Author's Address

John C Klensin
1770 Massachusetts Ave, #322
Cambridge, MA 02140
klensin+srch@jck.com

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Expires July 2003