INTERNET-DRAFT                                John C. Klensin
May 28, 2001
Expires November 2001


                  Role of the Domain Name System
                 draft-klensin-dns-role-01.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
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This document represents a summary of the personal opinions of the
author on the subject covered and is not intended to evolve into a
standard of any kind.

Copyright Notice

Copyright (C) The Internet Society (2000).  All Rights Reserved.



0. Abstract

The original function and purpose of the DNS is reviewed, and
contrasted with some of the functions into which it is being forced
today 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.

A mailing list has been initiated for discussion of this draft,
its successors, and closely-related issues at
ietf-i18n-dns-directory@imc.org.   See
http://www.imc.org/ietf-i18n-dns-directory/ for subscription
and archival information.


1. History

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 we got to where we are today, but they probably don't, of
themselves, invalidate the inferences and conclusions.

1.1  Context for DNS development

During the entire 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, 811, 952].  This table was just a list in an
agreed-upon format; sites were expected to frequently obtain copies
of, and install, new versions.  The host tables themselves were
introduced to

  * 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.

  * 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.

  * Some hosts (so-called "multihomed" ones) needed multiple
  addresses to reflect different types of connectivity and topology.
  Again, the names were very useful for avoiding the requirement that
  would otherwise exist for users and other hosts to track these
  multiple host numbers and addresses. 

Toward the end of that long (in network time) period, the community
concluded that the host table model did not scale adequately and that
it would not adequately support new service variations.  A working
group was created, and the DNS was the result of that effort.  The
role of the DNS was to preserve the capabilities of the host table
arrangements (especially unique, unambiguous, host names), provide
for addition of additional services (e.g., the special record types
for electronic mail routing which rather quickly followed
introduction of the DNS), and to do so on the base of a robust,
hierarchical, distributed, name lookup system.  That system 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

The DNS was designed primarily 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 through
the addition of new record types to the initial "INternet" class.
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-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 are historically not [even] ASCII, but a very
restricted subset of it, a subset that derives primarily 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. X.9, X.29).

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 large ratio of names representing physical
hosts to total names.  There are domains that follow this model: many
university and corporate domains use fairly deep hierarchies, as do a
few country code TLDs (".US" is an excellent example).  However, the
RIPE hostcount list is now showing a count of SOA records that is
approaching (and may have passed) the number of distinct hosts.
While recent experience 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 huge, flat,
structure under ".COM"), 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, with the sole
exception (at least in the "IN" class) of one field of the SOA
record, electronic mail addresses in the Internet have preserved the
original, pre-DNS, "user at location" conceptual format rather than a
flatter or strictly faceted one.  Location, in that instance, is a
reference to a host.

Both the DNS architecture itself and the two-level provisions for
email and similar functions (e.g., see the finger protocol), also
anticipated a relatively high ratio of users to actual hosts.  It was
never clear that the DNS was intended to, 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.

Like the host table before it, the DNS has provided criticial
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 evolve and original
assmumptions are abused, the system is 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 working
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, 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 who have been anxious to "sell" additional names).  And,
of course, the perception that one needs a top-level domain per
product, rather than a (usually organizational) collection of network
resources has led to a rapid acceleration in the number of names
being registered, a phenonenum that has clearly benefited registrars
charging on a per-name basis, "cybersquatters", and others in the
business of "selling" names, but has not obviously benefitted the
Internet as a whole.

The 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 --possibly including significant changes to the underlying
legislation and conventions-- and 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 but by depending largely on main force, 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 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, 

While additional implications are still being discovered and
seriously evaluated, it appears, not surprisingly, that rewriting DNS
names in the middle of the network, or trying to give them different
values or interpretations depending on the topological location of
the user trying to resolve the name interferes, in the general case,
with end-to-end applications.  These problems occur even if the
rewriting machinery is accompanied by additional workarounds for
particular applications: security associations and applications that
need to identify "the same host" as the applications for which these
tools have been designed often run into one problem or another.


1.4 A pessimistic history of the evolution of Internet applications
protocols.

At the applications level, few of the protocols in active, widespread
use on the Internet reflect the 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 permit 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.  


2. Signs of DNS overloading

Parts of the historical discussion above identify areas in which it
is becoming clear that the DNS is becoming overloaded (semantically
if not in the mechanical ability to resolve names).  While we seem to
still be well within the "just about good enough" range -- current
mechanisms and proposals to deal with these problems are all focused
on patching or working around limitations within the DNS rather than
dramatic rethinking -- the number of these issues that are arising
at the same time may argue for rethinging mechanisms and
relationships, not just more patches and kludges.  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 doesn't deal
especially well with high-multiple names per host (needed for 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 differentiators 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 may claim trademark
rights to do so, even though conflict or confusion would not occcur
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.  Arguably, the name resolution mechanism should
provide information about multiple sites that can provide information
associated with the same name and sufficient attributes associated
with each of those sites to permit applications to make sensible
choices, or should accept client-site attributes and utilize them in
the search process.  

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 and queries may be slightly ambiguous or
fuzzy.  The DNS can accomodate only one set of (quite rigid) matching
rules.  Current proposals to permit different rules in different
localities help to identify the problem, but, if applied directly to
the DNS, either don't provide the level of flexibility that would be
desirable or tend to isolate different parts of the Internet from
each other (or both).  Fuzzy or ambiguous searches are desirable for
(at least) resolution of business names that might have spelling
variations and for names that can be resolved into different sets of
glyphs depending on context.  This goes beyond "mere"
canonicalization differences (different ways of representing the same
character or ordering the same string) and into such relationships as
the use of different alphabets for the same language, Kanji-Hiragana
relationships, Simplified and Traditional Chinese, etc.

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.  Cf RFC 2825.

o In order to provide proper functionality to the Internet, the DNS
must have a single unique root (see RFC 2826 for a discussion of this
issue).  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) 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 targets
(i.e., by value, not just by name (label)).  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 and it can be simulated only by
extracting all of the relevant records (perhaps by zone transfer if
the source doesn't prohibit that through access lists) 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 of protection of that information and
making different information available based on the credentials and
authorization of the source of the inquiry.  As with site locational
and proximity information (as discussed above), the DNS protocols
make the mechanisms needed to do this 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.

Several of the above problems are addressed well by a good directory
system (supported by the LDAP protocol or otherwise) 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 kludges are bad enough,
or will scale up to bad enough, that new solutions are needed and can
be deployed.



3.  The directory story.

3.1 Overview 

The constraints of the DNS argue for introducing an intermediate
protocol mechanism, referred to here as a "directory layer".  The
terms "directory" and "directory system" are used interchangably with
"searchable system" in this document although the latter is far more
precise.  Directory 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 involving searching other systems, rather than looking up
identifiers in the DNS itself.  This would permit us to relax several
constraints and produce a more comprehensive system.

Ultimately, many of the issues with domain names arise as the result
of people attempting to use the DNS as a directory.  While there has
not been enough pressure/demand to justify a change to date, it has
already been 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.

In particular...

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

o A directory system could permit explicit association of attributes
of, 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 one provides, the greater the
possibility of real or imagined trademark conflicts, but we would
have the opportunity to design a directory structure that dealt with
those issues in an intelligent way, while DNS constraints arguably
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, 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 a
recipient trying to contact a person can access romanized spellings
and numbers when the original language may not be comprehensible to
that recipient) can be easily handled in a directory system by
inserting both sets of entries.

o One can easily imagine a directory system 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 use of the DNS in trademark-significant
areas tends to require worldwide "flattening" of the trademark
system. 

3.2 Some details and comments.

As several proposals have noted, almost any internationalization
(i18n) 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, 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" stories and
multi-attribute ones.  The DNS requires strict hierarchies, limiting
its ability to handle differentiation 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 argument for a single directory structure (implying
a need for mechanisms for registration, delegation, etc.).  But it 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).

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 IDN purposes and might require "charset" if we cannot
agree on a character set and encoding.  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 might argue for a few other
attributes (as outlined above).


4.  Examining internationalization

Much of the thinking underlying this document has been 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 ASCII (or in
the traditional DNS subset of ASCII).  Much of this work has been
done in the "IETF Internationalized Access to Domain Names" (IDN)
Working Group.  This section contains an evaluation of what that
group has learned and how that learning might reasonably impact
IETF's next steps.  It assumes familiarity with the work and
terminology of that working group.

When the IDN effort started, several of us made the observation that
the first important task for the WG 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.  That has clearly been
accomplished.  With the exception of some continuing background
noise, the simplistic stuff, with promises of one-year deployment,
has just disappeared and almost no one thinks this is simple any more.

But some of the lessons learned are quite painful and should give us
pause, both generally and in the context of the remarks above:

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, I think, even ASCII if we let the rest of the ISO 646
non-BV characters in) is more complex than hostname-
restricted-ASCII.  In some cases, 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 [just] 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 (I am using that word, rather
than "glyph", deliberately here).  And, in others, there are
questions as to whether two glphs "match", which may be a
distance-function question, not one with a binary answer.  We
have tried to solve this set of problems with "nameprep" (see
below).

4.2.  "Nameprep" and its complexities

The model for getting around the various problems described above and
elsewhere has evolved into a notion that all 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 host-table-subset ASCII is trivial and
essentially adds only overhead.  For other scripts, the impact is, of
necessity, quite significant.

Defining that process was quite complex.  Although the general notion
was simple, the devil is often in the details, and there are many
details.  A design team worked on it for months, with considerable
effort placed into clarifying and fine-tuning the protocol.  Despite
general agreement that the IETF would avoid getting into the business
of defining character sets, character codings, and the associated
conventions, the group has several times taken excursions into
special treatment of code positions to more nearly match the
distinctions of Unicode with user-perceptions about similarities and
differences between characters.  The IETF-specific code position work
has been removed from the protocol draft, but the fact that the
temptation has been strong may indicate problems we haven't solved to
everyone's satisfaction.

At the same time, the nameprep work has been extremely useful, both
in identifying many of the problem code points and issues and
providing a reasonable set of rules.  The problem is arguably not
with nameprep, but with the DNS-imposed requirement that nameprep, 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.


4.3 The UCS Stability Problem

ISO 10646 basically defines only code points, and not rules for using
or comparing the characters.  This is a long- standing issue with
standards coming out of ISO/IEC JTC1/SC2; internationalization
issues, as contrasted with character-listing and code point
assignment issues, are just not dealt with effectively in that group.
The Unicode Technical Committee has defined some rules for
canonicalization and comparision, many of which have been factored
into the "nameprep" work, but we are still in progress on figuring
out how to make or define those rules in a sufficiently precise and
permanent fashion that the DNS can depend on them.  Perhaps more
important, our nameprep efforts have identified several areas in
which the UTC rules do not adequately define things to make matching
precise and unambiguous.  That 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.

In addition, JTC1 has recently assigned some (most?) of these issues
to JTC1/SC22/WG20 (the Internationalization WG within the
subcommittee that deals with programming languages, systems, and
environments).  WG20 is historically strong and deals with
internationalization issues thoughtfully and in depth.  Whether or
not they get it right, assignment of these matters to WG20
significantly increases the risk of an eventual ISO standard that
specifies different behavior from the UTC specification.

4.4 Audiences, end users, and the UI problem

Part of what has "caused" the DNS i18n 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 culturally-dependent
meaning to non-specialist users.

The WG, and others, have attempted to avoid addressing the
implications of that transition by taking "someone else's problem"
approaches or by suggesting that we can adopt conventions and people
will just get used to them.  I suggest that neither will work: 

  * If we want to make it a problem in a different part of the
  UI structure, we need to figure out where it goes in order
  to have proof of concept of our solution.  Unlike those
  whose sole [business] model is the selling or registering of
  names, any solution IETF produces actually needs to work, in
  applications context, for the end user.

  * The "they will get used to our conventions and adapt"
  principle is fine if we are writing rules for programming
  languages or an API.  But the conventions we are talking
  about aren't part of a semi-mathematical system, they are
  deeply ingrained in culture.  No matter how often we tell an
  English-speaking American 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 (anglicisation?) of
  Montr‰al (with an acute accent mark over the "e"), but we
  are as unlikely to get 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-- as we are to get 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.  In the use of
human languages by humans, we have many cases in which things that do
not match are nonetheless interpreted as matching.  The
Norwegian/Danish glyph "°" (lower case 'o' with forward slash) and
the German glyph "" (lower case 'o' with umlaut) are clearly
different and no matching program should yield an "equal" comparison.
But they are more similar than either of them is to, e.g., "e", and
humans are able to mentally make the correction in context and can be
surprised if computers can't do so.  

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 IDN discussions of the last year or
so is that problems like this 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
deeply embedded.  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, or one in Egypt or Israel will find
it acceptable to write a word with or without vowels or stress marks,
but, if they are included, that they must be the correct ones, there
are issues with the relevant language.  We are dealing with culture,
not identifier symbol-strings for geeks or computers, and the efforts
of the last year have made it ever more clear that, if we ignore that
distinction, we are solving an insufficient problem.


4.5 Business cards and other natural uses of natural languages

We have some established local conventions in the world for dealing
with multilingual situations.  Looking at them may be helpful.  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.  This is usually a high-tolerance situation: exact
translations are often not possible, and people typically smile at
errors, appreciate the effort, and move on.  The DNS situation
differs from this in at least two ways: since we need a global
solution, 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.  And the opportunities
for tolerance don't exist: the DNS requires a exact match or the
lookup fails.

4.6 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 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.

4.7 A pessimistic summary of IDN WG directions

It appears, from the cases above and others, that none of the
intra-DNS-based solutions for "multilingual names" are workable.
They just 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 they cannot easily be told apart); that we can either deploy
EDNS or that long names aren't really important; that the Chinese
Government (and others) will either give up their IS 2022-based
solutions (for which UTC adding large fractions of a million new code
points is almost certainly a necessary, but probably not sufficient
condition) or build leakproof 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, we can
get about 80% or 90%, but it is not clear that is going to be good
enough.  For example, suppose someone can spell her name 90%
correctly: is that likely to be considered adequate?


6.  The Key Controversies

6.1. One directory or many

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
directory with universal applicability, a single directory but
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 we have assigned more and more names per host address.  

Locally-tailored search 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, which is not, in
general, a desirable situation.

And, of course, completely separate directories would permit
translation and transliteration functions to be embedded in the
directory, given 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 roots.

6.2 Why not a proposal?

As this document has gone through various preliminary drafts and
reviews, the question has been raised as to whether it should contain
a specific proposal: a specific directory mechanism, schema, and so
on.  It deliberately does not take that step.  It has been difficult
to get directory systems deployed in significant ways in the Internet
infrastructure, partially because we have a surplus of options.
There are also some approaches that could be used to implement the
general concepts described here, such as the Common Name Resolution
Protocol [RFC2972], which some would not consider directory protocols
at all.  Consequently, it appeared better to present the general
concepts and arguments here and leave the specifics to other sources,
documents, and proposals.
 

7.  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 this purpose would presumably need to be as
carefully protected against unauthorized changes as the DNS itself.
There also might be new opportunities for problems in the two-layer
arrangement; but those problems are not more severe than a two-stage
lookup in the DNS.


8.  References

RFC 625 On-line hostnames service. M.D. Kudlick, E.J. Feinler.
Mar-07-1974.

RFC 811 Hostnames Server. K. Harrenstien, V. White, E.J. Feinler.
Mar-01-1982.

RFC 952 DoD Internet host table specification. K. Harrenstien, M.K.
Stahl, E.J. Feinler. Oct-01-1985.

RFC 882 Domain names: Concepts and facilities. P.V. Mockapetris.
Nov-01-1983.

RFC 883 Domain names: Implementation specification. P.V. Mockapetris.
Nov-01-1983.

RFC 1035 Domain names - implementation and specification. P.V.
Mockapetris. Nov-01-1987.

RFC 1591 Domain Name System Structure and Delegation. J. Postel.
March 1994.

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

RFC 2826 IAB Technical Comment on the Unique DNS Root. IAB. May 2000.

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

ITU Recommendation X.9

ITU Recommendation X.25

9. 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, Leslie Daigle, Patrik Faltstrom, Eric A.
Hall, and Paul Hoffman for challenging the assumptions of earlier
versions and suggesting ways to improve them.


10. Culprit address

John Klensin
AT&T Labs
99 Bedford Street
Boston, MA 02111
klensin@att.com

Expires November 2001
