draft-klensin-idn-tld-00.txt

bind-3.2.

"on the wire", i.e., in protocols between network hosts.  Exceptions to
this general principle have been made when different clients were
required to utilize data or interpret values in compatible ways to
preserve interoperability: the standards for email and web body formats,
and IDNA itself, are examples of these exceptions.  Regardless of what
is required to be standardized, it is almost never required, and often
unwise, that a user interface, by default, present on-the-wire formats
to the user.  However, in most cases when the presentation format and
the wire format differ, the client program must take precautions that
the wire format can be reconstructed from user input, or to keep the
wire format, while hidden, bound to the presentation mechanism so that
it can be reconstructed.  And, while it is rarely a goal in itself, it
is often necessary that the user be at least vaguely aware that the wire
("real") format is different from the presentation one and that the wire
format be available for debugging.


2.1 IDNA and the client

As mentioned above, IDNA itself is entirely a client-side protocol.  It
works by providing labels to the DNS in a special format (so-called
"ACE").  When labels in that format are encountered, they are
transformed, by the client, back into internationalized (normally
Unicode) characters.  In the context of this document, the important
obvservation about IDNA is that any application program that supports it
is already doing considerable transformation work on the client; it is
not simply presenting the on-the-wire formats to the user.


2.2 Local translation tables for TLD names

We suggest that, in addition to maintaining the code and tables required
to support IDNA, clients may want to maintain a table that contains a
list of TLDs and that maps between them and locally-desirable names.
For ccTLDs, these might be the names (or locally-standard abbreviations)
by which the relevant countries are known locally (whether in ASCII
characters or others).  With some care on the part of the application
designer (e.g., to ensure that local forms do not conflict with the
actual TLD names), a particular TLD name input from the user could be
either in local or standard form without special tagging or problems.
When DNS names are received by these client programs, the TLD labels
would be mapped to local form before IDNA is applied to the rest of the
name; when names are received from users, local TLD names would be
mapped to the global ones before being passed into IDNA or for other DNS
processing.


3. Advantages and disadvantages of local translation

3.1 Every TLD in the local language and character set

The notion of a top-level domain whose name matches, e.g., the name that
is used for a  country in that country or the name of a language in that
language as, as mentioned above, immediately appealing.  But most of the
reasons for it argue equally strongly for other TLDs being accessible
from that language.  A user in Korea who can access the national ccTLD
in the Korean language and character set has every reason to expect that
both generic top level domains and and domains associated with other
countries would be similarly accessible, especially if the second-level
domains bear Korean names.  A user in Spain or Portugal, or in Latin
America, would presumably have similar expectations, but would expect to
use Spanish names, not Korean ones.  

That level of local optimization is not realistic --some would argue not
possible-- with the DNS since it would ultimately require that every top
level domain be replicated for each of the world's languages.  That
replication process would involve not just the top level domain itself:
in principle, all of its subtrees would need to be completely replicated
as well (or at least all of the subtrees for which a the language
associated with the a given replicant was relevant).  The administrative
hierarchy characteristics of the DNS (see section 1.2.1) turn the
replication process into an administrative nightmare: every
administrator of a second-level domain in the world would be forced to
maintain dozens, probably hundreds, of similar zone files for the the
replicates of the domain.  Even if only the zones relevant to a

particular country or language were replicated, the administrative and
tracking problems to bind these to the appropriate top-level domain and
keep all of the replicas synchronized would be extremely difficulty at
best.  And many administrators of third- and fourth-level domains, and
beyond, would be faced with similar problems.

By contrast, dealing with the names of TLDs as a localization problem,
using local translation, is fairly simple.  Each function represented by
a TLD -- a country, generic registrations, or purpose-specific
registrations -- could be represented in the local language and
character set as needed.  And, for countries with many languages, or
users living, working, or visiting countries where their language was
not dominant, "local" could be defined in terms of the needs or wishes
of each particular user.

3.2 Unification of country code domains

It follows from some of the comments above that, while there appears to
be some immediate appeal from having (at least) two domains for each
country, one using the ISO 3166-1 code and another one using a name
based on the national name in the national language, such a situation
would create considerable problems for registrants in the multiple
domains.  For registrants maintaining enterprise or organizational
subdomains, ease of administration in a single family of zone files will
usually make a registration in a single top-level domain preferable to
replicated sets of them, at least as long as their functional
requirements (such a local-language access) are met by the unified
structure.

Of course, having replicated domains might be popular with registries
and registrars, since replication would almost inevitably increase the
total number of domains to be registered.

3.3 User understanding of local and global references

While the IDNA tables (actually Nameprep and Stringprep -- see the IDNA
specification) must be identical globally for IDNA to work reliably, the
tables for mapping between local names and TLD names could be locally
determined, and differ from one locale to another, as long as users
understood that international interchange of names required using the
standard forms.  That understanding could be assisted by software.  It
is likely that, at least for the foreseeable future, DNS names being
passed among users in different countries, or using different languages,
will be forced to be in ACE form to guarantee compatibility in any
event, so the marginal knowledge or effort needed to put TLD names into
standard form and transmit them that way would be very small.

3.4 Limits on TLD propagation

The concept of using local translation does have one side-effect, which
some portions of the Internet community might consider undesirable.
The size and complexity of translation tables, and maintaining those
tables, will be, to a considerable extent, a function of the number of
top-level domains, the frequency with which new domains are added, and
the number of domains that are added at a time.  A country or other
locale that wished to maintain a few set of translations (i.e., so that
every TLD had a representation in the local language) would presumably
find setting up a table for the current collection of a few hundred

domains to be a task that would take some days.  If the number of TLDs
was relatively stable, with a relatively small number being added at
infrequent intervals, the updates could probably be dealt with on an ad
hoc basis.   But, if large numbers of domains were added frequently, or
if the total number of TLDs became very large, maintaining the table
might require dedicated staff. Worse, updating the tables stored on
client machines might require update and synchronization protocols and
all of the related complexities.

4. Security Considerations

IDNA provides a client-based mechanism for presenting Unicode names in
applications while passing only ASCII-based names on the wire.  As such,
it constitutes a major step along the path of introducing a client-based
presentation layer into the Internet.  Client-based presentation layer
transformations introduce risks from variant tables that can change
meaning without external protection.  For example, if a mapping table
normally maps A onto C and that table is altered by an attacker so that
A maps onto D instead, much mischief can be committed.  On the other
hand, these are not the usual sort of network attacks: they may be
thought of as falling into the "users can always cause harm to
themselves" category.  The local translation model outlined here does
not significantly increase the risks over those associated with IDNA,
but may provide some new avenues for exploiting them.

Both this approach and IDNA rely on having updated programs present
information to the user in a very different form than the one in which
it is transmitted on the wire.  Unless the internal (wire) form is
always used in interchange, there are possibilities for ambiguity and
confusion about references.

5. References

[DNSROLE] Klensin, J.C., "Role of the Domain Name System", work in
    progress (draft-klensin-dns-role-04.txt).

[IDNA] Faltstorm, F., P. Hoffman, A. M. Costello, "Internationalizing
    Domain Names in Applications (IDNA)", work in progress
	(draft-ietf-idn-idna-13.txt)

[LDH] STD13 and comments

[MIME]  Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail
    Extensions): Mechanisms for Specifying and Describing the Format of
	Internet Message Bodies", RFC 1341, June 1992.  Updated and replaced
	by Freed, N. and N. Borenstein, "Multipurpose Internet Mail
	Extensions (MIME) Part One: Format of Internet Message Bodies",
	RFC2045, November 1996.   Also, Moore, K., "Representation of
	Non-ASCII Text in Internet Message Headers", RFC 1342, June 1992.
	Updated and replaced by Moore, K., "MIME (Multipurpose Internet
	Mail Extensions) Part Three: Message Header Extensions for
	Non-ASCII Text", RFC 2047, November 1996. 

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

[RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection", RFC 2672,
    August 1999.


[STD3] Braden, R., Ed., "Requirements for Internet Hosts - Application and
    Support", RFC1123, October 1989.

[STD13] Mockapetris, P.V., 1034 "Domain names - concepts and
    facilities", RFC 1034, and "Domain names - implementation and
	specification", RFC 1035, November 1987. 

6. Acknowledgements

This document was inspired by a number of conversations in ICANN, IETF,
MINC, and private contexts about the future evolution and
internationalization of top level domains.  Discussions within, and
about, the ICANN IDN Committee have been particularly helpful, although
several of the members of that committee may be surprised about where
those discussions led.

7. Author's Address

John C Klensin
1770 Massachusetts Ave, #322
Cambridge, MA 02140 USA
email: [e-mail]