Single-letter names (was: Re: Update of RFC 2606 based on the recent ICANN changes?)

Vint Cerf vint at
Fri Jul 4 21:33:18 CEST 2008


my reaction was specific to IDN single character TLDs. In some  
languages these are complete words.


On Jul 4, 2008, at 1:50 PM, John C Klensin wrote:

> Vint,
> In the ASCII space, there have been three explanations offered
> historically for the one-character prohibition on top and
> second-level domains.   I've written variations on this note
> several times, so will just try to summarize here.  Of the
> three, the first of these is at best of only historical interest
> and may be apocryphal and the second is almost certainly no
> longer relevant.  The third remains significant.
> (1) Jon has been quoted as suggesting that we could have
> eliminated many of the problems we now face with TLDs and
> simultaneously made the "no real semantics in TLD names" rule
> much more clear had we initially allocated "b".."y" as TLDs.
> Then, when someone asked for an assignment, it would have been
> allocated at random to one of those domains.  While this has a
> certain amount of appeal, at least in retrospect, there is
> probably no way to get from where we are today to that model...
> unless actions taken in the near future so ruin the current DNS
> tree as a locus for stable and predictable references that we
> need to start over with a new tree.  I don't think that a "have
> to start over" scenario is at all likely, but I no long believe
> it to be impossible.
> (2) There was an idea floating around for a while that, if some
> of the popular TLDs "filled up", one could create single-letter
> subdomains and push subsequent registrations down the tree a
> bit.  For example, if .COM were declared "full", then "",
> "", etc., would be allocated and additional reservations
> pushed into subdomains of those intermediate domains rather than
> being registered at the second level.  Until and unless the
> conventional wisdom that adding more names to .COM merely
> requires more hardware  and/or bandwidth, that won't be a
> "filled up" point at which this sort of strategy could be
> triggered.  Worse, trying to use single-letter subdomains as an
> expansion mechanism would raise political issues about putting
> latecomers at an advantage that would be, IMO, sufficient to
> completely kill the idea.  In the current climate, I think the
> community would decide that it preferred a disfunctional DNS if
> that were ever the choice (see the "start over" remark above).
> (3) At least in the discussions that led up to RFC 1591, and
> probably much earlier, there were concerns about reducing the
> likelihood of false hits if the end user made single-character
> typing errors.  With only 26 (or maybe 36) possible characters,
> it could just about be guaranteed that all of them would be
> registered and that _any_ typing error would yield a false
> match.  That, in itself, has been considered sufficient to
> prohibit single-letter labels and, by extension, to be fairly
> careful about two-letter ones.   There have been arguments on
> and off over the years as to whether this is a "technical"
> reason or an attempt to set policy.  Even though the mismatches
> would obviously not cause the network to explode or IP to stop
> working, at least some of us consider the informational
> retrieval and information theoretic reasons to insist on more
> information in domain name labels in order to lower the risk of
> false positive matches to be fully as "technical" as something
> that would have obvious lower-level network consequences.
> Others --frankly especially those who see commercial advantage
> in getting single-letter names-- have argued that this position
> is just a policy decision in disguise.
> Note that, with slight modifications, the second and third
> arguments apply equally well to TLD allocations and to SLD
> allocations, especially in popular domains.
> The reasoning associated with the third case also applies to any
> other script that contains a fairly small number of characters.
> One could manage a long philosophical discussion as to whether
> there are sufficient characters in the fully-decorated
> Latin-derived collection to eliminate the problem, but an
> analysis of keyboard and typing techniques/ input methods for
> that range of characters would, IMO, yield the same answer --
> single-letter domains are just not a good idea and two-letter
> ones near the top of the tree should be used only with great
> caution.
> On the other hand, the same reasoning would break down when
> confronted with a script that contains thousands of characters,
> such as the "ideographic" ones.  There are enough characters
> available in those scripts that one can presumably not worry
> about single-character typing errors (and one can perhaps worry
> even less if the usual input methods involve typing
> phonetically, using a different script, and then selecting the
> relevant characters from a menu -- in those cases, the phonetic
> representations are typically more than a character or two long
> and the menu selection provides an extra check about false
> matches).
>      john
> --On Thursday, 03 July, 2008 19:04 -0400 Vint Cerf
> <vint at> wrote:
>> seems odd to me too, James.
>> vint
>> On Jul 3, 2008, at 6:14 PM, James Seng wrote:
>>>> At the moment, the condition is "no single Unicode code
>>>> point." To the extent that a single CJK ideograph can be
>>>> expressed using a single Unicode code point, this would
>>>> represent the situation to which you say you would object. I
>>>> will dig through my notes to find out why the "single
>>>> character" condition was adopted -
>>> Would you be able to explain why the condition is "no single
>>> Unicode code point"? Whats the technical basis for that?

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