A-label definition

[Frank Ellermann]

John C Klensin wrote:

> let's move in the direction of getting a BCP document together
> that makes recommendations about whatever the IETF thinks is
> the best/ most desirable practice in this area.

> IMO, we should be talking about best practice recommendations
> because, for reasons that Mark and I have been discussing from
> our rather different perspectives, the underlying DNS protocol
> is able to handle a lot of strings that no sensible person would
> use... these are really recommendations about how the DNS is
> used in the protocols that call on it and hence about
> registration policies, not the DNS protocol itself.  If we go
> that route, the BCP should explicitly update/ quality the
> language in 1034, 1123, 1591, etc.   

Sounds good, BCP or PS will do.  You forgot "obsoletes 952".

> the "no strings that have hyphens in positions 3 and 4 and
> are not A-labels" text should come out of "Rationale".  It
> would either belong in the BCP (if consensus exists) or not
> at all.

Not at all.  Folks hate obscure restrictions.  Even if their
only purpose is to show that it's a bad idea and futile (for
the "nic", "whois", and "www" labels in the test-tlds draft).

> The IDNA2008 documents would presumably still have something
> to say about strings that start in "xn--" but that are not
> valid A-labels, at least wrt IDNA-aware applications.

+1  

> I don't have a strong opinion about whether the BCP effort
> should be on this WG's task list or not.

Without IDNA it would be the "editorial" erratum that it is
at the moment.  Let's do it here.

> I don't think the text is very complicated.

+1  With your "must start with ALPHA" proposal a <toplabel>
is clear, there is no chance to confuse it with 0x or octal,
and "xn--" does start with ALPHA => problem solved.  Compare
<http://article.gmane.org/gmane.ietf.usenet.format/30441> :-)

> Getting consensus on its provisions probably would be

"No IETF consensus for IDN TLDS, film at 11".  Not really.

> Does that help?

Yes... </t><figure><artwork type="abnf">
  hostname = *( label "." ) toplabel 
  label    = alnum [ 1*61( ldh ) alnum ]
  toplabel = ALPHA [ 1*61( ldh ) ] alnum
  ldh      = ALPHA / DIGIT / "-"    ; letter digit hyphen
  alnum    = ALPHA / DIGIT 
  ALPHA    = <see STD 68>           ; ASCII letter 
  DIGIT    = <see STD 68>           ; 0-9
</artwork></figure><t> ...something like this.

 Frank