Subject: Re: Last Call: 'Domain Name System (DNS) Case Insensitivity Clarification' to Proposed Standard

From: Ian Jackson <[email-masked]>
Date: Wed, 2 Feb 2005 15:49:02 +0000

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The IESG writes ("Last Call: 'Domain Name System (DNS) Case Insensitivity  Clarification' to Proposed Standard "):
> The IESG has received a request from the DNS Extensions WG to consider the 
> following document:
> 
> - 'Domain Name System (DNS) Case Insensitivity Clarification '
>    <draft-ietf-dnsext-insensitive-05.txt> as a Proposed Standard

I am astounded that this much-needed clarification document still
fails to unambiguously specify exactly which DNS labels are to be
considered equivalent !  In particular, it fails to state clearly that
the results of the comparison depends only on the individual separate
comparisons of corresponding octets, and it fails to give a clearly
stated (and clearly stated to be exhaustive) specification of the set
of equivalence classes for octets.

For example, it is not 100% clear, according to
draft-ietf-dnsext-insensitive-05, whether an implementation may
consider 0xCC as equivalent to 0xEC.  An implementor trying to defend
a bizarre and ancient implementation might argue that `0xCC is upper
case L with top bit set, which compares equal to 0xEC because 0xEC is
lower case L with top bit set'.  This appears, on the face of it, to
be difficult to square with the example of 0xDD != 0xFD, but 0xDD and
0xFD are not `ASCII letters with the top bit set'.  This shows the
danger of attempting to specify almost entirely by example !

I suggest the addition of text along the following lines, after
section 3.3:

 3.4. Equivalence of label strings

 Two labels of type 0x0 MUST be considered equivalent if they are of
 the same length and every octet in one label is considered equivalent
 to the corresponding octet in the other label.  Otherwise the labels
 MUST be considered and treated as different labels.

 A pair of octets MUST be considered equivalent according to the
 following rules:

  A. One octets is in the range 0x41-0x5A (upper case ASCII
     letters) and the other is in the range 0x61-0x7A (lower case
     ASCII letters):

     They MUST be considered equivalent if the octet values differ by
     exactly 0x20, and MUST be considered NOT equivalent if the octet
     values differ by some different amount.

  B. Any other pair of octets (ie, at least one of the two octets
     outside either of the two ranges in B above, or both of the
     octets in the same one of the two ranges in B above):

     They MUST be considered equivalent if their octet values are the
     same, and MUST be considered NOT equivalent if they differ.

Ian.

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---

From: Donald Eastlake III <[email-masked]>
Date: Thu, 3 Feb 2005 08:48:32 -0500 (EST)

I think it is just a matter of style. As a clarification updating RFCs 
1034 and 1035, the import is exactly the same as your suggested text. It 
is just that it is in the style of commentary. If there is consensus to 
do so, I suppose I could rewrite the whole document in Official 
Standards Very Harsh Imperative Style, as you suggest.

Thanks,
Donald
  ====================================================================
  Donald E. Eastlake 3rd                       [email-masked]
  155 Beaver Street              +1-508-634-2066(h) +1-508-786-7554(w)
  Milford, MA 01757 USA                   [email-masked]

On Wed, 2 Feb 2005, Ian Jackson wrote:

> Date: Wed, 2 Feb 2005 15:49:02 +0000
> From: Ian Jackson <[email-masked]>
> To: [email-masked]
> Cc: IETF-Announce <[email-masked]>, [email-masked]
> Newsgroups: chiark.mail.ietf.announce
> Subject: Re: Last Call: 'Domain Name System (DNS) Case Insensitivity
>     Clarification' to Proposed Standard 
> 
>

---

From: Ian Jackson <[email-masked]>
Date: Thu, 3 Feb 2005 16:01:27 +0000

> Standards Very Harsh Imperative Style, as you suggest.
..

No, the import in the draft's text is not the same.  Consider my

> > danger of attempting to specify almost entirely by example !

If you don't like my overly formal language then I'm sure there are
other ways of putting it.  But just a couple of examples does not
constitute a clarification !

Ian.