Re: back by popular demand - a DNS calculator

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On 2/15/2013 3:17 PM, John C Klensin wrote:


--On Friday, February 15, 2013 14:10 -0800 Joe Touch
<touch@xxxxxxx> wrote:

Let's just say that there doesn't appear to be disagreement
that the DNS can handle a-z/0-9/'-'.

Other values _may or may not_ be permitted or handled opaquely
in the lookup, AFAICT. It remains a question AFAICT.

Joe,

Except for IDNs (or labels starting with "xn--" more
specifically), for which there are special rules, it appears to
me that the spec is _extremely_ clear that a lookup operation
that fails to deal with those "other values" in labels
--including even properly-escaped embedded "." characters -- is
unambiguously non-conforming.

Seems clear to me:

RFC1035:

The labels must follow the rules for ARPANET host names.  They must
start with a letter, end with a letter or digit, and have as interior
characters only letters, digits, and hyphen.  There are also some
restrictions on the length.  Labels must be 63 characters or less.

--

If any label were allowed, then why does IDN conversion go so far out of its way to exclude particular strings, e.g., those beginning/ending with '-' and encodes everything 0..7F into a-z/0-9?

(I was focused on looking up A records given FQDNs)

Joe


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