Re: [ga] Domains are not the equivalent of DNS.

[Karl Auerbach <karl@CaveBear.com>]

On Tue, 15 Apr 2003, Ross Wm. Rader wrote:

> Domains are a way of mapping alpha-numeric labels to hosts/endpoints
> (x).

I don't quite agree.

Fully qualified domain names (FQDN) are more than simply alpha-numeric.  
The relevant RFC's define the character set as being all 256 possible
patterns in 8-bit octets.  The alphanumeric limitation only applies when
the name is somehow associated with a "hostname".  Various applications
and library routines (e.g. sendmail and gethostbyname()) have drifted into
this ambiguity and created a deployed base anchor that, as a practical
matter, nullifies the 8-bit clean aspect of DNS that is found in the
actual DNS standards.)

In addition, the result of the mapping from a FQDN isn't necessary a 
referent to a host/endpoint.  Rather, the result is to a set of records, 
possibly of multiple types with possibly multiple instances of each type.

There are many different record types.  They range from simple text
records (TXT) to more complex things, like regex expressions in NAPTR
records or latitude/longitude/elevation coordinates in LOC records.

IP Address related records comprise only a small portion of the possible
DNS record types that are defined.

And for each type there may be multiple results.  It is not atypical for a
single FQDN query for address-related records (PTR, CNAME, A) to result in
more than one record coming back.  A good example of this is to do a look
for "any" type of record on "www.whitehouse.gov".

ENUM is an interesting case.  I find it easiest to think of ENUM as a 
directory layered *on top of DNS* that itself is constructed using DNS 
components.  That way I can analyse the top part of ENUM - the NAPTR 
records, the application of the regular expressions, and the selection 
among the resulting URI's as a directory - and analyse the use the use of 
the domain name part of the selected URI as a classical DNS matter.

For fun, I have a DNS zone that has virtually no address related records.  
Rather it contains the text of the Magna Carta.  You can view it via the 
command:

	dig @npax.cavebear.com mc.cavebear.com axfr

(I'm not sure whether "dig" is widely available to folks who use those
proprietary "operating systems". ;-)

		--karl--





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