DNS for IP address lookup
barmar at alum.mit.edu
Wed Jan 12 05:58:21 UTC 2005
In article <crvl3q$2o6j$1 at sf1.isc.org>, Danny Mayer <mayer at gis.net>
> At 04:14 PM 1/10/2005, John Smith wrote:
> >since nobody else responded, i will.
> >if you type in an IP address anywhere for network connectivity, eg web
> >browser, command prompt, even a news reader, no DNS (or WINS
> >depending on situation) lookups are needed or performed - unless you have
> >some sort of logging or some other feature that requires reverse lookups
> >(ip address to name lookup).
> If only that were true. There's plenty of badly written software out there
> that will attempt to do lookups even though there's no need.
> Just ask the root operators about the traffic that they see.
How is it supposed to know there's no need? For all it knows, when you
type 184.108.40.206 you actually meant a host in the .4 top-level domain. A
reasonable algorithm is to first try the given string as a hostname; if
that fails, and it looks like a dotted quad, parse it as an IP address.
Yes, it's true that there's no such TLD. And there's also a rule that
says that labels can't be all-numeric. But rules like that are subject
to change, so it can be a bad idea to hard-code them into applications
(once upon a time the rule was that the first letter of a label had to
be a letter -- the rule was relaxed when 3Com got onto the Internet and
was allowed to register 3COM.COM). The algorithm I describe will
automatically adapt to current conventions.
Barry Margolin, barmar at alum.mit.edu
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