Subject: Re: WebAddress resolutions

From: "Aronson, David" <[email-masked]>
Date: Fri, 21 Sep 2001 13:01:49 -0400

I already sent this to the original asker, and cc'ed the list, but for some
reason, the cc bounced.  B-(  Anyhoo, if my understanding of how DNS works
is faulty, please correct us....

-----Original Message-----
From: Aronson, David 
Sent: Friday, September 21, 2001 10:20 AM
To: 'USELESS SSELESU'
Cc: [email-masked]'
Subject: RE: WebAddress resolutions

This concept of "resolving" a domain name to an IP address is handled by
something called Domain Name Service, or DNS for short.  I am not too clear
on it myself (I'm sure someone here will correct me if I'm wrong), since
I've never really had to deal with it in detail, but I think the way it
works is:

If you want to get to, say, www.example.com, your computer first looks in
the "DNS cache", which is where it temporarily stores DNS "resolutions" it
got before, recently.  If it doesn't find it there, it looks in a few tables
where some resolutions are set up permanently.  If it's still not found, it
goes to the IP address you configured as its "DNS server".  If THAT one
doesn't know, then it tells you where to look it up in the official records,
which is the main answer.  It should know the IP address of at least one
system that is "authoritative" about all .com domains, including
example.com.  (And likewise one for each of the other "official" domains, or
at least where to find out about such official DNS servers.)  But that's not
all -- remember that www part.  However, just because a system knows where
example.com is, that doesn't mean it knows where www.example.com is.  So,
rather than ask just "what's the IP address for www.example.com", it asks,
"what's the IP address for a DNS server that knows about domains under
example.com?".  There must be at least one such server registered.  Your PC
then goes to *that* server, asks where www.example.com is, and stores the
answer in its DNS cache.

Or, to anthropomorphize:

You: Hmmm, www.example.com isn't in my DNS cache.  Nope, not in the hosts
table either.  Hey, DNS Server, where's www.example.com?

DNS Server: I dunno, but since it's a .com, you can ask InterNIC, over at
198.41.0.6.

You: Okay, thanks.  Hey, InterNIC!  Who can tell me about domains under
example.com?

InterNIC: Their primary registered DNS server is DNS-R-Us, over at
666.123.456.789.  [Yes, I know that IP is bogus.  That's on purpose.  -dave]

You: Okay, thanks.  Hey DNS-R-Us!  Where's www.example.com?

DNS-R-Us: 666.123.456.5.

BTW, this works not just for "web" addresses, but for *all* IP traffic
addressed by name, be it email, instant messages, phone calls, whatever.

-- 
Dave Aronson, Software Engineer, +1-571-434-2039 V, +1-571-434-2001 F.
Opinions above are MINE, ALL MINE -- but for rent at reasonable rates.
Cryptek Secure Communications, 1501 Moran Rd., Sterling, VA 20166 USA.
SW ENGINEERS, EES: see http://www.cryptek.com and send me your resume.