> if i am, then in theory, it appears to me that one could essentially build a
> reasonably accurate list of valid IP Addresses for a given URL... in order
> to maintain the accuracy, one would have to continually 'build/maintain' the
> list, but it seems that it could be done.. am i missing something?

Lots. There's no guarantee that you can ever get a "reasonably accurate
list of valid IP addresses" for a domain name (note: URL's don't have IP
addresses). There's no way to know if the response you've been given is
the same as that being given to other queries, or if it's been generated
programatically based on your IP address, your location, destination load
balancing issues, destination shortest-path strategies, the number of
seconds since the creation of the universe, total randomness, etc.

The only thing you can know is that the domain name owner wanted to map
the domain name to the particular IP address you were given, for reasons
which may never be known to you.

> also, if i get an IP Address for a given URL, how do you determine if it's
> really valid? would you have to go back to the authoritative DNS to see if
> the IP is valid. is there a list somewhere for a URL of the valid IP
> Addesses for that URL?

See above.

Oh, and, hi Brad. LTNS.

.... JG
Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.