Detecting a non-existent domain

[Kee Hinckley <nazgul () somewhere com>]

Getting practical for a minute.  What is the optimal way now to see 
if a given host truly exists?  Assume that I can't control the DNS 
server--I need to have this code run in any (*ix) environment. 
Assume also that I don't want to run around specialcasing specific IP 
addresses or TLDs--this needs to work reliably no matter what the 
domain.  User gives me a string, and I need to see if the given host 
is a real machine.

An answer from Verisign would be most appropriate here, since they 
have done "extensive research" on the impact of their new service, so 
presumably they figured out the answer to this problem and have code 
samples available for distribution.  However I get the feeling from 
their press releases that they've forgotten there is more to the 
internet than just the web.
--
Kee Hinckley
http://www.messagefire.com/         Next Generation Spam Defense
http://commons.somewhere.com/buzz/  Writings on Technology and Society

I'm not sure which upsets me more: that people are so unwilling to accept
responsibility for their own actions, or that they are so eager to regulate
everyone else's.