RE: Detecting a non-existent domain

["David Schwartz" <davids () webmaster com>]

> Getting practical for a minute.  What is the optimal way now to see
> if a given host truly exists?

        You first have to define what you mean by 'exists'. I have a machine here
that I call 'stinky'. It's not on the Interent though. Does the 'host'
'stinky' exist?

> 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.

        How would you do this before? Does an A record for a hostname mean that a
host with that name exists? If so, then all *.com 'hosts' now 'exist'. If
not, what did you mean by exist before?

> 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.

        Forgive me for defending Verisign, but if you want to know if a given DNS
name corresponds with an A record, you can still determine that. If you want
to determine something else, you can still do that, depending upon what that
something else is.

        As for 'fsck.de', a good argument can be made that this is not really a
legal domain. It's a host. Checking for an SOA is a good way to tell if a
domain is valid, depending upon what you mean by 'domain' and 'valid'.

        I'm reminded of the classic programmers question, "how do you tell if a
machine is online?". The answer is "define what you mean by a machine being
online and test for that".

        So you aren't asking a comprehensible question yet.

        DS