Rich Kulawiec wrote:
>
> On Mon, Nov 30, 1998 at 05:09:54AM -0800, Javilk wrote:
> > Before I start writing ping routines and such, what is the quickest,
> > simplest way of determining whether a host exists?
>
> The host may *not* exist: for example, there is no such machine as gsp.org,
> it's just an MX record. (And existence of an MX record alone doesn't
> mean that the host actually will accept mail, or that it will accept
> mail 24x7.) Hosts can be located behind firewalls which disallow ICMP
> traffic, so even though they're real, they can't be pinged from the Internet.
> Or the host itself may disallow pings.
>
> And knowing that the host exists doesn't tell you that the address
> is legitimate; it could be a valid host but an invalid username...
> and since most sites turn off finger and disallow SMTP EXPN and VRFY,
> there's often no way to verify that.
>
> So my response to this problem is to classify it as "essentially unsolvable"
> and forget it.
>
<<SNIP>>
A work-around that we use is a delayed response via e-mail. We assume
that the request is coming from a valid e-mail address. By sending
e-mail back, if the address is not valid, it bounces.
Not a perfect/fool-proof solution; however, it does help keep an
electronic "paper-trail".
--
John Stewart
SUPSHIP San Diego
Information Systems Security Mgr
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