http://$sum(7,18,-9.4).x42.com/ ??

Tue Nov 2 23:12:31 UTC 1999

> Barry Margolin responded:
> > <aldenr at my-deja.com> wrote:
> > >    I am a little confused with this URL ( http://$sum(7,18,-
> > >9.4).x42.com/ ) .  [...is some DNS trickery...?]

> > The x42.com domain has the following entry:
> > *.x42.com.	7200	A	195.100.134.30

> > So if you put anything before ".x42.com" other than weller, localhost,
> > namnsdag, or getz (the names that are explicitly listed in the domain) it
> > will use this entry.

> There's a wee bit more to it.  The URL as given looks for a host name:
> 	$sum(7,18,-9  DOT  4)  DOT  x42  DOT  com
> Those first two components are not legal host names, and are rejected
> by BIND.  But if the browser will automatically do the sum - and I
> WOULD NOT use one that would! Too risky! - then you are looking for:

   No, this is not the browser.  For example:

% telnet '$sum(7,18,-9.4).x42.com'
Trying 195.100.134.30...

   This is a classic example of the internet principal
   "be liberal in what you accept".  '$sum(7,18,-9.4).x42.com'
   may be "illegal", but the resolver dutifly passes it
   on to x42.com's nameserver which returns a valid (wildcarded)
   address.

   And then if you are using it in a URL it gets passed
   as text to the bizzare webserver at 195.100.134.30
   which uses it in its silly little computation.

   Try:

% telnet '$sum(7,18,-9.4).x42.com' 80            <-- telnet to web port (YMMV)
GET / HTTP/1.0                                   <-- you enter
Host: $sum(7,18,-9.4).x42.com                    <-- you enter
                                                 <-- you type blank line here
and you will get back:

<!DOCTYPE HTML ...
 ...  <B>Result:<P>15.6</B> ...

John