john at iastate.edu
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 126.96.36.199
> > 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'
This is a classic example of the internet principal
"be liberal in what you accept". '$sum(7,18,-9.4).x42.com'
may be "illegal", but the resolver dutifly passes it
on to x42.com's nameserver which returns a valid (wildcarded)
And then if you are using it in a URL it gets passed
as text to the bizzare webserver at 188.8.131.52
which uses it in its silly little computation.
% telnet '$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> ...
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