Problem: proxy servers
Short introduction to proxy servers:
Proxy servers are computers which are located between the surfer and
the accessed web server.
Proxy servers are an invention to accelerate slow internet connections.
They function as a cache, similar to the way locally installed browsers
cache data, i.e. store them temporarily. The speed advantage comes about
since information which has already been requested does not have to be
loaded a second time, since it is already there.
Proxy servers make use of the fact that several surfers access one proxy
server and often request the same contents. In the case of often-visited
websites the speed advantage is certainly noticeable, as long as the
proxy server is not itself overloaded.
In our graphic we have pictured two internet connections. The
"green" one symbolises a direct connection to our system
and the "blue" one a connection with an
Our problem with proxy servers:
prevent direct contact between the requesting computer and the accessed
computer, since the proxy server is in-between.
Our system automatically determines the IP of the requesting computer.
In the case of a direct connection we can determine your dynamic IP. If,
however, a proxy server is in use, we determine the IP of the proxy
Of course, there is a solution:
The internet offers several
possibilities. Surfing, FTP downloads, emails, ...
In order for an internet server to be able to respond with the desired
information, each connection between your computer and an internet server
includes, in addition to your IP address (return address), a
"port number". Based on this "port number", the
internet server knows which service it should offer.
is (usually) serverd via port 80. FTP, for example, via port 21. For
both systems there are proxy servers - for FTP and WWW.
Our trick consists of using port 81 for determining the IP. There is
usually not a proxy server listening on this port, i.e. a direct connection,
bypassing the proxy server, can be set up.
Port 81 in practice:
We offer various web sites via port 80 and port 81. When the pages
are accessed nornmally (via port 80), the result can be corrupted by a
proxy server. Test it yourself!
The appropriate web page can be accessed via appending ":81" to
the URL. Note that the URL is preceeded by "http://".
You will quickly notice whether your connection is via an obligatory
proxy server, as long as you have not defined a proxy server in your