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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 "accelerator" in-between.

Our problem with proxy servers:
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 server.

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.
The WWW 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://". und 
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 browser configuration.


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