The exchange of information on the Internet is based on the “client-server” model. The client sends a request (what files it needs), and the server sends a response (requested files). For close interaction (so to speak, “full understanding”) between the client and the server, the client sends additional information about himself: version and name of the operating system, browser configuration (including the name and version number of your browser), etc. This information may be needed for the server to know what web page to present to the client: There may be different versions of web pages for different browser configurations. However, because web pages are usually browser-independent, it makes sense to hide some of this information from the web server.
What information is sent to the web server
This information is mostly sent by the browser, but some information can be added by the proxy server:
- Name and version of the operating system;
- Name and version of the browser;
- Browser settings;
- The client IP address;
- If a proxy server is used;
- Your real IP address can be added by the proxy server;
- Other information.
The most important part of this information (and “absolutely unnecessary” for a web server) is the information about your IP address and the fact of using a proxy. Private proxies can hide almost everything about you, including your IP and private information.
If your IP is not hidden from a website then it can tell a lot about you:
- Country where you are;
- Your ISP and e-mail address;
- Your physical address!
The information which the client sends to the server is available to the server as environment variables. Each unit of information is the value of a variable. If some piece of information isn’t transmitted then the corresponding variable is empty (its value is undefined).