Don't forget your packets
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The CGI spec was orginally devised by NCSA during development of 
NCSA httpd and Mosaic, but it's never become an <i>official</i> 
Internet standard. You can check out NCSA's incomplete 
spec for CGI 1.1, published in 1996, at <a 
href="http://hoohoo.ncsa.uicu.edu/cgi/overview.html">NCSA's CGI 
site.</a> Or, for a more complete spec, take a look at the
<a href="http://web.golux.com/coar/cgi/">CGI RFC Project Page.</a><br>
<br>
So, the HTTP_-prefixed variables come from the browser's 
request header. But where does the server get all that other 
information, like the remote IP address?<br>
<br>
Most browsers profess ignorance of their local IP addresses. 
(An exception is recent Linux versions of Netscape Navigator. 
Linux Netscape, when surfing the 'Net through a proxy, 
will send <i>Client_IP_Address</i> in its request header.)<br>
<br>
The IP address is usually encoded at a much lower level -- in the 
IP header of every packet sent across the Internet. <br>
<br>
Usually, the server grabs this information from the socket 
handling the connection with the browser. To see how this 
information is available, add these lines to Bounce.java:<br>
<br>
<code>
String IP = client.getInetAddress().getHostAddress();
int port = client.getPort();
...
out.println(Remote address: " + IP);
out.println(Remote port: " + port);
</code>
<br>
While a Web server normally listens on port 80, the browser 
sends out it requests on another port entirely. If you point 
your browser to Bounce running on localhost:9000, you'll notice
that the port it uses is usually over 1,000. <br>