Far not all users have wide unlimited cable to the Internet. Such guys sooner or later ask yourselves "for what I spend money" or even so "why I spend so much money for so few bytes". After that they're digging through a Google and finally finding out one of the suitable decisions like a traffic compressor.

But we're not talking about that (though you've already understood my hint, haven't you?). The most of auxiliary services/programs between an user computer and the Internet are configured through a proxy server. Certainly, it is possible to type all settings by hands in all programs, and change them each time at a change of a proxy. However there is more simple and, that is not less important, the elegant decision. I speak about use of the automatic configuration script.

It is enough to create a file with special contents, to write down the reference to it (unitary) in all your programs for the Internet (sometimes it is necessary to do only in a browser properties), and you always have only one place where your settings are. So, let's go:

• first of all I'll give you an example of file contents (save it as 'proxy.pac' for example).
  
  
  function FindProxyForURL(url, host)
  {
  if (url.substring(0, 6) == "https:"
     || isInNet(host, "192.168.0.0", "255.255.0.0")
     || isInNet(host, "10.0.0.0", "255.0.0.0")
     || shExpMatch(host, "*mail.google*")
     || shExpMatch(host, "*localhost*"))
      return "DIRECT";
  else
      return "PROXY 127.0.0.1:8090; DIRECT";
  // return "SOCKS host:port"; also possible
  }
  
  
  Next, you should save it on the disk and after that

 
• go through the LAN settings and fill in the reference to it into automatic configuration script field.
  
  

  Note: Pay attention to a file path, it is necessary to write it clearly for a browser (like URL).

  Note: The file can be placed at any remote host, accessed directly (without a proxy).

• The same settings are mandatory in all programs with their own settings for the Internet (e.g. the browser Opera).

• the file contains obligatory FindProxyForURL(url, host) function, it's possible to write user defined functions
• contents of a file are JavaScript with the several predetermined methods, full list of them could be found in the Internet
• this example informs a browser, that all protected (https:) connections, local networks (192.168.x.x and 10.x.x.x), Google mail, and also localhost (127.0.0.1) should pass to the Internet over a proxy. All other connections should go through the port 8090, and in case of its inaccessibility - directly
• in the return operator the enumeration of several proxies (followed by a semicolon) is possible, that will allow to set a priority of each type of connection.

In summary, I'll give some arguments pro of using the automatic configuration script:

• using of several proxies
• the possibility to point their priority
• setting of various proxies for different protocols (https:, ftp:, http:...)
• ban (restriction) of use of selected sites
• ease of file editing at configuration changes
• use of various proxies, for example, depending on day of week, time of day, etc.
• usability for programs of the traffic compression (read about it in following articles)
• editing of settings only in one place.

Have I convinced you?

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