What’s In a PAC File?

While doing LAN settings of your browser you must have thought that what the automatic configuration script is.

Script is saved as PAC files and guides your browser to connect to different websites. PAC file is a text file that holds some JavaScript coding as well. Normally it is called as proxy.pac but also named differently. For normal users there is no need of script but since they are directly connected to network.

Users using different proxies for different sites need to have PAC file. Basic function of PAC file is not that technical but just to instruct browser to find a suitable proxy for a specific URL or website. The return value of the function is like, PROXY myProxy.com:8080; DIRECT, that means that all requested websites will firstly pass through myProxy.com server using the port 8080. If the request is failed it will then bypass the proxy and will go directly. For instance your proxy for the internet is myProxy.com and it uses port 8080.

As you place the URL in the browser, firstly the browser will check the script. Due to this importance of script, all the URL requests pass through the proxy first and if not found by the proxy then it goes to the internet server directly. Normally PAC file is stored in the local drive of your system but for large scale purpose in companies it is been stored in the folder of C:Windowssystem32driversetc, as this folder is basically reserved for all system files. Therefore, as PAC file is a system file that’s why it is been stored in this folder as well. In order to use this file go into the LAN settings in your browser from the tool menu option and selecting Internet options where Connection tab will help you in locating LAN settings.

After clicking the LAN settings, you will see an automatic configuration portion in another popup window appeared on your screen. Further you can check the “Use automatic configuration script” and then you can specify the address. As the address you can use“file://C:/Windows/system32/drivers/etc/proxy.pac. This value assumes that your script is named proxy.pac and you have your windows installed at the C drive. Basically a PAC file is kind of way of using proxies, having one simple function or sometimes also as complex as having multiple functions.