What's in a PAC File?

You've been into the LAN settings of yourwebsite in your browser, the browser will try to
browser many times and you probably wonderedcheck the script first. Since the script has this
what the automatic configuration script is. Thatvalue, all your website requests will go through
script is basically a file stored as a PAC file. A PACthe proxy. If your request can't be found by that
file instructs your browser how to connect to theproxy, then the request will go directly to the
different sites in the internet.internet server, as defined by your provider.
This PAC file is basically a text file which hasThis PAC file can reside anywhere in your local
some JavaScript codes in it. It is commonly calleddrive. But for organizational purpose and
proxy.pac, but it can be named differently. Forcorrectness, this file should be in this folder,
most of the home users, this script is not neededC:\Windows\system32\drivers\etc. This folder is
since they are connected to the internet directly.reserved for system files. This PAC file should be
But if you're using a number of proxies, and eachplaced there since it is a system file.
proxy is dedicated to some sites, you will need toTo use this file, open your browser and go to the
use this file.LAN settings. From the Tools menu of your
A very basic PAC file contains a single functionbrowser, select Internet Options.... Go to the
defining the instruction. Without being too technical,Connections tab in the popup window and locate
that function basically finds the appropriate proxythe LAN settings at the bottom. Click the LAN
for a particular URL or website request. Asettings button and on the top of another popup
particular return value of that function can bewindow is the automatic configuration portion.
"PROXY myProxy.com:8080; DIRECT." This returnCheck the "Use automatic configuration script"
value states that all requested URLs will gothen specify the address. You should use "file://C:
through server using the port 8080. And if thatWindows/system32/drivers/etc/proxy.pac" as
request fails, the request will bypass the proxythe address. This value assumes that your script
and go direct. Let's say your proxy for theis named proxy.pac and you have your windows
internet is and uses port 8080. When you type ainstalled at the C drive.