PAC Files Whitepaper Download

If you’re managing your school’s web filter, chances are you’ve heard of PAC files. But what is it, how is it used, and how can you use them to proxy websites through the filter? Is using a PAC File Selective Proxy method best for your unique needs?

At Lightspeed Systems, we know each member of our community handles PAC files a little differently and created a helpful resource to help you understand PAC files and how to best utilise them for your unique filtering needs. Download the PAC file whitepaper using the form on this page.

To start, here are some key pieces of knowledge to help you understand PAC files. Then, download the whitepaper to learn more about each topic.

What is a PAC File?

Proxy-auto Configuration (PAC) Files are a set of instructions that determine whether web browser requests go directly to their desired destination, or rather, are forwarded to a web proxy server.

In an education web filter setting, PAC Files are helpful to only proxy sites that you choose to proxy, keeping student privacy at the forefront as well as keeping Lightspeed Systems Rocket appliance processes low.

How Does a PAC File Work?

A PAC file is a JavaScript function referenced any time a URL is loaded on a device.

The domain, URL and other information like the device IP can be evaluated and rules based on this information are used to determine whether to send the traffic to a proxy or directly to the Internet.

What Are PAC File Functions?

The PAC files provides essential security to ensure traffic is always proxied when it should be.

Using PAC files allow you to leverage a flexible, script-driven method to controlling the routing of web requests. It can also have rules to route traffic requests by internet vs. intranet, IP address, host of the requested website and even date and time.

Why Use a PAC File?

In the Lightspeed Systems Web Filter, using Selective Proxy via PAC files allows for the most configuration among the other ways to proxy.

In addition, it allows for network traffic to experience a smaller impact as only some requests are being proxied. Hardware impact is also reduced as while packets increase, they only do so for the sites chosen to proxy.

How to Create a PAC File

IT can create and edit PAC files using a simple text editor. Once created, they can be uploaded to the Web Filter PAC file settings.

Here’s an example of a PAC file:

function FindProxyForURL(url, host) {
// This is a template PAC file for schools built by Lightspeed Systems
// Your proxy server name and port
var proxy_yes = “PROXY YOUR_PROXY_FQHN:PORT”;
var proxy_no = “DIRECT”;
// If the hostname matches, send to proxy.
if (shExpMatch(url, “*.google.com/*”))
return proxy_yes;
// DEFAULT RULE: All other traffic, send direct
return proxy_no;

Download the sample PAC file template here.

How to Add a Chrome PAC File

Once you’ve uploaded your PAC files in your Lightspeed Systems Web Filter, you’ll simply copy the URL of those uploaded files and open Settings in your Chrome browser. From there, head to Show advanced settings>Network>Change proxy settings.

In the Internet Properties window, you’ll find Connections>LAN settings and follow the instructions below:

  • Uncheck “Automatically detect settings”
  • Check “Use a proxy server for your LAN”
  • Enter your proxy server IP address in the Address field
  • Enter your port number in the Port field
  • Press OK

Then, open the LAN settings window, check the box for “Use automatic configuration script” and paste your PAC file URL that you copied from the Web Filter interface. Click OK.

Review more detailed instructions on pushing a PAC file on Chrome with helpful screenshots here.

Lightspeed Systems is here to help answer these questions and more in the downloadable whitepaper, A Guide to PAC Files for Schools.

Ready to learn more? Fill out the below form to download this whitepaper and learn:
-Rules for proxying
-How to add domains to the PAC file
-How to add on- and off-network rules to the PAC file
-How to test your PAC file
-Tips and tricks for troubleshooting your PAC file

Download the PAC file Whitepaper

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