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Forcepoint Web Security PAC File Best Practices > How is a PAC file consumed?
How is a PAC file consumed?
PAC File Best Practices | Forcepoint Web Security | v8.4.x, v8.5.x
Web browsers are configured to look for and read the PAC file each time the browser is started, or at regular intervals when pushed by a Group Policy Object (GPO).
When a URL request is made, the browser calls the FindProxyForURL(url, host) function to determine the request's routing disposition (to a proxy or direct to the destination).
Although the PAC file can be placed on each individual client machine, this is an uncommon and inefficient approach. The common arrangement is to host the PAC file on a server that all clients have access to. In smaller deployments, the Content Gateway host system can be used. In large enterprises the PAC file should be hosted on an existing (dedicated) web server that all clients have access to. Alternatively, the Web Proxy Auto-discovery Protocol (WPAD) can be used to assist browsers in locating and retrieving the WPAD file, which contains the PAC function definition. WPAD not an option with the Forcepoint Web Security Hybrid Module; see Using a PAC file with Forcepoint Web Security and the Forcepoint Web Security Hybrid Module, below.
 
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Note 
Internet Explorer includes a feature called Automatic Proxy Result Cache. This feature can cause problems in environments that use a PAC file and have multiple proxy servers. See What is Internet Explorer Automatic Proxy Result Cache?
WPAD: Web Proxy Autodiscovery Protocol
The Web Proxy Autodiscovery Protocol (WPAD) is a method used by web browsers to locate the URL of a PAC file automatically, without manual configuration. WPAD can be used with Content Gateway, but is not an option with the Forcepoint Web Security Hybrid Module.
WPAD uses two methods to publish the location of the proxy configuration file—the Dynamic Host Configuration Protocol (DHCP), and the Domain Name System (DNS). A web browser using this method sends a query to the local DHCP server and if it does not send back the desired information, uses DNS.
For more information about using WPAD with Content Gateway, see Content Gateway Manager Help.
Specifying the PAC location
The exact mechanism for configuring a browser to locate and use a PAC file depends on the browser and network environment.
If you are using Microsoft Active Directory and Internet Explorer, you can automate the process via a Group Policy Object (GPO). This is the recommended, best practice. A GPO is a simple, versatile tool for configuring computers and user settings for members of Active Directory Domain Services.
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For configuration details, see How do I configure a Group Policy so that Internet Explorer uses the PAC file?
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For an introduction to Group Policy, see these Microsoft TechNet articles: Group Policy for Beginners and Managing Browser Settings with Group Policy Tools.
Unfortunately, use of GPO to configure other browsers is usually unsupported. Search the Internet for the availability of GPO add-on support for the browser used in your organization.
Users can also set up their browsers manually. The most popular browsers implement this feature in very similar ways.
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For Internet Explorer:
1.
Navigate to Tools > Internet Options > Connections > LAN Settings.
2.
Select Use automatic configuration script field, and enter the following in the Address field:
http://<CG_Domain_Name_or_IP_Address>:8083/proxy.pac
Ensure everything under Proxy server panel is unchecked.
3.
Click OK.
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For Mozilla Firefox:
1.
Navigate to Tools > Options > Advanced > Network  > Connection > Settings.
2.
Select Automatic proxy configuration URL field, and enter:
http://<CG_Domain_Name_or_IP_Address>:8083/proxy.pac
3.
Click Reload, and then click OK.
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For Opera:
1.
Navigate to Tools > Preferences > Advanced tab.
2.
Select Network > Proxy Servers > Use Automatic proxy configuration (check only this option).
3.
Enter the location of the PAC file. For example, file://c:/proxy.pac
See the documentation for your browser for details.

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