Cisco Cisco Web Security Appliance S170 Guida Utente

Web browsers and other user agents sometimes need to know how to connect to the Web Proxy in order 
to access the World Wide Web. When you deploy the Web Security appliance in explicit forward mode, 
you must configure client applications so they use the Web Proxy. If you deploy the appliance in 
transparent mode, you can choose whether or not to configure client applications to explicitly use the 
Web Proxy. 

You can configure client applications to explicitly use the Web Proxy by using any of the following 
configuration methods:

Manual. Manual configuration involves typing the Web Security appliance hostname and port 
number, such as 3128, in each client application. If the appliance changes, you must edit each 
application individually. You might want to manually configure an application when you are testing 
proxy access on a single client machine. Cisco does not recommend manually configuring each 
client application to use the appliance Web Proxy.

Proxy auto-config (PAC) file. For web browsers, you can configure each browser to use a PAC file 
to find the Web Proxy. Then you can edit the PAC file to specify the appliance Web Proxy 
information. For more information, see 

.

For more information about how to configure client applications to use a proxy, see the client application 
documentation.

A proxy auto-config (PAC) file is a text file that defines how web browsers can automatically choose the 
appropriate proxy server for fetching a given URL. 

When you use a PAC file, you only need to configure each browser once with the PAC file information. 
Then, you can edit the PAC file multiple times to add, delete, or change Web Proxy connection 
information without editing each browser. This way you can configure the proxy information about your 
network in a centralized location and update it easily.

Once a browser has read a PAC file, it stores it in memory for the remainder of the browser session.

You might want to use a PAC file for the following reasons:

Centralized management. You can manage the PAC file in a single, central location.

Complex network environment. If the network of proxy servers is complicated, you can create a 
PAC file to accommodate different server and client needs.

Changing network environment. If your network environment is likely to change in the future, you 
can easily add, edit, or delete proxy servers in the PAC and have the changes automatically affect all 
browsers.

Failover. If you have multiple proxy servers, you can provide redundancy in case of failure. You can 
either program the PAC file to be redundant, or if a failure occurs, change the PAC file to use a 
different proxy server.

Different browsers take different amounts of time to fail over to a secondary proxy. For example, 
Internet Explorer takes about 25 seconds, and Firefox takes about 50 seconds.