Access control lists (acls) are often the most difficult part of the configuration of a Squid cache: the layout and concept is not immediately obvious to most people. Hang on to your hat!
Unless chapter 3 is still fresh in your mind, you may wish to skip back and review the access control section of that chapter before you continue. This chapter assumes that you understood the difference between an acl and an acl-operator.
The primary use of the acl system is to implement simple access control: to stop other people using your cache infrastructure. (There are other uses of acls, described later in this chapter; in the meantime we are going to discuss only the access control function of acls.) Most people implement only very basic access control, denying access to people that are not on their network. Squid's access system is incredibly flexible, but 99% of administrators only use the most basic elements. In this chapter some examples of the less common uses of acls are covered: hopefully you will discover some Squid feature which suits your organization - and which you didn't think was part of Squid before.