Access control lists
Access Control Lists are the base elements in the Squid configuration file, which help in identifying web transactions, by various attributes of that transaction. We have already learned about the syntax for constructing ACLs in Chapter 2. So, let's write an ACL element that can identify all the requests from a group of clients in the IP range 192.0.2.1 to 192.0.2.127.
acl clients src 192.0.2.0/25
That was quite easy, as 192.0.2.0/25 denotes that the first 25 bits of the available 32 bits in the IP address are fixed and only the last seven bits can vary, which will result in the range 0-127. In the configuration above, 192.0.2.0/25 denotes a subnet with 127 possible IP addresses. For more information on subnets, please check http://en.wikipedia.org/wiki/Subnetwork#IPv4_subnetting.
In the previous ACL element, we used the src ACL type to identify the IP address of the source of the request. There are various other ACL types available, which can be used to identify requests...
