Specifying Client IP Addresses

The configuration options so far have been basic, and you can use many more to enhance the proxying system you want.

After you are past deciding which rules work for you locally, it is time to spread them out to other machines. You do so by specifying IP ranges that should be allowed or disallowed access, and you enter these into Squid using more ACL lines.

If you want to, you can specify all the IP addresses on your network, one per line. However, for networks of more than about 20 people or using Dynamic Host Control Protocol (DHCP), that is more work than necessary. A better solution is to use classless interdomain routing (CIDR) notation, which allows you to specify addresses like this:

192.0.0.0/8 192.168.0.0/16 192.168.0.0/24 

Each line has an IP address, followed by a slash and then a number. That last number defines the range of addresses you want covered and refers to the number of bits in an IP address. An IP address is a 32-bit number, but we are used to seeing it in dotted-quad notation: A.B.C.D. Each of those quads can be between 0 and 255 (although in practice some of these are reserved for special purposes), and each is stored as an 8-bit number.

The first line in the previous code covers IP addresses starting from 192.0.0.0; the /8 part means that the first 8 bits (the first quad, 192) is fixed and the rest is flexible. So, Squid treats that as addresses 192.0.0.0, 192.0.0.1, through to 192.0.0.255, then 192.0.1.0, 192.0.1.1, all the way through to 192.255.255.255.

The second line uses /16, which means Squid will allow IP addresses from 192.168.0.0 to 192.168.255.255. The last line has /24, which allows from 192.168.0.0 to 192.168.0.255.

These addresses are placed into Squid using the src ACL line, as follows:

acl internal_network src 10.0.0.0/24 

That line creates a category of addresses from 10.0.0.0 to 10.0.0.255. You can combine multiple address groups together, like this:

acl internal_network src 10.0.0.0/24 10.0.3.0/24 10.0.5.0/24 192.168.0.1 

That example allows 10.0.0.0 through 10.0.0.255, then 10.0.3.0 through 10.0.3.255, and finally the single address 192.168.0.1.

Keep in mind that if you are using the local machine and you have the web browser configured to use the proxy at 127.0.0.1, the client IP address will be 127.0.0.1, too. So, make sure you have rules in place for localhost.

As with other ACL lines, you need to enable them with appropriate http_access allow and http_access deny lines.