Specifications

What is a Proxy Cache?
Squid acts as a proxy cache. It behaves like an agent that receives requests
from clients, in this case web browsers, and passes them to the specified
server provider. When the requested objects arrive at the agent, it stores a
copy in a disk cache.
Benefits arise when different clients request the same objects: these will be
served directly from the disk cache, much faster than obtaining them from
the Internet, and, at the same time, saving overall bandwidth for the system.
Tip
Squid covers a wide range of features, including intercommunicating
hierarchies of proxy servers to divide the load, defining strict access
control lists to all clients willing to access the proxy, and, with the help
of other applications, allowing or denying access to specific web pages.
It also can obtain statistics about the most visited web sites, user usage
of the Internet, and others.
Tip
Squid is not a generic proxy. It proxies normally only between HTTP connec-
tions. It does also support the protocols FTP, Gopher, SSL, and WAIS, but it
does not support other Internet protocols such as Real Audio, news, or video-
conferencing. Because Squid only supports the UDP protocol to provide com-
munication between different caches, many other multimedia programs will
not be supported.
Some Facts About Cache Proxying
Squid and Secur ity
It is also possible to use Squid together with a firewall to secure internal net-
works from the outside using a proxy cache. The firewall denies all external
services except for Squid, forcing all World Wide Web connections to be es-
tablished by the proxy.
If it is a firewall configuration including a DMZ, set the proxy there. In this
case, it is important that all computers in the DMZ send their log files to
hosts inside the secured network.
One way to implement this feature is with the aid of a “transparent” proxy.
It will be covered in Section B on page 178.
168 What is a Proxy Cache?