Proxy servers intercept all requests to real servers to see if it can complete the requests themselves. It usually sits between client applications, such as internet browsers, and the actual server that to request is trying to access. If it cannot complete the request, the real server is forwarded the request.
Two main purposes of proxy servers:
Performance Enhancing: Proxy servers save the results of requests for a
certain period of time,
which causes a significant improvement in
performance for users. For example, assume that user
A tries to access a
website through a proxy server. Later on, user B tries to access the
same website
through the same proxy server. Because the request for the
information that was sent by user
A was saved, the proxy server returns
the website to user B fairly quickly. This is a much faster operation,
mainly because the proxy server is usually on the same network as the
users. Also, hundreds,
or even thousands, of users can be supported by a
real proxy server. Some companies that use proxy servers,
for example,
include MSN, Yahoo, and AOL.
Filter Requests: Another purpose of proxy servers are that filter
requests can be made through them.
Some proxy servers are used by
companies to block certain web sites from their employees.
This causes
the employees to receive an error, instead of seeing the actual site.