In
an enterprise that uses the Internet, a proxy server is
a server that acts as an intermediary between a workstation
user and the Internet so that the enterprise can ensure
security, administrative control, and caching service. A
proxy server is associated with or part of a gateway server
that separates the enterprise network from the outside network
and a firewall server that protects the enterprise network
from outside intrusion.
A proxy server receives a request for an Internet service
(such as a Web page request) from a user. If it passes filtering
requirements, the proxy server, assuming it is also a cache
server, looks in its local cache of previously downloaded
Web pages. If it finds the page, it returns it to the user
without needing to forward the request to the Internet.
If the page is not in the cache, the proxy server, acting
as a client on behalf of the user, uses one of its own IP
addresses to request the page from the server out on the
Internet. When the page is returned, the proxy server relates
it to the original request and forwards it on to the user.
To
the user, the proxy server is invisible; all Internet requests
and returned responses appear to be directly with the addressed
Internet server. (The proxy is not quite invisible; its
IP address has to be specified as a configuration option
to the browser or other protocol program.)
An
advantage of a proxy server is that its cache can serve
all users. If one or more Internet sites are frequently
requested, these are likely to be in the proxy's cache,
which will improve user response time. In fact, there are
special servers called cache servers. A proxy can also do
logging.
The
functions of proxy, firewall, and caching can be in separate
server programs or combined in a single package. Different
server programs can be in different computers. For example,
a proxy server may in the same machine with a firewall server
or it may be on a separate server and forward requests through
the firewall.
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