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HTTP Proxy Servers and Proxying
(Page 2 of 3)
Comparing Proxies and Caches
Proxying and caching are concepts
that have a number of similarities, especially in terms of the impact
that they have on basic HTTP operation. Like caching, proxying has become
more important in recent years, and also complicates HTTP in a number
of ways. The HTTP/1.1 standard includes a number of specific features
to support proxies, and also addresses a number of concerns related
The fact that both proxying and caching
represent ways in which basic HTTP client/server communication is changed,
combined with the ability of proxies to perform caching, sometimes leads
people to think caches and proxies are the same, when they are not.
A proxy is actually a separate element that resides in the HTTP request/response
chain, where caches can be implemented within any device in that chain,
including a proxy.
Another key way that caches and proxies
differ is that caches are used automatically when they are
enabled, where proxies are not. To use a proxy, client software must
be told to use the proxy, and supplied with its IP address or domain
name. The client then sends all requests to the proxy rather than to
the actual server that the user specifies.
Note: Most of my explanations here have focused on hardware proxy servers, but proxies are also commonly implemented as software in a client device. A software proxy performs the same tasks of processing requests and responses; it is much cheaper to implement than a hardware proxy, but cannot be shared by many devices.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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