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HTTP: The Definitive Guide

Cover of HTTP: The Definitive Guide by David Gourley... Published by O'Reilly Media, Inc.

Proxy Redirection Methods

So far, we have talked about general redirection methods. Content also may need to be accessed through various proxies (potentially for security reasons), or there might be a proxy cache in the network that a client should take advantage of (because it likely will be much faster to retrieve the cached content than it would be to go directly to the origin server).

But how do clients such as web browsers know to go to a proxy? There are three ways to determine this: by explicit browser configuration, by dynamic automatic configuration, and by transparent interception. We will discuss these three techniques in this section.

A proxy can, in turn, redirect client requests to a different proxy. For example, a proxy cache that does not have the content in its cache may choose to redirect the client to another cache. As this results in the response coming from a location different from the one from which the client requested the resource, we also will discuss several protocols used for peer proxy-cache redirection: the Internet Cache Protocol (ICP), the Cache Array Routing Protocol (CARP), and the Hyper Text Caching Protocol (HTCP).

Explicit Browser Configuration

Most browsers can be configured to contact a proxy server for content—there is a pull-down menu where the user can enter the proxy's name or IP address and port number. The browser then contacts the proxy for all requests. Rather than relying on users to correctly configure their browsers to use proxies, ...

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