There can be many reasons to reroute incoming Web requests. For instance, sometimes it's necessary to redirect a browser to a page based on user criteria without passing long lists of parameters in the URL. In the past, the only way to intercept such page requests and send them elsewhere was with ISAPI. Now, in ASP.NET, the IHttpModule interface provides notification of server requests, and lets you easily reroute them based on criteria other than browser type or version. Here the author demonstrates the use of IHttpModule for interception and explains the use of ISAPI filters for anyone who isn't yet using ASP.NET.
MSDN Magazine August 2002
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