What are ISAPI Extenions?

ISAPI consists of two components: Extensions and Filters. In the last post we briefly discussed the laster. Now I’d like to shed some light on ISAP Extensions.

Most of the modern web sites do more than just deliver static HTML. When a site requires dynamic content, an application is needed to handle the requests, process them and respond.
ISAPI Extensions are true applications that run on IIS. They act as the engine for which the actual server side code is written. Clients can access ISAPI extensions in the same way they access a static HTML page. Certain file extensions can be mapped to be handled by an ISAPI extension ( Just like file associations in Windows , ex. Doc files are associated with WinWord.Exe).

Common ISAPI applications implemented as ISAPI extensions:

  • ASP.dll extension processes traditional ASP Pages
  • aspnet_isapi.dll extension processes ASP.NET Pages.

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