ASP.NET Integration Architecture

ASP.NET Integration Architecture

In IIS 6.0 and previous releases, ASP.NET was implemented as an IIS ISAPI extension.
In these earlier releases, IIS processed a request to an ASP.NET content type and then forwarded that request to the ASP.NET ISAPI DLL, which hosted the ASP.NET request pipeline and page framework. Requests to non-ASP.NET content, such as ASP pages or static files, were processed by IIS or other ISAPI extensions and were not visible to ASP.NET.
The major limitation of this model was that services provided by ASP.NET modules and custom ASP.NET application code were not available to non-ASP.NET requests. In addition, ASP.NET modules were unable to affect certain parts of the IIS request processing that occurred before and after the ASP.NET execution path.

Figure 1: IIS 6.0 & ASP.NET Pipelines
In IIS 7, the ASP.NET request-processing pipeline overlays the IIS pipeline directly, essentially providing a wrapper over it instead of plugging into it.
IIS 7 processes requests that arrive for any content type, with both native IIS modules and ASP.NET modules providing request processing in all stages. This enables services that are provided by ASP.NET modules, such as Forms authentication or output cache, to be used for requests to ASP pages, PHP pages, static files, and so on.
The ability to plug in directly into the server pipeline allows ASP.NET modules to replace, run before, or run after any IIS 7 functionality. This enables, for example, a custom ASP.NET Basic authentication module that is written to use the Membership service and SQL Server user database to replace the built-in IIS Basic authentication feature that works only with Windows accounts.
In addition, the expanded ASP.NET APIs use direct integration to enable more request-processing tasks. For example, ASP.NET modules can modify request headers before other components process the request, by inserting an Accept-Language header before ASP applications execute, which forces localized content to be sent back to the client based on user preference.

Figure 2: IIS 7 Integrated Mode
Because of the runtime integration, IIS 7 and ASP.NET can use the same configuration to enable and order server modules, and to configure handler mappings. Other unified functionality includes tracing, custom errors, and output caching.