NEW Modules & Handlers in Asp net 2.0

In ASP.NET, requests are passed from the Web server through an Internet Server Application Programming Interface (ISAPI) filter and on to the actual ASP.NET runtime

When IIS receives a request, the extension is mapped to an ISAPI filter according to the IIS settings. The extensions .aspx, .asmx, .asd, and others are mapped to the aspnet_isapi.dll which is simply an ISAPI filter that launches the ASP.NET runtime. Once a request hits the ASP.NET runtime, it starts at the HttpApplication object, which acts as the host for the ASP.NET Web application. The HttpApplication object:

1. Reads the machine and application level configuration files
2. Passes the request through one or more HttpModule instances. Each HttpModule provides a service such as session maintenance, authentication or profile maintenance. These modules pass the request back to the HttpApplication.
3. Passes the request to an HttpHandler based on the verb and the path. The verb refers to the HTTP verb used in the request (GET, POST, FTP, etc.) and the path refers to a URL within the application. Depending on how the handlers are configured, the request may be processed as an ASP.NET page (System.Web.UI.Page is an implementation of IHttpHandler), or the request may trigger another action such as batch-compilation of all Web pages (precompilation.asd triggers the PrecompHandler).

In ASP.NET 2.0, this model stays intact. However several new modules and handlers have been added to provide additional services. As with ASP.NET 1.x, you can extend, replace or reconfigure any of the module or handler classes in order to provide your own custom functionality.

New Modules
Naturally, new HttpModules have been added to support the new services offered in ASP.NET 2.0. Specifically, an ASP.NET application with default module settings will include new modules for:
SessionID—The session identification mechanism has been split off the ASP.NET 1.x Session module in order to provide greater control over cookies, URL rewriting and other forms of session ID generation.
Role Management—A new module has been added for providing role based services in support of the new user identification mechanisms. This module helps link ASP.NET applications to the role based security built into the .NET framework.
Anonymous Identification—The new personalization features support anonymous users. This module helps keep track of which features an anonymous user can access and how these features are maintained between requests.
Profile Management—The profile module links to the new profile service and helps provide user specific persistent data storage.

New Handlers
In addition to the new modules, ASP.NET 2.0 introduces new handlers to support the application configuration tools and other new features such as the batch compilation request. The most important of the new handlers include the ".axd" family which process Website administration requests. These handlers launch the internal administration tools that allow developers to configure ASP.NET users as well as other settings. The administrative handlers include:
Web Administration—The WebAdminHandler is the main page for the administrative Website. This handler provides the starting point for administering ASP.NET 2.0 Web applications.
Trace—The ASP.NET 1.x TraceHandler has been improved and is the only "axd" handler that was available in ASP.NET 1.x.
Web Resources—Web resources can now be configured post-deployment thanks to the new administrative tool and the WebResourcesHandler.
Cached Images—The CachedImageServiceHandler provides support for caching graphical components.
Precompile—As mentioned earlier, the PrecompHandler can be used to batch compile all of the ASPX pages in an ASP.NET application.
Web Part Export—The WebPartExportHandler provides support for storing and transferring Web Part layouts. Web Parts are a new mechanism for personalizing the look and contents of a portal style Web application.
As always, the HttpForbiddenHandler is linked to any file type that should never be returned. In ASP.NET 2.0, the list of forbidden file types has been expanded to include master pages, skin files and other new developer components