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IIS URL Rewriting vs ASP.NET Routing

Posted by Al Tenhundfeld on Oct 26, 2008 11:49 PM

Community: .NET
Topics: Web Frameworks ,; .NET Framework
Tags: IIS ,; ASP.NET

With the recent release of URL-rewrite module for IIS 7.0 and the inclusion of ASP.NET routing into the .NET Framework 3.5 SP1, many ASP.NET developers are questioning how these two features relate to each other and when each should be used.

Ruslan Yakushev has an instructive post on LearnIIS.net.

The essential difference is that IIS URL rewriting is handled at a lower level than ASP.NET routing and is invisible to the client.

Ruslan provides a visual workflow of the IIS 7 URL Rewriting process. You'll see that the URL Rewrite Module is activated before the request is passed to a request handler, e.g., the ASP.NET managed ASPX handler. IIS URL rewriting is unaware of specific request handlers.

He also provides a visual workflow the ASP.NET Routing process. You'll see the ASP.NET routing is a request dispatcher and must be fully aware of which handler a specific request should be routed to.

From Ruslan's description:

1. URL rewriting is used to manipulate URL paths before the request is handled by the Web server. The URL-rewriting module does not know anything about what handler will eventually process the rewritten URL. In addition, the actual request handler might not know that the URL has been rewritten.

2. ASP.NET routing is used to dispatch a request to a handler based on the requested URL path. As opposed to URL rewriting, the routing component knows about handlers and selects the handler that should generate a response for the requested URL. You can think of ASP.NET routing as an advanced handler-mapping mechanism.

The IIS URL-rewrite module can be used with any type of Web application, which includes ASP.NET, PHP, ASP, and static files. ASP.NET routing can be used only with .NET Framework-based Web applications.

The IIS URL-rewrite module works the same way regardless of whether integrated or classic IIS pipeline mode is used for the application pool. For ASP.NET routing, it is preferable to use integrated pipeline mode. ASP.NET routing can work in classic mode, but in that case the application URLs must include file extensions or the application must be configured to use "*" handler mapping in IIS.

The URL-rewrite module can make rewriting decisions based on domain names, HTTP headers, and server variables. By default, ASP.NET routing works only with URL paths and with the HTTP-Method header.

In addition to rewriting, the URL-rewrite module can perform HTTP redirection, issue custom status codes, and abort requests. ASP.NET routing does not perform those tasks.

The URL-rewrite module is not extensible in its current version. ASP.NET routing is fully extensible and customizable.