Url rewritng in ASP.net 4.0

What is URL Routing?

URL routing was a capability we first introduced with ASP.NET 3.5 SP1, and which is already used within ASP.NET MVC applications to expose clean, SEO-friendly “web 2.0” URLs. URL routing lets you configure an application to accept request URLs that do not map to physical files. Instead, you can use routing to define URLs that are semantically meaningful to users and that can help with search-engine optimization (SEO).

For example, the URL for a traditional page that displays product categories might look like below:

http://www.mysite.com/products.aspx?category=software

Using the URL routing engine in ASP.NET 4 you can now configure the application to accept the following URL instead to render the same information:

http://www.mysite.com/products/software

With ASP.NET 4.0, URLs like above can now be mapped to both ASP.NET MVC Controller classes, as well as ASP.NET Web Forms based pages.
For more info please visits scottgu's article..
http://weblogs.asp.net/scottgu/archive/2009/10/13/url-routing-with-asp-net-4-web-forms-vs-2010-and-net-4-0-series.aspx