Routing in ASP.NET 4.0 vs Routing in ASP.Net 3.5

ASP.NET Routing allows us to define routing rules, which map a route pattern – such as Categories/CategoryName – to a class that handles the request. These routing rules are defined when the application starts, in Global.asax’s Application_Start event handler. In ASP.NET 3.5, we must create a route handler class, which passes information about the incoming request and returns an HTTP Handler to process the request.