Step 1:
 Asp.net routing  is a component build in to the asp.net platform in System.Web.Routing.

Route is class and has some attributes like IRouteHandler.

Step 2 :
IRouteHandler calls the GetHttpHandler(HttpContext).

• Request related information in the HttpContext .
• Route related information in the Route Object.

Step 3 : 
There are 2 different types of route handlers.

•  Mvc Route Handler -> Which is associated with Mvc route.
•  Page Route Handler-> which is associated with Web Forms.

Step 4 :

• Mvc Route Handler creates and returns on instance of Mvc Handler.
• Mvc Handler expects important key value pairs.
• Controller Name  -> Name of the Controller.
• Action Name  -> Name of the Action Method.

Step 5:

• Mvc Handler calls the Default Controller Factory : IControllerFactory
• Its uses the reflection to call the Controller name from the Project Dll.
• Find the below image for your reference.