Routing is the process of directing an HTTP request to a controller and the functionality of this processing is implemented in System.Web.Routing. This assembly is not part of ASP.NET MVC. It is actually part of the ASP.NET runtime, and it was officially released with the ASP.NET as a .NET 3.5 SP1.

System.Web.Routing is used by the MVC framework, but it's also used by ASP.NET Dynamic Data. The MVC framework leverages routing to direct a request to a controller. The Global.asax file is that part of your application, where you will define the route for your application.

Following is the code from the application start event in Global.asax for an MVC application.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.Mvc;

using System.Web.Routing;

 

namespace MVCFirstApp {

   public class MvcApplication : System.Web.HttpApplication {

      protected void Application_Start(){

         AreaRegistration.RegisterAllAreas();

         RouteConfig.RegisterRoutes(RouteTable.Routes);

      } }}

 

Following is the implementation of RouteConfig class, which contains one method RegisterRoutes.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.Mvc;

using System.Web.Routing;

namespace MVCFirstApp {

   public class RouteConfig {

      public static void RegisterRoutes(RouteCollection routes){

         routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

         routes.MapRoute(

            name: "Default",

            url: "{controller}/{action}/{id}",

            defaults: new{ controller = "Home", action = "Index", id = UrlParameter.Optional});

      } }}

You will define the routes and those routes will map URLs to a specific controller action. An action is just a method on the controller. It can also pick parameters out of that URL and pass them as parameters into the method.

So, this route that is defined in the application is the default route. As seen in the above code, when you see a URL arrive in the form of (something)/(something)/(something), then the first piece is the controller name, second piece is the action name, and the third piece is an ID parameter.

 

Understanding Routes

MVC applications use the ASP.NET routing system, which decides how URLs map to controllers and actions.

When Visual Studio creates the MVC project, it adds some default routes to get us started. When you run your application, you will see that Visual Studio has directed the browser to port 63664. You will almost certainly see a different port number in the URL that your browser requests because Visual Studio allocates a random port when the project is created.