How to handler 404 errors when using URL Routing in ASP.Net

 Hi ,

I have been using using System.Web.Routing for url routing in global.asax file  code is as below.

 public static void RegisterRoutes(RouteCollection routes)
        {
           
            routes.MapPageRoute("Home", "", "~/Home.aspx");
          
        
            routes.MapPageRoute("Posts", "Posts/{blog_url}", "~/blog-description.aspx");
            
          
        }
        protected void Application_Start(object sender, EventArgs e)
        {
            RegisterRoutes( RouteTable.Routes);
        }

Now this works fine on local  but when i move the same to live it shows error 404 .I want to create a log actually what url is called.