U can use 2 routes together:
routes.MapRoute( //for localhost/Product/This-Is-The-Name-Of-The-Product/Item456.aspx
name: "",
url: "Product/{ProductName}/item{id}.aspx",
defaults: new { controller = "Product", action = "Index", id= UrlParameter.Optional }
);
routes.MapRoute( //this url for localhost/Product/123
name: "",
url: "Product/{id}",
defaults: new { controller = "Product", action = "Index", id = UrlParameter.Optional }
);