.net MVC:如何隐藏真实的网址？

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        // 自定义路由规则
        routes.MapRoute(
            name: "CustomRoute",
            url: "custom/{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        );

        // 默认路由规则
        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
        );
    }
}

<system.webServer>
  <rewrite>
    <rules>
      <rule name="RewriteRule">
        <match url="^custom/(.*)" />
        <action type="Rewrite" url="{R:1}" />
      </rule>
    </rules>
  </rewrite>
</system.webServer>