怎么判断某个.asmx链接有效？

try
            {

                System.Net.WebRequest myRequest = System.Net.WebRequest.Create(

                "http://192.168.0.6/rootserver/DirService.asmx ");


                System.Net.WebResponse myResponse = myRequest.GetResponse();


                return "ok ";
            }
            catch (Exception ex)
            {
                return ex.Message.ToString();
            }