public static string GetClientIPv4Address()
        {
            string ipv4 = String.Empty;

            foreach (IPAddress ip in Dns.GetHostAddresses(GetClientIP()))
            {
                if (ip.AddressFamily.ToString() == "InterNetwork")
                {
                    ipv4 = ip.ToString();
                    break;
                }
            }

            if (ipv4 != String.Empty)
            {
                return ipv4;
            }
            // 利用 Dns.GetHostEntry 方法，由获取的 IPv6 位址反查 DNS 纪录，
            // 再逐一判断何者为 IPv4 协议，即可转为 IPv4 位址。
            foreach (IPAddress ip in Dns.GetHostEntry(GetClientIP()).AddressList)
            //foreach (IPAddress ip in Dns.GetHostAddresses(Dns.GetHostName()))
            {
                if (ip.AddressFamily.ToString() == "InterNetwork")
                {
                    ipv4 = ip.ToString();
                    break;
                }
            }

            return ipv4;
        }
        public static string GetClientIP()
        {
            if (null == HttpContext.Current.Request.ServerVariables["HTTP_VIA"])
            {
                return HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
            }
            else
            {
                return HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
            }
        }