获取外网IP地址

public static string GetRealIP()
{
            string result = String.Empty;
            result = HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
            if (null == result || result == String.Empty)
            {
                result = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
            }
            if (null == result || result == String.Empty)
            {
                result = HttpContext.Current.Request.UserHostAddress;
            }
            if (null == result || result == String.Empty)
            {
                return "0.0.0.0";
            }
            return result == "127.0.0.1" ? GetUserIP() : result;
}

 public static string GetUserIP()
 {
            WebClient client = new WebClient();
            client.Encoding = System.Text.Encoding.Default;
            string response = client.UploadString("http://iframe.ip138.com/ipcity.asp", "");
            Match mc = Regex.Match(response, @"location.href=""(.*)""");
            response = client.UploadString(mc.Groups[1].Value, "");
            int i = response.IndexOf("[") + 1;
            string ip = response.Substring(i, response.IndexOf("]") - i);
            string ips = ip.Replace("]", "").Replace(" ", "");
            return ips;
 }