用正则表达式判断是不是正确的IP地址的代码

 /// <summary>
       /// 判断是否是Ip地址
       /// </summary>
       /// <param name="str1"></param>
       /// <returns></returns>
        public static bool IsIPAddress(string str1)
        {
            if (str1 == null || str1 == string.Empty || str1.Length < 7 || str1.Length > 15) return false;

            string regformat = @"^\d{1,3}[\.]\d{1,3}[\.]\d{1,3}[\.]\d{1,3}$";

            Regex regex = new Regex(regformat, RegexOptions.IgnoreCase);
            return regex.IsMatch(str1);
        }