C#获取真实IP地址（IP转为长整形、判断是否内网IP的方法）

    /// <summary>
    /// C#获取客户端真实IP地址
    /// </summary>
    /// <returns></returns>
    public static string GetIP()
    {
        string ip = HttpContext.Current.Request.ServerVariables["http_x_forwarded_for"];
        if (UserCheck.IsNull(ip)) ip = HttpContext.Current.Request.ServerVariables["remote_addr"];
        return ip;
    }

 /// <summary>
    /// C#将IP地址转为长整形
    /// </summary>
    /// <param name="ip"></param>
    /// <returns></returns>
    public static long IpToNumber(string ip)
    {
        string[] arr = ip.Split('.');
        return 256 * 256 * 256 * long.Parse(arr[0]) + 256 * 256 * long.Parse(arr[1]) + 256 * long.Parse(arr[2]) + long.Parse(arr[3]);
    }
    /// <summary>
    /// C#判断IP地址是否为私有/内网ip地址
    /// </summary>
    /// <param name="ip"></param>
    /// <returns></returns>
    public static bool IsPrivateIp(string ip)
    {
        long ABegin = IpToNumber("10.0.0.0"), AEnd = IpToNumber("10.255.255.255"),//A类私有IP地址
         BBegin = IpToNumber("172.16.0.0"), BEnd = IpToNumber("172.31.255.255"),//'B类私有IP地址
         CBegin = IpToNumber("192.168.0.0"), CEnd = IpToNumber("192.168.255.255"),//'C类私有IP地址
         IpNum = IpToNumber(ip);
        return (ABegin <= IpNum && IpNum <= AEnd) || (BBegin <= IpNum && IpNum <= BEnd) || (CBegin <= IpNum && IpNum <= CEnd);
    }
    /// <summary>
    /// C#获取真实IP地址
    /// </summary>
    /// <returns></returns>
    public static string GetIP()
    {
        string ip = HttpContext.Current.Request.ServerVariables["http_x_forwarded_for"];
        if (UserCheck.IsNull(ip)) ip = HttpContext.Current.Request.ServerVariables["remote_addr"];
        else//代理ip地址有内容，判断是否符合ipv4地址或者是否为内网地址
        {
            ip = ip.Trim().Replace(" ", "");
            if (!Regex.IsMatch(ip, @"^\d+(\.\d+){3}$") || IsPrivateIp(ip))
                ip = HttpContext.Current.Request.ServerVariables["remote_addr"];//不符合规则或者内网/私有地址使用remote_addr代替
        }
        return ip;
    }