asp.net获取IP与MAC

用于获取客户端的IP与MAC，MAC内网可以用，外网无用！

using System.Runtime.InteropServices;

    [DllImport("Iphlpapi.dll")]
    private static extern int SendARP(Int32 dest, Int32 host, ref   Int64 mac, ref   Int32 length);
    [DllImport("Ws2_32.dll")]
    private static extern Int32 inet_addr(string ip);

 protected void Page_Load(object sender, EventArgs e)
{
        //获取IP
        this.ip_textbox.Text = GetClientIP();
        //获取MAC
        this.MAC_textbox.Text = GetClientMAC();
}

    ///<summary>
    ///得到客户端ip
    ///</summary>
    ///<returns>ip</returns>
    private string GetClientIP()
    {
        string 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;
        }
        return result;
    }


    ///<summary>
    /// 利用客户端ip得到客户端mac
    ///</summary>
    ///<param name="remoteip">客户端ip</param>
    ///<returns>int16类型的mac</returns>
    static private Int64 getremotemac(string remoteip)
    {
        Int32 ldest = inet_addr(remoteip);
        try
        {
            Int64 macinfo = new Int64();
            Int32 len = 6;
            int res = SendARP(ldest, 0, ref   macinfo, ref   len);
            return macinfo;
        }
        catch (Exception err)
        {
            Console.WriteLine("error:{0}", err.Message);
        }
        return 0;
    }


    ///<summary>
    /// int64类型的mac转换成正确的客户端mac
    ///</summary>
    ///<returns>mac</returns>
    private string GetClientMAC()
    {
        Int64 macid = getremotemac(GetClientIP());
        if (macid == 0)
            return "0";
        string beforeMacAddr = Convert.ToString(macid, 16);
        string endMacAddr = "";
        string[] macArray = new string[6];
        for (int i = 0; i < 6; i++)
        {
            macArray[i] = beforeMacAddr.Substring(i * 2, 2);
        }
        for (int i = 0; i < 6; i++)
        {
            endMacAddr += macArray[5 - i] + "-";
        }
        endMacAddr = endMacAddr.Substring(0, endMacAddr.Length - 1);
        endMacAddr = endMacAddr.ToUpper();
        return endMacAddr;
    }