ARP Table entries

Question

I am using following code to retrieve MAC address for an IP address.

 public string GetMACAddressFromARP(string ipAddress)
        {
            IPAddress ipAdd;
            try
            {
                ipAdd = IPAddress.Parse(ipAddress);
            }
            catch (Exception ex)
            {
                return null;
            }


            byte[] macAddr = new byte[6];
            uint macAddrLen = (uint)macAddr.Length;
            if (SendARP((int)ipAdd.Address, 0, macAddr,
            ref macAddrLen) != 0)
                return null;

            StringBuilder macAddressString = new StringBuilder();

            for (int i = 0; i < macAddr.Length; i++)
            {
                if (macAddressString.Length > 0)
                    macAddressString.Append(":");

                macAddressString.AppendFormat("{0:x2}", macAddr[i]);
            }

            return macAddressString.ToString();
        } 

but, I want to get complete MAC address which usually we can see by using arp -a command.

Any idea?