C＃将IPv6转换为ASN字符串

Question

我正在尝试将IPv6转换为ASN。我已经能够获得两个64位的部分，但我不知道如何将它组合在一起以获得单个ASN作为字符串，以便我可以在数据库中查找它。

到目前为止的代码：

byte[] addrBytes = System.Net.IPAddress.Parse(ipv6Address).GetAddressBytes();
if (System.BitConverter.IsLittleEndian)
{
    //little-endian machines store multi-byte integers with the
    //least significant byte first. this is a problem, as integer
    //values are sent over the network in big-endian mode. reversing
    //the order of the bytes is a quick way to get the BitConverter
    //methods to convert the byte arrays in big-endian mode.
    System.Collections.Generic.List<byte> byteList = new   System.Collections.Generic.List<byte>(addrBytes);
    byteList.Reverse();
    addrBytes = byteList.ToArray();
}
ulong addrWords1, addrWords2;
if (addrBytes.Length > 8)
{
    addrWords1 = System.BitConverter.ToUInt64(addrBytes, 8);
    addrWords2 = System.BitConverter.ToUInt64(addrBytes, 0);
}
else
{
    addrWords1 = 0;
    addrWords2 = System.BitConverter.ToUInt32(addrBytes, 0);
}

请帮助将addrWords1和addrWords2放在一起代表ASN的字符串？

E.g。 2001：200 ::应该返回ASN 42540528726795050063891204319802818560