The main flowc limitation is impossibility correct aggregation of tcp connections based on client port number. As result, the netflow database is large especially on heavy traffic routers. This limitation is a feature of NetFlow technology, because it is not possible to know, which side was an initiator of tcp connection. In case if one tcp port is less than 1024, then this port is tcp server port and another port belongs to tcp client. In this case the client port number aggregation is possible. This feature significantly reduce the netflow database size.