nfdump is a set of tools to collect and process netflow data. It's fast and has a powerful filter pcap like syntax. It supports netflow versions v1, v5, v7, v9 and IPFIX as well as a limited set of sflow. It includes support for CISCO ASA (NSEL) and CISCO NAT (NEL) devices, which export event logging records as v9 flows.
nfdump is fully IPv6 compatible.