softflowd listens promiscuously on a network interface and
semi-statefully tracks network flows. These flows can be reported
using NetFlow version 1, 5 or 9 datagrams. softflowd is fully IPv6
capable: it can track IPv6 flows and export to IPv6 hosts.

More details about softflowd's function and usage may be found in the
softflowd wiki in following URLs:
https://github.com/irino/softflowd/wiki/softflowd
https://github.com/irino/softflowd/wiki/softflowctl