John M. Stagger writes "Sometimes it is required to collect statistics on network traffic, e.g., for security purposes or for usage-based billing. One of the most preferred ways is to use a Cisco router that exports traffic data in a Netflow stream. Cisco routers are good. But what to do when dealing with a PC-router? The solution is to use a Netflow probe, a daemon that intercepts packets on a network interface of the router, captures statistics, and exports it in a stream of Netflow packets.
NDSAD (NetUP Data Stream Accounting Daemon) is a Netflow traffic probe. Developed by NetUP originally, NDSAD is now an open-source (GPL'ed) tool that captures packets and generates a Netflow (v5) accounting stream. It may be used for traffic accounting in the ISP billing system "UTM5" or for any other Netflow analyzing system."