Enterprise networks are facing ever-increasing security threats from worms, port scans, DDoS, and network misuse, and thus effective monitoring approaches to quickly detect these activities are greatly needed. Firewall and intrusion detection systems (IDS) are the most common ways to detect these activities, but additional technology such as NetFlow can be a valuable enhancement.

NetFlow is a traffic profile monitoring technology developed by Darren Kerr and Barry Bruins at Cisco Systems, back in 1996. As a de facto industry standard, NetFlow describes the method for a router to export statistics about the routed socket pairs, and it's now a built-in feature for most Cisco routers as well as Juniper, Extreme and some other vendor's routers and switches.

When a network administrator enables the NetFlow export on a router interface, traffic statistics of packets received on that interface will be counted as "flow" and stored into a dynamic flow cache.

By Yiming Gong at SecurityFocus.

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