Using NetFlow Data For More Robust Network Security

While NetFlow data may traditionally be seen as a network infrastructure tool, smart security teams can get tons of benefits out of the collection of IP traffic statistics, too.

"Security professionals should consider every NetFlow and IPFIX router a security camera that allows them to go back in time and investigate suspect traffic reported by any number of security appliances," says Michael Patterson, CEO of Plixer.

According to Dr. Vincent Berk, CEO of FlowTraq, security pros may have to battle to get their hands on the data if other infrastructure people—the ones 'responsible for moving packets but not securing them—are at all territorial. But it is worth the effort.

"This has created a climate where security professionals have increasingly had trouble getting their hands on streams of NetFlow throughout their organizations," Berk says. "However, the advanced values that a security professional can get from NetFlow is enormous. Patterns of traffic, such as scans, worm-propagation behavior and brute-force password attacks show up very clearly in NetFlow. So do DDoS attacks."

[Are you using your human sensors? See Using The Human Perimeter To Detect Outside Attacks.]

According to experts, just as log data analysis and SIEM help contextualize security events, so too can NetFlow data offer a safety net for catching unwanted behavior.

"Understanding who is talking to whom; how they are talking; and for how long; can all add a much needed dimension to network situational awareness," says Matt Webster, CTO for Lumeta.

NetFlow analytic data is particularly great at detecting anomalous "hot-spots" of activity that could indicate existing issues or an active breach, says Jody Brazil, president and CTO of FireMon

"For example, NetFlow data can be leveraged to isolate compromised hosts by identifying those communicating with botnet command and control machines, or to highlight those hosts utilizing unusual ports," Brazil says.

Similarly, NetFlow data can also help spot malicious server behavior indicating compromise there, says Nicole Pauls, director of product management at SolarWinds.

"It can help monitor for unexpected or unwanted server activity-since servers are going to have more well-known behavior patterns-looking for volume, ports and destinations unknown," Pauls says.

Brazil also says that NetFlow data can offer enough visibility into traffic to see how cloud-based applications are being used by showing which applications are being accessed over the network at any given time. This can be a huge benefit for security teams seeking to sniff out rogue IT functions that may not be handling data in a secure or compliant manner. And speaking of compliance, NetFlow data can also offer solid documentation to prove compliance with network-related security policies.

"Since flow data can be archived indefinitely, in many cases it allows companies to provide demonstrable evidence of IT compliance with internal governance policies, external regulations, and industry best practices," he says.

As organizations seek to up their security game through NetFlow data, Berk offers some friendly advice—don't just look at traffic at the network edge.

"People that only look at their border traffic will miss large ranges of visibility on what is happening inside the network," he says. "Data exfiltrations, theft and other intelligence gathering may be going on inside the network, and you will never see it if you only grab the NetFlow from your border devices. Deploy far and wide."

Of course, as with any security data stream, NetFlow data could pose the potential of overwhelming a security analyst. But there are ways to winnow down the stream and sift through that information to make it useful.

"One of the big challenges with NetFlow is that it can be like trying to watch every CCTV camera in a large city - it's overwhelming to consume, and most of the data is pretty boring," says Dwayne Melancon, CTO of Tripwire. "Smart enterprises watching suspicious changes in system state as a filter for NetFlow data - they monitor configuration changes, new executable 'payloads' showing up on a system, new listening ports being opened and then use that to focus on NetFlow."

Have a comment on this story? Please click "Add Your Comment" below. If you'd like to contact Dark Reading's editors directly, send us a message.