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Correlating NetFlow Data for Proactive Security: Network Notoriety


In this short article the reader will first learn what NetFlow is and how it works. Next the reader will understand how it can be as an important security tool. Finally, a technique for correlating NetFlow results with public sources of Internet reputation, along with the tool “Netoriety,” which implements the technique, will be introduced and explained.
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Virtual Switching: Fundamentals of VSS

December 14, 2011 at 6:22 am PST

Cisco’s been doing virtualization in various forms on the network side for quite a long time. One incredibly powerful feature that I think is still amazingly under utilized is the Cisco VSS or Virtual Switching System.

The ability to make two 6500′s look like a single switch so that you can have your cake and eat it too.  Its the epitome of giving us the redundancy and availability we need while simultaneously allowing us to use the extra capacity that could normally sit unused. Easier management and configuration make this a no-brainer that more network managers should consider as ‘required’ in their design. Check out our ‘Fundamentals of VSS‘ to get yourself started.

Even more after the jump…

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Objective – Net Superiority

I’ve had some recent discussions with colleagues in the armed forces regarding cyber security and how they consider “cyber” to be the fourth warfighting domain along with land, air, and sea. They describe how cyber has its own terrain made up of computing resources. As I further thought through this concept I saw a striking resemblance between the network and air warfare. To elaborate on this thought I must first set the context around the concept of air supremacy.

There are probably many different variations of the definition of air supremacy but let’s just use “the degree of air superiority wherein the opposing air force is incapable of effective interference” for the purpose of this blog.  I borrowed this definition from NATO.  There are two key words in the definition, “degree” and “effective.” Prior to achieving supremacy one must first move from parity, through superiority to eventually supremacy. Air parity is the lowest degree in which a force can control the skies above friendly units. In other words, prevention of opposing air assets from overwhelming land, air, and sea units. Read More »

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Observations from the Darknet

Sometimes it is interesting to take a look at darknet data and see what you come across.  If you are not familiar with the term “darknet,” I am using the definition used by some in the service provider community where a darknet is a set of address space which contains no real hosts. That means no client workstations to initiate conversations with servers on the Internet.  It also means no advertised services from those ranges, such as a webserver, a DNS server, or a database server.  There is really no reason to see any traffic destined for addresses within those ranges.  From a network point of view, it should be as desolate and deserted as the town of Pripyat in the Ukraine, within the evacuation zone due to the Chernobyl disaster back in the 1980s. However, in practice, you do see traffic to those address ranges, which is what makes that traffic somewhat interesting.  Traffic destined to those ranges could be the result of malware attempting to locate machines to infect, part of a research project or it could be as simple as a misconfiguration or a typographical error.  One example of traffic resulting from a typo would come from attempting to ping a host and typing the wrong address in.  However, it would be hard to believe that all of the traffic seen in a darknet is the result of a mistake.

Setting up a darknet does not have to be hard to do.  If your organization has address space that is not being used, then all that you need to do is advertise a route for those addresses and leave them unused.   In our case, we have advertised several ranges and we collect Netflow data for the traffic destined to them from a nearby Cisco router.  That Netflow data is exported to a collector, such as nfcapd, where it is aggregated for further analysis.

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Security and NetFlow: The time is now!

For those of you that have been around the networking world for a while, NetFlow is far from a new technology. Cisco developed NetFlow years ago and it has become the industry standard for generating and collecting IP traffic information. NetFlow quickly found a home within network management providing valuable telemetry for overall network performance and management. Nine versions later NetFlow is growing in popularity not solely due to its value to network management but as a critical component of security operations. Over the past 12 months I have encountered more and more large enterprises that view NetFlow as one of their top tools for combating advanced threats within their perimeters.

The dynamic nature of the cyber threat landscape and growing level of sophistication and customization of attacks are requiring organizations to monitor their internal networks at a new level. IP flow monitoring (NetFlow) coupled with security focused NetFlow collectors like Lancope’s StealthWatch is helping organizations quickly identify questionable activity and anomalous behavior. The value that NetFlow provides is unsampled accounting of all network activity on an IP flow enabled interface. I bring up unsampled because of its importance from a security perspective. While flow sampling is a valid method for network management use cases sampling for the sake of security leaves too much in question. An analogy would be having two different people listen to the same song. One person gets the song played in its entirety, unsampled, and the other only hears the song in 30-second intervals. While neither may be musically inclined the person who had the advantage of listening to the song in its entirety would be able more accurately hum or sing back that song than the person that only heard 30 second snippets of the song. Furthermore the ability to identify that song during radio airplay would be in favor of the individual that was able to listen to the song in its entirety. This holds true for IP flow information when leveraging the information for detecting malicious or anomalous traffic. Some malicious code will only send a single packet back to a master node, which would most likely be missed, in a sampling scenario.

Further increasing the value of IP flow monitoring is Cisco’s recent release of Flexible NetFlow (FnF). FnF introduces two new concepts to flow monitoring. The first is the use of templates and the second expands the range of packet information that can be collected as well as monitor more deeply inside of a packet. This allows greater granularity in the information that is to be monitored as well a providing different collector sources for different sets of information. You can search for Flexible NetFlow on Cisco’s main website to get more technical details.

Are you using NetFlow for security operations? I welcome any feedback, good or bad regarding your experience and opinions on the value that IP flow information provides for detecting this ever-changing threat landscape.

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