Thursday, April 14, 2011


Team Cymru defines a darknet as "a portion of routed, allocated IP space in which no active services or servers reside" ( Darknets, as it turns out, are an analytical goldmine. Why is this you ask? The answer has to do with signal-to-noise ratio.

Since there are no legitimate services or servers on "dark" portions of the network, all the traffic destined for the darknet becomes suspect and therefore analytically interesting. For example, consider an aggregate analytic that looks at the top destination ports for inbound TCP traffic by number of sessions. If we were to look at traffic across the whole network, we would probably get something like this after running our analytic:

Port | Session Count
80 | #######
53 | #######
25 | #######

Not surprisingly, we see that our routine web, DNS (yes, even DNS over TCP), and SMTP traffic (all necessary and expected for normal business operations) would top the list. In this case, standard business traffic is the noise that hides the signal of the suspicious/malicious traffic. Could we somehow lower the noise to make the signal jump out at us? Yes -- through the power of darknet!

What happens, however, if we look at the same aggregate analytic, but now restrict it to look only at traffic destined for our darknet? That's where we might get a more interesting result:

Port | Session Count
5678 | #####

Why would we have traffic inbound to TCP port 5678 (which I chose purely for illustrative purposes)? I don't know why, but I do know that what we now have is a jumping off point. Is someone attempting reconnaissance of our network? If they are, what are they looking for? Do we have other systems communicating with the outside world on that port that we never noticed before? These questions and others would need to be answered by network traffic analysis via deep-diving into the data with the end result of determining the true nature of the traffic.

So, this is just a quick example of traffic analysis triggered via a darknet provided jumping off point. Hopefully it has helped to illustrate the broader power of the darknet. Darknets are truly an analytical goldmine.

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