Greynets: A definition and evaluation of sparsely populated darknets

Darknets are often proposed to monitor for anomalous, externally sourced traffic, and require large, contiguous blocks of unused IP addresses---not always feasible for enterprise network operators. We introduce and evaluate the Greynet---a region of IP address space that is sparsely populated with 'darknet' addresses interspersed with active (or 'lit') IP addresses. Based on a small sample of traffic collected within a university campus network we saw that relatively sparse greynets can achieve useful levels of network scan detection.