Ourmon and network monitoring performance
James R. Binkley, Bart Massey · 2005
Abstract Ourmon is an open-source network management andanomaly detection system that has been developed over a period of several years at Portland State University.Ourmon monitors a target network both to highlight abnormal network traffic and measure normal traffic loads.In this paper, we describe the features and performance characteristics of Ourmon.Ourmon features include a novel mechanism for running multiple concurrent Berkeley Packet Filter (BPF)expressions bound to a single RRDTOOL-style graph, as well as various types of "top talker " (top-N) filtersaimed at conventional network flow measurements and anomaly detection. These features permit a variety ofuseful and easily-understood measurements. One problem that sniffer-based network monitor sys-tems face is network-intensive attacks that can overwhelm monitoring and analysis resources. Lab experi-ments with an IXIA high-speed packet generator, as well as experiences with Ourmon in a real network environ-ment, demonstrate this problem. Some recent modifications to Ourmon have greatly improved its performance.However, minimum-size packets in a high-speed network can still easily make a host lose packets even atrelatively slow rates and low monitor workloads. We contend that small packet performance is a general net-work security problem faced by current monitoring systems including both open source systems such as Our-mon and Snort, and commercial systems. 1 Introduction The Ourmon [15] network monitoring system is anopen-source tool for real-time monitoring and measurement of traffic characteristics of a computer network. Itruns on FreeBSD, and Linux. (There is also code for Solaris, although it is currently unmaintained.) Ourmon'sfeature set includes various top talker filters and multiple instances of the Berkeley Packet Filter (BPF) whichtaken together allow us to capture interesting features of the envelope of incoming IP packets. Network mon-itoring and data visualization are typically performed