DDOS

In this particular incident, the initial tip-off led directly to the departmental network containing the compromised hosts. This information is not always so readily available, since IP spoofing can also be used to simulate traffic from machines on many different networks. Such a situation could be handled by repositioning the network monitor on the backbone (at M’ in the diagram, for example), and again examining the source MAC addresses of attack packets (but note that performance is likely to be a concern, with monitors dropping traffic at gigabit speeds).

Our monitor is a Linux system running the Snort lightweight intrusion detection system [3]. Demands on hardware are not very high: we use a redundant Pentium 133-based system with two 10/100Mbit/s network interface cards, 128MB memory and 4GB disk space. This allows us to use one interface to access the console, while the other is dedicated to the RSPAN traffic. It is configured with a minimum number of services running and no user accounts [4].

GD/NOTE/001 (01/01) This paper has been contributed by a Janet customer site, and records their experiences in investigating a denial-of-service attack committed using hosts at their site. We are very grateful to them for allowing us to publish this information and hope that it will be useful to others.