One class of tools that's come to the forefront in network security in recent years is network intrusion detection systems (NIDS). These systems can be deployed on your network and monitor the traffic until they detect suspicious behavior, when they spring into action and notify you of what is going on. They are excellent tools to use in addition to your logs, since a network IDS can often spot an attack before it reaches the intended target or has a chance to end up in your logs.
Currently, there are two main types of NIDS. The first type detects intrusions by monitoring the traffic for specific byte patterns that are similar to known attacks. A NIDS that operates in this manner is known as a signature-based intrusion detection system. The other type of network IDS is a statistical monitor. These monitor the traffic on the network, but instead of looking for a particular pattern or signature, they maintain a statistical history of the packets that pass through your network, and report when they see a packet that falls outside of the normal network traffic pattern. NIDS that employ this method are known as anomaly-based intrusion detection systems.
In this chapter you'll learn how to set up Snort, a signature-based IDS. You'll also learn how to set up Snort with SPADE, which adds anomaly-detection capabilities to Snort, giving you the best of both worlds. This chapter also demonstrates how to set up several different applications that can help you to monitor and manage your NIDS once you have it deployed.
Finally, you'll see how to set up a system that appears vulnerable to attackers, but is actually quietly waiting and monitoring everything it sees. These systems are called honeypots, and the last few hacks will show you how to quickly and easily set one up, and how to monitor intruders that have been fooled and trapped by it.