Excerpts

Introduction Our goal in writing Network Intrusion Detection, Third Edition has been toempower you as an analyst. We believe that if you read this book cover to cover,and put the material into practice as you go, you will be ready to enter theworld of intrusion analysis. Many people have read our books, or attended ourlive class offered by SANS, and the lights have gone on; then, they are off tothe races. We will cover the technical material, the workings of TCP/IP, andalso make every effort to help you understand how an analyst thinks throughdozens of examples. Network Intrusion Detection, Third Edition is offered in five parts. Part I,"TCP/IP," begins with Chapter 1, ranging from an introduction to thefundamental concepts of the Internet protocol to a discussion of RemoteProcedure Calls (RPCs). We realize that it has become stylish to begin a booksaying a few words about TCP/IP, but the system Judy and I have developed hasnot only taught more people IP but a lot more about IP as well--more thanany other system ever developed. We call it "real TCP" because thematerial is based on how packets actually perform on the network, not theory.Even if you are familiar with IP, give the first part of the book a look. We areconfident you will be pleasantly surprised. Perhaps the most important chapterin Part I is Chapter 5, "Stimulus and Response." Whenever you look ata network trace, the first thing you need to determine is if it is a stimulus ora response. This helps you to properly analyze the traffic. Please take the timeto make sure you master this material; it will prevent analysis errors as youmove forward. Tip Whenever you look at a network trace, thefirst thing you need to determine is if it is a stimulus or a response. The book continues in Part II, "Traffic Analysis" with a discussionof traffic analysis. By this, we mean analyzing the network traffic byconsideration of the header fields of the IP and higher protocol fields.Although ASCII and hex signatures are a critical part of intrusion detection,they are only tools in the analyst's tool belt. Also in Part II, we beginto show you the importance of each field, how they are rich treasures tounderstanding. Every field has meaning, and fields provide information bothabout the sender of the packet and its intended purpose. As this part of thebook comes to a close, we tell you stories from the perspective of an analystseeing network patterns for the first time. The goal is to help you prepare forthe day when you will face an unknown pattern. Although there are times a network pattern is so obvious it almost screamsits message, more often you have to search for events of interest. Sometimes,you can do this with a well-known signature, but equally often, you must searchfor it. Whenever attackers write software for denial of service, or exploits,the software tends to leave a signature that is the result of crafting thepacket. This is similar to the way that a bullet bears the marks of the barrelof the gun that fired it, and experts can positively identify the gun by thebullet. In Part III of the book, "Filters/Rules for NetworkMonitoring" we build the skills to examine any field in the packet and theknowledge to determine what is normal and what is anomalous. In this section, wepractice these skills both with TCPdump and also Snort. In Part IV, we consider the larger framework of intrusion detection. Wediscuss where you should place sensors, what a console needs to support for dataanalysis, and automated and manual response issues to intrusion detection. Inaddition, this section helps arm the analyst with information about how theintrusion detection capability fits in with the business model of theorganization. Finally, this book provides three appendixes that reference common signaturesof well-known reconnaissance, denial of service, and exploit scans. We believeyou will find this to be no fluff, packed with data from the first to the lastpage. Network Intrusion Detection, Third Edition has not been developed byprofessional technical writers. Judy and I have been working as analysts since1996 and have faced a number of new patterns. We are thankful for thisopportunity to share our experiences and insights with you and hope this bookwill be of service to you in your journey as an intrusion analyst. (c) Copyright Pearson Education. All rights reserved. Excerpted from Network Intrusion Detection: An Analyst's Handbook by Stephen Northcutt, Judy Novak All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.