Quickly develop and apply the skills needed to detect, prevent, and respond to new and emerging computer security exploits.

Former Air Force intelligence officer Richard Bejtlich is a security engineer at ManTech International Corporation's Computer Forensics and Intrusion Analysis division

Welcome toThe Tao of Network Security Monitoring: Beyond Intrusion Detection. The goal of this book is to help you better prepare your enterprise for the intrusions it will suffer. Notice the term "will." Once you accept that your organization will be compromised, you begin to look at your situation differently. If you've actually worked through an intrusiona real compromise, not a simple Web page defacementyou'll realize the security principles and systems outlined here are both necessary and relevant. This book is aboutpreparationfor compromise, but it's not a book aboutpreventingcompromise. Three words sum up my attitude toward stopping intruders:prevention eventually fails. Every single network can be compromised, either by an external attacker or by a rogue insider. Intruders exploit flawed software, misconfigured applications, and exposed services. For every corporate defender, there are thousands of attackers, enumerating millions of potential targets. While you might be able to prevent some intrusions by applying patches, managing configurations, and controlling access, you can't prevail forever. Believing only in prevention is like thinking you'll never experience an automobile accident. Of course you should drive defensively, but it makes sense to buy insurance and know how to deal with the consequences of a collision. Once your security is breached, everyone will ask the same question:now what?Answering this question has cost companies hundreds of thousands of dollars in incident response and computer forensics fees. I hope this book will reduce the investigative workload of your computer security incident response team (CSIRT) by posturing your organization for incident response success. If you deploy the monitoring infrastructure advocated here, your CSIRT will be better equipped to scope the extent of an intrusion, assess its impact, and propose efficient, effective remediation steps. The intruder will spend less time stealing your secrets, damaging your reputation, and abusing your resources. If you're fortunate and collect the right information in a forensically sound manner, you might provide the evidence needed to put an intruder in jail. Audience This book is for security professionals of all skill levels and inclinations. The primary audience includes network security architects looking for ways to improve their understanding of their network security posture. My goal is to provide tools and techniques to increase visibility and comprehension of network traffic. If you feel let down by your network-based intrusion detection system (NIDS), this book is definitely for you. I explain why most NIDS deployments fail and how you can augment existing NIDS with open source tools. Because this book focuses on open source tools, it is more likely to be accepted in smaller, less bureaucratic organizations that don't mandate the use of commercial software. Furthermore, large organizations with immense bandwidth usage might find some open source tools aren't built to handle outrageous traffic loads. I'm not convinced the majority of Internet-enabled organizations are using connections larger than T-3 lines, however. While every tool and technique hasn't been stress-tested on high-bandwidth links, I'm confident the material in this book applies to a great majority of users and networks. If you're a network security analyst, this book is also for you. I wrote this book as an analyst, for other analysts. This means I concentrate on interpreting traffic, not explaining how to install and configure every single tool from source code. For example, many books on "intrusion detection" describe the Transmission Control Protocol/Internet Protocol (TCP/IP) suite and how to set