Introduction

In 1998, when we first started writing Advanced IP Network Design, we had no idea that the future would bring us more and more deeply into the realms of routed network design or that we would work together in the same place in closely related teams for all of these years. We originally wrote Advanced IP Network Design to help answer some of the questions we heard on a regular basis as engineers working in the Cisco Technical Support Center Routing Protocol and Escalation teams.

In many ways, we wrote this book for the same reason: to help customers we meet on a daily basis with the answers to the questions we always hear. What is the best way to build addressing for my network? How do I redistribute between two protocols without blowing up my network? When and why should I use BGP?

In other ways, however, this book is completely different. Of course, the most obvious difference is that the authors have worked on thousands more networks and interacted with thousands of different customers since that book was written. Each time a network engineer approaches us with a new problem to be solved or we see a good solution for a problem, we learn more about network design.

Less obvious, though, are the lessons that failed networks and bad designs have given us. Each time we propose something that does not work, we learn new things about routing design that we did not know before, and we learn to watch for new problems that we might not have expected before. Our goal in this book was to amalgamate these experiences, both good and bad, into a readable, understandable whole so that network engineers at all skill levels can draw on them. We are in a position to see new networks, new problems, and new solutions every day; this book is an attempt to share that experience with other network engineers.