As a delivery vehicle for email, web pages, text, audio, and video, the global IP network is inspiring and intimidating in its vigor and resilience. While we could discuss at length the reasons for its vigor, the resilience of this network is in large part due to IP routing. This book introduces the reader to the intricacies of IP routing as it is implemented using Cisco routers. Each section leads the reader through the basics of configuring routing protocols. This approach gives the reader a quick start with the routing protocol under discussion and reveals the underlying concepts of IP routing. What is the packet-forwarding process? How is the routing table maintained? How do Distance Vector algorithms work? How do classful and classless route lookups differ? These and other concepts are illustrated in the discussions of static routing, RIP, IGRP, and EIGRP. The limitations of these traditional routing protocols will also become obvious to the reader.Variable Length Subnet Masks, route summarization, and fast convergence are key features in the design of any large IP network. These features are discussed in the OSPF chapter, which includes an introduction to Dijkstra's algorithm, the foundation for Link State protocols. Finally, BGP-4 is described in detail, showing the reader how to use BGP-4 attributes to set routing policies. This book is intended for anyone interested in IP routing. While it is appropriate for a beginner, it will also be useful for anyone already familiar with IP routing who is seeking a better understanding of the underlying concepts.