Part II: Routing Protocol Basics
Although this book is primarily concerned with exterior gateway protocols—routing between different autonomous systems—it makes sense to look at internal gateway protocols as a first step because, conceptually and in practice, the two will affect each other's behavior. Thus, Chapter 4 begins with a consideration of protocols intended for routing within an autonomous system before moving into exterior gateway protocols. Chapter 4 concludes with an overview of the particular exterior gateway protocol, Border Gateway Protocol (BGP), which we will focus on. Chapter 5 provides an overview of how BGP Version 4 (BGP-4) operates and how and what it negotiates with neighboring routers. In addition, Chapter 5 covers the multiprotocol extensions to BGP-4, Capabilities Negotiation with BGP-4, and the TCP MD5 Signature Option for BGP. Understanding the basics of BGP, as described in Part II, is necessary before we can put the protocol's capabilities to use in practical routing design problems throughout the rest of the book.