Chapter 1. The Border Gateway Protocol

When networks were small, there was no concept of interior and exterior gateway protocols; a network ran a routing protocol, and that was the end of it. The Internet, for instance, ran the Hello Protocol on devices called fuzzballs (before they were called routers), until some problems in the Hello Protocol led to the development of RIP (Routing Information Protocol). RIP was run as the only routing protocol on the Internet for many years. Over time, however, the Internet grew (and grew and grew), and it became apparent that something more was needed in routing protocols—a single ubiquitous protocol couldn't do all the work that routing protocols were being required to do and scale in any reasonable manner.

In January 1989 at the 12th IETF meeting in Austin, Texas, Yakov Rekhter and Kirk Lougheed sat down at a table and in a short time a new exterior gateway routing protocol was born, the Border Gateway Protocol (BGP). The initial BGP design was recorded on a napkin rumored to have been heavily spattered with ketchup. The design on the napkin was expanded to three hand-written sheets of paper from which the first interoperable BGP implementation was quickly developed. A photocopy of these three sheets of paper (see Foreword) now hangs on the wall of a routing protocol development area at Cisco Systems in Santa Clara, CA.

From this napkin came the basis for BGP as we know it today. Now, with countless contributors and hundreds of pages in tens of documents, deployed in thousands of networks, interdomain routing in the Internet today is defined as BGP.

This book is about BGP, from the basics of the BGP protocol itself to information on deploying BGP in networks stretching from small and simple to very large and extremely complex. We'll begin with an overview of the BGP protocol itself here in Chapter 1. We'll then move into various deployment situations, starting with small enterprise networks using BGP internally and to connect to the Internet. From there we'll continue to move through ever-larger scale deployments of BGP, discussing how BGP and its extensive policy mechanisms fit into network architectures. We continue by providing details about finely tuning BGP to perform optimally and scale effectively in an array of deployment scenarios. We finish with in-depth discussions on debugging and troubleshooting various problems within the protocol and BGP networks.