Cisco Cookbook

Chapter 9. BGP

9.0. Introduction

Border Gateway Protocol (BGP) Version 4 is the lifeblood of the Internet. It is responsible for exchanging routing information between all of the major Internet Service Providers (ISPs), as well between larger client sites and their respective ISPs. And, in some large enterprise networks, BGP is used to interconnect different geographical or administrative regions.

Primarily to support the complexity of the public Internet, Cisco has added several clever and useful features to its BGP implementation. This book is focused on solutions to real-world problems, so we will not try to describe all of these features. And it would take a whole book to describe how to operate BGP in a large ISP network, so we will avoid discussing extremely large-scale BGP problems. Instead, we will look at two main classes of BGP problems: connecting a network to the public Internet, and interconnecting two or more Interior Gateway Protocols (IGP) in a private network.

A detailed discussion of the BGP protocol and its features is out of the scope of this book. For this type of information, we recommend referring instead to IP Routing by Ravi Malhotra (O’Reilly), or BGP by Iljitsch van Beijnum (O’Reilly). However, we will include a brief review of the most critical concepts.

Basic Terminology

BGP is an Exterior Gateway Protocol (EGP), which means that it exchanges routing information between Autonomous Systems (ASes). This is different from purely IGPs, such as RIP, EIGRP, and ...