3.1 Introduction

This chapter presents the technical details of how to design large IP networks. An ad hoc collection of routers and nodes grown organically could lead to an unstable and congested network. The principles presented here are therefore not optional for large network designs. Anyone planning to design a large IP network should read this chapter those only interested in the physical topology of a scalable network may want to skip section 3.3.4 on 'Routing Design', while those with an interest in routing protocols should read section 3.3.4.

The design of large Internet protocol (IP) networks, such as a Global Internet backbone, involves many design parameters, e.g. the number of anticipated customers, connections to other service provider networks, anticipated traffic flows, routing implementation and many others. In all these areas scaling is vital to ensure the network not only works and is stable initially, but can grow to accommodate more customers, increased traffic and more points of connection.

The chapter uses the design of BT's and Concert's IP backbones, which form part of the global Internet, to demonstrate the techniques employed. Particular attention is given to the approaches used to scale the network while maintaining stability of the routing protocols employed.

3.2 Design Requirements

Many factors have to be considered in designing a large Internet network. An example of some of the typical requirements that have to be considered in the design process, broadly grouped into different categories, are listed below. Scaling has to be...