Overview
Only a few years ago, TCP/IP networks relied on simple distance-vector routing protocols and classful, 32-bit IP addressing. These technologies offered a limited capacity for growth. Today, network designers must retool, work around, or completely abandon these early technologies to build networks that can handle rapid growth and constant change. This course explores networking technologies that have evolved to meet this demand for scalability.

In networking, scalability is the capability to grow and adapt without major redesign or reinstallation. Allowing for growth seems simple enough, but it can be difficult to do without significant and costly redesign. For example, a network may provide a small company with access to e-mail, the Internet, and shared files. What would happen if that company tripled in size and demanded streaming video or e-commerce? Would the original networking media and devices adequately serve these new applications? Organizations can ill afford to completely re-cable and redesign their networks every time workers are moved, new nodes are added, or new applications are introduced.

Good design is the key to a network's capability to scale. More often than not, it is a poor design, and not an outdated protocol or router, that prevents a network from scaling gracefully. To be scalable, a network design should follow a hierarchical model. This chapter discusses the components of the hierarchical network design model and the key characteristics of scalable internetworks.