Overview
A scalable network requires an addressing scheme that allows for growth. As you add new nodes and new networks to the enterprise, existing addresses may need to be reassigned, bloated routing tables may bog down routers, and the supply of available addresses may simply run out. You can avoid these unpleasant consequences with careful planning and deployment of a scalable network-addressing system.

Although network designers can choose among many different network protocols and addressing schemes, the emergence of the Internet and its nonproprietary protocol, TCP/IP, has meant that virtually every enterprise must implement an IP addressing scheme. In fact, as companies such as Apple and Novell have recently migrated their network software to TCP/IP (and away from their proprietary protocols), many organizations opt to run TCP/IP as the only routed protocol on the network. The bottom line is that today's administrators must find ways to scale their networks by using IP addressing.

Unfortunately, the architects of TCP/IP could not have predicted that their protocol would eventually sustain a global network of information, commerce, and entertainment. 20 years ago, IP version 4 (IPv4) offered an addressing strategy that, although scalable for a time, resulted in an inefficient allocation of addresses. Over the past two decades, engineers have successfully modified IPv4 so that it could survive the Internet's exponential growth. Meanwhile, an even more extendible and scalable version of IP, IP version 6 (IPv6), has been defined and developed. Today IPv6 is slowly being implemented in select networks. Eventually, IPv6 may replace IPv4 as the Internet's dominant protocol.

This chapter explores the evolution and extension of IPv4, including the key scalability features that engineers have added to it over the years: subnetting, classless interdomain routing (CIDR), variable-length subnet masking (VLSM), and route summarization. Finally, this chapter examines advanced IP implementation techniques, such as IP unnumbered, Dynamic Host Configuration Protocol (DHCP), and helper addresses.