Summary

When the IPv4 address space started to suffer under the strain of the Internet's explosive growth, the IETF responded quickly with a broad series of parallel efforts. Some of these efforts, as we've seen in this chapter, were the simplest of mechanisms. Others were remarkably complex and required years to develop. The hope was that the combination of the various short-term initiatives would buy enough time for the real solution (IPv6) to be developed. It is imperative that you appreciate the significance of many of these mechanisms. They have become so successful at recovering addresses and reducing the need for unique addresses that they have, together, become quite viable long-term solutions to the original problem of a vanishing address space. Consequently, they are still very much in effect today, and you need to understand their implications and constraints on IP addressing.

Initiatives notably absent from this chapter are private addresses, Network Address Translation (NAT), and Classless Interdomain Routing (CIDR). Together, these initiatives represent nothing less than a complete rewrite of the rules and architecture that governed the IPv4 address space. As such, they merit more than just a passing mention in a chapter. At the very least, they require their own chapters. The next chapter focuses on private addresses and NAT. We'll conclude our examination of the IETF's emergency evolution of IPv4 in Chapter 7 when we look at CIDR.