Summary

Despite its beginning as an illegitimate child of an IETF ratified technology, "flexible subnetting" proved itself vastly superior to the original form of subnetting with fixed-length masks. In and of itself, VLSM (as it later became known) represented a tremendous advance in the sophistication of the IP address space. Yet it would have an even greater contribution in the futurea contribution that no one could have foreseen. You see, in the mid-1990s, the Internet was experiencing unprecedented, phenomenal growth. This growth rate sorely tested the scalability of the Internet's mechanisms, including its address space.

Sadly, the IP address space demonstrated that its original architecture was not up to the task. The IETF sprang into action, launching numerous working groups to evaluate how best to shore up the failing address space. Numerous efforts were focused on developing stopgap fixes to shore up the sagging address space. These fixes are outlined and described in the next chapter. One notable development was Classless Interdomain Routing (CIDR). CIDR was made possible by having VLSM break the psychological barrier of variable-length network prefixes. CIDR is an important-enough aspect of the IP address space to warrant its own chapter. We will explore it in detail in Chapter 6.