Summary

Subnetting was an invaluable extension of the original IP address space's hierarchy. As useful as it was, its original form quickly demonstrated its limitations. These limitations, as you've seen in this chapter, are directly related to the inflexibility of carving a network address into fixed-length subnetwork blocks. Simply put, one size seldom fits all. Out of this inflexibility were borne waste and inefficiency. In retrospect, fixed-length subnet masks seemed revolutionary at their inception but have proven themselves more valuable for leading the way to the future. Thus, even though the original concept was vindicated, the execution left much to be desired.

Over time, a more sophisticated approach to subnetting was developed that enabled much greater flexibility. This approach, known as variable-length subnet masking (VLSM), is explained in the next chapter.