Software-defined networking is one of the hottest buzzwords of 2014, but saying exactly what SDN is can be a challenge. SDN has its roots in the early 1990s, when both network managers and service providers began to express frustration with typical network architectures that inhibited innovation and change, were plagued by complexity and rigidity, and yielded high investment and operations costs. Many networking technicians have concluded that large networks can be built differently (and can deliver better results). A simple example of such a problem with current networks has a short name: IPv6. If networks had been built differently, the migration from IPv4 to IPv6 would not be the challenge that it is for many network managers.