Why didn't strategies like network functions visualization (NFV) and software-defined networking (SDN) emerge at the same time that compute and storage capacities were being virtualized and delivered through cloud computing? Well, it turns out that network virtualization is a lot harder than compute and storage virtualization...
Because of the tight coupling, the virtual networking is inherently harder to scale than the virtual compute or storage. Of course, the hypervisor vendors took the easiest possible route, used simplistic VLAN-based layer-2 switches in the hypervisors and pushed all the complexity to the network edge/core, while at the same time complaining how rigid the network is compared to their software switches.
– Ivan Pepelnjak
Read the full article on blog.ipspace.net to get an interesting, concise rundown of the technological challenges that NFV and SDN are trying to surmount.