A Brief Introduction To OpenFlow, November 14, 2011 OpenFlow is a specification now managed by the Open Networking Foundation, which defines the functions and protocols used to centrally manage switches via a centralized controller.
The problem with today's network stems from how Ethernet was originally designed as a simple framing protocol. As LANs became more complex, the Spanning Tree had to be introduced to remove the possibility of broadcast storms from loops in the network, thus reducing the network to a single rooted tree (not all paths could be used).
Quality of service is implemented on a per-device basis with no context of the neighborhood, resulting in inefficient traffic management. VLANs were introduced to segment traffic and extend Layer 2 networks across a campus or wide area. Link Aggregation (LAG), a.k.a. bonding, was developed to increase capacity between switches over multiple physical interfaces, but often less than 75% total capacity could be used.