This document discusses software defined networking (SDN) and VMware's implementation of SDN using NSX. It defines SDN as separating the network control plane from the forwarding plane so that a control plane can control multiple devices. This allows network control to be directly programmable and infrastructure to be abstracted. The document outlines VMware NSX components that enable network virtualization and segmentation within a virtualized server environment. It also discusses how NSX supports routing between VMs on the same and different ESX hosts and provides network services through edge gateways.