VMware NSX is an SDN solution for mostly virtualized environments that addresses the intrinsic issues of traditional networks in the virtual world: slow adaptation to changes, forklift upgrades for new functionalities, multi-tenancy operational and implementation overhead, heavy reliance on hardware functionality, and limited scalability.
To successfully provide these benefits, the NSX solution must fit well with the underlying physical network infrastructure while keeping the benefits of a flexible, scalable, multi-tenant network fabric.