Internet has grown abruptly from last decade. Existing Internet resources like infrastructure, connection policies and management tools are not effective and difficult to manage. To decouple control plane from routing plane Software-Defined Networking (SDN) concept is evolved. This paper revisits a) SDN brief history, definition b) SDN Layered architecture c) Mininet overview, and installation basics d) Simulating the SDN using Mininet emulator with sample experiments . This paper provides overview SDN research& tools towards network sofwarization.