Recently Software Defined Network (SDN) technology has become important and openflow is focused on as basic building block of SDN. Those technologies are important for creating test bed for experimental protocol by standardizing protocol to manage switches and production use to reduce maintenance cost of network by automation via software as network virtualization. As they are emerging technology, the development of software to use openflow is hot area. In this presentation, I review SDN, openflow and openvswitch which is opensource software implementation of openflow. And then survey openflow controllers describing their features and goal. The target audience is those who would like to take overview of those technology. No deep knowledge is required.