sentences:  In 2007, Casado, McKeown and Shenker co-founded Nicira Networks, a Palo Alto, California based company working on network virtualization, acquired by VMWare for $1.26 billion in July 2012.McKeown is active in the software-defined networking (SDN) movement, which he helped start with Scott Shenker and Martin Casado.SDN and OpenFlow arose from the PhD work of Casado at Stanford University, where he was a student of McKeown.