The IEEE Software Defined Networks' eLearning Module "An Introduction to Software Defined Networking (SDN)" is the 101 module in this series and covers some basic technologies and concepts to provide the foundation for the upcoming modules. By the end of SDN 101, participants will have: Taken a look at networking past, and discovered that it lives on in the future; An understanding of the evolution of SDN and how it fits onto the networking landscape; An understanding of the basic architectures of SDN. We will put the pieces and layers together. This is to lay the groundwork for the next module: SDN 102. Finally, a brief look at the Open Source communities' invaluable contribution to SDN and how this drives innovation, disruption and sometimes chaos.