This article is the first part in the series about SD-WAN technology where we learn step by step what exactly Software Defined WAN (SD-WAN) is, how to build and use it, how and why using this concept could be beneficial for enterprises or even service providers and how to transform the current enterprise WAN to a SD-WAN solution. We are going to start with looking closely at Cisco Viptela product, however later on, we will describe other SD-WAN platforms in a similar manner.