A software-defined wide area network (SD-WAN) can be seen as a combination of a software-defined networking (SDN) technology and a Wide Area Network (WAN) using common connections such as the Internet or Multiprotocol Label Switching (MPLS), a routing technique often used by service providers. But how does an SD-WAN look like and what are its implications on security? And how do the initial steps for a security assessment look like? This article is about to clarify those questions and provides an SD-WAN security assessment checklist at the end.