A growing misconception is that software-defined networking (SDN) is a one-size-fits-all technology that solves a multitude of problems anywhere in an enterprise network. The LAN and WAN, however, are fundamentally different and have their own characteristics. By design, they require unique approaches to SDN.
Let's consider what makes them different.
Quality of service - The LAN implements QoS to mark traffic in a way that leads to prioritization in the WAN. Therefore, the SD LAN focuses on classification and marking. In contrast, applying SDN in the WAN focuses on shaping, prioritizing, and selective dropping. These are different functions, but usually classified together under the QoS umbrella.
Despite all these differences, we can find some common ground when applying SDN principles to the WAN and the LAN, especially around segmentation and simplified operations. With respect to network segmentation, SD-LAN has traditionally been at the forefront, with virtual LANs, virtual extensible LANs, and overlay tunnels. SD-WAN is now catching up in this area.
So while the goal of deploying SDN, namely agility and operational simplicity, is equally applicable to the WAN and the LAN -- the challenges they address in these two segments of the network are markedly different. Before you commit to either or both, make sure you understand the unique challenges of your network environment!
