What is SDN? How Software-Defined Networking Changed Everything


The internet began as a system for applying addresses to servers. Now it’s a means for giving names to services, and distributing those services across the planet. SDN gave rise to a new way of implementing computing on the broadest scale of infrastructure, and has become, for better or worse, the whole point of networking.

The phrase software-defined networking (SDN) was coined when it was necessary to distinguish the concept from the hardware-based variety. Since that time, “SDN” has come to mean the type of dynamic configuration that takes place whenever software-based services in a data center network are made accessible through an Internet Protocol (IP) address. More to the point, SDN is networking now….

Much of the logic for SDN is moved inside the servers’ central processor, as just another user function. Some of it is moved inside simple switch and router appliances, where software is comprised of open-source operating systems and open-source controllers. Yet all of these phenomena are the side-effects of SDN, not the purpose. These changes happen because the real purpose of SDN is to move networking logic to a place where it can be more directly controlled and managed, and even more importantly, changed to suit the dynamics of variable workloads.


Here are SDN’s principal architectural tenets:

The flow of user data is separated from the flow of control instructions. In a physical network, data packets that belong to an application take the same route as internal instructions the network components need to coordinate their actions. As SDN engineers put it, the control plane is separated from the data plane. 

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