What is SDN (Software Defined Network)?

This is actually a very easy one to answer — it’s an umbrella term encompassing several kinds of network technology aimed at making the network as agile and flexible as the virtualised server and storage infrastructure of the modern data centre.

Simple, right? Well, if you’ve been out of the IT game for a while, or you’re just getting acquainted this might not make much sense. Perhaps the most important element to this terminology is to first understand that it is a concept, based around a way of formatting a network to enable greater control and visibility. In essence, a way of constructing a network that is better suited and more adaptable to modern times.

That is not to say that it is necessarily correct in all situations. It is something that owes its emergence to the rise of Big Data, virtualisation, and BYOD (bring your own device). These working realities require instant versatility, and so SDN, rightly or wrongly, has been hailed as the solution.

There are many technical explanations of the concept, most focusing on the idea that SDN simply involves the decoupling of the control plane from the forwarding plane and therefore redirects its functions to a centralised controller. Rather than the forwarding decisions in the network happening independently, a centralized software-based and server based controller is responsible for directing traffic. The controller effectively maintains the forwarding instructions across the network.

Think of it like traffic, but traffic involving people and train stations. The data centre is Victoria Station at 8.30am. Sheer chaos, with many different packets of data (commuters) all wanting to go in different directions to different places. If you were to arrive from the underground but need to find the right information and get on the train, all the while avoiding everyone else trying to do the same.

But there are many different trains to get to any one location. And many different ways to get to any of those trains. The station is large with multiple platforms. Some might be closed, some exits busy. Some ticket stands full, and some malfunctioning.

Given all these conditions, you could get delayed very easily. But if you had an omniscient, omnipotent route planner that knew everyone’s location, their destination, and could point everyone in the right direction at once, how much easier would that be?

Software-defined networking is essentially a software-based version of this omniscient being for all those travelling packets. What separates it from traditional, hardware-based “thinking” switches is that it uses software — which is much faster than physical switches — to do the thinking. At the click of a button, IT managers can define protocols on the basis of availability, efficiency, or capacity. What’s more it can be done remotely via an all-in-one dashboard.