< back to overview

SDN. Like Thinking.

Sep 30, 2014

A non-technical, easy guide to explaining SDN.  

Software-Defined Networking (SDN) is an emerging network architecture that is used in many real-world applications of network computing. For those not in the technical trenches, SDN may seem hard to understand, mainly due to its complex technical nature. If you haven’t grasped SDN just yet, this post for you.

Let’s start with the ONF definition of SDN:

“The physical separation of the network control plane from the forwarding plane, and where a control plane controls several devices.”

For someone who is new to SDN, this technical definition may not help you understand what SDN is or what it can do. Instead of our getting bogged down in the technical weeds, I like to think of a software-defined network like the human body.

As noted in the organization definition, the network’s control and forwarding planes are separated in a software-defined network. Comparing this to the body, a controller acts as the brain and provides a birds-eye view of overall network functions and performance. The forwarding plane acts as the nerves and muscles. This plane does the heavy lifting by sending messages to the limbs, or in SDN terms, the switches and routers. This function enables a network administrator to easily command the performance of the limbs, much like deciding to move your arm and doing so via control of the brain. What is important is that you do not have to consciously send signals to each muscle or organ to get your body to function properly. You only need to think that you want to, say, move your arm to pick up that glass. Your brain translates that desire into the many specific commands to your muscles.  And just as your brain automatically knows to send signals to move the appropriate limb, the software-defined network is programmed to perform as needed (this is where the software part comes in). Applications merely convey their needs, desires, or intent and the network takes care of the rest.

This is not a one-way transaction. The brain (controller) can also receive messages from the limbs (switches and routers). It controls the amount of information being sent to the limbs and makes sure that they aren’t overloaded with commands. Similar to the human body, software-defined networks can experience strain, and by having messages sent to and from the brain, the system is programmed to alleviate issues if something arises.

In its simplest form, SDN allows network managers to stop focusing on hardware and manual configuration, and instead focus on the services that are running across the network. We don’t have to painfully think through every action and nerve impulse; the body just does it. With SDN, networks can operate effortlessly with increased flexibility and agility in delivering new applications and services.

Now that you have a basic understanding of SDN, feel free to impress your friends and colleagues with your newfound knowledge.

How do you explain SDN to others? Share with us in the comments.

–          Dan Pitt, Executive Director