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Despite all the buzz about software-defined networking (SDN), many organizations don’t yet have a clear idea of how it will benefit them. In this blog, I’ll tackle the what and why of SDN, and explain the different approaches you can consider.

What: A Disruptive Approach to Network Control

For the last quarter century, network devices have performed two types of processing:

So, if your network includes 200, 2000, or 20,000 network devices, that means you’re managing 200, 2000, or 20,000 control planes and keeping all of them up to date.

This network architecture remained about the same until 2007. That’s when Stanford University created a program called Clean Slate, which challenged program participants to propose how they would design the Internet if they could start with a clean slate and 20-30 years of hindsight. One of the ideas that took hold was SDN, defined as decoupling the control plane from the data plane. The control plane is implemented not on the network element, but on a centralized appliance or server. Applications can directly access the control plane—either to harvest network information or to program network behavior such as reserving bandwidth, assigning priority to traffic from certain IP addresses, and so on (Figure 1).

Figure 1  Traditional SDN Architecture: Control Plane Resides on a Centralized Server Instead of on Each Network Element


The standard SDN architecture shown in Figure 1 includes four components. One is the control plane, which resides on a server. Northbound APIs on the controller allow applications and the network to communicate. Agents on the network devices fulfill requests from the controller. Finally, OpenFlow is the Layer 2 protocol that the controller and agents use to communicate.

OpenFlow is part of the SDN story, but not the whole story. I’ll get back to that later in this blog.

Why Should You Care About SDN?

The goal of SDN is to let each business application (and not you) program the network to optimize its own performance. Use cases for SDN are still unfolding, but here are some of the more popular ones:

How Cisco Is Advancing Network Programmability

Cisco provides several approaches for network programmability, and all of them together are called Cisco Open Network Environment (ONE). The three approaches are:

Figure 2  Virtual Overlays Provide Another Approach to Network Programmability


Summing Up

SDN and network programmability are an important advance for IT teams as well as users because they:

Keep in mind that SDN is more than OpenFlow. Depending on your business needs, the best solution might be a traditional OpenFlow controller architecture, or it might be onePK APIs or virtual overlays.

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  1. Thanks for the great insight into sdn Joe!


  2. Great thread, Joe. really worthwhile read thru


  3. We are using Cisco routers and switches in our office and are very satisfied with it. Cisco is definitely making our lives easy :)


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