What’s an SDN? Who Cares? The Question is, Does It Help?

Mike Fratto
Mike Fratto

Summary Bullets:

  • There isn’t any consensus on the definition of SDN, but in the many variations are value propositions that may be useful to you.
  • In the drive to define SDN, established and start-up networking vendors are developing products that can improve your network operations, and that is what is important.

Chalk it up to my extensive studies in philosophy, but I like definitions that are clear, concise, and differentiate one thing from another. At times I can be pedantic and get dragged down in details, but I’m also practical and I know that while theory can be fun and games, at some point, stuff has to get done. What was more important to me when I ran a small data center was getting things done. I didn’t really care about what I called whatever technology I was using. What I cared about, and what the IT professionals that I talk to care about, is how will this new technology make my job better, more efficient, less prone to error, or more cost effective. What matters is not the foundational ideas underpinning a new technology, but the practical applications.

Software defined networking (SDN) is one of the current new technologies that is experiencing significant growing pains. There are multiple definitions of SDN which at least fit neatly under the SDN label. There are those who think SDN is synonymous with controller-based architectures like Openflow. Others think SDN requires abstracting the actual network from the physical network via encapsulation. Still others think SDN focuses on automating network configuration using existing tools. All of these definitions define the network, or parts of the network, via software. Until there is universal consensus on a definition of SDN (fat chance of that happening), every presentation, paper, or discussion is going to start with a definition of some type. Consider those definitions as perspectives from which the speaker is coming from rather than a definition of SDN as a whole.

How an OpenFlow start-up defines SDN will be very different from how an established network vendor defines it. Start-ups are doing something new and perhaps innovative, while the incumbents are leveraging what already exists in perhaps innovative ways. The question is, which strategy makes the most sense for you?

With OpenFlow, you can make flows cross the network like Billy in a Family Circus cartoon or you can make flows cross the network as the crow flies irrespective of all other flows. In either case, you can do so in an automated fashion. With traditional networking, you can use packet tagging, ACLs, and route injection to do something similar, but your choices are hampered by the underlying protocols.

Ultimately, you’re not going to implement an SDN. You’re going to automate and orchestrate network definitions across your enterprise. You might use transports as diverse as Ethernet, OpenFlow, an overlay, or multi-path Ethernet like SPB or TRILL, but you’re going to change how you design, implement, and monitor the network. The days of statically defined networks and managing devices via a CLI are numbered, because the tasks the network will perform will act in concert with other systems. That’s the aspect of SDN that’s exciting.

What do you think?

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