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A Software-Defined Network (SDN) is the latest "coming soon" for the enterprise datacenter. Understand the basics to prepare for the inevitable questions and meetings in your future.
Is your enterprise ready for SDN? Just as virtualization defines complete servers in terms of 1s and 0s, and thus makes them a snap to provision, move, clone, and back up, defining network services in terms of 1s and 0 promises similar levels of agility. SDN is a big umbrella, the term meaning different things to different providers and technical approaches varying considerably. But the over-arching goal is to make networks much easier to reconfigure and to instantly and automatically adapt themselves to every change in demand.
The Controller is key
Current networks require manual intervention when changes are required. Whenever a change is needed to a network -- say, to tightly link a bunch of servers and storage systems that run a vital application -- network engineers have to reconfigure each and every switch and router involved. Each network component must be programmed individually. In a world of virtual servers and elastic computing clouds, the network's ability to adapt can become a significant bottleneck in the system.
As one former Yahoo CTO puts it, reconfiguring today's networks is like solving one of those puzzles in which you slide a set of 15 tiles around within a 16-tile grid to form a certain pattern. Every move can have bad side-effects.
SDN promises to free networks so that altering the network is as easy as point and click. Or even more agile than that: Software-defined networks can automatically allocate bandwidth to new flows of data immediately as they arrive, matching the flexibility and speed of elastic virtual server creation. The key to all this? Centralized control.
SDN calls for the implementation of a new networking component known as a controller that will, in a manner of speaking, sit above the network's physical fabric of cables and switches. From this vantage point, the controller will be able not only to "see" the network and its activities, but also command individual nodes to change their policies and behavior exactly as needed, moment by moment.
This controller's software will maintain a highly-detailed model of the network's many physical elements, the policies that govern different types of services (video gets priority over email, say, or servers A through J are never to be sent traffic-type X or Y), and all of the activities the network is handling right now.
It is this model, of course, that gives SDN its name. It will be an executable model, not just a static description, and it will enable the controller to make optimal decisions about how to provide different kinds of network service at any given moment.
In addition to making networks more agile, SDN promises to make them more secure, too. As it is, some datacenter networks are so large and complex that it's just about impossible to determine all of the possible pathways between any two servers. With a central controller in charge, however, all pathways can be identified and controlled, thus making security much tighter.
More is required than just this all-knowing controller. Switches that can understand the controller's commands are also needed. Today's switches are not ready to do this; generally, the know-how and tools needed to change their behavior more than a little are proprietary. For SDN to take off, switch makers will have to open their boxes to receive and act on commands generated by SDN controllers.
In addition, SDN requires the final acceptance of a concept that has been gaining speed in the industry: The divorce of the control plane and data plane within the network switch and fabric. Flexible, elastic SDN depends on being able to dynamically change the structure of the network through manipulation of the control plane while those changes are reflected in the behavior of the data plane. It's a significant change in the way that switches are designed and deployed.
Unfortunately, this change is not going to happen overnight, so don't expect SDN to dominate the market anytime soon. But SDN holds the potential, everyone agrees, to open up the networking equipment market to competition as never before and thereby bring prices down -- a change, of course, that incumbent suppliers are not necessarily keen to see.
If established switch makers open their boxes to work with standardized SDN schemes, they risk losing much of the control over the market they have enjoyed for decades, along with the profits that go with that control. Seeing this possibility, the Cisco Systems, Brocades, HPs, and Juniper Networks of the world are moving quite cautiously, proposing their own versions of SDN even as they voice support for emerging SDN standards such as OpenFlow and XMPP.
Still, standardized SDN protocols may well disrupt the networking market in a major way. If early-stage, standards-oriented SDN companies such as Big Switch, Nicira Networks (acquired by VMware last year for whopping $1.2 billion), Embrane, Midokura, and Vyatta get their way, their SDN controllers will be able to harness white-box commodity switches, selling at rock-bottom prices, into powerful networks. In fact, Google, an early and avid user of SDN, already has begun building its own networking gear, much as it does with servers. And Facebook is developing its own open-source switch.
It's early days for SDN, and for now, only the largest datacenters will be taking advantage of it. But here's how the forward-thinking CIO can get ready for the SDN revolution:
- Be proactive with your vendors. Get to know your current networking vendors's stand vis-à-vis SDN.
- Keep in mind that there will be many flavors of SDN hitting the market, some aimed at the datacenter, some at the wide-area network. Each has its own characteristics.
- Stay in touch with peers and industry consortia: see how they may be implementing the technology.
- Have your organization's networking chief explore the technology, perhaps by attending a training course or seminar. Make sure they share their information with the entire staff on their return.
- Hold onto your hat. SDN promises to be quite disruptive for suppliers and customers alike.