SDN is coming soon to a network near you

What’s SDN?

Software Defined Networking (SDN) is an emerging network architecture that reduces cost while increasing quality and service agility over existing networks. Cost includes both capital and operational expenditures. Quality spans network security, robustness, manageability, mobility and flexibility. Service agility allows rapid introduction of new services on the network. (“Why SDN?” offers a good overview.)

A traditional networking device, for example a switch or a router, lumps network control functions together with a data-forwarding mechanism. These components are complex and proprietary, resulting in major shortcomings with the current networking technology. SDN separates these functions with open interfaces. It simplifies networking and lets us innovate.

Do we have a problem?

Conceptually, there are two major layers inside a networking device, one stacked on top of the other. The top layer, called control plane, is the device’s backbone. It controls the network data flow through the device and builds a logical map of the entire network by talking to its neighbors. The switch applications (for example, Telnet, HTTP) are built on top of the control plane. These programs use the logical map to provide their services. The lower layer, called the data plane, consists of a packet forwarding engine and network path data. This data is sourced from the logical map. The control plane runs in software whereas the data plane executes in hardware (Figure 1). Let’s now look at the current issues with traditional networking.

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Figure 1. An example of a traditional network.

First, traditional network devices are expensive. The control planes and their interfaces are proprietary and closed. Let’s say you have two switches from two different vendors in the same network. The data planes of any of these switches (assuming that such sharing is possible) cannot use the control plane of the other. These two planes contain significant intellectual capital of the vendor. This capital takes a tremendous amount of investment in money, effort and time to develop. It is only fair that the vendor look for a return on the investment.

Second, there’s high operational cost to manage the complex network devices. The vendors are innovating but inside their walls. This results in more proprietary features, complexity and therefore more effort to manage these devices.

Third, quality is affected by division of network intelligence across the vendor silos. An application does not have a single view of the underlying network. This often makes a desirable feature difficult to implement. For example, security policies cannot be defined centrally and enforced uniformly.

Fourth, operators are limited by the complex and proprietary hardware to introduce new services. This affects both service types and the deployment speed.

How SDN does it?

SDN separates the control plane from the data plane. The control plane and its applications are run as software on an appliance. The data plane runs on low-cost switch hardware. Multiple such switches can connect and be controlled by a single control plane instance. SDN also has two additional features. First, it uses software to logically centralize network intelligence and the entire network view. Second, it allows external software applications to customize the network.

For more information, see:

So you can now write application software to customize your network! These applications run on the SDN controller.

Figure 2 shows the how SDN extracts the control plane in Figure 1 to flatten the network. The open nature of SDN allows you and me to extend it in our own ways. There lies its flexibility and strength.

Speaking of open interfaces, there’s one called Open Flow that’s gaining serious attention from the industry. OpenFlow is managed by a nonprofit consortium called the Open Networking Foundation (ONF). It currently has more than 80 member companies including IBM.

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Figure 2. SDN network corresponding to the traditional network in Figure 1.

Isn’t SDN too new to pay any serious attention?

Despite it being new on the scene, there’s huge industry support for SDN from IBM and other major vendors. How does $1.26 billion sound to get your attention? Or what about the following examples:

SDN clearly has strong market support!

But wait; what about some SDN implementation proof points? Check out this massive implementation.

So what, specifically, is IBM doing with SDN? The IBM Programmable Network Controller from IBM System Networking is an OpenFlow-based network control appliance. The IBM RackSwitch G8264 is the industry’s first OpenFlow single-chip switch to pass the one terabit per second barrier! IBM is also developing DOVE (Distributed Overlay Virtual Ethernet), an SDN software overlay technology. It uses SDN to build virtual network infrastructure. DOVE abstracts the physical network from hypervisor hosts. You can use DOVE to make network changes in software rather than in hardware.

Here are a couple of proof points from the field using joint IBM and NEC OpenFlow solutions:

  • Tervela confirmed predictable performance of big data for their complex and demanding business environments.
  • Selerity improved near real-time decision making for global financial markets.

What you can do

  • Educate yourself about SDN even if you have no use for it now. It will come in really handy in the near future.
  • Ask questions—a lot of questions. Talk to the vendors (about their approach and products), your colleagues (about technology fit and its benefits), people who are using it today and the experts.
  • Ignore the hype. Look for real-world proof points.


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Sandip Lahiri

About Sandip Lahiri

Sandip Lahiri is an IBM Healthcare Industry Architect, CPHIMS. He works across all IBM brands covering hardware, software and services. His focus areas are PureSystems, Social Media and Analytics. He has been in the IT industry for 20 years. He has hands-on experience in solution design, delivery, sales and marketing across several industries. Sandip has deep skills in RFID. He wrote the RFID Sourcebook and has seven U.S. patents.