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10 key questions about software-defined networking (SDN)

Software-defined networking promises to deliver enormous benefits, from reduced costs to more efficient network operations. Here’s why SDN belongs on your network roadmap.
Written by Mary Shacklett, Contributor

Software-defined networking (SDN) is a way to virtualize networks for ease of configuration and maintenance in the same way that servers and storage are being virtualized. The difference is that SDN as a network solution is not nearly as far along as virtualization in the server and storage worlds.

Nevertheless, SDN is coming — and the more IT decision-makers and business leaders know about it, the better they'll be able to determine where and when to introduce it to their data centers. Here are 10 of the questions they're asking about SDN.

1: What does SDN do?

Like the server hypervisors used in virtualization, SDN introduces a layer of software between bare metal network components and the network administrators who configure and set them.  This software layer gives network administrators an opportunity to make their network device adjustments through a software interface instead of having to manually configure hardware and actually physically access network devices.

2: What does it mean when people talk about SDN decoupling hardware from software?

There are two planes in network devices — a control plane that determines where traffic is sent and a data plane that forwards traffic based on what the control plane tells it to do. With SDN, these two planes have been detached (or decoupled) from each other. The data plane (or data forwarding plane) remains with the network hardware — but the control plane (or controller) that makes decisions about where traffic will be sent is now executed through software. This separation makes network virtualization possible because you're no longer executing all the command or control rules on the hardware itself.

3: Why would you want to do this?

In today's networks, proprietary firmware on the switch determines where packets of data are forwarded. In an SDN, network administrators can actually shape network traffic. They can do this from a centralized network console that integrates the information and controls of all their network switches into a kind of network fabric. They can also change the data traffic rules on the fly if they need to.

The network administrator has complete control over network traffic through a software interface that SDN provides. This allows organizations to decrease their reliance on more expensive switches with proprietary firmware that performs these functions — and that must be set manually.

4: What other benefits does SDN provide?

SDN is an open-source product and as such is open and vendor-neutral software. Because SDN adheres to open standards, it can theoretically operate with any vendor's network hardware. From an IT perspective, this gives organizations the ability to avoid vendor lock-in for a host of network products. It also gives IT enormous agility because an open standards solution like SDN simplifies the task of connecting up to different clouds, applications, and network devices — and it allows network administrators to use software for much of the work they used to do manually.

5: What is the difference between SDN and OpenFlow?

OpenFlow is a protocol that uses APIs (application programming interfaces) to configure the switches in a network. SDN is software that gives network administrators a console interface where they can provision, manage, and break down networks without having to physically set up network switches and devices.

6: Will SDN provide end-to-end IT infrastructure visibility?

No, it won't. SDN can be centralized through a single console for an overview of the network, but it is only one of numerous elements that must be linked together into an end-to-end view of an application as the app traverses servers, storage, and the network. Where SDN contributes is by interfacing with an overall IT infrastructure management software that can track an application through servers, storage — and elements of the network.

7: Which technology vendors have embraced SDN?

Most of the big-name vendors all have SDN initiatives. Among them are Cisco, IBM, Alcatel, Juniper Networks, Broadcom, Citrix, Dell, Google, HP, Intel, NEC, and Verizon. With this much investment going into product development, SDN will assume a role in IT infrastructure at some point.

8: Why is SDN taking so long to adopt?

In some respects, SDN is a lot like the cloud when people first started talking about it. Enterprises are having trouble getting a handle on SDN and how it will specifically save them on network costs while improving overall network operations. And vendors haven't presented compelling use cases, either. As long as IT decision makers are confused, they will shy away from making the business case for SDN.

9: Can we afford to live without SDN indefinitely?

SDN's promise is in its ability to virtualize IT infrastructure. So far, the biggest portion of infrastructure that remains unvirtualized is the network. From an agility standpoint, enterprises will want to federate networks and move into and out of private and public clouds. This is where a facile technology like SDN begins to pay off. Sure, all these network hookup and breakdown operations can be done 'by hand' as they are now. But in the future, compressed project timeframes will drive IT to look for more efficient ways to configure and break down networks.

10: Is SDN a mature technology?

Not yet. Major technology vendors, while acknowledging that SDN is a future direction, have yet to agree on a common set of interoperability standards for all their network products, despite SDN's open heritage. Until these standards disputes are resolved, only early adopters whose businesses can't afford to live without a technology like SDN (think Google) will move forward with broad implementation. This doesn't mean that SDN shouldn't be on your IT roadmap. Network interoperability through software will come to the enterprise in one form or another. Today, SDN is the best bet.

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