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OpenFlow specification emerges: Rise of the software-defined network

OpenFlow switches and networks were all the rage at Interop 2011, indicating the rise of the software-defined network. But what exactly does that mean?

The OpenFlow specification burst onto the networking scene in the last few weeks with the launch of the Open Networking Foundation (ONF) and support of the specification announced by nearly all of the major networking vendors. In fact, OpenFlow switches were unveiled at Interop Las Vegas 2011 this week and software-defined networking was the buzz at the conference.

SDN allows network engineers to control and manage their networks to best serve their individual needs in order to increase network functionality while lowering the cost associated with operating networks. The Open Networking Foundation supports the OpenFlow specification, which ultimately enables software-defined networking.

What is the OpenFlow specification?

OpenFlow is a set of software APIs that allows a “controller” to communicate configuration information to a switch. The configuration usually refers to a “flow” and some “action” that is attached to it.

A “flow” is a defined set of frames or packets (similar to an MPLS flow) and a set of actions. Let me give some examples:

- Source IP/Port, Destination IP/Port and Drop.

- Source IP, Destination IP and QoS Action.

- Source MAC, Destination MAC and L2 Path

Using OpenFlow, you would send a set of rules to a switch or a router that “configure” the device. Each device will then use the data according to it’s type. A switch would update it’s MAC address tables for frame forwarding, a router would add access lists, a firewall might update it’s rules.

What is software-defined networking?

When organizations move the configuration of the network from the device to a software platform, switches become simpler and cheaper. But the key benefit is that the network configuration can be driven by a central controller.

The controller is a piece of software that has algorithms, maths, analysis and rules that derive into sets of rules that then use OpenFlow to download the configuration into the network devices. This makes it possible for the network to be dynamically reconfigured as the controller evaluates and rebalances the configuration. This is known as software-defined networking.

How are vendors using OpenFlow?

HP Networking: HP has significant resources allocated to OpenFlow. I saw a demonstration of the QoS capabilities that HP has delivered to the consortium, and the company has solid software programs underway for the controller platform.

NEC: You may not have heard of NEC as a networking vendor, but the company has a full range of products that NEC America has started to market. NEC has made several very large contributions to OpenFlow, and it has a complete range of switches that support OpenFlow. NEC is demonstrating its OpenFlow Controller at Interop.

Cisco: The networking giant is a member of the Open Networking Foundation, but I haven’t been able to find out its plans for OpenFlow. It’s possible that Cisco will feel that OpenFlow undermines the IOS software as a premium product. One of the most clearly defined benefits of OpenFlow is the reduction in cost of hardware switches, which doesn't lend itself to furthering any networking vendor's sales.

Avaya: The company is working hard on its Shortest Path Bridging strategy, but according to the people I spoke to, the company has no plans for OpenFlow at this time.

Arista: The networking upstart is not planning any OpenFlow releases and points out that it’s impossible to manage every flow on a device. Cisco has also made this point, however I understand this to be a mistaken view on how OpenFlow works. While it is possible to work per-flow with OpenFlow, it’s not a requirement; it’s a configuration choice.

Big Switch Networks: This recently funded startup focuses on OpenFlow solutions specifically for network virtualization. There are no details on the Big Switch website, but my guess is that they are developing controllers and switches.

If OpenFlow gets enough customers, it will radically change the networking industry because the control protocols that we use today (such as OSPF or Spanning Tree or DCB) will be replaced by a software controller. This drives commoditization of the hardware, but software controllers will become a whole new part of the networking industry. Functions, features and reliability of the software is what will define the success of OpenFlow.

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