The controller is the logical control center of the SDN network, communicating with switches via its "southbound" interface to provide networking instructions and communicating with applications via its "northbound" interface.
In SDN's purest form, the controller has all the intelligence: Switches are dumb, commercial off-the-shelf (COTS) devices that are managed by the controllers.
Operators that find this pure approach too rigorous can instead opt for an overlay, espoused by Cisco Systems Inc. (Nasdaq: CSCO), VMware Inc. (NYSE: VMW) and other vendors. In the overlay approach, the SDN network runs as a software layer on top of existing networks. Switches can be either COTS or proprietary.
SDN controller deployments are mostly to be found in data centers currently, but they have also been deployed in wide area enterprise networks and are creeping into wide area service provider networks too as carrier-class capabilities come to market and business cases are identified.
SDN, in theory, allows networks to be programmable, flexible and cheaper to run. It's foundational to the New IP -- the transformation of carrier networks from cost centers to revenue drivers delivering value to customers. (See Introducing 'The New IP' .)
Light Reading took a quick look at the SDN controller marketplace and compiled a list of vendors and open source organizations that are offering, or have developed, SDN controllers or the code that can be used to develop one (in the case of the open source community).
The list is split into two: vendors with commercial products; and the open source projects/organizations that are engaging the wider community to develop SDN controller software. Many of the commercial vendor controllers are based on open source code, particularly that developed by OpenDaylight , a collaborative project set up by the Linux Foundation .
Brocade Communications Systems Inc. (Nasdaq: BRCD) recently threw its weight behind open source SDN, introducing the Vyatta Controller based on OpenDaylight. (See Brocade Debuts OpenDaylight SDN Controller.)
In the commercial marketplace, VMWare and Cisco are the two giants competing for control. Cisco's SDN weapon is its Application Centric Infrastructure (ACI), while VMware's arms itself with its NSX software.
Cisco and VMware support the philosophy that intelligence should be in the software, but Cisco's proposition supports its own proprietary hardware that shares network management responsibilities with its controller. VMware runs as a layer atop other companies' networking hardware.
Other companies fighting for SDN market share have mostly developed products that are based on the OpenFlow protocol and its associated networking philosophy. OpenFlow is the vanguard of the pure SDN approach.
And it's not just the vendors that are developing SDN controllers: AT&T Inc. (NYSE: T) is developing a home-grown SDN controller. (See AT&T Working on Home-Grown SDN Controller for Later in 2014 .)
One of the major considerations for data center and network operators looking to deploy SDN controllers is whether they are truly interoperable and multivendor: One of the main promises of SDN is that it will free operators from vendor lock-in.
Multivendor support is a big deal, notes Roz Roseboro, senior analyst at Heavy Reading . "Operators don't want to be tied down. They don't want the choice of controllers to influence what switches they can use. They want to mix and match with whatever integration work is required," Roseboro says. Operators want to be able to work with the networking hardware they have, without ripping anything out.
Operators also need to consider whether to adopt a centralized or distributed approach, says Roseboro, who is preparing a report on SDN controllers. "There are some who believe there should be a master controller that watches over everything, and others who believe some of the intelligence should be on the hypervisor so it can make local decisions," she says.
So, here is our list of SDN controllers. If there are others out there, we can easily add them in as they emerge. Let us know about additions and updates using the comment board below.
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