Does SDN require a controller?
A specialized SDN controller, whether or not it uses the OpenFlow protocol, is not required to implement a software-defined network. A controller enables SDN functionality by allowing network users to "control" or modify network flows independently from physical network devices.
In the OpenFlow community, for example, with standards developed by the Open Networking Foundation, the answer is yes. Most OpenFlow implementations will include an OpenFlow controller from providers that include Big Switch, HP, IBM, NEC, DELL (and many others), or via open source software.
Other SDN options don't necessarily include a controller. VMware 's Nicira acquisition, for example, will enable the company to implement SDN protocols in its vSwitch software, which does not require an OpenFlow controller. Cisco' s SDN architecture -- Open Network Environment (ONE) -- supports OpenFlow, but Cisco does not require an SDN controller, preferring to embed intelligence in its Ethernet switches and network management software. Similarly, Brocade supports OpenFlow, but does not require its use. Embrane provides a different example of SDN functionality that does not require OpenFlow or a controller. Embrane's Heleos platform has Layer 4-7 software including load balancers, firewalls, VPNs and WAN optimization. ADARA, Pertino and LineRate are additional examples of SDN start-ups that do not require OpenFlow or a controller.
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