Christy says an SDN that distributes the controller to the switches would improve the performance of communication between switch and controller, and improve the operation of the SDN. He says Juniper's QFabric architecture is an example of an SDN with a distributed control plane.
Arista Networks says its switch customers can implement SDNs using either controllers or distributed network control. The company says there are pros and cons to both approaches, but that both are required to implement a comprehensive SDN.
Arista defines four "pillars" of software-defined cloud networking: cloud topology, distributed control, network virtualization and management/automation. OpenFlow is one API among several that can be used in the management/automation pillar if the SDN is controller-based, according to Arista. Others are existing CLIs, SNMP, XMPP, Netconf, OpenStack, and APIs in VMware's vSphere virtualization software, Arista says.
There are use cases for each, says Jayshree Ullal, Arista CEO. For OpenFlow, she sees the use case as dynamic packet redirection for network tap aggregation, lawful intercept/CALEA, and topology-agnostic network segmentation deployments.
Whether that translates into broad adoption remains to be seen.
"The more use cases it can be deployed in, the stronger its applicability long term," she says.
Software-defined networking has the opportunity to be ubiquitous, she agrees. But whether OpenFlow will be the one API, or OpenStack, or Netconf, or XMPP, or VMware or another hypervisor is difficult to predict. Ullal says they all promise topology-agnostic network virtualization optimized for application and workload mobility.
At VMworld, Arista demonstrated how to build clouds with one-touch provisioning of virtual machines and up to 50,000 network nodes using the tools in its EOS operating system software and CloudVision interface. XMPP is the API in CloudVision. [Also see: "Ex-Cisco exec drawn to startup Arista's software architecture"]
"There's no reason tomorrow it couldn't be an OpenFlow or OpenStack API," Ullal says. "But here's a well-defined interface. Today we do Netconf and XMPP because it was easy to implement, well-defined specs and we had some customer interest there."
Ullal says Arista's EOS will support a suite of APIs for different "use cases" that customers demand. Right now, Arista is detecting initial demand for OpenFlow among research institutions, and in data centers to redirect flows to taps and tap aggregators.
"One new technology does not preclude the pragmatic approach of also enhancing existing technologies," she says with regard to SDNs. "In operational environments where legacy prevails, enhancing existing technologies is even more important than innovation."
Rather than OpenFlow driving SDNs, SDNs will drive OpenFlow, Ullal believes.
"The combination of OpenFlow with broader SDN APIs is vital for OpenFlow to be more broadly deployed," she says.
Big Switch's Forster says SDNs would not have the buzz or momentum in the market today were it not for OpenFlow. And with myriad APIs each tailored for a specific "use case," that means there needs to be fewer to program to.