A communications protocol for controlling switches and routers remotely, OpenFlow grew out of the Clean Slate Lab, an ongoing project based at Stanford University with the grandiose aspiration of redesigning the Internet from scratch. In March, it became the banner technology of the Open Networking Foundation (ONF), a group formed by Deutsche Telekom, Facebook, Google, Microsoft, Verizon, and Yahoo to promote what they call software-defined networking (SDN), or networks that are as flexible and adaptable as computers. The ONF believes that this is necessary because cloud computing blurs the distinction between networks and computers as well as between public and private networks.
Though it started as a vision for the Internet, ONF has also gained traction among enterprise vendors, including Cisco, Brocade, and IBM. "It definitely is an enterprise technology," said Guido Appenzeller, the former head of Clean Slate who led the team that developed OpenFlow. "The Open Networking Foundation is biased towards carriers right now, but the majority of OpenFlow deployments are in the enterprise." In March 2010, he left Stanford to co-found Big Switch, which currently has 10 to 20 employees and a controller in beta testing with several enterprise customers.
OpenFlow's great promise is simpler management, separating logical connections from the underlying physical infrastructure. Instead of configuring multiple switches, network administrators only need to configure a single controller that can automatically govern the behavior of switches and routers. The architecture is conceptually similar to controller-based wireless access points, except that the controller communicates with switches using a standardized protocol (OpenFlow) so customers shouldn't be locked in to single-vendor networks. Whereas users of wireless controllers need to buy access points from the same company as the controller, Big Switch isn't even making a switch, it is instead testing its controller with switches from other Open Networking Foundation members.
The biggest barrier to implementation could be support, as no switches currently use OpenFlow out of the box. However, several vendors plan to demonstrate an OpenFlow network at the Interop show in Las Vegas next month, and Appenzeller is optimistic that enterprises will be able to add it to their installed base of networking gear. "Usually, all that's required is a BIOS upgrade," he said in an interview. This is because OpenFlow relies less than current enterprise networks on intelligence within Ethernet switches, replacing much of the software inside today's edge devices with a simple flow table. Complex routing and quality-of-service decisions are offloaded to the centralized controller, an architecture intended to make the network more scalable and flexible. The hope is that IT administrators will be able to treat a whole network as single virtual switch.
Because it aggregates multiple resources together, some ONF members describe OpenFlow as a virtualization technology. "We think we can be the VMware of networking," said Appenzeller. That's a bold claim, especially as VMware is itself a member of ONF. He emphasizes that Big Switch is not focused on storage or I/O, the most common uses for network virtualization so far. It aims to virtualize the entire network, from core optical switches to individual client devices across both LAN and WAN.
Managing just one switch instead of many has an obvious appeal, but Big Switch still has to prove that it can deliver on its promises. OpenFlow's move towards simpler switching is also a major reversal of the long-term trend in Ethernet switching, which is to add functionality and complexity. Modern application-aware switches look deep inside each data packet to fine-tune security settings or reduce the load on servers, and other approaches to making the network programmable involve running applications or virtual appliances on switches. The two aren't necessarily in conflict, but figuring out which to use in different parts of the network will be a challenge.