OpenFlow Technology
OpenFlow is similar to Virtualization Technology (VT) as an hardware-assisted virtualization technology. By giving direct access to the dataplane's forwarding tables, OpenFlow allows the virtual network elements to set complex rules and behaviors to the switch's forwarding planes. These virtual network elements can somewhat be compared to FlowVisor experiments
OpenFlow can also be "emulated" by the virtual network element in an upcoming feature upgrade. While not all forwarding plane capabilites are available many of these features can be emulated by sending the appropriate set of commands and configurations on the devices. This enables OpenFlow support in legacy devices without any firmware upgrade but can be more limited than native implementations.