The diagram (source Intel: Virtual Machine Direct Connect (VMDc)) illustrates the close relationship between the network adapter and the virtual switch in providing networking to virtual machines. Currently most virtual server systems use a software virtual switch (vSwitch) to share access to the network adapter among the virtual machines (VMs).
The Single Root I/O Virtualization (SR-IOV) standard being implemented by 10G network adapter vendors provides hardware support for virtualization, allowing virtual machines to directly share the network adapter without involving the software virtual switch. Hardware sharing improves performance and frees CPU cycles to be used by the virtual machines. Software is still needed to configure and manage the switching function on the network adapter and integrate it with the management of the virtual machines. Virtual switch software is evolving, offloading performance critical functions to the network adapter, while continuing to provide the management interface.
Maintaining visibility and control of the edge is a critical component of an effective data center management strategy. Since virtual switches provide the first layer of switching in a virtualized environment, they comprise the network edge. Integrating the virtual switches into the overall network management system is essential.
Previously, the role of the VEPA protocol in integrating software virtual switches with hardware switches was discussed. VEPA support in the network adapter offers integration between a hardware switch and the network adapter. Most switch vendors support sFlow for traffic monitoring, and the combination of sFlow and VEPA would provide visibility and control of virtual machine traffic.
Ultimately, the evolving functionality of the network adapter/virtual switch is likely to deliver the visibility, performance, security and quality of service capabilities needed from the network edge. This trend is illustrated by the roadmap for the Open vSwitch, which includes support for both sFlow and SR-IOV on its roadmap, along with OpenFlow for control of the edge.