vSphere 5.1 and later releases support Single Root I/O Virtualization (SR-IOV). You can use SR-IOV for networking of virtual machines that are latency sensitive or require more CPU resources.

SR-IOV is a specification that allows a single Peripheral Component Interconnect Express (PCIe) physical device under a single root port to appear as multiple separate physical devices to the hypervisor or the guest operating system.

SR-IOV uses physical functions (PFs) and virtual functions (VFs) to manage global functions for the SR-IOV devices. PFs are full PCIe functions that are capable of configuring and managing the SR-IOV functionality. It is possible to configure or control PCIe devices using PFs, and the PF has full ability to move data in and out of the device. VFs are lightweight PCIe functions that support data flowing but have a restricted set of configuration resources.

The number of virtual functions provided to the hypervisor or the guest operating system depends on the device. SR-IOV enabled PCIe devices require appropriate BIOS and hardware support, as well as SR-IOV support in the guest operating system driver or hypervisor instance. See SR-IOV Support.

In vSphere, a virtual machine can use an SR-IOV virtual function for networking. The virtual machine and the physical adapter exchange data directly without using the VMkernel as an intermediary. Bypassing the VMkernel for networking reduces latency and improves CPU efficiency.

In vSphere 5.5 and later, though a virtual switch (standard switch or distributed switch) does not handle the network traffic of an SR-IOV enabled virtual machine connected to the switch, you can control the assigned virtual functions by using switch configuration policies at port group or port level.