Microsoft Hyper-V is a virtualization package for Windows Server 2008 and later releases on an x86-64 hardware platform. Hyper-V uses x86 hardware virtualization extensions (for example, Intel VT-x) to implement a hypervisor that hosts VMs as userspace processes. With VM-FEX for Hyper-V, the hypervisor performs no switching of VM traffic. Working with an installed VIC adapter, the hypervisor acts as an interface virtualizer, performing the following functions:

• For traffic going from a VM to the VIC, the interface virtualizer identifies the source vNIC so that the VIC can explicitly tag each of the packets generated by that vNIC.
• For traffic received from the VIC, the interface virtualizer directs the packet to the specified vNIC.

            All switching is performed by the external fabric interconnect, which can switch not only between   

            physical ports, but also between virtual interfaces (VIFs) that correspond to the vNICs on the VMs.