virtual machines

Hyper-V Traffic Flow with SR-IOV

Q: If I have two virtual machines using SR-IOV provided by the same network card, will the traffic be sent to the connected network switch?

A: No. SR-IOV enables the network adapter to provide "virtual functions" that act like virtual NICs that are directly mapped to vmNICs that are configured for SR-IOV, completely bypassing the Hyper-V switch and enabling the lowest latencies but losing the ability to use features of the Hyper-V switch. Each virtual function on a NIC maps to one vmNIC. If multiple virtual machines on the same host have vmNICs that are connected to virtual functions on the same physical network card that are communicating with each other, then that traffic won't be sent to the network switch. Instead, the network adapter acts as a switch though a hardware-embedded switch that performs virtual function to virtual function routing (VF-VF). This means even though SR-IOV is being used, traffic between virtual machines using SR-IOV on the same network adapter will never leave the host, just as traffic between virtual machines on the same Hyper-V host using the Hyper-V virtual switch never leaves the host.

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