Does accelerated network interfaces gets added after all synthetic interfaces are added ?

Question

Hi team ,
Have a question with respect to Azure Accelertated Networking. When a virtual machine (VM) is created in Azure, a synthetic network interface is created for each virtual NIC. If the VM is configured with Accelerated Networking, a second network interface is created for each virtual NIC.Lets call this interface as vf interfaces. So if i deploy a virtual machine with 3NIC configuration , the VM would totally have 6 interfaces 3 synthetic and 3 vf interfaces. My question is whether vf interfaces are added to VM only after ALL synthetic interfaces are added ?
https://learn.microsoft.com/en-us/azure/virtual-network/accelerated-networking-how-it-works

Answer 1

Hello sharath babu,

Welcome to microsoft Q&A,Thankyou for posting your query here.

Yes, the VF interfaces are added to the VM only after all synthetic interfaces are added. This is because the synthetic and VF interfaces are paired together to act as a single interface.

When the VM is configured with Accelerated Networking, a second network interface is created for each virtual NIC that is configured.

The second interface is an SR-IOV Virtual Function (VF) offered by the physical network NIC in the Azure host.

The VF interface shows up in the Linux guest as a PCI device, and uses the Mellanox mlx4 or mlx5 driver in Linux, since Azure hosts use physical NICs from Mellanox.

The bonding is done by the netvsc driver, and the unique serial number provided by the Azure host is used to allow Linux to do the proper pairing of synthetic and VF interfaces for each virtual NIC.

Depending on the Linux distro, udev rules and scripts might help in naming the VF interface and in network configuration.

If the VM is configured with multiple virtual NICs, the Azure host provides a unique serial number for each one. It's used to allow Linux to do the proper pairing of synthetic and VF interfaces for each virtual NIC.

Both the synthetic and VF interfaces have the same MAC address. Together they constitute a single NIC from the standpoint of other network entities that exchange packets with the virtual NIC in the VM.

Hope this helps you.

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