A Virtual Network Interface Card (vNIC) is a software-defined representation of a Media Access Control (MAC) interface of physical network interfaces. It is basically a virtual network card for a virtual machine. Multiple vNICs can share a physical network interface of a host node. In a way, networking starts with vNIC when a virtual machine sends data to other virtual machines or networking devices within a virtual environment or physical environment. In the following screenshot, the example virtual machine has a virtual network interface named net0 assigned with the virtio driver and configured with the bridge vmbr0:

The virtio is a Linux kernel driver used to virtualize virtual network interfaces and virtual disk devices. This is the default vNIC for new virtual machines in Proxmox. When virtio drivers are used inside a guest virtual machine operating system, the VM is fully aware that it is located inside a virtual environment. Thus the OS does not need to emulate a physical device. Any emulation adds extra overhead, robbing performance. The virtio has now become the virtualization standard for network and disk devices in a virtual environment.

Proxmox has four models of virtual network interfaces: Intel e1000, VirtIO, Realtek RTL8139, and VMware vmxnet3. Out of these four models, VirtIO provides the maximum network performance for a VM. All Linux-based operating systems come equipped with VirtIO drivers. For Windows, the VirtIO interface driver can be downloaded from http://www.linux-kvm.org/page/WindowsGuestDrivers/Download_Drivers.

For Mac OS, the VirtIO interface driver can be downloaded from https://github.com/pmj/virtio-net-osx.