OpenStack deployments are most often configured to use the libvirt KVM/QEMU driver to provide platform virtualization. When an instance is booted for the first time, OpenStack creates a port for each network interface attached to the instance. A virtual network interface called a tap interface is created on the compute node hosting the instance. The tap interface corresponds directly to a network interface within the guest instance and has the properties of the port created in Neutron, including the MAC and IP address. Through the use of a bridge, the host can expose the guest instance to the physical network. Neutron allows users to specify alternatives to the standard tap interface, such as Macvtap and SR-IOV, by defining special attributes on ports and attaching them to instances.