OpenStack is responsible for configuring and managing many different types of virtual and physical network devices and technologies across the cloud infrastructure.
OpenStack uses the libvirt KVM/QEMU driver to provide platform virtualization in default Nova configurations. When an instance is booted for the first time, Neutron assigns a virtual port to each network interface of the instance. KVM creates a virtual network interface called a tap interface on the compute node hosting the instance. The tap interface corresponds directly to a network interface within the guest instance. Through the use of a bridge, the host can expose the guest instance to a physical network.