OpenStack Networking with OVS is used by default and is the only supported networking mode in the reference architecture for the CPI use case.
Neutron configuration for the CPI use case enables distributed virtual router (DVR) by default. Overlay networks are created using the VxLAN encapsulation. Access to the external networks is provided by source network address translation (SNAT) working on dedicated network nodes or gateway nodes.
Neutron supports external access to the virtual server instances in the cloud through the floating IP assigned to the virtual servers through the networking API.
Neutron OVS requires setting up of a specific network node, which is sometimes called gateway, that handles the routing across the internal networks, as well as the outbound routing.