MAC learning in a controller-less VXLAN overlay VXLAN standard does not specify any control plane protocol to exchange MAC-IP bindings between VTEPs. Instead it relies on data plane flood-and-learn behaviour, just like a normal switch. To force this behaviour in an underlay, the standard stipulates that each VXLAN network should be mapped to its own multicast address and each VTEP participating in a network should join the corresponding multicast group.
