[irq]: techie interrupted

The current VXLAN draft is very explicit: VXLAN has no control plane. There is no out-of-band mechanism that a VXLAN host could use to discover other hosts participating in the same VXLAN segment, or MAC addresses of VMs attached to a VXLAN segment.

VXLAN is a very simple technology and uses existing layer-2 mechanisms (flooding and dynamic MAC learning) to discover remote MAC addresses and MAC-to-VTEP mappings, and IP multicast to reduce the scope of the L2-over-UDP flooding to those hosts that expressed explicit interest in the VXLAN frames.

Ideally, you’d map every VXLAN segment (or VNI – VXLAN Network Identifier) into a separate IP multicast address, limiting the L2 flooding to those hosts that have VMs participating in the same VXLAN segment. In a large-scale reality, you’ll probably have to map multiple VXLAN segments into a single IP multicast address due to low number of IP multicast entries supported by typical data center switches.