It's worth noting that you can use Ethernet without a full IP stack. Protocols like CoAP are specifically designed to run on a UDP-only stack (ARP/ICMP/IP/UDP)

It's worth noting that you can use Ethernet without a full IP stack. Protocols like CoAP are specifically designed to run on a UDP-only stack (ARP/ICMP/IP/UDP) to save on code-space for tiny microcontrollers. If you only need local connectivity, raw-Ethernet messages have even less overhead.