In one example in accordance with the present disclosure, a system for auto-negotiation over extended backplane includes an enclosure and a switch external to the enclosure. The enclosure has a NIC (network interface controller) for a server in the enclosure and a DEM (downlink extension module). The DEM has a single DEM PHY connected to the NIC via a backplane and also connected to the switch via an external connection. The DEM PHY facilitates auto-negotiation between the switch and the NIC.