This paper proposes an Ethernet-based in-vehicle control network and its hardware realization. Since modern premium-class vehicles contain nearly a hundred electronic control units (ECUs), multiple control networks needed for the ECUs become considerably complex. In order to reduce the network complexity, the proposed network connects the ECUs by employing an Ethernet-based unidirectional ring topology. In addition, a new Ethernet media access controller (MAC) is proposed to automatically relay mismatched frames. As a result, the proposed ring network can be constructed without any switching device. A hardware platform employing the proposed MAC as a network controller is implemented on a field programmable gate array to evaluate the realistic performance of the proposed network. Experimental results show that the proposed MAC increases the communication speed by 123%. Moreover, the performance of the proposed network with a large number of ECU nodes is evaluated using the OMNET++ simulation tool, which shows that the proposed network provides the ECUs with much higher communication speed than the conventional CAN and FlexRay do.