In local area networks (LANs), Ethernet is a widely used layer-2 networking technology due to the low cost and self-configuring ability. It allows computers and switches to form a broadcast domain to exchange data, which means that many protocols built on Ethernet rely on sending data to every node. However, as the network grows, the efficiency of Ethernet degrades since the network is flooded with spam packets caused by broadcast. Even worse, traditional layer-2 switches do not well support multicast protocols but realize them by also broadcasting packets. To conquer these problems, the paper develops an Adaptive Broadcast and multicast traffic Cutting (ABC) framework based on software-defined networking (SDN). By taking two Ethernet protocols, ARP and IGMP, as examples, we show how to exploit SDN to restrain unnecessary traffic to improve Ethernet efficiency via our framework. With Mininet simulations, we verify that the ABC framework not only greatly reduces spam packets than legacy Ethernet but also saves controller overhead comparing with other SDN-based solutions. Moreover, we also implement the ABC framework on the campus network to demonstrate its practicability.