With the expansion of the size of data centers, software-defined networking (SDN) is becoming a trend for simplifying the data center network management with central and flexible flow control. To achieve L2 abstractions in a multitenant cloud, Open vSwitch (OVS) is commonly used to build overlay tunnels (eg, Virtual eXtensible Local Area Network [VXLAN]) on top of existing underlying networks. However, the poor VXLAN performance of OVS is of huge concern. Instead of solving the performance issues of OVS, in this paper, we proposed a circuit-based logical layer 2 bridging mechanism (CBL2), which builds label-switched circuits and performs data-plane multicasting in a software-defined leaf-spine fabric to achieve scalable L2 without overlay tunneling. Our evaluations indicate that direct transmission in OVS improves throughput performance by 58% compared with VXLAN tunneling, and data-plane multicasting for ARP reduces address resolution latency from 149 to 0.5 ms, compared with control-plane broadcast forwarding. The evaluation results also show that CBL2 provides 0.6, 0.4, and 11-ms protection switching time, respectively, in the presence of switch failure, link failure, and port shutdown in practical deployment.