A data center system includes: at least two data center subsystems interconnected through a layer-2 network, each of the data center subsystems comprising a plurality of hosts, a plurality of layer-2 switches connected with the plurality of hosts, a firewall group connected with the layer-2 switches, and a layer-2 extension device connected with the layer-2 switches; wherein the firewall groups of the at least two data center subsystems are configured to transmit synchronization information to each other through a synchronization channel in a first virtual local area network; wherein the layer-2 extension devices of the at least two data center subsystems are configured to transmit service information through a service channel in a second virtual local area network; and wherein the first virtual local area network and the second virtual local area network are implemented in the layer-2 network.