A network device including a main bridge, a first bridge, a controller, and an Ethernet port is provided. When the Ethernet port is connected to a mesh network, the processing unit performs the following steps: controlling the Ethernet port to transmit a first broadcast packet; when the Ethernet port receives a second broadcast packet, parsing the second broadcast packet to extract the packet path information to determine whether a path loop exists; determining, according to the Ethernet interface weight (EIW), the slave interface uplink weight (SIUW), and the master device weight (MW) carried by the first broadcast packet and the second broadcast packet, (1) whether the network device plays a master device role, (2) whether the bridge of the Ethernet port is set as the main bridge or the first bridge, and (3) whether the Ethernet port allows data transmission.