UMN:CLI User ManualV8102364Meanwhile, the rapid spanning tree protocol (RSTP) defined in IEEE 802.1w dramaticallyreduces the time of network convergence on the spanning tree protocol (STP). It is easyand fast to configure new protocol. The IEEE 802.1w also supports backward compatibil-ity with IEEE 802.1d.9.4.1 STP OperationThe 802.1d STP defines port state as blocking, listening, learning, and forwarding. WhenSTP is configured in LAN with double paths, switches exchange their information includ-ing the bridge ID.It is named as BPDU (Bridge Protocol Data Unit). Switches decide port state based onthe exchanged BPDU and automatically decide an optimized path to communicate withthe root switch.9.4.1.1 Root SwitchThe most important information to decide the root switch is bridge ID. A bridge ID is com-posed of 2 bytes-priority and 6 bytes-MAC address. The root switch has the lowest bridgeID.Fig. 9.20 Root SwitchAfter configuring STP, these switches exchange their information. The priority of SWITCHA is 8, the priority of SWITCH B is 9, and the priority of SWITCH C is 10. In this case,SWITCH A is automatically configured as the root switch.
