Operation Manual – MSTPH3C S7500 Series Ethernet Switches Chapter 1 MSTP Configuration1-73) A spanning tree is figured out as follows:z Determining the root bridgeThe root bridge is selected by configuration BPDU comparing. The switch with thesmallest root ID is selected as the root bridge.z Determining the root portFor each switch in a network, the port through which the configuration BPDU with thehighest priority is received is chosen as the root port of the switch.z Determining the designated portFirst, the switch generates a designated port configuration BPDU for each of its portsusing the root port configuration BPDU and the root port path cost, with the root IDbeing replaced with that of the root port configuration BPDU, root path cost beingreplaced with the sum of the path cost of the root port configuration BPDU and the pathcost of the root port, the ID of the designated bridge being replaced with that of theswitch, and the ID of the designated port being replaced with that of the port.The switch then compares the resulting configuration BPDU with the originalconfiguration BPDU received from the corresponding port on another switch. If thelatter takes precedence over the former, the switch blocks the local port and remainsthe port's configuration BPDU unchanged, so that the port can only receiveconfiguration messages and cannot forward packets. Otherwise, the switch sets thelocal port to the designated port, replaces the original configuration BPDU of the portwith the resulting one and releases it regularly.1.1.4 MSTP Implementation on SwitchesMSTP is compatible with both STP and RSTP. That is, switches with MSTP employedcan recognize the protocol packets of STP and RSTP and use them to generatespanning trees. In addition to the basic MSTP functions, H3C series switches alsoprovide the following other functions for the convenience of users to manage theirswitches.z Root bridge retainingz Root bridge backupz Root guardz BPDU guardz Loop guard1.2 Root Bridge ConfigurationComplete the following tasks to configure Root Bridge:
