99• If you specify multiple secondary root bridges for the instance, the secondary root bridge with thelowest MAC address is given priority.• If you do not specify a secondary root bridge, a new root bridge is calculated.You can specify one root bridge for each spanning tree, regardless of the device priority settings. Onceyou specify a device as the root bridge or a secondary root bridge, you cannot change its priority.You can configure a device as the root bridge by setting the device priority to 0. For the device priorityconfiguration, see "Configuring the device priority."Configuring the current device as the root bridge of a specificspanning treeStep Command Remarks1. Enter system view. system-view N/A2. Configure the currentdevice as the rootbridge.• In STP/RSTP mode:stp root primary• In PVST mode:stp vlan vlan-id-list root primary• In MSTP mode:stp [ instance instance-list ] root primaryBy default, a device does notfunction as the root bridge.Configuring the current device as a secondary root bridge of aspecific spanning treeStep Command Remarks1. Enter system view. system-view N/A2. Configure the currentdevice as a secondary rootbridge.• In STP/RSTP mode:stp root secondary• In PVST mode:stp vlan vlan-id-list root secondary• In MSTP mode:stp [ instance instance-list ] rootsecondaryBy default, a device does notfunction as a secondary rootbridge.Configuring the device priorityDevice priority is a factor in calculating the spanning tree. The priority of a device determines whether thedevice can be elected as the root bridge of a spanning tree. A lower value indicates a higher priority.You can set the priority of a device to a low value to specify the device as the root bridge of the spanningtree. A spanning tree device can have different priorities in different spanning trees.During root bridge selection, if all devices in a spanning tree have the same priority, the one with thelowest MAC address is selected. You cannot change the priority of a device after it is configured as theroot bridge or as a secondary root bridge.
