Configuring the Root Bridge 463c CAUTION:■ Upon specifying the current device as the root bridge or a secondary rootbridge, you cannot change the priority of the device.■ During root bridge selection, if all devices in a spanning tree have the samepriority, the one with the lowest MAC address will be selected as the rootbridge of the spanning tree.Configuration example# Set the device priority in MST instance 1 to 4096. system-view[Sysname] stp instance 1 priority 4096Configuring theMaximum Hops of anMST RegionBy setting the maximum hops of an MST region, you can restrict the region size.The maximum hops setting configured on the regional root bridge will be used asthe maximum hops of the MST region.After a configuration BPDU leaves the root bridge of the spanning tree in the MSTregion, its hop count is decremented by 1 whenever it passes a device. When itshop count reaches 0, it will be discarded by the device that has received it. As aresult, devices beyond the maximum hops are unable to take part in spanning treecomputing, and thereby the size of the MST region is restricted.When a device becomes the root bridge of the CIST or MSTI of an MST region, themaximum hop in the configuration BPDUs generated by this device defines thenetwork diameter of the spanning tree to define how far the spanning tree canreach in this MST region. All the devices other than the root bridge in the MSTregion use the maximum hop value set for the root bridge.Configuration procedureFollow these steps to configure the maximum hops of the MST regionn A larger maximum hops setting means a larger size of the MST region. Only themaximum hops configured on the regional root bridge can restrict the size of theMST region.Configuration example# Set the maximum hops of the MST region to 30. system-view[Sysname] stp max-hops 30Configure the priority of thecurrent devicestp [ instance instance-id ]priority priorityOptional32768 by defaultTo do... Use the command... RemarksTo do... Use the command... RemarksEnter system view system-view -Configure the maximum hopsof the MST regionstp max-hops hops Optional20 by default
