Operation Manual – MSTPH3C S3100 Series Ethernet Switches Chapter 1 MSTP Configuration1-221.3.3 Specifying the Current Switch as a Root Bridge/Secondary Root BridgeMSTP can automatically choose a switch as a root bridge through calculation. You canalso manually specify the current switch as a root bridge by using the correspondingcommands.I. Specify the current switch as the root bridge of a spanning treeTable 1-9 Specify the current switch as the root bridge of a spanning treeOperation Command DescriptionEnter system view system-view —Specify the current switchas the root bridge of aspanning treestp [ instance instance-id ] rootprimary [ bridge-diameterbridgenumber [ hello-timecenti-seconds ] ]RequiredII. Specify the current switch as the secondary root bridge of a spanning treeTable 1-10 Specify the current switch as the secondary root bridge of a spanning treeOperation Command DescriptionEnter system view system-view —Specify the current switchas the secondary rootbridge of a specifiedspanning treestp [ instance instance-id ] rootsecondary [ bridge-diameterbridgenumber [ hello-timecenti-seconds ] ]RequiredUsing the stp root primary/stp root secondary command, you can specify the currentswitch as the root bridge or the secondary root bridge of the spanning tree instanceidentified by the instance-id argument. If the value of the instance-id argument is set to0, the stp root primary/stp root secondary command specify the current switch asthe root bridge or the secondary root bridge of the CIST.A switch can play different roles in different spanning tree instances. That is, it can bethe root bridges in a spanning tree instance and be a secondary root bridge in anotherspanning tree instance at the same time. But in the same spanning tree instance, aswitch cannot be the root bridge and the secondary root bridge simultaneously.When the root bridge fails or is turned off, the secondary root bridge becomes the rootbridge if no new root bridge is configured. If you configure multiple secondary rootbridges for a spanning tree instance, the one with the smallest MAC address replacesthe root bridge when the latter fails.You can specify the network diameter and the hello time parameters while configuring aroot bridge/secondary root bridge. Refer to section 1.3.8 “Configuring the Network
