3Com Switch 7750 SeriesCommand Reference Guide – MSTP Chapter 1 MSTP Configuration Commands1-39recommended to set the network diameter and leave the Forward delay and Max ageparameters being automatically determined by the network diameter you set.Caution:z You can configure only one root bridge for a spanning tree instance and canconfigure one or more secondary root bridges for a spanning tree instance.Configuring multiple root bridges for a spanning tree instance causes unpredictablespanning tree computing results.z Once a switch is configured as the root bridge or a secondary root bridge, its prioritycannot be modified.Example# Configure the current switch as the root bridge of spanning tree instance 1, setting thenetwork diameter of the switched network to 4, and the Hello time to 500 centiseconds.<3Com> system-viewSystem View: return to User View with Ctrl+Z.[3Com] stp instance 1 root primary bridge-diameter 4 hello-time 5001.1.37 stp root secondarySyntaxstp [ instance instance-id ] root secondary [ bridge-diameter bridgenum ][ hello-time centi-seconds ]undo stp [ instance instance-id ] rootViewSystem viewParameterinstance-id: Spanning tree instance ID ranging from 0 to 16. A value of 0 specifies theCIST.bridgenum: Network diameter of the specified spanning tree. This argument rangesfrom 2 to 7 and defaults to 7.centi-seconds: Hello time in centiseconds of the specified spanning tree. This argumentranges from 100 to 1,000 and defaults to 200.
