Cisco WS-C3560X-24T-L Command Reference - Page 625
spanning-tree mst root
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Chapter 2 Catalyst 3560 Switch Cisco IOS Commands spanning-tree mst root spanning-tree mst root Use the spanning-tree mst root global configuration command to configure the multiple spanning-tree (MST) root switch priority and timers based on the network diameter. Use the no form of this command to return to the default settings. spanning-tree mst instance-id root {primary | secondary} [diameter net-diameter [hello-time seconds]] no spanning-tree mst instance-id root Syntax Description instance-id root primary root secondary diameter net-diameter hello-time seconds Range of spanning-tree instances. You can specify a single instance, a range of instances separated by a hyphen, or a series of instances separated by a comma. The range is 0 to 4094. Force this switch to be the root switch. Set this switch to be the root switch should the primary root switch fail. (Optional) Set the maximum number of switches between any two end stations. The range is 2 to 7. This keyword is available only for MST instance 0. (Optional) Set the interval between hello bridge protocol data units (BPDUs) sent by the root switch configuration messages. The range is 1 to 10 seconds. This keyword is available only for MST instance 0. Defaults The primary root switch priority is 24576. The secondary root switch priority is 28672. The hello time is 2 seconds. Command Modes Global configuration Command History Release 12.1(19)EA1 12.2(25)SEC Modification This command was introduced. The instance-id range changed to1 to 4094. Usage Guidelines Use the spanning-tree mst instance-id root command only on backbone switches. When you enter the spanning-tree mst instance-id root command, the software tries to set a high enough priority to make this switch the root of the spanning-tree instance. Because of the extended system ID support, the switch sets the switch priority for the instance to 24576 if this value will cause this switch to become the root for the specified instance. If any root switch for the specified instance has a switch priority lower than 24576, the switch sets its own priority to 4096 less than the lowest switch priority. (4096 is the value of the least-significant bit of a 4-bit switch priority value.) 78-16405-05 Catalyst 3560 Switch Command Reference 2-593