Spanning-Tree Mst Root - Cisco Catalyst 3750 Command Reference Manual

Chapter 2 Catalyst 3750 Switch Cisco IOS Commands

spanning-tree mst root

Use the spanning-tree mst root global configuration command on the switch stack or on a standalone
switch 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.
Syntax Description instance-id
root primary
root secondary
diameter net-diameter
hello-time seconds
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(14)EA1
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.)
78-16181-03
spanning-tree mst instance-id root {primary | secondary} [diameter net-diameter
[hello-time seconds]]
no spanning-tree mst instance-id root
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 15.
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.
Modification
This command was introduced.
spanning-tree mst root
Catalyst 3750 Switch Command Reference
2-531