Spanning-Tree Mst Root - Cisco Catalyst 2960-X Command Reference Manual

spanning-tree mst root

spanning-tree mst root
To designate the primary and secondary root switch and set the timer value for an instance, use the
spanning-tree mst root command in global configuration mode. To return to the default settings, use the no
form of this command.
spanning-tree mst instance root {primary| secondary}
no spanning-tree mst instance root
Syntax Description
instance
primary
secondary
Command Default
None
Command Modes
Global configuration (config)
Command History
Release
Cisco IOS 15.0(2)EX
Usage Guidelines
Use this command only on backbone switches. You can enter instance-id as a single instance or a range of
instances, for example, 0-3,5,7-9.
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.)
When you enter the spanning-tree mstinstance-id root secondary command, because of support for the
extended system ID, the software changes the switch priority from the default value (32768) to 28672. If the
root switch fails, this switch becomes the next root switch (if the other switches in the network use the default
switch priority of 32768 and are therefore unlikely to become the root switch).
Catalyst 2960-X Switch Layer 2 Command Reference, Cisco IOS Release 15.0(2)EX
102
Instance identification number. The range is 0 to
4094.
Forces this switch to be the root switch.
Specifies this switch to act as the root switch, if the
primary root fail.
Modification
This command was introduced.
Layer 2 Commands
OL-29043 -01