Command Line Interface
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• RSTP only works on point-to-point links between two bridges. If you designate
a port as a shared link, RSTP is forbidden. Since MSTP is an extension of
RSTP, this same restriction applies.
Example
spanning-tree mst cost
This command configures the path cost on a spanning instance in the Multiple
Spanning Tree. Use the no form to restore the default.
Syntax
spanning-tree mst instance_id cost cost
no spanning-tree mst instance_id cost
• instance_id - Instance identifier of the spanning tree.
(Range: 0-4094, no leading zeroes)
• cost - Path cost for an interface. (Range: 1-200,000,000)
The recommended range is -
- Ethernet: 200,000-20,000,000
- Fast Ethernet: 20,000-2,000,000
- Gigabit Ethernet: 2,000-200,000
- 10 Gigabit Ethernet: 200-20,000
Default Setting
By default, the system automatically detects the speed and duplex mode used
on each port, and configures the path cost according to the values shown
below. Path cost “0” is used to indicate auto-configuration mode.
• Ethernet – half duplex: 2,000,000; full duplex: 1,000,000; trunk: 500,000
• Fast Ethernet – half duplex: 200,000; full duplex: 100,000; trunk: 50,000
• Gigabit Ethernet – full duplex: 10,000; trunk: 5,000
• 10 Gigabit Ethernet – full duplex: 1000; trunk: 500
Command Mode
Interface Configuration (Ethernet, Port Channel)
Command Usage
• Each spanning-tree instance is associated with a unique set of VLAN IDs.
• This command is used by the multiple spanning-tree algorithm to determine
the best path between devices. Therefore, lower values should be assigned
to interfaces attached to faster media, and higher values assigned to
interfaces with slower media.
• Use the no spanning-tree mst cost command to specify auto-configuration
mode.
• Path cost takes precedence over interface priority.
Console(config)#interface ethernet ethernet 1/5
Console(config-if)#spanning-tree link-type point-to-point
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