Spanning Tree Commands
29-16
29
• 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: 0 for auto-configuration, 1-65535
for short path cost method
36
, 1-200,000,000 for long path cost method)
The recommended path cost range is listed in Table 29-2 on page 29-12.
The recommended path cost is listed in Table 29-3 on page 29-12.
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. When the
short path cost method is selected and the default path cost recommended by
the IEEE 8021w standard exceeds 65,535, the default is set to 65,535. The
default path costs are listed in Table 29-4 on page 29-12.
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
36. Use the spanning-tree pathcost method command on page 29-6 to set the path cost method.
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