Chapter 17
| Spanning Tree Commands
– 459 –
◆ When automatic detection is selected, the switch derives the link type from the
duplex mode. A full-duplex interface is considered a point-to-point link, while a
half-duplex interface is assumed to be on a shared link.
◆ 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
Console(config)#interface ethernet 1/5
Console(config-if)#spanning-tree link-type point-to-point
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 auto-configuration mode.
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)
cost - Path cost for an interface. (Range: 0 for auto-configuration, 1-65535
for short path cost method
8
, 1-200,000,000 for long path cost method)
The recommended path cost range is listed in Table 88 on page 456.
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 89 on page 457.
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.
8. Use the spanning-tree pathcost method command to set the path cost method.
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