User's Manual

Configuring the Port Cost
The MST path cost default value is derived from the media speed of an interface. If a loop occurs, MST uses
the cost when selecting an interface to put in the forwarding state. You can assign lower cost values to interfaces
that you want selected first and higher cost to interfaces values that you want selected last. If all interfaces
have the same cost value, MST puts the interface with the lowest interface number in the forwarding state
and blocks the other interfaces.
MST uses the long pathcost calculation method.Note
Procedure
PurposeCommand or Action
Enters configuration mode.switch# configure terminal
Step 1
Specifies an interface to configure, and enters interface
configuration mode.
switch(config)# interface {{type
slot/port} | {port-channel
number}}
Step 2
Configures the cost.switch(config-if)# spanning-tree
mst instance-id cost [cost | auto]
Step 3
If a loop occurs, MST uses the path cost when selecting an
interface to place into the forwarding state. A lower path cost
represents higher-speed transmission as follows:
•
For instance-id, 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 from 1 to
4094.
•
For cost, the range is from 1 to 200000000. The default
value is auto, which is derived from the media speed of
the interface.
This example shows how to set the MST interface port cost on Ethernet 3/1 for MSTI 4:
switch# configure terminal
switch(config)# interface ethernet 3/1
switch(config-if)# spanning-tree mst 4 cost 17031970
Configuring the Switch Priority
You can configure the switch priority for an MST instance so that it is more likely that the specified switch
is chosen as the root bridge.
Cisco Nexus 3000 NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U3(1)
106 OL-26590-01
Configuring Multiple Spanning Tree
Configuring the Port Cost