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Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide
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Chapter15 Configuring MSTP
Configuring MSTP Features
Configuring Path Cost
The MSTP path cost default value is derived from the me dia speed of an NNI. I f a loop occu rs, the MS TP
uses cost when selecting an interface to put in the forwarding state. You can assign lower cost values to
NNIs that you want selected first and higher cost values that you want sel ected last . If all interf aces hav e
the same cost value, the MSTP puts the interface with the lowe st interface n umber in the f orwarding state
and blocks the other interfaces.
Beginning in privileged EXEC mode, follow these steps to configure the MSTP cost of an inter face. This
procedure is optional.
Note The show spanning-tree mst interface interface-id privileged EXEC command displays information
only for ports that are in a link-up operative state. Otherwise, you can use the show running-config
privileged EXEC command to confirm the configuration.
To return the interface to its default setting, use the no spanning-tree mst instance-id cost interface
configuration command.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify an interface to configure, and enter interface
configuration mode. Valid interfaces include physical NNIs and
NNI port-channel logical interfaces. The port-channel range is 1
to 48.
Note If a physical interface is not an NNI, enter the port-type
nni interface configuration command before you
configure MST path cost.
If the interface is a port channel, all members of the port
channel must be NNIs.
Step3 spanning-tree mst instance-id cost cost Configure the cost.
If a loop occurs, the MSTP uses the path cost when selecting an
interface to place into the forwarding state. A lower path cost
represents higher-speed transmission.
•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 0 to 15.
•For cost, the range is 1 to 200000000; the default value is
derived from the media speed of the interface.
Step4 end Return to privileged EXEC mode.
Step5 show spanning-tree mst interface interface-id
or
show spanning-tree mst instance-id
Verify your entries.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.