Configuring Path Cost - Cisco ME 3400G-2CS - Ethernet Access Switch Software Configuration Manual

Configuring Spanning-Tree Features

Configuring Path Cost

The spanning-tree path cost default value is derived from the media speed of an interface (NNI or port
channel of multiple NNIs). If a loop occurs, spanning tree uses 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 values that you want selected last. If all NNIs (or port channels) have the same cost value,
spanning tree puts the interface with the lowest interface number in the forwarding state and blocks the
other interfaces.
Beginning in privileged EXEC mode, follow these steps to configure the cost of an interface. This
procedure is optional.
Command
Step 1
configure terminal
Step 2
interface interface-id
Step 3
spanning-tree cost cost
Step 4
spanning-tree vlan vlan-id cost cost
Step 5
end
Step 6
show spanning-tree interface interface-id
or
show spanning-tree vlan vlan-id
Step 7 copy running-config startup-config
Note The show spanning-tree 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.
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Purpose
Enter global configuration mode.
Specify an interface to configure, and enter interface
configuration mode. Valid interfaces include physical NNIs and
port-channel logical interfaces (port-channel
port-channel-number) that contain only NNIs.
Configure the cost for an interface.
If a loop occurs, spanning tree uses the path cost when selecting
an interface to place into the forwarding state. A lower path cost
represents higher-speed transmission.
For cost, the range is 1 to 200000000; the default value is derived
from the media speed of the interface.
Configure the cost for a VLAN.
If a loop occurs, spanning tree uses the path cost when selecting
an NNI to place into the forwarding state. A lower path cost
represents higher-speed transmission.
• For vlan-id, you can specify a single VLAN identified by
VLAN ID number, a range of VLANs separated by a hyphen,
or a series of VLANs separated by a comma. The range is 1
to 4094.
For cost, the range is 1 to 200000000; the default value is
•
derived from the media speed of the interface.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 14 Configuring STP
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