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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 20 Configuring STP and Prestandard IEEE 802.1s MST
Configuring STP
Fastethernet 4/4 is a trunk. Several VLANs are configured and active as shown in the example. The port
priority configuration applies to all VLANs on this interface.
Note
The
show spanning-tree interface
command only displays information if the port is connected and
operating. If this condition is not met, enter a
show running-config interface
command to verify the
configuration.
This example shows how to configure the VLAN port priority of Fast Ethernet port 4/4:
Router#
configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#
interface fastEthernet 4/4
Router(config-if)#
spanning-tree vlan 200 port-priority 64
Router(config-if)#
^Z
Router#
The configuration entered in the example only applies to VLAN 200. All VLANs other than 200 still
have a port priority of 160.
This example shows how to verify the configuration:
Router#
show spanning-tree interface fastethernet 4/4
Vlan Role Sts Cost Prio.Nbr Status
---------------- ---- --- --------- -------- --------------------------------
VLAN0001 Back BLK 200000 160.196 P2p
VLAN0006 Back BLK 200000 160.196 P2p
...
VLAN0199 Back BLK 200000 160.196 P2p
VLAN0200 Desg FWD 200000 64.196 P2p
Router#
You also can display spanning tree information for VLAN 200 using the following command:
Router#
show spanning-tree vlan 200 interface fastEthernet 4/4
Interface Role Sts Cost Prio.Nbr Status
---------------- ---- --- --------- -------- --------------------------------
Fa4/4 Desg LRN 200000 64.196 P2p
Configuring STP Port Cost
The STP port path cost default value is determined from the media speed of a LAN interface. If a loop
occurs, STP considers port cost when selecting a LAN interface to put into the forwarding state. You can
assign lower cost values to LAN interfaces that you want STP to select first and higher cost values to
LAN interfaces that you want STP to select last. If all LAN interfaces have the same cost value, STP
puts the LAN interface with the lowest LAN interface number in the forwarding state and blocks other
LAN interfaces. The possible cost range is 0 through 200000000 (the default is media specific).
STP uses the port cost value when the LAN interface is configured as an access port and uses VLAN
port cost values when the LAN interface is configured as a trunk port.