Configuring Stp Port Priority - Cisco 4500M Software Manual

Chapter 14 Understanding and Configuring STP

Configuring STP Port Priority

In the event of a loop, a spanning tree considers port priority when selecting an interface to put into the
forwarding state. You can assign higher priority values to interfaces that you want a spanning tree to
select first and lower priority values to interfaces that you want a spanning tree to select last. If all
interfaces have the same priority value, a spanning tree puts the interface with the lowest interface
number in the forwarding state and blocks other interfaces. The possible priority range is 0 through 240,
configurable in increments of 16 (the default is 128).
The Cisco IOS software uses the port priority value when the interface is configured as an access port
Note
and uses VLAN port priority values when the interface is configured as a trunk port.
To configure the spanning tree port priority of an interface, perform this task:
Command
Step 1
Switch(config)# interface {{fastethernet |
gigabitethernet | tengigabitethernet} slot / port }
| {port-channel port_channel_number }
Step 2
Switch(config-if)# [no] spanning-tree
port-priority port_priority
Step 3
Switch(config-if)# [no] spanning-tree vlan
vlan_ID port-priority port_priority
Step 4
Switch(config-if)# end
Step 5
Switch# show spanning-tree interface
{{fastethernet | gigabitethernet} slot / port } |
{port-channel port_channel_number }
show spanning-tree vlan vlan_ID
This example shows how to configure the spanning tree port priority of a Fast Ethernet interface:
Switch# configure terminal
Switch(config)# interface fastethernet 5/8
Switch(config-if)# spanning-tree port-priority 100
Switch(config-if)# end
Switch#
This example shows how to verify the configuration of a Fast Ethernet interface when it is configured as
an access port:
Switch# show spanning-tree interface fastethernet 3/1
Vlan
---------------- ---- --- --------- -------- --------------------------------
VLAN0001
VLAN1002
VLAN1003
VLAN1004
VLAN1005
Switch#
OL-6696-01
Role Sts Cost Prio.Nbr Status
Desg FWD 19 128.129
Desg FWD 19 128.129
Desg FWD 19 128.129
Desg FWD 19 128.129
Desg FWD 19 128.129
Purpose
Specifies an interface to configure.
Configures the port priority for an interface. The
port_priority value can be from 0 to 240, in increments
of 16.
You can use the no keyword to restore the defaults.
Configures the VLAN port priority for an interface. The
port_priority value can be from 0 to 240, in increments
of 16.
You can use the no keyword to restore the defaults.
Exits configuration mode.
Verifies the configuration.
P2p
P2p
P2p
P2p
P2p
Software Configuration Guide—Release 12.2(25)EW
Configuring STP
14-13