Configuring Stp Port Priority - Cisco Catalyst 4500 Series Configuration Manual

Chapter 20 Configuring STP and MST
Bridge ID
Interface
---------------- ---- --- --------- -------- --------------------------------
Fa3/1
Fa3/2
Fa3/48
Switch#

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).
Note The Cisco IOS software uses the port priority value when the interface is configured as an access port
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
OL-25340-01
Hello Time 2 sec Max Age 20 sec
Priority 32768
Address 0003.6b10.e800
Hello Time 2 sec Max Age 20 sec
Aging Time 300
Role Sts Cost
Desg FWD 19
Desg FWD 19
Desg FWD 19
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
Forward Delay 15 sec
Forward Delay 15 sec
Prio.Nbr Status
128.129 P2p
128.130 P2p
128.176 Edge P2p
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.
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.
Use the no keyword to restore the defaults.
Exits configuration mode.
Verifies the configuration.
Configuring STP
20-13