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Chapter 15
Configuring STP and IEEE 802.1s MST
To configure a Catalyst 6500 series switch as the secondary root bridge, perform this task:
Command
Step 1
Router(config)# [no] spanning-tree vlan vlan_ID
root secondary [diameter hops [hello-time
seconds]]
Router(config)# no spanning-tree vlan vlan_ID
root
Step 2
Router(config)# end
This example shows how to configure the Catalyst 6500 series switch as the secondary root bridge for
VLAN 10, with a network diameter of 4:
Router# configure terminal
Router(config)# spanning-tree vlan 10 root secondary diameter 4
Router(config)# end
Router#

Configuring STP Port Priority

If a loop occurs, STP considers port priority when selecting a LAN port to put into the forwarding state.
You can assign higher priority values to LAN ports that you want STP to select first and lower priority
values to LAN ports that you want STP to select last. If all LAN ports have the same priority value, STP
puts the LAN port with the lowest LAN port number in the forwarding state and blocks other LAN ports.
The possible priority range is 0 through 240 (default 128), configurable in increments of 16.
Cisco IOS uses the port priority value when the LAN port is configured as an access port and uses VLAN
port priority values when the LAN port is configured as a trunk port.
To configure the STP port priority of a Layer 2 LAN interface, perform this task:
Command
Step 1
Router(config)# interface {{type
{port-channel port_channel_number}}
Step 2
Router(config-if)# spanning-tree port-priority
port_priority
Router(config-if)# no spanning-tree port-priority
Step 3
Router(config-if)# spanning-tree vlan vlan_ID
port-priority port_priority
Router(config-if)# [no] spanning-tree vlan
vlan_ID port-priority
Step 4
Router(config-if)# end
78-14099-04
Purpose
Configures a Catalyst 6500 series switch as the secondary
root bridge. The vlan_ID value can be 1 through 4094,
except reserved VLANs (see
Clears the root bridge configuring.
Exits configuration mode.
Purpose
1
Selects an interface to configure.
slot/port} |
Configures the port priority for the LAN interface. The
port_priority value can be from 1 to 252 in increments
of 4.
Reverts to the default port priority value.
Configures the VLAN port priority for the LAN interface.
The port_priority value can be from 1 to 252 in
increments of 4. The vlan_ID value can be 1 through
4094, except reserved VLANs (see
page
Reverts to the default VLAN port priority value.
Exits configuration mode.
Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
Table 9-1 on page
9-2).
Configuring STP
9-2).
Table 9-1 on
15-27

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