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Chapter 7
Configuring Spanning Tree
To configure a switch as the primary root switch for an instance, perform this task in privileged mode:
Task
Configure a switch as the primary root switch for
an instance.
This example shows how to set the primary root for an instance:
Console> (enable) set spantree root mistp-instance 2-4 dia 4
Instances 2-4 bridge priority set to 8192
VLInstances 2-4 bridge max aging time set to 14 seconds.
Instances 2-4 bridge hello time set to 2 seconds.
Instances 2-4 bridge forward delay set to 9 seconds.
Switch is now the root switch for active Instances 1-6.
Console> (enable)
Configuring a Secondary Root Switch
You can set a secondary root switch on a VLAN when the switch is in PVST+ mode or on a MISTP
instance when the switch is in MISTP mode.
The set spantree root secondary command reduces the bridge priority to 16,384, making it the probable
candidate to become the root switch if the primary root switch fails. You can run this command on more
than one switch to create multiple backup switches in case the primary root switch fails.
To configure a switch as the secondary root switch, perform this task in privileged mode:
Task
Configure a switch as the secondary root switch.
This example shows how to configure the secondary root switch for VLANs 22 and 24:
Console> (enable) set spantree root secondary 22,24 dia 5 hello 1
VLANs 22,24 bridge priority set to 16384.
VLANs 22,24 bridge max aging time set to 10 seconds.
VLANs 22,24 bridge hello time set to 1 second.
VLANs 22,24 bridge forward delay set to 7 seconds.
Console> (enable)
To configure a switch as the secondary root switch for an instance, perform this task in privileged mode:
Task
Configure a switch as the secondary root switch
for an instance.
This example shows how to set the secondary root for an instance:
Console> (enable) set spantree root secondary mistp-instance 2-4 dia 4
Instances 2-4 bridge priority set to 8192
VLInstances 2-4 bridge max aging time set to 14 seconds.
78-12647-02
Software Configuration Guide—Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4
Command
set spantree root mistp-instance instance [dia
network_diameter] [hello hello_time]
Command
set spantree root [secondary] vlans [dia
network_diameter] [hello hello_time]
Command
set spantree root [secondary] mistp-instance
instance [dia network_diameter]
[hello hello_time]
Configuring a Root Switch
7-29
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Troubleshooting
