Spanning Tree Protocol Configuration Guide, Cisco Catalyst IE9300 Rugged Series Switches

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Spanning Tree Protocol Configuration Guide, Cisco Catalyst IE9300 Rugged Series Switches

Configure the secondary root switch

Updated: March 2, 2026

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Learn how to configure a switch as the secondary root by modifying its priority, ensuring it becomes the root switch if the primary fails and other switches use the default priority.

You can configure a switch as the secondary root by modifying the switch priority from the default value (32768) to 28672.

This task ensures that the switch is likely to become the root switch for the specified VLAN if the primary root switch fails. This is based on the assumption that other network switches use the default switch priority of 32768.

Before you begin

When you configure a switch as the secondary root, the switch priority changes from the default value (32768) to 28672. With this priority, the switch is likely to become the root switch for the specified VLAN if the primary root switch fails. This is based on the assumption that the other network switches use the default switch priority of 32768 and are, therefore, unlikely to become the root switch.

Procedure

1.

Use the enable command to enter privileged EXEC mode.

Example:

Switch> enable

Enter your password if prompted.
2.

Use the configure terminal command to enter global configuration mode.

Example:

Switch# configure terminal
3.

Use the spanning-tree vlan root secondary command to configure a switch to become the secondary root for the specified VLAN.

Example:

Switch(config)# spanning-tree vlan 20 root secondary diameter 4

For vlan-id, you can specify a single VLAN identified by VLAN ID number, a range of VLANs separated by a hyphen, or a series of VLANs separated by a comma. The valid range is 1 to 4094.

(Optional) For diameter net-diameter, specify the maximum number of switches between any two end stations. The valid range is 2 to 7.

Use the same network diameter value as that configured for the primary root switch.
4.

Use the end command to return to privileged EXEC mode.

Example:

Switch(config)# end