Command
Spanning-Tree VLAN Root Secondary
Use
This command sets the switch to become backup root for a given VLAN. It works by lowering the priority of the switch until it becomes one priority higher then the root, so it will take over if the root fails. Once the switch is root it will not prevent any other switch from becoming root.
Syntax
Switch(config)#ispanning-tree vlan <vlan range> root secondary
Example
In the below example we will configure SW2 to become the backup root for VLAN 10. Currently, we see that SW2 is not root for VLAN 10. Notice the priority is currently 24576
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SW1(config)#do show spanning vlan 10 VLAN0010 Bridge ID Priority 24586 (priority 24576 sys-id-ext 10) Interface Role Sts Cost Prio.Nbr Type Interface Role Sts Cost Prio.Nbr Type Fa0/20 Desg FWD 19 128.20 P2p |
Now we will configure SW2 to become the backup root for VLAN 10.
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SW2(config)#spanning vlan 10 root secondary |
We can see that SW2 is now has a priority of 28672.
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SW2(config)#do show spanning vlan 10 VLAN0010 Bridge ID Priority 28682 (priority 28672 sys-id-ext 10) Interface Role Sts Cost Prio.Nbr Type |
