Command
Spanning-Tree VLAN Root Primary
Use
This command sets the switch to become root for a given VLAN. It works by lowering the priority of the switch until it becomes root. Once the switch is root, it will not prevent any other switch from becoming root.
Syntax
Swith(cconfig)#spanning-tree vlan <vlan range> root primary
Example
In the below example we will configure SW1 to become the root for VLAN 10. Currently, we see that SW1 is not root for vlan 10. Notice the priority is currently 32768
SW1(config)#do show spanning vlan 10 VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 24586 Address 0019.0606.b600 Cost 19 Port 23 (FastEthernet0/23) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32778 (priority 32768 sys-id-ext 10) Address 0012.00cb.6c80 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 15 Interface Role Sts Cost Prio.Nbr Type —————- —- — ——— ——– ——————————– Fa0/1 Desg FWD 19 128.1 P2p Fa0/2 Desg FWD 19 128.2 P2p Fa0/4 Desg FWD 19 128.4 P2p Fa0/5 Desg FWD 19 128.5 P2p Fa0/8 Desg FWD 19 128.8 P2p Fa0/9 Desg FWD 19 128.9 P2p Fa0/10 Desg FWD 19 128.10 P2p Interface Role Sts Cost Prio.Nbr Type —————- —- — ——— ——– ——————————– Fa0/19 Desg FWD 19 128.19 P2p Fa0/20 Desg FWD 19 128.20 P2p Fa0/21 Desg FWD 19 128.21 P2p Fa0/22 Desg FWD 19 128.22 P2p Fa0/23 Root FWD 19 128.23 P2p Fa0/24 Altn BLK 19 128.24 P2p
Now we will configure SW1 to become root for Vlan 10.
SW1(config)#spanning vlan 10 root primary
We can see that SW1 is now root for Vlan 10. Notice the priority is now 24576.
SW1(config)#do show spanning vlan 10 VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 24586 Address 0012.00cb.6c80 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 24586 (priority 24576 sys-id-ext 10) Address 0012.00cb.6c80 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 Interface Role Sts Cost Prio.Nbr Type —————- —- — ——— ——– ——————————– Fa0/1 Desg FWD 19 128.1 P2p Fa0/2 Desg FWD 19 128.2 P2p Fa0/4 Desg FWD 19 128.4 P2p Fa0/5 Desg FWD 19 128.5 P2p Fa0/8 Desg FWD 19 128.8 P2p Fa0/9 Desg FWD 19 128.9 P2p Fa0/10 Desg FWD 19 128.10 P2p Fa0/19 Desg FWD 19 128.19 P2p Interface Role Sts Cost Prio.Nbr Type —————- —- — ——— ——– ——————————– Fa0/20 Desg FWD 19 128.20 P2p Fa0/21 Desg FWD 19 128.21 P2p Fa0/22 Desg FWD 19 128.22 P2p Fa0/23 Desg FWD 19 128.23 P2p Fa0/24 Desg FWD 19 128.24 P2p