Command
Spanning-Tree Uplinkfast
Use
This command allows the switch to quickly select another root port if it detects a failure. The new root port moves from blocking to forwarding in under 5 seconds.
Syntax
Switch(config)#spanning-tree uplinkfast
Example
In the below example we will configure SW2 to use uplinkfast. After that, we will disable the links to its root switch SW1. First, we configure uplinkfast globally.
SW2(config)#spanning uplinkfast
Looking at spanning tree, we see that Fa0/23 is currently the root port.
SW2(config-if-range)#do show spanning vlan 10 VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 8202 Address 0019.060c.4f80 Cost 19 Port 25 (FastEthernet0/23) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 16394 (priority 16384 sys-id-ext 10) Address 0019.060c.cb00 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 15 Interface Role Sts Cost Prio.Nbr Type —————- —- — ——— ——– ——————————– Fa0/19 Desg FWD 19 128.21 P2p Fa0/20 Desg FWD 19 128.22 P2p Fa0/21 Desg FWD 19 128.23 P2p Fa0/22 Desg FWD 19 128.24 P2p Fa0/23 Root FWD 19 128.25 P2p Fa0/24 Altn BLK 19 128.26 P2p
After disabling both ports to SW1, spanning-tree makes Fa0/21 root and moves the port to forwarding.
SW2(config)#int ra fa0/23-24 SW2(config-if-range)#shut SW2(config-if-range)# 00:20:26: %LINK-5-CHANGED: Interface FastEthernet0/23, changed state to administratively down 00:20:26: %LINK-5-CHANGED: Interface FastEthernet0/24, changed state to administratively down 00:20:27: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/23, changed state to down SW2(config-if-range)# 00:20:27: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/24, changed state to down SW2(config-if-range)#do show spanning vlan 10 VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 8202 Address 0019.060c.4f80 Cost 38 Port 23 (FastEthernet0/21) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 16394 (priority 16384 sys-id-ext 10) Address 0019.060c.cb00 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 15 Interface Role Sts Cost Prio.Nbr Type —————- —- — ——— ——– ——————————– Fa0/19 Altn BLK 19 128.21 P2p Fa0/20 Altn BLK 19 128.22 P2p Fa0/21 Root FWD 19 128.23 P2p Fa0/22 Altn BLK 19 128.24 P2p
SW2(config-if-range)#do show spanning vlan 10 VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 8202 Address 0019.060c.4f80 Cost 19 Port 25 (FastEthernet0/23) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 16394 (priority 16384 sys-id-ext 10) Address 0019.060c.cb00 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 15 Interface Role Sts Cost Prio.Nbr Type —————- —- — ——— ——– ——————————– Fa0/19 Desg FWD 19 128.21 P2p Fa0/20 Desg FWD 19 128.22 P2p Fa0/21 Desg FWD 19 128.23 P2p Fa0/22 Desg FWD 19 128.24 P2p Fa0/23 Root FWD 19 128.25 P2p Fa0/24 Altn BLK 19 128.26 P2p