Spanning-Tree Uplinkfast Command on CISCO Router/Switch

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

Spanning-Tree Uplinkfast Command on CISCO Router/Switch 1

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

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