This is pretty basic, but you need to remember a couple of important things when tasked with tweaking spanning-tree timers:
1) Make the changes on the root bridge.
2) The root bridge settings are the timers that are used – not the local settings on the non-root bridge(s).
You can see the timers with the “show spanning-tree vlan x” command. The timers are set on the root. Non-root bridges will still show the local timer values, but will use the root values:
sw2#sh span v 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 24577
Address 0012.018f.d580
Cost 19
Port 15 (FastEthernet0/13)
Hello Time 2 sec Max Age 20 sec Forward Delay 4 sec <-noteBridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0012.009c.ca00 <-sw2 is not the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec <-note
Aging Time 300Interface Role Sts Cost Prio.Nbr Type
—————- —- — ——— ——– ——————————–
Fa0/1 Desg FWD 19 128.3 P2p
Fa0/13 Root FWD 19 128.15 P2p
Fa0/14 Altn BLK 19 128.16 P2p
Fa0/15 Altn BLK 19 128.17 P2pBring up a port in VLAN 1:
sw2(config)#int fa0/1
sw2(config-if)#no sh
sw2(config-if)#^Z*Mar 1 22:33:42: %SYS-5-CONFIG_I: Configured from console by console
*Mar 1 22:33:43: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to down
*Mar 1 22:33:44: set portid: VLAN0001 Fa0/1: new port id 8003
*Mar 1 22:33:44: STP: VLAN0001 Fa0/1 -> listening
*Mar 1 22:33:46: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up
*Mar 1 22:33:47: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up
*Mar 1 22:33:48: STP: VLAN0001 Fa0/1 -> learning [listen to learn = 4 seconds]
*Mar 1 22:33:52: STP: VLAN0001 sent Topology Change Notice on Fa0/13
*Mar 1 22:33:52: STP: VLAN0001 Fa0/1 -> forwarding [learn to forward = 4 seconds]
The non-root bridge uses the root bridge’s Forward Delay timer of 4 seconds rather than its local timer of 15 seconds.
**************************
3 different ways to change the forward delay back to default (15 seconds)
We set the forward delay to 4 seconds (sw1 is on the root bridge):
sw1(config)#do sh sp v 1 | i ID|Forward
Root ID Priority 24577
Hello Time 2 sec Max Age 20 sec Forward Delay 4 sec
Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
Hello Time 2 sec Max Age 20 sec Forward Delay 4 sec
1) “no spanning-tree vlan 1 forward-time 4”
sw1(config)#no sp v 1 f 4
sw1(config)#do sh sp v 1 | i ID|Forward
Root ID Priority 24577
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
2) “default spanning-tree vlan 1 forward-time”
sw1(config)#default sp v 1 f
sw1(config)#do sh sp v 1 | i ID|Forward
Root ID Priority 24577
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
3) “spanning-tree vlan 1 forward-time 15”
sw1(config)#sp v 1 f 15
sw1(config)#do sh sp v 1 | i ID|Forward
Root ID Priority 24577
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec