CCIE Routing & Switching v5 Workbook -
CCIE R&S v5 Advanced Technology Labs -
LAN Switching
Tuning STP Convergence Timers
A Note On Section Initial Configuration Files: You must load the
initial configuration files for the section, named LAN Switching Initial
Spanning Tree, which can be found in
. Reference the Virtual Routers &
Physical Switches Diagram to complete this task.
Task
Configure the root bridge so that switches generate Spanning-Tree hello packets
every 3 seconds.
When a new port becomes active, it should wait 20 seconds before transitioning to
the forwarding state.
If the switches do not hear a configuration message within 10 seconds, they should
attempt reconfiguration.
This configuration should affect all currently active VLANs and any additional VLANs
created in the future.
Configuration
SW1:
spanning-tree vlan 1-4094 hello-time 3
spanning-tree vlan 1-4094 forward-time 10
spanning-tree vlan 1-4094 max-age 10
Verification
Verify the default STP timers before being changed.
SW1#show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol ieeeRoot ID Priority 4106
Address0013.605f.f000
This bridge is the rootHello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority4106 (priority 4096 sys-id-ext 10)
Address
0013.605f.f000Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time
300 sec
InterfaceRole Sts CostPrio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/19Desg FWD 19
128.21 P2p
Fa0/20Desg FWD 19
128.22 P2p
Fa0/23Desg FWD 19
128.25 P2p
Fa0/24Desg FWD 19
128.26 P2p
!
!SW2#show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol ieeeRoot ID Priority 4106
Address
0013.605f.f000
Cost
19
Port
25 (FastEthernet0/23)Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority16394 (priority 16384 sys-id-ext 10)
Address000a.b832.3a80Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
InterfaceRole Sts CostPrio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/19Desg FWD 19
128.21 P2p
Fa0/20Desg FWD 19
128.22 P2p
Fa0/23Root FWD 19
128.25 P2p
Fa0/24Altn BLK 19
128.26 P2p
Modify STP timers, and verify that these have been learned from the STP root
bridge.
SW1#show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol ieee
Root IDPriority4106
Address0013.605f.f000
This bridge is the rootHello Time 3 sec Max Age 10 sec Forward Delay 10 sec
Bridge ID Priority4106 (priority 4096 sys-id-ext 10)
Address
0013.605f.f000Hello Time 3 sec Max Age 10 sec Forward Delay 10 sec
Aging Time
300 sec
InterfaceRole Sts CostPrio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/19Desg FWD 19
128.21 P2p
Fa0/20Desg FWD 19
128.22 P2p
Fa0/23Desg FWD 19
128.25 P2p
Fa0/24Desg FWD 19
128.26 P2p
!
!SW2#show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol ieeeRoot ID Priority 4106
Address
0013.605f.f000
Cost
19
Port
25 (FastEthernet0/23)Hello Time 3 sec Max Age 10 sec Forward Delay 10 sec
Bridge ID Priority16394 (priority 16384 sys-id-ext 10)
Address000a.b832.3a80Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
InterfaceRole Sts CostPrio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/19Desg FWD 19
128.21 P2p
Fa0/20Desg FWD 19
128.22 P2p
Fa0/23Root FWD 19
128.25 P2p
Fa0/24Altn BLK 19
128.26 P2p
Downstream devices from the root bridge inherit the timers configured on the root.
With a forward delay of 10 seconds configured on SW1, the downstream switches
should take 10 seconds in each of the listening and learning phases during
convergence. The below timestamps indicate that a new root port was elected at
23:36:59 on SW3, which transitions from blocking to listening. 10 seconds later, at
23:37:09, the port transitions from listening to learning. Finally, 10 seconds after
that, at 23:37:19, the port transitions into forwarding.
SW3#debug spanning-tree events
Spanning Tree event debugging is onSW3#debug condition vlan 10
Condition 1 set
!SW3#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.SW3(config)#service timestamps debug
SW3(config)#logging console 7
SW3(config)#interface FastEthernet0/19
SW3(config-if)#shutdown
!
23:36:59: STP: VLAN0010 new root port Fa0/20, cost 1923:36:59: STP: VLAN0010 Fa0/20 -> listening
23:36:59: STP[10]: Generating TC trap for port FastEthernet0/19
!
23:37:02: STP: VLAN0010 sent Topology Change Notice on Fa0/2023:37:09: STP: VLAN0010 Fa0/20 -> learning
!
23:37:19: STP: VLAN0010 sent Topology Change Notice on Fa0/20
23:37:19: STP: VLAN0010 Fa0/20 -> forwarding
!
!SW3#undebug all
All possible debugging has been turned off
!SW3#undebug condition all
Removing all conditions may cause a flood of debugging
messages to result, unless specific debugging flags
are first removed.
Proceed with the removal of all conditions? [yes/no]: yes
1 conditions have been removed