Spanning Tree (STP 802.1d and RSTP 802.1w) Debug & Notes

I am going to simulate a failure scenario while running 802.1d and then while running 802.1w. Currently Port Gi1/47(Green) and Gi1/48(Red) are configured as trunk ports and are allowing all vlans through. Gi1/48 is in a blocking(ALTN) state for Vlan 25 . I am going to admin down Gi1/47 and Enable debugging so we can see the events that occur. At the same time I will ping from SW01 to SW02 to see how long it takes to converge.

Figure 1

Verifications: 

Cisco_4948E_02#show spanning-tree root

                                        Root    Hello Max Fwd
Vlan                   Root ID          Cost    Time  Age Dly  Root Port
---------------- -------------------- --------- ----- --- ---  ------------
VLAN0001         20481 4055.39a8.1000         0    2   20  15
VLAN0025         32793 4055.39a7.bb80         4    2   20  15  Gi1/47
VLAN0026         32794 4055.39a8.1000         0    2   20  15
VLAN0052         32820 4055.39a8.1000         0    2   20  15

Cisco_4948E_02#show spanning-tree vlan 25

VLAN0025
  Spanning tree enabled protocol ieee
  Root ID    Priority    32793
             Address     4055.39a7.bb80
             Cost        4
             Port        47 (GigabitEthernet1/47)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32793  (priority 32768 sys-id-ext 25)
             Address     4055.39a8.1000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/47              Root FWD 4         128.47   P2p
Gi1/48              Altn BLK 4         128.48   P2p


Cisco_4948E_02#

Enable Debugging & Setup Ping:

Cisco_4948E_02#debug spanning-tree events
Spanning Tree event debugging is on
!
Cisco_4948E_02#terminal monitor
Cisco_4948E_02#

Cisco_4948E_01#ping 192.168.25.2 repeat 100000 timeout 5

Fail Over: 
Now we shutdown Gi1/47 while running 802.1d.





 Cisco_4948E_02(config)#int gi 1/47
Cisco_4948E_02(config-if)#shut
Cisco_4948E_02(config-if)#
*Nov 23 11:51:10.423: STP: VLAN0025 new root port Gi1/48, cost 4
*Nov 23 11:51:10.423: STP: VLAN0025 Gi1/48 -> listening
*Nov 23 11:51:12.419: %HSRP-5-STATECHANGE: Vlan25 Grp 25 state Standby -> Init
*Nov 23 11:51:12.423: STP: VLAN0025 sent Topology Change Notice on Gi1/48
*Nov 23 11:51:13.331: STP: VLAN0001 Topology Change rcvd on Gi1/48
*Nov 23 11:51:13.331: STP: VLAN0026 Topology Change rcvd on Gi1/48
*Nov 23 11:51:25.423: STP: VLAN0025 Gi1/48 -> learning
*Nov 23 11:51:40.423: STP: VLAN0025 Gi1/48 -> forwarding
*Nov 23 11:52:05.347: %HSRP-5-STATECHANGE: Vlan25 Grp 25 state Speak -> Standby

 Results:

It took forty seconds for spanning tree to converge. This can be seen from the below ping output which was set with a time out of 5 seconds.  By default it can take up to 50 seconds plus any additional time it takes your first hop redundancy protocols.

!!!!!!!........!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!
Success rate is 99 percent (9246/9254), round-trip min/avg/max = 1/1/28 ms
Cisco_4948E_01#

Lets do the same test while running 802.1w and all timers are default.

 Cisco_4948E_02#show spanning-tree root

                                        Root    Hello Max Fwd
Vlan                   Root ID          Cost    Time  Age Dly  Root Port
---------------- -------------------- --------- ----- --- ---  ------------
VLAN0001         20481 4055.39a8.1000         0    2   20  15
VLAN0025         32793 4055.39a7.bb80         4    2   20  15  Gi1/47
VLAN0026         32794 4055.39a8.1000         0    2   20  15
VLAN0052         32820 4055.39a8.1000         0    2   20  15
Cisco_4948E_02#show spanning-tree vlan 25

VLAN0025
  Spanning tree enabled protocol rstp
  Root ID    Priority    32793
             Address     4055.39a7.bb80
             Cost        4
             Port        47 (GigabitEthernet1/47)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32793  (priority 32768 sys-id-ext 25)
             Address     4055.39a8.1000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/47              Root FWD 4         128.47   P2p
Gi1/48              Altn BLK 4         128.48   P2p


Cisco_4948E_02(config-if)#
*Nov 23 14:13:30.643: RSTP(25): updt roles, root port Gi1/47 going down
*Nov 23 14:13:30.643: RSTP(25): Gi1/48 is now root port


Cisco_4948E_01#ping 192.168.25.2 repeat 100000 timeout 2

Type escape sequence to abort.
Sending 100000, 100-byte ICMP Echos to 192.168.25.2, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!
Success rate is 99 percent (984/985), round-trip min/avg/max = 1/1/16 ms
Cisco_4948E_01#

Since RSTP is much faster then legacy STP I set the timeout for 2 seconds. We can see that it converges well within 2 seconds. Compare that to the 40 seconds we waited for legacy STP.

Notes:

Default 802.1d Timers and States:
Disabled: Port is admin down.
Blocking: Port is up but not building the cam table or forwarding any frames via this interface.
Max Age: 20 Seconds -  How long the bridge(Switch) should wait before it stops hearings hellos.
Listening: 15 Seconds - Receiving BPDU's but not building the cam(MAC) table.
Learning: 15 Seconds -Starts building the cam (MAC) table.
Forwarding: Processing Frames.
Legacy Spanning Tree - The root bridge controls the forwarding delay as it is responsible for sending out BPDU.

Data rate	STP Cost (802.1D-1998)
4 Mbit/s	250
10 Mbit/s	100
16 Mbit/s	62
100 Mbit/s	19
1 Gbit/s	4
2 Gbit/s	3
10 Gbit/s	2
Data rate	RSTP Cost (802.1D-2004 / 802.1w)[3]
4 Mbit/s	5,000,000
10 Mbit/s	2,000,000
16 Mbit/s	1,250,000
100 Mbit/s	200,000
1 Gbit/s	20,000
2 Gbit/s	10,000
10 Gbit/s	2,000