Spanning Tree Topology changes in continuous (SG220-CoreSw, SG200,SG200), Timeouts in whole networks!

[Imma]

Hello all,

we have 3 switches connected in star topology. There is just one vlan configured. All the switches are experiencing spanning tree topology changes, in continuous. And all the network is experiencing some timeouts.  A sample of logging events are as below:

*May 03 2019 13:27:21: STP-6: GigabitEthernet38 STP port state is set to Forwarding
*May 03 2019 13:27:18: STP-6: GigabitEthernet38 STP port state is set to Learning
*May 03 2019 13:26:59: STP-6: GigabitEthernet38 STP port state is set to Blocking
*May 03 2019 13:26:59: Port-5: GigabitEthernet38 link up
*May 03 2019 13:26:53: STP-6: GigabitEthernet38 STP port state is set to Disabled
*May 03 2019 13:26:52: Port-5: GigabitEthernet38 link down
*May 03 2019 13:26:50: STP-6: GigabitEthernet38 STP port state is set to Blocking
*May 03 2019 13:26:50: Port-5: GigabitEthernet38 link up
*May 03 2019 13:23:23: STP-6: GigabitEthernet13 STP port state is set to Forwarding
*May 03 2019 13:23:23: STP-6: GigabitEthernet13 STP port state is set to Blocking
*May 03 2019 13:23:23: Port-5: GigabitEthernet13 link up
*May 03 2019 13:23:19: STP-6: GigabitEthernet13 STP port state is set to Disabled
*May 03 2019 13:23:19: Port-5: GigabitEthernet13 link down
*May 03 2019 13:19:06: STP-6: GigabitEthernet14 STP port state is set to Forwarding
*May 03 2019 13:19:04: STP-6: GigabitEthernet14 STP port state is set to Learning
*May 03 2019 13:18:45: STP-6: GigabitEthernet14 STP port state is set to Blocking
*May 03 2019 13:18:45: Port-5: GigabitEthernet14 link up

CoreSw#show spanning-tree

Spanning tree enabled mode RSTP
Default port cost method: long
Loopback guard: Disabled

Root ID Priority 4096
Address 2c:ab:eb:d4:d3:62
This switch is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Number of topology changes 9194 last change occurred 00:10:49 ago
Times: hold 0, topology change 0, notification 0
hello 2, max age 20, forward delay 15

Interfaces
Name State Prio.Nbr Cost Sts Role PortFast Type
--------- -------- -------- -------- ------ ---- -------- -----------------
gi3 enabled 128.3 20000 Frw Desg No P2P (RSTP)
gi4 enabled 128.4 20000 Frw Desg No P2P (RSTP)
gi5 enabled 128.5 20000 Frw Desg No P2P (RSTP)
gi7 enabled 128.7 20000 Frw Desg No P2P (RSTP)
gi12 enabled 128.12 20000 Frw Desg Yes P2P (RSTP)
gi13 enabled 128.13 20000 Frw Desg Yes P2P (RSTP)
gi15 enabled 128.15 20000 Frw Desg No P2P (RSTP)

...

CoreSW#show spanning-tree interfaces GigabitEthernet 7

Port gi7 enabled
State: forwarding Role: designated
Port id: 128.7 Port cost: 20000
Type: P2P (RSTP) Edge Port: No
Designated bridge Priority : 4096 Address: 2c:ab:eb:d4:d3:62
Designated port id: 128.7 Designated path cost: 0
BPDU Filter: Disabled BPDU guard: Disabled
BPDU: sent 267822, received 0

Any idea why happen this situation? 

Many thanks,

Regards,

Denisa

[Sebastian Fernandez]

Its not a spanning tree issue, you have your ports flapping. Please check on them, STP state transition is a process that a port has to go through if it goes down and then comes back up.

[amanchanpura]

Hi Engineer,

I am also facing the same issue as mentioned above. Switchport is flapping and changing the states.. and it results whole network down for 10-15 minutes. 

what is the permanent solution for this issue?

[amanchanpura]

HFL-SYD-SW02#show spanning-tree

Spanning tree enabled mode RSTP
Default port cost method: long
Loopback guard: Disabled

Root ID Priority 4096
Address 4c:a6:4d:de:e7:9c
Cost 20000
Port gi24
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 16384
Address 4c:a6:4d:de:e7:30
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Number of topology changes 510 last change occurred 16:17:15 ago
Times: hold 0, topology change 0, notification 0
hello 2, max age 20, forward delay 15

Interfaces
Name State Prio.Nbr Cost Sts Role PortFast Type
--------- -------- -------- -------- ------ ---- -------- -----------------
gi1 enabled 128.1 20000 Frw Desg No P2P (RSTP)
gi2 enabled 128.2 200000 Frw Desg No P2P (RSTP)
gi3 enabled 128.3 200000 Frw Desg No P2P (RSTP)
gi4 enabled 128.4 200000 Frw Desg No P2P (RSTP)
gi6 enabled 128.6 200000 Frw Desg No P2P (RSTP)
gi7 enabled 128.7 200000 Frw Desg No P2P (RSTP)
gi8 enabled 128.8 200000 Frw Desg No P2P (RSTP)
gi9 enabled 128.9 200000 Frw Desg No P2P (RSTP)
gi10 enabled 128.10 200000 Frw Desg No P2P (RSTP)
gi12 enabled 128.12 200000 Frw Desg No P2P (RSTP)
gi13 enabled 128.13 20000 Frw Desg No P2P (RSTP)
gi15 enabled 128.15 200000 Frw Desg No P2P (RSTP)
gi16 enabled 128.16 200000 Frw Desg No P2P (RSTP)
gi19 enabled 128.19 200000 Frw Desg No P2P (RSTP)
gi21 enabled 128.21 20000 Frw Desg No P2P (RSTP)
gi22 enabled 128.22 200000 Frw Desg No P2P (RSTP)
gi24 enabled 128.24 20000 Frw Root No P2P (RSTP)
gi25 enabled 128.25 20000 Frw Desg No P2P (RSTP)
gi26 enabled 128.26 20000 Frw Desg No P2P (RSTP)
HFL-SYD-SW02# show loggin

Logging service is enabled

Console Logging: level notice
Buffer Logging : level info
File Logging : disabled

Buffer Logging
--------------
*May 19 2022 08:06:24: AAA-5: New ssh connection for user cisco, source 10.254.102.29 ACCEPTED
*May 19 2022 07:32:11: AAA-5: New ssh connection for user cisco, source 10.254.102.29 ACCEPTED
*May 18 2022 15:56:27: AAA-5: New ssh connection for user cisco, source 10.254.102.29 ACCEPTED
*May 18 2022 15:56:20: AAA-5: New ssh connection, source 10.254.102.29 REJECTED
*May 18 2022 15:48:35: STP-6: GigabitEthernet13 STP port state is set to Forwarding
*May 18 2022 15:48:33: STP-6: GigabitEthernet13 STP port state is set to Learning
*May 18 2022 15:48:14: STP-6: GigabitEthernet13 STP port state is set to Blocking
*May 18 2022 15:48:14: Port-5: GigabitEthernet13 link up
*May 18 2022 15:47:39: STP-6: GigabitEthernet13 STP port state is set to Disabled
*May 18 2022 15:47:39: Port-5: GigabitEthernet13 link down
*May 18 2022 15:19:28: STP-6: GigabitEthernet21 STP port state is set to Forwarding
*May 18 2022 15:19:26: STP-6: GigabitEthernet21 STP port state is set to Learning
*May 18 2022 15:19:06: STP-6: GigabitEthernet21 STP port state is set to Blocking
*May 18 2022 15:19:06: Port-5: GigabitEthernet21 link up
*May 18 2022 15:19:02: STP-6: GigabitEthernet21 STP port state is set to Disabled
*May 18 2022 15:19:02: Port-5: GigabitEthernet21 link down
--More--
HFL-SYD-SW02#show spanning-tree interfaces GigabitEthernet 5

Port gi5 enabled
State: disabled Role: disabled
Port id: 128.5 Port cost: 20000
Type: Shared (RSTP) Edge Port: No
Designated bridge Priority : 0 Address: 00:00:00:00:00:00
Designated port id: 0.0 Designated path cost: 0
BPDU Filter: Disabled BPDU guard: Disabled
BPDU: sent 0, received 0

[Seb Rupik]

Hi there,

Looking at your output, gi24 appears to be your uplink. All ports have a link type of point-to-point, which means any switchport state change will cause a TCN to be generated and sent towards the root bridge, which in turn will set its TC flag on its BPDU which will cause all switches in the STP topology to clear their MAC tables, resulting in an outage.

I assume that all ports other than gi24 are actually connected to end devices and as such should have a link type of edge, this can be set by enabling PortFast on those switchports. An edge port does not cause TCNs to be generated, which should solve your issue.

cheers,

Seb.

[paul driver]

Hello
make sure you have ALL your edge ports enabled with 

spanning-tree portfast
spanning-tree bpduguard 

Otherwise every time a user logs off and on the network without portfast you will incur tcn changes on all non edge specified ports

Bpduguard will negate any edge port from bridging any unauthorised switch bpdus it receives thus negating any potential loop  

[amanchanpura]

Hi All,

How can I monitor these TCN events with SNMP ?