Spanning Tree Topology is changing in continuous-(SG220 CoreSW, SG200, SG200)!

[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

[balaji.bandi]

Make Core with Low Priority for Spanning Tree, Rest 2 Switch increase the Priority to high value.

Edited :

After posting the above suggestion i have later looked deep, change the STP Tweak also check the Physical connectivity stability between switches

[Imma]

Hi Balaji,

thank you for you advice. I have already done that. I made the coreSW root Bridge ID value:4096

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 9489 last change occurred 17:07:47 ago

The other switches have the below value: 

Designated Root
Bridge ID:	32768-00:e1:6d:8d:48:82
Root Bridge ID:	4096-2c:ab:eb:d4:d3:62
Root Port:	GE17
Root Path Cost:	20000
Topology Changes Counts:	108
Last Topology Change:	3D/15H/46M/39S

Designated Root
Bridge ID:	32768-00:e1:6d:8d:3d:b9
Root Bridge ID:	4096-2c:ab:eb:d4:d3:62
Root Port:	GE17
Root Path Cost:	2000
Topology Changes Counts:	7817
Last Topology Change:	7D/0H/23M/3S

It worked just one day. then the situation is same again, all port state transition. (it seems that the transition happen when the PC start up or when they go to sleep or shutdown.)

There is not any redundancy. Should I create one?

Or should I remove the Spanning Tree?

I think also the firmware update of 2 switches have to do somehow with this issue? I have planned to proceed today with this.

Thank you in advanced,

Denisa

[Imma]

Hi again balaji,

I checked the physical cables (on the switch that end up in wall jack), are like twisted, not bend properly.

Has this to do with SPT tweak ?

Thank you,

Denisa

[Sebastian Fernandez · Accepted solution]

Its not the Spanning-Tree issue, the log indicates that the link is going down. STP will just converge through its states whenever the link flaps. If this access-port, consider using spanning-tree portfast. But you looking into why is the link flapping.

- 

Sebastian

[Imma]

I checked the ports. There isn't any error. All the ports of the 3 switches experience STP transition. I have noticed STP events appear when PC change their power status (start up, sleep, shutdown, or restart). 

Yes, I have changed access port into portfast and bpdu enabled.

Actually there is not any vlan. All three switches are in the same broadcast domain.

Thank you,

Denisa

[Imma]

This standard has not been followed, during the cable installation:
"The minimum bend radius for Category 6, 5, and 5e cable is four times the
cable diameter, or approximately 1 inch. When cabling is bent beyond this
specified radius, it can cause transmission failures. Cable manufacturers
will normally provide the minimum radius to bend the cable without
compromising it during installation and use. These bend radius
specifications may be different."