spanning tree issue root changed for vlan x

[erwee1973]

Hello,

We have a strange issue with spanning tree. We are looking for a solution all this morning but so far without any luck.

We have a 2960 switch which gives continuously the messages:

002752: *Mar  3 18:07:16.912: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002753: *Mar  3 18:07:18.933: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002754: *Mar  3 18:07:18.933: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002755: *Mar  3 18:07:20.938: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002756: *Mar  3 18:07:20.938: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002757: *Mar  3 18:07:22.952: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002758: *Mar  3 18:07:22.952: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002759: *Mar  3 18:07:24.965: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002760: *Mar  3 18:07:24.965: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002761: *Mar  3 18:07:26.978: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002762: *Mar  3 18:07:26.978: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002763: *Mar  3 18:07:28.991: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002764: *Mar  3 18:07:28.991: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002765: *Mar  3 18:07:31.005: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002766: *Mar  3 18:07:31.005: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002767: *Mar  3 18:07:33.035: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002768: *Mar  3 18:07:33.035: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002769: *Mar  3 18:07:35.056: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002770: *Mar  3 18:07:35.056: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002771: *Mar  3 18:07:37.070: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002772: *Mar  3 18:07:37.070: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002773: *Mar  3 18:07:39.074: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002774: *Mar  3 18:07:39.074: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002775: *Mar  3 18:07:41.096: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91
002776: *Mar  3 18:07:41.096: %SPANTREE-5-ROOTCHANGE: Root Changed for vlan 91: New Root Port is GigabitEthernet0/2. New Root Mac Address is c08c.609f.aa80
002777: *Mar  3 18:07:43.101: %SPANTREE-5-TOPOTRAP: Topology Change Trap for vlan 91

When we shut all ports except this gig 0/2 , the messages keep on coming. Is this a bug or what can be the issue?

Info about this switch:

SER1-2960-2#sh vers
Cisco IOS Software, C2960 Software (C2960-LANBASEK9-M), Version 15.0(2)SE6, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2014 by Cisco Systems, Inc.
Compiled Wed 09-Apr-14 03:40 by prod_rel_team

ROM: Bootstrap program is C2960 boot loader
BOOTLDR: C2960 Boot Loader (C2960-HBOOT-M) Version 15.0(2r)EZ1, RELEASE SOFTWARE (fc2)

ALM1-SER1-2960-2 uptime is 2 days, 18 hours, 11 minutes
System returned to ROM by power-on
System image file is "flash:/c2960-lanbasek9-mz.150-2.SE6/c2960-lanbasek9-mz.150-2.SE6.bin"

Spanning tree mode is rapid pvst.

Does anybody have a clue what can be wrong?

With kind regards,

Ralph Willemsen

Arnhem, Netherlands.

[Peter Paluch · Accepted solution]

Hi Ralph,

Is there a possibility that in the VLAN 91, the root switch is 18 or more "hops" away? That would cause the BPDUs to expire before a new BPDU can arrive. BPDUs in legacy STP expire after MaxAge-MesageAge seconds, which is 20 seconds at the firs hop switch next to the root switch, 19 seconds at the second hop switch from the root switch, etc.

Alternatively, have you tweaked the existing STP timers in your network? Are you using a non-standard MaxAge setting?

Best regards,
Peter

[erwee1973]

Hello Peter,

Thank you for your quick response! It appeared that with our customer they have a switch infrastructure with some switches which are more than 18 hops away from the stp root bridge (!)

We are tuning it now (and will do a recommendation for redesign...)

Regards and thanks again,

Ralph