STP - high number of topology changes

Unanswered Question
Jan 15th, 2010

RD-CORE-1#sh spanning-tree detail

VLAN0010 is executing the rstp compatible Spanning Tree protocol
  Bridge Identifier has priority 8192, address 00d0.02d5.740a
  Configured hello time 2, max age 20, forward delay 15, tranmsit hold-count 6
  We are the root of the spanning tree
  Topology change flag set, detected flag not set
  Number of topology changes 13589 last change occurred 00:00:33 ago
          from GigabitEthernet3/41
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 1, notification 0, aging 300

I would appreciate any comments on the topology change number in question here.  Is this something I should be concerned about?

I have this problem too.
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Ganesh Hariharan Fri, 01/15/2010 - 06:53

Hi Jason,

TCN comes into picture in switching world when ever there is link up/down has happen in the switching domain,so by default in all cisco swirtches run PVST so if any change or any port goes up/down it will result in TCN and STP convergence for taht particular vlan.

As per the logs in vlan 10 it can happen that any host is getting booted or getting some problem with the switch port which is connected with host getting fluctuated result in TCN and stp convergence for that VLAN 10.

To avoid the TCN frequently portfast is the only feature which can be used in switching before enabling portfast just check out the necessaity check before enabling.

check out below link in understanding of TCN in switching domain hope that helps out your query !!



lusandi Fri, 01/15/2010 - 16:00


I would like to ask you if you can provide me this information.

show version of the switch, also if you can provide me the show run of the unit, and a description of the edge points of your topology in order to confirm what is creating the topology changes.

I will be waiting for your information.



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