Spanning Tree "time since last change" refreshes but no spanning tree related entry in logs

[Renata_Petras]

Hi, 

in the show spanning tree output we can see that the "time since last change" changed, but often there is no stp-related output in the "show logging" output..furthermore often there is no entry in the "show span root-history .." output.. still the time since last change keeps changing...
It's driving me nuts.. event though all the switches in our lan have STP enabled, but not all refresh the "time since last change"..
i checked all the participating switches with "show span details" to see if there might be some "bad devices" sending BPDUs, but it all looked fine...
Does anyone know why sometimes there are log entries in "show logg" outout saying "stp changed from... to this device" and also the time since last change changes, but sometimes only the "time since last change" changes, but there is no output in show logging??? and as mentioned before, not completely all devices refresh their timer...

Please help!
Thanks

[Richard Brodie_1]

A switch may see a topology change without its own designated root changing. So it's probably an edge switch of some sort - perhaps a blade or virtual switch that you haven't considered.

I would take a topology drawing of your network and mark up the switches that show these changes.. You can get dot1dStpTimeSinceTopologyChange through SNMP,  to speed things up. I think it might show a path from the root to the switch where the problem is. If so I'd look carefully what "show span details" shows there.

Sorry, I'm not enough of a RSTP guru to know exactly what to expect. I've been meaning to look for my education for a while.

[Renata_Petras]

Hi, FYI on a switch where a printer was connected, I enabled portfast on that port and the "time since last change"-timer stopped changing.. a TCN doesn't mean that there was a spanning tree root change... Just that a device went from down to blocking state.. (I tried the thing with portfast on a cisco switch, but I guess it will bring the same result for the HP switches)