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Cisco Employee

how to see abnormal state when looping occur in spanning tree and it is very slow to type command and show result in telnet?

how to see abnormal state when looping occur in spanning tree and it is very slow to type command and show result in telnet?

when this occur, we are urgent to shutdown port to stop looping, 

but it is very slow to type command and show result in telnet

i guess not enough time to see this wonderful moment

moreover, when reading how to troubleshooting looping, 

i see that hundred thousand times of TCN is also considered as normal due to not configured port fast.

and high input and low output rate is also considered as normal at root port, it seems  these symptoms can not be used in troubleshooting looping

in all cases

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VIP Mentor

thats why you should have serial console access to devices and a separate mgmt network running parallel , when STP loops occur networks go into a spin , so it will be very difficult to troubleshoot over the same network thats spiking through mgmt protocols

If your constantly seeing changes when you check STP then theirs an issue

you follow the fault like finding a mac at layer 2 , using show command then cdp to see where its coming from , then move onto next switch and run it again until you find the source of the issue

This will show you is something is constantly recalculating

show spanning-tree detail | inc ieee|occurr|from|is exec

The  timers will keep resetting every time there is an issue

 VLAN0001 is executing the rstp compatible Spanning Tree protocol
  Number of topology changes 48 last change occurred 7w0d ago
          from Port-channel2
 VLAN0032 is executing the rstp compatible Spanning Tree protocol
  Number of topology changes 25 last change occurred 8w6d ago
          from Port-channel1

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