Loop Detection in Nortel Baystack 470-48T

[bishnupoudel]

My core switch is Cisco 6500 and there i see heavy number of TCN received from Nortel Baystack 470-48T.

How can i detect loop in Nortel Baystack 470-48T. Please share the command to see the TCN changes in Nortel.

Thank you in advance.

[Dominik]

I suggest you have a problem with the different versions of spanning Tree.
The ES470 uses IEEE standard STP per default and your Cisco Cat6500 is using pvst.

Check out wich version you running on your switches and make sure you have the same on both
sides.

Use this command to determine wich version of STP you are running on your ES470:
sho spanning-tree op-mode

Good Luck

[bishnupoudel]

Thank you Dominik for the info.

Current STP Operation Mode: STPG is running on Nortel Baystack 470-48T and RSTP is running on C6500.

Actually what is happening is randomly some of the desktops are going out of network for 1 mins and reconnects on its own. The issue is sporadic in nature. Upon checking at Cisco 6500 i see TCN changes counter is very high coming from interface where nortel 470-48T is connected. Also i see some of the edge ports in Nortel switch rate-limit counters is showing 99% traffic for multicast and Broadcast.

So i assume it could be the issue with any sorts of loop. But i am new to nortel environment and dont have much idea to see the TCN changes in Nortel.

Also, i m not sure if it is because of loop, can anyone help to understand the such issue?

Really appreciate your help. Thank you.

[Dominik]

I would recommand to run the same Spanning Tree Version on all devices of one network.
In your case you can change STP mode to RSTP on your ES470.
Make sure you have STP activated on all edge ports.

Sometimes the rate limiting counter shows 99 to 100% multicast when the client is sending no unicast packest and nearly all traffic on that port is broadcast/multicast, this is the normal behavior of a client that
is not communicating over the network.

To get more details use the sho port-statistics command.

[bishnupoudel]

I will do so. Also could you please tell the command to see the TCN changes coutnters from which port in Notel 470-48T and Nortel 4550 switch.

Like below we get from Cisco6500.

c6500#show spanning-tree detail | inc ieee|occurr|from|is exec
 VLAN0015 is executing the rstp compatible Spanning Tree protocol
  Number of topology changes 12195 last change occurred 02:44:18 ago
          from GigabitEthernet 1/3