Hello Anukalp.
When a bridged loop occurs in the network, meaning a layer 2 loop or spanning-tree loop as you want to call it, the switch will report host flapping.
What is a Host flapping ?
This is a host(computer, server ... any device that owns a mac address) in this case 0032.35E5.BBB1, that is being learned across two different interfaces, in this case Gig2/5 and Gig3/24.
As you know the same mac-address should be learnt in two different interfaces at the same time. unless those two interfaces are bundle in a etherchannel.
From the log message, we understand that your network is having a layer 2 loop affecting vlan 155.
- Make sure that spanning is running an instance of vlan 155 in all switches on your network!!!! then following the steps below:
- Try to find out what is the device that is owns 00:32:35:E5:BB:B1, is it a pc, server...
- If this is a server wit multiple NIC, and all NIC in the server are teamed, (NIC teaming) then you should configure gig2/5 and gig3/24 as a port-channel.
- Verify what is connected behind these two interfaces. If there are switches connected downstream most likely the problem comes from down there... you will need to check the logs for more mac notifications and follow the interfaces flapping in downstream switches until find the end device causing the problem.
- Check their configuration.
00:32:35:E5:BB:B1
Regards.
Wilson B
