Hi Atirak,
The network topology can happen in a network due to different reasons like a link failure, a Switch (Bridge) failure, or a port transitioning to forwarding state.
The topology change must be notified to all Switches (Bridges) in the network and the process involves two steps:
• The Switch (Bridge) notifies the topology change to Root Bridge
• The Root Switch (Bridge) bridge broadcasts the topology change information into the whole network.
In case 6500 is the Root bridge for VLAN 106 & Po 50 receiving TCN notification and i would like to know below information.
++Which interface is flapping ? please trace the link flap & if it is a end port enable the port fast or shutdown interface -- Verify
++Does the CUCM or client has valid GW address to reach GW?
++When you ping from CUCM to 172.16.6.254 GW , you mentioned -LOSS- Have you checked is it learning ARP ?
++Ping from 6500 to 172.16.6.41 or client on vlan 106 by sourcing 172.16.6.254-Verify
++Connect a Pc directly to 6500 switch & ping to 172.16.6.254 -share the outputs.
Kindly let me know your convenient time, so we can schedule webex to check configuration & path from 6500 to vlan 106 client.