When the status of the interface at point T changes, a downstream device continuously sends TCN BPDUs to the upstream device.
The upstream device processes only the TCN BPDUs received on the designated port and drops TCN BPDUs on other ports.
The upstream device sets the TCA bit of the Flags field in the configuration BPDUs to 1 and returns the configuration BPDUs to instruct the downstream device to stop sending TCN BPDUs.
The upstream device sends a copy of the TCN BPDUs toward the root bridge.
Steps 1, 2, 3 and 4 are repeated until the root bridge receives the TCN BPDUs.
The root bridge sets the TC bit of the Flags field in the configuration BPDUs to 1 to instruct the downstream devices to delete MAC address entries.