CBPDU: Configuration Bridge Protocol Data Unit
A type of packet that is sent between bridging devices in a network to configure these devices' interfaces in either forwarding or blocking state. This is done to build a spanning tree, so that looping packets don't digest the endetire bandwidth of the network. These CBPDUs are sent from each bridging device, and lets these devices configure themselves so that only one physical path exists between the bridging devices at any given time.

A CBPDU contains the following information:
These CBPDUs allow the bridges to: CBPDUs are a vital part of bridging and spanning trees.