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:

• Advertisement for the root bridge
• Total cost of the interfaces it has been transmitted from
• The MAC Address of the interface the CBPDU was first transmitted on

These CBPDUs allow the bridges to:

• Select the root bridge
• Select the designated bridge
• Determine whether an interface should be put in blocking or forwarding state
• Keep only one physical path to another bridge active at any given time, which leads to:
• No looping occurs

CBPDUs are a vital part of bridging and spanning trees.