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Bridge protocol data unit

Bridge protocol data unit

(also bridge protocol data unit frame, BPDU, BPDU frame)

Bridge protocol data unit definition

A bridge protocol data unit is a frame (a single network packet used in data transmission) with information on the spanning tree protocol (a protocol used to prevent loops that lead to broadcast storms and network instability). Using bridge protocol data unit frames, switches can determine the best paths to the root bridge, identify redundant ones, and block those that have the potential to loop the network.

See also: digital switch, packet switched network, virtual switch, jumbo frame, logical topology

Information carried by bridge protocol data units

Bridge protocol data units contain information about the sending switch and its priority, the port on which the packet was sent, and the network topology (such as the root bridge, the path cost, and the status of ports on the switch).

Types of bridge protocol data units

• Configuration: Configuration bridge protocol data units are used to exchange configuration information between switches. They are sent out by the root bridge to inform all the other switches in the network about the current state of the spanning tree protocol.
• Topology change notification (TCN): TCN bridge protocol data units are used to update spanning tree protocol switches about detected network changes, such as link failures or new paths. TCN bridge protocol data units are sent by the switch that made the discovery to the root bridge, which issues an updated configuration unit to all the other switches in the network.