Bridge Protocol Data Unit

What Does Bridge Protocol Data Unit Mean?

A bridge protocol data unit (BPDU) is a data message transmitted across a local area network to detect loops in network topologies. A BPDU contains information regarding ports, switches, port priority and addresses.

Advertisements

BPDUs contain the information necessary to configure and maintain spanning tree topology. They are not forwarded by switches, but the information is used by switches to calculate their own BPDUs for information passing.

Techopedia Explains Bridge Protocol Data Unit

When devices are initially attached to switch ports, they do not start data transmission immediately. Instead, they moves through different states while BPDU processing determines the network topology. A topology change notification (TCN) BPDU informs other switches of port changes. They are injected into the network by a non-root switch and propagated to the root. When a TCN is received, the root switch will set a topology change flag in its normal BPDU. This flag is propagated to all other switches to instruct them to rapidly age out their forwarding table entry
switches.

When a root receives the TCN BPDU, it transmits a configuration BPDU message on all the ports with topology change flag set to 1. Switches that receive this BPDU on the root port filter the database and generate their own configuration BPDUs on designated ports. This propagates down the tree to the end of the path.

Advertisements

Related Terms

Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.