BPDU

BPDUs are control messages used by STP/RSTP to build a loop-free topology.

Updated: 2026-03-05

Definition

Bridge Protocol Data Units (BPDUs) are exchanged between switches to elect the root bridge and determine port roles/states.

They carry information like root ID, path cost, and bridge ID.

Key points

STP control-plane messages
Used for root election and topology decisions
Receiving unexpected BPDUs on edge ports indicates risk

Common mistakes

Ignoring BPDU Guard on access ports.
Assuming STP is unnecessary in modern networks.

Related exams

Cisco CCNA (200-301)

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