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Routing & Switching · Intermediate

Bridge Protocol Data Unit (BPDU)

The STP message switches exchange to elect the root bridge and compute the loop-free topology.

Definition

Configuration BPDUs are sent every 2 seconds (hello time) by designated ports, to multicast MAC 01:80:C2:00:00:00 (IEEE) or 01:00:0C:CC:CC:CD (Cisco PVST+). They contain root bridge ID, root path cost, sender bridge ID, port ID and timers. TCN BPDUs signal topology changes in 802.1D.

Example

debug spanning-tree bpdu

Exam tip

In RSTP every switch generates BPDUs; in 802.1D only the root originates and others relay.

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