Bridge Protocol Data Units (BPDUs) are messages exchanged between switches running Spanning Tree Protocol to share information. BPDUs contain details like switch IDs, port priorities, and costs. Switches use BPDUs and a mathematical algorithm to detect and prevent network loops by shutting down redundant ports. There are three types of BPDUs: Configuration, Topology Change Notification, and Topology Change Notification Acknowledgment. The purpose is to avoid switching loops and broadcast storms.

1. Bridge Protocol Data Unit (BPDU)

2.  The Spanning Tree Protocol (STP) enabled switches in a
redundant Local Area Network (LAN) need to exchange
information between each other for Spanning Tree Protocol
(STP) to work properly.
 Bridge Protocol Data Units (BPDUs) are messages
exchanged between the switches inside an interconnected
redundant Local Area Network (LAN).
 Bridge Protocol Data Units (BPDUs) frames contain
information regarding the Switch ID, originating switch
port, MAC address, switch port priority, switch port cost etc.

3.  Bridge Protocol Data Units (BPDUs) frames are sent out as
multicast messages regularly at multicast destination MAC
address 01:80:c2:00:00:00.
 When Bridge Protocol Data Units (BPDUs) are received, the
Switch uses a mathematical formula called the Spanning
Tree Algorithm (STA) to know when there is a Layer 2 Switch
loop in network and determines which of the redundant ports
needs to be shut down.

4.  Three types of Bridge Protocol Data Units (BPDUs) are
Configuration BPDU (CBPDU), Topology Change Notification
(TCN) BPDU and Topology Change Notification
Acknowledgment (TCA).
 The basic purpose of the Bridge Protocol Data Units
(BPDUs) and the Spanning Tree Algorithm (STA) is to
avoid Layer 2 Switching loops and Broadcast storms.