A BPDU contains several fields you should know. The Root Bridge ID identifies the switch that the sender believes is root. The Root Path Cost shows the total cost to reach that root. The Sender Bridge ID identifies who sent this BPDU. The Port ID identifies which port sent it. Timers include Hello Time, Max Age, and Forward Delay. When a switch receives a BPDU, it compares these values against its own. The switch with better information wins, and topology decisions follow.
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$ curl repovive.com/roadmaps/network-design/spanning-tree-and-link-aggregation/bpdu-contents
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