What's the role of Spanning Tree Protocol (STP) and how is the root bridge elected?

STP prevents loops in switched networks by blocking redundant paths. Root bridge election: switch with the lowest Bridge ID (Priority + MAC address) wins. Default priority is 32768 (or 32768 + VLAN ID for PVST+). Lower priority = better candidate. Once root is elected, every switch calculates the lowest-cost path to the root and blocks alternate paths. Variants: STP (802.1D), RSTP (802.1w, faster convergence), MST (802.1s, multiple instances).

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