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Routing & Switching · Foundational

Root Bridge

The switch with the lowest bridge ID, which acts as the reference point of the STP topology; all its ports are designated.

Definition

Every other switch calculates its lowest-cost path to the root. Root placement should be engineered at the distribution or core layer using priority, ideally aligned with the FHRP active gateway. Root guard protects root placement.

Example

spanning-tree vlan 1-100 root primary

Exam tip

Relying on default priority makes the oldest switch (lowest MAC) the root, usually a poor choice.

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