200-301 Question #1381: Real Exam Question with Answer & Explanation

Question

What is the role of the root port in a switched network?

Options

• AIt replaces the designated port when the designated port fails.
• BIt replaces the designated port when the root port fails.
• CIt is the best path to the root from a nonroot switch.
• DIt is administratively disabled until a failover occurs.

Explanation

The root port on a non-root switch identifies the most efficient path to reach the root bridge in a Spanning Tree Protocol (STP) network.

Common mistakes.

• A. A root port's function is to provide the best path to the root bridge, not to replace a designated port if it fails; designated ports are selected on network segments to forward traffic.
• B. This statement is nonsensical; a root port's role is not to replace a designated port, and if a root port fails, the STP process reconverges to select a new root port.
• D. Root ports are active and forwarding traffic to the root bridge, not administratively disabled awaiting a failover event, which describes the behavior of a blocked or backup port.

Concept tested. Spanning Tree Protocol root port role

Reference. https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10556-16.html

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