352-001 Question #462: Real Exam Question with Answer & Explanation

Question

Options

• AIt makes the port go immediately into the forwarding state after being connected.
• BIt does not generate a spanning-tree topology change upon connecting and disconnecting a
• CIt allows small, unmanaged switches to be plugged into ports of access switches without the risk
• DIt prevents switch loops by detecting one-way communications on the physical port.
• EIt prevents switch loops caused by unidirectional point-to-point link condition on Rapid PVST+ and
• FIt prevents switched traffic from traversing suboptimal paths on the network.

Explanation

Root guard prevents unauthorized switches from becoming the STP root bridge, ensuring traffic always follows the network designer's intended optimal forwarding paths.

Common mistakes.

• A. Placing a port immediately into the forwarding state upon connection describes PortFast, which bypasses the STP listening and learning states for edge ports, not root guard.
• B. Suppressing STP topology change notifications when a port transitions is a secondary behavior of PortFast, not a function of root guard.
• C. Protecting access ports from unmanaged switches that could disrupt STP describes BPDU Guard, which error-disables a port the moment any BPDU is received.
• D. Detecting one-way communication failures on a physical link describes Unidirectional Link Detection (UDLD), which operates independently of STP and has no relation to root guard.
• E. Protecting against unidirectional point-to-point link failures in Rapid PVST+ specifically describes UDLD aggressive mode, not root guard.

Concept tested. STP root guard preventing suboptimal traffic paths

Reference. https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10588-74.html

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