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352-001 · Question #462

Which option describes a design benefit of root guard?

The correct answer is F. It prevents switched traffic from traversing suboptimal paths on the network. Root guard prevents unauthorized switches from becoming the STP root bridge, ensuring traffic always follows the network designer's intended optimal forwarding paths.

Layer 2 Control Plane

Question

Which option describes a design benefit of root guard?

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.

How the community answered

(26 responses)
  • A
    4% (1)
  • D
    4% (1)
  • E
    4% (1)
  • F
    88% (23)

Why each option

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

AIt makes the port go immediately into the forwarding state after being connected.

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.

BIt does not generate a spanning-tree topology change upon connecting and disconnecting a

Suppressing STP topology change notifications when a port transitions is a secondary behavior of PortFast, not a function of root guard.

CIt allows small, unmanaged switches to be plugged into ports of access switches without the risk

Protecting access ports from unmanaged switches that could disrupt STP describes BPDU Guard, which error-disables a port the moment any BPDU is received.

DIt prevents switch loops by detecting one-way communications on the physical port.

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.

EIt prevents switch loops caused by unidirectional point-to-point link condition on Rapid PVST+ and

Protecting against unidirectional point-to-point link failures in Rapid PVST+ specifically describes UDLD aggressive mode, not root guard.

FIt prevents switched traffic from traversing suboptimal paths on the network.Correct

Root guard places a port into a root-inconsistent blocking state when a superior BPDU is received, preventing a connected switch from usurping the root bridge role. By locking the root bridge to its designed location, root guard ensures the STP topology matches the intended design and traffic traverses optimal, pre-planned paths rather than being rerouted through an unexpected root. Without root guard, a rogue switch advertising a lower bridge ID could redirect traffic through suboptimal or unplanned segments of the network.

Concept tested: STP root guard preventing suboptimal traffic paths

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

Topics

#root guard#spanning tree#STP design#traffic optimization

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