Cisco Catalyst: PortFast BPDU Guard | Exam 200-125 Answers

PortFast BPDU Guard

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Which Cisco Catalyst feature automatically disables the port in an operational PortFast upon receipt of a BPDU?



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A. B. C. D. E.


We only enable PortFast feature on access ports (ports connected to end stations). But if someone does not know he can accidentally plug that port to another switch and a loop may occur when BPDUs are being transmitted and received on these ports. With BPDU Guard, when a PortFast receives a BPDU, it will be shut down to prevent a loop.

The correct answer is D. BPDU Guard.

PortFast is a Cisco Catalyst feature that is used to bypass the listening and learning phases of the spanning tree protocol, thereby allowing a switch port to become operational faster. This feature is typically used for access ports, where there is no risk of creating a loop in the network.

However, if a BPDU (Bridge Protocol Data Unit) is received on a PortFast-enabled port, it could mean that a loop has been created in the network, and the switch should take action to prevent further issues. BPDU Guard is a feature that automatically disables a PortFast-enabled port if a BPDU is received, thereby preventing the port from causing any loops in the network.

BackboneFast and UplinkFast are both features used to improve the convergence time of the spanning tree protocol, but they do not address the issue of a PortFast-enabled port causing a loop in the network.

Root Guard is a feature that protects against unauthorized changes to the spanning tree root bridge, but it does not address the issue of a PortFast-enabled port causing a loop in the network.

BPDU Filter is a feature that allows a switch port to be configured to either forward or discard BPDUs, but it does not automatically disable a PortFast-enabled port upon receipt of a BPDU.