Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A switch should automatically disable any access port that receives a BPDU from an attached device. Which feature directly provides that behavior?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
Root Guard
Root Guard prevents a port from becoming a root port if superior BPDUs are received, but it does not simply err-disable edge ports on any BPDU.
B
Distractor review
Loop Guard
Loop Guard protects against unidirectional-link conditions on non-designated STP ports.
C
Best answer
BPDU Guard
BPDU Guard disables an edge port if it receives a BPDU.
D
Distractor review
PortFast
PortFast accelerates transition to forwarding; it does not by itself shut down on BPDUs.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is confusing BPDU Guard with Root Guard or Loop Guard. Candidates may incorrectly select Root Guard because it involves BPDUs and port blocking, but Root Guard only prevents a port from becoming a root port and does not err-disable the port. Loop Guard is often mistaken as it protects against unidirectional link failures but does not disable ports on BPDU receipt. The key distinction is that BPDU Guard immediately disables the port upon receiving any BPDU, which is the behavior the question describes. Misunderstanding these differences can lead to incorrect answers.
Technical deep dive
How to think about this question
BPDU Guard is a Cisco switch feature designed to protect the Spanning Tree Protocol (STP) topology by disabling ports that receive unexpected Bridge Protocol Data Units (BPDUs). BPDUs are frames exchanged between switches to detect loops and maintain a loop-free Layer 2 topology. Edge ports, typically connected to end devices like PCs or printers, should not receive BPDUs because these devices do not participate in STP. BPDU Guard enforces this by err-disabling any port that receives a BPDU, preventing potential topology changes or loops caused by misconfigurations or malicious devices. When BPDU Guard is enabled on a port configured with PortFast, the switch monitors incoming frames for BPDUs. If a BPDU is detected on that port, the switch immediately places the port into an err-disabled state, effectively shutting it down to protect the network. This behavior is crucial in environments where edge ports should never participate in STP, ensuring that no rogue switches or miswired devices can influence the spanning tree topology. Other STP protection features like Root Guard and Loop Guard serve different purposes and do not err-disable ports upon receiving BPDUs. A common exam trap is confusing BPDU Guard with Root Guard or Loop Guard. Root Guard prevents a port from becoming a root port if superior BPDUs are received but does not disable the port. Loop Guard protects against unidirectional link failures on non-designated ports but also does not err-disable ports on BPDU receipt. Understanding that BPDU Guard specifically disables edge ports on BPDU receipt is key to answering questions about protecting STP edge ports and maintaining topology stability in Cisco networks.
KKey Concepts to Remember
- BPDU Guard disables a switch port by placing it into an err-disabled state if the port receives any BPDU frames, protecting the STP topology.
- Edge ports configured with PortFast should have BPDU Guard enabled to prevent accidental or malicious introduction of switches into the network.
- Root Guard prevents a port from becoming a root port when superior BPDUs are received but does not disable the port upon BPDU receipt.
- Loop Guard protects against unidirectional link failures on non-designated STP ports but does not err-disable ports on BPDU reception.
- Ports with BPDU Guard enabled immediately shut down upon receiving BPDUs, preventing potential Layer 2 loops or topology changes.
- BPDU Guard is essential for securing access layer ports that connect to end devices, ensuring they do not participate in STP.
- A port placed into an err-disabled state by BPDU Guard requires manual intervention or errdisable recovery to be re-enabled.
- Enabling BPDU Guard on PortFast ports helps maintain network stability by preventing rogue switches from affecting the spanning tree.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
BPDU Guard disables a switch port by placing it into an err-disabled state if the port receives any BPDU frames, protecting the STP topology.
What is the correct answer to this question?
The correct answer is: BPDU Guard — BPDU Guard is designed for edge ports that should never see BPDUs. If a BPDU arrives, the port is placed into an err-disabled state to protect the topology. Root Guard and Loop Guard solve different STP problems.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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