Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A switch receives BPDUs on a user-facing port configured as an edge port, but instead of just blocking the port role it fully error-disables it. Which protection feature most likely explains 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
Best answer
BPDU Guard
This is correct because BPDU Guard typically error-disables an edge port that receives BPDUs.
B
Distractor review
Root guard
This is wrong because root guard is more about role/topology protection than this classic err-disable behavior.
C
Distractor review
Port security
This is wrong because port security focuses on MAC-address learning behavior.
D
Distractor review
DHCP snooping
This is wrong because DHCP snooping does not error-disable a port for receiving BPDUs.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is mistaking Root Guard for BPDU Guard because both involve BPDU handling and port protection. However, Root Guard only blocks a port from becoming a root port when superior BPDUs are received but does not error-disable the port. Candidates might also confuse Port Security with BPDU Guard since both can error-disable ports, but Port Security reacts to MAC address violations, not BPDUs. Misunderstanding these differences can lead to selecting incorrect answers about port protection mechanisms in STP environments.
Technical deep dive
How to think about this question
Bridge Protocol Data Units (BPDUs) are fundamental to the Spanning Tree Protocol (STP), which prevents Layer 2 loops in Ethernet networks. Switch ports configured as edge ports (also known as PortFast ports) are intended to connect directly to end devices like PCs, not other switches. These ports do not expect to receive BPDUs because they are not part of the STP topology calculation. BPDU Guard is a Cisco feature designed to protect these edge ports by monitoring for unexpected BPDUs. When BPDU Guard is enabled on an edge port, the switch immediately error-disables the port if it receives any BPDU frames. This behavior is a strict enforcement mechanism to prevent potential Layer 2 loops or topology changes caused by unauthorized switches or misconfigurations. Unlike Root Guard, which blocks ports from becoming root ports but keeps them operational, BPDU Guard takes a more aggressive approach by shutting down the port entirely to maintain network stability. A common exam trap is confusing BPDU Guard with Root Guard or Port Security. Root Guard blocks superior BPDUs to maintain root bridge placement but does not error-disable the port. Port Security focuses on MAC address violations and does not react to BPDUs. DHCP Snooping protects against rogue DHCP servers and is unrelated to BPDU handling. Understanding these distinctions is critical for correctly identifying BPDU Guard's role in protecting edge ports and ensuring the network's Layer 2 topology remains loop-free and stable.
KKey Concepts to Remember
- BPDU Guard disables a switch port immediately when it receives Bridge Protocol Data Units (BPDUs) on a port configured as an edge port to prevent potential Layer 2 topology loops.
- An edge port is configured to connect directly to end devices and is expected not to receive BPDUs, so BPDU Guard protects the network by error-disabling the port if BPDUs appear.
- Root Guard prevents a switch port from becoming a root port by blocking superior BPDUs but does not error-disable the port upon receiving BPDUs.
- Port Security limits MAC address learning on a port and can error-disable a port on violations but does not react specifically to BPDUs.
- DHCP Snooping protects against rogue DHCP servers and does not error-disable ports based on BPDU reception.
- BPDU Guard enforces strict Layer 2 topology integrity by shutting down ports that violate the expected BPDU behavior, which is critical in STP environments.
- The error-disable state caused by BPDU Guard requires manual or automatic recovery to bring the port back online, ensuring network stability.
- Configuring BPDU Guard on edge ports is a best practice to prevent accidental or malicious bridging loops caused by unauthorized switches.
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
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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 immediately when it receives Bridge Protocol Data Units (BPDUs) on a port configured as an edge port to prevent potential Layer 2 topology loops.
What is the correct answer to this question?
The correct answer is: BPDU Guard — BPDU Guard most likely explains that behavior. In practical terms, BPDU Guard is used to protect ports that are expected to face ordinary endpoints, not other switches. If BPDUs appear on such a port, the device treats that as a serious topology-policy violation and shuts the port down. This is different from features that merely influence spanning-tree role choice without fully error-disabling the interface.
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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