Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
An administrator wants an access-layer interface to shut down immediately if another switch is connected accidentally. Which feature best meets that requirement?
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
Distractor.
B
Distractor review
PortFast
Distractor.
C
Best answer
BPDU Guard
Correct choice.
D
Distractor review
Loop Guard
Distractor.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is selecting Root Guard or Loop Guard instead of BPDU Guard. Root Guard only blocks a port from becoming a root port but does not disable the port immediately upon receiving BPDUs. Loop Guard protects against unidirectional link failures by preventing a port from transitioning to forwarding when BPDUs are lost but does not shut down the port. Candidates may also confuse PortFast as it is related to edge ports but it only speeds up STP convergence and does not disable ports. Understanding that BPDU Guard uniquely disables the port immediately upon receiving BPDUs on an edge port is essential to avoid this trap.
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 monitoring edge ports, typically access-layer interfaces connected to end devices. These ports are expected not to receive BPDUs because they connect to hosts, not switches. If a BPDU is received on such a port, it indicates that another switch might have been connected accidentally or maliciously, which could cause loops or topology changes. When BPDU Guard is enabled on a PortFast-enabled port, it immediately places the interface into an err-disabled state upon receipt of a BPDU. This automatic shutdown prevents the port from participating in STP and stops potential loops or topology instability. The err-disabled state requires manual intervention or configured automatic recovery to bring the port back up, ensuring that network administrators are alerted to the issue. A common exam trap is confusing BPDU Guard with Root Guard or Loop Guard. Root Guard blocks ports from becoming root ports but does not disable them immediately. Loop Guard prevents ports from transitioning to forwarding when BPDUs are lost but also does not shut down ports. BPDU Guard’s immediate shutdown behavior is unique and critical for protecting access ports from accidental switch connections, making it the best choice for the scenario described.
KKey Concepts to Remember
- BPDU Guard immediately disables a port if it receives a Bridge Protocol Data Unit (BPDU) on an edge port, preventing accidental switch connections.
- PortFast enables a switch port to transition quickly to the forwarding state but does not shut down the port upon receiving BPDUs.
- Root Guard prevents a port from becoming a root port by blocking superior BPDUs but does not disable the port immediately.
- Loop Guard protects against indirect link failures by preventing a port from transitioning to a forwarding state when BPDUs are lost, but it does not shut down the port.
- BPDU Guard is typically enabled on access-layer ports configured with PortFast to protect the spanning-tree topology from unauthorized switches.
- When BPDU Guard is triggered, the port enters an err-disabled state, requiring manual or automatic recovery to re-enable the interface.
- The presence of BPDUs on a PortFast-enabled port indicates a potential network topology change or misconfiguration, which BPDU Guard addresses by disabling the port.
- Using BPDU Guard helps maintain network stability by preventing loops caused by unintended switch connections at the access layer.
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 immediately disables a port if it receives a Bridge Protocol Data Unit (BPDU) on an edge port, preventing accidental switch connections.
What is the correct answer to this question?
The correct answer is: BPDU Guard — BPDU Guard is designed for edge ports. If the port receives a BPDU, the switch treats that as a sign that another switch has been connected and places the interface into an err-disabled state to protect the spanning-tree topology.
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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