Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
show port-security interface gi1/0/10 Port Status : secure-shutdown Violation Mode : shutdown Maximum MAC Addresses : 1 Total MAC Addresses : 2
Exhibit: An access switch shows Gi1/0/10 as err-disabled shortly after an IP phone and a workstation are connected through the same wall jack. What is the most likely cause?
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
The native VLAN is missing
A missing native VLAN would not by itself trigger err-disable from port security.
B
Best answer
The port security maximum is too low for the connected devices
A phone plus a PC commonly requires more than one secure MAC address.
C
Distractor review
BPDU Guard blocked the port because a workstation was attached
A workstation does not send BPDUs in a normal case.
D
Distractor review
DHCP snooping denied the voice VLAN
That would not match the err-disabled symptom shown.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is selecting BPDU Guard as the cause of the err-disabled state because the question mentions a workstation connected to the port. Candidates may incorrectly assume the workstation sent BPDUs, triggering BPDU Guard. However, workstations do not normally generate BPDUs. Another trap is blaming DHCP snooping or native VLAN issues, which do not cause err-disable due to multiple MAC addresses. The key is recognizing that port security violations occur when the maximum allowed MAC addresses is exceeded, which is common with IP phones and PCs sharing a port.
Technical deep dive
How to think about this question
Port security is a fundamental Cisco switch feature designed to enhance network security by limiting the number of MAC addresses that can be learned on a single switch port. This is especially important in access layer switches where end devices connect. When an IP phone and a workstation connect through the same physical port, the switch sees two MAC addresses: one from the phone and one from the PC. This is a common deployment scenario because IP phones often have an integrated switch to connect a PC through the phone. The port security configuration must accommodate multiple MAC addresses on such a port. If the port security maximum is set to one, the switch detects a violation when it learns the second MAC address. This violation triggers the port to enter an err-disabled state, effectively shutting down the port to prevent potential security risks. The err-disabled state requires manual intervention or automatic recovery mechanisms to re-enable the port. A common exam trap is to confuse err-disable causes with other features like BPDU Guard or DHCP snooping. BPDU Guard disables ports that receive unexpected BPDUs, but workstations do not send BPDUs, so this is unlikely. DHCP snooping protects IP address assignment but does not cause err-disable due to multiple MAC addresses. Understanding the interaction between port security and multi-device connections on a single port is critical for correct troubleshooting and exam success.
KKey Concepts to Remember
- Port security on Cisco switches limits the number of MAC addresses learned on a single access port to prevent unauthorized devices from connecting.
- When an IP phone and a workstation share the same access port, the switch sees two distinct MAC addresses, one from each device.
- If port security is configured with a maximum of one MAC address, the presence of two MAC addresses triggers a security violation.
- A port security violation typically causes the switch to place the interface into an err-disabled state to protect the network.
- The native VLAN mismatch does not cause err-disable due to port security but can cause other connectivity issues.
- BPDU Guard disables ports that receive Bridge Protocol Data Units (BPDUs) unexpectedly, but workstations normally do not send BPDUs.
- DHCP snooping protects against rogue DHCP servers but does not directly cause err-disable states related to multiple MAC addresses on a port.
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.
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Question 2
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Question 3
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Question 4
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Question 5
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Question 6
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FAQ
Questions learners often ask
What does this 200-301 question test?
Port security on Cisco switches limits the number of MAC addresses learned on a single access port to prevent unauthorized devices from connecting.
What is the correct answer to this question?
The correct answer is: The port security maximum is too low for the connected devices — With a phone and a PC on the same access port, the switch may legitimately see two MAC addresses. Port security set to a maximum of 1 causes a violation and can place the interface into err-disabled state.
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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