- A
The fiber cable is damaged
Why wrong: A damaged cable would cause the port to show 'down' or 'notconnect', not 'err-disabled', which is a software-disabled state.
- B
A duplex mismatch exists between the switches
Why wrong: Duplex mismatch causes high error rates and poor performance but typically results in 'down' or 'flapping' ports, not 'err-disabled'.
- C
Port security has been violated
Port security violations, such as exceeding the maximum MAC addresses, cause the switch to disable the port and place it in err-disabled state.
- D
The VLAN configuration is incorrect
Why wrong: Incorrect VLAN config would allow the port to be up but traffic may not pass; it would not cause err-disabled state.
Question 6 of 1,020
What Causes an Err-Disabled Switch Port?
This 220-1201 practice question tests your understanding of network configuration concepts. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A technician is troubleshooting a network where users on one floor cannot access a server on another floor. Both floors are connected via a single fiber optic link. The technician checks the link and sees the switch port shows 'err-disabled' status. What is the most likely cause of this state?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Quick Answer
The answer is a port security violation, which is the most likely cause of an err-disabled switch port in this scenario. When a switch detects an unauthorized MAC address or exceeds the allowed MAC address limit on a port, it automatically places the port into an err-disabled state to prevent unauthorized access or network loops. This state can also be triggered by other protective mechanisms like BPDU guard, but on the CompTIA A+ Core 1 220-1201 exam, port security violations are the classic cause tested for err-disabled ports. A common trap is confusing this with a physical cable fault—while a bad cable can cause errors, it typically results in a down or flapping port, not an err-disabled status. To remember, think of “security first”: the switch disables the port to protect the network, not because the link is broken.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Port security has been violated
The 'err-disabled' state on a switch port is commonly triggered by a port security violation. When a device attempts to connect with a MAC address that exceeds the configured maximum or is not on the allowed list, the switch disables the port to prevent unauthorized access. This matches the scenario where users on one floor cannot reach a server, as the link is physically intact but logically blocked.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The fiber cable is damaged
Why it's wrong here
A damaged cable would cause the port to show 'down' or 'notconnect', not 'err-disabled', which is a software-disabled state.
- ✗
A duplex mismatch exists between the switches
Why it's wrong here
Duplex mismatch causes high error rates and poor performance but typically results in 'down' or 'flapping' ports, not 'err-disabled'.
- ✓
Port security has been violated
Why this is correct
Port security violations, such as exceeding the maximum MAC addresses, cause the switch to disable the port and place it in err-disabled state.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The VLAN configuration is incorrect
Why it's wrong here
Incorrect VLAN config would allow the port to be up but traffic may not pass; it would not cause err-disabled state.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between physical link issues (cable damage, duplex mismatch) and software-induced states like 'err-disabled', where candidates mistakenly attribute the state to hardware faults rather than security or error-disable mechanisms.
Trap categories for this question
Command / output trap
A damaged cable would cause the port to show 'down' or 'notconnect', not 'err-disabled', which is a software-disabled state.
Detailed technical explanation
How to think about this question
Port security violation triggers the 'err-disabled' state when the switch detects a MAC address that violates the configured policy (e.g., sticky MAC limit exceeded or a security violation action set to 'shutdown'). The switch immediately disables the port and logs a message like '%PORT_SECURITY-2-PSECURE_VIOLATION'. To recover, an administrator must manually issue 'shutdown' followed by 'no shutdown' on the interface, or configure 'errdisable recovery cause psecure-violation' for automatic recovery.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
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.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
What to study next
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FAQ
Questions learners often ask
What does this 220-1201 question test?
Network Configuration Concepts — This question tests Network Configuration Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Port security has been violated — The 'err-disabled' state on a switch port is commonly triggered by a port security violation. When a device attempts to connect with a MAC address that exceeds the configured maximum or is not on the allowed list, the switch disables the port to prevent unauthorized access. This matches the scenario where users on one floor cannot reach a server, as the link is physically intact but logically blocked.
What should I do if I get this 220-1201 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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