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220-1201 Practice Question: A technician is troubleshooting a network where a…
A technician is troubleshooting a network where a user's computer cannot obtain an IP address via DHCP. The computer is connected to a switch, and other devices on the same switch work fine. The technician checks the switch and sees that the port is up and the link light is green. What should the technician check next?
⚠ Common exam trap
The 220-1201 exam often tests the misconception that a green link light guarantees full Layer 2 connectivity, when in fact security features like Port Security can block traffic at the MAC layer while the physical layer remains operational.
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
✓
Check if the switch port is configured with Port Security that is blocking the MAC address.
Since the switch port is up and other devices on the same switch obtain IP addresses correctly, the DHCP server and the general network path are functional. The most likely cause is a Layer 2 security feature, such as Port Security, which can be configured to block unknown or specific MAC addresses, preventing the computer from communicating with the DHCP server even though the physical link is active.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Replace the Ethernet cable.
Why it's wrong here
Replacing the Ethernet cable is an inappropriate first step when the link light is already green. A green link light indicates that a valid physical connection (Layer 1) has been established between the computer and the network device, confirming the cable is physically functional. DHCP issues typically stem from problems at higher layers (Layer 2 or 3), making a cable replacement an unlikely solution for a device that already shows a physical link.
- ✓
Check if the switch port is configured with Port Security that is blocking the MAC address.
Why this is correct
Port Security is a Layer 2 switch feature that restricts input to an interface by limiting and identifying MAC addresses of devices allowed to access the port. If the switch port is configured to allow only a specific MAC address or a limited number of MAC addresses, and the computer's MAC address is not permitted or the limit is exceeded, the switch will block traffic. This prevents the computer from sending its DHCP Discover request, effectively blocking it from obtaining an IP address.
- ✗
Reboot the DHCP server.
Why it's wrong here
Rebooting the DHCP server is an unnecessary and disruptive action if other devices on the network are successfully obtaining IP addresses. The fact that other clients are functioning correctly indicates the DHCP server itself is operational and capable of assigning leases. Troubleshooting should focus on the specific client or the network path between the client and the server, rather than impacting all network users by restarting a functional core service.
- ✗
Set a static IP address on the computer.
Why it's wrong here
Setting a static IP address on the computer would bypass the DHCP issue but does not resolve the underlying problem preventing dynamic IP assignment. This approach merely circumvents the symptom and could introduce new issues, such as IP address conflicts if the chosen static IP is already in use or falls within the DHCP server's scope. Proper troubleshooting aims to restore the automated DHCP service for reliable network management.
Visual reference
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 |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1201 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1201 exam.