The correct answer is A. Virtual LAN (VLAN).
According to CompTIA A+ Core 1 220-1201 objectives under Networking:
* VLANs are used to segment a physical network into multiple logical networks. By assigning the accounting department to a separate VLAN, users on other VLANs cannot access its network traffic without routing, thereby isolating sensitive departments while using the same physical switch.
* VLANs improve security, reduce broadcast traffic, and allow network administrators to enforce access controls at the layer 2 level.
Why the other options are incorrect:
* B. DHCP reservations: Ensure that specific devices always receive the same IP address, but do not restrict network access.
* C. Content filtering: Controls web or application traffic based on content, not segmenting network access between departments.
* D. Port security: Limits which devices can connect to a port but does not provide full network segmentation for an entire department.
References:
CompTIA A+ Core 1 (220-1201) Exam Objectives - Networking: "Given a scenario, configure network devices and settings including VLANs to isolate traffic and enhance security." Mike Meyers' CompTIA A+ Certification Guide, 13th Edition, Chapter on Network Segmentation and VLANs.