Which layer bridges user access devices and the core network, handling inter-subnet routing?

• A. Core Layer
• B. Access Layer
• C. Aggregation Layer
• D. Distribution Layer

Answer: (D)

In a three-tier network design, the distribution layer is the bridge between user access devices and the core, and it is responsible for routing between different subnets (VLANs). It aggregates traffic from many access switches, enforces policies, and handles inter-subnet routing so devices in different subnets can communicate. The core layer serves as a fast backbone for moving large amounts of traffic with minimal processing, not typically where inter-subnet routing decisions are made. The access layer is where end-user devices connect and where initial VLAN segmentation happens, but it doesn’t route between subnets. The aggregation layer is often discussed as the middle hop, but in this context the layer that explicitly handles inter-subnet routing and connects toward the core is the distribution layer.