Which layer is at the top of the Cisco hierarchical internetworking model?

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

Answer: (C)

The Core Layer sits at the top of Cisco’s three-layer hierarchical model. This layer acts as the fast backbone that interconnects all distribution blocks, providing high-speed, scalable transport across the network. It’s designed for rapid forwarding and redundancy, with minimal policy enforcement or routing decisions, so traffic can move quickly between different parts of the network.

The bottom layer hosts end devices and access switches, where users connect. The middle, or distribution, layer aggregates traffic from the access layer, enforces policies, and handles inter-VLAN routing. The Aggregation Layer isn’t part of the standard three-layer model, and when people use it, it’s typically as a descriptor for a role within the distribution space, not the top tier.

So, the topmost layer is the Core Layer because it functions as the high-speed backbone that interconnects the network’s distribution blocks.