The Evolving Network Model

The Hierarchical Design Model

The hierarchical network model is a useful high-level tool for designing a reliable network infrastructure. It provides a modular view of a network, making it easier to design and build a scalable network.

The Hierarchical Network Model

As you may recall from CCNA Exploration: LAN Switching and Wireless, the hierarchical network model divides a network into three layers:

Access layer-Grants user access to network devices. In a network campus, the access layer generally incorporates switched LAN devices with ports that provide connectivity to workstations and servers. In the WAN environment, it may provide teleworkers or remote sites access to the corporate network across WAN technology.
Distribution layer-Aggregates the wiring closets, using switches to segment workgroups and isolate network problems in a campus environment. Similarly, the distribution layer aggregates WAN connections at the edge of the campus and provides policy-based connectivity.
Core layer (also referred to as the backbone) - A high-speed backbone that is designed to switch packets as fast as possible. Because the core is critical for connectivity, it must provide a high level of availability and adapt to changes very quickly. It also provides scalability and fast convergence.


The figure represents the Hierarchical Network Model in campus environments. The Hierarchical Network Model provides a modular framework that allows flexibility in network design, and facilitates ease of implementation and troubleshooting in the infrastructure. However, it is important to understand that the network infrastructure is only the foundation to a comprehensive architecture.

Networking technologies have advanced considerably in recent years, resulting in networks that are increasingly intelligent. The current network elements are more aware of traffic characteristics and can be configured to deliver specialized services based on such things as the types of data they carry, the priority of the data, and even the security needs. Although most of these various infrastructure services are outside the scope of this course, it is important to understand that they influence network design. In the next topic, we will explore the Cisco Enterprise Architecture, which expands upon the hierarchical model by making use of network intelligence to address the network infrastructure.