Explore Hierarchical Networks: Access, Distribution, Core Layers

Posted on Dec 9, 2023 by

In the world of computer networking, hierarchical networks are a fundamental concept that provides a structured approach to network design. A hierarchical network architecture organizes devices into distinct layers, each serving a specific purpose. In this article, we will learn about various relevant details of hierarchical networks.

What Is Hierarchical Network?

Hierarchical network design has emerged as a widely adopted industry best practice for establishing reliable, scalable, and cost-effective networks. In the early days, networks utilized a flat design, expanding in a single direction through hubs and switches, which posed challenges in filtering undesirable traffic and controlling broadcasts. As networks grew larger, response times suffered, necessitating a new network design approach that led to the adoption of the hierarchical model. Although flat network design still has its applications, it is mostly used for small networks or cost-conscious designs aiming to minimize the use of routers or switches.

Flat Network Design

On the other hand, a hierarchical design divides a network into distinct layers, each with defined functions that determine its role within the network. This enables network designers to select the most suitable hardware, software, and features for each layer's specific responsibilities. Furthermore, data management becomes much more efficient in a hierarchical design. Local traffic remains local within a layer and only traverses to a higher layer when destined for another network.

Hierarchical Network

Typical Hierarchical Network Design

The hierarchical structure of the network usually consists of access, distribution, and core layers. While a three-layer design is common, it is not mandatory.

Access Layer

The access layer, also known as the network edge, encompasses the end devices (such as end-users and local servers) that directly access the network.

Its primary functions include:

  • Facilitating the connection of diverse end devices to the LAN network.

  • Ensuring network security by preventing unauthorized devices from accessing the LAN through the enforcement of security policies such as port security, DHCP snooping, and static MAC address configuration.

  • Providing layer-2 switching capabilities and supporting various layer-2 switching services like spanning trees, virtual access control, Quality of Service (QoS), Power over Ethernet (PoE), and Address Resolution Protocol (ARP).

Distribution Layer

The distribution layer basically serves as a boundary between the access layer and the core layer, providing policy-based connectivity. It's responsible for both data filtering and routing within the network.

Its primary functions include:

  • Providing connectivity between access layer switches in the network.

  • Serving as upstream services for the access layer switches (if a separate core layer exists).

  • Implementing Access Control Lists (ACLs) to control and filter network traffic based on predefined rules.

  • Using VLANs to control broadcast traffic and segregate network traffic into logical groups.

  • Offering routing services between different VLANs and routing domains.

  • Serving as boundaries between different LANs and broadcast domains, ensuring network segmentation and control.

  • Distribution layer switches consolidate and aggregate LAN and WAN links, allowing for efficient traffic management.

  • Providing load balancing and redundancy.

Core Layer

The core layer is commonly referred to as the backbone of the network because it serves as a high-speed transport infrastructure between the switches located in the distribution layer. It acts as the central aggregation point for multiple networks within the overall network infrastructure.

Its primary functions include:

  • Consisting of high-speed network devices: Prioritize fast packet switching.

  • Interconnectivity between distribution layer devices: The core layer facilitates seamless connectivity and communication between the various devices present in the Distribution Layer.

  • Offloading CPU-intensive tasks: The core layer plays a critical role in offloading CPU-intensive tasks like security services (restrictive ACLs), Quality of Service (QoS) classification, inspection, and other packet manipulations. By handling these tasks at the core layer, it prevents performance degradation on other network devices.

  • Reliability and fault tolerance: It is designed to provide high availability and fault tolerance to ensure maximum network performance and minimize disruptions.

Advantages of Hierarchical Network

Enhanced Network Performance

A hierarchical network design improves performance by routing data through high-performance switches at near wire-rate speeds, avoiding lower-performance intermediary switches. The distribution and core layers, consisting of high-performance switches, increase speeds and minimize network bandwidth issues. With a well-designed network, data can travel at nearly wire speed between devices, optimizing performance, reducing latency, and ensuring efficient data transmission throughout the network. Taking FS S5860-48SC switch as an example, it's suitable for placement in the core layer to support high-capacity data transmission and routing functions for medium to large-scale campus environments, providing reliable connectivity and fast data exchange for the campus network.

Advanced Security

When it comes to security, hierarchical networks offer increased control and customization. Access control lists can be implemented with greater complexity and granularity, enabling more effective shaping and blocking of network traffic. Moreover, these security policies can be applied at various levels, such as individual users, specific departments, or the entire organization. This flexibility allows network administrators to create tailored network traffic plans that align with the specific requirements of the enterprise. By keeping network details restricted from most users, intentional or unintentional network issues become less of a concern. This, in turn, enhances productivity and boosts the overall performance of the network while maintaining a secure environment.

Improved Flexibility and Scalability

Hierarchical networks offer increased flexibility compared to other network architectures. They allow for seamless addition of segments and elements without causing major disruptions to the existing network. The modular nature of hierarchical networks enables the replication and repetition of design elements. This consistency across modules empowers network administrators to effectively plan and implement network expansion, ensuring that the topology remains unchanged from one module to another. As a result, network growth can seamlessly align with organizational needs, minimizing or eliminating any potential downtime.

Simplified Management

Hierarchical networks are easier to manage due to their consistent functionality across network layers. For example, making changes to one access layer switch can be confidently replicated across others with the same role. Deploying new switches is simplified as configurations can be easily copied. Troubleshooting and recovery processes are also streamlined, as issues can be isolated and resolved more efficiently within specific layers. Overall, hierarchical networks simplify management tasks and enhance operational efficiency.

Efficient Cost Control

When designing a network, it's important to consider budget constraints. Instead of going all out with expensive hardware, a hierarchical network design allows for incremental expansion based on the organization's needs and available resources. By making strategic decisions and prioritizing equipment allocation, the network can be designed to meet requirements while staying within budgetary limitations. This approach ensures a balance between functionality and cost-effectiveness, allowing for gradual network growth while managing costs effectively.


In conclusion, hierarchical network designs bring order and efficiency to complex network infrastructures. They offer clear advantages such as simplified management, enhanced scalability and so on. By dividing the network into distinct layers and applying appropriate security measures, organizations can ensure the integrity and confidentiality of their data. Furthermore, the hierarchical design provides a framework for seamless expansion and adaptability to evolving business needs. Adopting a hierarchical network design is a prudent choice for organizations seeking a reliable, scalable, and manageable network solution.

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