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What is Three Tier Architecture in Switch Networking?

Author Leslie

Date 01/17/2024

This article tells you the advantages and disadvantages of the three tier architecture and its specific application so that you have a better understanding of it after reading.

With the rapid advancement of network technology and the ever-expanding demands, the three tier architecture has become a pivotal technology in network design. As network scales grow and data volumes increase, the performance and reliability of networks become paramount. In this context, the three tier network architecture has emerged as a key solution by dividing the network into distinct layers, offering a more flexible and reliable approach to network design.

What is the Three Tier Architecture? 

The three tier network architecture comprises three crucial layers: the core layer, aggregation layer, and access layer. These layers undertake different connections and functionalities, aiming to enhance the network architecture's performance, reliability, and flexibility.

Core Layer: The core layer serves as the backbone of the network, responsible for connecting multiple distribution layer switches. It is typically used for transmitting large volumes of data, ensuring high-speed, high-bandwidth communication, and providing ample redundant connections. While ensuring reliability, the core layer achieves the fastest data transmission speeds.

Aggregation Layer: The aggregation layer acts as an intermediary connecting the core layer to the access layer, playing a role in coordinating and managing traffic. Responsibilities include access control, policy formulation, and fault isolation. Upon receiving data at the aggregation layer, it is integrated and sent to the core layer for swift processing and forwarding.

Access Layer: The access layer directly connects with end devices such as IP phones, APs, ACs, and end-users. It primarily provides user access, device connectivity, and authentication of user and device identities. Additionally, the access layer can implement traffic management and priority control, ensuring effective allocation and utilization of network resources.

What is the Advantage of Three Tier Architecture?

The three tier architecture, a predominant network structure in use today, boasts several advantages such as enhanced performance, ease of maintenance, flexible scalability, reliability, and higher redundancy. Below, we will provide a detailed overview of these advantages:

Enhanced Performance:

The three tier network architecture, through the segmentation into three network tiers, allocates specific tasks to each tier, ultimately collaborating for efficient operation. This facilitates a coordinated effort among devices at different tiers, ensuring the most effective data information processing. The access layer establishes direct connections with terminal devices, handling data access and transmission. Meanwhile, the aggregation layer is responsible for consolidating data streams from multiple access layers and forwarding them to the core layer. The core layer, characterized by high transmission speeds and ample bandwidth, rapidly executes data routing and forwarding. Such tiered division and collaboration significantly enhance the overall performance of the network.

Ease of Maintenance:

Due to the three layer architecture network that divides the entire network into three levels, this layered structure enhances the modularity of network design, with each level serving specific functions, resulting in a clearer division. This modular design facilitates easier localization and resolution of issues during maintenance, as it allows for the examination of only the levels where faults may occur, eliminating the need to troubleshoot the entire network. The clear and modular design of these hierarchical layers makes the entire network more accessible for troubleshooting and maintenance of faults.

Flexible Scalability:

The three layer architecture network allows for the direct addition of new devices in the layers that require expansion, facilitating network extension without disrupting the existing infrastructure. This is possible due to the independent functionalities of each layer, allowing them to operate and upgrade independently. Therefore, during network expansion, there is no need to interrupt the entire network for adjustments.


Due to the modular design of the three tier architecture network, each layer is equipped with specific functionalities, reducing the interdependence among layers. This ensures that in the event of a failure at a particular layer, the other layers can continue to operate smoothly. Furthermore, the three tier architecture can implement redundancy and load-balancing strategies to enhance reliability. The redundancy mechanism ensures the network's continued operation in case of device or link failures. Load balancing distributes traffic across multiple paths or devices, preventing any specific point from becoming a single point of failure.

In the event of a failure, the three tier network can swiftly implement fault recovery mechanisms. When a device experiences a failure, it can rapidly identify alternative paths, achieving quick fault switching and minimizing network downtime. Additionally, the three tier network architecture facilitates the decentralization of network functionalities and traffic, establishing isolation mechanisms to limit the spread of faults and reduce their impact on the entire network.

What are the Disadvantages of the Three Tier Network Architecture?

While the three tier network architecture has many advantages, like anything else in the world, it is not without its imperfections.

Complexity: In comparison to the spine-leaf network architecture, the three tier network architecture experiences an increase in complexity due to its three layers, whereas the spine-leaf network architecture only has two layers. Managing and configuring devices across multiple layers may become more intricate. Conversely, the spine-leaf network architecture is typically simpler, requiring configuration for only two layers of devices, reducing the complexity of network management.

Scalability: Despite possessing good scalability, the three tier network architecture is designed for north-south traffic. This design is constrained by the STP protocol, supporting a maximum of 100 switches. As network business requirements continue to expand, these limitations may result in port blocking and restricted scalability. In contrast, the spine-leaf network structure utilizes east-west traffic, fundamentally addressing the scalability bottleneck in the three tier network architecture.

Adaptability: Due to its more intricate layering, the three tier network architecture is relatively less flexible in response to dynamically changing network requirements. In contrast, the spine-leaf network architecture comprises only a core and leaf layer, and its simplicity and modular characteristics make it more adaptable to continuously changing network environments.


Application of Three Tier Architecture

Enterprise Networking Solution

In the enterprise office network, the network environment is typically complex, encompassing diverse business transactions and various network strategies employed by different business departments. Additionally, a plethora of distinct terminal devices, such as printers, access points (APs), access controllers (ACs), and others, need to be interconnected. In an enterprise network, ensuring not only transmission performance but also reliability and scalability is crucial to meet potential challenges in the future. In such scenarios, deploying a three tier architecture network is undoubtedly a prudent choice. The access layer switches cater to the requirements of various terminal devices, while the aggregation layer switches allow for the adjustment of network strategies based on the distinct needs of different business departments. The core layer switches ensure the smooth operation of the entire network through high-speed and high-performance data processing and transmission. To address the continuously growing load demands, the MLAG (Multi-Chassis Link Aggregation Group) functionality can be employed to achieve bandwidth expansion and redundancy capabilities.


The three tier architecture enhances network performance by dividing it into three distinct layers, each endowed with specific functionalities. This approach improves maintainability, provides greater flexibility for expansion, and ensures higher reliability. These characteristics enable it to meet business requirements effectively in complex network environments. If you have any questions about the PoE switch or PoE technology, please feel free to contact QSFPTEK's CCIE/HCIE engineers at support@qsfptek.com.


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