An Overview of Three-Tier Architecture and Spine-Leaf Architecture

The data center is at the core of all modern growing enterprises that use different software technologies. For several years, these data centers used three-tier architecture. However, now they are being replaced by spine-leaf architecture. The spine-leaf architecture, also known as Clos designs, is similar to three-tier architecture in many ways. Today, businesses follow hybrid architecture with software and cloud solutions used equally. Thus, they are keen to maximize the value of their existing data center for software architecture and cloud functions. The spine-leaf architecture allows them to do so easily. How does it help? What are the advantages of using this data center architecture over the traditional three-tier architecture? This post answers these questions and more.

Traditional Three-Tier Architecture, its Advantages, and its Limitations Discussed Briefly

To understand spine-leaf architecture, one needs to understand the traditional three-tier architecture, its advantages, as well as limitations.

•  Design: The three-tier architecture comprises three layers – a core, aggregation, and an access layer.

o  Core: This layer comprises L3 routers that separate pods.

o  Aggregation: It comprises L2/3 switches that create borders between the pods.

o  Access: They comprise L2 switches that provide loop-free pod designs, and utilize either virtual link aggregation (VLAG) or spanning tree protocol.

• Advantages: This architecture offers benefits such as easy availability, security, performance, scalability, as well as simplicity, which has contributed to their popularity all these years.  
• Limitations: Three-tier architecture cannot withstand the demands of virtualization, scalability, and convergence that most modern data centers demand. Virtualization needs moving data across different devices sharing common information at their backend. Convergence focuses on storage traffic to be distributed across devices on the same segment in the network. All these processes demand high bandwidth utilization, which is difficult to achieve in three-tier architecture, thereby adding to its redundancy.
• Due to its limitations, this architecture is now limited to small networks. It is ideal for “North-South” traffic, which enters and leaves the data center. Here, the latency of transmission is not a big concern. However, it can be a big concern in campus networks and fast-growing enterprises. The next section explores how spine leaf architecture is becoming the choice of players for data centers that leverage cloud and software architectures with “East-West” traffic.

An Introduction to the Spine-Leaf Data Center Architecture Design

The following characteristics of spine-leaf architecture have contributed to their popularity.

When compared to three-tier architecture, the spine-leaf architecture comprises two devices – the spine and the leaf.

• In this topology, each leaf switch is connected to each spine switch in a full-mesh topology.
• The leaf layer is made of access switches, which are connected to firewalls, servers, and edge routers.
• The spine layer acts as the network backbone and it is a routing layer. This layer uses fixed-port switches over modular switches.
• This connection supports “East-West” traffic, where the data travels and circulates within the data center.

3 Reasons to Choose Spine-Leaf Data Center Architecture over Traditional Three-Tier Architecture

The simple, yet effective spine-leaf architecture plays a key role in the functioning of data centers. The following advantages offered by this architecture have spearheaded its quick adoption.

1. Routing Through Layer 3: All routes in this architecture are configured as active routes. This means all connections can be used simultaneously while assuring network stability and avoiding network loops. This is all possible due to equal-cost multipathing (ECMP), which also enables users to utilize the available bandwidth to its fullest without keeping 50% in reserve to use during a network failure. In traditional three-tier networks, usually, 50% bandwidth is reserved for use during a network failure.
2. Flexibility: The spine-leaf data center architecture enables users to take advantage of virtual server applications. This only possible due to routing through layer 3 and Software Defined Access network, which also enables utilizing mobile servers to its fullest extent within the data center. Thus, if you operate in a campus network or enterprise and wish to get rid of an unstable network or take advantage of a Software-Defined Access Network, then spine-leaf architecture is the best option.
3. Scalability: Oversubscription has been one of the key challenges in the three-tier architecture. Oversubscription is caused when a link handles more traffic than required. To cope with this extra traffic, additional switches and link are added. This needs entire network reconfiguration, improved investments, and time. However, in leaf and spine networks, this issue is resolved by adding a spine switch to a leaf switch. Reconfiguration is automatic in Software-Defined access network environment, so there is no downtime, and no additional efforts are needed.  

As seen, network switches form the core of spine-leaf architecture. Thus, it is important to use the right switches. VERSITRON offers a comprehensive range of network switches that are designed to meet the constantly evolving demands of the data center environments across organizations. These switches stand out due to their non-blocking architecture and excellent performance. Being at the forefront of the fiber optics revolution, VERSITRON understands what businesses want and what solutions may best work for them. The experts at the company work with to you deliver the solution that helps you optimize the value of your data center investments.