What is Spine-Leaf Architecture and How Does It Work?

In the last few years, with the rapid proliferation of servers and with data center switching layer comprised of multiple tiers, Spine-Leaf architecture is starting to take on the existing three-tier architecture as the leading architecture, due to its horizontal scaling and availability advantages. Want to know about spine-leaf architecture? So, how do you build one? Delve into our guide, where we demystify the concept of spine-leaf architecture and provide insights into its design and implementation.

  

What Is Spine-leaf Architecture?

  

The spine-leaf architecture comprises just two layers of switches: spine and leaf switches. The spine layer, serving as the network core, undertakes routing functions. The leaf layer, on the other hand, includes access switches linking servers, storage units, and end-users. This topology reduces hop count, and reduces network latency in data center networks.

            

In the spine-leaf architecture, each leaf switch connects to each spine switch. This design ensures that any server can communicate with any other server, and between any two leaf switches, there exists no more than one interconnected switch path.

  

  

Why Do You Need A Spine-leaf Architecture?

 

The spine-leaf architecture, now widely adopted in data centers, brings many benefits, including scalability and enhanced network performance. Three advantages of spine-leaf architecture are outlined below.

 

Increased Redundancy

 

The spine-leaf architecture establishes a robust connection between servers and the core network, offering greater flexibility in hyper-scale data centers. By deploying the leaf switch as a bridge between servers and the core network, each leaf switch connects to all spine switches, forming a sizable non-blocking fabric. This configuration significantly enhances redundancy, minimizing traffic bottlenecks.

 

Performance Enhancement

 

The spine-leaf architecture efficiently alleviates traffic congestion through the adoption of protocols and methodologies like TRILL and SPB. With the flexibility to operate at either Layer 2 or Layer 3, the spine-leaf architecture allows the addition of uplinks to the spine switch. This expansion of inter-layer bandwidth reduces oversubscription, ensuring network stability.

 

Scalability

 

The spine-leaf architecture incorporates multiple links capable of handling increased traffic. Adding switches to the architecture not only improves scalability but also facilitates the expansion of enterprises. This scalability feature positions businesses to expand their operations in the future seamlessly.

               

The Spine-leaf Architecture vs Traditional Architecture: Three-Tier 

              

The key differentiation between spine-leaf architecture and the 3-tier architecture is rooted in the number of network layers and the orientation of traffic flow—whether it's north-south or east-west.

            

In the conventional three-tier network architecture, illustrated below, three layers—core, aggregation, and access—are present. Access switches link to servers and storage devices; the aggregation layer consolidates access layer traffic and offers redundant connections, while the core layer handles network transmission. However, this three-layer structure is primarily designed for north-south traffic and relies on the Spanning Tree Protocol (STP), supporting a maximum of 100 switches. This design may potentially result in port blocking and limited scalability due to an explosion in network data.

                 

Whereas the spine-leaf architecture achieves east-west traffic parallelism as an addition to the backbone's north-south network architecture in order to eliminate the bottleneck problem found in the traditional three-tier network approach. It augments the exchange layer beneath the access layer, enabling direct data transmission between two nodes at this level, thus circumventing the bottleneck problem in the backbone network transmission. Unlike the traditional three-tier setup, the spine-leaf architecture establishes a connection through the spine with a single hop between leaves, minimizing latency and bottlenecks. Importantly, in spine-leaf architectures, the switch configuration remains fixed, eliminating the need for network changes in dynamic server environments.

 

 

How to Design Spine-leaf Architecture?

 

When designing a spine-leaf architecture, you need to ensure that critical considerations have been made and two of the most pressing considerations are the oversubscription rate and the spine switch size . A detailed example is also included below for reference.

 

Oversubscription Rate

 

The oversubscription rate denotes the contention rate when all devices transmit traffic simultaneously. This metric is assessed in the north/south (data center entry/exit traffic) and east/west (traffic between devices within the data center) directions. For contemporary network architectures, the ideal oversubscription ratio is 3:1 or lower. This ratio, expressed as the upstream bandwidth (to backbone switches) versus downstream capacity (to servers/storage), ensures optimal performance. For instance, if a leaf switch features 48 x 10G ports (totaling 480Gb/s) and 4 x 40G uplink ports connected to a 40G spine switch (with 160Gb/s uplink capacity), the ratio is 3:1. It's crucial to ensure that uplink speeds consistently surpass downlink speeds to prevent port link blockage.

 

Leaf and Spine Sizing

 

In topology, the spine switch counts are dependent on the port density of the backbone switch. Concurrently, the number of spine switches is determined by factors such as the required throughput between leaf switches, the quantity of redundant/ECMP (equivalent multipath) paths, and their respective port densities. Consequently, meticulously considering the number of spine-leaf switches and their port density is essential to avert potential network issues.

              

Layer 2 or Layer 3 Design

           

A two-tier spine-leaf fabric design can be implemented either at Layer 2 (involving VLAN configuration) or Layer 3 (utilizing subnetting). These Layer 2 techniques stress maximum flexibility: VLANs can be stretched across multiple segments, and MAC addresses can be migrated easily. At the same time, Layer 3 designs tend to favor very rapid convergence times and a much larger scaling, including fan-out ECMP support for up to 32 or more spine active switches.

              

Consequently, by considering these factors, we can build a spine-leaf architecture that will not only perform remarkably well, be scalable, and cater to the particular requirement of a data center network but be a good one in practice!

           

Build Spine-leaf Architecture With Spine-leaf Switches

 

After understanding these principles and knowledge, we will build a spine-leaf switch architecture. This new spine-leaf architecture aims to create a new high-density server network structure. Here, we present a practical example.

 

For the spine switch, we opt for the S7600-32C, equipped with 100G ports, while the leaf switch is represented by the S7600-48Y8C, featuring 100G/25G ports. This configuration ensures a 100G uplink bandwidth and a 25G downlink bandwidth. Throughout the entire link transmission, the switches support MLAG, VXLAN, or EVPN-VXLAN, and various related virtual technologies concurrently, ensuring robust structural reliability.

  

  

Conclusion: How to Choose The Right Spine-leaf Switches?

 

Understand the performance capabilities of spine and leaf switches for aspects such as port density, virtualization technology, hardware redundancy, etc. Then, customize the switch choice according to the exact needs of the deployment to complete network architecture. We cannot ignore QSFPTEK S7600 series switches that support a complete virtualization software system. Utilizing these switches enables increased network performance and faster deployment towards achieving your networking goals.