Modern applications require a modern data center infrastructure, and Two-Tier, spine-leaf architectures offers many advantages over traditional Three-Tier designs.
More than 70 percent of all traffic today moves from server to server, or what we consider East-West traffic. Traditional data center networks were initially designed for resiliency and were concerned with speed into and out of the data center, not within it.
Three-Tier data center networks were the generally recommended data center network design in the past. They worked very well when most of the traffic moved North-South (from outside the data center in) or vice versa. A packet flows to the core, is routed to the correct distribution switch, then forwarded on to the access switch where the server was connected; moving through only 3 physical hops which limits the amount of latency added per-packet flow.
Three-Tier data center networks introduced loops, which you can see in the graphic above — this requires correct spanning-tree protocol configuration. Spanning-tree issues are notorious for causing network outages as a spanning-tree failure causes continuous looping.
What is Spine and Leaf Network Architecture?
A spine-leaf architecture is data center network topology that consists of two switching layers—a spine and leaf. The leaf layer consists of access switches that aggregate traffic from servers and connect directly into the spine or network core. Spine switches interconnect all leaf switches in a full-mesh topology.
Every leaf switch in a leaf-spine architecture connects to every switch in the network fabric. No matter which leaf switch a server is connected to, it has to cross the same number of devices every time it connects to another server. (The only exception is when the other server is on the same leaf.) This minimizes latency and bottlenecks because each payload only has to travel to a spine switch and another leaf switch to reach its endpoint. Spine switches have high port density and form the core of the architecture.
· Spine Switches are very high-throughput, low-latency and port-dense switches that have direct high-speed (40-300Gbps) connections to each leaf switch.
· Leaf Switches are very similar to traditional TOR switches in that they are often 24 or 48 port 1, 10 or 40Gbps access layer connections, but have the increased capability of either 40, 100 or 300Gbps uplinks to each spine switch.
Why are spine-leaf architectures becoming more popular?
Given the prevalence of cloud and containerized infrastructure in modern data centers, east-west traffic continues to increase. East-west traffic moves laterally, from server to server. This shift is primarily explained by modern applications having components that are distributed across more servers or VMs.
With east-west traffic, having low-latency, optimized traffic flows is imperative for performance, especially for time-sensitive or data-intensive applications. A spine-leaf architecture aids this by ensuring traffic is always the same number of hops from its next destination, so latency is lower and predictable.
Capacity also improves because STP is no longer required. While STP enables redundant paths between two switches, only one can be active at any time. As a result, paths often become oversubscribed. Conversely, spine-leaf architectures rely on protocols such as Equal-Cost Multipath (ECPM) routing to load balance traffic across all available paths while still preventing network loops.
In addition to higher performance, spine-leaf topologies provide better scalability. Additional spine switches can be added and connected to every leaf, increasing capacity. Likewise, new leaf switches can be seamlessly inserted when port density becomes a problem. In either case, this “scale-out” of infrastructure doesn’t require any re-architecting of the network, and there is no downtime.
Limitations of Spine and Leaf Architecture
As we have advantages and benefits, we also have limitations in implementing spine-leaf architecture in our network:
1- Number of Cables – We need to run more copper or fiber cables since each leaf must be connected to every spine device.
2- Limited Hosts – The number of hosts that we can support can be limited. Spine port counts can restrict the number of leaf switch connections.
As technology advances, more data center traffic is moving from server to server instead of moving in and out of the data center. As network engineers or future network engineers, we should learn to plan, build and manage spine-leaf architecture.
Summery:
It is important to understand the 2-tier leaf spine architecture as it offers unique benefits over the traditional 3-tier architecture model. With easily adaptable configurations and design, leaf-spine has improved the IT department’s management of oversubscription and scalability. Deploying leaf-spine network architecture and buying high-performance data center switches are imperative for data center managers as leaf-spine environment allows data centers to thrive while accomplishing all needs and wants of the business.
