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Spine-leaf Architecture vs Traditional Architecture

Understanding the difference between spine-leaf architecture vs traditional architecture is foundational to selecting, organizing, and optimizing data center network topology for performance, capacity, speed, and scalability. The difference between the two is straightforward: traditional architecture uses a three-tier model, whereas spine-leaf architecture operates on a two-tier model.

This article will fully explore the difference between spine-leaf architecture vs traditional network architecture, dissect the history and advantages of each, and will conclude with a list of Juniper, Arista, and Cisco devices that support each network architecture.

Spine and Leaf Architecture: Explained

Spine and leaf architecture includes only two layers: spine and leaf.

  • Spine: the network core that interconnects all leaf switches. Spine switches are port dense and offer high throughput and speed and low latency to the leaf switches.
  • Leaf: composed of access switches that connect directly to the spine.

Leaf-spine architecture is a full-mesh topology where every access leaf is connected to the spine. It’s designed to enhance east to west traffic flows between access switches within the same data center.

With a spine and leaf network architecture, connections through the spine only require hopping from one leaf to the next, which minimizes latency and bottlenecking.

Traditional Network Architecture: Explained

Traditional 3-tier network architecture consists of three layers: core, aggregation, and access.

  • Core: provides network transmission.
  • Aggregation: combines access-layer traffic, providing multiple connections to the access layer.
  • Access: connects end node devices to aggregation layer devices.

Traditional network architecture topology utilizes STP protocol and is designed for north to south traffic.

Advantages of Spine-leaf Architecture

Technician holding digital tablet while examining server in server room

What is spine and leaf architecture’s greatest benefit in modern data center frameworks?

One of the greatest advantages of spine-leaf architecture vs traditional architecture is that traditional architecture is optimized for North to South traffic and communication between clients and servers.

While this application has historically been effective, increases in server-to-server communication — due to the prevalence of cloud and containerized infrastructure — can cause latency and bottleneck issues, especially for time-sensitive or data-intensive applications. That being the case, increased efficiency and overall performance, in terms of speed, are the greatest spine and leaf architecture benefits.

It is imperative for modern applications that have components distributed across more devices to have low latency and optimized traffic flow for performance. The spine and leaf architecture advantages for latency and scale cannot be understated, as traffic is continuously the same number of hops from each destination, which offers lower latency, as well as higher predictability.

Additionally, leaf and spine architecture collapses a tier from the original three-tier traditional network. In doing so, Spanning Tree Protocol (STP) is no longer necessary, resulting in an improved capacity.

Spine-leaf network architecture topologies are also easier to effectively scale as additional spine switches can be seamlessly integrated and connected to each leaf. Conversely, new leaf switches are easy to add to existing spine devices for higher port density. In fact, with a spine-leaf topology, re-architecting the network does not require downtime, another hugely impactful benefit.

The limitations and disadvantages of leaf and spine network architecture include a limit on the number of hosts that can be supported with leaf switch connections, as well as the necessity for a large amount of copper and/or fiber cables as each leaf must be connected to every spine device (leaf devices have a lower port density than aggregation-level devices, which translates into more devices, in general).

Advantages of Traditional Network Architecture

Technician using laptop while analyzing server in server room

Traditional network architecture — also commonly referred to as a three-tier architecture or a hierarchical internetworking model — includes core layer switches that connect to distribution layer switches that connect to access layer switches (ToR switches). This topology allows for more flexibility in regards to network configuration, as the additional layer allows for a greater level of customization.

However, traditional network architecture was designed to primarily support North-South traffic — the packet flows to the core, is routed to the correct distribution switch, and then forwarded to the access switch, which is connected to end-node devices. However, the three physical hops that are required reduce the per-packet flow latency and may require the use of the STP protocol, which is a common culprit for network issues, outages, and failures as a result of continuous looping.

Network Architecture Support Across Different Original Equipment Manufacturer (OEM) Devices

A traditional three-tier architecture is designed so North to South traffic between nodes within the same rack can be sent with low latency and to support a lot of ports along the access switch layer.

However, this architecture model fell short of supporting east to west traffic as it requires multiple hops between nodes. As hops between racks increase with east to west traffic, congestion of communication and bottlenecking occurs, even when traffic must be routed back to the original rack.

The growth of server virtualization and cloud-based platforms further popularized east-to-west communication, as devices could be located anywhere within the virtualized network infrastructure.

Furthermore, due to a limit on the number of virtual local area networks based on the IEEE 802.1Q standard, facilities must often be divided into multiple virtualization clusters, which limits the ability to properly load manage. Devices are limited to communicating solely within their respective cluster, meaning devices at capacity are unable to move traffic to devices if they’re outside the cluster.

Using a traditional network architecture also makes it difficult to implement changes to the network infrastructure, as increases to capacity require additional racks that support another top-of-rack switch, as well as aggregation switches and free ports within the core switch.

More modern network designs such as spine-leaf architecture support a horizontal flow of information — i.e. east to west communication. Spine-leaf architecture vs traditional architecture also offers simplicity in terms of adding capacity without sacrificing downtime as each top of rack switch, in essence, becomes a leaf that is attached to two differing spine switches — making every leaf in the pod only one hop within the fabric. Moreso, if more capacity is needed within a spine-leaf architecture network, spine switches and leaf switches can easily be interconnected to increase the overall capacity.

The structure of spine-leaf architecture vs traditional architecture ensures the same number of hops between devices, regardless of the source or destination, which offers loop-free movement and load balance, providing predictable latency, delay times, and resilience.

Another difference between spine-leaf architecture vs traditional architecture is that many OEM devices are designed to support one or the other — i.e. spine and leaf architecture or the traditional three-tier architecture. These classifications identify how the switches fit within their respective architectures and are designed for either traditional three-tier or spine and leaf architecture.

That all being said, traditional architecture remains a common setup for all kinds of devices, and it’s typically a more cost-effective approach. Spine and leaf architecture — though more efficient — is typically less cost effective, but does not require the same variety of devices as traditional.

The spine-leaf architecture vs traditional architecture devices for Juniper, Arista, and Cisco are as follows:

Architecture Supported on Juniper Devices

Spine and leaf architecture on Juniper devices is available on the following QFX Series switches:

  • QFX5100 series
  • QFX5110 series
  • QFX5120 series
  • QFX5200 series
  • QFX5210 series
  • QFX10002 series
  • QFX10000 series
  • QFX10008 series
  • QFX 10016 series

See all the QFX Series devices BrightStar Systems stocks and sells on our QFX hub page.

Traditional architecture on Juniper devices is supported on the following EX Series switches:

See all the EX Series devices BrightStar Systems stocks and sells on our EX Series hub page.

Architecture Supported on Arista Devices

On Arista, leaf-spine architecture is supported on the following R-Series devices:

It’s also supported on the following X-Series devices:

Leaf-spine architecture is supported on the Arista 7170 series as well.

Traditional architecture is supported on the following Arista series:

We stock several R-Series and X-Series devices, as well as 7170 Series devices, and several others. Visit our Arista switches page to see all the Arista switches we sell.

Architecture Supported on Cisco Devices

Spine and leaf architecture on Cisco devices is available on the following routers and switches:

  • NCS 7000 series
  • NCS 7700 series
  • NCS 5500 series
  • NCS 5600 series
  • NCS 6000 series
  • N9K-C9364C series
  • N9K-C9332C series

And traditional architecture is supported on the following Cisco Nexus 9000 Series devices:

  • Nexus 9200 series
  • Nexus 9300 series
  • Nexus 9500 series

Traditional architecture is also supported on Cisco ASR series devices.

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