Advance applications require a new data center infrastructure, and Two-Tier or spine-leaf architectures offers many advantages over traditional Three-Tier designs
Three-Tier data center networks:
Core switches are usually large modular chassis with very high throughput and advanced routing capabilities.
Distribution layer switches are mid-tier speed switches with emphasis on uplink speeds. Services, such as load balancing or firewalls, could often be found at this layer.
Access Switches are the traditional top-of-rack (TOR) switch that regularly consists of 24 to 48 ports of 1 or 10Gbps ports with similarly sized uplinks.
Three-Tier data center networks were the generally recommended data center network design in the past. They worked very well when the majority of 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.
The issue with this design for the modern data center is that much more intra-DC traffic is the new norm. Due to server to server traffic, three hops now quickly become four, five or more, adding significant latency per flow as well as adding more possibility for bottlenecks, buffer overruns and dropped packets.
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.
Two-Tier data center networks:
Today, we recommend Two-Tier, or spine-leaf achitectures (also called Folded-CLOS), to meet the needs of advance applications: high-throughput and low-latency.
Advantages of Two-Tier, spine-leaf architectures
- Latency: There is a maximum of 2 hops for any East-West packet flows so ultra-low-latency is standard.
- Resiliency: Each leaf switch connects to every spine switch, spanning-tree is not needed and due to TRILL, SPB or SDN protocols, every uplink can be used concurrently.
- Performance: True active-active uplinks enable traffic to flow over the least congested high-speed links available.
- Scalability: You are able to increase leaf switch quantity to desired port capacity and add spine switches as needed for uplinks.
- Adaptability: Multiple spine-leaf networks across a multicloud ecosystem can be connected and managed from a single pane of glass. Also, this topology has benefits in other areas of the enterprise network (for example, industrial cell architecture or corporate LAN).
Considerations for using Two-Tier, spine-leaf architectures
With a Two-Tier architecture, the data center will need to be re-cabled. Each leaf will need to connect to each spine. This new design requires a considerable amount of cable as well as optics for connectivity.
Two-Tier, spine-leaf architectures may still require core switches for layer three routing. Planning both the physical and logical network is critical before purchasing the hardware for a new data center.
Conclusion:
Advance or new applications require a modern data center infrastructure design; Two-Tier, spine-leaf architecture offers many advantages over traditional Three-Tier architectures.
