Evil CCIE left a lengthy comment on one of my blog posts including this interesting observation:

It's always interesting to hear all kind of reasons from people to deploy CLOS fabrics in DC in Enterprise segment typically that I deal with while they mostly don't have clue about why they should be doing it in first place. […] Usually a good justification is DC to support high amount of East-West Traffic....but really? […] Ask them if they even have any benchmarks or tools to measure that in first place :)

What he wrote proves that most networking practitioners never move beyond regurgitating vendor marketing (because that’s so much easier than making the first step toward becoming an engineer by figuring out how technology really works).

Note that I decided to call some people working in networking practitioners because I honestly can’t see where they’d be applying any engineering methodology to their work.

There’s another really good reason to use leaf-and-spine fabrics: equidistant bandwidth. Regardless of where a device is connected to the fabric, it has the same (minimum average) bandwidth to every other device connected to the same fabric, removing all restrictions on server- or workload placement… or even the discussions about optimal firewall- or load balancer placement. Compare that to traditional 3-tier architectures (or watch the Introduction section of Leaf-and-Spine Fabric Architectures webinar).

This argument obviously applies only when your fabric needs more than just two switches. Also note that leaf-and-spine fabrics are nothing new.

In slightly larger fabrics, the leaf-and-spine architecture with more than two spine switches allows you to use fixed-size switches instead of more complex and more expensive chassis switches. Russ White and Shawn Zandi talked about this topic (and single-SKU data center fabric) in Open Networking webinar.

Finally, if you build a leaf-and-spine fabric with more than two spine nodes, you decrease the performance hit you take on spine switch failure, and (potentially) remove the need for maintenance window when doing spine switch upgrades.

Next steps

Found something interesting in this blog post? Maybe you want to explore the leaf-and-spine fabrics a bit further: