You could build much larger fabrics if you split leaf switch uplinks into individual lanes (100GE ports into four 25GE lanes), but you don’t want to know how messy the cabling gets with the octopus cables or complex behind-the-scenes wiring between patch panels.īrad Hedlund explained that idea in the Leaf-and-Spine Fabric Architectures webinar.Īnother dose of reality: most of the above doesn’t matter.That makes your design totally flexible regarding the number of uplinks and the oversubscription ratio, but the breakout cables could get messy, although not as much as the next option 1. Obviously you could also buy switches with high-speed ports (example: 100GE) and use some of those as four lower-speed ports (example: 25GE) with breakout cables.The maximum fabric size is still limited by the number of ports on the spine switches though. These days, a lot of switches come with six or eight uplinks, making it easier to build fabrics with more spines and thus lower oversubscription ratio. Most leaf switches used to have four uplinks. The number of uplink ports on the leaf switches limits the maximum number of spine switches.
Next step: an exciting configuration exercise unless you’ve decided to use unnumbered leaf-to-spine links when deploying the fabric. Adding a spine switch often results in the rewiring of the physical fabric the only exception would be going from three to four spines when you’re using leaf switches with four uplinks (and similarly for switches with eight uplinks).It is true that you’re pretty low on redundancy if you have just two spines and one of them exploded, so make that three. It doesn’t matter whether you have two or sixteen spines – the blast radius is the same.Also, it looks like adding spine switches reduces the blast radius. Isn’t that wonderful? If you need more bandwidth, sprinkle the magic spine powder on your fabric, add water, and voila! Problem solved. One of the main benefits of a CLOS folded spine topology is the scale out spine where you can scale out the number of spine nodes increasing your leaf-spine n-way ECMP as well as minimizing the blast radius with the more spine nodes the more redundancy and resiliency. I’m always envious of how easy networking challenges seem when you’re solving them in PowerPoint, for example, when an innovation specialist explains how scalability works in leaf-and-spine fabrics in a LinkedIn comment:
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