Spine and Leaf Nodes

This drawing (or one resembling it) seems to keep popping up in Spine and Leaf discussions.  This is an incomplete view of the mechanism of the art.  The Spine and leaf architecture is certainly compelling for a variety of good reasons, not the least of which is a horizontal scaling model that far exceeds more traditional methods of networking.

See  sdxcentral article

The actual story of this design model may actually much more interesting to the network developer.  If this model were the sole construct of the network design, it wouldn't be, necessarily, special.

But if the design model indicated a requirement for redundancy in the Top of Rack (ToR) or if there was a special need physical configuration like a 3-cabinet-wide Logical Rack, those may also be supported by the Spine and Leaf Network model, fairly simply in the guise of a Leaf Node arrangement.

That's not all though.  To scale above the reasonable size of a traditional network, it may be necessary to start thinking about the routing protocol, in order to avoid those pesky all encompassing broadcast domains, delivering what is largely L3 all the way down to the host.

Then topping it off with a healthy dose of the art of the possible, utilizing the routing protocol constructed in the previous model to create a delivery platform for logically isolated networks utilizing VxLAN.  Also, when you get to this size, don't forget to add the Management Network VRF, need a way for those 1000's upon 1000's of physical systems to get back to the monitoring and management.

Hopefully you can recognize the original drawing in the last drawing.  It's still there, but nothing like the switched network of old.