Leaf-spine data center architectures

http://longwhiteclouds.com/2015/03/26/configuring-scalable-low-latency-l2-leaf-spine-network-fabrics-with-dell-networking-switches/?utm_source=tuicool&utm_medium=referral

http://bradhedlund.com/2012/01/25/construct-a-leaf-spine-design-with-40g-or-10g-an-observation-in-scaling-the-fabric/

http://searchdatacenter.techtarget.com/feature/Data-center-network-design-moves-from-tree-to-leaf

http://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/guide-c07-730115.html

https://keepingitclassless.net/2014/06/spine-leaf-topology-ansible/