1. Logistics:
   * Turn in design report today on GitHub.
   * Office hours today because I'll have to end half hour early on Wednesday.

2. The origins of datacenters and cloud computing:
   * Large-scale web search
   * Clusters for web crawling
   * Many cheap servers vs. a few expensive servers
   * Amazon EC2's cloud-computing service in 2006, Azure and Google Cloud in 2008.
   * Lots of built-up capacity

3. Datacenter topology: the network topology of the datacenter
   * The one big-switch-abstraction is desirable: simplifies job placement
   * Hard to achieve: can't build an N-port switch
   * Can emulate it using smaller port-count switches
     --> Goes back to Charles Clos in telephone networks
   * Leaf-spine example

4. Load balancing in the datacenter
   * Clos topologies are useful only if load is spread out evenly
   * Can't load balance on every packet: leads to packet reordering causing TCP to react.

5. Taking stock:
   * Few expensive switches vs. many cheap switches (NOW project applied to networking instead of compute).
   * Comparing leaf-spine switch to a single switch
   * Scaling to more layers (e.g., 3 layers).