Key Ideas of Software-Defined Networking (SDN)
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1. Separation of control
   - control plane: routing, SW, smarts, policy, etc.
   - data plane: forwarding, HW, fast, simple, etc.

2. Logical centralization
   - one or more SDN controllers to manage AS

3. Flexibility of generalized forwarding
   - can do routers, switches, firewalls, NAT, load balancers, etc.
   
4. OpenFlow API for "programming" routers
   - simple TCP-based protocol for manipulating flow tables