The crux of Scott's argument was this: Reasoning about the behavior of fully distributed algorithms is hard. And distributed algorithms are at the heart of networking. There is a reason why people who can configure BGP correctly in complex environments are highly sought after and widely viewed as wizards.
The solution proposed in Scott's talk was to create a new layer of abstraction. The central SDN controller presents the abstraction of the network as one big switch, which is much easier to reason about than the distributed algorithms that underpin traditional networking.
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