Openflow is the “father of software defined networks” in the minds of many engineers. To understand Openflow, however, you cannot just look at the protocol itself; rather you must go back to the beginning, in the mists of old networking. It is important to start here: in the “old days,” when I was still taking network cases in the routing protocols team at a major vendor, when we wanted to understand how routing worked, we looked at the code. What is the point? Networking has always been about software control planes. So networks have always been built on software; hence the “software” in software defined networking (SDN) cannot have ever meant “building control planes in software,” because that is the way it has always been done. —ECI

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