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SDN: Software Defined Networks by Ken Gray, Thomas D. Nadeau

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Chapter 2. Centralized and Distributed Control and Data Planes

One of the tenets expressed early in the introduction of SDN is the potential advantage in the separation of a network device’s control and data planes. This separation affords a network operator certain advantages in terms of centralized or semi-centralized programmatic control. It also has a potential economic advantage based on the ability to consolidate in one or a few places what is often a considerably complex piece of software to configure and control onto less expensive, so-called commodity hardware.

Introduction

The separation of the control and data planes is indeed one of the fundamental tenets of SDN—and one of its more controversial, too. Although it’s not a new concept, the contemporary way of thinking has some interesting twists on an old idea: how far away the control plane can be located from the data plane, how many instances are needed to exist to satisfy resiliency and high-availability requirements, and whether or not 100% of the control plane can be, in fact, relocated further away than a few inches are all intensely debated. The way we like to approach these ideas is to think of them as a continuum of possibilities stretching between the simplest, being the canonical fully distributed control plane, to the semi- or logically centralized control plane, to finally the strictly centralized control plane. Figure 2-1 illustrates the spectrum of options available to the network operator, as well as some ...

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