The biggest difference between a traditional network and SDN is that the latter is a software-based network. Traditional networks rely on physical infrastructure such as switches and routers to make connections and run properly. In contrast, a software-based network allows the user to control the allocation of resources at a virtual level through the control plane. Rather than interacting with physical infrastructure, the user is interacting with software to provision new devices.
From this perspective, an administrator can ascertain network paths and actively configure network services. An SDN also has more ability to communicate with devices throughout the network than a traditional switch. The core difference between the two can be summed up as virtualization. SDN virtualizes your entire network. Virtualization creates an abstract version of your physical network which allows resources to be provisioned from a centralized location.
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