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what is the purpose of an sdn controller
An SDN controller is an application in a software defined networking architecture that manages flow control for improved network management and application performance.
What does the SDN controller run on
The SDN controller runs on a server
How do SDN controllers direct traffic
SDN controllers direct traffic according to forwarding policies that a network operator puts in place, thereby minimizing manual configurations for individual network devices.
How do SDN controllers communicate
The SDN controller communicates with applications, such as firewalls or load balancers, via northbound interfaces

Question: What is a major benefit of the controllers
Self-contained rewrite: What is a major benefit of SDN controllers