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We introduce ReversePTP, a novel approach to clock synchronization in Software Defined Networks (SDN). ReversePTP is based on the Precision Time Protocol (PTP), but is conceptually reversed; in ReversePTP all nodes (switches) in the network distribute timing information to a single node, the controller, that tracks the state of all the clocks in the network. Hence, all computations and bookkeeping are performed by the controller, whereas the `dumb' switches are only required to send it their current time periodically. In accordance with the SDN paradigm, the controller is the 'brain', making ReversePTP flexible and programmable from an SDN programmer's perspective.