Controller in network control system

A network control system for generating physical control plane data for managing first and second managed forwarding elements that implement forwarding operations associated with a first logical data path set is described. The system includes a first controller instance for converting logical control plane data for the first logical data path set to universal physical control plane (UPCP) data. The system further includes a second controller instance for converting UPCP data to customized physical control plane (CPCP) data for the first managed forwarding element but not the second managed forwarding element. The system further includes a third controller instance used for receiving the UPCP data generated by the first controller instance, identifying the second controller instance as a controller instance responsible for generating the CPCP data for the first managed forwarding element and providing the received UPCP data to the second controller instance.