METHOD AND APPARATUS FOR INTERACTING WITH A NETWORK INFORMATION BASE IN A DISTRIBUTED NETWORK CONTROL SYSTEM WITH MULTIPLE CONTROLLER INSTANCES

A control system including several controllers for managing several switching elements. A first controller registers a second controller for receiving a notification when a data tuple changes in a network information base (NIB) storage of the first controller that stores data for managing a set of switching elements. The first controller changes the data tuple in the NIB. The first controller sends the notification to the second controller of the change to the data tuple in the NIB. The first and second controllers operate on two different computing devices. Each controller receives logical control plane data for specifying logical datapath sets and converts the logical control plane data to physical control plane data for enabling the switching elements to implement the logical datapath sets.