Distributed network control system with one master controller per logical datapath set

A non-transitory machine readable medium storing a program which when executed by at least one processing unit implements a logical switching element, the program comprising sets of instructions for:

• generating data for programming a set of two or more physical forwarding elements to implement the logical switching element;
• using a first controller to distribute at least a first portion of the generated data to a first plurality of physical forwarding elements in the set of physical forwarding elements;
• and
• using a second controller to distribute at least a second portion of the generated data to a second plurality of physical forwarding elements in the set of physical forwarding elements,
• said first controller serving as the master controller for the first plurality of physical forwarding elements and the second controller serving as the master controller for the second plurality of physical forwarding elements.