1. A non-transitory machine readable medium of a controller computer storing a program which when executed by at least one processing unit of the controller computer manages a plurality of managed forwarding elements that forward data through a network, the program comprising sets of instructions for: receiving inputs that define forwarding performance constraints of a set of managed forwarding elements; based on the inputs, generating a set of universal flow entries for configuring the set of managed forwarding elements to apply the forwarding performance constraints to data traffic forwarded by the managed forwarding elements; and from the controller computer, sending the generated set of universal flow entries to a controller that manages a managed forwarding element wherein the controller (1) directs the managed forwarding element to create a set of network constructs for applying the forwarding performance constraints based on the set of universal flow entries and (2) converts the set of universal flow entries into a set of customized flow entries for the managed forwarding element based on information about the created set of network constructs received from the managed forwarding element.