1. A method for controlling for a logical switching element comprising one or more logical ports, the logical switching element implemented in one or more managed switching elements that forward data in a network, the method comprising: assigning a first queue to a logical port through which to receive data, the first queue defining a set of performance constraints for the data; and associating the first queue with a second queue for a managed port, the second queue for queuing the data to apply the performance constraints to the data before sending the data through the managed port.