A method of converting an abstract quality of service policy into a new configuration for one or more network devices of managed network, as routers. The abstract quality of service policy is received and converted into a first set of one or more basic commands. A current configuration of one of the network devices is obtained, e.g. through device discovery. The configuration is received in the form of one or more first command line interface (CLI) commands that represent the current configuration of the network device. A second set of one or more basic commands that correspond to the current configuration of the network device is determined, based on the first CLI commands. The first and second sets of basic commands are transformed into one or more second CLI commands which, when executed by the network device, will create a new configuration for the network device that implements the abstract quality of service policy. Merging and aggregation, based on state values associated with the basic commands, is carried out to remove any duplicate commands.