A network control system for interconnecting several separate networks. The system includes i) several interconnection switching elements, each of which is for connecting one of the separate networks to a common interconnecting network, ii) a first set of network controllers for managing a first set of the interconnection switching elements at a first set of separate networks in order for machines at different networks within the first set to communicate with each other, iii) a second set of network controllers for managing a second set of interconnection switching elements at a second set of separate networks in order for machines at different networks within the second set to communicate with each other, and iv) a third set of network controllers for managing the first and second sets of network controllers in order for machines at networks in the first set to communicate with machines at networks in the second set.