Dynamic network adaptation

A method to adapt a software defined network (SDN) 200, the SDN constituting a logical arrangement of network appliances and connections that are controlled by a SDN controller 202. A network optimiser 204 receives a measure of a performance metric 208 and also receives a forecast demand 210 indicating a demand for a network resource which is expected to be placed on the SDN. The network optimiser accesses a library 206 which contains possible adaptations that can be applied to the SDN. The network optimiser uses heuristic search techniques, such as simulated annealing, hill climbing or guided local search, to search the library. The search may be terminated according to a predetermined stopping condition such as availability of time within a specified time window. The search results in a sequence of adaptations being identified that when implemented will satisfy the forecast demand for the SDN and provide an improved measure of the performance metric. The sequence of adaptations is applied to the SDN by the SDN controller modifying the existing logical arrangement of the SDN.