The following invention relates to methods, systems, computer programs and computer program products for supporting said method, and different embodiments thereof, for monitoring data packet flows between Virtual Machines, VMs, within a data centre. The method comprises collecting flow data for data packet flows between VMs in the data centre, and mapping the flow data of data packet flows between VMs onto data centre topology to establish flow costs for said data packet flows. The method further comprises calculating an aggregated flow cost for all the flows associated with a VM for each VM within the data centre, and determining whether to reschedule any VM, or not, based on the aggregated flow cost.