Method of forwarding packet flows in a network and network system

A network system, the network system comprising:

• an SDN controller;
• a plurality of SDN switches that are under control of the SDN controller;
• a plurality of end hosts;
• a sink node;
• and
• predefined routing paths configured to enable transmission of packet flows originating from the plurality of end hosts to the sink node,
• wherein a routing path for packet flows of a respective end host includes one or more designated SDN switches of the plurality of SDN switches, wherein the one or more designated SDN switches include an edge switch having at least one port connected to the end host, and
• wherein the one or more designated switches are configured to enable forwarding of a packet flow from the respective end host via a dedicated door-opener packet that, when being processed at the one or more designated switches, effectuates activation or installation of a forwarding rule within the one or more designated switches for forwarding the packet flow to a next switch along the routing path.