A method for sampling packets for a network flow, includes: receiving a packet at a network port of a network switch appliance, the network switch appliance comprising an instrument port for communication with a network monitoring instrument; determining whether the packet belongs to a network flow that is desired to be monitored, wherein the act of determining is performed based at least in part on one or more information in a control plane using a processing unit; and passing the packet to the instrument port if the packet belongs to the network flow.