A method comprising: at a network controller in a network: in response to a packet drop occurring in the network, sending to a first intermediate node (30) among a plurality of intermediate nodes (30 -30) in a path in the network, a command that causes the first intermediate node to include a flag in an In-situ Operations, Administration, and Maintenance, IOAM, header of a packet to trigger a plurality of further intermediate nodes after that node to export metadata accumulated in the packet; at each of the plurality of further intermediate nodes (30 -30) that receive the packet having the flag set: receiving the packet, the packet header including metadata (232, 234) that has been accumulated as the packet travels along the path in the network; detecting whether a trigger condition has occurred, wherein the trigger condition comprises presence of the flag in the header; and in response to detecting that the trigger condition has occurred, exporting, to the network controller, at least a portion of the metadata that has been accumulated in the header so that the portion of the metadata is removed from the header after it has been exported; and at the network controller, correlating the exported metadata received from the plurality of further intermediate nodes to isolate the cause and/or location of the packet drop, at a network controller in a network: in response to a packet drop occurring in the network, sending to a first intermediate node (30) among a plurality of intermediate nodes (30 -30) in a path in the network, a command that causes the first intermediate node to include a flag in an In-situ Operations, Administration, and Maintenance, IOAM, header of a packet to trigger a plurality of further intermediate nodes after that node to export metadata accumulated in the packet; at each of the plurality of further intermediate nodes (30 -30) that receive the packet having the flag set: receiving the packet, the packet header including metadata (232, 234) that has been accumulated as the packet travels along the path in the network; detecting whether a trigger condition has occurred, wherein the trigger condition comprises presence of the flag in the header; and in response to detecting that the trigger condition has occurred, exporting, to the network controller, at least a portion of the metadata that has been accumulated in the header so that the portion of the metadata is removed from the header after it has been exported; and receiving the packet, the packet header including metadata (232, 234) that has been accumulated as the packet travels along the path in the network; detecting whether a trigger condition has occurred, wherein the trigger condition comprises presence of the flag in the header; and in response to detecting that the trigger condition has occurred, exporting, to the network controller, at least a portion of the metadata that has been accumulated in the header so that the portion of the metadata is removed from the header after it has been exported; and at the network controller, correlating the exported metadata received from the plurality of further intermediate nodes to isolate the cause and/or location of the packet drop,