The present invention provides apparatuses, methods, computer programs, computer program products and computer-readable media regarding SDN security. The method comprises checking whether messages in the user plane comply to a preconfigured rule, and if it is determined that the messages comply to the preconfigured rule, checking whether a number of specific signaling messages related to address allocation that are sent to a controller has reached a predetermined threshold, and if the predetermined threshold has been reached, throttling transmission of the specific signaling messages to the controller.