The embodiments of the present invention relate to apparatuses in the form of a first network unit and a device, and also relates to a method for enabling protection of a bootstrap message in a device management network system. The method comprises: receiving at the first network unit, a request to bootstrap the device; transmit a request for a bootstrap key, to a second network unit; receiving a message comprising the bootstrap key and further comprises trigger information and transmitting the trigger information to the device to trigger generation of the bootstrap key internally in the device. Thereafter a protected bootstrap message can be transmitted to the device from the first network unit, and when the device verifies and/or decrypts the bootstrap message, device management (DM) sessions can start between the device and the first network unit.