A computer implemented method, data processing system, and computer program product for discovering an unauthorized router in a network. The process in the illustrative embodiments first obtains a physical address of a suspected router or destination device. A data packet is created which comprises at least a destination media access control field, a destination internet protocol field, and a time-to-live field, wherein the destination media access control field comprises the physical address of the destination device, wherein the destination internet protocol field comprises a bogus internet protocol address, and wherein the time-to-live field comprises a value indicating the data packet has exceeded a time limit. The data packet is sent to the destination device using the physical address in the destination media access control field. If a time exceeded message is received from the destination device, the destination device is determined to be enabled for routing.