A packet of data and a packet-identification value are transmitted to a network device having an identifier. The stored packet-identification value and the identifier are recorded. The stored packet-identification value is then increased and the process repeats. To receive data, an expected identification value is stored in association with the identifier. A packet and a packet-identification value are received from the network device. The identifier and an indication of receipt are stored. If the received value does not match the expected value for the identifier, the received value is stored. If the values match, the stored packet-identification value and identifier are recorded. If the received value exceeds the expected value, the stored packet-identification value, the identifier and the received identifier are recorded. Subsequently, the stored expected value is increased. The process repeats. Network devices and systems are described.