enabled : each incoming ICMP 'Timestamp' message addressed to local system is answered with an RFC792-compliant ICMP 'Timestamp-Reply' message. This is the default behavior of the system. disabled: incoming ICMP 'Timestamp' messages addressed to local system are silently discarded. extended: if an incoming ICMP 'Timestamp' message contains data appended after the three timestamp fields (which is a deviation of RFC792), the system replies with a modified 'Timestamp-Reply' message which contains a copy of the received data appended after the three timestamp fields. This behaviour is not RFC792-compliant and should be reserved for testing purposes.