C. The stratum level of an NTP server shows its level of precision and accuracy, and a stratum level of 16 means the server is unsynchronized and cannot be used as a time source. This means the configured NTP server is not working and cannot supply correct time to the ASA. The engineer should verify the NTP server configuration and availability; also, it's important to check whether the NTP server is reachable and set to use the correct IP address.

Selected Answer: C ONNLY RANGE FORM 0-15 , 15 is meaning not usable time server. the higher number means worse. The NTP Stratum Model The NTP Stratum model is a representation of the hierarchy of time servers in an NTP network, where the Stratum level (0-15) shows the device's distance to the reference clock. Stratum 0 means a device is directly connected to e.g., a GPS antenna. Stratum 0 devices cannot distribute time over a network directly, though, so they must be linked to a Stratum 1 time server that will distribute time to Stratum 2 servers or clients, and so on. The higher the Stratum number, the more the timing accuracy and stability degrade. The NTP protocol does not allow clients to accept time from a Stratum 15 device, so Stratum 15 is the lowest NTP Stratum. A group of NTP servers at the same Stratum level (Stratum 2, for example) are considered NTP Peers to each other. NTP Servers at a higher Stratum level, on the other hand, are referred to as NTP Servers.