220.127.116.11 Authentication Response Behavior
When the server receives a message from the client, the server examines the message length. If the message length is 68 bytes, the server processes the request as a Client NTP Request and responds with a Server NTP Response message. If the message length is 120 bytes, the server processes the request as a Client ExtendedAuthenticator NTP Request and responds with a Server ExtendedAuthenticator NTP Response message. If the NTP message length is 48 bytes, the message is processed as specified in [RFC1305] section 3.4.3.<22> NTP messages of other lengths are ignored. As a result of this, the authentication mechanism defined in [RFC1305] Appendix C.1 is not supported.
The MS-SNTP protocol supports modes according to [RFC1305] section 3.4.2 (Table 5 "Modes and Actions"), except that it does not support broadcast clients, NTP control message, or symmetric passive mode. If the server receives a message with an unsupported mode, the message MUST be ignored as specified in [RFC1305] section 3.4.3. The NTP Authentication Extensions are defined only for the following NTP and SNTP association modes (as specified in [RFC1305] sections 3.2.1 and 3.3): client, server, and symmetric active.