2.1 Transport
All NTP messages are transported through the User Datagram Protocol (UDP) in the NTP data format, as specified in [RFC1305] Appendix A.
NTP messages do not include a message length field. The NTP message length is calculated based on the payload length in the UDP header and excludes the length of the UDP header.
Security parameters used in the NTP Authentication Extensions are key identifiers, as described in sections 3.1.6 and 3.2.5.