Ntp Message Format - 3Com 4210G Series Configuration Manual

NTP Message Format

NTP uses two types of messages, clock synchronization message and NTP control message. An NTP
control message is used in environments where network management is needed. As it is not a must for
clock synchronization, it will not be discussed in this document.
All NTP messages mentioned in this document refer to NTP clock synchronization messages.
A clock synchronization message is encapsulated in a UDP message, in the format shown in
25-2.
Figure 25-2 Clock synchronization message format
0 1 4
LI VN Mode
Main fields are described as follows:
LI: 2-bit leap indicator. When set to 11, it warns of an alarm condition (clock unsynchronized);
when set to any other value, it is not to be processed by NTP.
VN: 3-bit version number, indicating the version of NTP. The latest version is version 3.
Mode: a 3-bit code indicating the work mode of NTP. This field can be set to these values: 0 –
reserved; 1 – symmetric active; 2 – symmetric passive; 3 – client; 4 – server; 5 – broadcast or
multicast; 6 – NTP control message; 7 – reserved for private use.
Stratum: an 8-bit integer indicating the stratum level of the local clock, with the value ranging from
1 to 16. The clock precision decreases from stratum 1 through stratum 16. A stratum 1 clock has
the highest precision, and a stratum 16 clock is not synchronized and cannot be used as a
reference clock.
7 15
Stratum
Root delay (32 bits)
Root dispersion (32 bits)
Reference identifier (32 bits)
Reference timestamp (64 bits)
Originate timestamp (64 bits)
Receive timestamp (64 bits)
Transmit timestamp (64 bits)
Authenticator (optional 96 bits)
23
Poll
25-3
31
Precision
Figure