F3215-HP Load Balancing Module System Management Configuration Guide-6PW101

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NTP uses two types of messages: clock synchronization messages and NTP control messages. NTP
control messages are used in environments where network management is needed. Because NTP control
messages are not essential for clock synchronization, they are not described in this document.
A clock synchronization message is encapsulated in a UDP message, as shown in Figure 68.
Figure 68 Clock synchronization message format
The main fields are described as follows:
• LI (Leap Indicator)—A 2-bit leap indicator. If set to 11, it warns of an alarm condition (clock
unsynchronized). If set to any other value, it is not to be processed by NTP.
• VN (Version Number)—A 3-bit version number that indicates the version of NTP. The latest version
is version 4.
• Mode—A 3-bit code that indicates 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 that indicates the stratum level of the local clock, taking the value of 1 to
16. 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.
• Poll—An 8-bit signed integer that indicates the maximum interval between successive messages,
which is called the poll interval.