H3C Technologies H3C SecBlade LB Cards - Manual (Page 121)

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NTP message format
All NTP messages mentioned in this document refer to NTP clock synchronization messages.
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 75 .
Figure 75 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