H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – NTP
H3C S7500E Series Ethernet Switches Chapter 1 NTP Configuration
1-2
Advantages of NTP:
z NTP uses a stratum to describe the clock precision, and is able to synchronize
time among all devices within the network.
z NTP supports access control and MD5 authentication.
z NTP can unicast, multicast or broadcast protocol messages.
1.1.2 How NTP Works
Figure 1-1 shows the basic work flow of NTP. Switch A and Switch B are interconnected
over a network. They have their own independent system clocks, which need to be
automatically synchronized through NTP. For an easy understanding, we assume that:
z Prior to system clock synchronization between Switch A and Switch B, the clock of
Switch A is set to 10:00:00 am while that of Switch B is set to 11:00:00 am.
z Switch B is used as the NTP time server, namely Switch A synchronizes its clock
to that of Switch B.
z It takes 1 second for an NTP message to travel from one device to the other.
IP network
IP network
IP network
IP network
Switch BSwitch A
Switch B
Switch A
Switch B
Switch A
Switch B
Switch A
10:00:00 am 11:00:01 am
10:00:00 am
NTP message 10:00:00 am 11:00:01 am 11:00:02 am
NTP message
NTP message
NTP message received at 10:00:03 am
1.
3.
2.
4.
Figure 1-1 Basic work flow of NTP
The process of system clock synchronization is as follows:
z Switch A sends Switch B an NTP message, which is timestamped when it leaves
Switch A. The time stamp is 10:00:00 am (T1).
z When this NTP message arrives at Switch B, it is timestamped by Switch B. The
timestamp is 11:00:01 am (T2).