H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 487)

54-2
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All devices must use the same reference clock in a charging system.
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To implement certain functions, such as scheduled restart of all devices within the network, all
devices must be consistent in timekeeping.
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When multiple systems process a complex event in cooperation, these systems must use that
same reference clock to ensure the correct execution sequence.
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For increment backup between a backup server and clients, timekeeping must be synchronized
between the backup server and all the clients.
Advantages of NTP:
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NTP uses a stratum to describe the clock precision, and is able to synchronize time among all
devices within the network.
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NTP supports access control and MD5 authentication.
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NTP can unicast, multicast or broadcast protocol messages.
How NTP Works
Figure 54-1 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:
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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.
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Switch B is used as the NTP time server, namely Switch A synchronizes its clock to that of Switch
B.
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It takes 1 second for an NTP message to travel from one switch to the other.
Figure 54-1 Basic work flow of NTP
IP network
IP network
IP network
IP network
Switch B Switch 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.