2050 CHAPTER 111: NTP CONFIGURATION■ For increment backup between a backup server and clients, timekeeping mustbe synchronized between the backup server and all the clients.Advantages of NTP:■ NTP uses a stratum to describe the clock precision, and is able to synchronizetime among all devices within the network.■ NTP supports access control and MD5 authentication.■ NTP can unicast, multicast or broadcast protocol messages.How NTP Works Figure 610 shows the basic work flow of NTP. Device A and Device B areinterconnected over a network. They have their own independent system clocks,which need to be automatically synchronized through NTP. For an easyunderstanding, we assume that:■ Prior to system clock synchronization between Device A and Device B, the clockof Device A is set to 10:00:00 am while that of Device B is set to 11:00:00 am.■ Device B is used as the NTP time server, namely Device A synchronizes its clockto that of Device B.■ It takes 1 second for an NTP message to travel from one device to the other.Figure 610 Basic work flow of NTPThe process of system clock synchronization is as follows:■ Device A sends Device B an NTP message, which is timestamped when it leavesDevice A. The time stamp is 10:00:00 am (T1 ).IP networkIP networkIP networkIP networkDevice BDevice ADevice BDevice ADevice BDevice ADevice BDevice A10:00:00 am 11:00:01 am10:00:00 amNTP message 10:00:00 am 11:00:01 am 11:00:02 amNTP messageNTP messageNTP message received at 10:00:03 am1.3.2.4.
