H3c-technologies H3C WX6000 Series Access Controllers Instrukcja Użytkownika Pobierz pdf (Strona 70)

6-2

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.

How NTP Works

Figure 6-1 shows the basic workflow of NTP. Device A and Device 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 Device A and Device B, the clock of Device A is set

to 10:00:00 am while that of Device B is set to 11:00:00 am.

z Device B is used as the NTP time server, namely, Device A synchronizes its clock to that of Device

z It takes 1 second for an NTP message to travel from one device to the other.

Figure 6-1 Basic work flow of NTP

IP network

Device BDevice A

Device B

Device A

Device B

Device A

Device B

Device 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 received at 10:00:03 am

The process of system clock synchronization is as follows:

z Device A sends Device B an NTP message, which is timestamped when it leaves Device A. The

time stamp is 10:00:00 am (T1).

z When this NTP message arrives at Device B, it is timestamped by Device B. The timestamp is

11:00:01 am (T2).

z When the NTP message leaves Device B, Device B timestamps it. The timestamp is 11:00:02 am

(T3).

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H3c-technologies H3C WX6000 Series Access Controllers Instrukcja Użytkownika Strona 70