292
C
HAPTER
35: NTP C
ONFIGURATION
Working Principle of NTP
The working principle of NTP is shown in Figure 89.
In Figure 89, The Ethernet switch A (LS_A) is connected to the Ethernet switch B
(LS_B) through their Ethernet ports. Both of them have system clocks of their own,
and they need to synchronize the clocks of each other through NTP. For ease of
understanding, suppose that:
■
Before the system clocks of LS_A and LS_B are synchronized, the clock of LS_A is
set to 10:00:00am, and the clock of LS_B is set to 11:00:00am.
■
LS_B serves as the NTP time server, that is, the clock of LS_A will be synchronized
to that of LS_B.
■
It takes one second for a packet sent by one switch to reach the other.
Figure 89
Working principle of NTP
The procedures of synchronizing system clocks are as follows:
■
LS_A sends an NTP packet to LS_B, with the timestamp identifying the time when
it is sent (that is, 10:00:00am, noted as T
1
) carried.
■
When the packet arrives at LS_B, LS_B inserts its own timestamp, which identifies
11:00:01am (noted as T
2
) into the packet.
■
Before this NTP packet leaves LS_B, LS_B inserts its own timestamp once again,
which identifies 11:00:02am (noted as T
3
).
■
When receiving the response packet, LS_A inserts a new timestamp, which
identifies 10:00:03am (noted as T
4
), into it.
Netw ork
Netw ork
NTP Packet10:00:00am
Netw ork
Netw ork
11:00:01am
10:00:00am
11:00:01am
11:00:02am
10:00:00am
NTP Packet received at 10:00:03
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Netw ork
Netw ork
NTP Packet10:00:00 am
Netw ork
Netw ork
11:00:01 am
10:00:00 am 11:00:01 am
11:00:02 am
10:00:00 am
NTP Packet received at 10:00:03 am
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Netw ork
Netw ork
NTP Packet10:00:00am
Netw ork
Netw ork
11:00:01am
10:00:00am
11:00:01am
11:00:02am
10:00:00am
NTP Packet received at 10:00:03
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Netw ork
Netw ork
NTP Packet
10:00:00 am
Netw ork
Netw ork
11:00:01 am
10:00:00 am 11:00:01 am 11:00:02 am
10:00:00 am
NTP Packet received at 10:00:03 am
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Netw ork
Netw ork
NTP Packet10:00:00am
Netw ork
Netw ork
11:00:01am
10:00:00am
11:00:01am
11:00:02am
10:00:00am
NTP Packet received at 10:00:03
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Netw ork
Netw ork
NTP Packet10:00:00 am
Netw ork
Netw ork
11:00:01 am
10:00:00 am 11:00:01 am
11:00:02 am
10:00:00 am
NTP Packet received at 10:00:03 am
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Netw ork
Netw ork
NTP Packet10:00:00am
Netw ork
Netw ork
11:00:01am
10:00:00am
11:00:01am
11:00:02am
10:00:00am
NTP Packet received at 10:00:03
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Netw ork
Netw ork
NTP Packet
10:00:00 am
Netw ork
Netw ork
11:00:01 am
10:00:00 am 11:00:01 am 11:00:02 am
10:00:00 am
NTP Packet received at 10:00:03 am
1.
2.
3.
4.
LS_A
LS_A
LS_A
LS_A
LS_B
LS_B
LS_B
LS_B
NTP Packet
NTP Packet
Summary of Contents for 4200G 12-Port
Page 10: ...8 CONTENTS...
Page 14: ...4 ABOUT THIS GUIDE...
Page 46: ...32 CHAPTER 5 LOGGING IN THROUGH WEB BASED NETWORK MANAGEMENT SYSTEM...
Page 48: ...34 CHAPTER 6 LOGGING IN THROUGH NMS...
Page 60: ...46 CHAPTER 9 VLAN CONFIGURATION...
Page 64: ...50 CHAPTER 10 MANAGEMENT VLAN CONFIGURATION...
Page 80: ...66 CHAPTER 13 GVRP CONFIGURATION...
Page 98: ...84 CHAPTER 15 LINK AGGREGATION CONFIGURATION...
Page 112: ...98 CHAPTER 18 MAC ADDRESS TABLE MANAGEMENT...
Page 126: ...112 CHAPTER 19 LOGGING IN THROUGH TELNET...
Page 162: ...148 CHAPTER 20 MSTP CONFIGURATION...
Page 274: ...260 CHAPTER 29 IGMP SNOOPING CONFIGURATION...
Page 276: ...262 CHAPTER 30 ROUTING PORT JOIN TO MULTICAST GROUP CONFIGURATION...
Page 298: ...284 CHAPTER 33 SNMP CONFIGURATION...
Page 304: ...290 CHAPTER 34 RMON CONFIGURATION...
Page 338: ...324 CHAPTER 36 SSH TERMINAL SERVICES...
Page 356: ...342 CHAPTER 38 FTP AND TFTP CONFIGURATION...
Page 365: ...Information Center Configuration Example 351 S4200G terminal logging...
Page 366: ...352 CHAPTER 39 INFORMATION CENTER...
Page 378: ...364 CHAPTER 40 BOOTROM AND HOST SOFTWARE LOADING...
Page 384: ...370 CHAPTER 41 Basic System Configuration and Debugging...
Page 388: ...374 CHAPTER 43 NETWORK CONNECTIVITY TEST...
Page 406: ...392 CHAPTER 45 CONFIGURATION OF NEWLY ADDED CLUSTER FUNCTIONS...