H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – NTP
H3C S7500E Series Ethernet Switches Chapter 1 NTP Configuration
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II. Symmetric peers mode
Figure 1-4 Symmetric peers mode
A device working in the symmetric active mode periodically sends clock
synchronization messages, with the Mode field in the message set to 1 (symmetric
active); the device that receives this message automatically enters the symmetric
passive mode and sends a reply, with the Mode field in the message set to 2
(symmetric passive). By exchanging messages, the symmetric peers mode is
established between the two devices. Then, the two devices can synchronize, or be
synchronized by, each other. If the clocks of both devices have been already
synchronized, the device whose local clock has a lower stratum level will synchronize
the clock of the other device.
III. Broadcast mode
Network
Client
Server
After receiving the first
broadcast message the client
sends a request
Clock synchronization message
exchange (Mode 3 and Mode 4)
Periodically broadcasts clock
synchronization messages (Mode 5)
Calculates the network delay
between client and server and
enters the broadcast client mode
Periodically broadcasts clock
synchronization messages (Mode 5)
Receives broadcast messages
and synchronizes its local
clock
，
Figure 1-5 Broadcast mode
In the broadcast mode, a server periodically sends clock synchronization messages to
the broadcast address 255.255.255.255, with the Mode field in the messages set to 5
(broadcast mode). Clients listen to the broadcast messages from servers. After a client
receives the first broadcast message, the client and the server start to exchange
messages, with the Mode field set to 3 (client mode) and 4 (server mode) to calculate