H3C Technologies H3C S6300 Series Switches - Manual (Page 23)

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To ensure time accuracy and availability, you can specify multiple NTP servers for a device. The device
selects an optimal NTP server as the clock source based on parameters such as stratum. The clock that
the device selects is called the reference source. For more information about clock selection, see the
related protocols and standards.
If the devices in a network cannot synchronize to an authoritative time source, you can select a device that
has a relatively accurate clock from the network, and use the local clock of the device as the reference
clock to synchronize other devices in the network.
Association modes
NTP supports the following association modes:
• Client/server mode
• Symmetric active/passive mode
• Broadcast mode
• Multicast mode
Table 1 NTP association modes
Mode Working process Principle Application scenario
Client/server
On the client, specify the IP
address of the NTP server.
A client sends a clock
synchronization message to the
NTP servers. Upon receiving the
message, the servers
automatically operate in server
mode and send a reply.
If the client can be synchronized
to multiple time servers, it selects
an optimal clock and
synchronizes its local clock to the
optimal reference source after
receiving the replies from the
servers.
A client can be
synchronized to a server,
but a server cannot be
synchronized to a client.
As Figure 6 shows, this
mode is intended for
configurations where
devices of a higher stratum
are synchronized to
devices with a lower
stratum.