H3C Technologies H3C MSR 5600 - Manual (Page 74)

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many NTP hops away a device is from the primary time server. A stratum 2 time server receives its time
from a stratum 1 time server, and so on.
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 2 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 synchronize 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 synchronize
to a server, but a server
cannot synchronize to a
client.
As Figure 26 shows, this
mode is intended for
configurations where
devices of a higher stratum
are synchronized to
devices with a lower
stratum.