H3C SR6600-X Configuration Manual page 82

Table 2 NTP association modes
Mode Working process
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
Client/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.
On the symmetric active peer,
specify the IP address of the
symmetric passive peer.
A symmetric active peer
periodically sends clock
synchronization messages to a
symmetric passive peer. The
symmetric passive peer
Symmetric automatically operates in
active/passive symmetric passive mode and
sends a reply.
If the symmetric active peer 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.
Principle
A client can synchronize
to a server, but a server
cannot synchronize to a
client.
A symmetric active peer
and a symmetric passive
peer can be
synchronized to each
other. If both of them are
synchronized, the peer
with a higher stratum is
synchronized to the peer
with a lower stratum.
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Application scenario
As Figure 27 shows, this
mode is intended for
configurations where
devices of a higher stratum
synchronize to devices
with a lower stratum.
As Figure 27 shows, this
mode is most often used
between servers with the
same stratum to operate as
a backup for one another.
If a server fails to
communicate with all the
servers of a lower stratum,
the server can still
synchronize to the servers
of the same stratum.