HPE FlexNetwork 10500 SERIES, Configuration Manual

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Table 2 NTP association mode
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 synchronize
to a server, but a server
cannot synchronize to a
client.
As Figure 33 shows, this
mode is intended for
configurations where
devices of a higher
stratum synchronize to
devices with a lower
stratum.
Symmetric
active/passive
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
automatically operates in
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.
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.
As Figure 33 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.
Broadcast
A server periodically sends clock
synchronization messages to the
broadcast address
255.255.255.255. Clients listen
to the broadcast messages from
the servers to synchronize to the
server according to the
broadcast messages.
When a client receives the first
broadcast message, the client
and the server start to exchange
messages to calculate the
network delay between them.
Then, only the broadcast server
sends clock synchronization
messages.
A broadcast client can
synchronize to a
broadcast server, but a
broadcast server cannot
synchronize to a
broadcast client.
A broadcast server sends
clock synchronization
messages to synchronize
clients in the same
subnet. As
Figure 33
shows, broadcast mode is
intended for
configurations involving
one or a few servers and a
potentially large client
population.
The broadcast mode has
a lower time accuracy
than the client/server and
symmetric active/passive
modes because only the
broadcast servers send
clock synchronization
messages.