H3C Technologies H3C S6300 Series Switches - Manual (Page 24)

11
Mode Working process Principle Application scenario
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 6 shows, this
mode is most often used
between two or more
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 higher stratum,
the server can be
synchronized 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
be synchronized to a
broadcast server, but a
broadcast server cannot
be synchronized to a
broadcast client.
A broadcast server sends
clock synchronization
messages to synchronize
clients in the same subnet.
As
Figure 6 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.
Multicast
A multicast server periodically
sends clock synchronization
messages to the user-configured
multicast address. Clients listen to
the multicast messages from
servers and synchronize to the
server according to the received
messages.
A multicast client can be
synchronized to a
multicast server, but a
multicast server cannot
be synchronized to a
multicast client.
A multicast server can
provide time
synchronization for clients
in the same subnet or in
different subnets.
The multicast mode has a
lower time accuracy than
the client/server and
symmetric active/passive
modes.
In this document, an "NTP server" or a "server" refers to a device that operates as an NTP server in
client/server mode. Time servers refer to all the devices that can provide time synchronization, including
NTP servers, NTP symmetric peers, broadcast servers, and multicast servers.