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H3C Technologies H3C MSR 5600 User Manual

Page 75

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62

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
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 symmetric active peer
and a symmetric passive

peer can synchronize 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 26

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 lower stratum,

the server can 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 26

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
synchronize to a
multicast server, but a

multicast server cannot

synchronize 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.

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