3Com S7906E - Switch, Руководство по настройке

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1-6
Multicast mode
Figure 1-6 Multicast mode
Network
Client Server
After receiving the first
multicast message, the
client sends a request
Clock synchronization message
exchange (Mode 3 and Mode 4)
Periodically multicasts clock
synchronization messages (Mode 5)
Calculates the network delay
between client and the server
and enters the multicast
client mode
Periodically multicasts clock
synchronization messages (Mode 5)
Receives multicast
messages and synchronizes
its local clock
In the multicast mode, a server periodically sends clock synchronization messages to the
user-configured multicast address, or, if no multicast address is configured, to the default NTP multicast
address 224.0.1.1, with the Mode field in the messages set to 5 (multicast mode). Clients listen to the
multicast messages from servers. After a client receives the first multicast message, the client and the
server start to exchange messages, with the Mode field set to 3 (client mode) and 4 (server mode) to
calculate the network delay between client and the server. Then, the client enters the multicast client
mode and continues listening to multicast messages, and synchronizes its local clock based on the
received multicast messages.
In symmetric peers mode, broadcast mode and multicast mode, the client (or the symmetric active peer)
and the server (the symmetric passive peer) can work in the specified NTP working mode only after
they exchange NTP messages with the Mode field being 3 (client mode) and the Mode field being 4
(server mode). During this message exchange process, NTP clock synchronization can be
implemented.
Multiple Instances of NTP
The client/server mode and symmetric mode support multiple instances of NTP and thus support clock
synchronization within an MPLS VPN network. Namely, network devices (CEs and PEs) at different
physical location can get their clocks synchronized through NTP, as long as they are in the same VPN.
The specific functions are as follows:
z
The NTP client on a customer edge device (CE) can be synchronized to the NTP server on another
CE.
z
The NTP client on a CE can be synchronized to the NTP server on a provider edge device (PE).
z
The NTP client on a PE can be synchronized to the NTP server on a CE through a designated VPN
instance.