H3C Technologies H3C SecPath F1000-E - Manual (Page 118)

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Figure 6 Multicast mode
In 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. When 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 multicast client mode and continues
listening to multicast messages, and synchronizes its local clock based on the received multicast
messages.
NOTE:
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. In other words, 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:
• The NTP client on a customer edge device (CE) can be synchronized to the NTP server on another
CE.
• The NTP client on a CE can be synchronized to the NTP server on a provider edge device (PE).
• The NTP client on a PE can be synchronized to the NTP server on a CE through a designated VPN
instance.
• The NTP client on a PE can be synchronized to the NTP server on another PE through a designated
VPN instance.
• The NTP server on a PE can synchronize the NTP clients on multiple CEs in different VPNs.