H3C Technologies H3C MSR 50 - Manual (Page 43)

The client continues listening to broadcast messages and synchronizes its local clock based on the
received broadcast messages.
Multicast mode
Figure 15 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 server. Then, the client enters multicast client mode. It 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 operate 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.
NTP for VPNs
The device supports multiple VPN instances when it functions as an NTP client or a symmetric active peer
to realize clock synchronization with the NTP server or symmetric passive peer in an MPLS VPN network.
For more information about MPLS L3VPN, VPN instance, and PE, see MPLS Configuration Guide.
As shown in
Figure 16 , users in VPN 1 and VPN 2 are connected to the MPLS backbone network through
PE devices, and services of the two VPNs are isolated. If you configure the PEs to operate in NTP client
or symmetric active mode, and specify the VPN to which the NTP server or NTP symmetric passive peer
belongs, the clock synchronization between PEs and CEs of the two VPNs can be realized.
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