R3166-R3206-HP High-End Firewalls System Management and Maintenance Configuration Guide-6PW101

Multicast mode

Figure 41 Multicast mode

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.

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 the

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 a 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:

• 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.