3com S7906E 설치 설명서

 

1-6 

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. 

 

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.