3Com 4500G Family Configuration Manual page 1162

Configuring NTP Multicast Mode
Network requirements
As shown in Figure
segments and synchronizes the time among multiple devices. To realize this requirement, perform the
following configurations:
The local clock of Switch C is to be used as the master clock, with a stratum level of 2.
Switch C works in the multicast server mode and sends out multicast messages from
VLAN-interface 2.
Switch A and Switch D work in the multicast client mode and receive multicast messages through
VLAN-interface 3 and VLAN-interface 2 respectively.
1-10, Switch C functions as the NTP server for multiple devices on different network
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