3Com 4210 9-Port Configuration Manual page 562

In the symmetric peer mode, the local Switch 4210 serves as the symmetric-active peer and sends
clock synchronization request first, while the remote server serves as the symmetric-passive peer
automatically.
If both of the peers have reference clocks, the one with a smaller stratum number is adopted.
Broadcast mode
Figure 1-4 Broadcast mode
Multicast mode
Figure 1-5 Multicast mode
Table 1-1 describes how the above mentioned NTP modes are implemented on Switch 4210.
Table 1-1 NTP implementation modes on Switch 4210
NTP implementation
mode
Server/client mode
Symmetric peer mode
Broadcast mode
Configuration on Switch 4210
Configure the local Switch 4210 to work in the NTP client mode. In
this mode, the remote server serves as the local time server, while the
local switch serves as the client.
Configure the local Switch 4210 to work in NTP symmetric peer
mode. In this mode, the remote server serves as the
symmetric-passive peer of the Switch 4210, and the local switch
serves as the symmetric-active peer.
Configure the local Switch 4210 to work in NTP broadcast server
mode. In this mode, the local switch broadcasts NTP messages
through the VLAN interface configured on the switch.
Configure the Switch 4210 to work in NTP broadcast client mode.
In this mode, the local Switch 4210 receives broadcast NTP
messages through the VLAN interface configured on the switch.
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