Symmetricom ND-SERIES User Manual page 18

The default, well-known port for NTP service is 123. This can be changed as desired (using the Telnet application).
[Note: some NTP/SNTP servers will expect NTP clients to operate on port 123 and cannot be configured to utilize alternate
ports.]
Query NTP server for time (Unicast Mode for NTP) - By default, the ND clock will operate only in Unicast /Query
mode using server port 123.
This mode is selected exclusively when neither the listen for NTP broadcast nor the listen for NTP multicast modes
are selected.
Listen for NTP broadcasts
for NTP via broadcast address [255,255,255,255]" checkbox.
ND Clocks User Manual - Rev 2.0.1 Sep-08
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The network clock can configured to listen to NTP broadcasts by selecting the "Listen
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