Hirschmann RS20 Reference Manual page 47

Time 3.1 SNTP configuration
Note: If you are receiving the system time from an external/redundant server
address, you do not accept any SNTP Broadcasts (see "Accept SNTP
Broadcasts"). Otherwise you can never distinguish whether the device is
displaying the time from the server entered, or that of an SNTP Broadcast
packet.
Figure 18: SNTP dialog
RM Web L2B
47
Release 5.0 04/09