PLANET SG-1000 - Manual (Page 227)

Detect Land Attack:
„ Some Systems may shut down when receiving packets with the same source and
destination addresses, the same source port and destination port, and when SYN on
the TCP header is marked. Enable this function to detect such abnormal packets.
After System Manager enable External Alert, if the SG-1000 has detected any abnormal
situation, the alarm message will appear in External Alarm in Attack Alarm. And if the
system manager starts the E-mail Alert Notification in Settings, the device will send e-mail to
alarm the system manager automatically.