SMC Networks BR21VPN - annexe 1 Manual page 198

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 SMC BR21VPN 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.
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