Fortinet FortiGate FortiGate-50, Installation And Configuration Manual

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Network Intrusion Detection System (NIDS) Preventing attacks
FortiGate-50 Installation and Configuration Guide
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For example, setting the icmpflood signature threshold to 500 will allow 500 echo
requests from a source address, to which the system sends echo replies. If the
number of requests is 501 or higher, the FortiGate unit will block the attacker to
eliminate disruption of system operations.
If you enter a threshold value of 0 or a number out of the allowable range, the
FortiGate unit uses the default value.
To set Prevention signature threshold values:
1 Go to NIDS > Prevention .
2 Select Modify beside the signature for which you want to set the Threshold value.
Signatures that do not have threshold values do not have Modify icons.
3 Type the Threshold value.
4 Select the Enable check box.
5 Select OK.
Table 6: NIDS Prevention signatures with threshold values
Signature
abbreviation Threshold value units Default
threshold
value Minimum
threshold
value Maximum
threshold
value
synflood Maximum number of SYN segments
received per second
200 30 3000
portscan Maximum number of SYN segments
received per second
128 10 256
srcsession Total number of TCP sessions initiated
from the same source
2048 128 10240
ftpovfl Maximum buffer size for an FTP
command (bytes)
256 128 1024
smtpovfl Maximum buffer size for an SMTP
command (bytes)
512 128 1024
pop3ovfl Maximum buffer size for a POP3
command (bytes)
512 128 1024
udpflood Maximum number of UDP packets
received from the same source or sent
to the same destination per second
2048 512 102400
udpsrcsession Total number of UDP sessions initiated
from the same source
1024 512 102400
icmpflood Maximum number of UDP packets
received from the same source or sent
to the same destination per second
256 128 102400
icmpsrcsession Total number of ICMP sessions
initiated from the same source
128 64 2048
icmpsweep Maximum number of ICMP packets
received from the same source per
second
32 16 2048
icmplarge Maximum ICMP packet size (bytes) 32000 1024 64000