As with any IDS, there is always a high probability of false positives. Hence, every IDS should be equipped with a whitelisting capability by which certain systems, networks, ports, or protocols can be excluded from any detection mechanism and (most importantly) any automated response features. Because certain IP addresses or networks may be known bad actors, there should also be a provision to blacklist them.

These requirements are met in psad's auto_dl file, which follows this syntax:

ip/network danger level optional protocol/optional ports

If the danger level is set to zero, psad will completely ignore the IP address or network. However, the danger level can be set as high as five if a particular IP address or network is known to be extremely malicious.

For example, the first of the following two lines ensures that psad will ignore all traffic from the IP address; the second line immediately escalates all TCP port 22 (SSH) traffic to a danger level of five from the network:

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