This protection trigs when a load goes beyond one of the thresholds configured by the file /etc/dpi/fastdpi.conf

ddos_reqsec_threshold=300
ddos_reqsec_variation=5

Here ddos_reqsec_threshold - is the number of requests per second addressed to the protected site. It is configured usually to be equal to maximal number of requests observed in normal operation.
ddos_reqsec_variation - is the deviation from requests' number specified by ddos_reqsec_threshold that causes the protection to be switched on and off. It is used to prevent random switches between states. It is expressed in percent and equals to 5% by default.

ddos_pktsec_threshold=5000
ddos_pktsec_variation=5

Here ddos_pktsec_threshold - is the number of packets per second that comes to the protected site. It is configured usually to be equal to maximal number of packets observed in normal operation.
ddos_pktsec_variation - is the deviation from packets' number specified by ddos_pktsec_threshold that causes the protection to be switched on and off. It is used to prevent random switches between states. It is expressed in percent and equals to 5% by default.

The parameter ddos_reqsec_threshold has the priority over ddos_pktsec_threshold in case both are specified. The latest value is ignored in this case.

One can collect the list of legit IP addresses during the normal operation. Its pre-activation allows to reduce the number of legit users that face a need to overcome the detector.

The list of legit IP addresses can be obtained by the analysis of the protected site's WEB server's logs. (The script to process these logs can be implemented independently or by the support.) Alternatively, the list can be formed based on DPI logs.

This list is loaded to DPI by the instruction:

fdpi_ctrl load --service 8 --file ip_list.txt

Here ip_list.txt is the generated trusted list. You can learn more about fdpi_ctrl instruction and how to ensure data persistence here: Configuring subscribers. Users of the site under protection are considered to be subscribers in this case.

DPI can generate the access log by itslef, as described here: СОРМ. After configuring the log parameters, IP adresses collection is started by the instruction:

fdppi_ctrl setenv --ddos_ip_gathering 1

It is switched off by sending 0 by this command.

The following parameter specifies the page containing CAPTCHA. One is redirected to this page for verification:

ddos_check_server=server_name/path/page.html?