I’ve not found any software to install on Debian Linux to prevent DoS attacks, but found some scripts on the internet. Those scripts take same IP connections count, and if IP connection count greater then already specified value (you can specify this value) it shows this IP, but I wanted to block attacker IP for few seconds and then allow again. So I wrote simple shell script. The script denies access from attacker IP on specified time and after the time allows access again. You can specify max connection number from same IP when connection number exceeds limit, the script will block access from the IP on server.