Synblock is a project mainly written in Shell, it's free.
Script to mitigate DDoS Attacks (SYN Flood)
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## www.Anti-Hack.net #
## SynBlock Version 0.3 #
## by Florian Reith #
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_ _ _
___ _ _ _ __ | |__ | | ___ ___| | __
/ __| | | | '_ \| '_ \| |/ _ \ / __| |/ /
\__ \ |_| | | | | |_) | | (_) | (__| <
|___/\__, |_| |_|_.__/|_|\___/ \___|_|\_\
|___/
Installation:
1. chmod +rx install.sh
2. ./install.sh