Stop Synflood DoS via Torrent

Etwas was interessant sein könnte,
wenn man den ein solches DoS Problem hat.
Textfile hatte ich noch hier rumliegen,
stammt allerdings nicht von mir ->Credits to the original author.

Die Anleitung erklärt,
wie die Anzahl der neuen Verbindungen von einer IP mittels IPtables begrenzt werden kann.

Quick “fix” for synflood DoS via. torrent tracker:
-> allow only 10 new connections within 5 seconds per source ip

iptables -N syn_80_recent
iptables -A syn_80_recent -m recent –set –name DEFAULT –rsource
iptables -A syn_80_recent -m recent –update –seconds 5 –hitcount 10 –name DEFAULT –rsource -j DROP
iptables -A syn_80_recent -j ACCEPT
iptables -A INPUT -p tcp -m state –state NEW -m tcp –dport 80 -j syn_80_recent

If you still block to many valid users, try to play with the seconds/hitcount settings.

Also enable syncookies on Linux kernel (if not done already):
sysctl -w net.ipv4.tcp_syncookies=1

No guarantee/warranty, use/test at your own risk. Feel free to contact us.

HTH,
Sven Michels
sectoor GmbH

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