Setup iptables in Linux

Ubuntu does come with iptables preset like in Fedora. Here's the base set up for iptables.

Add iptable rules.

Block Null Packets

iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP

Reject Syn-Flood Attack

iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP

Reject XMAS/recon packets

iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP

Allow custom ports

<here>

Accept Established Connections

iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

iptables -A INPUT -j REJECT iptables -A FORWARD -j REJECT

iptables -A FORWARD -i eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT

iptables -A FORWARD -j REJECT

iptables -A OUTPUT -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT

Use iptables-save to save it to a file.

iptables-save > /etc/iptables.rules

Edit rc.local to import iptables rules during boot up.

iptables-restore < /etc/iptables.rules