Basic iptables firewall on Ubuntu

IPT=/sbin/iptables
# Flush old rules
$IPT --flush
$IPT --delete-chain
# Default policies
$IPT -P INPUT ACCEPT
$IPT -P FORWARD ACCEPT
$IPT -P OUTPUT ACCEPT
# Loopback
$IPT -A INPUT -i lo -j ACCEPT
$IPT -A OUTPUT -o lo -j ACCEPT
# Require SYN for new TCP sessions
$IPT -A INPUT -p tcp ! --syn -m state --state NEW -s 0.0.0.0/0 -j DROP
# Allow established connections
$IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
# Allow SSH and HTTP
$IPT -A INPUT -p tcp --dport 22 -m state --state NEW -j ACCEPT
$IPT -A INPUT -p tcp --dport 80 -m state --state NEW -j ACCEPT
# Save
dpkg-reconfigure iptables-persistent