iptables

#list rules
iptables -L

#accept all estimated traffic
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

#accept input from ssh and port 80
iptables -A INPUT -p tcp --dport ssh -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j ACCEPT

#deny all other traffic
iptables -A INPUT -j DROP

#save firewall rules to a file
iptables-save >/etc/iptables.rules

#load files after each reboot with crontab
vi /etc/crontab
@reboot root iptables-restore /etc/iptables.rules