export SERVER_IP="x.x.x.x"

Flushing all rules

iptables -F

iptables -X

Setting default filter policy

iptables -P INPUT DROP

iptables -P OUTPUT DROP

iptables -P FORWARD DROP

Allow incoming and outgoing ssh only

iptables -A INPUT -p tcp -s 0/0 -d $SERVER_IP --sport 513:65535 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT

iptables -A OUTPUT -p tcp -s $SERVER_IP -d 0/0 --sport 22 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT

Make sure nothing comes or goes out

iptables -A INPUT -j DROP

iptables -A OUTPUT -j DROP

Save and load rules

iptables-save > /etc/iptables.rules

vim /etc/network/if-pre-up.d/iptablesload

#!/bin/sh
iptables-restore < /etc/iptables.rules
exit 0

vim /etc/network/if-post-down.d/iptablessave

#!/bin/sh
iptables-save -c > /etc/iptables.rules
if [ -f /etc/iptables.downrules ]; then
   iptables-restore < /etc/iptables.downrules
fi
exit 0

chmod +x /etc/network/if-post-down.d/iptablessave

chmod +x /etc/network/if-pre-up.d/iptablesload