# reset defaults
iptables -F;
iptables -P OUTPUT ACCEPT;
iptables -P FORWARD DROP;
iptables -P INPUT DROP;

# maintenance
iptables -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT;

# accept as INPUT all already ESTABLISHED connections
iptables -A INPUT  -m state --state RELATED,ESTABLISHED -j ACCEPT;