iptables -I INPUT -i lo -s 127.0.0.0/8 -j ACCEPT
iptables -I OUTPUT -o lo -d 127.0.0.0/8 -j ACCEPT

iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP

# per consentire la connessione host-vm, in questo esempio Router:

iptables -I INPUT -i eth3 -s 192.168.56.1 -d 192.168.56.202 -p tcp --dport 22 -j ACCEPT
iptables -I OUTPUT -i eth3 -d 192.168.56.1 -s 192.168.56.202 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT