#flush rules:

iptables -F INPUT
iptables -F OUTPUT
iptables -F FORWARD

# allow the loopback device (127.0.0.1)
iptables -A INPUT -i lo -j ACCEPT

# INPUT
iptables -A INPUT -p 47 -j ACCEPT
iptables -A INPUT -p tcp --sport 1723 -j ACCEPT
iptables -A INPUT -p tcp --dport 1723 -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

# OUTPUT
iptables -A OUTPUT -p 47 -j ACCEPT
iptables -A OUTPUT -p tcp --sport 1723 -j ACCEPT
iptables -A OUTPUT -p tcp --dport 1723 -j ACCEPT
iptables -A OUTPUT -p tcp --dport 22 -j ACCEPT

# REJECT THE REST

iptables -A INPUT -j REJECT
iptables -A OUTPUT -j REJECT
iptables -A FORWARD -j REJECT