blah

/bin/cp -f /etc/iptables.rules /etc/iptables.rules.old
cat > /etc/iptables.rules <<EOF
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:ICMPALL - [0:0]
:ZREJ - [0:0]
-A INPUT -m conntrack --ctstate INVALID -j DROP
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p icmp --icmp-type 255 -j ICMPALL
-A INPUT -p udp --dport 67:68 --sport 67:68 -j ACCEPT
-A INPUT -p tcp --dport 22 -j ACCEPT
-A INPUT -p udp -m multiport --dports 500,4500 -j ACCEPT
-A INPUT -p udp --dport 1701 -m policy --dir in --pol ipsec -j ACCEPT
-A INPUT -p udp --dport 1701 -j DROP
-A INPUT -j ZREJ
-A FORWARD -i eth+ -o ppp+ -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -i ppp+ -o eth+ -j ACCEPT
-A FORWARD -j ZREJ
-A ICMPALL -p icmp --fragment -j DROP
-A ICMPALL -p icmp --icmp-type 0 -j ACCEPT
-A ICMPALL -p icmp --icmp-type 3 -j ACCEPT
-A ICMPALL -p icmp --icmp-type 4 -j ACCEPT
-A ICMPALL -p icmp --icmp-type 8 -j ACCEPT
-A ICMPALL -p icmp --icmp-type 11 -j ACCEPT
-A ICMPALL -p icmp -j DROP
-A ZREJ -p tcp -j REJECT --reject-with tcp-reset
-A ZREJ -p udp -j REJECT --reject-with icmp-port-unreachable
-A ZREJ -j REJECT --reject-with icmp-proto-unreachable
COMMIT
*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -s 192.168.42.0/24 -o eth+ -j SNAT --to-source ${PRIVATE_IP}
COMMIT
EOF

cat > /etc/network/if-pre-up.d/iptablesload <<EOF
#!/bin/sh
/sbin/iptables-restore < /etc/iptables.rules
exit 0
EOF