EXTERNAL=eth0 INTERNAL=eth1 EXTERNALIP1=x.x.x.x INTERNALIP1=192.168.0.2
echo 1 > /proc/sys/net/ipv4/ip_forward echo "Setting up NAT (Network Address Translation)..." iptables -F iptables -F -t nat # by default, nothing is forwarded. iptables -P FORWARD DROP # Allow all connections OUT and only related ones IN
iptables -A FORWARD -i $EXTERNAL -o $INTERNAL -m state --state ESTABLISHED,RELA TED -j ACCEPT iptables -A FORWARD -i $INTERNAL -o $EXTERNAL -j ACCEPT # enable MASQUERADING iptables -t nat -A POSTROUTING -o $EXTERNAL -j MASQUERADE
# IMAP to EXCH gateway iptables -A FORWARD -i $EXTERNAL -o $INTERNAL -p tcp --dport 143 -j ACCEPT iptables -A FORWARD -i $EXTERNAL -o $INTERNAL -p tcp --dport 110 -j ACCEPT iptables -A FORWARD -i $EXTERNAL -o $INTERNAL -p tcp --dport 587 -j ACCEPT iptables -A FORWARD -i $EXTERNAL -o $INTERNAL -p tcp --dport 993 iptables -A PREROUTING -t nat -p tcp -d $EXTERNALIP1 --dport 993 -j DNAT iptables -A PREROUTING -t nat -p tcp -d $EXTERNALIP1 --dport 143 -j DNAT --to $ INTERNALIP1:143 iptables -A PREROUTING -t nat -p tcp -d $EXTERNALIP1 --dport 110 -j DNAT --to $ INTERNALIP1:110
iptables -A PREROUTING -t nat -p tcp -d $EXTERNALIP1 --dport 587 -j DNAT --to $ INTERNALIP1:587
