port maping

echo "1" > /proc/sys/net/ipv4/ip_forward
echo "1" > /proc/sys/net/ipv4/ip_dynaddr

port mapping
iptables -A PREROUTING -t nat -i eth0 -p tcp --dport 3000 -j DNAT --to 192.168.1.51:3000
iptables -A FORWARD -p tcp -i eth0 -o eth1 -d 192.168.1.51 --dport 3000 -j ACCEPT

IPS (router for internet sharing)
iptables -t nat -A POSTROUTING -o eth1 -s 192.168.1.0/24 -j MASQUERADE