NATing (iptables)
Forward connectons on WAN IP 1.1.1.1 to a machine on the the local network of 192.168.1.1 on port 80:
sudo iptables -D PREROUTING -t nat -d 1.1.1.1/32 -p tcp -m tcp --dport 80 -j DNAT --to-destination 192.168.1.1:80
Forward connectons on WAN IP 1.1.1.1 to a machine on the the local network of 192.168.1.1 on port 80:
sudo iptables -D PREROUTING -t nat -d 1.1.1.1/32 -p tcp -m tcp --dport 80 -j DNAT --to-destination 192.168.1.1:80