Here is the commands, for example you want to forward port 8080 to another host 192.168.100.2:8080
preparation, enable ip forward
sysctl net.ipv4.ip_forward=1
first we need to masquerade the packet
iptables -t nat -I POSTROUTING -p tcp -j MASQUERADE
Second, change the destination to another host
iptables -t nat -I PREROUTING -p tcp --dport 8080 -j DNAT --to-destination 192.168.100.2:8080
Or, listen on specific ip
iptables -t nat -I PREROUTING -p tcp -d 192.168.100.1 --dport 8080 -j DNAT --to-destination 192.168.100.2:8080
This last is optional, you may need it if your FORWARD chain default REJECT
iptables -I FORWARD -d 192.168.100.2 -p tcp --dport 8080 -j ACCEPT
Note:
* iptables rules is not persistent, you can make it persistent using iptables-persistent
* you can also use ufw rules, save in the file /etc/ufw/before.rules
Source: https://askubuntu.com/questions/320121/simple-port-forwarding