Test system: Ubuntu 20.04 LTS
Persistent iptables rules, install netfilter-persistent:
sudo apt install -y netfilter-persistent
Save current iptables rules:
sudo netfilter-persistent save
Load current saved iptables rules:
sudo netfilter-persistent reload
Saved files path:\
/etc/iptables/rules.v4
/etc/iptables/rules.v6
When you reboot, it will load rules.v4 and rules.v6 rules for iptables.
Forward tcp local port to another host port:\
sudo iptables -t nat -A PREROUTING -p tcp -m tcp --dport 'localPort' -j DNAT --to-destination 'forwardIP:forwardPort'
sudo iptables -t nat -A POSTROUTING -d 'forwardIP' -p tcp -m tcp --dport 'forwardPort' -j SNAT --to-source 'localIp'