sudo nano /etc/netplan/00-installer-config.yaml

gw@gw:~$ sudo netplan generate

gw@gw:~$ sudo netplan apply

gw@gw:~$ ping hient.net

PING hient.net (64.131.64.91) 56(84) bytes of data.
64 bytes from server2.twdomain.com (64.131.64.91): icmp_seq=1 ttl=50 time=197 ms
64 bytes from server2.twdomain.com (64.131.64.91): icmp_seq=2 ttl=50 time=196 ms

gw@gw:~$ sudo apt update

Hit:1 http://tw.archive.ubuntu.com/ubuntu bionic InRelease
Hit:2 http://tw.archive.ubuntu.com/ubuntu bionic-updates InRelease

sudo nano /etc/sysctl.conf

Find and uncomment the following line:

net.ipv4.ip_forward=1

gw@gw:~$ sysctl net.ipv4.ip_forward

net.ipv4.ip_forward = 0

gw@gw:~$ sudo reboot

gw@gw:~$ sysctl net.ipv4.ip_forward

net.ipv4.ip_forward = 1

sudo iptables -t nat -A POSTROUTING -o wlx7cdd90ea4126 -j MASQUERADE

sudo apt-get install iptables-persistent -y

ipv4 -- yes 
ipv6 -- yes

sudo iptables -t nat -A PREROUTING -p tcp --dport 2210 -j DNAT --to-destination 192.168.40.10:22

sudo iptables -t nat -A PREROUTING -p tcp --dport 2220 -j DNAT --to-destination 192.168.40.20:22

sudo iptables -t nat -A PREROUTING -p tcp --dport 2221 -j DNAT --to-destination 192.168.40.21:22

sudo iptables -t nat -A PREROUTING -p tcp --dport 2222 -j DNAT --to-destination 192.168.40.22:22

sudo iptables -t nat -A PREROUTING -p tcp --dport 2223 -j DNAT --to-destination 192.168.40.23:22

sudo iptables -t nat -A PREROUTING -p tcp --dport 2230 -j DNAT --to-destination 192.168.40.30:22

• https://medium.com/@exesse/how-to-make-a-simple-router-gateway-from-ubuntu-server-18-04-lts-fd40b7bfec9