Ufw

sudo ufw enable
sudo ufw allow 22

/etc/default/ufw

DEFAULT_FORWARD_POLICY="ACCEPT"

/etc/ufw/sysctl.conf

net.ipv4.ip_forward=1
net.ipv6.conf.default.forwarding=1

/etc/ufw/before.rules

# nat Table rules
*nat
:POSTROUTING ACCEPT [0:0]

# Forward traffic from eth1 through eth0.
-A POSTROUTING -s 192.168.0.0/24 -o eth0 -j MASQUERADE

# don't delete the 'COMMIT' line or these nat table rules won't be processed
COMMIT

sudo ufw disable && sudo ufw enable