====== NAT on linux with iptables ======
''eth0'' is our external network and ''eth1'' is our intenral one:
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth0 -o eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT
to make all this permanent change the following parameter in ''/etc/sysctl.conf'' to ''1'':
net.ipv4.ip_forward = 1
then save the current iptables permanetnly. in **ubuntu** you do:
apt install iptables-persistent
choose ''yes'' at the end to save the current config and you're done! if you change other iptables rules, you can run the following command to update the saved settings:
iptables-save > /etc/iptables/rules.v4