In this tutorial, I will detail how to setup an Ubuntu server as a NAT router.
The server has 2-network interfaces: enp0s3 (WAN) and enp0s8(LAN). NAT is enabled on the WAN-NIC. A DHCP-Server is installed and it leases IP-addresses to clients over server's enp0s8 interface.
root@ubuntu-DHC-SVR-RTR:/home/tokunbo# lsb_release -a