Set up gateway on a Linux system

on the pc that will be the gateway:

iptables -F --to flush(drop) the firewall

ifconfig eth1(external interface) 142.204.57.31(external ip) netmask 255.255.255.192(subnetmask) up

ifconfig eth4(internal interface) 10.0.0.1(internal ip) netmask 255.255.255.0(subnetmask) up

echo 1 > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A POSTROUTING -o inetrnal interface -j MASQUERADE

An automated script was written a tutorial is posted HERE.