IP TABLES

Masquerading

Configure Firewall
iptables -t nat -A POSTROUTING -s <internal subnet>-o <outbound interface> -j MASQUERADE

You will also have to allow the services that you want to provide to the internal network

iptables -A INPUT -s <internal subnet> -p <protocol> --dport <port number> -j ACCEPT

iptables -A INPUT -s 192.168.190.0/24 -p tcp --dport 21 -j ACCEPT

Setup Routing
edit /etc/sysctl.conf
net.ipv4.ip_forward = 1
sysctl -p