What you are talking about is PAT. PAT unlike NAT requires firewall to operate. What he pointed out is that if you have a firewall you can provide security thr

What you are talking about is PAT. PAT unlike NAT requires firewall to operate. What he pointed out is that if you have a firewall you can provide security through that, you don't need NAT or PAT. In fact having just a firewall is safer, because it is simpler