I used OpenWRT, and bypassed the firewall with `iptables -I FORWARD -j ACCEPT`. There are no NAT-related rules in that chain, so I didn't do anything to the beh

I used OpenWRT, and bypassed the firewall with `iptables -I FORWARD -j ACCEPT`. There are no NAT-related rules in that chain, so I didn't do anything to the behavior of the NAT. > Regardless as I have repeatedly said, this isn't sufficient to invalidate my claim Okay, let's be clear: you've made an unsubstantiated claim with no evidence that isn't backed up by the known behavior of NAT. Your only support for this claim is to say that it's "trivial to prove" by doing this test, and when I actually went and did this test, it failed to prove your point. Rather than invalidating your claim, it would be more accurate to say that neither of us has been able to validate it. > This doesn't for one second disprove that NAT has pseudo-firewall behaviour for any traffic passing through your ISP, which is the case for 99.99% of real world security threats. You're in luck: I have the necessary setup to test this as well. I happen to have a server subnet that's reachable from the internet, so let's try NATing the outbound connections from it and seeing what happens. (I'm going to edit the prefix on these IPs because I don't particularly want to commit them to the public record, but the suffix remains unedited.) First, let's check what IP the outbound connections come from, and see what happens when we connect to that IP from a client elsewhere on the internet: webserver# curl http://icanhazip.com/ 203.0.113.136 internetclient# curl -i http://203.0.113.136/200 HTTP/1.1 200 OK That works. Now, let's add NAT and demonstrate that the source IP of outbound connections has changed: router# iptables -t nat -I POSTROUTING -o eth0 -j MASQUERADE webserver# curl http://icanhazip.com/ 203.0.113.129 And now, let's try the inbound connection again: internetclient# curl -i http://203.0.113.136/200 HTTP/1.1 200 OK So yeah, I added NAT and it did nothing to inbound connections coming from the internet, which demonstrates the lack of pseudo-firewall behavior for packets that traverse the ISP and not just ones from the next network over.