The New Internet

This is security theatre. People have been saying that NAT is not a security feature for over a decade:

* https://blog.ipspace.net/2011/12/is-nat-security-feature/

but the message still has not sunk in. The "Zero Trust" paper was published by John Kindervag in 2010:

* https://media.paloaltonetworks.com/documents/Forrester-No-Mo...

Most modern attacks start from a compromised internal host (e.g., from phishing), or through stolen credentials via a remote access method. The above is "castle-and-moat" thinking that tends to have weaker internal controls because it is thought the internal network is "hidden" from the dangerous outside network.

Set your firewall to default deny, then add a rule for allow outgoing connections, followed by only allow incoming connections if they are replies. For most machines (and networks), most of the time, this is what's needed: the above is applicable for both IPv6 and IPv4 (with or without NAT).

The protection comes from filtering (generally) and stateful packet inspection, not from hiding addresses.

> […] and having no distinction between a local IP and a public IP has a lot of disadvantages.

Just because something has a global addresses does not mean global reachability (see default deny above). Further you can layout your IPv6 address plan so that you can tell at a glance if hosts are externally accessible. Using a /48 a basis, you break out sixteen /52s, numbered $PREFIX:[0-f]000::/52.

To make it easier to remember what is externally accessible, you put all of those hosts in $PREFIX:e000::/52, where e stands for external. That /52 can then be broken down into:

* sixteen /56s

* 256 /60s

* 4096 /64s

or any combination thereof. See Figure A-5 for various ways to slice and dice:

* https://www.oreilly.com/library/view/ipv6-address-planning/9...

Everything in $PREFIX:[0-d,f]000::/52 is not externally reachable.

This is a lie. A "session through the NAT" does not really expose the host to the outside world, because in 99% of the cases this is a TCP session, and the NAT machine would drop all "out of order" packets.

>Most modern attacks start from a compromised internal host (e.g., from phishing), or through stolen credentials via a remote access method.

Your statement is a perfect example of https://en.wikipedia.org/wiki/Survivorship_bias.

Most modern attacks start from an internal host exactly because NAT makes external attacks infeasible for the majority of scenarios.

>Set your firewall to default deny, then add a rule for allow outgoing connections, followed by only allow incoming connections if they are replies.

What about I don't do it, and the system is still _automatically_ secure, because NAT does exactly that while being _required_ for the system to work.

>See Figure A-5

LOL. What about I don't see any figures, and the system still works and is secure for the 99% of the cases.

No, it's not. NAT only translates addresses and does not inspect the TCP "internals" (like sequence number etc, which would allow it to block certain packets).

What you are describing is a stateful firewall that allows "reply packets" for an established TCP-session.

Or, you know, because firewalls block stuff.

I've had hosts with public IPv4 addresses attacked on (e.g.) tcp/80 and tcp/443 because that's what the firewall allowed through so the web service was available to the public. I've had hosts with internal IPv4 addresses attacked on web ports because they were behind a (reverse proxy) load balancer for serving traffic: the fact that they had a 10/8 and were behind a NAT did not protect them from attack.

Before recently switching ISPs, my last one had IPv6 (new one does not). They activated IPv6 at some point, and I enabled it on my Asus, and suddenly all my internal devices got an IPv6 address (via RA), including things like my printer.

I had SSH enabled on my macOS laptop and desktop, but could not SSH into them from an outside source. My printer has a web interface on port 80 that I could connect to internally, but not externally. Even though all the devices had IPv6 addresses.

Just because a device is globally addressable does not mean it is globally reachable.

> What about I don't do it, and the system is still _automatically_ secure, because NAT does exactly that while being _required_ for the system to work.

Because NAT is doing that I describe, so you are doing it. The firewall is checking state on incoming packets and rejecting those that are not in its state table. The firewall is also coïncidentally just happening to also be fiddling some bits in the address field.

It is the stateful inspection that is protecting you.

* https://en.wikipedia.org/wiki/Stateful_firewall

> I've had hosts with internal IPv4 addresses attacked on web ports because they were behind a (reverse proxy) load balancer for serving traffic: the fact that they had a 10/8 and were behind a NAT did not protect them from attack.

You explicitly set up a NAT bypass (reverse proxy) and then claim NAT didn't protect them. If I am an external attacker coming in towards a single public IP where the backside hasn't set up UPNP/Port Forwarding/STUN/Reverse Proxy, NAT does exactly what the previous poster said. It drops packets because the 'destination' is the router itself in the packet. It has no where else to go, it has literally reached its destination.

A stateful firewall is in no way necessary for this functionality to exist. Even UDP stateless packets cannot bypass the NAT because there if there is no table tracking the conversation from the POV of the inside->out initiating the conversation because the router would have zero idea which interior host to forward the packet to and no reason to do so.

Yes it is. How would it forward response packets back if it doesn't track connections?

In real life I haven't seen "stateless NAT" for about 20 years.

But cgnat machines usually go beyond that and even verify sequence numbers.