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> I'm well aware that ipv4+nat is not "security"... yet it removes a whole class of problem (eg: windows print spooler is listening on [::] by default or something like that)

IPv4+NAT does not remove any more classes of problems than IPv6+firewall. Firewalls under IPv6 work exactly the same way as they do with IPv4.

An IP connection is started from the 'inside' to the 'outside', and the source-destination tuple is recorded. When an 'outside' packet arrives the firewall checks its parameters to see if it corresponds with an existing connection, and if it does it passes it through. If the parameters do not correspond with anything in the firewall's table/s it assumes that someone is trying to create a new connection, which is generally not allowed by default, and therefore drops it.

The main difference is that with IPv4 and NAT the original (RFC 1918?) source address and port are changed to something corresponding to the 'outside' interface of the firewall.

With IPv6 address/port, rewriting is not done. Only state tables are updated and checked.

New connections are not allowed past the firewall towards the inside with either protocol, and only replies to connections opened from the inside are passed through.

There's no magical security behind NAT: tuples and packet flags are read, looked up in a state table, allowed or not depending on either firewall rule or state presence.

The security comes from the state checking.

> […] and it was happily listening on the public internet for something to print.

I have a printer with an IPv6 stack. I also have IPv6 addresses from my ISP. Yet somehow my Asus AC-68U prevents the public Internet from reaching my printer…

> IPv4+NAT does not remove any more classes of problems than IPv6+firewall

NAT is automatic and works out of the box while most users, even tech-savvy ones don't bother configuring the firewall on their own laptop, let alone on the router/gateway.

And by the way, I'd like to see you explain that firewall thing to the average senile pc user (grandma/grampa).

There is nothing to figure out: you take your Linksys/Asus/whatever device, plug in the WAN side to your modem, and your computer(s) to the LAN ports. Perhaps enter your credentials if you're using PPPoE, and you're done.

I'm not sure why you think IPv6 is more complicated than IPv4 for home users when it comes to CPEs.

What exactly do you think needs to be done on an Asus/Linksys for IPv6 protection that is different than IPv4?

> There's no magical security behind NAT

That's exactly the point. Yes, I know the "security" NAPTv4 provides is just a side effect. But it is what was widely deployed in the field. If you want to push IPv6, you MUST make sure in field appliances match this "side effect" (as a properly implemented firewall).

And this is not happening.

NAPTv4 with a "block incoming connection" side effect is widely deployed, running on countless CPEs. Proper IPv6 firewall is not. Thus IPv6 is not ready for these users.

> NAPTv4 with a "block incoming connection" side effect is widely deployed, running on countless CPEs. Proper IPv6 firewall is not.

I've been running IPv6 through my Asus for years now and it's been no different than IPv4. Going to Advanced Settings > Firewall, under "IPv6 Firewall" it says:

> All outbound traffic coming from IPv6 hosts on your LAN is allowed, as well as related inbound traffic. Any other inbound traffic must be specifically allowed here.

It then has a table where you specify traffic to be allowed in to specific internal hosts on particular port (ranges), but since this is IPv6, you don't have to deal with reverse-NATing now.

* https://www.asus.com/us/support/FAQ/1013638/

Adding the right rules for a firewall is not more difficult for IPv6 than for IPv4 with NAT, if anything it is simpler.

It is true that usually NAT is configured by default to not accept connections from outside to inside, but any firewall should have default rules that forbid such connections for any protocol, both for IPv4 and for IPv6.

Nonetheless, you are probably right that many, maybe most, home routers/firewalls might come with bad default configurations, where instead of having sane default rules for IPv6, there might be just a default rule to pass all.

If that is the case, it is not the fault of IPv6 but of the device manufacturers. For NAT it is also possible to put stupid default firewall rules, that just is less common, because almost all customers use NAT and the bad defaults are frequently noticed and reported.

Most consumer NATs are intentionally configured to be leaky. A commonly used technique is hole punching (https://en.wikipedia.org/wiki/Hole_punching_(networking) ), which all consumer NATs are prone to support because otherwise many popular applications such as games, voice- and videoconferencing won't work. There are also formally specified protocols to expose hosts to connections from outside: https://en.wikipedia.org/wiki/Internet_Gateway_Device_Protoc... https://en.wikipedia.org/wiki/Port_Control_Protocol and others. All this is done with no or poor authentication, so any malware that managed to make it inside your network (e.g. by a guest carrying an infected device) can just request your home router to open ports. There have even been problems where such protocols were open to the outside internet, of course without auth. There have been problems with misdirected exposed ports when hosts go offline and addresses are reassigned. Those just don't make headline news because the protocols work as intended and each misconfiguration is unique, automatic and temporary.

So, first, your IPv4 NAT has crappy security already, by virtue of needing to accomodate services like realtime audio/video/control that won't work properly without incoming connections. Second, IPv6 is supported in the same way, PCP can just do the same for IPv6 firewall rules as it does for IPv4 NAT exposed ports.

There is absolutely no reason to not use IPv4 over IPv6, it'll work the same from an end-user's view. But it'll be slightly less messy because you just configure firewall rules per IPv6 address instead of translating the limited port space of your one external IPv4 address into a number of internal Port/IPv4 combinations. So the chance to screw up is lessened.

> it'll be slightly less messy because you just configure firewall rules per IPv6 address instead of translating the limited port space of your one external IPv4 address into a number of internal Port/IPv4 combinations. So the chance to screw up is lessened.

as mentioned, with ipv6 you now have to care/worry about multiple classes of numbers, so i'd argue that because the number-space is increased, so is the chance to screw up.

i grew up with windows 3.x computers having a public ip and no firewall and as nice as incoming connections by default are for an enthusiast, they are a unecessary danger for the masses.

as you said, hole-punching works on ipv6 as well and has to be initiated from the inside, so it's no argument for .

I do not know what you mean by "multiple classes of numbers".

A firewall must block everything by default.

You add then exceptions for the protocols, hosts and ports that you want to allow.

Regardless whether you use IPv4 or IPV6, you have the same number of protocols, hosts and ports for which you must add rules.

The only disadvantage of IPv6 is that you should be more careful when you copy and paste the host addresses into rules, because the IPv6 addresses are longer and it might be more difficult to notice typing errors in them.

On the other hand, you no longer need to add NAT rules.

i was refering to the multiple classes of ipv6 addresses. most ppl don't care about a clever numbering sheme and probably wouldn't if they understood.

does the firewall discard extension headers from the internets? what about relevant icmp?

public/private interface? ah right, can't tell from a look at the address...

nat-rules are very simple by comparison.

don't get me wrong; i am very happy with adopting an incompatible, new internet protocol for all the app- and smart-shiit.

Ah, the inevitable NAT security comment on every IPv6 discussion.

> yet it removes a whole class of problem (eg: windows print spooler is listening on [::] by default or something like that)

NAT is just address translation, that's it: it doesn't imply a firewall. What you're thinking is a typical CPE router which, along masquerading the usual RFC 1918 range, runs a stateful firewall that blocks all incoming connections by default (but can be easily punched, even automatically by NAT-PMP, UPnP and a bunch of other protocols).

Lifting the NAT doesn't mean lifting the firewall: new ISPs that deployed native IPv6 are doing exactly the same firewalling as before.

Congratulations, you missed the point

The ISP level yada yada doesn't matter, nobody cares about that at a consumer level.

NAT doesn't imply firewalling, that true, but NAT also means that hosts being the gateway are not exposed by default.

Exposing by default or not does not have anything to do with NAT.

It only depends on the default firewall rules.

The default rules should not allow connections from outside, regardless whether NAT is used or not and regardless whether IPv6 is used or not.

Any device with a network interface connected directly to Internet must have an active firewall.

Whoever downvoted this does not know how NAT and firewalls function.

That NAT and firewall are independent functions, even if they may be performed by the same program, is a simple true fact, which cannot be contested.

NAT cannot enhance security in any way. On the contrary, only the absence of any NAT can enhance the security of private IPv4 networks, because only when NAT does not exist, the computers with private addresses are no longer reachable from outside. Whenever a device that does NAT exists in your network, your internal private addresses become public addresses, no longer hidden from the Internet, because that is what NAT does. The fact that multiple internal addresses are mapped to a single external address may make more difficult the tracking of individual users, but it does not protect the internal computers in any way from external accesses. That is the job of the firewall, which filters the undesirable IP packets.

So anyone who believes that NAT is something that provides security is delusional.

I own a subnetwork of public IPv4 addresses and I have a private network of computers connected to the Internet through a router/firewall, which is a standard PC on which I have been managing the firewall and NAT for almost 20 years.

Neither of my 2 ISP's supports IPv6, so I use IPv4 with NAT.

However, if I could use IPv6, rewriting the firewall rules would not take more than a few minutes and the security would be exactly the same as it is with IPv4 and NAT.

> So anyone who believes that NAT is something that provides security is delusional.

If I understand NATs correctly, they cannot route incoming connections (from the Internet) to a computer on the local network because they don't know which computer to route them to. Hence incoming connections will always fail (unless configured to go to a specific computer, "port forwarding"). Thus a NAT (by design, because it cannot operate in another fashion), blocks incoming connections. I'd think this is a security benefit (over having a public IP address for every device in the network like in IPv6, but without a firewall).

Care to elaborate why my example doesn't work/misses your point?

It is true that for incoming connections you normally have to include in the NAT configuration the local IPv4 address to which the connection requests should be sent.

Otherwise the NAT would have to guess if they should be sent to one of the local addresses already seen to be in use.

In any case there is no difference between what happens when you use NAT and what happens when you have only public addresses in your internal network, either IPv6 or IPv4, it does not matter.

If you have internal public addresses, the incoming connections cannot reach them anyway, until you add a firewall rule allowing a connection with a certain protocol for a certain port and internal host, which is done exactly like when adding the same rule in the NAT case.

If the NAT does not allow incoming connections without express configuration, then it has correct default firewall filtering rules.

The fact that there may be multiple internal computers, is not something that would block the connection, because the NAT can choose the first of the internal addresses that it has seen, maybe rotating the addresses for the next connection requests.

So what blocks the incoming connections is the lack of permission to do that, not the fact that the NAT could not do that if allowed.

It would not surprise me if there are some NAT implementations that attempt to be too helpful so they might send the incoming connections to your local computer even without any configuration for this.

I haven't mentioned the ISP level networking anywhere. The router provided by an ISP with native IPv6 to you (or any consumer router you can buy, for that matter) is using the exact same firewall with the same rules: they just don't do NAT because it's not needed anymore.

By this I mean that new WAN to LAN connections are blocked by default, LAN to WAN connections are allowed by default, ICMP is allowed etc. The only difference is that in IPv4 to "open a port" you have to:

1. map a LAN port/address to a WAN port using a DNAT destination rule

2. write a firewall rule to allow WAN traffic through that port

while in IPv6 you just do 2. Same result, same level of security, just less steps. These two steps are usually bundled into one operation in your familiar home router web UI, and this is why many confuse NAT with a firewall/some kind of security feature.

> […] and it had got a public ipv6 (besides the ULA address and the link-local address) and it was happily listening on the public internet for something to print.

Another thought: perhaps 'appliances' should (by default? togglable?) have only ULA and link-local addresses? Basically anything that starts with "f" (fe80::/10, fc00::/7, multicast)?