All these systems are a reflection of the time that they were designed. IPv6 is 30 years old. At that time a lot of threats just didn't exist. One of my favorite is the decision to default to /64 blocks. There was a time when the designers believed that you'd use your 48 bit MAC address as part of this. Now we know that's a PII nightmare and nobody does it. Yet we're still stuck with the 128 bit addresses that came from that.

To your point, IPv6 sought to replace NAT with just having enough addresses but interestingly, that created a problem. If you used NAT and had a service on your computer request a port for incoming connections, that showed intent on behalf of the owner of that service. IPv6 doesn't have that intent, which forces home router makers do block addresses by default because you don't want most PCs on the Internet such that an external agent can scan your PC. You may end up with an unintended service on the open Internet.

So is the bigger address range better? Technically, maybe? But you have to consider defaults and intents of users. And that can take a good technical solution to a bad solution or at least create a whole bunch of problems.

I don't think this is inherently a problem. It's good for home routers to have sensible defaults. Blocking incoming IPv6 connections is such a thing. Opening a port in the firewall shows the same kind of intent as forwarding a port with NAT. The burden is on the router manufacturers to expose these options in a sensible way. My router for example has a similar UI to forwarding a port with IPv4 and opening the port for IPv6.

Using NAT as a firewall might work but it brings it's own problems. I find the IPv6 way better.

> There was a time when the designers believed that you'd use your 48 bit MAC address as part of this. Now we know that's a PII nightmare and nobody does it.

Nobody includes their MAC address in their public IPv6 addresses anymore, but every IPv6 setup that I've seen still gives every device a unique globally-routable IPv6 address, with no NAT at all.

> One of my favorite is the decision to default to /64 blocks.

The nice thing is that a /64 is big enough that clients can just randomly pick any address, and it will almost certainly be available, meaning that you don't need DHCP. This is actually widely implemented, and is known as SLAAC [0].

> Yet we're still stuck with the 128 bit addresses that came from that.

The extra address space only adds 16 bytes to every packet, and it ensures that we will never run out of addresses like we did with IPv4.

[0]: https://en.wikipedia.org/wiki/IPv6#Stateless_address_autocon...

> IPv6 doesn't have that intent, which forces home router makers do block addresses by default because you don't want most PCs on the Internet such that an external agent can scan your PC. You may end up with an unintended service on the open Internet.

Every residential router already has PCP (RFC 6887) and UPnP IGD to deal with the NAT44 non-sense that is the status quo, and both protocols support IPv6 hole punching, so IPv6 default deny as a policy is hardly an issue in the residential space.

MiniUPnPd, which many Linux-based CPEs use, has supported IGDv2 (needed for IPv6) since 2012 (as well as PCP).

The point of local networks of a minimum size of 64 bit isn't only to have MAC-based addresses (48 bit would have been enough for that, fwiw), but in general to support non-coordinated/probabilistic self-assignment schemes with negligible collision probability.

Picking a random local address (which is very important for privacy, as you've mentioned) is much easier if you don't have to do an elaborate dance of listen, announce, listen for collisions etc. first (practically that still happens, but collisions are the absolute exception).

> So is the bigger address range better?

Yes, because consider the alternative of re-doing all of this again in a future in which IP usage for some reason jumps by a few orders of magnitude again.

Due to hardware getting better over time, the per-packet cost of a few extra bits is going down all the time, while the cost of rolling out a future IPv7 increases with every new deployed host.

> Now we know that's a PII nightmare and nobody does it. Yet we're still stuck with the 128 bit addresses that came from that.

Randomizing the local address doesn't mean it isn't useful. You can't scan a /64 so that's already a major improvement. The fact that randomly selecting a number is effectively never going to collide greatly simplifies automatic network configuration.

The major issue is that the /64 isn't mandatory from a technical perspective. Being merely a subset of the larger address it's nothing more than a convention. In the end not all providers make it available to you even though supposedly they ought to.

If we're going to complain about anything it should be the godawful notation that so easily breaks parsers. Or the fact that the width is massively excessive which creates a usability nightmare due to normal humans not being able to readily recall 128 bit numbers (let alone how long it takes to type them in).