To add: The really sad thing about IPv6 is that it's a relic of a bygone era. The internet was envisioned as a thing where every device on every network could,

To add: The really sad thing about IPv6 is that it's a relic of a bygone era. The internet was envisioned as a thing where every device on every network could, in principle, initiate a connection to any other device on any other network. But then we started running out of addresses, ISP's wouldn't give you more than one for a household, so we started doing NAT, and that kind of sealed the internet's fate. Nowadays, we wouldn't want a world where everything was connectable, even if we had enough addresses. Everyone's network in essence has a firewall. If you run IPv4 and using NAT, you're going to be dropping unsolicited incoming packets no matter what (let alone that you wouldn't know where to route them even if you wanted to let them through) and with IPv6 you'd be insane to allow them. Devices have "grown up" in a world where we expect the router we're connecting to, to shield us from incoming unsolicited traffic. I certainly don't have the firewall enabled on my linux desktop. Windows I _think_ has it enabled by default, but I often turn it off because I want LAN connections to work. MacOS is probably similar. Suffice to say, if the IPv6 dream happened overnight and everyone's devices were instantly connectable, all hell would break loose. We need our routers to disallow traffic. (Edit: This wasn't all that clear, so let me restate: In both the IPv4 and IPv6 world, you'd be insane to disallow incoming unsolicited traffic, which is why basically everyone blocks it in IPv6 as well as IPv4. I'm not trying to say IPv6 can't do this... quite the contrary: IPv6 routers absolutely do, and should, block unsolicited incoming traffic. But my point is that this is what prevents the original vision of IPv6 from becoming a reality: We can't design software around the idea of direct peer-to-peer communication, without stuff like UPnP. Oh, and UPnP works with NAT and IPv4 anyway so, there's the rub.) So, even in a pure-IPv6 world, that instantly prevents any startup with an idea to allow true peer-to-peer communication using end-to-end routability. What are you going to do, train your users to log into their router and enable traffic? Approximately 0% of your customers know how to do that, even in a counterfactual universe where IPv6 happened and we all have routable IP's on our devices. Maybe in such a universe, people would be trained to use local firewalls on their device, and say "ok" to popups asking if you want to let software through. But I'd wager that a lot of people would prefer the simplicity of just having their gateway drop the traffic for them. No, the "all devices are routable" idea came from a naive world where there wasn't a financial incentive for malicious behavior at every turn. Where there aren't millions of hackers waiting for an open port to an exploitable service they can use to encrypt all your data and ransom it for bitcoin. The internet is a dark forest now. We don't _want_ end-to-end connectivity.