[formerly_proven]

Right. This is a big clash between the "v4 model" (as it has panned out in practice) and the "v6 model". The OG assumption of both was that there is _only one_ Network, but v4 in practice turned out to be segregated, private networks that happen to have a gateway to The Network. The original RFCs for private IPv4 networks and NAT explicitly call this change in stance out. So v6 was designed to go back to a world with only The One Network. The possibility of having a private v6 network was added much later (some time in the 2000s I think?).

This is probably why going to v6 is so confusing even for us Elite HN Readers; you don't have a private network connected to The Internet any more, The Internet directly extends to all devices. You can have a private network _in addition_ to that though.

This is actually pretty nice because it restores end-to-end connectivity, so P2P and mesh networking become easier; however, most everyone has a central firewall between their splinter of The Internet and The Greater Internet, so in practice you still need hole punching and some central services to offer hole punching duties, because hole punching works around NAT and opens a port in stateful firewalls; v6 only removes the NAT part in most instances. So in reality P2P with v6 is only slightly less messy than with v4.

[throw0101a]

> The possibility of having a private v6 network was added much later (some time in the 2000s I think?).

ULA seems to be RFC 4193 (October 2005). NTPv6 is RFC 6296 (June 2011).

* https://datatracker.ietf.org/doc/html/rfc4193

* https://datatracker.ietf.org/doc/html/rfc6296